United States Region III EPA 903-R-03-004
Environmental Protection Agency Chesapeake Bay Program Office October 2003
Technical Support
\ J Document for Identification
%PR0^
of Chesapeake Bay
Designated Uses and
Attainability
October 2003
-------
Technical Support Document for
Identification of Chesapeake Bay
Designated Uses and Attainability
October 2003
U.S. Environmental Protection Agency
Region III
Chesapeake Bay Program Office
Annapolis, Maryland
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iii
Contents
Foreword vii
Executive Summary ix
Acknowledgments xxi
I. Introduction 1
Background ¦ 1
Technical Support Document 3
Objective • 4
Structure and Content 4
Approach to Refining Tidal-Water Designated Uses 6
Determining attainment of current designated uses is not feasible .. 7
Justifying the refined tidal-water designated uses 8
Assessing attainability of the refined tidal-water designated uses . 9
Consideration of economic and social impacts 11
Jurisdiction Water Quality Standards and Tributary
Development Process 12
Literature Cited 12
II. The Chesapeake Bay and Its Watershed 13
Background 13
Chesapeake Bay Watershed 15
Chesapeake Bay Tidal-Water Quality Problems 18
Causes of Chesapeake Bay water quality problems 19
Human population increase 19
Loss of habitat 22
Excess nutrients 23
Excess sediments 25
Contents
-------
Sources of Nutrient Loads to the Chesapeake Bay
Tidal Waters 25
Nonpoint sources 29
Point sources 29
Atmospheric sources 32
Anthropogenic source inputs 34
III. Why Attaining the Current Tidal-Water Designated
Uses Appears Not to be Feasible 35
Background 35
Natural Conditions That May Prevent Attainment
of Current Designated Uses 36
Paleoecological record of natural conditions 36
Water quality conditions under completely forested
and pristine watersheds 38
Strengths and limitations of the all-forest and pristine scenarios . 40
Model-simulated natural dissolved oxygen conditions 40
Human-Caused Conditions That Cannot Be Remedied
Which Appear to Prevent
Attainment of Current Designated Uses 46
Findings and Conclusions 49
Literature Cited 49
t "
IV. Refined Designated Uses for the Chesapeake Bay
and Its Tidal Tributaries 53
Background 53
Renewed commitment to restore Chesapeake Bay Water quality . 53
Current state tidal-water designated uses 53
Refining Tidal-Water Designated Uses 59
Living resource-based refined designated uses
and protective criteria 60
Chesapeake Bay Tidal-Water Designated Uses 64
Migratory fish spawning and nursery designated use 64
Shallow-water bay grass designated use 67
Open-water fish and shellfish designated use 70
Deep-water seasonal fish and shellfish designated use 73
Deep-channel seasonal refuge designated use 76
Chesapeake Bay Tidal-Water Designated Use Boundaries 78
Migratory fish spawning and nursery designated use boundaries . 79
Open-water, deep-water and deep-channel designated
use boundaries 82
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V
Flow and circulation 85
Vertical density gradients and pycnoclines 86
Delineating the designated use boundaries 90
The boundary delineated process 90
Shallow-water bay grass designated use boundaries 105
Maximum depth of persistent or abundant plant
growth-based boundaries 106
Benefits of deeper underwater bay grass distribution 106
Historical underwater bay grass distribution 107
Underwater bay grass no-grow zones 108
Determining the maximum depth of persistent/abundant
plant growth .111
Underwater bay grass restoration goal-based boundaries 118
Shallow-water habitat area to support restoration
goal-based boundaries 123
Confirming That the Refined Designated Uses
Meet Existing Uses 123
Migratory spawning and nursery existing use 128
Shallow-water existing use 128
Open-water existing use 129
Deep-water and deep-channel existing uses 129
Literature Cited 129
V. Technological Attainability of the Refined Recommended
Designated Uses 135
Background .. 135
Defining and Determining Technological Attainability
for Dissolved Oxygen 136
Development of level-of-effort scenarios 136
Point sources 138
Onsite treatment systems 140
Nonpoint source agriculture ... 140
Nonpoint source urban 142
Nonpoint source forestry 143
Atmospheric deposition 143
Load reductions by tier 144
Development of the criteria attainability tables 144
Assessing criteria exceedance through the cumulative
frequency distributions 147
Applying the Kolmogorov-Smimov test for criteria
attainability using the CFD 149
Use of the' 10 percent default reference curve' versus
biological reference curves 150
Contents
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Consideration of Different Hydrology Periods 151
Technological attainability of the open-water, deep-water
and deep-channel designated uses 152
Migratory fish and spawning and nursery designated use
attainability 152
Open-water fish and shellfish designated use attainability 153
Deep-water seasonal fish and shellfish designated
use attainability 156
Deep-channel seasonal refuge designated use attainability 156
Sediment Reduction and Its Effect on Water Quality 157
Attainability of the Shallow-Water Designated Use 157
Attaining the shallow-water bay grass designated use 157
Measures to Attain the Shallow-Water Designated Use 159
Stream/Riverine BMPs 160
Shoreline BMPs 160
In-water BMPs 160
Literature Cited 160
VI. Summary of Economic Analyses 163
Estimated Costs ... 164
Screening-Level Impact Analysis 166
Economic Impacts and Benefits 168
Literature Cited ............ 170
Glossary 171
Acronyms 177
Appendices
A. Development of the Level-Effort Scenarios A-l
B. Data Supporting Determination of the Shallow-Water Designated
Use Depths and Underwater Bay Grasses Restoration Goals .... B-l
C. Underwater Bay Grasses No-Grow Zones C-l
D. Vertical Stratification and the Pycnoclines D-l
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vii
Foreword
In April 2003, the U.S. Environmental Protection Agency (EPA) Region III issued
guidance entitled Ambient Water Quality' Criteria for Dissolved Oxygen, Water
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries
(Regional Criteria Guidance). The development of the Regional Criteria Guidance
was the realization of a key commitment in the Chesapeake 2000 agreement. In that
agreement, the signatories (the states of Pennsylvania, Maryland and Virginia; the
District of Columbia; the Chesapeake Bay commission and the EPA) committed to,
"by 2001, define the water quality conditions necessary to protect aquatic living
resources." New York Delaware and West Virginia agreed to the same commitment
through a separate six-state memorandum of understanding with the EPA.
The EPA, in the Regional Criteria Guidance, defined the water quality conditions
called for in the Chesapeake 2000 agreement through the development of Chesa-
peake Bay-specific water quality criteria for dissolved oxygen, water clarity and
chlorophyll a. The EPA also identified and described five habitats, or designated
uses, that provide the context in which the EPA Region III derived adequately
protective Chesapeake Bay water quality criteria for dissolved oxygen, water clarity
and chlorophyll a. Collectively, the three water quality conditions provide the best
and most direct measures of the effects of too much nutrient and sediment pollution
on the Bay's aquatic living resources—fish, crabs, oysters, their prey species and
underwater bay grasses. These criteria were developed as part of a larger effort to
restore Chesapeake Bay water quality.
The Technical Support Document for the Identification of Chesapeake Bay Desig-
nated Uses and Attainability (Technical Support Document) was developed by the
EPA and its watershed partners to be a companion document to the Regional Criteria
Guidance. Because it describes the development and geographical extent of the
designated uses to which the water quality criteria may apply, the Technical Support
Document serves as a resource to the states to assist them in the development and
adoption of refined water quality standards. Specifically, the EPA developed the
Foreword
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Technical Support Document to help states in conducting use attainability analyses
(UAA) which they may conduct as part of their water quality standards development
and adoption processes.
The Technical Support Document is not law or regulation; it is guidance that states
in the Chesapeake Bay watershed may consider in the development and adoption of
revised water quality standards.
REBECCA W. HANMER, Director
Region III Chesapeake Bay Program Office
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ix
Executive Summary
In May 2003, the U.S. Environmental Protection Agency (EPA) Region III issued
guidance entitled Ambient Water Quality Criteria for Dissolved Oxygen, Water
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (Regional
Criteria Guidance). The EPA developed this guidance to achieve and maintain the
water quality conditions necessary to protect aquatic living resources of the Chesa-
peake Bay and its tidal tributaries. The Regional Criteria Guidance is intended to
assist the Chesapeake Bay jurisdictions—Maryland, Virginia, Delaware and the
District of Columbia—in adopting revised water quality standards to address nutrient
and sediment-based pollution in the Chesapeake Bay and its tidal tributaries. Part of
the jurisdictions' water quality standards development process may be to conduct use
attainability analyses (UAAs). The EPA developed the Technical Support Document
for Identifying Chesapeake Bay Designated Uses and Attainability (Technical
Support Document) to assist states in developing their individual UAAs.
The UAA process is traditionally conducted by individual states. However, the
multi-stakeholder body that guided the development of the water quality criteria for
the Chesapeake Bay, the Water Quality Steering Committee, determined that
providing UAA-related information on a watershed-wide scale would help promote
coordination and consistency across all jurisdictions. To that end, the Technical
Support Document provides a compilation of the basinwide analyses assimilated
collaboratively by the affected jurisdictions. The Technical Support Document is not
a regulation or a mandatory requirement. Rather, the EPA encourages the jurisdic-
tions to use the information in this document and, when appropriate, to perform
additional analyses tailored to each jurisdiction during their respective water quality
standards development processes.
In providing technical background information for the Bay jurisdictions to use in
their own UAAs, the Technical Support Document explains and documents why it
appears that the current designated uses for aquatic life protection cannot be attained
in all parts of the Chesapeake Bay and its tidal tributaries. The Technical Support
Document provides scientific data showing that natural and human-caused
Executive Summary
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X
conditions that cannot be remedied are the basis for the nonattainment and proposes
refined designated uses for the states to consider during their upcoming water quality
standards development and adoption processes. The document also provides scien-
tific data indicating that the refined designated uses are viable in many areas of the
Chesapeake Bay and its tidal tributaries and documents that the refined designated
uses protect existing aquatic life uses. Finally the document briefly summarizes
economic analyses performed by the Chesapeake Bay Program, including estimates
of the cost of implementing three of the four levels of control scenarios.
REGULATORY BACKGROUND
The Water Quality Standards Regulation (40 CFR 131.3) defines a UAA as "... a
structured scientific assessment of the factors affecting the attainment of a use which
may include physical, chemical, biological, and economic factors. . . (40 CFR
131.10[g]). The Water Quality Standards Regulation requires a state to conduct a
UAA when it designates uses that do not include those specified in Section 101(1 )(2)
of the Federal Water Pollution Control Act.1 A state must also conduct a UAA when
it wishes to remove a specified designated use of the Federal Water Pollution Control
Act or adopt subcategories of those specified uses that require less stringent criteria.
When conducting a UAA, a state must demonstrate that attaining the designated use
is not feasible due to one or more of six factors specified in Section 131.10(g) of the
Water Quality Standards Regulation. These factors are:
1. Naturally occurring pollutant concentrations prevent the attainment of the use;
2. Natural, ephemeral, intermittent, or low-flow conditions or water levels prevent
the attainment of the use, unless these conditions may be compensated for by
the discharge of a sufficient volume of effluent without violating state water
conservation requirements to enable uses to be met;
3. Human-caused conditions or sources of pollution prevent the attainment of the
use and cannot be remedied or would cause more environmental damage to
correct than to leave in place;
4. Dams, diversions or other types of hydrologic modifications preclude the
attainment of the use, and it is not feasible to restore the water body to its orig-
inal condition or to operate such modifications in a way that would result in the
attainment of the use;
5. Physical conditions related to the natural features of the water body, such as the
lack of a proper substrate, cover, flow, depth, pools, riffles and the like, unre-
lated to chemical water quality, preclude attainment of aquatic life protection
uses; and
'Section 101(a)(2) of the Federal Water Pollution Control Act states that "...it is the national goal that
wherever attainable, an interim goal of water quality which provides for the protection and
propagation of fish, shellfish, and wildlife and provides for recreation in and on the water be achieved
by July 1, 1983."
Executive Summary
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xi
6. Controls more stringent than those required by sections 301(b)(1)(A) and (B)
and 306 of the Act would result in substantial and widespread economic and
social impacts.
The Water Quality Standards Regulation also specifies that any change in designated
uses must show that the existing uses are still being protected. The EPA's 1983 Water
Quality> Standards Handbook provides two definitions for an existing use. First, an
existing use can be defined as fishing, swimming or other uses that have actually
occurred since November 28, 1975. The second definition of an existing use is that
the water quality of a water body is suitable to allow the use to be attained—unless
there are physical problems, such as substrate or flow, that prevent use attainment.
The Water Quality Standards Regulation, in turn, requires state anti-degradation
policies to protect existing water quality. Therefore, any recommendations regarding
refined designated uses for the Chesapeake Bay and its tidal tributaries must ensure
that existing aquatic life uses continue to be protected.
DOCUMENTING WHY CURRENT DESIGNATED USES
MAY NOT BE ATTAINABLE
The determination documented in the Technical Support Document that current
designated uses in the Chesapeake Bay and its tidal tributaries may not be attainable
is based on two of the six factors noted above—natural and human-caused condi-
tions that cannot be remedied. Output from model-simulated scenarios as well the
paleoecological record of the Chesapeake Bay ecosystem both provide evidence that
these two conditions prevent attainment of current designated uses.
To understand the feasibility of attaining current designated uses in the Chesapeake
Bay and its tidal tributaries, the Chesapeake Bay Program developed three watershed
modeling scenarios: 'all-forest,' 'pristine' and 'everything, everywhere by everyone,'
or the E3 scenario. The 'all-forest' and 'pristine' scenarios represent the Chesapeake
Bay Program's best effort to simulate water quality conditions prior to European
settlement and, in so doing, help characterize existing, naturally occurring pollutant
concentrations that prevent attainment of current designated uses. To represent
human-caused conditions that cannot be remedied and to determine the upper
boundaries of the watershed's technological capability for reducing nutrient and
sediment pollution, the Chesapeake Bay Program also developed the E3 scenario,
which the watershed partners consider physically implausible.
Figure 1 illustrates the results of these three model scenarios, which show that signif-
icant portions of the deep channel and deep waters of the Chesapeake Bay and its
tidal tributaries cannot meet a dissolved oxygen concentration of 5 mg/1. For the
pristine scenario, on a baywide basis for all tidal-water segments that have
deep-channel and deep-water areas, attainment is not achieved for portions (i.e.,
approximately 3 percent and 1 percent, respectively) of these areas during the
summer months. For the E3 scenario, 59 percent, 23 percent and 2 percent
Executive Summary
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xii
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40
30
20
10
Deep-Channel Deep-Water Open-Water
Refined Tidal-Water Designated Uses
Migratory
Figure 1. Percent nonattainment of a 5 mg/l monthly average dissolved oxygen concentration over
the June through September period for the E3 (physically implausible) (|), all-forest ([]) and pristine
(|) model scenarios by the refined tidal-water designated uses.
non-attainment are exhibited in the deep-channel, deep-water and open-water areas,
respectively, even after implementation of nutrient reduction measures that represent
limits of technology.
In addition to modeled information, the Chesapeake Bay Program has evidence from
the paleoecological record of the Chesapeake Bay ecosystem to support the concept
that natural conditions prevent attainment of current designated uses. An evaluation
of this information suggests that the main channel of the Chesapeake Bay most likely
experienced oxygen depletion before large-scale post-colonial land clearance took
place, due to natural factors such as climate-driven variability in freshwater inflow.
DEVELOPMENT OF THE REFINED DESIGNATED USES
Current designated uses for the Chesapeake Bay and its tidal tributaries do not fully
reflect natural conditions and are too broad in their definition of use to support the
adoption of more habitat-specific aquatic life water quality criteria. The current uses
also change across jurisdictional borders within the same water body. Therefore, in
Executive Summary
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xiii
refining the tidal-water designated uses, the six Bay watershed states and the District
of Columbia considered five principal factors:
• Habitats used in common by sets of species and during particular life stages
should be delineated as separate designated uses;
• Natural variations in water quality should be accounted for by the designated
uses;
• Seasonal uses of different habitats should be factored into the designated uses;
• The Chesapeake Bay criteria for dissolved oxygen, water clarity and chloro-
phyll a should be tailored to support each designated use; and
• The refined designated uses applied to the Chesapeake Bay and its tidal tribu-
tary waters will support the federal Clean Water Act goals and state goals for
uses existing in these waters since 1975.
The five refined designated uses reflect the habitats of an array of recreationally,
commercially and ecologically important species and biological communities. The
vertical and horizontal breadth of the designated use boundaries are based on a
combination of natural factors, historical records, physical features, hydrology,
bathymetry and other scientific considerations (Figure 2).
The migrator)' fish spawning and nursery designated use protects migratory and
resident tidal freshwater fish during the late winter to late spring spawning and
nursery season in tidal freshwater to low-salinity habitats. Located primarily in the
upper reaches of many Bay tidal rivers and creeks and the upper mainstem Chesa-
peake Bay, this use will benefit several species including striped bass, perch, shad,
herring, sturgeon and largemouth bass.
The shallow-water bay grass designated use protects underwater bay grasses and the
many fish and crab species that depend on the vegetated shallow-water habitat
provided by underwater grass beds.
The open-water fish and shellfish designated use focuses on surface water habitats
in tidal creeks, rivers, embayments and the mainstem Chesapeake Bay and protects
diverse populations of sport fish, including striped bass, bluefish, mackerel and sea
trout, as well as important bait fish such as menhaden and silversides.
The deep-water seasonal fish and shellfish designated use protects animals inhab-
iting the deeper transitional water-column and bottom habitats between the
well-mixed surface waters and the very deep channels. This use protects many
bottom-feeding fish, crabs and oysters, and other important species such as the bay
anchovy.
The deep-channel seasonal refuge designated use protects bottom sediment-
dwelling worms and small clams that bottom-feeding fish and crabs consume. Low
to occasional no dissolved oxygen conditions occur in this habitat zone during the
summer.
Executive Summary
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xiv
A. Cross-Section of Chesapeake Bay or Tidal Tributary
Shallow-Water
Bay Grass Use
Open-Water
Fish and Shellfish Use
Deep-Water
Seasonal Fish and
Shellfish Use
— Deep-Channel
Seasonal Refuge Use
B. Oblique View of the Chesapeake Bay and its Tidal Tributaries
Migratory Fish
Spawning and
, Nursery Use
Shallow-Water
Bay Grass Use
Open-Water
Fish and Shellfish Use
Deep-Water
Seasonal Fish and
Deep-Channel
Seasonal Refuge Use
Shellfish Use
Figure 2. Conceptual illustration of the five Chesapeake Bay tidal-water designated use zones.
ATTAINABILITY OF REFINED DESIGNATED USES
The Chesapeake Bay Program assessed attainability for the refined designated uses
based on dissolved oxygen for the migratory and spawning, open-water, deep-water
and deep-channel designated uses. Attainability for the shallow-water designated use
was assessed based on historic and recent data on the existence of underwater bay
grass acreage. The Chesapeake Bay Program did not assess attainability for the
chlorophyll a criteria, which applies to the open-water designated use, because this
Executive Summary
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XV
criteria is expressed in narrative terms and does not provide a numeric value around
which to perform attainability analyses.
For the refined designated uses to which the dissolved oxygen criteria applies, the
Chesapeake Bay Program evaluated attainability by comparing the modeled water
quality response to a series of technology-based nutrient reduction scenarios. This
series of scenarios was developed to represent the watershed's nutrient and sediment
reduction potential in terms of the types, extent of implementation and performance
of best management practices (BMPs), wastewater treatment technologies and storm
water controls.2 These scenarios range from Tier 1, which represents the current
level of implementation plus regulatory requirements implemented through 2010, to
a theoretical limit-of-technology scenario referred to as the E3 scenario ('everything,
everywhere by everybody'). Tier 2 and Tier 3 are intermediate scenarios between
Tier 1 and the E3 scenario. It is important to note that these tiers are artificial
constructs of technological levels of effort and do not represent actual programs that
the jurisdictions will eventually implement to meet the water quality standards.
Rather, the Chesapeake Bay Program developed the tiers as an assessment tool to
determine potential load reductions achievable by various levels of technological
effort, and to model water quality responses to controls.
The Chesapeake Bay Program used the Chesapeake Bay Watershed and Water
Quality Models to determine the water quality response to the pollutant reductions in
each scenario (Table 1) and then compared these modeled water quality observations
within the five refined designated uses to determine the spatial and temporal extent of
nonattainment with the respective dissolved oxygen criteria. Specifically, comparison
of model results for dissolved oxygen were made to a monthly average dissolved
oxygen concentration of 6 mg/1 for the migratory and spawning use, 5 mg/1 for the
open-water use, 3 mg/1 for the deep-water use and 1 mg/1 for the deep-channel use.
Table 1. Summary of pollutant loadings that result from applying the load
reductions associated with each scenario across all nutrient and sediment
sources (except shoreline erosion) in the watershed.
2000
2010
2010
2010
2010
Pollutant
Progress
Tier 1
Tier 2
Tier 3
E3
Nitrogen
284.8
260.9
221.3
180.8
116.4
Phosphorus
19.12
18.96
16.41
13.38
10.10
Sediment
5.044
4.644
4.144
3.625
2.953
2Sediment reduction is only reflected in the scenarios as that incidental to nutrient removal.
Executive Summary
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xvi
MIGRATORY AND SPAWNING DESIGNATED USE
Current monitoring data and Chesapeake Bay Water Quality Model outputs indicate
that the migratory and spawning designated use is essentially being attained in the
Chesapeake Bay and its tidal tributaries for dissolved oxygen. The few segments that
are not fully attaining the dissolved oxygen criterion would fully attain this use in
the Tier 1 scenario (lowest level of control technologies).
OPEN-WATER, DEEP-WATER AND DEEP-CHANNEL
DESIGNATED USES
Table 2 provides the results of the attainability analysis for dissolved oxygen for the
open-water (including shallow-water)3, deep-water and deep-channel designated
uses, by Chesapeake Bay Program segment. As Table 2 illustrates, current moni-
toring data (presented under the 'observed' column) indicate that the open-water
designated use is seldom fully attained. However, at Tier 3, attainment for about 60
percent of the segments is achieved for this refined designated use. In most cases
where nonattainment is indicated for open-water at Tier 3, it is less than 2 percent
nonattainment, and often, less than 1 percent. For the deep-water designated use for
dissolved oxygen criteria, almost no attainment is achieved based on current moni-
toring data and only some degree of attainment is seen at reduction levels equivalent
to Tier 2. At the reduction levels represented by the E3 scenario, attainment is
achieved for all segments of the Chesapeake Bay except for one (middle central
Chesapeake Bay, CB4MH). Table 2 illustrates that, under observed conditions, the
proposed dissolved oxygen criteria are not attained for the deep-channel designated
use. With increasing load reductions, however, 100 percent attainment is achieved at
the E3 scenario, and, at the levels of reduction represented by Tier 3, percent non-
attainment is primarily less than 2 percent.
SHALLOW-WATER BAY GRASS DESIGNATED USE
Attainability for the shallow-water bay grass designated use is based on historic and
recent data on the distribution of underwater bay grasses. Detailed analyses using
this data—including historical aerial photographs—were undertaken to map the
distribution and depth of historical underwater bay grass beds in the Chesapeake Bay
and its tidal tributaries. These analyses led to the adoption of the single best year
method that considers historical underwater bay grass distributions from the 1930s
through the early 1970s as well as more recent distributions since 1978 to present.
Using this method, the Chesapeake Bay Program and its watershed partners estab-
lished a baywide underwater bay grass restoration goal of 185,000 acres. Because of
limitations associated with mapping underwater bay grasses using historical photog-
raphy, the estimate of past underwater bay grass distributions is conservative.
Therefore, the restoration goal is conservative as well and considered attainable.
3Because the dissolved oxygen criteria is the same for the open-water as for the shallow-water use,
attainability for the shallow-water designated use is presented under the open-water designated use in
Table 2.
Executive Summary
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xvii
Table 2. Percent nonattainment of monthly averaged 5, 3 and 1 mg/l dissolved oxygen concentrations
applied to open-water, deep-water and deep-channel designated uses, respectively.
Model Scenarios
Chesapeake Bay Program Segment
DU
Observed
Tier 1
Tier 2
Tier 3
E 3
Northern Chesapeake Bay(CBlTF)
ow
A
A
A
A
A
Upper Chesapeake Bay (CB20H)
ow
1.92
0.68
0.43
0.17
A
Upper Central Chesapeake Bay (CB3MH)
ow
A
A
A
A
A
DW
4.18
2.24
1.61
0.73
A
DC
13.52
7.21
5.03
1.84
A
Middle Central Chesapeake Bay (CB4MH)
OW
0.05
A
A
A
A
DW
19.64
14.28
12.05
8.51
0.69
DC
45.19
28.94
18.81
3.93
A
Lower Central Chesapeake Bay (CB5MH)
OW
A
A
A
A
A
DW
6.16
3.75
2.58
1.08
A
DC
13.79
6.00
2.59
0.15
A
Western Lower Chesapeake Bay (CB6PH)
OW
5.87
3.68
2.71
1.30
0.01
DW
0.36
A
A
A
A
Eastern Lower Chesapeake Bay (CB7PH)
OW
4.55
2.81
1.82
0.74
A
DW
A
A
A
A
A
Mouth of Chesapeake Bay (CB8PH)
OW
A
A
A
A
A
Upper Patuxent River (PAXTF)
OW
A
A
A
A
0.38
Middle Patuxent River (PAXOH)
OW
9.79
1.84
1.62
0.86
A
Lower Patuxent River (PAXMH)
OW
7.40
1.69
1.04
0.01
A
DW
5.52
0.82
0.50
0.07
A
Upper Potomac River (POTTF)
OW
A
A
A
A
A
Middle Potomac (POTOH)
OW
2.10
1.08
0.63
0.31
0.01
Lower Potomac (POTMH)
OW
0.78
A
A
A
A
DW
6.90
4.53
3.11
1.12
A
DC
18.89
8.64
5.07
0.19
A
Upper Rappahannock River (RPPTF)
OW
A
A
A
A
A
Middle Rappahannock River (RPPOH)
OW
A
A
A
A
A
Lower Rappahannock River (RPPOH)
OW
0.44
0.10
A
A
A
DW
5.58
1.09
0.01
A
A
DC
6.39
3.38
1.65
A
A
Piankatank River (PIAMH)
OW
0.12
A
A
A
A
Upper Mattaponi River (MPNTF )
OW
33.26
25.87
27.23
33.73
52.14
Lower Mattaponi River (MPNOH)
OW
46.88
28.95
31.86
28.99
48.11
Upper Pamunkey River (PMKTF )
OW
62.25
42.07
30.35
32.94
54.50
continued
Executive Summary
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Table 2. Percent nonattainment of monthly averaged 5, 3 and 1 mg/l dissolved oxygen concentrations
applied to open-water, deep-water and deep-channel designated uses, respectively (cortt.).
Model Scenarios
Chesapeake Bay Program Segment
DU
Observed
Tier 1
Tier 2
Tier 3
E 3
Lower Pamunkey (PMKOH)
OW
42.15
12.66
13.86
10.32
11.39
Middle York River (YRKMH)
OW
18.08
3.31
2.32
0.42
A
Lower York River (YRKPH)
OW
1.48
A
A
A
A
DW
0.01
A
A
A
A
Mobjack Bay (MOBPH)
OW
2.30
1.60
1.10
0.34
A
Upper James River (JMSTF)
OW
0.66
A
A
A
A
Middle James River (JMSOH)
OW
A
A
A
A
A
Lower James River (JMSMH)
OW
A
A
A
A
A
Mouth of the James River (JMSPH )
OW
A
A
A
A
A
Eastern Bay (EASMH)
OW
A
A
A
A
A
DW
3.26
2.00
0.90
0.36
A
DC
20.23
11.26
6.49
0.67
A
Middle Choptank River (CHOOH)
OW
0.14
A
A
A
A
Lower Choptank River (CH0MH2)
OW
2.27
1.78
1.51
1.08
0.43
Mouth of the Choptank River (CHOMHl )
OW
0.33
A
A
A
A
Tangier Sound (TANMH)
OW
0.15
0.06
0.05
0.36
0.22
Lower Pocomoke River (POCMH)
OW
A
A
A
A
A
A = Applicable dissolved oxygen criteria fully attained; analysis based on monthly averaged dissolved oxygen concentrations 5 mg/l, 3 mg/l and
1 mg/l for open-water, deep-water and deep-channel designated uses.
DU = designated use; OW—open-water; DW—deep-water; DC-deep-channel.
CONFIRMATION THAT EXISTING USES ARE MET
In establishing the refined designated uses, the Chesapeake Bay Program took
explicit steps in developing the requirements and boundaries to ensure that existing
aquatic life uses would continue to be protected as the EPA Water Quality Standards
Regulation require. For some refined designated uses—the migratory fish spawning
and nursery, the deep-water and the deep-channel—the application of new dissolved
oxygen criteria will result in improvements to existing water quality conditions. The
refined open-water fish and shellfish designated use dissolved oxygen criteria will
provide an equal level of protection as the current state water quality standards afford
to the same tidal waters. Likewise, the refined shallow-water bay grass designated
use also ensures protection of existing underwater bay grass-related uses because the
single best year method is based on historical (1930s through the early 1970s) and
more recent (1978-present) underwater bay grass distributions.
Executive Summary
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xix
ECONOMIC ANALYSES
The Technical Support Document summarizes three types of economic analyses that
the Chesapeake Bay Program performed in conjunction with developing revised
water quality criteria, designated uses and boundaries for those uses in the Chesa-
peake Bay and its tidal waters. One analysis was undertaken to estimate the costs of
implementing the hypothetical control scenarios (represented by the Tier 1-3
scenarios). Screening-level analyses are the second type of analysis summarized.
These analyses were conducted to rule out areas that would not experience substan-
tial and widespread economic and social impacts if states implemented controls
more stringent than those required by sections 301 and 306 of the Clean Water Act.
The results of analyses to model regional economic impacts is the third type of
analysis summarized in the Technical Support Document.
A separate document entitled Economic Analyses and Impacts of Nutrient and
Sediment Reduction Actions in the Chesapeake Bay Watershed (Economic
Analyses) presents detailed descriptions of these three types of analysis and the
attendant findings.
Table 3 summarizes the results of the cost analyses described in detail in the
Economic Analyses document. Captured in the table are the total capital and annual
costs (annualized capital plus annual operation and maintenance [O&M] costs) asso-
ciated with the tier scenarios. The cost analysis and other economic analyses provide
information related to evaluating impacts from the implementation of the nutrient
reduction measures defined in the tier scenarios. However, the Chesapeake Bay
Program did not use these analyses to delineate boundaries for the refined designated
uses. Although this information may be useful to them in developing their own
UAAs, states will need to conduct more rigorous economic analyses than the
analyses performed by the Chesapeake Bay Program.
Table 3. Estimated cumulative costs and pollutant loading reductions associated
with the Tier 1-3 scenarios and the E3 scenario.
Tier
Total Nitrogen Reduction
from Levels in 2000
(millions pounds per year)1
Total Capital Costs
(in millions 2001 dollars)2
Total Annual Costs
(in millions 2001 dollars)2
Tier 1
23.9
$1,391
$196
Tier 2
63.5
$3,593
$553
Tier 3
104.0
$7,713
$1,125
E33
168.4
Not estimated
Not estimated
1. Loadings based on Phase 4.3 of the Chesapeake Bay Program's Watershed Model.
2. Costs include those paid by private-sector businesses and households in addition to those paid by public entities
that provide cost-share funding for nutrient reduction controls and BMPs.
3. The E3 scenario represents a theoretical limit-of-technology control scenario that provides a maximum loadings
reduction estimate.
Executive Summary
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xxi
Acknowledgments
This Technical Support Document for Identifying Chesapeake Bay Designated
Uses and Attainability was developed through the collaborative efforts, collec-
tive knowledge and applied expertise of the Chesapeake Bay Program Water Quality
Steering Committee's Use Attainability Analysis Workgroup; the Chesapeake Bay
Program's Modeling, and Monitoring and Assessment subcommittees; the Chesa-
peake Bay Program's Nutrient Subcommittee workgroups: the Agricultural Nutrient
Reduction Workgroup, the Forestry Workgroup, the Point Source Workgroup, the
Urban Storm Water Workgroup, the Tributary Strategy Workgroup and the Sediment
Workgroup.
USE ATTAINABILITY ANALYSIS WORKGROUP
Cheryl Atkinson, U.S. EPA Region III; Michael Bowman, Virginia Department of
Conservation and Recreation; Thomas Burke, Maryland Department of Natural
Resources; Eloise Castillo, SAIC; Karen Clark U.S. EPA Office of General Counsel;
Jared Creason, U.S. EPA National Center for Environmental Economics; Elleanore
Daub, Virginia Department of Environmental Quality; Robert Ehrhart, Virginia
Department of Environmental Quality; Richard Eskin, Maryland Department of the
Environment; David Frackelton; William Gerlach, Chesapeake Bay Foundation;
Jean Gregory, Virginia Department of Environmental Quality; Samuel Hamilton,
Virginia Agribusiness Council; Katherine Bunting Howarth, Delaware Department
of Natural Resources and Environmental Control; Lisa Huff, U.S. EPA Office of
Water; Wayne Jackson, U.S. EPA Region II; Jim Keating, U.S. EPA Office of Water;
Robert Krehely, Wyoming Valley Sanitary Authority; Norm LeBlanc, Hampton
Roads Sanitation District; Gary Madson; Chris Miller, U.S. EPA, Garrison Miller, U.
S. EPA Region III; Mark Morris, U.S. EPA Office of Water; Doug Parker, University
of Maryland; George Parsons, University of Delaware; Alan Pollock, Virginia
Department of Environmental Quality; Christopher Pomeroy, AquaLaw; John
Schneider, Delaware Natural Resources and Environmental Conservation; Roy
Seward, Virginia Department of Agriculture and Consumer Services; Carol Ann
Acknowledgments
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xxii
Siciliano; U. S. EPA Office of General Council; Tanya Tomasko Spano, Metropol-
itan Washington Council of Governments; Allison Wiedeman, U.S. EPA Chesapeake
Bay Program Office; Robert Wieland, Main Street Economics; Clyde Wilber, Greely
and Hanson; and Carol Young, Pennsylvania Department of Environmental Protec-
tion.
MODELING SUBCOMMITTEE
Lowell Bahner, National Oceanic and Atmospheric Administration; Mark Bennett,
US Geological Survey; Peter Bergstrom, NOAA Chesapeake Bay Office; Mike
Bowman, VA Department of Conservation and Recreation; Bill Brown, PA Depart-
ment of Environmental Protection; Arthur Butt, VA Department of Environmental
Quality; James R. Collier, DC Department of Health; Robin Dennis, US Environ-
mental Protection Agency; Lewis Linker, US Environmental Protection Agency;
Charles A Lunsford, VA Department of Conservation and Recreation; Robert
Magnien, MD Department of Natural Resources; Ross Mandel, Interstate Commis-
sion on the Potomac River Basin; Timothy J. Murphy, Metropolitan Washington
Council of Governments; Narendra Panday, MD Department of the Environment;
Kenn Pattison, PA Department of Environmental Protection; Jeff Raffensperger, US
Geological Survey; Helen Stewart, MD Department of Natural Resources; Peter
Tango, MD Department of Natural Resources; and Harry Wang, VA Institute of
Marine Science.
MONITORING AND ASSESSMENT SUBCOMMITTEE
Kurt Brandstaetter, Chesapeake Research Consortium; Mike Bowman, VA Depart-
ment of Conservation and Recreation; Claire Buchanan, Interstate Commission on
the Potomac River Basin; Jerry Griswold, Natural Resources Conservation Service;
Carlton Haywood, Interstate Commission on the Potomac River Basin; Rick
Hoffman, Department of Environmental Quality; Lewis Linker, US Environmental
Protection Agency; Robert Magnien, MD Department of Natural Resources; Paul
Massicot, MD Department of Natural Resources; Beth McGee, US Fish and Wildlife
Service; Hassan Mirsajadi, DE Department of Natural Resources and Environmental
Conservation; Matt Monroe, Department of Agriculture; Derek Orner, National
Oceanic and Atmospheric Administration; Scott Phillips, US Geological Survey;
Steve Preston, US Geological Survey; Richard Shertzer, PA Department of Environ-
mental Protection; and John Sherwell, MD Department of Natural Resources.
NUTRIENT SUBCOMMITTEE
Mike Bowman, VA Department of Conservation and Recreation; Terry Black, PA
Department of Environmental Protection; Michael Brown, DE Department of
Natural Resources and Environmental Control; Katherine Bunting-Howarth, DE
Department of Natural Resources & Environmental Control; Collin Burrell, DC
Department of Health; Sally Claggett, US Forest Service; Kim Collini, Chesapeake
Acknowledgments
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xxiii
Research Consortium; Martha Corrozi, Chesapeake Research Consortium; Scott
Crafton, VA Chesapeake Bay Local Assistance Department; Melanie Davenport,
Chesapeake Bay Commission; Bob Ehrhart, VA Department of Environmental
Quality; J Michael Foreman, VA Department of Forestry; Jeffrey Halka, MD
Geological Survey; Maggie Kerchner, National Oceanic and Atmospheric Adminis-
tration; Mike Langland, US Geological Survey; Scott Macomber, MD Department
of the Environment; Russell Mader, Natural Resources Conservation Service; Matt
Monroe, WV Department of Agriculture; John Murtha, PA Department of Environ-
mental Protection; Kenn Pattison, PA Department of Environmental Protection; Russ
Perkinson, VA Department of Conservation and Recreation; Steele Phillips, Citizens
Advisory Committee; Royden Powell, MD Department of Agriculture; Kelly Shenk,
US Environmental Protection Agency; John Sherwell, MD Department of Natural
Resources; Thomas W. Simpson, University of Maryland; Randolph Sovic, WV
Department of Environmental Protection; and Mark Waggoner, Natural Resources
Conservation Service.
AGRICULTURAL NUTRIENT REDUCTION WORKGROUP
Martha Corrozi, Chesapeake Research Consortium; John Davis, USDA-NRCS;
Doug Goodlander, PA State Conservation Commission; Jerry Griswold, Natural
Resources Conservation Service; Tom Juengst, PA Department of Environmental
Protection; Maggie Kerchner, National Oceanic and Atmospheric Administration;
Matt Monroe, WV Department of Agriculture; Russ Perkinson, VA Department of
Conservation and Recreation; Herb Reed, University of MD-Cooperative Extension;
Diana Reynolds, MD Department of Natural Resources; William Rohrer, Delaware
Nutrient Management Commission; Fred Samadani, MD Department of Agriculture;
Ron Wood, VA Chesapeake Bay Local Assistance Department.
POINT SOURCE WORKGROUP
Martha Corrozi, Chesapeake Research Consortium; Bob Ehrhart, VA Department of
Environmental Quality; Marya Levelev, MD Department of the Environment;
Russell Mader, Natural Resources Conservation Service; John Murtha, PA Depart-
ment of Environmental Protection; William Ruby, DC Department of Health;
Randolph Sovic, WV Department of Environmental Protection; Tanya Spano,
Metropolitan Washington Council of Governments; Allison Wiedeman, U.S. EPA
Chesapeake Bay Program Office; and Ning Zhou, VA Tech.
SEDIMENT WORKGROUP
Mike Bowman,VA Department of Conservation and Recreation; Owen Bricker, US
Geological Survey; Grace S. Brush, Johns Hopkins University; Kim Collini, Chesa-
peake Research Consortium; Thomas M Cronin, US Geological Survey; Lee Currey,
MD Department of the Environment; Robert E Edwards, Susquehanna River Basin
Commission; Jeffrey Halka, MD Geological Survey; Allen Gellis, US Geological
Acknowledgments
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xxiv
Survey; Normand Goulet, Northern VA Regional Commission; Jerry Griswold,
Natural Resources Conservation Service; Amy Guise, US Army Corps of Engineers;
Julie Herman, VA Institute of Marine Science; Lee Hill, VA Department of Conser-
vation and Recreation; Timothy Karikari, DC Department of Health; Mike Langla,
US Geological Survey; Kenn Pattison, PA Department of Environmental Protection;
Scott Phillips, US Geological Survey; Brian Rustia, Metropolitan Washington
Council of Governments; Larry Sanford, University of MD Center for Environ-
mental Science; Gary Shenk, US Environmental Protection Agency; Sean Smith,
MD Department of Natural Resources; Steve Stewart, Baltimore County Depart-
ment of Environmental Protection & Resource Management; and Debra Willard, US
Geological Survey
TRIBUTARY STRATEGY WORKGROUP
Mark Bennett, US Geological Survey; Sheila Besse, DC Department of Health;
Mike Bowman, VA Department of Conservation and Recreation; Katherine Bunting-
Howarth, DE Department of Natural Resources & Environmental Control; Twila
Carr, WV Department of Environmental Protection; Kim Collini, Chesapeake
Research Consortium; Donald Fiesta, PA Department of Environmental Protection;
Normand Goulet, Northern VA Regional Commission; Jerry Griswold, Natural
Resources Conservation Service; V'lent Lassiter, VA Department Of Conservation &
Recreation; Lewis Linker, US Environmental Protection Agency; Scott Macomber,
MD Department of the Environment; Russell Mader, Natural Resources Conserva-
tion Service; Kenn Pattison, PA Department of Environmental Protection; Diana
Reynolds, MD Department of Natural Resources; Brian Rustia, Metropolitan Wash-
ington Council of Governments; Gary Shenk, US Environmental Protection Agency;
Thomas W. Simpson, University of Maryland; Helen Stewart, MD Department of
Natural Resources; and Jeffrey Sweeney, University of Maryland.
URBAN STORM WATER WORKGROUP
Meg Andrews, Maryland Dept. of Transportation; Joseph Battiata, VA Department
of Transportation; David Beale, VA Department of Conservation and Recreation;
Ronald Bowen, Anne Arundel County Dept. of Public Works; Ted Brown, Center
for Watershed Protection; Walter Caldwell, DC Department of Health; John Carlock,
Hampton Roads Planning District Committee; R. Scott Christie, PA Department of
Transportation; Kim Coble, Chesapeake Bay Foundation; Larry Coffman, Prince
George's County; Martha Corrozi, Chesapeake Research Consortium; Scott
Crafton, VA Chesapeake Bay Local Assistance Department; Larry Gavan, VA
Department of Conservation and Recreation; Normand Goulet, Northern VA
Regional Commission; Lisa Grippo, US Navy; Timothy Karikari, DC Department of
Health; Kenneth Murin, PA Department of Environmental Protection; Ratilal B
Patel, PA Department of Environmental Protection; Ken Pensyl, MD Department of
the Environment; Brian Rustia, Metropolitan Washington Council of Governments;
Kelly Shenk, US Environmental Protection Agency; Bill Stack, Baltimore City;
Acknowledgments
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XXV
Steve Stewart, Baltimore Co. Dept. of Env. Protection & Resource Management;
Nancy Stoner, Natural Resources Defense Council; Burt Tuxford, VA Department of
Environmental Quality; and Raja Veeramachaneni, Maryland State Highway
Administration.
INDIVIDUALS
Richard Batiuk, U. S. EPA Chesapeake Bay Program; Christopher Day U.S. EPA
Region III, Dave Jasinski, University of MD; Wendy Jastremski, U.S. EPA Region
III, Bob Koroncai, U.S. EPA Region III; Marcia Olson, Chesapeake Bay Program
NOAA; Nita Sylvester, U.S. EPA Chesapeake Bay Program; and Howard Weinberg,
UMCES.
The technical editing, document preparation and desk-top publication contributions
of Donna An, Robin Bisland, Lois Gartner, Lauren Petruzzi and Susan Vianna are
hereby acknowledged.
Acknowledgments
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1
chapter |
Introduction
BACKGROUND
In 1987, the governors of Maryland, Virginia and Pennsylvania; the Mayor of the
District of Columbia, the U.S. Environmental Protection Agency (EPA) adminis-
trator and the chair of the Chesapeake Bay Commission signed the Chesapeake Bay
Agreement. This historic agreement stated that a 40 percent reduction in nutrients
entering the Chesapeake Bay would be necessary to restore its health (Chesapeake
Executive Council 1987). The goal targeted a 40 percent reduction of controllable
nutrient loads from point and nonpoint sources from 1985 levels by the year 2000.
The partners to the Chesapeake Bay Agreement committed that once achieved, these
levels of reduced nutrient loads would continue to be maintained into the future.
In spite of the widespread implementation of best management practices (BMPs) and
enhanced treatment technologies across the Chesapeake Bay watershed, nutrient- and
sediment-related water quality problems have persisted. Figure 1-1 illustrates the listed
nutrient- and/or sediment-impaired waterbodies in the Chesapeake Bay watershed.
Maryland's portion of the Chesapeake Bay and its tidal tributaries were listed on its
1996 and 1998 Clean Water Act (CWA) Section 303(d) lists of impaired waters. In
May 1999, EPA Region III included Virginia's portion of the Chesapeake Bay and
portions of several tidal tributaries on Virginia's 1998 CWA Section 303(d) list.
Delaware listed its tidally influenced portions of the Chesapeake Bay waters on their
1996 and 1998 lists, and the District of Columbia listed its Chesapeake Bay waters in
1998. Streams and rivers also are listed for nutrient and/or sediment in the nontidal
portions of the Chesapeake Bay watershed in all seven Chesapeake Bay watershed
jurisdictions, including West Virginia, Pennsylvania, and New York.
The new Chesapeake 2000 agreement was developed in response to a comprehen-
sive assessment of the Chesapeake Bay's restoration needs and delineated an
ambitious list of new restoration commitments (Chesapeake Executive Council
2000). The significant focus on restoration of Chesapeake Bay water quality resulted
from the listing of most of the Chesapeake Bay and its tidal tributaries on the 303(d)
list of impaired waters. Subsequently, the governors of Delaware, New York and
West Virginia signed a Memorandum of Understanding with Maryland, Virginia,
chapter i • Introduction
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2
Atlantic Ocean
Figure 1-1 Nutrient, sediment and dissolved oxygen impaired waterbodies in the Chesapeake Bay water-
shed from the 1998 303(d) list illustrated as points (•), linear (-) or area (solid black) events.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter i • Introduction
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3
Pennsylvania, the District of Columbia and the EPA committing to implement the
Water Quality Protection and Restoration section of the agreement (Chesapeake Bay
Watershed Partners 2001).
Chesapeake 2000 specifies a goal to remove the Chesapeake Bay and its tidal tribu-
taries from the list of impaired waterbodies for nutrients and sediments by 2010.
Thus, the development of a total maximum daily load (TMDL) for the entire Chesa-
peake Bay was delayed until 2011, anticipating that the Chesapeake Bay Program
partners can cooperatively achieve water quality standards by that time, making a
baywide TMDL unnecessary.
Chesapeake 2000 lists the following specific commitments as steps to achieve its
water quality goal of eliminating nutrient- and sediment-related impairments from
tidal waters:
1. By 2001, define water quality conditions (i.e., criteria) necessary to protect
aquatic living resources and then assign load reductions for nitrogen, phos-
phorus and sediment to each major tributary;
2. By 2002, complete a public process to develop and begin implementing revised
Tributary Strategies to achieve and maintain the assigned loading goals; and
3. By 2003, jurisdictions with tidal waters will use their best efforts to adopt new
or revised water quality standards consistent with the defined water quality
conditions.
Although the above commitments still stand, the schedule has changed. The current
schedule that all seven watershed jurisdictions and the EPA agreed to calls for:
• Final definitions of water quality conditions (i.e., criteria) by April 2003;
• Development of new and revised tributary strategies by April 2004; and
• Adoption of new and revised state water quality standards by 2005.
To implement and coordinate these actions, the Chesapeake Bay Program formed the
Chesapeake Bay Water Quality Steering Committee, composed of senior managers
from the EPA, state environmental quality, natural resource management, and agri-
cultural agencies, the Chesapeake Bay Commission, interstate river basin
commissions, the environmental community and wastewater treatment operators.
Under the Water Quality Steering Committee, a Use Attainability Analysis (UAA)
Workgroup was convened to collaboratively assess the attainability of the refined
designated uses for the Chesapeake Bay and its tidal tributaries.
TECHNICAL SUPPORT DOCUMENT
This document provides the Chesapeake Bay jurisdictions4 with information to assist
them in adopting water quality standards to protect aquatic life in the Chesapeake
4The jurisdictions that will develop and adopt revised water quality standards in response to this effort
are those with Chesapeake Bay and tidal tributary waters listed as state waters: Maryland, Virginia,
Delaware and the District of Columbia.
chapter i • Introduction
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4
Bay and its tidal tributaries against nutrient and sediment enrichment impairments.
Part of the jurisdictions' water quality standards development process may be to
conduct use attainability analyses. The Technical Support Document may be used to
assist states in developing their individual UAAs and state-specific documents.
While a UAA is traditionally a process conducted independently by a state, the
multi-stakeholder Water Quality Steering Committee decided to provide information
on a watershed-wide scale to promote coordination and consistency across all
jurisdictions.
OBJECTIVES
The EPA developed the Technical Support Document to:
• Document why it appears that the current designated uses for protecting
aquatic life cannot be attained in all parts of the Chesapeake Bay and its tidal
tributaries due to irremediable natural and human-caused conditions;
• Document the rationale and scientific basis for the refined designated uses for
the Chesapeake Bay and its tidal tributaries;
• Document that the refined designated uses are potentially attainable; and
• Provide technical background information for the four Chesapeake Bay jurisdic-
tions with tidal waters to use in developing their own jurisdiction-specific UAAs.
STRUCTURE AND CONTENT
Chapter II provides background information regarding Chesapeake Bay tidal-water
quality problems caused by excess nutrients and sediments. Chapter III demon-
strates that two factors-natural conditions and irremediable, human-generated
conditions-provide sufficient evidence that the current designated uses cannot be
met in certain portions of the Chesapeake Bay and its tidal tributaries.
Chapter IV provides information that jurisdictions may use in adopting refined tidal-
water designated uses based on the habitat quality needs of the plants and animals
that inhabit the different Chesapeake Bay tidal-water habitats and the Bay and its
tidal rivers' natural physical processes and features. The refined designated uses are
subcategories of current aquatic life protection uses, protected by new Chesapeake
Bay regional criteria for dissolved oxygen and, where appropriate, chlorophyll a and
water clarity (U.S. EPA 2003a). This chapter also presents the scientific basis under-
lying the geographic and temporal extent ('boundaries') of the refined designated
uses and documents that the refined designated uses protect uses existing since
November 1975, as required by the EPA Water Quality Standards regulation.
Assessments of the technological attainability of the refined designated uses—
migratory spawning and nursery habitat, open-water habitat, deep-water habitat and
chapter i • Introduction
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5
deep-channel habitat—were conducted by comparing model-simulated water quality
responses (measured as dissolved oxygen criteria attainment) of four level-of-effort
scenarios (or tiers) to the nutrient and sediment reductions accomplished at each
level. The water quality responses are summarized in Chapter Fin a series of 'attain-
ability tables,' that show which Chesapeake Bay tidal waters achieve attainment for
dissolved oxygen for each of the recommended refined designated uses. Attainability
of the shallow-water habitat designated use is assessed by examining the historical
and recent distributions of underwater bay grasses.
Chapter VI provides an overview of the estimated costs for each set of tiered levels
of implementation scenarios. This information is used also to conduct economic
impact analyses, which also are described in Chapter VI. The objective is to provide
the jurisdictions with preliminary estimates of the types of potential impacts that
could occur as a result of implementing the tier scenarios throughout the watershed.
However, it may be necessary for states to perform more comprehensive analyses for
their own state-specific UAAs. At the basinwide level, economic impacts were not
considered in determining the boundaries of designated uses. Rather, it will be up to
the individual jurisdictions conducting their own UAAs to determine where there
may be substantial and widespread social and economic impacts and to adjust their
final use boundary delineations as a result. The present economic information and
methodologies are intended only to assist the states with that decision.
The Technical Support Document is a compilation of basinwide guidance on UAA-
related analyses and was assembled collaboratively by the relevant jurisdictions; it
does not represent a regulation or a set of mandatory requirements. The EPA encour-
ages jurisdictions to use the information in this document and, when appropriate, to
perform additional analyses relevant to their respective water quality standards
development process. The general descriptions provided here may not apply to all
circumstances. Interested parties may raise questions and objections about the
substance of the Technical Support Document and its specific applications. The EPA
and other decision-makers retain the discretion to adopt approaches that differ from
those described in this document, where appropriate.
The Technical Support Document does not include a determination as to whether the
refined designated uses are attainable in specific areas; such decisions belong to the
states. Instead it provides information based on scientific data to show that revisions
of the current designated uses may be justified and that the refined designated uses
are viable in many areas of the Chesapeake Bay and its tidal tributaries.
It should be noted that the Technical Support Document presents information that is
current at the time of publication, and its analyses are works in progress. The EPA
expects Chesapeake Bay jurisdictions with Bay tidal waters to continue related
analyses and to seek assistance from the EPA and their Chesapeake Bay Program
partners during their tributary strategy development and water quality standards
adoption processes.
chapter i • Introduction
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6
Resource constraints prevented a fall evaluation of many issues such as local cost
and impact assessments, physical implementation constraints for technologies and
potential cap load impacts. However, the EPA anticipates that the four jurisdictions
with Chesapeake Bay tidal waters will explore such issues in greater detail, where
appropriate, during their respective water quality standards development processes.
APPROACH TO REFINING TIDAL-WATER DESIGNATED USES
The Chesapeake 2000 agreement and the subsequent six-state, District of Columbia
and EPA memoranda of understanding challenged the Chesapeake Bay watershed
jurisdictions to "define the water quality conditions necessary to protect aquatic
living resources" and to have the jurisdictions with tidal waters "use their best efforts
to adopt new or revised water quality standards consistent with the defined water
quality conditions." Against this backdrop of a renewed commitment to restore
Chesapeake Bay water quality, the Chesapeake Bay Program partners determined
that the current underlying tidal-water designated uses must be refined to better
reflect desired Chesapeake Bay water quality conditions.
The federal water quality standards regulation establishes that states must specify
appropriate water uses to be achieved and protected. Current designated uses applied
to the waters of the Chesapeake Bay and its tidal tributaries do not fally reflect
natural conditions and are too broad in their definition of 'use' to support the adop-
tion of more habitat-specific aquatic life criteria. Furthermore, they change across
jurisdictional borders in the same body of water.
Under the federal water quality standards regulation, states may adopt subcategories
of uses, seasonal uses and may remove uses under certain conditions (including
natural, physical and socio-economic conditions). If a state wishes to remove or estab-
lish a subcategory of a designated use that requires less stringent water quality
criteria, it must conduct a use attainability study. States must also demonstrate that all
water uses present on or after November 28, 1975, will always be protected. With
publication of the Technical Support Document, the EPA encourages states to
consider refining and subcategorizing their general aquatic life protection use applied
to Chesapeake Bay tidal waters, found in current state water quality standards.
The EPA, in close collaboration with the Chesapeake Bay Water Quality Steering
Committee, published new Chesapeake Bay regional water quality criteria for
dissolved oxygen, water clarity and chlorophyll a (U.S. EPA 2003a). Portions of the
Chesapeake Bay criteria are either equal, more, or less stringent than the current
dissolved oxygen criteria adopted by the Chesapeake Bay jurisdictions in their water
quality standards. Each jurisdiction that currently lists Chesapeake Bay tidal waters as
state waters (Maryland, Virginia, Delaware and the District of Columbia) is responsible
for submitting its own UAA to justify changes to state water quality standards for the
Chesapeake Bay tidal waters. This Technical Support Document provides the jurisdic-
tions with key information for conducting their own UAAs.
chapter i • Introduction
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7
DETERMINING ATTAINMENT OF CURRENT DESIGNATED USES
IS NOT FEASIBLE
The EPA Water Quality Standards Regulation (40 CFR 131.3) defines a UAA as:
A structured scientific assessment of the factors affecting the attainment of a
use which may include physical, chemical, biological and econom ic factors as
described in Section 131.10(g).
A UAA is required, according to Section 131.10 (j) of the EPA Water Quality Stan-
dards Regulation, when:
1. The state designates or has designated uses that do not include the uses speci-
fied in Section 101(a)(2) of the Act; or
2. The state wishes to remove a designated use that is specified in Section
101(a)(2) of the Act or to adopt subcategories of uses specified in Section
101(a)(2) that require less stringent criteria.5
In conducting a UAA, a state must be able to demonstrate that attaining the desig-
nated use is not feasible due to one or more of the six factors in Section 131.10(g)
listed below:
1. Naturally occurring pollutant concentrations prevent the attainment of the use;
2. Natural, ephemeral, intermittent or low-flow conditions or water levels prevent
the attainment of the use, unless these conditions may be compensated for by
the discharge of a sufficient volume of effluent without violating state water
conservation requirements to enable uses to be met;
3. Human-caused conditions or sources of pollution prevent the attainment of the
use and cannot be remedied or would cause more environmental damage to
correct than to leave in place;
4. Dams, diversions or other types of hydrologic modifications preclude the
attainment of the use, and it is not feasible to restore the water body to its orig-
inal condition or to operate such modification in a way that would result in the
attainment of the use;
5. Physical conditions related to the natural features of the water body, such as the
lack of a proper substrate, cover, flow, depth, pools, riffles and the like, unre-
lated to chemical water quality, preclude attainment of aquatic life protection
uses; and
6. Controls more stringent than those required by sections 301(b)(1)(A) and (B)
and Section 306 of the Act would result in substantial and widespread
economic and social impacts.
'Section 101(a)(2) Federal Water Pollution Control Act states that "...it is the national goal that wherever
attainable, an interim goal of water quality which provides for the protection and propagation of fish,
shellfish, and wildlife and provides for recreation in and on the water be achieved by July 1, 1983."
chapter i • Introduction
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The Technical Support Document focuses on the current designated uses in Chesa-
peake Bay tidal waters for the protection of aquatic life.6 Chapter III provides
scientific information that the states may use in determining whether current tidal-
water designated uses in Maryland, Virginia, Delaware and the District of Columbia,
with corresponding dissolved oxygen criteria of 4 mg/1 and 5 mg/1, are not achiev-
able in all portions of the Chesapeake Bay and tidal tributaries.
Factors 1 and 3, above, are applied in demonstrating why it appears that the current
uses may not be met in certain portions of the Chesapeake Bay and its tidal tribu-
taries. States may rely on one or more of the factors to demonstrate that attaining the
current designated use is not feasible. Factors 4 and 5 concerning unalterable hydro-
logic modifications and natural physical conditions that would preclude attainment
may also explain why the current designated uses are unattainable in certain tidal-
water habitats of the Chesapeake Bay. The Technical Support Document does not
explore these two factors in as great of detail as factors 1 and 3; however, the juris-
dictions may choose any of the preceding six factors in conducting their
state-specific UAAs.
JUSTIFYING THE REFINED TIDAL-WATER DESIGNATED USES
A UAA is not required to justify application of the refined designated uses, particu-
larly for areas in which the uses (criteria) will be more stringent than current ones.
The Chesapeake Bay Program's Water Quality Steering Committee decided,
however, that it was as important to document attainability of the more protective
refined designated uses as it was to justify changes to current designated uses.
Due to the shortcomings of current designated uses applied to the Chesapeake Bay
and its tidal tributaries, the Chesapeake Bay Program watershed partners concluded
that the underlying tidal-water designated uses need to be refined to reflect a greater
understanding of the complex Chesapeake Bay system and the needs of its living
resources. Specifically, the partners recommend that the following five refined
aquatic life designated uses be applied to the appropriate habitats in the Chesapeake
Bay and its tidal tributaries:
• Migratory fish spawning and nursery;
• Open-water fish and shellfish;
• Deep-water seasonal fish and shellfish;
• Deep-channel seasonal refuge; and
• Shallow-water bay grass.
Specifically, all state waters in Maryland are protected for Use I or water contact recreation and protec-
tion of aquatic life. All state waters in Virginia are designated for the following uses: "... recreational
uses, e.g., swimming and boating; the propagation and growth of a balanced, indigenous population of
aquatic life, including game fish which might reasonably be expected to inhabit them; wildlife; and the
production of edible and marketable natural resources, e.g., fish and shellfish." Delaware state waters
are designated for protection of "fish, aquatic life and wildlife" with similar provisions for "protection
and propagation of fish, shellfish and wildlife" in District of Columbia's waters.
chapter i • Introduction
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9
The first four designated use subcategories were derived chiefly to address season-
ally distinct habitats and living resource communities with widely varying dissolved
oxygen requirements. The shallow-water bay grass designated use would occur
seasonally in conjunction with the part of the year-round open-water use habitat for
waters that border the land along the tidal portions of the Chesapeake Bay and its
tributaries. It is intended to protect underwater bay grasses where the water clarity
criteria will apply.
The same factors used to show why it appears the current designated uses are unat-
tainable can also be applied in the development of the refined designated uses.
Factors 1 (natural conditions) and 3 (irremediable human-generated conditions)
were used to determine appropriate boundaries for the refined designated uses. The
Chesapeake Bay Program partners also took into consideration factors 4 and 5 as
part of the analysis for delineating the boundaries for the refined designated uses.
The monitoring data and model-simulated outputs described in Chapter IV show that
there are certain hydrologic and physical features that exist in the Chesapeake Bay
tidal waters today—some natural and some man-made, such as the shipping chan-
nels—which directly influence the horizontal as well as vertical extent of the
designated use boundaries.
ASSESSING ATTAINABILITY OF THE
REFINED TIDAL-WATER DESIGNATED USES
The question of whether the refined designated uses are attainable is a challenging
one. There is no precise approach or existing guidance for answering this question.
The challenge is particularly daunting for an area as large and complex as the Chesa-
peake Bay and its watershed, with its heterogeneous habitats and its vulnerability to
pollutants from point and nonpoint sources. The concept of attainability encom-
passes technological, economic and even political and legal perspectives. The
Technical Support Document addresses these viewpoints to a limited extent. The
states ultimately need to make their final determinations by applying information
tailored to their respective jurisdictions. This document specifically addresses tech-
nological attainability of the migratory spawning and nursery, open-water,
deep-water, deep-channel (based on dissolved oxygen criteria attainment) and
shallow-water designated uses (based on past and recently observed underwater bay
grass distributions). Because the Chesapeake Bay chlorophyll a criteria were
published in narrative form, attainability of the open-water designated use was not
assessed for this parameter.
From a legal perspective, 'existing uses' are, by definition, attainable. By regulation,
they must be protected by designated uses in water quality standards (40 CFR
131.10[g], 131.10[h][ 1 ] and 131.10[i]). Further, at a minimum, uses are considered
attainable if they can be achieved by implementing effluent limits (referred to as best
available technology or BAT) required under sections 301(b) and 306 of the Clean
Water Act and by implementing cost-effective and reasonable best management
practices (40 CFR 131.10[d] and 131.10[h][2]).
chapter i • Introduction
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10
Once a use is designated (as in the case of the Chesapeake Bay), it is presumed to be
attainable and may not be removed unless the state conducts a UAA and can demon-
strate that attaining the designated use is not feasible based on one of the six use
removal factors (40 CFR 131.10[g][l][6]). If a state conducts a UAA and demon-
strates that one or more of the six use removal factors are met for a particular
designated use, the state may remove the use. However, the state may not remove an
existing use and must revise water quality standards to reflect uses actually attained
(40 CFR 131.10[i]). In addition, designated uses not satisfying any of the six use
removal factors may not be removed.
As 40 CFR 131.2 states:
. . . water quality standards should, wherever attainable, provide water quality
for the protection and propagation offish, shellfish, and wildlife and for recre-
ation in and on the water and take into consideration their use and value of
public water supplies, propagation offish, shellfish, and wildlife, recreation in
and on the water. . .
If the use removal factors are cited to remove a designated use, the state must adopt
an 'appropriate' use or uses in place of the one removed (40 CFR 131.10[a]). Attain-
able uses are appropriate uses and may be expressed as subcategories of use.
Because the use removal factors are designed to determine whether to remove a
designated use when it is not attainable, they serve the purpose equally effectively
when considering whether a use is attainable and should be designated.
The Chesapeake Bay Program partners have devised a valuable tool for exploring
attainability from a technological perspective-a range of level-of-effort scenarios
that represent degrees of nutrient and sediment load reduction through simulated
implementation of best management practices and wastewater treatment upgrades.
These scenarios begin with Tier 1, which represents the current level of implemen-
tation in the watershed, including regulatory requirements implemented through the
year 2010, up to a scenario representing 'limits of technology' referred to as the E3
scenario or 'everything, everywhere by everybody,' which is acknowledged to be
physically implausible. Tier 2 and Tier 3 scenarios also were developed to represent
intermediate levels between the Tier 1 and E3 scenarios.
Each tier represents a nitrogen, phosphorus and sediment load reduction determined
by the technologies and levels of implementation assigned to it.7 These tiers are arti-
ficial constructs of technological levels of effort and do not represent actual
programs that the jurisdictions will eventually implement to meet the water quality
standards. These tiers are an assessment tool to determine potential load reductions
achievable by various levels of technological effort and were modeled to determine
water quality responses. Chapter V provides the results of the water quality model
7Sediment reduction is only estimated where it is incidental to implementation of BMPs directed toward
nutrient loading reductions.
chapter i • Introduction
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11
analyses for dissolved oxygen by tier, presented in a series of 'attainability tables,'
that estimate the level of attainment achieved within the designated use boundaries.
These analyses shows that most segments of the Chesapeake Bay and its tidal tribu-
taries realize attainment at the E3 levels. This attainment is also true for Tier 3 where,
if nonattainment does exist, it is generally at levels less than one percent, except for
Chesapeake Bay Program segment CB4MH or Middle Central Chesapeake Bay (see
Table V-6) where 8.51 percent nonattainment in deep-water remains.
Chesapeake Bay Program partners have used the E3 scenario to represent human-
caused conditions that cannot be remedied. The partners agree that reductions at E3
levels are not achievable and that the load reductions represented by Tier 3 are tech-
nologically achievable. Therefore, if a proposed use can be attained at load
reductions equal to or greater than Tier 3, but less than the E3 scenario, that use
should be designated. The jurisdictions may still, through their own analyses, show
that irremediable human-caused conditions prevent use attainment, or explain why
the uses cannot be attained based on substantial and widespread economic or social
impacts, or other factors in 40 CFR 131.10(g). However, the analyses published in
this Technical Support Document show that the refined designated uses can poten-
tially be attained in the Chesapeake Bay and its tidal tributaries.
Chapter V also addresses the attainability of the shallow-water designated use.
Restoration of underwater bay grasses to areas supporting "the propagation and growth
of balanced, indigenous populations of ecologically, recreationally and commercially
important fish and shellfish inhabiting vegetated shallow-water habitats" is ultimately
the best measure of attaining the shallow-water bay grass designated use. This docu-
ment provides the states with two means by which to determine the return of water
clarity conditions necessary to support restoration of underwater bay grasses and,
therefore, attainment of the shallow-water designated use.
CONSIDERATION OF ECONOMIC AND SOCIAL IMPACTS
The sixth factor to consider when conducting a UAA listed under Section 131.10(g)
("Controls more stringent than those required by Sections 301 [b] and 306 of the Act
would result in substantial and widespread economic and social impact") also has
been addressed to a limited extent in the Technical Support Document. The informa-
tion presented in Chapter III justifying why current designated uses cannot be met
does not require reliance on the substantial and widespread economic and social
impact factors as part of the justification to change the uses. Furthermore, the Chesa-
peake Bay Program partners delineated the use boundaries for the Chesapeake Bay
and its tidal tributaries based on estuarine living resources and their habitats, not on
economic impact information.
Conversely, it is logical to ask if the designated uses are affordable. The Technical
Support Document does not attempt to provide conclusions on affordability because
the Chesapeake Bay Program partners judged it premature to specify thresholds for
substantial and widespread economic and social impacts. On a regional, state or
chapter i • Introduction
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12
large watershed scale, economic impacts can be mitigated by cost-share, loans or
new federal or state funding programs. Cost and economic analyses to show impacts
that would preclude attainment of these refined uses must be more comprehensive
and rigorous than the present analyses.
JURISDICTION WATER QUALITY STANDARDS AND
TRIBUTARY STRATEGY DEVELOPMENT PROCESS
Upon publication of the Regional Criteria Guidance, the Chesapeake Bay tidal-
water jurisdictions of Maryland, Virginia, Delaware and the District of Columbia
began their respective water quality standards development and adoption processes.
At the same time, all Chesapeake Bay watershed jurisdictions, including Pennsyl-
vania, West Virginia and New York collaboratively allocated caps on nutrient and
sediment loads necessary to meet these anticipated water quality standards (i.e.,
Chesapeake Bay regional criteria and refined designated uses) (U.S. EPA 2003b).
States are scheduled to adopt water quality standards by 2005. Local watershed load
reduction action plans (referred to as 'tributary strategies'), based on achieving the
Chesapeake 2000 nutrient and sediment cap load allocations, will be completed by
April 2004. The development of tributary strategies will provide area-specific infor-
mation that jurisdictions can use in their water quality standards adoption process.
To promote consistency, jurisdictions will need to work cooperatively during their
tributary strategy development and water quality standards adoption processes,
particularly where tributary basins include more than one state in the Chesapeake
Bay watershed, such as the Potomac River basin.
LITERATURE CITED
Chesapeake Bay Watershed Partners. 2001. Memorandum of understanding among the state
of Delaware, the District of Columbia, the State of Maryland, the State of New York, the
Commonwealth of Virginia, the State of West Virginia and the U.S. Environmental Protec-
tion Agency regarding cooperative efforts for the protection of the Chesapeake Bay and its
rivers. Chesapeake Bay Program, Annapolis, Maryland.
Chesapeake Executive Council. 1987. 1987 Chesapeake Bay Agreement. Chesapeake Bay
Program, Annapolis, Maryland.
Chesapeake Executive Council. 2000. Chesapeake 2000 Agreement. Chesapeake Bay
Program, Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003a. Ambient Water Quality Criteria for Dissolved
Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
U.S. EPA, Region 3. EPA 903-R-03-002.
U.S. EPA. 2003b. Nutrient and Sediment Allocations for the Chesapeake Bay. U.S. EPA
Chesapeake Bay Program Office, Annapolis, Maryland. CBP/TRS 267/03.
U.S. EPA. 1998. Water Quality Standards Regulation. EPA 823-Z-98-002.
chapter i • Introduction
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13
chapter |
The Chesapeake Bay
and Its Watershed
BACKGROUND
The Chesapeake Bay is the nation's largest estuary and one of its most valuable
natural treasures. Even after centuries of intensive use, the Chesapeake Bay remains
a highly productive natural resource. It supplies millions of pounds of seafood, func-
tions as a major hub for shipping and commerce, provides habitat for an extensive
array of wildlife and offers a variety of recreational opportunities for residents and
visitors. The Chesapeake Bay supports 348 species of finfish, 173 species of
shellfish and more than 2,700 plant species. It is home to 29 species of waterfowl
and is a major resting ground along the Atlantic Migratory Bird Flyway. Every year,
1 million waterfowl winter in the Chesapeake Bay's basin.
The Chesapeake Bay proper is approximately 200 miles long, stretching from Havre
de Grace, Maryland, to Norfolk, Virginia. It varies in width from about 3.4 miles
near Aberdeen, Maryland, to 35 miles at its widest point, near the mouth of the
Potomac River. Including its tidal tributaries, the Chesapeake Bay encompasses
approximately 11,684 miles of shoreline.
On average, the Chesapeake Bay holds more than 15 trillion gallons of water.
Although the Bay's length and width are dramatic, the average depth is only about
21 feet. The Bay is shaped like a shallow tray, except for a few deep troughs believed
to be remnants of the ancient Susquehanna River. The troughs, which in some areas
are maintained by dredging, form a deep channel along much of its length. This
channel allows passage of large commercial vessels. Because it is so shallow, the
Chesapeake Bay is far more sensitive to temperature fluctuations and wind than the
open ocean.
The Chesapeake Bay is an estuary, where freshwater and saltwater mix. About half
of the Bay's water volume consists of saltwater from the Atlantic Ocean. The other
half drains into the Bay from an enormous 64,000-square-mile drainage basin or
watershed. Ninety percent of this freshwater is delivered from five major rivers: the
Susquehanna (which is responsible for about 50 percent), Potomac, James, Rappa-
hannock and York rivers.
chapter ii • The Chesapeake Bay and Its Watershed
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The distribution and stability of such an estuarine ecosystem depends on three
important physical characteristics of the water: salinity, temperature and circulation.
Salinity is a key factor influencing the Bay's morphology Seawater from the Atlantic
Ocean enters the mouth of the Chesapeake Bay; salinity is highest at that point and
gradually decreases farther north. Saltwater is more dense than freshwater, thus
salinity increases at greater depths while freshwater tends to remain at the surface.
Salinity levels within the Chesapeake Bay vary widely, both seasonally and from
year to year, depending on the volume of incoming freshwater.
Temperature dramatically changes the rate of chemical and biological reactions within
the water. Because the Chesapeake Bay is so shallow, its capacity to store heat over
time is relatively small. As a result, water temperature fluctuates throughout the year,
ranging from 34° to 84° Fahrenheit (2° to 52° Celsius). These changes in water temper-
ature influence the cycles in which plants and animals feed, reproduce, move locally
or migrate. The temperature profile of the Chesapeake Bay is fairly predictable.
The circulation of water transports plankton, fish eggs, shellfish larvae, sediment,
dissolved oxygen, minerals and nutrients throughout the Chesapeake Bay. Circula-
tion is driven primarily by the movements of freshwater from the north and saltwater
from the south. Circulation causes nutrients and sediments to be mixed and resus-
pended. This mixing creates a zone of maximum turbidity that, due to the amount of
available nutrients, fish and other organisms often use as nursery areas.
Salinity, temperature and circulation dictate the physical characteristics of water. The
warmer, lighter freshwater flows seaward over a layer of saltier and denser water
flowing upstream. The opposing movement of these two flows forms saltwater fronts
or gradients that move up and down the Chesapeake Bay in response to the input of
freshwater. These fronts are characterized by intensive mixing. A layer separating
water of different densities, known as a pycnocline, is formed. This stratification
varies within seasons, depending on river flow.
In autumn, the fresher surface waters cool faster than deeper waters and sink.
Vertical mixing of the two layers occurs rapidly. In the process nutrients are moved
up from the bottom, making them available to phytoplankton and other surface
organisms. This turnover also distributes much-needed dissolved oxygen to deeper
waters. In winter, water temperature and salinity are relatively constant from the
surface to the bottom. During spring and summer, surface and shallow waters are
warmer than deeper waters with the coldest water found at the bottom. This layering
of warmer waters over deeper waters is often broken down by turbulence.
The water's chemical composition also helps determine the distribution and abun-
dance of plant and animal life in the Chesapeake Bay. The Bay's waters contain
organic and inorganic materials, including dissolved gases, nutrients, inorganic salts,
trace elements, heavy metals and other chemicals.
Dissolved oxygen is essential for most aquatic animals. The amount of available
oxygen is affected by salinity and temperature. Cold water can hold more dissolved
chapter ii • The Chesapeake Bay and Its Watershed
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15
oxygen than wanner water, and freshwater holds more than saltwater. Thus, concen-
trations of dissolved oxygen vary, in part, with both location and time. Oxygen is
transferred from the atmosphere into surface waters by diffusion and the aerating
action of the wind. It also is released by aquatic plants in the process of photosyn-
thesis. Since photosynthesis requires light, the production of oxygen by rooted
aquatic plants is limited to waters that are usually no more than six feet deep. Surface
water is nearly saturated with oxygen most of the year, while deep bottom waters
range from saturated to anoxic (without oxygen).
In winter respiration levels of organisms are relatively low. Vertical mixing is good,
and there is little salinity or temperature stratification. As a result, dissolved oxygen is
plentiful throughout the water column. During the spring and summer, increased
levels of animal and microbial respiration and greater stratification may reduce
vertical mixing, resulting in low levels of dissolved oxygen in deep water. In fact, deep
parts of some tributaries like the Patuxent, Potomac and Rappahannock rivers and the
Chesapeake Bay's mainstem can become anoxic in summer. In the autumn when
surface waters cool, vertical mixing occurs and the deeper waters are re-oxygenated.
CHESAPEAKE BAY WATERSHED
The Chesapeake Bay receives about half its water volume from the Atlantic Ocean.
The rest drains into the Bay from its 64,000-square-mile drainage basin or water-
shed. Runoff from this enormous watershed flows into an estuary with a surface area
of 4,500 square miles resulting in a land-to-water ratio of 14 to 1. This ratio is one
of the key factors in explaining why the drainage area has such a significant influ-
ence on water quality. The watershed includes parts of six states—New York,
Pennsylvania, West Virginia, Delaware, Maryland and Virginia—and the entire
District of Columbia (Figure II-1). Threading through the Chesapeake Bay water-
shed are more than 100,000 streams and rivers that eventually flow into the Bay.
Although the Chesapeake Bay lies entirely within the Atlantic Coastal Plain, its
watershed includes parts of the Piedmont and Appalachian provinces. The waters
that flow into the Bay have different chemical identities, depending on the geology
where they originate. In turn, the nature of the Bay itself depends on the character-
istics and relative volumes of these contributing waters.
The Atlantic Coastal Plain is a flat, lowland area with a maximum elevation of about
300 feet. It is supported by a bed of crystalline rock, covered with southeasterly
dipping wedge-shaped layers of relatively unconsolidated sand, clay and gravel.
Water passing through this loosely compacted mixture dissolves many of the
minerals. The most soluble elements are iron, calcium and magnesium. The coastal
plain extends from the edge of the continental shelf, to the east, to a fall line that
ranges from 15 to 90 miles west of the Chesapeake Bay. This fall line forms the
boundary between the Piedmont Plateau and the coastal plain. Waterfalls and rapids
clearly mark this line, which is close to Interstate Highway 95. Here, the elevation
chapter ii • The Chesapeake Bay and Its Watershed
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New York
Pennsylvania
Maryland
West Virgini;
Delaware
DC
Virginia
Figure 11-1. The Chesapeake Bay watershed crosses the boundaries of six states—
Maryland, Virginia, Delaware, Pennsylvania, New York and West Virginia—and the
District of Columbia.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
rises to 1,100 feet. Cities such as Fredericksburg and Richmond in Virginia, Balti-
more in Maryland, and Washington, D.C., developed along the fall line taking
advantage of the potential water power generated by the falls. Since colonial ships
could not sail past the fall line, cargo was transferred to canals or overland shipping.
Cities along the fall line became important areas for commerce.
The Piedmont Plateau extends from the fall line in the east to the Appalachian
Mountains in the west. This area is divided into two geologically distinct regions by
Parrs Ridge, which traverses Carroll, Howard and Montgomery counties in Mary-
land and adjacent counties in Pennsylvania.
chapter ii • The Chesapeake Bay and Its Watershed
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Several types of dense crystalline rock, including slates, schists, marble and granite,
compose the eastern side. This variety results in a very diverse topography Rocks of
the Piedmont tend to be impermeable, and water from the eastern side is low in the
calcium and magnesium salts.
The western side of the Piedmont consists of sandstones, shales and siltstones,
layered over by limestone. This limestone bedrock contributes calcium and magne-
sium to its water, making it 'hard.' Waters from the western side of Parrs Ridge flow
into the Potomac River, one of the Chesapeake Bay's largest tributaries.
The Appalachian Province covers the western and northern part of the watershed and
is rich in coal and natural gas deposits. Sandstone, siltstone, shale and limestone
form the bedrock. Water from this province flows to the Chesapeake Bay mainly via
the Susquehanna River.
The hospitable climate, lush vegetation and natural beauty of the Chesapeake Bay
watershed have attracted people for thousands of years. Hunters and gatherers first
arrived about 10,000 years ago. Native Americans began cultivating crops and
settling in villages throughout the area around a thousand years ago. Arriving less
than 500 years ago, Europeans and later Africans (brought forcibly to the region
beginning in 1619) struggled to transform forests into farmland during the colonial
era between 1607 and 1775.
Since then, social, political, economic, and technological developments in metal-
lurgy, steam power, internal combustion engines, chemical engineering and, most
recently, electronics, have enabled people to transform regional environments in
dramatic ways. Excessive forest clearing and poor land management have increased
erosion, sending tons of sediment downstream. As a result, communities that once
served as important ports are now landlocked, and elsewhere, the construction of sea
walls and breakwaters has interfered with the natural flow of sand, causing beaches
to erode too rapidly.
The changes brought about during hundreds of years of forest clearing and urban
development have resulted in the following breakdown of current landuse in the
watershed: 58 percent forest, 23 percent agriculture, 9 percent urban/suburban and
10 percent mixed open (herbaceous lands that are not agricultural such as golf
courses or institutional grounds).
Today, nearly 16 million people live in the Chesapeake Bay watershed. Table II-1
provides a demographic summary of this population. Each resident lives just a few
minutes from one of the more than 100,000 rivers, streams and creeks that drain into
the Chesapeake Bay. Each tributary can be considered a pipeline from individual
communities into the Chesapeake Bay and its rivers. Because materials on land are
easily washed into streams and rivers, individual actions on the land ultimately affect
the quality of Chesapeake Bay. These activities even include the use of automobiles,
fertilizers, pesticides, toilets, water and electricity.
chapter ii • The Chesapeake Bay and Its Watershed
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Table 11-1. Chesapeake Bay watershed demographics
Race (%)
Educational Attainment (%)
No High School Diploma . . 23.1
High School Diploma 47.7
Associate Degree 5.3
Bachelor Degree 14.4
Graduate Degree 9.5
Housing
Location (%)
Means of Sewage
Disposal (%)
Source
of Water (%)
Transportation
to Work (%)
White . . 78.1
Black . . 18.5
Asian . . . 2.3
American
Indian . . . 0.3
Other 1
Urban ..71.7
Rural . . . 27.4
Farm .... 0.9
Other 1
Public
Septic
Other
74.1
24.6
. 1.3
Public . . . 77.6
Well .... 20.8
Other 1.6
Drive Alone . . . 70.3
Car Pool 15
Public Trans. ... 6.4
Bike/Walk 4.5
Work Home .... 3.2
Source: 1990 U.S. Census.
CHESAPEAKE BAY TIDAL-WATER QUALITY PROBLEMS
Water quality problems in the Chesapeake Bay and its tidal tributaries are illustrated
by the following environmental indicators which reveal the effects of excessive
nutrients and sediments in the water column.
A significant proportion of living resource habitats are currently unsuitable due to
low dissolved oxygen concentration during the summer months (Figure II-2). In
2001, half of the Chesapeake Bay's deeper waters had reduced dissolved oxygen
2.0 5 mg/L Hypoxia
2.0 2 mg/L Q Severe Hypoxia
0 2 mg/L | Anoxia
Better
Figure 11-2. Volume of the mainstem Chesapeake Bay lower layer waters with reduced
dissolved oxygen concentrations-June through September average 1985-2002.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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19
concentrations, a condition known as hypoxia. Hypoxic conditions stress aquatic life
and severely hypoxic waters may be lethal to aquatic plants and animals. If bottom
waters become completely without oxygen or anoxic, nutrients tied up in sediments
are released into the overlying waters, further fueling algal growth. Recent indica-
tions show an improving trend in dissolved oxygen since 1985, the year the
Chesapeake Bay Program's complete data collection efforts were initiated.
Chlorophyll a is an indicator of algal biomass. Algae serve as a crucial link in the
food chain; they reduce water clarity, and, left uneaten, fuel the loss of dissolved
oxygen from tidal waters. Measured as chlorophyll a, algae are the first to respond
to changes in nutrient levels. Recent trends in the Middle, Wicomico and Manokin
rivers show improvements in the level of algal biomass. Most areas show no signif-
icant change, although the Rappahannock River, Tangier Sound and the mouth of the
James River show degrading trends in terms of chlorophyll a (Figure II-3).
Water clarity is degrading in many parts of the basin (Figure II-4). Water clarity
criteria are not attained in many shallow-water designated use habitats. In portions
of the upper Chesapeake Bay, in the Elk and Middle rivers, in upper regions of the
Choptank River, in Piscataway and Mattawoman creeks, and in the South Branch
Elizabeth River, water clarity is improving.
CAUSES OF CHESAPEAKE BAY WATER QUALITY PROBLEMS
The Chesapeake Bay is part of an extremely productive and complex ecosystem that
consists not only of the Bay and its tributaries, but of the plant, animal and human
life they support. Through a significant investment in scientific research and coordi-
nated monitoring and modeling programs, the Chesapeake Bay Program partners
have gained deep understanding of how human activities affect the Bay's ecology
and have led to declines in water quality. Using modeling tools such as the Chesa-
peake Bay Watershed Model and the Water Quality Model, the partners have learned
a great deal about this unique resource by allowing for, among other things, the
calculation and projection of changes in loads and the resultant responses in water
quality. These models provide an estimate of management actions (such as air
controls and point source controls) which will reduce nutrient or sediment loads to
the tidal waters and lead to attainment of the Chesapeake Bay dissolved oxygen,
water clarity and chlorophyll a criteria.
HUMAN POPULATION INCREASE
The relentless encroachment of the human population threatens the ecological
balance of the Chesapeake Bay. Population in the Chesapeake Bay watershed has
doubled since the 1950s with population levels projected to reach almost 18 million
people by 2020 (Figure II-5). Each individual directly affects the Chesapeake Bay
by adding waste, consuming resources, and changing the character of the land, water
and air that surround it.
chapter ii • The Chesapeake Bay and Its Watershed
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Northeast
Gunpowder
VMiddle \
Back. \
Patapsco. \
Magothy, s
Severn ,
South y
Rhode ^
Piscataway
Creek
Mattawoman
Creek
/ \
Potomac^i \
Chickahomlny
Appomattox'
Patuxent
Pamunkey
James
Elizabeth
RappahannockJk"
Corrotoman<
Piankatank
Mobjack
Mattaponi
Elk
C&D Canal
hernia
Sassafrass
Upper Mainstem
Chester
Eastern Bay
Choptank
Middle Centr al Mainstem
Choptank
Nanticoke
/WicomicoV
Fishinq Bay
Honda3
Manokiriv
Bin Annemessex
Pocomoke
¦Tangier Sounds
ower Central Mainstem
¦Western Lower Mainstem
Eastern Lower Mainstem
Lower Mainstem
AMouth ot James
Trend
(1985-2002)
VDecreasinq
(Good)
A Increasing
(Bad)
Segments with
unchanged trends
have no symbol
Status*
(2000-2002)
~ Meets
¦ Fails
~ Not
Available
Figure II-3. Status and trends in summer Chesapeake Bay and tidal tributary chlorophyll
a concentrations relative to concentrations characteristic of mesotrophic conditions.
* 'Meets' means equal to or less than and 'fails' means above the following chlorophyll a
concentrations during the July through September timeframe:
25 ug/l tidal freshwaters
25 ug/l oligohaline waters
20 ug/l mesohaline waters
15 ug/l polyhaline waters.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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21
Northern MainstemAx
Bush,
Gunpowder
MiadleA
Back. \
Patapscox\ x
Magothy, x
Severn. »
South. V
RhodeA
West 00*.
Northeast
Piscataway
CreekA.
MattawoinanA
Creek
Potomac
ChickahomlnyT^g
Appomattox^
Patuxent
YorkT
Rappahannock
Corrotoman'
Piankatank
Mobjack Bay'
Mattaponi"^
Pamunkey.,
James
Elizabeth^
South Branch Eliza both A
ElkA
.C&D Canal
Bohemia
,Sassafrass
Upper Central Mainsteml
Chester
astern Bay
Upper ChoptankA
Mouth of ChoptankT
" 'iddle ChoptankT
Littje Choptank
,/HManticoke
--Middle Central Mainsteml
/Wicomico
Fishing Bay
Honga
Manokin ~
Big Annemessex
Lower PocomokeT
¦Tangier SoundT
Lower Central Mainstem*
Western Lower Mainsternl
Eastern Lower MainstemT
Lower MainstemT
Trend Criteria Attainment
(1985-2002) Status* (2000-2002)
~Degrading ~ Meets
A Improving B Fai|s
bwrnwiis with „ it
unchanged trerxis . . Not Available
have no symbol
Figure 11-4. Status and trends in underwater bay grass growing season water clarity in
Chesapeake Bay and tidal tributaries.
* 'Meets' equals nonexceedance; 'fails' equals exceedance of the water clarity criteria during
underwater bay grasses growing season applied in locations and depths where such grasses have
occurred since the 1930s (however, if the single best year of underwater bay grasses, measured
2000-2002, achieves the acreage goal for a segment, there is no need to meet the clarity criteria).
Application depths were based on: single best year percent of total potential habitat is > = 20%
or percent of total potential habitat is 10-19.9% and underwater bay grasses are persistent
(1978-2000).
NOTE: The criteria attainment status covers the entire segment only for purposes of illustration. The
water clarity criteria apply with the shallow-water designated use habitat which can extend as far out
as the 2-meter depth contour depending on the segment.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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22
25
w
c
o
E 20
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o
§ 15
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1—
1—
1—
1—
1—
1—
CM
CM
CM
CM
CM
Figure II-5. Chesapeake Bay watershed human population trends since 1950 and
projected through 2020.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
LOSS OF HABITAT
Historically, habitat provided by oyster bars, underwater bay grasses, wetlands and
forests enabled the Chesapeake Bay ecosystem to recycle nutrients and sediments
efficiently, resulting in one of the most productive ecosystems in the world. Dramatic
loss of these habitats has not only led to declines in the creatures that rely on them
for food and shelter; their loss also has reduced the ecosystem's capacity to fully
utilize nutrients and sediments leading to poor water quality in the Chesapeake Bay
and its tidal tributaries. Restoration, conservation, and preservation of the habitat
provided by oysters, underwater bay grasses, wetlands and forests are critical for
restoring living resources and for improving Chesapeake Bay water quality.
In addition to the aquatic reef habitat they provide, oysters are voracious feeders, and
each is capable of filtering up to 50 gallons of water per day. It is estimated that at
their peak abundance, the total population of oysters in the Chesapeake Bay could
filter an amount of water equal to all the water in the Chesapeake Bay in three days.
Today, due to decreased abundance, it takes a year for these animals to filter the same
volume of water. Oyster harvests in the Chesapeake Bay have declined due to over-
harvesting, disease, pollution and loss of oyster reef habitat. Two diseases,
discovered in the 1950s and caused by the parasites MSX and Dermo, have been a
major cause of the oyster's decline during recent times (Figure II-6).
Underwater bay grasses are important because they produce oxygen, provide food
for a variety of animals (especially waterfowl), serve as shelter and nursery areas for
many fish and shellfish, reduce wave action and shoreline erosion, absorb nutrients
such as phosphorus and nitrogen and trap sediments. Although underwater bay
chapter ii • The Chesapeake Bay and Its Watershed
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23
40
35 -
CO
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c
3
o
30 -
Q_
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25 -
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15
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¦ irginia
I I Maryland
h n n n
n
53
59
I I r"
2 5
8
1
80 83
92 95 98 2001
Figure II-6. Trends in Maryland and Virginia commercial harvest landings of oysters 1953-2001.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
grasses increased from a low point of 37,000 acres in 1984 to 85,000 acres in 2001,
the Chesapeake Bay Program watershed partners have adopted a new restoration
goal of 185,000 acres (Figure II-7).
Wetlands and forests (especially those buffering streambanks and shorelines)
provide critical habitat and also act as natural filters to minimize sediment loads and
absorb nutrients. Approximately 1.5 million acres of wetlands remain in the Chesa-
peake Bay watershed, less than half of the wetlands that were here during colonial
times. Forests that once covered 90 to 95 percent of the watershed now cover only
58 percent (Figure II-8).
EXCESS NUTRIENTS
Nutrients are essential; they provide crucial ingredients to help living things grow.
However, there is a delicate balance between what is needed for organisms to thrive,
and what is excessively harmful. The amount of nutrients that would naturally enter
the Chesapeake Bay has been adversely multiplied by anthropogenic sources over the
course of history. Runoff from fertilizers applied to agriculture and lawns, sewage and
industrial discharges, automobile emissions and power generation, are all sources that
create excessive amounts of nutrient pollution delivered to the Chesapeake Bay and
chapter ii • The Chesapeake Bay and Its Watershed
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24
200
180 "
Restoration oal (185,000 acres by 2010)
1 0
2 140 -
o
03
O
o
o
120
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03
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LO COOO-i-CMCO^lC CO G>
cocococococog^g^g^ooooooo
(DOOOOOOOOOOOOOOO}
o
o
o
o
o
CM CM
Figure II-7. Trends in the acreages of Chesapeake Bay and tidal tributary underwater
bay grasses compared to the new 185,000 acre restoration goal. Light blue area of
bar includes estimated additional acreage when flight restrictions or weather conditions
prevented collection of a complete set of aerial photographs.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
Land
abandoned
after Civil
War and
Depression
Early
Colonies
—I 1 1 1—
1 50 1800 1850 1900
1950 2000
Land
cleared for
agriculture
and timber
Figure II-8. Trends in Chesapeake Bay basin forests expressed as percentage of the
watershed that was forested since 1650.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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25
its tidal tributaries. These anthropogenic sources of nutrients, together with a decline
in the Chesapeake Bay's own natural capacity to assimilate these pollutants due to
loss of habitats and living resources, have created overwhelming stresses.
Excess amounts of nitrogen and phosphorus cause rapid growth of phytoplankton,
creating dense algal populations or blooms. These blooms become so dense that they
reduce the amount of sunlight available to underwater bay grasses. Without sufficient
light, these underwater plants cannot photosynthesize and produce the food they
need to survive. Algae also may grow directly on the surface of underwater bay
grasses, further blocking light. Another hazard of nutrient-enriched algal blooms
comes after the algae die. As the algal blooms decay, oxygen is consumed via
bacterial decomposition which can lead to dangerously low oxygen levels available
for aquatic organisms. Known as eutrophication, this nutrient over-enrichment,
ultimately leading to low dissolved oxygen levels in ambient waters, is a widespread
problem throughout the tidal waters.
EXCESS SEDIMENTS
The surrounding watershed and the tidal waters of the Chesapeake Bay and its tidal
tributaries transport huge quantities of sediments. Although sediments are a natural
part of the Chesapeake Bay ecosystem, accumulation of excessive amounts is un-
desirable. As sediments settle to the bottom of the Chesapeake Bay, they can smother
bottom-dwelling plants and animals, such as oysters and clams. Sediments
suspended in the water column cause the water to become cloudy, decreasing the
light available for underwater bay grasses. Sediment-related water quality problems,
however, tend to be more of a localized problem.
Individual sediment particles have a large surface area, and many molecules easily
adsorb or attach to them. As a result, sediments can act as chemical sinks by
adsorbing nutrients and other pollutants. Thus, areas of high sediment deposition
sometimes have high concentrations of nutrients which may later be released.
Reducing sediment loads to the Chesapeake Bay and its tidal tributaries is critical for
restoring water quality.
SOURCES OF NUTRIENT LOADS TO THE
CHESAPEAKE BAY TIDAL WATERS
When accounting for all the nutrients that enter the Chesapeake Bay from its water-
shed, the two largest anthropogenic contributors of both nitrogen and phosphorus are
nonpoint source runoff from agriculture and point sources. Forests are a natural
source of nutrients, but relative to anthropogenic sources, are a relatively small
percentage of the total nutrient load entering the Chesapeake Bay. The largest source
of sediments in the Bay is agriculture, followed by forest, urban runoff and mixed
open lands. Figures II-9 through 11-14 provide a breakdown of the nitrogen,
phosphorus, and sediment loads delivered to the Chesapeake Bay and its tidal tribu-
taries as well as estimated reductions achieved in these loads from 1985 to 2000
from each source. These loads do not include atmosphere deposition directly to tidal
waters—see "Atmospheric Sources" below.
chapter ii • The Chesapeake Bay and Its Watershed
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26
Non-Tidal Water
Deposition
Septic
Mixed Open
Urban Runoff
Agriculture
Forest
Point Source
Figure 11-9. Chesapeake Bay
Watershed Model-estimated nitrogen
loads by source delivered to the
Chesapeake Bay and its tidal tributar-
ies excluding direct atmospheric dep-
osition to tidal waters and shoreline
erosion. A total of 285 million
pounds/year were delivered to the
tidal waters based on the Watershed
Model's 2000 Progress scenario.
Source: Chesapeake Bay Program website
h 11 p ://www. chesapeakebay.net.
¦ Non-Tidal
Water
~ Deposition
Septic
~ Mixed Open
~ Urban
Runoff
~ Forest
~ Point
Source
~ Agriculture
Figure 11-10. 1985 and 2000 Chesapeake Bay Watershed Model-estimated nitrogen loads
by source delivered to the Chesapeake Bay and its tidal tributaries excluding
direct atmospheric deposition to tidal waters and shoreline erosion.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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27
Figure 11-11. Chesapeake Bay
Watershed Model-estimated
phosphorus loads by source
delivered to the Chesapeake Bay and
its tidal tributaries excluding direct
atmospheric deposition to tidal
waters and shoreline erosion. A
total of 19.1 million pounds/year
were delivered to the tidal waters
based on the Watershed Model's
2000 Progress scenario.
Source: Chesapeake Bay Program website
h tt p ://www. chesapeakebay.net.
Non-Tidal Water
Deposition
Mixed Open
Urban Runoff
Agriculture
Forest
Point Source
22
0.16 (1%)
2.18 (11%)
3.12 (16%)
0.41 (2%)
4.26 (22%)
11.57
8.99 (47%)
¦ Non-Tidal
Water
Deposition
I Mixed Open
~ Urban
Runoff
~ Forest
~ Point
Source
~ Agriculture
1985
2000 Progress
Figure 11-12. 1985 and 2000 Chesapeake Bay Watershed Model-estimated phosphorus
loads by source delivered to the Chesapeake Bay and its tidal tributaries excluding direct
atmospheric deposition to tidal waters and shoreline erosion.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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28
Mixed Open
Urban Runoff
Forest
Agriculture
Figure 11-13. Chesapeake Bay
Watershed Model-estimated
sediment loads by source delivered
to the Chesapeake Bay and its
tidal tributaries excluding direct
atmospheric deposition to tidal
waters and shoreline erosion. A
total of 5.04 million pounds/year
were delivered to the tidal waters
based on the Watershed Model's
2000 Progress scenario.
Source: Chesapeake Bay Program website
h tt p ://w w w. chesapeakebay.net.
-a cu
a o
o .>
—1 0)
V- c
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29
NONPOINT SOURCES
Nonpoint source pollution, unlike pollution from industrial and sewage treatment
plants, comes from many diffuse sources. Rainfall or melted snow moving over and
through the ground is one such source. As the runoff moves, it picks up and carries
away natural and anthropogenic pollutants, some of which are deposited into the
Chesapeake Bay and its tidal tributaries. Animal manure or chemical fertilizers
applied to lawns, gardens and farm fields can wash off the land into streams and rivers
or seep into the ground where they can be delivered to streams via groundwater.
Nonpoint source pollution in the Chesapeake Bay watershed emanates from six
sources: agriculture, forest, urban, mixed open, septic and atmospheric deposition.
As noted earlier, agriculture accounts for the largest percentage of nonpoint source
nitrogen pollution.
Agricultural runoff includes nutrients from chemical fertilizers and animal manure
applied to land, as well as eroded soil particles and organic matter. Improper storage
of animal wastes and mortality can result in additional nutrients being leaked into the
groundwater or carried off in rainwater. Animals pastured near streams and other
water bodies also contribute to the nutrient load delivered to the tributaries of the
Chesapeake Bay.
Septic systems leak nutrients into the groundwater since most systems currently do
not incorporate technologies to remove nitrogen from the wastewater they treat then
discharge. Such systems are a source of nitrogen to the watershed not only from the
treated effluent, but from systems that are not functioning properly due to age,
neglect in operation and maintenance, or improper siting and installation.
Increases in nutrient runoff from urban areas are expected to occur in the future due
to increasing development of forested and agricultural lands. Nitrogen loads from
septic systems are expected to increase as population increases, however, if people
continue to move away from the urban and suburban areas that are currently
serviced by public sewer facilities, projected loads may be even higher. Runoff from
farms is generally declining as farmers adopt nutrient management and runoff
control techniques, but also because the overall amount of farmland is declining.
POINT SOURCES
A point source is an outfall pipe associated with a point of entry, such as the end of a
pipe, where nutrients enter waterways. Industrial sites and wastewater treatment
plants are examples of point sources. As of 2000, point sources were estimated to
account for 22 percent of the total load of nitrogen and phosphorus to the Chesapeake
Bay and its tidal tributaries. The Chesapeake Bay Program, working with its partner
states and jurisdictions, assimilated a database on all of the point sources with signif-
icant contributions of nutrients to the watershed. (Sediments are not currently counted
as a component of point source effluents.) The point source database consists of
chapter ii • The Chesapeake Bay and Its Watershed
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facilities located in all the states and jurisdictions in the Chesapeake Bay watershed
(Table II-2). These point sources are divided into four principal categories.
• Significant municipal facilities, which are generally municipal wastewater
treatment plants that discharge flows of equal to or greater than 0.5 millions of
gallons per day (MGD). More specifically, significant municipal facilities are
defined slightly differently for each jurisdiction. For Virginia, these facilities
are those that have a design flow of 0.5 MGD or greater, and all facilities
located below the fall line, regardless of flow. For Maryland, significant facili-
ties are those having a current flow of 0.5 MGD or greater. For Pennsylvania,
significant facilities are those having average annual 1985 flows of 0.4 MGD
or greater. For Delaware, West Virginia, and New York, the Chesapeake Bay
Program selected as significant municipal facilities those in the EPA Permit
Compliance System database with current flows of 0.5 MGD or greater.
• Significant industrial facilities have been identified as those that discharge the
equivalent or greater amounts of nutrients as compared to a municipal waste-
water treatment facility's discharge of 0.5 MGD. These discharge loads would
roughly be equivalent to those of municipalities with flows of 0.5 MGD or
greater, or a total nitrogen load of 75 pounds per day, and a phosphorus load of
25 pounds per day or greater (based on a municipal facility effluent discharge
of 2.5 mg/1 total phosphorus and 18 mg/1 total nitrogen).
• Nonsignificant municipal facilities are those that are generally smaller than
discharge flows of 0.5 MGD. Only nonsignificant municipal facilities in Mary-
land and Virginia are included in the database due to the availability of data.
While there are approximately 185 nonsignificant municipal facilities across
the Chesapeake Bay watershed, the flow and corresponding nutrient loads from
these facilities are less than 5 percent of the total for all point sources.
• Combined sewer overflow loads only for the District of Colombia are included
in the database because it is the only location for which the Chesapeake Bay
Program has nutrient load data. Certainly other combined sewer overflows
exist in the watershed, however, to date these have not been quantified in terms
of nitrogen and phosphorus load discharges.
Table 11-2. Summary of point source facilities within the Chesapeake Bay watershed.
Point Source Number of Total 2000
Category Description Facilities Flow (MGD)
Significant Municipals*
Generally >0.5 MGD
304
1,554.4
Significant Industrials
Discharge loads generally
> 75 lb/day TN & 25 lb/day TP
49
524.7
Non-significant Municipals
Generally <0.5 MGD
185
10.8
Combined Sewer Overflows
Only for Blue Plains
1
7.6
Total
540
2,097.5
* Including the six Virginia plants to be built by 2010.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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Today, 83 of the 304 significant municipal wastewater treatment plants and many
industrial facilities as well, are using nutrient removal technology (NRT). By 2010,
that number is likely to increase to 156. Exponential advances in the development of
NRT in recent years, along with performance levels beyond what was traditionally
expected, have clearly shown the potential for this technology to achieve much lower
levels of nitrogen in discharges than the traditionally accepted performance levels. It
must be recognized that the enhanced performance seen to date is partly due to the
fact that some treatment plants are operating below their design capacity, and this
level of nutrient reduction may be difficult to maintain as flows increase. To date, 12
of the 49 significant industrial nutrient dischargers located in the Chesapeake Bay
watershed are practicing some form of nutrient removal, and that number is expected
to increase to 16 by 2010.
The nutrient load discharged from municipal point sources is directly linked to popu-
lation. Because of the implementation of NRT to date, these point sources
collectively have achieved a 53 percent reduction in phosphorus loads and a 28
percent reduction in nitrogen loads since 1985, despite the 15 percent increase in
population since then. But because the watershed's population is expected to
increase by an additional 14 percent by 2010, it will be increasingly more chal-
lenging to achieve nutrient reductions from point sources. Figures 11-15 and 11-16
illustrate the nitrogen and phosphorus loads, respectively, from point sources in the
100
20
90
80
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85 8 8 88 89 90 91 92 93 94 95 9 9 98 99 2000
Year
2010 2015 2020
Figure 11-15. Total nitrogen loads delivered to the Chesapeake Bay and its tidal tributaries from all
point source facilities in the watershed (|) compared with human population trends (—) in the
Chesapeake Bay watershed projected through 2020.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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32
10
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85 8
89 90 91 92 93 94 95
Year
98 99 2000
2010 2015 2020
Figure 11-16. Total phosphorus loads delivered to the Chesapeake Bay and its tidal tributaries from all
point source facilities in the watershed (|) compared with human population trends (—) in the
Chesapeake Bay watershed projected through 2020.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
past, present and for future projections based on NRT implementation plans by 2010,
and for the year 2020 if no more facilities than currently planned implement NRT.
Significant progress has been made since 1985 in achieving reductions, but popula-
tion growth will diminish these successes unless NRT is implemented in more of the
facilities, while simultaneously reaching far greater performance levels.
ATMOSPHERIC SOURCES
The sources of nitrogen emissions which contribute to atmospheric nitrogen deposi-
tion to the Chesapeake Bay and its watershed are primarily fossil fuels combustion
(e.g., electric power generation, on-road vehicles, and industry) which emit nitrogen
oxides (NOx) and agricultural activities (such as commercial fertilizers and animal
manure), which release ammonia into the air. Much of the atmospheric nitrogen that
deposits to the watershed and makes it way to the tidal waters originates from states
located in the nitrogen (NOx and ammonia) airsheds (Figure 11-17). The NOx airshed
is roughly 1,081,600 km2 in size and the ammonia airshed is roughly 688,000 km2
in size.
Atmospheric nutrient pollution that falls directly on the water is displayed as a sepa-
rate category and accounts for 8 percent of the total nitrogen load. Ultimately,
chapter ii • The Chesapeake Bay and Its Watershed
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REDUCED
0 IDI ED
Figure 11-17. Principal nitrogen airsheds for the Chesapeake Bay.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net/air/air.htm.
atmospheric nitrogen emissions can be viewed as a nonpoint source when they are
deposited on the land and reach the Chesapeake Bay as runoff. Atmospheric nitrogen
that falls on the land accounts for an additional 24 percent of the total nitrogen load
and is included as part of the agriculture, forest and urban and mixed open sources
in Figures II-9 and 11-10.
chapter ii • The Chesapeake Bay and Its Watershed
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ANTHROPOGENIC SOURCE INPUTS
Table II-3 was developed by estimating the relative nitrogen and phosphorus source
contributions from the perspective of anthropogenic inputs-atmospheric emissions,
chemical fertilizers and manure. This table includes atmospheric deposition directly
to tidal waters (20 million pounds), thus totaling a model-estimated 305 million
pounds/year of nitrogen delivered to the Chesapeake Bay and its tidal waters instead
of 285 million pounds/year as portrayed in Figures II-9 and 11-10. As also shown in
Table II-3, the combined atmospheric deposition directly to non-tidal and tidal
surface waters is 8 percent (7 percent plus 1 percent) of the total load.
Table II-3 provides estimates based solely on proportions of anthropogenic inputs.
There are three key inputs to the land surfaces-atmospheric deposition, chemical
fertilizer applications, and manure applications-from which the relative contribution
in delivered nitrogen loads is depicted based on their relative proportions. There are
natural sources of nitrogen loads to Chesapeake Bay tidal waters that cannot be
extracted and are, therefore, included in these source contributions.
Table 11-3. Chesapeake Bay Airshed and Watershed Model-estimated 2000 Progress scenario sources
of nitrogen and phosphorus loads (million pounds/year) delivered to the Chesapeake Bay and its
tidal tributaries based on anthropogenic inputs of atmospheric deposition, chemical fertilizers,
manure, point sources and septics, excluding shoreline erosion.
Source Loading Category
Total
Nitrogen
2000
Progress
Total
Nitrogen
(% of Total)
2000
Progress
Total
Phosphorus
2000
Progress
Total
Phosphorus
(% of Total)
2000
Progress
Atmospheric Deposition to Land
75,003,697
25%
5,900,372
29%
Atmospheric Deposition to Non-Tidal Water
3,559,840
1%
162,471
1%
Atmospheric Deposition to Tidal Water
20,467,458
7%
1,550,081
7%
Chemical Fertilizer Applications
to Agricultural Land
49,353,664
16%
3,456,104
17%
Chemical Fertilizer Applications
to Urban Land
18,146,154
6%
0
0%
Chemical Fertilizer Applications to
Mixed Open Land
9,872,122
3%
0
0%
Manure Applications to Agricultural Land
46,048,616
15%
4,646,036
22%
Animal Feeding Operation Runoff
8,026,157
3%
696,297
3%
Point Source
62,841,812
21%
4,257,314
21%
Septic
11,904,029
4%
0
0%
Bay-Wide Total
305,223,54
100%
20,668,675
100%
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • The Chesapeake Bay and Its Watershed
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chapter hi
Why Attaining the Current
Tidal-Water Designated Uses
Appears Not to be Feasible
BACKGROUND
Many natural biological, physical and chemical processes and interactions influence
water quality conditions and physical habitats in the Chesapeake Bay and its tidal
tributaries. In addition, the watershed and estuary have changed dramatically, and in
many ways, irreversibly, over the last four centuries as the population has grown to
nearly 16 million people. The current state designated uses cannot be met in the
deeper waters of the Chesapeake Bay mainstem and portions of the major lower trib-
utaries due to natural and human-caused conditions that cannot be remedied. The
current dissolved oxygen criteria adopted by Maryland and Virginia into their water
quality standards—>5 mg/1 at all times and >4 mg/1 minimum/>5 mg/1 daily
average, respectively—are unlikely to be achieved in deeper Chesapeake Bay tidal
waters during the summer season where physical processes (such as water-column
stratification and water circulation) and bottom bathymetry-related barriers prevent
the replenishment with oxygenated waters.
As described below, a combination of natural and human-caused conditions prevents
attainment of the dissolved oxygen concentrations necessary to meet the states'
current aquatic life designated uses in portions of the Chesapeake Bay and its tidal
tributaries. It should be noted that any of the six designated use removal factors spec-
ified in the EPA Water Quality Standards regulations (40 CFR 131.10[g]) and
described in Chapter I can be employed, where appropriate, to justify changing a
designated use. This chapter relies on two of those factors, but that reliance does not
prevent the states from using one or more additional factors in justifying refinements
to their tidal-water designated uses.
The model simulation of all-forested and pristine watersheds and findings from
scientific paleoecological records indicate that dissolved oxygen levels less than
5 mg/1 are a natural condition in some deeper waters of the Chesapeake Bay and its
tidal tributaries during the summer. Furthermore, even where natural conditions
could support a dissolved oxygen concentration of 5 mg/1, model simulations show
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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that areas exist where current state standards are unlikely to be met due to irremedi-
able human-caused conditions.
NATURAL CONDITIONS THAT MAY PREVENT
ATTAINMENT OF CURRENT DESIGNATED USES
Evidence from the paleoecological record of the Chesapeake Bay Watershed and
Water Quality models' simulations of a pristine and all-forested Chesapeake Bay
system indicates that natural conditions alone may prevent attainment of current
uses. In the absence of monitoring data from periods before human settlement
occurred, these findings and simulations provide the best available descriptions and
estimates of the Bay's tidal-water quality under natural conditions.
PALEOECOLOGICAL RECORD OF NATURAL CONDITIONS
Dissolved oxygen levels vary naturally in lakes, estuaries and oceans over temporal
and spatial scales due to many different biological, chemical and physical processes.
In estuaries such as the Chesapeake Bay, freshwater inflow that influences water-
column stratification; nutrient input and cycling; physical processes such as
density-driven circulation; and tides, winds, water temperature and bacterial activity
are among the most important factors. These processes can lead to large natural
seasonal and interannual variability in oxygen levels in many parts of the Chesa-
peake Bay and its tidal tributaries.
Superimposed on this natural dissolved oxygen variability is a progressive increase
in the intensity and frequency of hypoxia and anoxia over the past 100 to 150 years,
most notably since the 1960s. This human-induced eutrophication is evident both
from instrumental data and geochemical and faunal/floral 'proxies' of dissolved
oxygen conditions obtained from the sedimentary record.
The instrumental record, while incomplete prior to the inception of the multi-agency
Chesapeake Bay Monitoring Program in 1984, suggests that as early as the 1930s
(Newcombe and Home 1938) and especially since the 1960s (Taft et al. 1980),
summer oxygen depletion has been recorded in the Chesapeake Bay. Officer et al.
(1984), Malone (1992), Harding and Perry (1997) and Hagy (2002) provide useful
discussions of the instrumental record of dissolved oxygen and related parameters
such as chlorophyll a across this multi-decadal data record.
At issue is whether, and to what degree, dissolved oxygen reductions are a naturally
occurring phenomenon in the Chesapeake Bay. Long sediment core records
(17 meters to greater than 21 meters in length) indicate that the Chesapeake Bay
formed about 7,500 years ago (Cronin et al. 2000; Colman et al. 2002) when the
rising sea level after the final stage of Pleistocene deglaciation flooded the Susque-
hanna channel. The modern estuarine circulation and salinity regime probably began
in the mid- to late Holocene epoch, about 4,000-5,000 years ago (in the regional
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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climate of the early Holocene, Chesapeake Bay's salinity differed from that of the
late Holocene). This theory is based on the appearance of 'pre-coloniaP benthic
foraminiferal, ostracode and dinoflagellate assemblages. It is against this mid- to late
Holocene baseline that the post-European settlement and modern dissolved oxygen
regime of the Chesapeake Bay can be viewed.
During the past decade, studies of the Chesapeake Bay's late Holocene dissolved
oxygen record have been carried out using several proxies of past dissolved oxygen
conditions, which are preserved in sediment cores that have been dated using the
most advanced geochronological methods. These studies, using various indicators of
past dissolved oxygen conditions, are reviewed in Cronin and Vann (2003) and
provide information that puts the monitoring record of the modern Chesapeake Bay
into a long-term perspective and permits an evaluation of natural variability in the
context of restoration targets. The following types of measurements of oxygen-
sensitive chemical and biological indicators have been used: nitrogen isotopes
(Bratton et al. 2003); biogenic silica and diatom communities (Cooper and Brush
1991; Cooper 1995; Colman and Bratton 2003); molybdenum and other metals
(Adelson et al. 2000; Zheng et al. 2003); lipid biomarkers; acid volatile sulfur
(AVS)/chromium reducible sulfur (CRS) ratios; total nitrogen and total organic
carbon (Zimmerman and Canuel 2000); elemental analyses (Cornwell et al. 1996)
and paleoecological reconstructions based on dinoflagellate cysts (Willard et al.
2003); and benthic foraminiferal assemblages (Karlsen et al. 2000). Although space
precludes a comprehensive review of these studies, and the time period studied and
level of quantification vary, several major themes emerge, summarized below.
First, the 20th century sedimentary record confirms the limited monitoring record of
dissolved oxygen, documenting that there has been a progressive decrease in
dissolved oxygen levels, including the periods of extensive anoxia in the deep-
channel region of the Chesapeake Bay that have been prominent during the past 40
years. Most studies provide strong evidence that there was a greater frequency or
duration of seasonal anoxia beginning in the late 1930s and 1940s and again around
1970, reaching unprecedented frequencies or duration in the past few decades in the
mesohaline Chesapeake Bay and the lower reaches of several tidal tributaries
(Zimmerman and Canuel 2000; Hagy 2002). Clear evidence of these low dissolved
oxygen conditions has been found in all geochemical and paleoecological indicators
studied principally through their great impact on benthic and phytoplankton (both
diatom and dinoflagellate) communities.
Second, extensive late 18th and 19th century land clearance also led to oxygen reduc-
tion and hypoxia, which exceeded levels characteristic of the previous 2,000 years.
Best estimates for deep-channel mid-bay seasonal oxygen minima from 1750 to
around 1950 are 0.3 to 1.4-2.8 mg/1 and are based on a shift to dinoflagellate cyst
assemblages of species tolerant of low dissolved oxygen conditions. This shift is
characterized by a four- to fivefold increase in the flux of biogenic silica, a greater
than twofold (5-10 milliliter1) increase in nitrogen isotope ratios (15N) and periods
of common (though not dominant) Ammonia parkinsoniana, a facultative anaerobic
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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foraminifer. These patterns are likely the result of increased sediment influx and
nitrogen and phosphorous runoff due to extensive land clearance and agriculture.
Third, before the 17th century, dissolved oxygen proxy data suggest that dissolved
oxygen levels in the deep channel of the Chesapeake Bay varied over decadal and
interannual time scales. Although it is difficult to quantify the extremes, dissolved
oxygen probably fell to 3 to 6 mg/1, but rarely if ever fell below 1.4 to 2.8 mg/1.
These paleo-dissolved oxygen reconstructions are consistent with the Chesapeake
Bay's natural tendency to experience seasonal oxygen reductions due to its bathym-
etry, freshwater-driven salinity stratification, high primary productivity and organic
matter and nutrient regeneration (Boicourt 1992; Malone 1992; Boynton et al. 1995).
In summary, the main channel of the Chesapeake Bay most likely experienced
reductions in dissolved oxygen before large-scale post-colonial land clearance took
place, due to natural factors such as climate-driven variability in freshwater inflow
(Table III-l). However, this progressive decline in summer oxygen minima, begin-
ning in the 18th century and accelerating during the second half of the 20th century,
is superimposed on interannual and decadal patterns of dissolved oxygen variability.
Human activity during the post-colonial period has caused the trend towards hypoxia
and most recently (especially after the 1960s) anoxia in the main channel of the
Chesapeake Bay and some of its larger tidal tributaries. The impact of these patterns
has been observed in large-scale changes in benthos and phytoplankton communi-
ties, which are manifestations of habitat loss and degradation.
WATER QUALITY CONDITIONS UNDER ALL-FORESTED
AND PRISTINE WATERSHEDS
The natural relationships between processes on the land and in the water have been
altered to such a degree that it is now difficult to discern natural conditions in this
complex estuarine ecosystem. A 'natural' system is often considered to be the state
prior to European settlement, although pre-contact Native American activities had an
effect on the watershed and the Chesapeake Bay ecosystem as well. Pristine estu-
arine ecosystems no longer exist from which to reference water quality conditions
since human-induced changes now affect even the most remote regions of the planet.
Given the research and monitoring data limitations for measuring natural water
quality conditions, the Chesapeake Bay Program developed a paired set of model
scenarios that represent its best effort to simulate water quality conditions prior to
European settlement. By using the same model simulation tools to estimate pre-
settlement water quality conditions as those used in other aspects of the attainability
analyses presented in the Technical Support Document, reasonable comparisons
can be made among estimated nutrient and sediment loading results and resulting
simulated tidal-water quality responses.
The 'all-forest' scenario is a model simulation of what nutrient and sediment loads
might occur if the entire Chesapeake Bay watershed was forested and atmospheric
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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Table 111-1. Synthesis of five scientific experts' individual and collective findings
on the history of anoxia and hypoxic conditions in Chesapeake Bay tidal waters.
Chesapeake Bay Dissolved Oxygen Criteria
Team member Dr. Thomas Cronin, of the
U.S. Geological Survey (USGS), surveyed
five scientists8 who have studied the history
of anoxia and hypoxia in the Chesapeake
Bay over decadal and centennial time
scales, using geochemical and biological
proxies from sediment cores and instru-
mental and historical records. The
consensus of the five scientists is that the
Chesapeake Bay was seasonally anoxic
between 1900 and 1960. The seasonal
anoxia was extensive in the deep channel
and probably lasted several months.
Similarly, between 1600 and 1900, the
near-unanimous consensus is that the
Chesapeake Bay was seasonally anoxic for
probably weeks to months in the deep
channel. One researcher had reservations
about his group's earlier conclusion on
definitive evidence of anoxia prior to 1900,
but cannot exclude the possibility of anoxia
during this period. Anoxia during the 1900—
1960 period was probably geographically
less extensive in the Chesapeake Bay and
perhaps occurred less frequently (i.e., not
every year) than after the 1960s. In addition
to the geochemical and faunal proxies of
past trends in oxygen depletion, experts cite
the Sale and Skinner (1917) instrumental
documentation of hypoxia and probable
anoxia in the lower Potomac River in 1912.
For the period prior to European coloni-
zation (approximately 1600 AD), the
Source: U.S. EPA 2003.
consensus is that the deep channel of the
Bay may have been briefly hypoxic (less
than 2 mg/1), especially during relatively
wet periods (which did occur, based on the
paleo-climate record). Anoxia probably
occurred only during exceptional condi-
tions. It should be noted that the late
16th century and much of the 17th century
were extremely dry periods, not conducive
to oxygen depletion.
In sum, hypoxia, and probably periodic
spatially limited anoxia, occurred in the
Chesapeake Bay prior to the large-scale
application of fertilizer, but since the
1960s oxygen depletion has become
much more severe.
These experts also unanimously believe that
restoring the Chesapeake Bay to mid-20th
century, pre-1960 conditions might be
possible but very difficult (one expert
suggested an 80 percent nitrogen reduction
was necessary ), in light of remnant nutrients
in sediment in the Chesapeake Bay and
behind dams, likely increased precipitation
as the climate changes, population growth
and other factors. Most researchers believe
that restoring the Chesapeake Bay to con-
ditions prior to 1900 is either impossible,
or not realistic, simply due to the fact that
the temporal variability (year-to-year and
decadal) in 'naturally occurring' hypoxia
renders a single target dissolved oxygen
level impossible to define.
8T. M. Cronin (USGS, Reston, Virginia), S. Cooper (Bryn Athyn College), J. F. Bratton (USGS, Woods
Hole, Massachusetts), A. Zimmerman (Pennsylvania State University), G. Helz (University of Mary-
land, College Park).
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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deposition reduced to 10 percent of the current loading rates. The storage of nutri-
ents in the soil is still somewhat elevated under this scenario, and the nitrogen
delivered to the Bay's tidal waters is actually greater than the atmospheric inputs to
the watershed, owing to a 'draw-down' of nutrients in the soil. Shoreline erosion
loading rates are maintained at current levels.
The 'pristine' scenario is a model simulation of what may have occurred under pre-
settlement conditions. Atmospheric deposition is reduced to 10 percent of the current
loading rates as in the all-forest scenario, but the soil storage of nutrients is also
reduced, so that there is no 'draw-down' of nutrients during the simulation. In addi-
tion, steps were taken to restrict the conversion of particulate organic nitrogen to
solution organic nitrogen. Shoreline erosion was set to only 10 percent of current
levels to account for the pre-settlement presence of vast underwater grass beds and
intertidal oyster bar breakwaters. Unlike most model simulations, no fertilizer
applications to agricultural land, implementation of best management practices,
septic loads or discharges from point sources are shown in either the all-forest or
pristine scenarios.
STRENGTHS AND LIMITATIONS OF THE ALL-FOREST
AND PRISTINE SCENARIOS
It is extremely difficult to determine the accuracy of the predictions at one-tenth the
calibrated nitrogen loads for both the Chesapeake Bay Watershed and Water Quality
models. Overall, the extremes of the all-forest and pristine scenarios push all three
Chesapeake Bay models, including the Bay airshed model, to their limits since they
are calibrated to relatively current conditions.
The biological filtering capacities of a pristine Chesapeake Bay ecosystem are not
factored into the current Bay models. One of these processes involved the vast extent
of filter feeders, such as oysters, that consumed water-borne nutrients. In addition,
oyster reefs provided habitat for an enormous range of other animals such as worms,
snails, sea squirts, sponges, small crabs, and fishes, all of which are important
components of the estuarine food web.
Existing reservoirs, dams, and shipping channels are present in the all-forest and
pristine scenario landscapes and tidal waters because the Chesapeake Bay Watershed
and Water Quality models were calibrated with these human alterations in place. As
described in Chapter IV, these physical alterations can directly influence Chesapeake
Bay tidal-water quality conditions.
MODEL-SIMULATED NATURAL DISSOLVED OXYGEN CONDITIONS
By anticipating these limitations when characterizing pre-European settlement
effects on watershed loadings and tidal-water quality conditions, the paired all-forest
and pristine scenarios present the best quantitative estimate of where and when
"naturally occurring pollutant concentrations prevent the attainment of the use"
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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41
(40 CFR 131.10[g]). The range of nutrient and sediment loads from these two
scenarios yields the watershed partners' current best estimated range of "naturally
occurring pollutant concentrations" and resulting Chesapeake Bay tidal-water
quality conditions. Like all model results, the loads and water quality responses are
most useful when compared to other scenarios. In this case, adequate comparisons
can be made between the all-forest scenario results and those containing established
levels of anthropogenic effects.
Figure III-l illustrates the results of outputs from three scenarios of the Chesapeake
Bay Water Quality Model-the pristine, all-forest, and E3 scenarios. The outputs
provide the percent nonattainment of a 5 mg/1 monthly average dissolved oxygen
concentrations over 10 years of hydrology for the deep-channel, deep-water, open-
water and migratory designated uses as discussed in Chapter IV. These dissolved
oxygen concentrations are displayed over time (June 1 through September 30) and
volume of each respective designated use. Given the integration of the Chesapeake
Bay Water Quality Model with water quality monitoring data, the outputs are
currently generated as monthly averages although the water quality model operates
on hourly time scales (Table III-2).
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E
0
as
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^ 0
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^ 0
_ >
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« J
o 2
c g
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E <=
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tz c
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z 5?
z o
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0
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CL if)
CO
40
30
20
10
Deep-Channel Deep-Water Open-Water
Refined Tidal-Water Designated Uses
Migratory
Figure III-l. Percent nonattainment of a 5 mg/l monthly average dissolved oxygen concentration over
the June through September period for the E3 (physically implausible) (|), all-forest ([]) and pristine
(|) model scenarios by the refined tidal-water designated uses.
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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Table 111-2. Chesapeake Bay Watershed and Water Quality models.
The watershed and airshed models are
loading models. As such, they provide an
estimate of management actions through air
controls, agricultural best management
practices, or point source controls which
will reduce nutrient or sediment loads to
the Chesapeake. The advantage of using
loading models is that the full simulation
through different hydrologies of wet, dry,
and average periods can be simulated on
existing or hypothetical landuse patterns.
All of the Chesapeake Bay Program models
used in the attainability analyses simulate
the 10-year period of 1985 to 1994 (Linker
et al. 2000).
Chesapeake Bay Watershed Model
The Chesapeake Bay Watershed Model is
designed to simulate nutrient and sediment
loads delivered to the Chesapeake Bay under
different management scenarios (Donigian
et al. 1994; Linker et al. 1996; Linker 1996).
The simulation is an overall mass balance of
nitrogen and phosphorus in the basin, so that
the ultimate fate of the input nutrients is
incorporation into crop or forest plant mate-
rial, incorporation into soil, or loss through
river runoff. The Chesapeake Bay Watershed
Model has been in continuous operation
within the Chesapeake Bay Program since
1982, and has had many upgrades and
refinements since that time. The current
version of the Watershed Model, Phase 4.3,
is a comprehensive package for the simula-
tion of watershed hydrology, nutrient and
sediment export from pervious and imper-
vious landuses and the transport of these
loads in rivers and reservoirs.
Chesapeake Bay Water Quality Model
The complex movement of water within the
Chesapeake Bay, particularly the density-
driven vertical estuarine stratification, is
simulated with a Chesapeake Bay hydro-
dynamic model of more than 13,000 cells
(Wang and Johnson 2000). The Water
Quality Model is linked to the hydro-
dynamic model and uses complex
nonlinear equations describing 26 state
variables of relevance to the simulation of
dissolved oxygen, water clarity and chloro-
phyll a (Cerco 1993, 1995a, 1995b, 2000;
Thomann et al. 1994; Cerco and Meyers
2000). Coupled with the Water Quality
Model are simulations of settling organic
material sediment and its subsequent decay
and flux of inorganic nutrients from the
sediment (Di Toro 2001), as well as a
coupled simulation of underwater bay
grasses in the shallows (Cerco and
Moore 2001).
Integration of Monitoring and
Modeling for Criteria Assessment
The observed data is used to assess
criteria attainment during a 'base' period
corresponding to the years of calibration
for the Chesapeake Bay Water Quality
Model, 1985-1994. The Chesapeake Bay
Water Quality Model is used in scenario
mode to determine the effect of changes in
nutrient and sediment loads on water
quality concentrations. A modified
1985-1994 observed data set is generated
for each scenario using both the model and
the observations. The same criteria attain-
ment assessment process applied to the
observed data is then applied to this
'scenario' data to determine likely criteria
attainment under modified loading
scenarios. For a full discussion of this
procedure, see A Comparison of Chesa-
peake Bay Estuary Model Calibration with
1985-1994 Observed Data and Method
of Application to Water Quality Criteria
(Linker et al. 2002).
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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Under existing state water quality standards (see Chapter IV), the current dissolved
oxygen criteria for Chesapeake Bay tidal waters in Maryland is "greater than or
equal to 5 mg/1 at all times," and in Virginia the Chesapeake Bay tidal-water criteria
are "greater than or equal to 4 mg/1 minimum, and greater than or equal to 5 mg/1
daily average [see Table IV-1]." The analysis illustrated here for monthly average
dissolved oxygen concentrations is less stringent of an averaging period than the
current criteria in the states' water quality standards, given the monthly model output
limitation.
Results from the all-forest and pristine scenarios indicate that water quality in those
portions of the Chesapeake Bay that currently have deep-water and deep-channel
designated uses are unlikely to meet existing Maryland and Virginia state dissolved
oxygen water quality standards under natural conditions. Baywide, between 3
percent (pristine) and 28 percent (all-forest) of the volume and time over the summer
months of the 10-year simulation period would likely not attain the current desig-
nated uses in the deep channel (Figure III-l). The current designated uses would
likely not be attained up to 7 percent of the volume and time during the summer
months under natural conditions in the deep-water habitats.
An examination of all-forest and pristine scenario results on a segment-by-segment
scale documents similar findings. Table III-3 provides model-simulated results for
the summer months-June through September-which have the lowest ambient
dissolved oxygen concentrations. Results are presented for the 35 major Chesapeake
Bay Program segments. In the upper, middle and lower central Chesapeake Bay,
lower Potomac River, lower Rappahannock River and Eastern Bay segments there
are natural barriers (e.g., water-column stratification, bottom bathymetry) preventing
replenishment of dissolved oxygen to the deeper portions of the tidal waters under
the all-forest scenario. For these segments under the all-forest scenario, nonattain-
ment of the current state-adopted dissolved oxygen criteria assessed by the refined
deep-water and deep-channel designated use habitats ranged up to 41 percent of the
possible volume and time during the summer over the 10-year simulation period
(Table III-3). Nonattainment values were down in the range of 4 percent to 5 percent
under the pristine scenario.
These all-forest and pristine scenario findings are consistent with the conclusions
reached through analysis of the Paleoecological Records of Natural Conditions
described above.
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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Table 111-3. Percent nonattainment of 5 mg/l monthly averaged dissolved
oxygen concentrations over the June through September period from the E3,
all-forest and pristine model scenarios for the 35 major Chesapeake Bay
Program segments by the refined tidal-water designated uses.
Refined
Tidal-Water
Scenario
Chesapeake Bay Program Segment
Designated Use
E3
All-Forest
Pristine
Northern Chesapeake Bay (CBITF)
MIG
A
A
A
OW
A
A
A
Upper Chesapeake Bay (CB20H)
MIG
A
A
A
OW
A
A
A
Upper Central Chesapeake Bay (CB3MH)
MIG
A
A
A
OW
A
A
A
DW
6
A
A
DC
44
10
A
Middle Central Chesapeake Bay (CB4MH)
OW
A
A
A
DW
25
2
A
DC
81
41
4
Upper Central Chesapeake Bay (CB5MH)
OW
A
A
A
DW
8
1
A
DC
54
28
4
Western Lower Chesapeake Bay (CB6PH)
OW
A
A
A
DW
4
A
A
Eastern Lower Chesapeake Bay (CB7PH)
OW
A
A
A
DW
1
A
A
Mouth of Chesapeake Bay (CB8PH)
OW
A
A
A
Upper Patuxent River (PAXTF)
MIG
A
A
A
OW
A
5
5
Middle Patuxent River (PAXOH)
MIG
A
A
A
OW
A
A
A
Lower Patuxent River (PAXMH)
MIG
A
A
A
OW
A
A
A
DW
9
A
A
Upper Potomac River (POTTF)
MIG
A
A
A
OW
A
A
A
Middle Potomac River (POTOH)
MIG
A
A
A
OW
A
A
A
Lower Potomac River (POTMH)
MIG
A
A
A
OW
A
A
A
DW
8
A
A
DC
50
11
A
Upper Rappahannock River (RPPTF)
MIG
A
A
A
OW
A
A
A
Middle Rappahannock River (RPPOH)
MIG
A
A
A
OW
A
A
A
continued
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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Table 111-3. Percent nonattainment of 5 mg/l monthly averaged dissolved
oxygen concentrations over the June through September period from the E3,
all-forest and pristine model scenarios for the 35 major Chesapeake Bay
Program segments by the refined tidal-water designated uses (cont.).
Refined
Tidal-Water
Scenario
Chesapeake Bay Program Segment
Designated Use
E3
All-Forest
Pristine
Lower Rappahannock River (RPPMH)
MIG
A
A
A
OW
A
A
A
DW
6
A
A
DC
39
11
A
Piankatank River (PIAMH)
OW
A
A
A
Upper Mattaponi River (MPNTF)
MIG
A
A
A
OW
25
45
54
Lower Mattaponi River (MPNOH)
MIG
A
A
A
OW
48
56
59
Upper Pamunkey River (PMKTF )
MIG
A
A
A
OW
13
50
62
Lower Pamunkey River (PMKOH)
MIG
A
A
A
Middle York River ( YRKMH )
MIG
A
A
A
OW
A
A
A
Lower York River (YRKPH)
OW
A
A
A
DW
2
A
A
Mobjack Bay (MOBPH)
OW
A
A
A
Upper James River (JMSTF)
MIG
A
A
A
OW
A
A
A
Middle James River (JMSOH)
MIG
A
A
A
OW
A
A
A
Lower James River (JMSMH)
MIG
A
A
A
OW
A
A
A
Mouth of the James River (JMSPH)
OW
A
A
A
Eastern Bay (EASMH)
MIG
A
A
A
OW
A
A
A
DW
10
A
A
DC
61
22
A
Middle Choptank River (CHOOH)
MIG
A
A
A
OW
A
A
A
Lower Choptank River (CHOMH2)
MIG
A
A
A
OW
A
A
A
Mouth of the Choptank River (CHOMHT)
MIG
A
A
A
OW
A
A
A
Tangier Sound (TANMH)
OW
A
A
A
Lower Pocomoke River (POCMH)
OW
A
A
A
A = Applicable dissolved oxygen criteria fully attained; analysis based on monthly averaged dissolved oxygen
concentrations 5 mg/l, 3 mg/l and 1 mg/l for open-water, deep-water and deep-channel designated uses.
DU = designated use; OW = open-water; DW = deep-water; DC = deep-channel.
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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HUMAN-CAUSED CONDITIONS THAT CANNOT BE
REMEDIED WHICH APPEAR TO PREVENT ATTAINMENT
OF CURRENT DESIGNATED USES
Beyond natural conditions, some human-related conditions and alterations of the
watershed and tidal-water habitats must be considered in determining attainability of
the current designated uses. To conduct this component of the UAA, where and when
"human-caused conditions or source of pollution prevent the attainment of the use
and cannot be remedied" (CFR 131.10[g]) must be defined.
The Chesapeake Bay Program developed a series of level-of-effort scenarios as a
tool for assessing the Chesapeake Bay watershed's potential for nutrient and sedi-
ment reductions (Appendix A). These scenarios range from a Tier 1 level, which will
be in place by 2010 under current voluntary and regulatory programs, up to the
fourth, 'everything, everywhere by everybody,' or the E3 scenario. Each scenario
was based on 2010 projections of landuses, human population, agricultural animal
populations, point source flows and septic systems.
Reduction actions defined in the E3 scenario were simulated using the Chesapeake
Bay Program's Phase 4.3 Watershed Model and the EPA's Regional Acid Deposition
Model (RADM), resulting in estimated airshed and watershed loads for nitrogen,
phosphorus and sediment. The loading inputs from the airshed and watershed
models were then fed into the Chesapeake Bay Water Quality Model to simulate the
resulting dissolved oxygen concentrations.
The E3 scenario represents the limits of technology as known at the time of this
analysis (Table III-4) and is acknowledged not to be physically plausible in all cases
(Table III-5). This analysis assumes that any nutrient or sediment reductions equal
to or beyond the levels defined through the E3 scenario can be considered to repre-
sent human-caused conditions that cannot be remedied and can be used for justifying
why current designated uses cannot be met.
It is not possible to determine definitively human-caused conditions that cannot be
remedied. However, the E3 scenario represents the Chesapeake Bay Program part-
ners' best effort to capture those conditions by removing as much subjectivity as
possible in developing the scenario. Reported E3 scenario loading results from the
Chesapeake Bay watershed's land area, as a whole, represent theoretical minimum
loads equal to or beyond which it would be extremely difficult, if not impossible, in
many cases to achieve at this time. However, the reported E3 scenario-simulated
water quality response can be improved if opportunities for further controls on
shoreline erosion are incorporated.
It appears unlikely that current state water quality standards for dissolved oxygen
can be achieved in significant portions of the Chesapeake Bay and tidal tributaries'
deep-water and deep-channel habitats (see Table III-3). As approximated by a 5 mg/1
monthly average dissolved oxygen concentration, the existing state dissolved oxygen
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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47
Table 111-4. E3 scenario description.
The defined levels for technology and best
management practices implementation in
the 'everything, everywhere by everybody,'
or the E3 scenario, are theoretical. There are
no cost and few physical limitations applied
to implementing BMPs for point and
nonpoint sources. In addition, the E3
scenario includes new technologies,
management practices and programs that
are not currently part of Bay watershed
jurisdictional pollutant control strategies.
Appendix A details the assumptions and
methodologies used in developing each
technology and BMP-based implementation
level in the three tier and E3 scenarios for
all nutrient and sediment source categories.
Agricultural Nonpoint Source Controls
In the E3 scenario, it was assumed that the
load from every available acre of the rele-
vant land area was being controlled by a
full suite of existing or innovative practices
for most applied BMPs. In addition,
management programs converted landuses
from those with high-yielding nutrient and
sediment loads to those with lower loads
without regard to the economic viability of
such changes. Every acre of cropland is
conservation-tilled. Applications of fertil-
izers are set so that the crops do not receive
more than 98 percent of their need, well
below current recommended nutrient
management rates. All other components of
farm plans are fully implemented and the
cropland is planted in cover crops to maxi-
mize nutrient reduction benefits.
The E3 scenario designates 100-foot
riparian forest buffers on all unbuffered
stream miles in the Chesapeake Bay water-
shed. A total of 25,000 acres of cropland
are restored to wetlands. A quarter of the
crop and hay areas not converted to riparian
forest buffers or restored to wetlands are
retired to grass conditions. The E3 scenario
assumes there is rotational grazing on all
pasture land and that all unbuffered streams
through pastures are fully protected through
both riparian buffers and fencing to exclude
animals. The waste in animal feeding
operations is controlled to a degree that
there is no runoff. Another quarter of crop
acreage in the Chesapeake Bay basin is
replaced with long-term grasses that serve
as a carbon bank and could be converted to
energy through combustion.
Urban/Suburban Nonpoint Source
Controls
To minimize storm water runoff from urban
and suburban areas in the E3 scenario, all
land projected to be developed in the next
decade is employing environmental site
design or low-impact development prac-
tices. In addition, all existing urban areas
are retrofitted with a suite of practices to
significantly reduce nutrient and sediment
loads. Fifty-foot riparian forest buffers are
placed along all currently unbuffered urban
stream miles, while 100-foot buffers are
found on all herbaceous lands that are not
in agriculture. Also, all urban and nonagri-
cultural grass acres do not receive nutrient
applications from chemical fertilizers.
The E3 scenario calls for a 30 percent
reduction in projected urban growth in
Pennsylvania, Maryland, Virginia and the
District of Columbia over the next decade
to conform to commitments of the Chesa-
peake 2000 agreement. Specifically for this
model scenario, more urban areas are built
up rather than out, and 30 percent of the
forests are protected from development.
Point Source Controls
In the E3 scenario, all significant municipal
dischargers maintain annual averaged
effluent concentrations of 3 mg/1 total
nitrogen and 0.1 mg/1 total phosphorus. All
new septic systems employ denitrification
technologies and are maintained through
regular pumping to meet edge-of-septic-
field nitrogen loadings that are one-quarter
of typical loads. In addition, E3 atmos-
pheric deposition assumes emission controls
on utilities, industry and mobile sources
beyond what the Clean Air Act requires.
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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48
Table 111-5. E3 scenario possible over- and underestimations of attainable load
reductions.
Physical Limitations
In all appropriate circumstances, BMP
implementation levels in the E3 scenario
were applied to all relevant landuse areas
or current limits of technology. In many
cases and to remove the subjectivity in
determining human-caused conditions that
cannot be remedied, there were no physical
limitations to employing the practices or
programs.
For many BMPs, the E3 implementation
levels could not physically be achieved. For
example, space may not be available for 50-
foot riparian buffers in urban areas or
certain developed lands may not allow for
retrofitting with practices that attain pollu-
tant reduction efficiencies used in the E3
scenario. In addition, certain crop types
cannot be conservation-tilled and it may be
physically impossible to completely elimi-
nate runoff from animal feeding operations.
It is also unlikely that every homeowner and
farmer would efficiently apply fertilizers so
that only the needs of the vegetation are met
and that waterfront property owners would
plant 50-foot buffers even if it were physi-
cally possible. As a whole, 'feasible'
participation levels are not built into the E3
scenario. All of these instances are exam-
ples of where the E3 scenario may
overestimate reductions.
Underestimations of Load Reductions
Attainable under the E3 Scenario
By contrast, some BMP implementation
levels physically could be even higher than
those currently defined in the E3 scenario.
For example, it is physically possible that
more than 25,000 acres of cropland and hay
in Chesapeake Bay watershed could be
restored to wetlands. This limitation on
wetland acres restored in the E3 scenario for
Pennsylvania, Maryland and Virginia was
used to reflect the Chesapeake 2000 goal.
As another example, 25 percent of cropland
was replaced with long-term grasses that
serve as a carbon bank and could be
converted to energy through combustion.
Benefits of a carbon sequestration program,
in terms of lower pollutant loads, would
increase as more agricultural land is
converted. Conversion of more than 25
percent of cropland is physically possible.
In addition, the 30 percent reduction in
urban sprawl over a decade could be set at a
higher level. This rate was employed in the
E3 scenario to adhere to a Chesapeake 2000
goal.
The E3 scenario only includes shoreline
erosion controls at current levels due to a
current inability to define a 'maximum'
limit that would not be entirely subjective.
It has been demonstrated through modeling
efforts that additional controls of shoreline
erosion can significantly improve tidal-
water quality. In general, much opportunity
exists for reducing sediment and nutrient
loads from eroding shorelines that is not
reflected in the E3 scenario water quality
model results.
If greater BMP implementation levels than
those designated in the E3 scenario could
be physically achieved for any BMPs,
pollutant loadings would decrease and there
would be corresponding improved
responses in water quality. For the most
part, however, the E3 scenario did not
consider real physical limitations to BMP
implementation or participation levels.
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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49
criteria protecting the current designated uses could not be attained in these habitats
even after implementation of technologies and management practices at levels
defined in the E3 scenario (see Figure III-l).
FINDINGS AND CONCLUSIONS
The combined results of the E3, all-forest and pristine scenarios (see Figure III-l and
Table III-3) along with the scientific conclusions from the paleoecological record,
strongly indicate that current state aquatic life designated uses cannot be achieved in
the Chesapeake Bay's and tidal tributaries' deep-water and deep-channel habitats
where natural physical processes and bottom bathymetry-related barriers prevent
oxygen replenishment (see Chapter IV). Natural conditions, as well as human-
caused conditions that cannot be remedied, would result in even higher levels of
nonattainment of the states' existing 4 mg/1 daily minimum and 5 mg/1 daily aver-
aged dissolved oxygen criteria than illustrated in Figure III-l and summarized in
Table III-3, given the application of a 5 mg/1 monthly average dissolved oxygen
concentration for this analysis.
LITERATURE CITED
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anoxia; molybdenum in Chesapeake Bay sediments. Geochemica el Cosmochemica Acta
65:237- 252.
Boicourt, W. C. 1992. Influences of circulation processes on dissolved oxygen in Chesapeake
Bay. In Smith, D., M. Leffler and G. Mackiernan (eds.). Oxygen dynamics in Chesapeake
Bay: A Synthesis of Research. University of Maryland Sea Grant College Publications,
College Park, Maryland. Pp. 7-59.
Boynton, W. R., J. H. Garber, R. Summers and W. M. Kemp. 1995. Inputs, transformations,
and transport of nitrogen and phosphorous in Chesapeake Bay and selected tributaries. Estu-
aries 18:285-314.
Bratton, J. F., S. M. Colman, R. R. Sea and P. C. Baucom. In press. Isotopic record of
nitrogen and carbon cycling in Chesapeake Bay over the last 2,700 years and implications for
modern oxygen depletion. Limnology and Oceanography.
Cerco, C. F., L. Linker, J. Sweeney, G. Shenk and A. J. Butt. 2002. Nutrient and solids
controls in Virginia's Chesapeake Bay tributaries. Journal of Water Resources Planning and
Management May/June: 179-189.
Cerco, C. F. and K. Moore. 2001. System-wide submerged aquatic vegetation model for
Chesapeake Bay. Estuaries 24(4):522-534.
Cerco, C. and M. Meyers. 2000. Tributary Refinements to Chesapeake Bay Model. Journal
of Environmental Engineering 126(2): 164-174.
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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Cerco, C. F. 2000. Phytoplankton kinetics in the Chesapeake Bay Eutrophication Model.
Journal of Water Quality and Ecosystem Modeling 1( l-4):5-49.
Cerco, C. F. 1995. Response of Chesapeake Bay to nutrient load reductions. Journal of Envi-
ronmental Engineering 121(8): 549-556.
Cerco, C. F. 1995. Simulation of Long-Term Trends in Chesapeake Bay Eutrophication.
Journal of Environmental Engineering 121(4):298-310.
Cerco, C. F. 1993. Three-Dimensional Eutrophication Model of Chesapeake Bay. Journal of
Environmental Engineering 119(6): 1006-1025.
Colman, S. M. and J. F. Bratton. 2003. Anthropogenically induced changes in sediment and
biogenic silica fluxes in Chesapeake Bay. Geology 3 l(l):71-74.
Colman, S. M., P. C. Baucom, J. Bratton, T. M. Cronin, J. P. McGeehin, D. A. Willard, A.
Zimmerman and P. R. Vogt. 2002. Radiocarbon dating of Holocene sediments in Chesapeake
Bay. Quaternary Research 57:58-70.
Cooper, S. R. 1995. Chesapeake Bay watershed historical land use: Impact on water quality
and diatom communities. Ecological Applications 5:703-723.
Cooper, S. R. and G. S. Brush. 1991. Long-term history of Chesapeake Bay anoxia. Science
254:992-996.
Cornwell, J. C., D. J. Conley, M. Owens and J. C. Stevenson. 1996. A sediment chronology
of the eutrophication of Chesapeake Bay. Estuaries 19:488-499.
Cronin, T. M., ed. 2000. Initial Report on IMAGES V Cruise of the Marion-Dufresne to
Chesapeake Bay June 20-22, 1999. USGS Open-file report 00-306.
Cronin, T. M. and C. Vann. 2003. The sedimentary record of anthropogenic and climatic
influence on the Patuxent estuary and Chesapeake Bay ecosystems. Estuaries 26(2A):196-
209.
Di Toro, D. M. 2001. Sediment Flux Modeling. John Wiley and Sons, Inc. New York. 624p.
Donigian, J. A., B. R. Bicknell, A.S. Patwardhan, L.C. Linker, C.H. Chang and R. Reynolds.
1994. Watershed Model Application to Calculate Bay Nutrient Loadings: Final Findings and
Recommendations. U. S. EPA Chesapeake Bay Program, Annapolis, Maryland.
Hagy, J. D. 2002. Eutrophication, hypoxia and trophic transfer efficiency in Chesapeake Bay.
Ph.D. dissertation, University of Maryland, College Park, Maryland.
Harding, L. W. and E. S. Perry. 1997. Long-term increase of phytoplankton biomass in
Chesapeake Bay, 1950-1994. Marine Ecology Progress Series 157:39-52
Karlsen, A. W., T. M. Cronin, S. E. Ishman, D. A. Willard, R. Kerhin, C. W. Holmes and M.
Marot. 2000. Historical trends in Chesapeake Bay dissolved oxygen based on benthic
foraminifera from sediment cores. Estuaries 23:488-508.
Linker, L. C., G. W. Shenk, P. Wang, C. F. Cerco, A. J. Butt, P. J. Tango and R. W. Savidge.
2002. A Comparison of Chesapeake Bay Estuary Model Calibration with 1985-1994
Observed Data and Method of Application to Water Quality Criteria. Modeling Subcom-
mittee, Chesapeake Bay Program Office, Annapolis, Maryland.
Linker, L. C., G. W. Shenk, D. L. Dennis and J. S. Sweeney. 2000. Cross-Media Models
of the Chesapeake Bay Watershed and Airshed. Water Quality arid Ecosystem Modeling 1(1-
4):91-122.
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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51
Linker, L. C., 1996. Models of the Chesapeake Bay. Sea Technology 37(9):49-55.
Linker, L. C., C. G. Stigall, C. H. Chang and A. S. Donigian, Jr. 1996. Aquatic accounting:
Chesapeake Bay Watershed Model quantifies nutrient loads. Water Environment, and
Technology 8(l):48-52.
Malone, T. C. 1992. Effects of water-column processes on dissolved oxygen: Nutrients,
phytoplankton and zooplankton. In: Smith, D., M. Leffler and G. Mackiernan (eds.). Oxygen
Dynamics in Chesapeake Bay: A Synthesis of Research. University of Maryland Sea Grant
College Publications, College Park, Maryland. Pp. 61-112.
Newcombe, C. L. and W. A. Home. 1938. Oxygen-poor waters of the Chesapeake Bay.
Science 88:80-81.
Officer, C. B., R. B. Biggs, J. L. Taft, L. E. Cronin, M. A. Tyler and W. R. Boynton. 1984.
Chesapeake Bay anoxia: Origin, development, and significance. Science 223:22-27.
Taft, J. L., W. R. Taylor, E. O. Hartwig and R. Loftus. 1980. Seasonal oxygen depletion in
Chesapeake Bay. Estuaries 3:242-247.
Thomann, R. V., J. R. Collier, A. Butt, E. Casman and L. C. Linker. 1994. Response of the
Chesapeake Bay Water Quality Model to Loading Scenarios. Chesapeake Bay Program
Office, Annapolis, Maryland.
Wang, H. V. and B. H. Johnson. 2000. Validation and application of the second generation
three- dimensional hydrodynamic model of Chesapeake Bay. Journal of Water Quality and
Ecosystem Modeling l(l-4):51-90.
Willard, D. A., T. M. Cronin, S. Verardo. 2003. Late-Holocene climate and ecosystem history
from Chesapeake Bay sediment cores, USA. The Holocene Vol. 13.
Zheng, Y., B. Weinman, T. M. Cronin, M. Q. Fleisher and R. F. Anderson. In press. A rapid
procedure for thorium, uranium, cadmium and molybdenum in small sediment samples by
inductively coupled plasma-mass spectrometry: Application in Chesapeake Bay. Applied
Geochemistiy.
Zimmerman, A. R. and E. A. Canuel. 2000. A geochemical record of eutrophication and
anoxia in Chesapeake Bay sediments: Anthropogenic influence on organic matter composi-
tion. Marine Chemistry 69:117-137.
chapter iii • Why Attaining the Current Tidal-Water Designated Uses Appears Not to be Feasible
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chapter IV
Refined Designated Uses
for the Chesapeake Bay and
Tidal Tributaries
BACKGROUND
RENEWED COMMITMENT TO RESTORE
CHESAPEAKE BAY WATER QUALITY
The Chesapeake 2000 agreement and the subsequent six-state, District of Columbia
and EPA memoranda of understanding challenged the Bay watershed jurisdictions
to, "by 2010, correct the nutrient- and sediment-related problems in the Chesapeake
Bay and its tidal tributaries sufficiently to remove the Bay and the tidal portions of
its tributaries from the list of impaired waters under the Clean Water Act." (Chesa-
peake Executive Council 2000; Chesapeake Bay Watershed Partners 2001.)
These agreements included commitments to "define the water quality conditions
necessary to protect aquatic living resources" and to have the jurisdictions with tidal
waters "use their best efforts to adopt new or revised water quality standards consis-
tent with the defined water quality conditions." Against this backdrop of a renewed
commitment to restore Bay water quality (in part through the adoption of a consis-
tent set of Chesapeake Bay water quality criteria as state standards), the Chesapeake
Bay watershed partners recognized that the underlying tidal-water designated uses
must be refined to better reflect desired Bay water quality conditions.
CURRENT STATE TIDAL-WATER DESIGNATED USES
Virginia, Maryland, Delaware and the District of Columbia have identified parts of
the Chesapeake Bay and its tidal tributaries as 'state waters.' The current designated
uses for these state waters are for the protection of aquatic life (Table IV-1; figures
IV-1 through IV-4). The accompanying current criteria addressing nutrient and sedi-
ment enrichment impairments are limited to different dissolved oxygen
concentrations, which apply separately to each jurisdiction's tidal waters.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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54
Table IV-1. Summary of current designated uses for states' Chesapeake Bay
and tidal tributary waters.
Current Designated Use for Chesapeake Bay and
State
Tidal Tributary Waters
Maryland
• Use II (shellfish harvesting waters)—Chesapeake Bay proper
• Use I (water contact recreation, protection of aquatic life )—
All surface waters
Virginia • Class II (estuarine waters) for tidal water—Coastal zone to fall
line—Primary and secondary contact recreation, fish and shellfish
consumption, aquatic life and wildlife
"All state waters, including wetlands, are designated for the
following uses: recreational uses, e.g., swimming and
boating; the propagation and growth of a balanced,
indigenous population of aquatic life, including game fish
which might reasonably be expected to inhabit them; wildlife;
and the production of edible and marketable natural resources,
e.g., fish and shellfish."
Delaware • Broad Creek, Nanticoke River—Industrial water supply, primary
contact recreation, secondary contact recreation, fish and aquatic
life and wildlife, agriculture water supply with additional
classification as "waters of exceptional recreational and
ecological significance" (ERES waters).
District of Columbia • Potomac River Class A (primary contact recreation), B (primary
contact recreation and aesthetics), C (protection and propagation
of fish, shellfish, and wildlife), D (consumption of fish and
shellfish) and E (navigation).
chapter i • Introduction
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55
| Use l-P Use I plus public water supply
1 I Use II only Shellfish Harvesting Waters
Note: Use I applies to all dually
influenced waters of the Chesapeake
Bay and its tributaries.
Water contact recreation
Use I only ancj protection of Aquatic Life
Figure IV-1, Current designated uses for Chesapeake Bay and tidal tributary waters
located in Maryland.
Source: Code of Maryland Regulations 26.08.02 for water quality dated November 1, 1993.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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56
All state waters are designed for the following uses:
recreational uses, e.g. swimming and boating; the propa-
gation and growth of a balanced, indigenous population
or aquatic life, including game fish, which might reasonably
be expected to inhabit them; and the production of edible
and marketable natural resources, e.g. fish and shellfish.
Boundaries for Class II Waters are established for deter-
mining application of the appropriate aquatic life criteria.
Freshwater criteria apply in the tidal freshwaters. The
more stringent of either the freshwater or saltwater criteria
apply in transition zone waters. Saltwater criteria apply in
estuarine waters.
The Class II waters are Tidal Water—coastal zone to fall line.
Designated Uses
~ Class II Tidal Freshwater
~ Class II Transition Zone
1. Class II Estuarine
Figure IV-2, Current designated uses for Chesapeake Bay and tidal tributary waters
located in Virginia.
Source: Virginia State Water Control Board Regulation 9 VAC 25-260-5-et. seq. Water Quality
Standards dated December 10, 1997.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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57
.apeake
Nanticoke River
1,3-6
Broad Creek
1,3-6
I Wicomico River
River
Elk River
River
C&O Canal
1,3-5
Designated Uses
1. Industrial Water Supply
2. Agricultural Water Supply
3. Primary Contact Recreation
4. Secondary Contact Recreation
5. Fish, Aquatic Life, and Wildlife
6. Waters of Exception Recreational
or Ecological Significance
Drainage System
Basin Willi tidal waters of Ills Chesapeake Bay
Basin with non-tidal waters of the Chesapeake Bay
| j Chssapeake Bay walerstied in Maryland
— j Chesapeake Bay tidal tributaries
Figure IV-3, Current designated uses for Chesapeake Bay tidal tributary waters located
in Delaware.
Source: State of Delaware Water Quality Regulations.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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58
Rickey Run
B.C.D
Watts Branch
B.C.D
Washington Channef
. A.B.CAE
Anacostia River
A.B.C.O.E
Designated Uses
A. Primary contact recreation.
B. Secondary contact recreation and aesthetic enjoyment.
C. Protection and propagation offish, shellfish, and wildlife.
D. Protection of human health related to consumption of fish
and shellfish.
^ E. Navigation.
\ , Rivers and streams either outside of DC or
non-tidal sections are a lighter gray.
Figure IV-4, Current designated uses for Chesapeake Bay tidal tributary waters located
in the District of Columbia.
Source: District of Columbia Department of Consumer and Regulatory Affairs Notice of Final
Rulemaking.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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59
REFINING TIDAL-WATER DESIGNATED USES
The Chesapeake Bay Program watershed partners determined that the underlying
tidal-water designated uses must be refined to better reflect the desired and attain-
able Chesapeake Bay water quality conditions called for in the Chesapeake 2000
agreement. In refining the current tidal-water designated uses, the six Chesapeake
Bay watershed states and the District of Columbia took into account five principal
considerations:
• Habitats used in common by sets of species and during particular life stages
should be delineated as separate designated uses;
• Natural variations in water quality should be accounted for by the designated
uses;
• Seasonal uses of different habitats should be factored into the designated uses;
• The Chesapeake Bay criteria for dissolved oxygen, water clarity and chloro-
phyll a should be tailored to support each designated use; and
• The refined designated uses applied to the Chesapeake Bay and its tidal tribu-
tary waters will support the federal Clean Water Act goals and state goals for
uses existing in these water since 1975.
The Chesapeake Bay watershed partners are proposing five refined subcategories of
the current broad aquatic life designated uses contained in the existing state water
quality standards of the four jurisdictions bordering directly on Chesapeake Bay and
its tidal tributaries. Figure IV-5 illustrates the conceptual framework of the refined
tidal-water designated uses; Table IV-2 provides general descriptions of the five
designated uses and the aquatic communities they were established to protect.9 Four
of the refined designated uses were derived largely to address seasonally distinct
habitats and living resource communities with widely varying dissolved oxygen
requirements:
• Migratory fish spawning and nursery;
• Open-water fish and shellfish;
• Deep-water seasonal fish and shellfish; and
• Deep-channel seasonal refuge.
The fifth refined designated use, the shallow-water bay grass designated use, occurs
seasonally in conjunction with that part of the year-round open-water use which
borders the land along the tidal portions of the Chesapeake Bay and its tributaries
(Figure IV-5).
'Note that for brevity, these refined designated uses may be referred to as migratory spawning and
nursery, shallow-water, open-water, deep-water and deep-channel.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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A. Cross-Section of Chesapeake Bay or Tidal Tributary
Shallow-Water
Bay Grass Use
Open-Water
Fish and Shellfish Use
Deep-Water
Seasonal Fish and
Shellfish Use
—¦ Deep-Channel
Seasonal Refuge Use
B. Oblique View of the Chesapeake Bay and its Tidal Tributaries
Migratory Fish
Spawning and
, Nursery Use
Shallow-Water
Bay Grass Use
Open-Water
Fish and Shellfish Use
Deep-Water
Seasonal Fish and
Deep-Channel
Seasonal Refuge Use
Shellfish Use
Figure IV-5. Conceptual illustration of the five Chesapeake Bay tidal-water designated
use zones.
LIVING RESOURCE-BASED REFINED DESIGNATED USES AND
PROTECTIVE CRITERIA
The five refined designated uses were derived to reflect the habitats of an array of
recreationally, commercially and ecologically important species. The supporting
prey communities were given fall consideration along with the 'target species' in
defining the designated uses.
Two extensive syntheses of habitat requirements for important target species and
communities in the Chesapeake Bay and its tidal tributaries formed the basis from
which these refined designated uses were conceived and developed (Chesapeake Bay
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-2. General descriptions of the five proposed Chesapeake Bay tidal-water
designated uses.
Migratory Fish Spawning and Nursery Designated Use: Aims to protect migratory
finfish during the late winter/spring spawning and nursery season in tidal freshwater to
low-salinity habitats. This habitat zone is primarily found in the upper reaches of many
Bay tidal rivers and creeks and the upper mainstem Chesapeake Bay and will benefit
several species, including striped bass, perch, shad, herring and sturgeon.
Shallow-Water Designated Use: Designed to protect underwater bay grasses and the
many fish and crab species that depend on the shallow-water habitat provided by
underwater bay grass beds.
Open-Water Fish and Shellfish Designated Use: Aims to improve water quality in the
surface water habitats within tidal creeks, rivers, embayments and the mainstem Chesapeake
Bay year-round. This use protects diverse populations of sport fish including striped bass,
bluefish, mackerel and sea trout, bait fish such as menhaden and silversides, as well as the
listed shortnose sturgeon.
Deep-Water Seasonal Fish and Shellfish Designated Use: Aims to protect living
resources inhabiting the deeper transitional water column and bottom habitats between
the well-mixed surface waters and the very deep channels during the summer months.
This use protects many bottom-feeding fish, crabs and oysters, as well as other important
species, including the bay anchovy.
Deep-Channel Seasonal Refuge Designated Use: Designed to protect bottom sediment-
dwelling worms and small clams that act as food for bottom-feeding fish and crabs in
the very deep channel in summer. The deep-channel designated use recognizes that low
dissolved oxygen conditions prevail in the deepest portions of this habitat zone and will
naturally have very low to no oxygen during the summer.
Living Resource Task Force 1987; Funderburk et al. 1991). Only when coupled with
analyses of the extensive Chesapeake Bay Monitoring Program's water quality,
biological and living resource databases, now spanning 19 years, could the refined
tidal-water designated uses described below be documented and delineated across all
tidal-water habitats without constraints by jurisdictional borders.
The five tidal-water designated uses, in turn, provided the context for deriving
dissolved oxygen, water clarity and chlorophyll a water quality criteria for the
Chesapeake Bay and its tidal tributaries. These criteria, derived to protect each of the
five refined designated uses, were based on effects data from a wide array of biolog-
ical communities to capture the range of sensitivity of the thousands of aquatic
species inhabiting the Chesapeake Bay and tidal tributary estuarine habitats (U.S.
EPA 2003). Table IV-3 shows the proposed refined designated uses by Chesapeake
Bay Program segment.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-3. Recommended tidal-water designated uses by Chesapeake Bay Program segment.
Chesapeake Bay Program (CBP)
Segment Name
CBP
Segment
Migratory
Spawning
and Nursery
(Feb. 1-
May 31)
Op en-Water
(Year-Round)
Deep-Water Deep-Channel
(June 1- (June 1-
Sept. 30) Sept. 30)
Shallow-Water
(April 1-
Oct. 30)
Northern Chesapeake Bay
CB1TF
X
X
X
Upper Chesapeake Bay
CB20H
X
X
X
Upper Central Chesapeake Bay
CB3MH
X
X
X X
X
Middle Central Chesapeake Bay
CB4MH
X
X
X X
Lower Central Chesapeake Bay
CB5MH
X
X X
X
Western Lower Chesapeake Bay
CB6PH
X
X
X
Eastern Lower Chesapeake Bay
CB7PH
X
X
X
Mouth of the Chesapeake Bay
CB8PH
X
X
Bush River
BSHOH
X
X
X
Gunpowder River
GUNOH
X
X
X
Middle River
MIDOH
X
X
X
Back River
BACOH
X
X
X
Patapsco River
PATMH
X
X
X
X
Magothy River
MAGMH
X
X
X
Severn River
SEVMH
X
X
X
South River
SOUMH
X
X
X
Rhode River
RHDMH
X
X
X
West River
WSTMH
X
X
X
Upper Patuxent River
PAXTF
X
X
X
Western Branch (Patuxent River)
WBRTF
X
X
X
Middle Patuxent River
PAXOH
X
X
X
Lower Patuxent River
PAXMH
X
X
X
X
Upper Potomac River
POTTF
X
X
X
Anacostia River
ANATF
X
X
X
Piscataway Creek
PISTF
X
X
X
Mattawoman Creek
MATTF
X
X
X
Middle Potomac River
POTOH
X
X
X
Lower Potomac River
POTMH
X
X
X X
X
Upper Rappahannock River
RPPTF
X
X
X
Middle Rappahannock River
RPPOH
X
X
X
Lower Rappahannock River
RPPMH
X
X
X X
X
Corrotoman River
CRRMH
X
X
X
Piankatank River
PIAMH
X
X
X
Upper Mattaponi River
MPNTF
X
X
X
Lower Mattaponi River
MPNOH
X
X
X
Upper Pamunkey River
PMKTF
X
X
X
Lower Pamunkey River
PMKOH
X
X
X
Middle York River
YRKMH
X
X
X
Lower York River
YRKPH
X
X
X
continued
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-3. Recommended tidal-water designated uses by Chesapeake Bay Program segment (cont.).
Chesapeake Bay Program (CBP)
Segment Name
CBP
Segment
Migratory
Spawning
and Nursery
(Feb. 1-
May 31)
Open-Water
(Year-Round)
Deep-Water Deep-Channel
(June 1- (June 1-
Sept. 30) Sept. 30)
Shallow-Water
(April 1-
Oct. 30)
Mobjack Bay
MOBPH
X
X
X
Upper James River
JMSTF
X
X
X
Appomattox River
APPTF
X
X
X
Middle James River
JMSOH
X
X
X
Chickahominy River
CHKOH
X
X
X
Lower James River
JMSMH
X
X
X
Mouth of the James River
JMSPH
X
X
Western Branch Elizabeth River
WBEMH
X
Southern Branch Elizabeth River
SBEMH
X
Eastern Branch Elizabeth River
EBEMH
X
Mouth to mid-Elizabeth River
ELIMH
X
Lafayette River
LAFMH
X
Mouth of the Elizabeth River
ELIPH
X
X X
Lynnhaven River
LYNPH
X
X
Northeast River
NORTF
X
X
X
C&D Canal
C&DOH
X
X
X
Bohemia River
BOHOH
X
X
X
Elk River
ELKOH
X
X
X
Sassafras River
SASOH
X
X
X
Upper Chester River
CHSTF
X
X
X
Middle Chester River
CHSOH
X
X
X
Lower Chester River
CHSMH
X
X
X X
X
Eastern Bay
EASMH
X
X X
X
Upper Choptank River
CHOTF
X
X
Middle Choptank River
CHOOH
X
X
X
Lower Choptank River
CHOMH2
X
X
X
Mouth of the Choptank River
CHOMH1
X
X
X
Little Choptank River
LCHMH
X
X
Honga River
HNGMH
X
X
Fishing Bay
FSBMH
X
X
X
Upper Nanticoke River
NANTF
X
X
X
Middle Nanticoke River
NANOH
X
X
X
Lower Nanticoke River
NANMH
X
X
X
Wicomico River
WICMH
X
X
X
Manokin River
MANMH
X
X
X
Big Annemessex River
BIGMH
X
X
X
Upper Pocomoke River
POCTF
X
X
Middle Pocomoke River
POCOH
X
X
X
Lower Pocomoke River
POCMH
X
X
X
Tangier Sound
TANMH
X
X
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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CHESAPEAKE BAY TIDAL-WATER DESIGNATED USES
The migratory fish spawning and nursery designated use is described first, given its
unique seasonal role in protecting the spawning and nursery grounds of Chesapeake
Bay and East Coast anadromous fish species. The shallow-water bay grass desig-
nated use is then described, as it protects the vegetated shallow-water habitats that
are so critical to many individual estuarine species and living resource communities.
Next, the open-water, deep-water and deep-channel designated uses are described as
a series of year-round and seasonal subcategory designated uses formed around
unique habitats defined largely by natural conditions (e.g., stratification of the water
column, water circulation patterns) and physical barriers (Bay and tidal-water
bottom bathymetry) in the tidal waters.
The watershed states with tidally influenced Chesapeake Bay waters (Maryland,
Virginia and Delaware) and the District of Columbia ultimately are responsible for
defining and adopting the designated uses into their state water quality standards.
These uses will be adopted as subcategories of current state tidal-water designated
uses, which are designed to protect aquatic life. The formal process for refining
designated uses will meet the requirements of the Clean Water Act and any appli-
cable jurisdiction-specific environmental laws or regulations.
The adopted designated uses will protect existing aquatic and human uses of the tidal
waters that have been present since 1975. These designations go beyond minimum
requirements (131.10[d] and [h] [2]) and satisfy all requirements for meeting Clean
Water Act goals (131.10 [a]), downstream waters maintenance and protection
(131.10[b]) and for subcategorization as allowed by 131.10(g). The specific use defi-
nitions and the spatial application of the final designated uses will undergo public
review through the four jurisdictions' respective regulatory adoption processes prior
to EPA approval of the states' water quality standards.
MIGRATORY FISH SPAWNING AND NURSERY DESIGNATED USE
Waters with this designated use shall support the survival, growth and propagation
of balanced indigenous populations of ecologically, recreationally and commercially
important anadromous, semi-anadromous and tidal freshwater resident fish
species inhabiting spawning and nursery grounds from February 1 through May 31
(Table IV-4).
Designated Use Rationale
Based on a commitment within the 1987 Chesapeake Bay Agreement (Chesapeake
Executive Council 1987), a list of target anadromous and semi-anadromous species
was identified, including striped bass, American shad, hickory shad, alewife, blue-
back herring, white perch and yellow perch, based on their commercial, recreational
and ecological value and "the threat to sustained production due to population
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-4. Migratory fish spawning and nursery designated use summary.
Applicable Criteria: Dissolved Oxygen:
6.0 mg/1 7-day mean (only tidal habitats with 0-0.5 ppt salinity)
5.0 mg/1 instantaneous minimum
February 1 through May 31
This designated use supports the survival, growth and
propagation of balanced, indigenous populations of
ecologically, recreationally and commercially important
anadromous, semi-anadromous and tidal freshwater resident
fish species inhabiting spawning and nursery grounds.
The boundaries of this use extend from the upriver extent
of tidally influenced waters to the downriver and upper
Chesapeake Bay end of spawning and nursery habitats that
have been determined through a composite of all targeted
anadromous and semi-anadromous fish species' spawning
and nursery habitats. The use extends horizontally from the
shoreline of the body of water to the adjacent shoreline, and
extends down through the water column to the bottom
sediment-water interface.
Source for the Applicable Criteria: U.S. EPA 2003.
decline or serious habitat degradation" (Chesapeake Bay Living Resources Task
Force 1987). These species form a representative subset of species comprising a
"balanced, indigenous population." Other ecologically important anadromous and
semi-anadromous fish species also will be protected under this designated use.
Chesapeake Bay tidal waters support spawning and nursery areas that are important
not only to Bay fishery populations, but also to populations that inhabit the entire East
Coast, such as striped bass. The eggs, larvae and early juveniles of anadromous and
semi-anadromous species often have more sensitive habitat quality requirements than
other species and life stages (Funderburk et al. 1991; Jordan et al. 1992). These same
habitats are critical spawning and nursery grounds for tidal freshwater resident fish
species from February 1 to May 31 (U.S. EPA 2003). Thus, the combined migratory
and tidal freshwater resident fish spawning and nursery habitats were delineated as a
refined tidal-water designated use for the Chesapeake Bay and its tidal tributaries.
Designated Use Boundary Delineation
The boundaries of the migratory fish spawning and nursery designated use were
delineated from the upriver extent of tidally influenced waters to the downriver and
upper Chesapeake Bay end of spawning and nursery habitats that have been
determined through a composite of all targeted anadromous and semi-anadromous
fish species' spawning and nursery habitats (Figure IV-6).
Application:
Designated Use:
Designated Use Boundary:
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Migratory Fish ^
Spawning and Nursery,
T^JDesignated Use^?^
Figure IV-6. Illustration of the boundaries of the migratory fish spawning and nursery
designated use.
Critical Support Communities—Food and Shelter
In this designated use, spawning adults and the resulting larvae and early juvenile
fish depend on phytoplankton, zooplankton, bottom-dwelling worms and clams and
forage fish as prey (Funderburk et al. 1991). The presence of underwater bay grasses
in the shallows of the designated use habitat provides essential shelter for young
juveniles as well as many prey species.
Seasonal Use Application
The migratory fish spawning and nursery designated use applies from February 1
through May 31. The defined season for applying this use is based on a composite
of the full range of spawning and nursery periods of all the target anadromous and
semi-anadromous species.
Striped bass and juveniles of other migratory spawners are passively dispersed as
eggs and larvae and move farther downstream as they grow. Most juveniles do not
leave the boundaries of their respective spawning and nursery areas. Adult yellow
perch migrate from downstream to their spawning areas in the lower-salinity upper
reaches of the tidal tributaries from mid-February through March (Richkus and
Stroup 1987; Tsai and Gibson 1971). By early June, young-of-the-year juvenile
striped bass begin to move shoreward, spending the summer and early fall in shoal
waters less than six feet deep (Setzler-Hamilton et al. 1981). As juveniles grow, they
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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67
move progressively downriver (Boreman and Klauda 1988; Dey 1981; Setzler-
Hamilton et al. 1981). The February 1 beginning date reflects the initiation of the
yellow perch spawning season; the May 31 end date reflects when the eggs and
larvae have finished their transition to the juvenile life stage for all the target anadro-
mous and semi-anadromous species.
Applicable Chesapeake Bay Water Quality Criteria10
The migratory fish spawning and nursery designated use is seasonally defined and
occurs in conjunction with the year-round open-water designated uses and the
seasonal shallow-water designated uses (see Figure IV-5). The migratory fish
spawning and nursery designated use provides for the protection of the early life
stages of anadromous, semi-anadromous and resident tidal-fresh species through the
application of dissolved oxygen criteria derived for that purpose (U.S. EPA 2003).
From February 1 through May 31, the migratory fish spawning and nursery
dissolved oxygen criteria ensure protection of the egg, larval and early juvenile life
stages (Table IV-4). Free-flowing streams and rivers, where several of the target
species (e.g., shad, river herring) migrate for spawning, are protected through other
existing state water quality standards.
The open-water fish and shellfish designated use dissolved oxygen criteria were
derived to be protective of juvenile and adult life stages of anadromous and semi-
anadromous species after May 31 (see Table IV-6; U.S. EPA 2003). The overlapping
nature of these discrete designated uses will thus ensure that water quality conditions
protective of different species' life stages are present in those designated use habi-
tats. See chapters 3 and 6, respectively, in U.S. EPA 2003 for more details on the
individual dissolved oxygen criteria and criteria implementation procedures.
SHALLOW-WATER BAY GRASS DESIGNATED USE
Waters with this designated use support the survival, growth and propagation of
rooted, underwater bay grasses necessary for the propagation and growth of
balanced, indigenous populations of ecologically, recreationally and commercially
important fish and shellfish inhabiting vegetated shallow-water habitats (Table IV-5).
Designated Use Rationale
The shallow-water bay grass designated use protects a wide variety of species, such
as largemouth bass and pickerel, which inhabit vegetated tidal-fresh and low-salinity
habitats; juvenile speckled sea trout in vegetated higher salinity areas; and blue crabs
that inhabit vegetated shallow-water habitats covering the full range of salinities
encountered in the Chesapeake Bay and its tidal tributaries. Underwater bay grasses,
'"Maryland, Virginia, Delaware and the District of Columbia currently have water quality standards in
place that address pH conditions within the migratory fish spawning and nursery habitats.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-5. Shallow-water bay grass designated use summary.
Applicable Criteria: Water Clarity:
13 percent ambient light through water (tidal habitats with
0-5 ppt salinity)
22 percent ambient light through water (tidal habitats with
greater than 5 ppt salinity )
Application: April 1 through October 31 for tidal-fresh, oligohaline and
mesohaline habitats (0-18 ppt salinity); March 1 through
May 31 and September 1 through November 30 for
polyhaline habitats (>18 ppt salinity)
Designated Use: Waters with this designated use support the survival, growth
and propagation of rooted underwater bay grasses necessary
for the propagation and growth of balanced, indigenous
populations of ecologically, recreationally and commercially
important fish and shellfish inhabiting vegetated shallow-
water habitats.
Designated Use Boundary: Tidally influenced waters from the intertidal zone out to a
Chesapeake Bay Program segment-specific depth contour
that varies from 0.5 to 2 meters.
Source for the Applicable Criteria: U.S. EPA 2003.
the critical community that the designated use protects, provide the shelter and food
that make shallow-water habitats so unique and integral to the productivity of the
Chesapeake Bay ecosystem. Many Chesapeake Bay species depend on vegetated
shallow-water habitats at some point during their life cycle (Funderburk et al. 1991).
Given the unique nature of this habitat and its critical importance to the Chesapeake
Bay ecosystem, shallow waters were delineated as a refined tidal-water designated
use for the Chesapeake Bay and its tidal tributaries.
The shallow-water bay grass designated use is intended specifically to delineate the
habitats where the water clarity criteria would apply. The open-water fish and
shellfish designated use and the accompanying dissolved oxygen criteria will fully
protect the biological communities inhabiting shallow-water habitats. The
open-water designated use extends into the intertidal zone and protects shallow-
water organisms beyond underwater bay grasses. The seasonal shallow-water bay
grass designated use, similar to the migratory fish spawning and nursery use,
actually occurs in conjunction with the year-round open-water designated use (see
Figure IV-5) and provides specific protection for underwater bay grasses through the
application of water clarity criteria.
Designated Use Boundary Delineation
The shallow-water bay grass designated use covers tidally influenced waters, from
the intertidal zone out to a Chesapeake Bay Program segment-specific depth contour
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Shallow-Water'
Designated Use
Figure IV-7. Illustration of the boundaries of the shallow-water bay grass designated use.
that varies from 0.5 to 2 meters (Figure IV-7). The segment-specific depths were
based on rules described in detail in "Shallow-Water Bay Grass Designated Use
Boundaries" (see page 105) along with two other approaches to defining shallow-
water use boundaries.
Critical Support Communities—Food and Shelter
Phytoplankton, zooplankton, forage fish and bottom-dwelling worms and clams feed
many fish, crab and mollusk species that inhabit shallow-water habitats for part or
all of their life stages (Funderburk et al. 1991). Water quality criteria necessary to
fully support the shallow-water designated use must provide for the survival, growth
and successful propagation of prey communities in sufficient quantities.
Applicable Bay Water Quality Criteria
The shallow-water bay grass designated use is a seasonal use designation that occurs
in conjunction with the year-round open-water use and the seasonal migratory
spawning and nursery designated uses (see Figure IV-5). The shallow-water bay
grass designated use boundary delineates where specific levels of water clarity must
be restored to support restoration of underwater bay grasses. The applicable salinity
regime-based water clarity criteria apply during the appropriate underwater bay
grass growing season: April 1 through October 31 for tidal-fresh, oligohaline and
mesohaline habitats and March 1 through May 31 and September 1 through
November 30 for polyhaline habitats (see Table IV-5; U.S. EPA 2003).
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Underlying the seasonal shallow-water bay grass designated use is the year-round
open-water fish and shellfish designated use to support grass living resource commu-
nities inhabiting these shallow-water areas (see Table IV-6; U.S. EPA 2003). The
open-water fish and shellfish dissolved oxygen criteria apply into the shallows to the
intertidal zone. Therefore, nonvegetated shallow-water habitats and the living
resource communities that depend on those habitats will receive protection under the
open-water designated use. See chapters 3, 4 and 6, respectively in U.S. EPA 2003
for more details on the individual dissolved oxygen criteria, water clarity criteria and
criteria implementation guidelines.
OPEN-WATER FISH AND SHELLFISH DESIGNATED USE
Waters with this designated use support the survival, growth and propagation of
balanced, indigenous populations of ecologically, recreationally and commercially
important fish and shellfish species inhabiting open-water habitats (Table IV-6).
Designated Use Rationale
The natural temperature and salinity stratification of open waters influences
dissolved oxygen concentrations and, thus, the distribution of Chesapeake Bay
species. Surface mixed-layer waters with higher oxygen levels located above the
pycnocline support a different community of species than deeper waters from late
spring to early fall. Several well-known species that inhabit these open waters are
menhaden, striped bass and bluefish. Their habitat requirements and prey needs
differ from those of species and communities inhabiting deeper water habitats during
the summer months. See the deep-water "Designated Use Rationale" on page 74 for
more detailed documentation.
Clear evidence from the Chesapeake Bay as well as other estuarine and coastal
systems, including Long Island Sound (Howell and Simpson 1994), Albemarle-
Pamlico Sound (Eby 2001) and the Gulf of Mexico (Craig et al. 2001), indicates that
the fish and other organisms inhabiting open-water habitats will use deeper within-
pycnocline and below-pycnocline habitats, given suitable dissolved oxygen
conditions. It is the lack of sufficient oxygen, not the presence of stratification, that
limits the use of these deeper habitats. Therefore, the open-water designated use
applies to transitional pycnocline and bottom mixed-layer below-pycnocline habitats
where these below-pycnocline and pycnocline waters are sufficiently reoxygenated
by oceanic or riverine waters.
During their first winter of life, members of five important Chesapeake Bay species—
white perch, striped bass, Atlantic croaker, shortnose sturgeon and Atlantic
sturgeon—are constrained to oligohaline and mesohaline regions (< 20 ppt) in the
upper Chesapeake Bay mainstem, and seek out warmer temperatures that occur in
deeper channel waters below the thennocline. From October through May, the deep-
channel habitats in the upper Bay adjacent to shallower summer and fall habitats
should be considered important nursery habitats for young-of-the-year juvenile white
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-6. Open-water fish and shellfish designated use summary.
Applicable Criteria: Dissolved Oxygen
5.5 mg/1 30-day mean (tidal habitats with 0-0.5 ppt salinity)
5.0 mg/1 30-day mean (tidal habitats with greater
than 0.5 ppt salinity)
4.0 mg/1 7-day mean
3.2 mg/1 instantaneous minimum
Chlorophyll a:
Concentrations of chlorophyll a in free-floating microscopic
aquatic plants (algae) shall not exceed levels that result in
ecologically undesirable consequences-such as reduced water
clarity, low dissolved oxygen, food supply imbalances, prolif-
eration of species deemed potentially harmful to aquatic life or
humans or aesthetically objectionable conditions-or otherwise
render tidal waters unsuitable for designated uses.
Application: Year-round: open-water designated use and dissolved
oxygen criteria.
March 1 through May 31 and July 1 through September 30:
chlorophyll a criteria.
Designated Use: Waters with this designated use support the survival, growth
and propagation of balanced, indigenous populations of
ecologically, recreationally and commercially important fish
and shellfish species inhabiting open-water habitats.
Designated Use Boundary: From June 1 through September 30 the open-water
designated use includes tidally influenced waters extending
horizontally from the shoreline to the adjacent shoreline.
If a pycnocline is present and, in combination with bottom
bathymetry and water-column circulation patterns, presents a
barrier to oxygen replenishment of deeper waters, the open-
water fish and shellfish designated use extends down into the
water column only as far as the measured upper boundary of
the pycnocline. If a pycnocline is present but other physical
circulation patterns (such as influx of oxygen rich oceanic
bottom waters) provide for oxygen replenishment of deeper
waters, the open-water fish and shellfish designated use
extends down into the water column to the bottom water-
sediment interface.
From October 1 through May 31, the open-water designated
use includes all tidally influenced waters extending
horizontally from the shoreline to the adjacent shoreline,
extending down through the water column to the bottom
water-sediment interface.
Source for the Applicable Criteria: U.S. EPA 2003.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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72
perch, striped bass, and Atlantic croaker (Pothoven et al. 1997) as well as Atlantic and
shortnose sturgeon (Miller et al. 1997; Secor et al. 2000; Welsh et al. 2000).
During the coldest months, the interaction between temperatures and salinity toler-
ances may result in a 'habitat squeeze' or bottleneck, forcing juveniles into
deep-channel habitats seeking preferred temperatures. Unpublished data from the
Maryland Environmental Service indicate that a thennocline, separating the warmer
deep waters from colder overlaying waters, typically occurs at a 10-to 20-meter
depth in the deep channel from October through February. Therefore, from fall
through late spring when the open-water designated use applies to these natural
channel habitats, it also protects indigenous populations of important fish species
that depend on deep-channel habitats for overwintering.
Based on these natural conditions and their influence on oxygen levels and the
seasonal distributions of Chesapeake Bay species, open waters were delineated as a
refined tidal-water designated use in the Chesapeake Bay.
Designated Use Boundary Delineation
From June 1 through September 30 the open-water designated use includes tidally
influenced waters extending horizontally from the shoreline to the adjacent shoreline
(Figure IV-8). If a pycnocline is present and, in combination with bottom bathymetry
and water-column circulation patterns, presents a barrier to oxygen replenishment of
deeper waters, the open-water fish and shellfish designated use extends down into
the water column only as far as the measured upper boundary of the pycnocline
Open-Water
Designated Use
Figure IV-8. Illustration of the boundaries of the open-water fish and shellfish
designated use.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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(Figure IV-9). If a pycnocline is present but other physical circulation patterns (such
as influx of oxygen rich oceanic bottom waters) provide for oxygen replenishment
of deeper waters, the open-water fish and shellfish designated use extends down
through the water column to the bottom water-sediment interface.
From October 1 through May 31, the boundaries of the open-water designated use
includes all tidally influenced waters extending horizontally from the shoreline to the
adjacent shoreline, extending down through the water column to the bottom water-
sediment interface.
Figure IV-9. Illustration of the vertical boundaries for the refined open-water fish
and shellfish designated use.
Critical Support Communities—Food and Shelter
Water column-dwelling phytoplankton, zooplankton and forage fish constitute the
major prey for other species in the Chesapeake Bay's open waters (Funderburk et al.
1991). Water quality criteria to support the open-water designated use fully must
provide for the survival, growth and successful propagation of quality prey com-
munities in sufficient quantities.
Applicable Bay Water Quality Criteria
The open-water dissolved oxygen criteria apply year-round (see Table IV-6). The
applicable salinity regime-based chlorophyll a criteria apply only in spring (March
1 through May 31) and summer (July 1 through September 30) to the open-water
designated use habitats. See chapters 3 and 5, respectively, in U.S. EPA (2003) for
more details on the individual dissolved oxygen and chlorophyll a criteria and
chapter 6 for detailed criteria implementation procedures.
DEEP-WATER SEASONAL FISH AND SHELLFISH DESIGNATED USE
Waters with this designated use protect the survival, growth and propagation of
balanced, indigenous populations of important fish and shellfish species inhabiting
deep-water habitats (Table IV-7).
Open-Water
Shallow
Water
Shallow
Water
Upper Pycnocline
Boundary
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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74
Table IV-7. Deep-water seasonal fish and shellfish designated use summary.
Applicable Criteria:
Dissolved Oxygen:
3 mg liter1 30-day mean
2.3 mg liter1 1-day mean
1.7 mg liter1 instantaneous minimum
Application: June 1 through September 30
Designated Use:
Waters with this designated use protect the survival, growth
and propagation of balanced, indigenous populations of
ecologically, recreationally, and commercially important
fish and shellfish species inhabiting deep-water habitats.
Designated Use Boundary: Tidally influenced waters located between the measured depths
of the upper and lower boundaries of the pycnocline in areas
where the measured pycnocline, in combination with bottom
bathymetry and water circulation patterns, presents a barrier to
oxygen replenishment of deeper waters. In some areas where a
lower boundary of the pycnocline is not calculated, the deep-
water designated use extends from the measured depth of the
upper boundary of the pycnocline down through the water
column to the bottom sediment-water interface.
Source for the Applicable Criteria: U.S. EPA 2003.
Designated Use Rationale
In an eutrophic system such as the Chesapeake Bay, excess organic matter settles to
the bottom, where it fuels microbial activity (e.g., Malone et al. 1986; Tuttle et al.
1987). With more fuel, more oxygen is consumed and, where replenishment with
oxygen-saturated waters is restricted, the water becomes more severely oxygen-
depleted. There is evidence that hypoxic and anoxic conditions existed in the deeper
waters of the Chesapeake Bay prior to European settlement (Cooper and Brush
1991). These same data indicate that anthropogenic activity has increased the extent,
frequency and severity of oxygen depletion in the Chesapeake Bay (Zimmerman and
Canuel 2000; Hagy 2002).
Many parts of the Chesapeake Bay become, on a seasonal basis, vertically stratified
because of depth-related density differences in the water column, caused primarily
by variations in salinity and, to a lesser degree, temperature. Warmer, freshwater
from the rivers floats on top of the cooler, denser saltwater at the bottom that enters
the Bay from the ocean. The gravitational force of the downriver flow of freshwater
causes a wedge of deeper, saltier water to move up the Bay and upriver. Vertically,
at some point in the water column, a zone of maximum density difference is reached,
which inhibits or prevents the exchange between water above and below it. This
region is called the pycnocline. In the summer months, respiration by organisms
living below the pycnocline can deplete concentrations of dissolved oxygen.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Because waters in and below the pycnocline are isolated from well-mixed surface
waters, dissolved oxygen concentrations can decrease until they are stressful or
lethal to higher organisms.
The formation of the pycnocline is a natural process. In areas where stratification is
common, the pycnocline generally forms at about the same depth range, but is
subject to seasonal and annual variations in depth due to river flow, temperature and
salinity patterns. It is generally shallower at the mouths of rivers and the Chesapeake
Bay and deeper at the heads of rivers. The effect of the pycnocline also is not the
same everywhere in the Chesapeake Bay and is influenced by local characteristics
such as bathymetry, vertical and horizontal water circulation patterns, and proximity
to the ocean and major river fall-lines. In some parts of the Bay and its tidal rivers,
these factors create a more complex stratification pattern: a second pycnocline is
formed lower in the water column, dividing it into three layers. If a region is
contained by the pycnocline above and by bottom bathymetry laterally, it is even
more isolated from oxygen-replenishing waters.
Bay anchovy is a target species whose egg and larval life stages are spent in pycno-
cline waters (Keister et al. 2000; Rilling and Houde 1999; MacGregor and Houde
1996). Blue crabs, oysters, softshell clams, hard clams, spot, croaker, flounder and
catfish inhabit the near-bottom waters in the deep-water habitats (Funderburk et al.
1991). The oxygen requirements of these species differ from those of species inhab-
iting shallow-water, open-water and deep-channel habitats. Their feeding patterns
and distribution of eggs and larvae are greatly influenced by natural features of the
water column such as the pycnocline.
Deep waters were delineated as a refined tidal-water designated use for the Chesa-
peake Bay and its tidal tributaries based on the unique nature of the pycnocline
region as an important living resource habitat and the transitional nature of its water
quality conditions.
Designated Use Boundary Delineation
The deep-water designated use includes the tidally influenced waters between the
measured upper and lower boundaries of the pycnocline where, in combination with
bottom bathymetry and water circulation patterns, the pycnocline limits oxygen
replenishment of deeper waters (Figure IV-10). In some areas where a lower
boundary of the pycnocline is not calculated, the deep-water designated use extends
from the measured depth of the upper boundary of the pycnocline down through the
water column to the bottom sediment-water interface.
Critical Support Communities—Food and Shelter
Bottom-dwelling worms and clams and reef-dwelling forage fish are important food
sources for the fish and crabs in deep-water habitats (Funderburk et al. 1991). Water
quality criteria to support the deep-water designated use must provide for the
survival, growth and successful propagation of quality prey communities in suf-
ficient quantities.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Deep-Water
Upper Pycnocline
Boundary
Lower Pycnocline
Boundary
Figure IV-10. Illustration of the vertical boundaries for the refined deep-water
designated use.
Seasonal Use Application
The deep-water seasonal fish and shellfish designated use applies from June 1
through September 30. By June, a combination of natural water-column stratification
and increased biological oxygen consumption driven by higher water temperatures
prevents the Chesapeake Bay's deep waters from retaining high concentrations of
dissolved oxygen. These natural conditions generally persist into September. From
October 1 through May 31 the open-water fish and shellfish designated use applies
to these same waters.
Applicable Bay Water Quality Criteria
The deep-water dissolved oxygen criteria apply from June 1 through September 30
(see Table IV-7). See chapters 3 and 6, respectively in U.S. EPA 2003 for more
details on the deep-water dissolved oxygen criteria and criteria implementation
procedures.
DEEP-CHANNEL SEASONAL REFUGE DESIGNATED USE
Waters with this designated use must protect the survival of balanced, indigenous
populations of ecologically important benthic infaunal and epifaunal worms and
clams, which provide food for bottom-feeding fish and crabs (Table IV-8).
Designated Use Rationale
In the Chesapeake Bay, researchers have determined the oxygen minimum to be in
the below-pycnocline waters throughout the deep trough in the mainstem Chesa-
peake Bay in the late spring to early fall (Smith et al. 1992). Isolated from aerated
surface waters, low dissolved oxygen concentrations in this region are due to excess
oxygen consumption from bacterial breakdown of organic material over oxygen
additions from ocean waters flowing in from far down-Bay. North of this region, the
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-8. Deep-channel seasonal refuge designated use summary.
Applicable Criteria: Dissolved Oxygen:
1.0 mg/1 instantaneous minimum
Application: June 1 through September 30
Designated Use: Waters with this designated use must protect the survival of
balanced, indigenous populations of ecologically important
benthic infaunal and epifaunal worms and clams, which
provide food for bottom-feeding fish and crabs.
Designated Use Boundary: Deep-channel designated use waters are defined as tidally
influenced waters at depths greater than the measured lower
boundary of the pycnocline in areas where, in combination
with bottom bathymetry and water circulation patterns, the
pycnocline presents a barrier to oxygen replenishment of
deeper waters. The deep-channel designated use is defined
laterally by bathymetry of the trough and vertically by the
lower boundary of the pycnocline above, and below, at the
bottom sediment-water interface.
Source for the Applicable Criteria: U.S. EPA 2003.
trough quickly becomes shallow and bottom waters are oxygenated as they mix with
aerated waters in the shoals. Below-pycnocline waters to the south are reoxygenated
through mixing with oxygenated oceanic waters entering the Chesapeake Bay mouth.
These deep channels are sinks for excess organic material which, in the process of
decaying, increase oxygen consumption. They are isolated from surface and oceanic
sources of oxygen replenishment. Vertical stratification and gravitational and hori-
zontal circulation often cause severe, sudden oxygen depletion beginning just below
the lower boundary of the pycnocline and extending to the bottom (Smith et al.
1992). Given the physical nature of the deep trough leading to naturally severe
oxygen depletion during the summer, the deep-channel was delineated as a refined
tidal-water designated use for Chesapeake Bay.
Designated Use Boundary Delineation
Deep-channel designated use waters are defined as tidally influenced waters at
depths greater than the measured lower boundary of the pycnocline in areas where
the pycnocline, in combination with bottom bathymetry and water circulation
patterns, presents a barrier to oxygen replenishment of deeper waters (Figure IV-11).
The deep-channel designated use is defined laterally by bathymetry of the trough and
vertically by the lower boundary of the pycnocline above, and below, at the bottom
sediment-water interface.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Lower Pycnocline
Boundary
Deep Channel
Figure IV-11. Illustration of the vertical boundaries of the refined deep-channel
seasonal refuge designated use.
Critical Support Communities—Food and Shelter
Bottom-dwelling worms and clams are the principal food source of bottom-feeding
fish and crabs in the deep-channel (Funderburk et al. 1991). Water quality criteria
for the deep-channel designated use must provide for the survival of these prey
communities.
Seasonal Use Application
The deep-channel designated use applies from June 1 through September 30. By
June, a combination of natural water-column stratification and increased water
temperature prevents the Chesapeake Bay's deep-channel waters from retaining high
concentrations of dissolved oxygen. These natural conditions generally persist
through September. From October 1 through May 31 the open-water designated use
applies to these same habitats.
Applicable Bay Water Quality Criteria
The deep-channel dissolved oxygen criteria apply from June 1 through September
30 (see Table IV-8). See chapters 3 and 6, respectively in U.S. EPA 2003 for more
details on the deep-channel dissolved oxygen criteria and criteria implementation
procedures.
CHESAPEAKE BAY TIDAL-WATER
DESIGNATED USE BOUNDARIES
Correct application of the Chesapeake Bay water quality criteria depends on the
accurate delineation of the five tidal-water designated uses. Each of the designated
uses has different dissolved oxygen criteria derived to match the respective level of
protection required by different living resource communities. In case of the shallow-
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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water bay grass designated use, the location of the boundaries is critical to providing
sufficient suitable habitat for the restoration of the desired number of acres of under-
water bay grasses.
The vertical depth and horizontal breadth of the designated use boundaries are based
on a combination of factors: natural water-column stratification, bottom bathymetric
features and circulation patterns, among other considerations. It is important to note
that these boundaries have been developed without consideration of attainability
from the perspective of potentially widespread social and economic impacts. The
states may find they need to adjust these boundaries according to such impacts
(131.19[g][6]), which may prevent attainment of the designated use, and must justify
these adjustments during their water quality standards adoption processes. The tech-
nology-based attainability of these refined tidal-water designated uses and their
boundaries is documented in Chapter V.
Four of the six factors defined in 40 CFR 101.10(g) justify deriving the boundaries
described in this chapter for the refined tidal-water designated uses:
• Natural, ephemeral, intermittent or low-flow conditions or water levels (e.g.,
application of a 10-year water quality data record (1985-1994) reflecting a
wide range of watershed hydrologic and tidal bay hydrodynamic conditions);
• Dams, diversion or other types of hydrologic modifications (e.g., dredged
shipping channels);
• Physical conditions related to the natural features of the water body, such as the
lack of a proper substrate, cover, flow, depth, pools, riffles and the like (e.g.,
water-column stratification, bottom bathymetry); and
• Naturally occurring pollutant concentrations (see Chapter III).
MIGRATORY FISH SPAWNING AND NURSERY
DESIGNATED USE BOUNDARIES
The boundaries of the migratory fish spawning and nursery designated use were
delineated from the upriver extent of tidally influenced waters to the downriver and
upper Chesapeake Bay end of spawning and nursery habitats that have been deter-
mined through a composite of all targeted anadromous and semi-anadromous fish
species' spawning and nursery habitats (Figure IV-12). Free-flowing streams and
rivers, where several of the target species (e.g., shad and river herring) migrate for
spawning, are protected through other existing state water quality standards.
To generate these boundaries, habitat distribution maps, drawn from the Habitat
Requirements for Chesapeake Bay Living Resources-Second Edition (Funderburk et
al. 1991), were used. The distribution maps used during delineation of the migratory
spawning and nursery designated use included:
• Alewife spawning and nursery;
• Alewife nursery;
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Figure IV-12. Map showing the migratory spawning and nursery designated use for the
Chesapeake Bay and its tidal tributaries (black areas).
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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• American shad spawning and nursery;
• American shad nursery;
• Hickory shad spawning and nursery;
• Herring spawning and nursery;
• Herring nursery;
• Striped bass spawning reaches;
• Striped bass spawning rivers;
• White perch nursery;
• White perch spawning; and
• Yellow perch spawning and nursery.
For those species that had multiple habitat distribution maps for related life stages,
the maps were merged into a single coverage. Then individual species maps were
superimposed on a composite spawning and nursery habitat map.
The striped bass habitat distribution maps used in this process were originally titled
"Striped Bass Chesapeake Bay Spawning Reaches and Spawning Rivers" by
Funderburk et al. (1991). The sources of the spawning reach distributions were
research and monitoring findings synthesized by Setzler-Hamilton and Hall (1991).
However, the mapped extent of the nursery areas, referred to as spawning rivers in
the original map, was based on Maryland and Virginia legislative definitions,11 not
on fisheries survey findings.
Those regulations, which define "spawning rivers and areas," did not attempt to
define "early juvenile nursery habitat" but rather those rivers in which striped bass
spawn. The spawning reach designation in the regulation was used to describe areas
where striped bass eggs and larvae had been found. This justification was based on
icthyoplankton collections done in the 1950s in Maryland (Mansueti and Hollis
1963). Tresselt (1952) defined spawning reaches in Virginia.
To further enhance understanding of nursery areas, discussions were held with
fishery scientists Herb Austin and Deane Este of the College of William and Mary's
Virginia Institute of Marine Science, and Eric Durell, Maryland Department of
Natural Resources, who are responsible for their respective states' juvenile striped
bass seine surveys. The primary nursery areas for young-of-the-year striped bass
were delineated based on a comparison of long-term Maryland and Virginia seine
survey data with the legislatively-defined extent of early juvenile nursery habitat. In
any given year, juvenile striped bass can be found throughout a broader range of
Chesapeake Bay tidal waters. The primary nursery areas where the highest concen-
trations of early juvenile life-stage striped bass are almost always found in the spring
"Code of Maryland Regulations 08.02.05.02 and Virginia Marine Resources Commission Regulation
450-01-0034 as cited inChesapeake Bay Living Resources Task Force (1987).
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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were identified and incorporated into the composite map described above (e.g.,
Austin et al. 2000). The striped bass nursery areas were supplemented to ensure that
shad and river herring spawning and nursery areas were fully represented within the
migratory fish spawning and nursery designated use boundaries (Rulifson 1994;
Olney 2002).
From February 1 through May 31, the migratory fish spawning and nursery desig-
nated use occurs in conjunction with, and, therefore, encompasses specific portions
of the seasonal shallow-water bay grass and year-round open-water fish and shellfish
designated use habitats (see shaded sections in Figure IV-5). The designated use
extends horizontally from the shoreline across the body of water to the adjacent
shoreline, and extends down through the water column to the bottom sediment-water
interface.
The exact spatial and temporal extent of migratory fish spawning and nursery
designated use would vary annually due to regional climatic patterns if actual
observed salinity and temperature were used to define year-by-year boundaries.
Because use of year-by-year delineation of the exact boundaries of the migratory fish
spawning and nursery designated adds complexity, a fixed set of boundaries was
established. The migratory fish spawning and nursery designated use habitat shown
in Figure IV-12 reflects both long-term, decadal average salinity conditions and
decades' worth of fisheries-independent beach seine and trawl monitoring data.
States can adopt an approach (to be defined) for defining migratory spawning and
nursery designated use boundaries on a year-to-year basis by directly factoring in the
influence of interannual climatic patterns on the use boundaries.
OPEN-WATER, DEEP-WATER AND DEEP-CHANNEL
DESIGNATED USE BOUNDARIES
Background
The open-water, deep-water and deep-channel designated uses, the habitats they
represent and the dissolved oxygen criteria for ensuring their protection are inextri-
cably related to physical structure (water-column stratification, bottom bathymetry)
and to physical, chemical, meteorological and fluvial forces and processes. Under-
standing these factors will enhance understanding of the designated use delineation
process as well as the issues underlying application of the dissolved oxygen criteria.
The following section provides background on these three principal factors: bathym-
etry, flow and circulation, and vertical density gradients and pycnoclines.
Bathymetry
Although the Chesapeake Bay is a relatively shallow estuary, bathymetric features
play a large role both in defining the Bay's habitats as well as the eutrophication-
related water quality problems observed throughout most of the tidal waters.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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The most prominent bathymetric feature in the Bay is the deep trench that runs from
the Chesapeake Bay Bridge between Annapolis and Kent Island, Maryland, to an
area midway between the southern shore of the mouth of the Potomac River and the
northern shore of the mouth of the Rappahannock River (figures IV-13 and IV-14).
The trench ranges from 24 to 48 meters in depth and extends generally midchannel
between the western and eastern shores of the mainstem Chesapeake Bay It is
thought to be a remnant of the ancient Susquehanna River. A shallower trench
extends down along the Virginia Eastern Shore (Figure IV-15). Similar, smaller
trenches and holes exist elsewhere in Bay tidal waters, generally in the larger tidal
tributary rivers near their mouths. These are described later in the more detailed
regional descriptions that follow.
Mainstem Deep Trench
As described above. the mainstem deep trench
extends down a significant portion of the
mainstem bay. At its northern extent, it shoafs
rapidly at the Chesapeake Bay bridge The
southern extent is at a point roughly mid way
between the Potomac and Rappahannock rivers.
The beginning and end of this trench are fairly
abrupt which effectively closes it at both ends.
This leaves exchange with surface waters as the
primary avenue of oxygen replenishment. Once
the pycnocline is established, this avenue Is cut
off.
York Trench
The trench in the downstream end of the
York River extends from Queen Creek,
down into the Chesapeake Bay. The
deepest point is an approximately 28
meters hole off Gloucester Point The
ends of the York trench are defined by
fairly gradual shoaling and aren't really
closed.
Patuxent Trench
The Patuxenl trench extends from the mouth of
Patuxent River up-river to Battle Creek, The
up-river terminus of the Irench shoals gradually
and. therefore, does nol come to an abrupt
close. The down river end of the Irench comes
to a close as it terminates in a sill between Ihe
mouth of the Patuxenl River and the mainstem
trench.
Potomac Trench
A deep Irench area in the Potomac River
extends from Ragged Point to the mainstem
Bay deep trench. The upstream end shoafs
rapidly and is closed while the downstream
end is connected to Ihe Bay. It is
approximately 28 meters at its deepest
Virginian Sea
This region of Ihe mainstem 8ay extends from
the Rappahannock to the mouth of Ihe Bay I I
is characterized by a wide area where the
depth ranges from 11-17 meters. Meandering
generally along the eastern extent of this
deeper region is a trench that is 17 - 22 meters
deep but has a hole approximately 50 meters
deep. This hole is located north of the mouth off
of Cherrystone Intel.
Baltimore Harbor
Baltimore has been extensively dredged and is connected to Ihe head' of Ihe
mainstem trench via a shipping channel. Although the channels within the harbor are
not 'trench-like' in depth, they are maintained artificially, not through Ihe action of
flow. The Baltimore Harbor channels are approximately 15 meters al their deepest.
Chester Trench
The Chester River has a deeper region that
extends from the mouth, up river to Piney
Point on Tilghman Neck. The Chester Trench
is closed at it's up and down river ends and is
10-20 meters deep.
Eastern Bay
The Eastern Bay trench is connected to the
mainslem trench and extends up-river to the
mouth of Ihe Miles River. This Irench ranges
from 10-25 meters deep.
Bathymetry
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Rappahannock Trench
The trench in the downstream
end of the Rappahannock
extends from Long Point to the
river mouth. Both the upstream
and downstream ends are
closed. The trench is
approximately 28 meters at its
deepest.
Figure IV-13. Major bathymetric trenches within the Chesapeake Bay and its tidal tributaries.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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84
Figure IV-14. Three-dimensional view of the Chesapeake Bay mainstem trench as
viewed from the south looking north. The depth versus width relationship has been
enhanced to improve viewing.
Figure IV-1 5. Three-dimensional view of the 'Virginian Sea' as viewed from the south
looking north. The depth versus width relationship has been enhanced to improve
viewing.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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These deep regions contrast with the Chesapeake Bay as a whole, which has an
average depth of only 6 meters. They also figure prominently in the Chesapeake
Bay's dissolved oxygen problems. When it is overlain by a stratified water column,
the bottom water in the trenches and holes is isolated from the oxygenated surface
water and can become oxygen-depleted. This situation generally occurs in the late
spring and summer when oxygen-consuming activity is high and discontinuity in
water density through the water column can act as a barrier, i.e., act as a 'lid,'
capping off the exchange of oxygenated water with the oxygen-depleted waters in
the trenches and holes. However, some of the deep areas of the Chesapeake Bay,
although capped as described, do not suffer from chronically low dissolved oxygen.
These areas generally have their downstream or seaward end open so that deep-water
exchange with the oxygenated deep water from the ocean can occur.
FLOW AND CIRCULATION
Processes within the Chesapeake Bay and its tidal tributaries are strongly influenced
by flow and circulation patterns. These factors affect the mixing of the Bay's waters
and the distribution of salinity, dissolved compounds and planktonic organisms. Like
most estuaries, the Chesapeake Bay has a two-layer flow pattern. Net flow in the
upper layer moves down the Bay or downriver, while net flow in the bottom layer
moves up the Bay or upriver.
This two-layer flow is caused primarily by the difference in density between the less
dense, low-salinity water that flows off the land and the more dense, high-salinity
water that flows in from the ocean. The less dense, more buoyant, low salinity water
floats on the surface of higher salinity water. The tendency of ocean water in summer
to be cooler than freshwater also contributes to its higher density. Interannual and
seasonal differences in freshwater inflow to the rivers and the Chesapeake Bay, due
largely to meteorological factors, affect the interaction of the two layers.
Tidal forces move water into and out of the Chesapeake Bay and its rivers. Tidal
currents interact with the bathymetric surfaces of the bottom, with the seaward flow
of freshwater and with the air-water interface affecting internal turbulence and
mixing. Tied to lunar cycles, the daily, monthly and seasonal tidal rhythms are rela-
tively predictable components of flow and circulation.
The Coriolis force is another important physical circulation process in the Chesa-
peake Bay. The Coriolis force is related to the earth's rotation and causes moving
objects such as fluids to veer to the right (clockwise) in the Northern Hemisphere
and to the left (counter-clockwise) in the Southern Hemisphere. This force increases
with proximity to the poles. Currents in the Northern Hemisphere tend to move
clockwise over their course unless they encounter a barrier such as a land mass. Thus
ocean water flowing into the Chesapeake Bay at the mouth is deflected north due to
the Coriolis force. The current continues around to the right until it encounters the
Eastern Shore, which directs the flow up the Bay. Water flowing down and out of the
Chesapeake Bay on the surface, flows primarily down the Western Shore as the
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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86
Coriolis force tends to push it to the right. This same phenomenon of inflow on the
bottom on the right and outflow on the surface on the left occurs in the Bay's tidal
tributaries as well.
VERTICAL DENSITY GRADIENTS AND PYCNOCLINES
In many parts of the Chesapeake Bay the water column becomes stratified because
of differences in water density. These differences are caused primarily by differences
in salinity and, to lesser degree, in temperature. The water column becomes verti-
cally stratified when, at some depth, a difference in water density from one depth to
the next is large enough to inhibit or prevent exchange between water above and
below it. Fisher et al. (2003) found the density gradient for defining inhibition or
prevention of water exchange in the Chesapeake Bay to be 0.1 kg/m4. The depth
nearest the surface where this first occurs is referred to as the pycnocline. The
discontinuity may be gradual, as shown in Figure IV-16a, exhibiting a generally
uniform gradient of increasing density from one depth to the next through the water
column. In such cases, one refers to the region of the pycnocline.
a.
b.
w
<1)
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87
In areas where stratification is common, the pycnocline typically forms at about the
same depth, but is subject to seasonal and annual variations in depth due to river
flow, temperature and salinity patterns. The pycnocline is generally shallower at the
mouths of tidal rivers and the Chesapeake Bay and deeper with distance upriver and
up-Bay. In the central, deepest part of the mainstem Chesapeake Bay, the pycnocline
tends to deepen and 'tilt' slightly on the east-west axis, depending on the strength
and direction of prevailing winds as well as the relative balance of the several forces
controlling Chesapeake Bay circulation. North of this area, where the Bay narrows
and grows shallow, and north-moving bottom water shoals up from the deep trench,
the pycnocline is generally found closer to the surface. In upriver areas of tidal trib-
utaries, pycnoclines may occur occasionally depending on episodic intrusions of
saline waters. In other areas, such as the mouth of Tangier Sound in the lower Chesa-
peake Bay, pycnoclines are occasional or intermittent because fresh and saline
waters are typically well-mixed by tidal currents and bathymetric features.
In some areas, the many factors acting on circulation create a more complex stratifi-
cation structure. Below the surface mixed layer, there is a layer where density
continues to change with depth. Then a second, sharp density discontinuity is
encountered, creating a discrete bottom mixed layer (Figure IV-16b). A density
gradient of 0.2 kg/m4 was found to inhibit upward vertical exchange and form a
boundary for this lower mixed zone. (See Appendix D for a more thorough explana-
tion of the methods for determining the pycnocline.)
For these reasons, the shape of a density profile can be highly variable within and
between locations. The profile in Figure IV-16b is common in medium-to-deep areas
of the mainstem Chesapeake Bay and lower tributaries during the summer months.
There is an upper mixed layer several meters thick, followed by a distinct change in
the density gradient. This change marks the upper depth of the pycnocline and the
lower depth of the upper mixed layer. The thickness of the inter-pycnocline region
in this example is 9 meters, about a third of the water column. The bottom mixed
layer is fairly thick in this case, extending approximately 13 meters to the bottom.
The figure illustrates the effect of the pycnocline and density gradient on oxygen
concentration in this part of the Chesapeake Bay. Oxygen in the surface mixed layer
is close to saturation. Below the upper pycnocline depth, oxygen levels fall with
increasing distance from the oxygenated upper layer. The bottom mixed layer is
consistent at about 1 mg/1 through the entire thickness to the bottom.
Figure IV-17a shows a pycnocline type that is common to shallow to medium-depth
areas of the mainstem Chesapeake Bay and mid-to-lower areas of the tidal tribu-
taries. There is a well-defined surface mixed layer, marked by a sharp density
discontinuity, but no lower mixed layer. The pycnocline extends through the water
column to the bottom sediment-water interface, with dissolved oxygen concentra-
tions decreasing with distance from the upper pycnocline boundary. Figure IV-17b
shows a different density structure at the same location on a different date. There is
no density discontinuity, the upper mixed layer extends through the entire water
column and dissolved oxygen levels greater than 5 mg/1 are sustained through to the
bottom sediment-water interface. The vertical profiles in figures IV-17a and IV-17b
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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88
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Figure IV-18. 'Snapshot' of water density and dissolved oxygen vertical depth profiles at various water quality
monitoring program stations in the Chesapeake Bay and its tidal tributaries in the summer of 1997.
Source of data: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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90
illustrate the difference small and large variations in density can have on dissolved
oxygen concentrations as described above. For example, at monitoring station EE3.2
in Tangier Sound, the decrease in dissolved oxygen concentration (about 2 mg/1) at 14
meters has a density difference just large enough to be considered a pycnocline.
Downstream, at station CB7.2, the change in density is much larger but induces about
the same magnitude of decrease in the dissolved oxygen concentration gradient.
DELINEATING THE DESIGNATED USE BOUNDARIES
Vertical stratification has direct implications for delineating the designated use
boundaries. Much of the water in the Chesapeake Bay and its tidal tributaries is
shallow and well-mixed or easily aerated. These areas plus the surface mixed layers
overlying stratified water in channels and holes constitute the open-water fish and
shellfish designated use. The upper layer mixes on time scales of minutes to hours
(Alldredge et al. 2002), which means that all of the water in this layer comes in close
contact with the atmosphere and should be able to attain the most protective surface
water dissolved oxygen criterion. The open-water designated use boundary is, there-
fore, defined as the upper mixed layer, extending from the water surface to the
bottom water-sediment interface, where no stratification occurs or to the measured
depth of the upper pycnocline where, in combination with bottom bathymetry and
water-column circulation, it presents a barrier to oxygen replenishment of deeper
waters. From June through September, the open-water designated use accounts for
approximately 70 percent of the total volume of the Chesapeake Bay and its tidal
tributaries, and many Chesapeake Bay Program segments have only this one desig-
nated use (Table IV-9).
Water in the bottom mixed layer is essentially trapped. The bottom mixed layer is
separated from the upper mixed layer by the pycnocline and receives very limited
oxygen from either mixing or diffusion. Biological respiration and decomposition
processes deplete the ambient dissolved oxygen, and bottom sediments exert addi-
tional oxygen demand. The shape of the bottom mixed layer or deep-channel
designated use is essentially a thin layer along the bottom in most areas, with thicker
sections in some deeper areas of the Chesapeake Bay. Water within the pycnocline
between the upper and lower mixed layers is defined as the deep-water designated use.
However, as noted and illustrated above, a pycnocline and density gradient do not
affect dissolved oxygen concentration conditions to the same degree in all areas of
the Chesapeake Bay and its tidal tributaries. There are regional peculiarities in
bathymetry and flow that strongly influence the effect of a pycnocline on dissolved
oxygen concentrations, and these must be taken into account.
THE BOUNDARY DELINEATION PROCESS
The process of identifying and delineating the open-water, deep-water and deep-
channel designated use boundaries employed observed and model-simulated
characterizations of dissolved oxygen concentrations and the theoretical effects of
the physical and chemical processes discussed above. The process first identified the
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-9. The tidal-water volume of the designated uses by Chesapeake Bay
Program segment. Calculations are based on the 1998-2000 summer (June
through September) mean depths of the upper and lower pycnoclines.
Volume (cubic kilometers)
Chesapeake Bay
Program Segment
Migratory
Open-Water
Deep-Water
Deep Channel
CB1TF
.35/4%
.35/1%
CB20H
1.22/14%
1.23/2%
CB3MH
2.27/27%
1.05/2%
.87/6%
.47/5%
CB4MH
4.26/9%
2.73/9%
2.25/26%
CB5MH
7.57/15%
3.17/15%
4.62/52%
CB6PH
5.03/10%
5.03/10%
CB7PH
10.29/21%
10.29/21%
CB8PH
3.16/6%
BSHOH
.05/
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92
Table IV-9. The tidal-water volume of the designated uses by Chesapeake Bay
Program segment. Calculations are based on the 1998-2000 summer (June
through September) mean depths of the upper and lower pycnoclines (cont.).
Volume (cubic kilometers)
Chesapeake Bay
Program Segment
Migratory
Open-Water
Deep-Water
Deep Channel
JMSTF
.26/3%
,27/
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93
deep-channel designated use habitats: the areas of the Chesapeake Bay and its tidal
tributaries that suffer chronic low dissolved oxygen concentrations due to the natural
interplay of water-column stratification, bottom bathymetry and water circulation
patterns. These areas are so strongly isolated by these factors that they become
immune from remediation. The next step was to identify the deep-water designated
use habitats—areas with chronically low dissolved oxygen concentrations driven
largely by water-column stratification, bottom bathymetry and water circulation
patterns, but with hypoxic conditions (extent and severity) that are responsive to
change, including changes in anthropogenic inputs. The rest of the tidal Bay habitats
were identified as open-water designated use habitats.
First it was necessary to identify potential areas for delineation as deep-channel and
deep-water designated use habitats by examining empirical dissolved oxygen
concentration and distribution data under the 'best' observed conditions. The 17-year
dissolved oxygen record from the Chesapeake Bay Program's Water Quality Moni-
toring Program, 1984-2000, was reviewed to find the best summer dissolved oxygen
conditions in this time period.12 Using hypoxic volume-days as the metric, 1997 was
chosen. The dissolved oxygen conditions of that year largely reflect the effect of low
freshwater inflow and lower nutrient and sediment inputs from reduced rain and
subsequent runoff.
Maps of bottom-water dissolved oxygen concentrations in the summer of 1997
revealed the areas with the most recalcitrant low dissolved oxygen concentrations.
These maps also revealed areas with adequate dissolved oxygen concentrations, but
with episodic low dissolved oxygen concentra-
tions under other flow and runoff loading
conditions. Maps of the spatial extent of waters
with concentrations of 1 mg/1 and 3 mg/1 over the
17-year period helped identify areas where phys-
ical processes strongly influence dissolved
oxygen concentrations and where low dissolved
oxygen persists over a wide range of flows and
associated nutrient loads. The regions identified
as having chronic low dissolved oxygen concen-
trations attributable to the combined affects of
pycnocline, bathymetry and flow were as follows:
• Upper, middle and lower central Chesapeake
Bay segments (CB3MH, CB4MH and
CB5MH);
• Northern reaches of the western and eastern
lower Chesapeake Bay (CB6PH and
CB7PH);
12Historical dissolved oxygen data were available from as early as the 1950s; however, the temporal and
spatial coverage prior to 1984 was uneven and too coarse for this analysis.
Dissolved Oxygen
and Temperature
As the temperature of a liquid
increases, the ability of gases
to dissolve into it decreases.
In other words, as water gets
warmer, the concentration
of gases, such as oxygen,
within it decreases. This
change has implications for
the Chesapeake Bay in the
summer time because, as the
water's temperature increases,
it can hold less and less
oxygen.The inability to hold
oxygen happens at a time
when overall metabolism in
the Bay is increasing with
temperature. Higher metabo-
lism is coupled with increased
dissolved oxygen consumption.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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94
• Patapsco River (PATMH);
• Mesohaline segments of the Chester, Eastern Bay, Patuxent, Potomac and Rappa-
hannock rivers (CHSMH, EASMH, PXTMH, POTMH and RPPMH); and
• Polyhaline segment of the York River (YRKPH) (Figure IV-19).
How water-column stratification, bottom bathymetry and water circulation patterns
affect dissolved oxygen conditions and, therefore, the designated use boundaries in
each of these regions are discussed and illustrated below.
Upper Central Chesapeake Bay
The upper central Chesapeake Bay, or segment CB3MH, includes the 'head' of the
mainstem Chesapeake Bay trench at its northern border near the Chesapeake Bay
Bridge (Figure IV-19). In this segment the flow shifts from a single to a two-layer
flow. The exact point where this occurs shifts south and north as the flow from the
Susquehanna River increases and decreases with seasonal and interannual variation.
Its location in the center of this estuarine transition zone puts segment CB3MH at
the extreme end of oxygen dynamics in the Chesapeake Bay. As ocean water moves
up the Bay beneath the pycnocline, metabolic processes are consuming its reserve of
dissolved oxygen. By the time this water reaches segment CB3MH, it has traveled
approximately 220 kilometers and, depending on the time of year, it can be partly or
completely deprived of dissolved oxygen. Because of this, the very southern portion
of segment CB3MH is the first part of the Chesapeake Bay mainstem to show
oxygen depletion in the spring and the last to become reoxygenated in the fall. As
the northward-flowing bottom water encounters the head of the mainstem trench, it
spills into the shallower waters of the middle portion of segment CB3MH before
meeting and mixing with the south-flowing waters of the Susquehanna River (Figure
IV-20). Therefore, even though this middle portion of segment CB3MH is not
'trench-like' in depth, this area has deep-channel and deep-water designated uses.
Middle Central Chesapeake Bay
The middle central Chesapeake Bay, or segment CB4MH, encompasses the entire
northern half of the Chesapeake Bay mainstem trench with the exception of the head,
which lies in segment CB3MH (Figure IV-19). The trench runs 20 to 35 meters deep
along the eastern side of the segment. Once a pycnocline develops in this segment,
it acts as a lid over the trench and effectively isolates below-pycnocline waters from
the overlying waters. The source of the below-pycnocline water in segment CB4MH
is the already depleted below-pycnocline water of segment CB5MH (Figure IV-21).
Therefore, the only source of dissolved oxygen for below-pycnocline segment
CB4MH water is the occasional storm-induced downwelling event. Given the size of
this segment, these events are relatively localized and short-lived. Because the pycn-
ocline so effectively isolates the deeper waters in this segment, along with bottom
bathymetry and water circulation patterns, these within-pycnocline waters are desig-
nated as deep-water and the below-pycnocline waters are designated as deep-channel
designated use habitats.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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95
Lower
River
(RPPMH)
Lower
York River
(YRKPH)
Western Lower
Chesapeake Bay
(CB6PH)
EH Selected Segments
Bathymetry
I I -5.5 - 0 m
I I -ll.I - -5.6
| 1 -16.7 - -11.2
' ~| -22.3 - -16.8
I I -27.9 - -22.4
-33.5 28.0
H 391 33 6
U 44.7 -39.2
¦ 50.3 - -44.8
| No Data
Patapsco River
(PATMH)
Upper Central
Chesapeake
(CB3MH)
Lower
Potomac River
(POTMH)
Lower
Chester River
(CHSMH)
Eastern Bay
(EASMH)
Lower Central
Bay
(CB5MH)
Eastern Lower
Chesapeake Bay
(CB7PH)
Middle Central
Chesapeake Bay
(CB4MH)
Lower
Patuxent River
(PXTMH)
Figure IV-19. Chesapeake Bay Program segments identified as having chronic low dissolved oxygen
attributable to the combined effects of pycnocline, bathymetry and flow.
Lower Central Chesapeake Bay
The lower central Chesapeake Bay, or segment CB5MH, encompasses the entire
southern half of the Bay's mainstem trench (see Figure IV-19). As in segment
CB4MH, the pycnocline in this segment can 'cap' waters in the trench so that the
only significant source of exchange is water flowing into the southern end of the
trench, beneath the pycnocline. During most of the year, as this source water enters
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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96
Shipping channel to
Baltimore Harbor in
the Patapsco River.
Pycnocline
Oxygen depleted water flows
up-bay under the pycnocline in
the mainstem trench. Upon
reaching the northern terminus
of the trench, it flows up and
into the shallower waters of
northern CB3MH and into the
Patapsco River via the
shipping channel.
,ern terminus of
the mainstem trench.
Up-bay movement of oxygen-
depleted sub-pycnocline water
from the mainstem trench mixes
with down-bay flow from the
Susquehanna and becomes
re-oxygenated.
Figure IV-20. Three-dimensional schematic of the northern terminus of the mainstem Chesapeake Bay
trench. Flow is depicted by thick arrows. Above and below pycnocline waters are shaded differently.
Region depicted is boxed on inset map.
Pycnocline
As ocean water moves up the
bay, under the pycnocline, it
becomes gradually depleted
in dissolved oxygen until it is
hypoxic/anoxic when it
reaches the head of the
Chesapeake Bay mainstem
trench.
Patapsco
Patuxent
Potomac
Rappahannock
Figure IV-21. Three-dimensional schematic of the hydrodynamics of the Chesapeake Bay mainstem
trench. View is from the southeast looking northwest.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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97
the trench, its dissolved oxygen concentration is still relatively undepleted, because
it is not far from its ocean source. However, during July and August, temperatures in
the southern mainstem Chesapeake Bay can be warm enough and benthic metabo-
lism high enough for this source water to have depleted oxygen supplies (see
"Dissolved Oxygen and Temperature" sidebar, above). As this water moves up the
trench during the late spring and summer months, metabolic processes under the
pycnocline gradually consume the available dissolved oxygen until it is severely
depleted by the time it reaches the northern part of segment CB5MH (Figure IV-21).
The southern half of segment CB5MH is generally the last part of the Chesapeake
Bay mainstem to become oxygen-depleted and the first to become replenished.
Because the pycnocline so effectively isolates the bottom waters in this segment,
along with bottom bathymetry and water circulation patterns, the within-pycnocline
waters are designated as deep-water designated use habitat and the below-pycnocline
waters are designated as deep-channel designated use habitat.
Western and Eastern Lower Chesapeake Bay
The western and eastern lower Chesapeake Bay, segments CB6PH and CB7PH,
respectively, together make up the broadest region of the Chesapeake Bay mainstem.
The entire region is heavily influenced by the ocean. A 17- to 22-meter trench runs
along the axis of segment CB7PH, extending from the northern end of the segment
almost to its southern boundary (see Figure IV-19). The trench is approximately
2.5 kilometers wide and deepens to an approximately 50-meter hole near its southern
terminus. Although the trench becomes capped by a pycnocline, below-pycnocline
dissolved oxygen concentrations within the trench are usually not affected. As ocean
water flows into the Chesapeake Bay mouth along the bottom, the Coriolis force
swings this flow northward along the lower eastern shore of the Chesapeake Bay. This
waterflow pattern carries ocean water directly into the trench in segment CB7PH and
provides a steady supply of oxygenated water to the below-pycnocline habitats.
Ocean water similarly replenishes the below-pycnocline waters of segment CB6PH.
Only the very northern portions of segments CB6PH and CB7PH appear to have a
chronic dissolved oxygen depletion problem related to the pycnocline and local
bottom bathymetry. The northern boundary of these two segments forms a line,
inclining northeastward from the mouth of the Rappahannock River to a point at the
southern tip of the islands forming Tangier Sound (see Figure IV-19). The line
approximates the location of a broad shoal or sill on the Chesapeake Bay bottom.
The sill defines the southern terminus of the mainstem Chesapeake Bay deep trench
and functions as a 'hydrologic control point' for waters passing over it.
A shipping channel cuts through the sill, connecting the trench in segment CB7PH
to the trench in the middle Chesapeake Bay (Figure IV-22). The channel enables an
exchange of oxygen-depleted bottom waters from the mainstem trench with water in
the northern portions of segments CB6PH and CB7PH.
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Although the overall direction of flow in the bottom layer is northward in this region,
the smaller-scale actions of the outgoing tide can pulse bottom waters down-estuary
(Figure IV-22). Oxygen-deficient water intrudes on the bottom and as lenses into
mid-water depths. This effect can be intensified during a strong north-westerly wind
event (see sidebar, "Tides Affected by Moon and Sun" on page 100).
The deep-water designated use, therefore, extends below the sill in these two segments.
Its lower boundary runs along a line more or less parallel to, but south of, the northern
segment line (Figure IV-23). The delineation of the boundary was determined by
examining maps of contemporary dissolved oxygen concentration distributions and the
anecdotal historical dissolved oxygen concentration data record.
Subpycnocline water from the
mainstem trench can move down
bay through the shipping channel.
This movement usually occurs To Tangier
due to the effects of wind and tide. Sill Sound
Shipping
Channel
Pycnocline
As ocean water encounters the sill
that forms the southern terminus of
the mainstem trench, it moves up
and over the sill and into the trench.
Ocean water also moves through
the shipping channel in the sill and
into Tangier Sound.
Figure IV-22. Three-dimensional schematic of the hydrodynamics of the northern portion of segments
CB6PH and CB7PH. View is from the south. Area portrayed is boxed on the inset map.
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Open Water, surface to
bottom
No
Shading
Open Water over Deep
Water
Open Water over Deep
Water over Deep Channel
Figure IV-23. Map showing the dissolved oxygen designated uses of the Chesapeake Bay and its
tidal tributaries.
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100
Tides Affected By Moon and Sun
Tides are controlled by the gravitational pull
of the sun as well as the moon. When the
moon and the sun are aligned, such as during
a full moon or a new moon, tides achieve
their highest highs and lowest lows. This
phenomenon is called a 'spring' tide. When
the pull of the sun and moon are at right
angles, they act to cancel each other out, and
tidal amplitude is at its lowest. This is called a
'neap' tide.
The higher amplitude tide that occurs during
'spring' tide results in increased tidal flow.
This can be beneficial as when this increased
flow advects oxygen rich water into an
estuary. Conversely, it can be detrimental if
the advected water is coming from deeper
waters with low dissolved oxygen.
Sun
Gravitational
Diagram depicts
'spring' tide
alignment of
sun and moon.
Patapsco River
The Patapsco River, segment PATMH, is a highly urban-
ized tidal waterway, home to a large industrial center and
one of the largest shipping ports on the eastern seaboard.
It is heavily and routinely dredged, and a significant
portion of its shoreline has been hardened. Its shipping
channel is directly connected to the Chesapeake Bay
mainstem trench, allowing for the advection of oxygen-
depleted water to its below-pycnocline layer (figures
IV-20 and IV-24). The river has a complex three-layer
flow structure. The middle, pycnocline waters of the
Patapsco River are designated as a deep-water use, and
the below-pycnocline waters are designated as a deep-
channel use.
Chester River
The downriver, mesohaline portion of the Chester River,
segment CHSMIT, contains a trench that ranges in depth
from 20 to 25 meters (see Figure IV-19), The trench is
separated from the mainstem Chesapeake Bay by a sill.
This sill can potentially affect dissolved oxygen levels in
the deep waters of the trench that are chronically low in
the summer months. The pycnocline can form a 'lid' over
the trench, cutting off the exchange with surface waters.
Because of the sill at the mouth of the river, tidal flushing
by bottom waters can be restricted, reducing the replen-
ishment of the bottom waters of the trench as well as the
Figure IV-24. The image on the left shows the bathymetry of the shipping channel
approach to Baltimore Harbor and how it is connected to the 'head' of the Chesapeake
Bay mainstem trench at the bottom of the picture (middle to right side). The image on
the right is of the bathymetry of Baltimore Harbor. To improve visualization, the depth
versus width relationship has been enhanced.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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101
potential mixing force that the inflow might have. It may also be the case that during
extreme (spring) tidal events (see sidebar, "Tides Affected by Moon and Sun," on
previous page) low dissolved oxygen bottom water from the mainstem trench is
advected into the Chester River trench, where it is sequestered under the pycnocline
(Figure IV-25).
When a measurable pycnocline is observed (often due to these 'spill-over events'),
the within-pycnocline waters of the lower Chester River (river mouth up to the sill
at Ringgold Point on Eastern Neck) have a deep-water designated use, and the
below-pycnocline waters have a deep-channel designated use. In the absence of
Western Shore
Eastern Shore
Pycnocline
A Mainstem Trench
Easterly Wind
<
Water is pushed
to the western shore
B
Easterly Wind
<
.... Downward displacement of
Pressure from water that
western pycnocline forces
piles up on western shore
, , subpycnocline water out of
exerts a downward pressure ,
.. trench and into the shallow
on the pycnocline. r ,
waters of the eastern shore
and into the eastern shore
tributaries.
c
Figure IV-25. Panel A shows the
'normal' state of the pycnocline over
the Chesapeake Bay mainstem trench.
In Panel B, a strong easterly wind pushes
water from the eastern shore to the
western shore. As water 'piles up' on
the western shore in Panel C, it exerts a
downward pressure on the pycnocline
there. As the pycnocline is pushed down
on the western shore, a pressure differen-
tial is created between the west and east
shores causing water to be displaced up
and out of the Chesapeake Bay mainstem
trench and into the shallow waters of the
eastern shore and into the eastern shore
tributaries. Strong westerly winds result
in the opposite phenomena, where the
pycnocline tilts in the opposite direction
and subpycnocline water is advected to
the western shore.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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water-column stratification, the open-water designated use will apply throughout the
water column to the bottom sediment-water interface in the lower Chester River.
Eastern Bay
In the Eastern Bay, segment EASMH, a trench extends from the river mouth, where
it connects with the mainstem trench to a point halfway up the Bay (see Figure IV-
19). This connection with the mainstem Chesapeake Bay trench has implications for
dissolved oxygen in the bottom waters of lower Eastern Bay, since the below-
pycnocline waters of this portion of Eastern Bay and the mainstem Chesapeake Bay
trench exchange freely. This region of the mainstem trench has some of the worst
dissolved oxygen conditions in the entire Chesapeake Bay. Because of this, below-
pycnocline waters in lower Eastern Bay are chronically low in dissolved oxygen in
summer. When a measurable pycnocline is observed, the within-pycnocline waters
of Eastern Bay have a deep-water designated use and the below-pycnocline waters
have a deep-channel designated use (see Figure IV-23). In the absence of water-
column stratification, the open-water designated use will apply throughout the water
column to the bottom sediment-water interface in Eastern Bay.
Patuxent River
The trench in the lower Patuxent River, segment PXTMH, contains one of the
deepest points in the Chesapeake Bay just off of Point Patience. The Patuxent River
trench terminates at a sill at the mouth of the river (Figure IV-26). Dissolved oxygen
concentrations become depressed beneath the pycnocline in the summer, but not to
the degree they do in the mainstem Chesapeake Bay trench. These depressed
dissolved oxygen concentrations may be due to pycnocline-disrupting turbulence as
the river flows through the constriction at Point Patience. Below-pycnocline
dissolved oxygen does not become completely replenished, but these waters do natu-
rally reoxygenate enough to maintain levels high enough for a deep-water designated
use (see Figure IV-23). Given the depth of this trench, it is likely that hypoxia is a
natural condition below the pycnocline in the summer.
Potomac River
The lower Potomac River trench, located in segment POTMH, extends from the
mouth of the river up to Ragged Point and averages 15 to 25 meters deep (see Figure
IV-19). A 10- to 15-meter shelf extends from the sides of the trench and connects
with a similar region in the mainstem Chesapeake Bay (Figure IV-27). Although the
Potomac trench is not connected to the mainstem Bay trench there is not a sill across
the mouth of the Potomac. The pycnocline effectively isolates the water volume in
the trench from the surface waters. In addition, given the size of the Potomac River
watershed, a relatively large amount of organic matter could be delivered to the
below-pycnocline waters of the Potomac trench. It is very likely that, due to the size
and depth of this deep-water area coupled with strong water-column stratification,
low dissolved oxygen conditions are a natural feature of the Potomac trench. The
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Figure IV-26. Bathymetry at
the mouth of the Patuxerit River.
To improve visualization, the
depth relative to the width
has been enhanced.
Figure IV-27. Bathymetry at
the mouth of the Potomac River.
To improve visualization, the
depth relative to width has
been enhanced.
pycnocline waters of the lower Potomac River (POTMH) have a deep-water
designated use and the below-pycnocline waters have a deep-channel designated use
(see Figure IV-23).
Rappahannock River
The Rappahannock trench, located in segment RPPMH, extends from the mouth of
the Rappahannock River to Belle Isle (see Figure IV-19). The downriver end of the
trench terminates in a sill that extends across the mouth of the river. Dissolved
oxygen concentrations in the bottom waters of the trench are affected by the forma-
tion of the pycnocline. However, bottom water in the upriver half of the trench is
more affected than the downriver half. This phenomenon may be related to strong
currents flowing in the Rappahannock River along the bottom and over the sill. Chao
and Paluskiewicz (1991) found that lower-layer density currents flowing over a sill
cause downward mixing upriver of the sill (Figure IV-28). If this downward mixing
is occurring in the downriver half of the Rappahannock trench, it would explain why
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Figure IV-28. Diagram of the hydrodynamics of flow over a sill. As lower layer waters
flow over the sill, downwelling surface waters occur.
Source: Chao and Paluszkiewicz 1991.
bottom water dissolved oxygen is less affected by the pycnocline in this region. In
the Virginia rivers, bottom layer, upriver flow in the Rappahannock River is second
only to that of the James River and is greater, on average, than in the Potomac River
(Wang 2003, personal communication). Given this rapid upriver flow beneath the
pycnocline, the below-pycnocline waters of the Rappahannock trench are not
depleted of dissolved oxygen until they reach the head of the trench. Based on a
decadal-scale analysis of dissolved oxygen within the trench, it appears that low
dissolved oxygen in the upriver portion is a chronic condition.
Because of the unique hydrodynamics of the lower Rappahannock River, the deep-
water and deep-channel designated uses are not uniform across this segment. From
the upriver shore of the Corrotoman River to the mouth of the Rappahannock River,
the deep-water designated use extends from the upper pycnocline to the bottom sedi-
ment-water interface. Upriver of this section to Belle Isle, the pycnocline volume has
a deep-water designated use and the below-pycnocline volume a deep-channel desig-
nated use (see Figure IV-23).
York River
The York trench, located principally in segment YRKMH, extends from where the
York River empties into Mobjack Bay up-river to Kings Creek. A 10-15 meter
channel runs from the down-river terminus of the trench, through Mobjack Bay to a
point in the mainstem Bay adjacent to the Chesapeake Bay mouth (see Figure IV-
19). This channel effectively connects the lower York River to ocean water flowing
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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105
into the Chesapeake Bay. This connection apparently is a benefit to bottom water
dissolved oxygen as concentrations below the pycnocline in this region do not get as
low as they do in other below-pycnocline trench areas of the Bay For this reason, the
waters below the upper pycnocline down to the bottom sediment-water interface
from the York River mouth to Timberneck Creek have a deep-water designated use
(see Figure IV-23).
SHALLOW-WATER BAY GRASS DESIGNATED USE BOUNDARIES
Restoration of underwater bay grasses to acreages supporting "the propagation and
growth of balanced, indigenous populations of ecologically, recreationally and
commercially important fish and shellfish inhabiting vegetated shallow-water habi-
tats" is ultimately the best measure of attainment of shallow-water bay grass
designated use. Therefore, delineation of the shallow-water designated use bound-
aries must reflect the desired acreage of underwater bay grass restoration. In
shallow-water habitats out to the 2-meter depth contour, the exact shallow-water
designated use boundaries can:
• Follow a Chesapeake Bay Program segment-specific depth contour;
• Reflect an established segment-specific acreage of underwater bay grasses to
be restored; or
• Match an established segment-specific acreage of shallow-water habitat meet-
ing the water clarity criteria necessary to support achievement of the
underwater bay grasses restoration goal acreage.
The Chesapeake Bay Program segment-specific maximum depth of persistent, abun-
dant underwater bay grasses growth sets the initial boundary for the habitat
necessary for supporting the shallow-water designated use. That same segment-
specific maximum depth was used in combination with the single best year of
underwater bay grass distribution mapped across the available 1930-2000 data
record to set the new restoration goals on a segment-by-segment basis. Finally, the
ratio of the above shallow-water habitat out to the maximum depth of persistent,
abundant plant growth and the corresponding segment-specific underwater bay
grasses restoration acreage are used to calculate an acreage of shallow-water habitat
meeting the water clarity criteria necessary to support achievement of the restoration
goal acreage.
The following sections describe and quantify these three approaches to setting the
shallow-water designated use boundaries, which are consistent with options the EPA
put forth for measuring attainment of the Chesapeake Bay shallow-water underwater
bay grass designated use (U.S. EPA 2003). EPA recommends the states adopt one (or
more) of the three approaches to defining the shallow-water designated use bound-
aries in addition to adoption of numerical water clarity criteria into their water
quality standards. States can adopt shallow-water designated use boundaries
covering higher acreages or greater depths than those provided here during their
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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upcoming water quality standards adoption processes once the expanded river-
specific information has become available to be incorporated. During future state
triennial reviews of their water quality standards, states also may expand their
shallow-water designated use boundaries to reflect resulting levels of restoration of
underwater bay grasses in prior years.
MAXIMUM DEPTH OF PERSISTENT OR ABUNDANT
PLANT GROWTH-BASED BOUNDARIES
The 2-meter depth contour was selected as the maximum depth for the lower vertical
boundary of the shallow-water designated use. This is the maximum depth to which
underwater bay grasses could be restored in many of the tidal tributaries and main-
stem Chesapeake Bay shallow-water habitats. Although historical underwater bay
grass beds in the Chesapeake Bay probably grew to 3 meters or more, the 2-meter
depth was chosen following an extensive evaluation of grass bed distribution over the
past 70 years (1930s-2000) and of light levels anticipated to be required to restore
viable shallow-water habitats out to the 2-meter depth (Batiuk et al. 1992; Dennison
et al. 1993; Moore et al. 1999; Batiuk et al. 2000; Moore et al. 2001; Naylor 2002).
The intertidal zone was selected as the inner boundary for the shallow-water bay
grass designated use because some species can grow in the upper end of the inter-
tidal zone (Batiuk et al. 2000; Koch 2001). Numerous field studies of underwater bay
grass distributions in the Chesapeake Bay and its tidal tributaries have indicated that
what is controlling the minimum depth of their distribution is not wave action or
other factors, but length of exposure to air at low tide (Moore, unpublished data;
Naylor, unpublished data).
Shallow-water habitats also may be offshore flats such as those observed in Tangier
Sound and Poquoson Flats in the lower mainstem Chesapeake Bay. These areas may
have an inner boundary not in the intertidal zone but rather a relatively deep and wide
channel between them and the shore. These areas are included in the delineation of
shallow-water bay grass designated use habitats if they have or have had underwater
bay grasses and met the decision rules described below.
BENEFITS OF DEEPER UNDERWATER BAY GRASS DISTRIBUTION
There are obvious benefits to restoring underwater bay grasses to greater depths
than where they currently exist in the Chesapeake Bay and its tidal tributaries
(Table IV-10). Increasing the depth and, therefore, the areal distribution of the
grasses can greatly increase the habitat and food available to the Chesapeake Bay's
fish, crabs and waterfowl.
It is important to note that underwater bay grass distribution is directly related to the
tidal bathymetry of the basins in which the beds occur. In a shallow bay with a gradual
slope to deeper waters, such as the Chesapeake Bay, even a moderate increase in water
clarity can result in tremendous increases in the areal extent of bay grasses.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-10. Ecological and water quality benefits of deeper underwater bay
grasses distribution in the Chesapeake Bay and its tidal tributaries.
• Ensures growth of underwater bay grasses where previously there may have been none
because wave energy at shallower depths prevented plants from rooting in the bottom
sediments (e.g., the beds that formerly grew on the western side of Kent Island,
Maryland, at depths greater than where the critical wave energy threshold exists);
• Adds habitat below the grazing depth of non-native mute swans and non-migratory
Canada geese (approximately 1 and 0.5 meters, respectively) to increase food
availability for native waterfowl;
• Reduces the likelihood of ice damage to the beds;
• Reduces the negative effects of unusually low tides;
• Minimizes thermal stress (as deeper beds are inherently cooler);
• Stabilizes sediments at greater depths (through the reduction of water velocity
within the underwater bay grass beds);
• Increases overall nutrient uptake and supports increased denitrification;
• Increases summertime oxygen production (which is particularly important in the
headwaters of tidal creeks); and
• Increases habitat for fish, crabs and macroinvertebrates.
HISTORICAL UNDERWATER BAY GRASS DISTRIBUTION
The distribution and, therefore, the depth of historical underwater bay grass beds
were mapped from photographs dating from the late 1930s through the mid-1960s
by scientists at the Maryland Department of Natural Resources and the Virginia
Institute of Marine Science. Historical underwater bay grass distribution data from
Maryland and Virginia were aggregated into a single data set using Arclnfo GIS soft-
ware. The two states' approaches reflect differences in the quality and quantity of
historical aerial photographs available for interpretation. Full documentation of the
methods employed and the detailed results are reported in Moore et al. (1999, 2001)
and Naylor et al. (2002).
To determine historic underwater bay grass acreage, aerial photos of Maryland's
portion of the Bay taken in 1938, 1952, 1957 and 1964 were evaluated to determine
the year in which the most underwater bay grass was visible for each area (Naylor
2002). The photos for the year of greatest abundance in each area were then scanned,
geo-referenced and photo-interpreted to determine the extent of underwater bay
grass beds during these years.
In the Virginia portion of the Chesapeake Bay and its tidal tributaries, historical
underwater bay grass acreage in the James River was mapped using photographs
taken in 1937, 1947, 1948, 1953, 1954, 1958, 1959, 1963, 1968, 1969, 1970 and
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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1973, with the historical coverage defined by the composite of the individual years
(Moore et al. 1999). Historical and recent ground survey results were superimposed
on the maps of historical underwater bay grass distributions to help determine
whether the patterns exhibited in the photographs were actually those of underwater
bay grass beds (Moore et al. 1999).
For the Rappahannock and York rivers and the adjacent smaller western shore rivers,
creeks and embayments, a series of photographs from 1952 to 1956 was chosen to
delineate the maximum coverage of bay grasses in these areas (Moore et al. 2001).
The 1936 and 1937 photographs of these rivers showed less underwater bay grass
coverage compared to the 1950s photographs. The difference appeared to be related
to poorer overall atmospheric and water clarity conditions (Moore et al. 2001).
The interpretation of these historic aerial photographs closely followed current
methods to delineate underwater bay grass beds throughout the Chesapeake Bay and
its tidal tributaries through annual aerial underwater bay grass surveys (e.g., Orth et
al. 2000). In neither state did a single year of photography provide comprehensive
coverage of each state's tidal shorelines.
These state-specific analyses provide a consetvative estimate of past underwater bay
grass distributions prior to the 1970s. The conservative nature of the estimate is due,
in part, because the older photographs were not collected specifically to map under-
water bay grasses, but were gathered to assist in analyzing land use or farming
practices. While atmospheric criteria were usually met, the factors that are important
for delineating and mapping underwater bay grasses (such as tidal stage, water trans-
parency and plant growth stage) often were not met. Underwater bay grasses likely
grew at greater depths between the 1930s and 1960s, according to published and
anecdotal information, than was observed in a number of segments in the historical
photographs. Grasses that grow beyond the 1-meter depth contour become increas-
ingly difficult to map, given the conditions under which the historical photographs
were collected. There were limited numbers of years—often only three to five—for
which historical photographs of a particular shallow-water habitat region were avail-
able for interpretation and mapping between the 1930s and early 1970s. Evidence
suggests that underwater bay grass distributions already had declined by the time
photographs of suitable quality were available for interpretation (Moore et al. 1999).
All of these factors led to conservative estimates of past underwater bay grasses
distributions and depths of bed growth.
UNDERWATER BAY GRASS NO-GROW ZONES
A series of underwater bay grass 'no-grow zones' were originally delineated in 1992
in the Chesapeake Bay Submerged Aquatic Vegetation Habitat Requirements and
Restoration Targets: A Technical Synthesis (Batiuk et al. 1992). Habitats exposed to
high wave energy or that have undergone physical modifications such that they could
not support underwater bay grasses growth were excluded based on an extensive
review of data available at the time. With the mapping of historical underwater bay
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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grass distributions, a composite of available distribution data from the 1930s through
2001 was superimposed on the 1992 bay grass no-grow zones. A number of shore-
line habitats previously considered no-grow zones showed clear evidence of
historical underwater bay grass growth and, therefore, their no-grow zone designa-
tion was dropped. These revised underwater bay grass no-grow zones also include
areas where the no-grow zone applies to a 1- to 2-meter depth contour as well as a
0- to 2-meter depth contour.
The revised underwater bay grass no-grow zones illustrated in Figure IV-29 show
shoreline habitats of 2 meters or less where underwater bay grasses are never
expected to grow due to:
• Extreme physical wave energy, which prevents the plants from rooting in the
bottom sediments (e.g., Calvert Cliffs on Maryland's lower western shore and
Willoughby Split to Cape Henry near the Chesapeake Bay mouth in Virginia);
• Permanent physical alterations to nearshore habitats, including dredging close
to shore accompanied by hardening of the shoreline and installation of perma-
nent structures (i.e., shipping terminals) as observed in the inner Baltimore
Harbor and the Elizabeth River;
• Natural, extreme discoloration of the water from tidal-fresh wetlands (e.g.,
tidal-fresh 'blackwater' rivers on the Eastern Shore); or
• No functional shallow-water habitat due to natural river channeling (e.g., tidal
headwaters of several lower Eastern Shore rivers).
These underwater bay grass no-grow zones reflect the full set of findings on under-
water bay grasses distributions from the historical (select years from the 193Os-early
1970s) and 1978-2001 data records, as well as altered nearshore/shoreline habitats
as described above. The no-grow zones illustrated in Figure IV-29 are based on the
best available information and are subject to future revision based on new research
and information.
If no physical reasons prevent underwater bay grasses from growing in a specific
shallow-water habitat, it should be expected that grasses can grow there, given
appropriate water quality conditions and local sources of propagules (i.e., reproduc-
tive vegetative materials such as seeds and rhizomes). For example, evidence exists
of underwater bay grasses growing within estuarine turbidity maximum zones in the
upper Chesapeake Bay mainstem and selected tidal tributaries (e.g., the Potomac
River), but not in other tidal tributaries. The Regional Criteria provides specific
guidance to the states on how to address estuarine turbidity maximum zones in
applying the Chesapeake Bay water clarity criteria (see Chapter 7 in U.S. EPA
2003). The lack of historical data on the presence of underwater bay grasses in a
particular habitat is not a valid reason to delineate that shallow-water area as an
underwater bay grass no-grow zone.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Bay Grass No Grow Zones
Figure IV-29. Map illustrating the revised underwater bay grass no-grow zones of the
Chesapeake Bay and its tidal tributaries.
Six Chesapeake Bay Program segments were not assigned a shallow-water bay grass
designated use depth boundary (see Table IV-13). The established bay grass no-grow
zones covered the 2-meter and less habitats along the entire tidal shoreline in each
of these segments-upper Choptank River, upper Pocomoke River, Western Branch
Elizabeth River, Southern Branch Elizabeth River, Eastern Branch Elizabeth River
and Lafayette River (see Appendix C).
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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DETERMINING THE MAXIMUM DEPTH OF
PERSISTENT/ABUNDANT PLANT GROWTH
The first step in the process to define the maximum depth of persistent and abundant
underwater bay grass beds by Chesapeake Bay Program segment (Table IV-11,
Figure IV-30) was to establish decision rules. The rules developed take full advan-
tage of the entire record of underwater bay grass distribution and abundance survey
data and reflect the findings published in scientific literature (Table IV-12). Also, the
decision rules help ensure full consistency between the establishment of the shallow-
water bay grass designated use depths (the depth at which the Chesapeake Bay water
clarity criteria will be applied) and the new quantitative underwater bay grasses
acreage restoration goal for Chesapeake Bay and its tidal tributaries.
The available data record included interpreted aerial photography from the 1930s to
the early 1970s as well as the annual baywide aerial survey data from 1978-2000.
From these photos and surveys, the acreage of underwater bay grasses within three
depth intervals was calculated for every Chesapeake Bay Program segment: 0-0.5
meters, >0.5-1 meter and >1-2 meters (Appendix B, Table B-l). Thus, each Chesa-
peake Bay Program segment has three 'segment-depth intervals' (e.g., CB4MH 1-2
meter is a segment-depth interval).
The total surface area within each segment-depth interval minus any delineated
underwater bay grass no-grow zones is an estimate of the area of potential under-
water bay grass habitat in that segment-depth interval. Thus, there is an acreage of
potential underwater bay grass habitat for each of the three segment-depth intervals
in every Chesapeake Bay Program segment except for those segments that are
entirely no-grow zones (Appendix C, Table C-l).
The decision rules described in Table IV-12 are based on the observed single best
year of underwater bay grass coverage for each Chesapeake Bay Program segment
(i.e., not the single best year by segment-depth) (Appendix B, Table B-2). Using
each segment's single best year, the percentage of available habitat at each segment-
depth interval that was occupied by underwater bay grasses in that single best year
was calculated (Appendix B, Table B-3). That percentage is a measure of the rela-
tive importance of each segment-depth interval as bay grass habitat. Upon
application of the decision rules (Table IV-12), a set of Chesapeake Bay Program
segment-specific shallow-water designated use depths was generated (Table IV-13).
Rationale for the 20 Percent and 10 Percent Rules
In setting application depths, it was important to select a percentage of cover high
enough to assure that underwater plants definitely occupied that habitat, but low
enough that the resulting depths realistically represented true light availability
attained during the available historical data record. Underwater bay grass beds in
tidal waters of the Chesapeake Bay display a spatial heterogeneity that is character-
istic of underwater grass beds elsewhere in the world (Lehmann et al.1997; Kuenen
and Debrot 1995; Carpenter and Titus 1984). This heterogeneity exists both in micro
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-11. Chesapeake Bay Program segmentation scheme segments.
Northern Chesapeake Bay CB1TF
Upper Chesapeake Bay CB20H
Upper Central Chesapeake Bay .... CB3MH
Middle Central Chesapeake Bay ... CB4MH
Lower Central Chesapeake Bay .... CB5MH
Western Lower Chesapeake Bay .... CB6PH
Eastern Lower Chesapeake Bay .... CB7PH
Mouth of the Chesapeake Bay CB8PH
Bush River BSHOH
Gunpowder River GUNOH
Middle River MIDOH
Back River BACOH
Patapsco River PATMH
Magothy River MAGMH
Severn River SEVMH
South River SOUMH
Rhode River RHDMH
West River WSTMH
Upper Patuxent River PAXTF
Western Branch Patuxent River .... WBRTF
Middle Patuxent River PAXOH
Lower Patuxent River PAXMH
Upper Potomac River POTTF
Anacostia River ANATF
Piscataway Creek PISTF
Mattawoman Creek MATTF
Middle Potomac River POTOH
Lower Potomac River POTMF1
Upper Rappahannock River RPPTF
Middle Rappahannock River RPPOH
Lower Rappahannock River RPPMF1
Corrotoman River CRRMH
Piankatank River PIAMH
Upper Mattaponi River MPNTF
Lower Mattaponi River MPNOH
Upper Pamunkey River PMKTF
Lower Pamunkey River PMKOH
Middle York River YRKMH
Lower York River YRKPH
Mobjack Bay MOBPH
Upper James River JMSTF
Appomattox River APPTF
Middle James River JMSOH
Chickahominy River CHKOH
Lower James River JMSMH
Mouth of the James River JMSPH
Western Branch Elizabeth River . . . WBEMH
Southern Branch Elizabeth River . . . SBEMH
Eastern Branch Elizabeth River .... EBEMH
Lafayette River LAFMH
Mouth to mid-Elizabeth River ELIPH
Lynnhaven River LYNPH
Northeast River NORTF
C&D Canal C&DOH
Bohemia River BOHOH
Elk River ELKOH
Sassafras River SASOH
Upper Chester River CHSTF
Middle Chester River CHSOH
Lower Chester River CHSMH
Eastern Bay EASMH
Upper Choptank River CHOTF
Middle Choptank River CHOOH
Lower Choptank River CHOMH1
Mouth of the Choptank River .... CHOMH2
Little Choptank River LCHMH
Honga River HNGMH
Fishing Bay FSBMH
Upper Nanticoke River NANTF
Middle Nanticoke River NANOH
Lower Nanticoke River NANMH
Wicomico River WICMH
Manokin River MANMH
Big Annemessex River BIGMH
Upper Pocomoke River POCTF
Middle Pocomoke River POCOH
Lower Pocomoke River POCMH
Tangier Sound TANMH
Source: Chesapeake Bay Program 1999.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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113
NORTF
CB1Tf
BSHOH—|
GUNOH—
MIDOHk
BACOHx
ELKOH
C&DOH
BOHOH
SASOH
ANATF
POTOH
JMSTF,
APPTF
PATM
MAGMH
SEVMH
SOUMH
RHDM
WSTMH
CHSTF
CHSOH
CHSMH
CB3M
EASMH
CHOTF
CHOMH1
CHOOH
CHOMH2
PAXTF
WBRTF
POTTF
PISTF
PAXOH
NANTF
NANOH
NANMH
MATTF
LCHMH
HNGMH
FSBMH
PAXMH
WICMH
MANMH
-BIGMH
POTMH
RPPTF
CB5MH
$
RPPOH
RPPMH
MPNTF
CRRMH
PMKTF
MPNOH
PiAMH
TANMH
CB6PH
PMKOH
CHKOH
YRKM
JMSOH
JMSMH
JMSPH
POCTF
POCOH
POCMH
CB7PH
MOBPH
CB8PH
LYNPH
ELIPH -1
WBEMH —'
—LAFMH
¦- EBEMH
SBEMH
Figure IV-30. The geographical location of the 78 Chesapeake Bay Program segments.
Source: Chesapeake Bay Program 1999.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-12. Methodology used in determining the shallow-water bay grass
designated use depths by Chesapeake Bay Program segment, which led to the
establishment of the 185,000 Chesapeake Bay baywide underwater grasses
restoration goal.
The baywide underwater bay grass goal acreage was established based on the single best
year acreage out to a shallow-water bay grass designated use depth determined as follows:
1. Bathymetry data and aerial photographs were used to divide the mapped single best year
underwater bay grasses acreage in each Chesapeake Bay Program segment into three
depth zones: 0-0.5 meters, > 0.5-1 meters and >1-2 meters. The delineated underwater
bay grass no-grow zones were then removed from consideration as shallow-water bay
grass designated use habitat.
2. The aerial photographs were used to determine the depth to which the mapped under-
water bay grass beds grew in each Chesapeake Bay Program segment with either a
minimum abundance or minimum persistence. The underwater bay grass goal for a
Chesapeake Bay Program segment is the portion of the single best year acreage mapped
out to the higher depth in the determined depth range. The decision rules for this process
were as follows:
In all segments, the 0-0.5 meter depth interval was designated for shallow-water
bay grass use. In addition, the shallow-water bay grass use was designated for
deeper depths within a Chesapeake Bay Program segment if either:
A) The single best year of underwater bay grasses distribution covered at least
20 percent of the potential habitat in a deeper depth interval; or,
B ) The single best year of underwater bay grass distribution covered at least
10 percent of the potential habitat in the segment-depth interval, and at least
3 of the 4 five-year periods of the more recent record (1978-2000) showed
at least 10 percent underwater bay grasses coverage of potential habitat
in the segment-depth interval.
3. The single best year underwater bay grasses distribution acreage of all Chesapeake Bay
Program segments were clipped at the deeper depth of the segment-depth interval deter-
mined above. The resulting underwater bay grass acreage for each segment were added,
resulting in the total baywide underwater bay grass acreage goal of 185,000 acres.
and macro scales, and as viewed by aerial photography results in a spatial distribu-
tion that is virtually never 100 percent coverage of available shallow-water habitat at
any depth. This growth pattern was true historically as well. Manning (1957) esti-
mated that lower Patuxent River underwater bay grass beds covered only about
one-third of shoal waters. Photography from Maryland from 1938 and 1952 revealed
an average percent cover of 35 percent (Naylor 2002) at depths of less than 1 meter.
Virginia photographic analysis revealed up to 48 percent coverage in the York and
Rappahannock rivers at the less than 1-meter depth (Moore et al. 2001). These find-
ings were supported by similar findings from analysis of the more recent 1978-2000
Chesapeake Bay underwater bay grass aerial survey distribution data.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-13.The single best year and maximum depth interval for applying the water clarity criteria
used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay
grass designated use boundary depths.
Maximum Depth Interval Recommended
Application of the Shallow-Water
Water Clarity Criteria (meters) Designated
Chesapeake Bay Program
(CBP) Segment Name
CBP
Segment
Single
Best Year
0-0.5 0.5-1 1-2
Use Depth
(meters)
Northern Chesapeake Bay
CB1TF
Historical
~
2
Upper Chesapeake Bay
CB20H
Historical
©
0.5
Upper Central Chesapeake Bay
CB3MH
1978
~
0.5
Middle Central Chesapeake Bay
CB4MH
Historical
~
2
Lower Central Chesapeake Bay
CB5MH
Historical
~
2
Western Lower Chesapeake Bay
CB6PH
Historical
~
1
Eastern Lower Chesapeake Bay
CB7PH
Historical
~
2
Mouth of the Chesapeake Bay
CB8PH
1996
©
0.5
Bush River
BSHOH
Historical
©
0.5
Gunpowder River
GUNOH
2000
~
2
Middle River
MIDOH
Historical
~
2
Back River
BACOH
*
©
0.5
Patapsco River
PATMH
Historical
~
1
Magothy River
MAGMH
Historical
~
1
Severn River
SEVMH
1999
~
1
South River
SOUMH
Historical
~
1
Rhode River
RHDMH
Historical
©
0.5
West River
WSTMH
Historical
~
0.5
Upper Patuxent River
PAXTF
1996
~
0.5
Western Branch (Patuxent River)
WBRTF
*
©
0.5
Middle Patuxent River
PAXOH
2000
©
0.5
Lower Patuxent River
PAXMH
Historical
~
1
Upper Potomac River
POTTF
1991
¦>
2
Anacostia River
ANATF
1991
©
0.5
Piscataway Creek
PISTF
1987
~
2
Mattawoman Creek
MATTF
2000
~
1
Middle Potomac River
POTOH
1998
¦>
2
continued
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Table IV-13. The single best year and maximum depth interval for applying the water clarity criteria
used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay
grass designated use boundary depths (cortt.).
Chesapeake Bay Program CBP Single
(CBP) Segment Name Segment Best Year
Maximum Depth Interval Recommended
Application of the Shallow-Water
Water Clarity Criteria (meters) Designated
Use Depth
0-0.5 0.5-1 1-2 (meters)
Lower Potomac River
POTMH
Historical
1
Upper Rappahannock River
RPPTF
2000
©
0.5
Middle Rappahannock River RPPOH
©
0.5
Lower Rappahannock River
RPPMH
Historical
Corrotoman River
CRRMH
Historical
Piankatank River
PIAMH
Historical
Upper Mattaponi River
MPNTF
1998
©
0.5
Lower Mattaponi River
MPNOH
©
0.5
Upper Pamunkey River
PMKTF
1998
©
0.5
Lower Pamunkey River
PMKOH
©
0.5
Middle York River
YRKMH
Historical
©
0.5
Lower York River
YRKPH
Historical
Mobjack Bay
MOBPH
Historical
Upper James River
JMSTF
Historical
©
0.5
Appomattox River
APPTF
Historical
0.5
Middle James River
JMSOH
1998
©
0.5
Chickahominy River
CHKOH
2000
©
0.5
Lower James River
JMSMH
Historical
©
0.5
Mouth of the James River
JMSPH
Historical
Western Branch Elizabeth River
WBEMH
*
~ ~
*
Southern Branch Elizabeth River
SBEMH
*
~ ~
*
Eastern Branch Elizabeth River
EBEMH
*
~ ~
*
Lafayette River
LAFMH
*
~ ~
*
Mouth to mid-Elizabeth River
ELIPH
*
©
0.5
Lynnhaven River
LYNPH
1986
©
0.5
Northeast River
NORTF
Historical
©
0.5
C&D Canal
C&DOH
1978
©
0.5
continued
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Table IV-13. The single best year and maximum depth interval for applying the water clarity criteria
used in determining the Chesapeake Bay Program segment-specific shallow-water underwater bay
grass designated use boundary depths (cortt.).
Chesapeake Bay Program CBP Single
(CBP) Segment Name Segment Best Year
Maximum Depth Interval Recommended
Application of the Shallow-Water
Water Clarity Criteria (meters) Designated
Use Depth
0-0.5 0.5-1 1-2 (meters)
Bohemia River BOHOH 2000 © 0.5
Elk River
ELKOH
2000
~
2
Sassafras River
SASOH
2000
~
1
Upper Chester River
CHSTF
*
©
0.5
Middle Chester River
CHSOH
Historical
©
0.5
Lower Chester River
CHSMH
Historical
~
1
Eastern Bay
EASMH
Historical
~
2
Upper Choptank River
CHOTF
*
~
~
~
*
Middle Choptank River
CHOOH
Historical
©
0.5
Lower Choptank River
CHOMH2
Historical
~
1
Mouth of the Choptank River
CHOMHl
Historical
~
2
Little Choptank River
LCHMH
Historical
~
2
Honga River HNGMH Historical ~ 2
Fishing Bay FSBMH Historical © 0.5
Upper Nanticoke River
NANTF
*
©
0.5
Middle Nanticoke River
NANOH
Historical
©
0.5
Lower Nanticoke River
NANMH
Historical
©
0.5
Wicomico River
WICMH
Historical
©
0.5
Manokin River
MANMH
Historical
~
2
Big Annemessex River
BIGMH
Historical
~
2
Upper Pocomoke River
POCTF
*
~
~
~
*
Middle Pocomoke River
POCOH
*
©
0.5
Lower Pocomoke River
POCMH
Historical
~
1
Tangier Sound
TANMH
Historical
~
2
© Decision rules not met - default depth interval of 0-0.5 meters applies.
~ Single best year percent of total potential habitat is 20 percent.
Percent of total potential habitat is 10-19.9% and underwater bay grasses are persistent (1978-2000).
~ Chesapeake Bay Program segment completely within the underwater bay grass no-grow zone.
*Denotes no data available or no underwater bay grasses mapped (1930s-2000).
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Several possible reasons account for less-than-complete habitat occupation. These
include small-scale sediment type differences, small-scale sediment movement
patterns, sediment slope, fetch, uneven seed distribution and localized disturbance. In
addition to these reasons for real variations in plant presence, only the most dense
areas of underwater bay grasses are visible using high-altitude photography. Very
sparse beds reveal no signature in the water and are never delineated through photo
interpretation. Each year, Chesapeake Bay researchers and resource managers find
dozens of underwater bay grass beds in places not identified in the annual aerial
survey due to these limitations. Thus, reporting of percent coverage is generally lower
than the total amount of habitat actually occupied by sparse plant beds, which further
lowers the total percent coverage. Given the starting point of 1 percent, and the typical
maximum of 35-48 percent from the historical photography, 20 percent was seen as a
defensible midpoint figure reflective of sufficient coverage to define maximum depth
of the underwater bay grasses growth (Moore 1999, 2001; Naylor 2002).
In order to provide an additional measure of the importance of a segment-depth
interval as underwater bay grass habitat, the record of underwater bay grass aerial
survey data from 1978-2000 (there is not a survey for every year between 1979-1983
and in 1988) was segmented into four five-year intervals (Appendix B, Table B-4).
The persistence of underwater bay grasses in each segment-depth interval was then
assessed by counting the number of five-year intervals in which at least 10 percent
of potential habitat was occupied by underwater bay grasses (see Table IV-12).
UNDERWATER BAY GRASS RESTORATION
GOAL-BASED BOUNDARIES
The Chesapeake 2000 agreement committed to revising the existing underwater bay
grass restoration goals and strategies:
... to reflect historic abundance, measured as acreage and density from the
1930s to present. The revised goals will include specific levels of water clarity'
which are to be met in 2010. Strategies to achieve these goals will address
water clarity, water quality and bottom disturbance.
The eligible segments and depths included in calculating the new underwater bay
grass restoration goal were limited to segment-depth intervals designated for
shallow-water bay grass use. The new restoration goal was derived from the total
single best year acreage summed over all the segment depths that were designated
for shallow-water bay grass use after considering a wide array of data and informa-
tion (Figure IV-31).
Data Used to Establish the Restoration Goal
It was essential to use historical underwater bay grass data in determining the under-
water bay grass acreage goal for the Chesapeake Bay. But using these data presented
obvious limitations. They were originally collected for agricultural landuse mapping
purposes and thus did not include all areas of tidal shallow-water habitats, which
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
-------
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chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
-------
120
resulted in an underestimate of the mapped acreage. Historic data also were limited
by the fact that pre-Hurricane Agnes (June 1972) underwater bay grass data exist
only for a limited number of years in each Chesapeake Bay Program segment. Thus,
using only historical data to determine a new goal would likely underestimate the
potential for underwater bay grass recovery.
Rationale for Use of the Single Best Year
The single best year of underwater bay grass growth observed in each Chesapeake
Bay Program segment from the entire available record of aerial photographs
(1930s-2000) is the best available data on underwater bay grass occurrence over the
long-term. Of the 62 Chesapeake Bay Program segments with mapped underwater
bay grasses, 68 percent of the segment single best year acreages occurred in the 1930s
to early 1970s time period; 3 percent occurred in 1978; 5 percent occurred between
1986 and 1991; and 24 percent occurred between 1996 and 2000 (see Table IV-13).
There were several obvious benefits in using the single best year approach to setting
the new restoration goal. The single best year acreage is the most solid available data
on underwater bay grass acreage over the multi-decade data record. Even in suitable
water quality conditions, underwater bay grass beds often move around within a
segment. By combining acreage over a number of years into a composite acreage it
would be possible to overestimate the likely future abundance of underwater bay
grasses in any single year.
Using the single best year as the basis for the new restoration goal ensures consistency
with the method for determining the segment-specific shallow-water designated use
depths and the resulting water clarity criteria application depths. The consistency
between methods links the segment-specific water clarity application depths, shallow-
water designated use boundaries and underwater bay grass restoration goals. This
method is scientifically valid because when the acreage goals for segments in the
same salinity range are totaled (see "Shallow-Water Habitat Area to Support Restora-
tion," below), the percentage of available habitat covered by the restoration goal
acreage is consistent with the average rate of habitat occupancy described in the
scientific literature as reflecting healthy underwater bay grass growth.
The new underwater bay grass goal focuses the restoration effort on areas that demon-
strated a minimal level of abundance or persistence in the past and which are likely to
respond to water clarity improvements in the future. Focusing on the single best year
versus a composite underwater bay grass coverage ensures that vegetated portions of
potential underwater bay grass habitats are not over-accounted-for based on underwater
bay grass beds that may have 'migrated' year-to-year over the past seven decades.
New Underwater Bay Grass Restoration Goal
Table IV-14 lists the Chesapeake Bay Program segment-specific single best year
acreage within the shallow-water bay grasses designated use depths that, added
together, make up the baywide 185,000 acre restoration goal.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
-------
121
Table IV-14. Chesapeake Bay underwater bay grass restoration goals by
Chesapeake Bay Program segment.
Segment Name
Segment
Single Best Year
Acres
Northern Chesapeake Bay
CB1TF
Historical
12,908
Upper Chesapeake Bay
CB20H
Historical
302
Upper Central Chesapeake Bay
CB3MH
1978
943
Middle Central Chesapeake Bay
CB4MH
Historical
2,511
Lower Central Chesapeake Bay
CB5MH
Historical
14,961
Western Lower Chesapeake Bay
CB6PH
Historical
980
Eastern Lower Chesapeake Bay
CB7PH
Historical
14,620
Mouth of the Chesapeake Bay
CB8PH
1996
6
Bush River
BSHOH
Historical
158
Gunpowder River
GUNOH
2000
2,254
Middle River
MIDOH
Historical
838
Back River
BACOH
*
0
Patapsco River
PATMH
Historical
298
Magothy River
MAGMH
Historical
545
Severn River
SEVMH
1999
329
South River
SOUMH
Historical
459
Rhode River
RHDMH
Historical
48
West River
WSTMH
Historical
214
Upper Patuxent River
PAXTF
1996
5
Western Branch (Patuxent River)
WBRTF
*
0
Middle Patuxent River
PAXOH
2000
68
Lower Patuxent River
PAXMH
Historical
1,325
Upper Potomac River
POTTF
1991
4,368
Anacostia River
ANATF
1991
6
Piscataway Creek
PISTF
1987
783
Mattawoman Creek
MATTF
2000
276
Middle Potomac River
POTOH
1998
3,721
Lower Potomac River
POTMH
Historical
10,173
Upper Rappahannock River
RPPTF
2000
20
Middle Rappahannock River
RPPOH
*
0
Lower Rappahannock River
RPPMH
Historical
5,380
Corrotoman River
CRRMH
Historical
516
Piankatank River
PIAMH
Historical
3,256
Upper Mattaponi River
MPNTF
1998
75
Lower Mattaponi River
MPNOH
*
0
Upper Pamunkey River
PMKTF
1998
155
Lower Pamunkey River
PMKOH
*
0
Middle York River
YRKMH
Historical
176
Lower York River
YRKPH
Historical
2,272
Mobjack Bay
MOBPH
Historical
15,096
continued
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
-------
122
Table IV-14. Chesapeake Bay underwater bay grass restoration goals by
Chesapeake Bay Program segment (cont.).
Segment Name
Segment
Single Best Year
Acres
Upper James River
JMSTF
Historical
1,600
Appomattox River
APPTF
Historical
319
Middle James River
JMSOH
1998
7
Chickahominy River
CHKOH
2000
348
Lower James River
JMSMH
Historical
531
Mouth of the James River
JMSPH
Historical
604
Western Branch Elizabeth River
WBEMH
*
0
Southern Branch Elizabeth River
SBEMH
*
0
Eastern Branch Elizabeth River
EBEMH
*
0
Lafayette River
LAFMH
*
0
Mouth to mid-Elizabeth River
ELIPH
*
0
Lynnhaven River
LYNPH
1986
69
Northeast River
NORTF
Historical
88
C&D Canal
C&DOH
1978
0
Bohemia River
BOHOH
2000
97
Elk River
ELKOH
2000
1,648
Sassafras River
SASOH
2000
764
Upper Chester River
CHSTF
*
0
Middle Chester River
CHSOH
Historical
63
Lower Chester River
CHSMH
Historical
2,724
Eastern Bay
EASMH
Historical
6,108
Upper Choptank River
CHOTF
*
0
Middle Choptank River
CHOOH
Historical
63
Lower Choptank River
CHOMH2
Historical
1,499
Mouth of the Choptank River
CHOMH1
Historical
8,044
Little Choptank River
LCHMH
Historical
3,950
Honga River
HNGMH
Historical
7,686
Fishing Bay
FSBMH
Historical
193
Upper Nanticoke River
NANTF
*
0
Middle Nanticoke River
NANOH
Historical
3
Lower Nanticoke River
NANMH
Historical
3
Wicomico River
WICMH
Historical
3
Manokin River
MANMH
Historical
4,359
Big Annemessex River
BIGMH
Historical
2,014
Upper Pocomoke River
POCTF
*
0
Middle Pocomoke River
POCOH
*
0
Lower Pocomoke River
POCMH
Historical
4,092
Tangier Sound
TANMH
Historical
37,965
Total acres
184,889
*No underwater grasses recorded for
any year within the available 1930s-2000 data record.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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123
SHALLOW-WATER HABITAT AREA TO SUPPORT RESTORATION
GOAL-BASED BOUNDARIES
As described previously, the restoration of underwater bay grasses within a segment
requires that shallow-water habitat meet the Chesapeake Bay water clarity criteria
over a greater acreage than the underwater bay grasses will actually cover. The ratio
of underwater bay grass acreage to the required shallow-water habitat acreage varies
based on the different species of underwater bay grasses that inhabit the Bay's four
salinity regimes. Shallow-water habitat acreage ratios have been derived scientifi-
cally through evaluation of extensive underwater bay grasses distribution data within
tidal fresh, low, medium and high salinity regimes (reflecting different levels of
coverage by different underwater bay grass communities).
The Chesapeake Bay Program segment-specific restoration goal acreage and
corresponding shallow-water designated use acreage (to the previously determined
maximum depth of abundant and persistent underwater plant growth) listed in
Table IV-15 were summed by major salinity regime-tidal fresh (0-0.5 ppt), oligoha-
line (> 0.5-5 ppt), mesohaline (> 5ppt-18 ppt) and polyhaline (>18 ppt).13 The
underwater bay grasses acreage to shallow-water habitat acreage ratios were then
expressed as a percentage of the total shallow-water designated use habitat.
Compared with a baywide value of 38 percent, the tidal-fresh (37 percent), mesoha-
line (39 percent) and polyhaline (41 percent) values were all very close to the
baywide value as well as the other salinity regime-specific values (Table IV-16).
These values are consistent with findings published in the scientific literature and the
35 to 48 percent range derived from evaluation of the 1930s through early 1970s
historical data record by Naylor (2002) and Moore (1999, 2001). Influenced by the
natural presence of the estuarine turbidity maximum, the value was 21 percent in
oligohaline habitats.
CONFIRMING THAT THE REFINED DESIGNATED USES
MEET EXISTING USES
The EPA Water Quality Standards regulations at 40 CFR 131.10(g) and (j) specify
that states may remove a designated use that is not an existing use, or establish
subcategories of a use, if they can demonstrate that attaining the designated use is
not feasible. The current regulation at 40 CFR Part 131 identifies the factors that
must be considered in making such a demonstration. As the regulation explains,
existing uses, by definition, are attainable and must be protected by designated uses
in water quality standards (40 CFR 131.10[g], 131.10[h][ 1 ] and 131.10[i]). Any
13Note that all Chesapeake Bay Program segments have been assigned to one of the four salinity regimes
based on an evaluation of almost two decades of salinity data. The segment-naming convention docu-
ments each individual segment's long-term averaged respective salinty regime: TF = tidal fresh, OH =
oligohaline, MH = mesohaline, and PH = polyhaline.
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
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Table IV-16. Percent of shallow-water designated use habitat covered by single
best year underwater bay grass acreage by salinity regime.
Tidal-Fresh Oligohaline Mesohaline Polyhaline
Median 37.2 20.5 39.2 41.3
Minimum 0 0 0.2 1.5
Maximum 85.7 33.8 54.3 45.9
No. of Segments 14 20 29 7
change in designated uses must show that the existing uses are still being protected.
As the EPA 1983 Water Quality Standards Handbook describes, an existing use can
be defined as fishing, swimming or other uses that have actually occurred since
November 28, 1975; or the water quality that is suitable to allow the use to be
attained—unless there are physical factors, such as substrate or flow, that prevent the
use from being attained (U.S. EPA 1983). Section 131.12(a)(1) in turn requires state
anti-degradation policies to protect existing water quality. This paragraph applies a
minimum level of protection to all waters. In setting the five subcategories of current
tidal-water designated uses, explicit steps were taken in developing the refined uses
and their boundaries to ensure that existing aquatic life uses would continue to be
protected.
MIGRATORY SPAWNING AND NURSERY EXISTING USE
The migratory fish spawning and nursery designated use will be protected by a set
of Chesapeake Bay-specific dissolved oxygen criteria that are more protective—
6 mg/1 7-day mean and 5 mg/1 instantaneous minimum-than current state water
quality standards that apply to these same habitats from February 1 through May 31
(U.S. EPA 2003). Existing uses within the migratory fish spawning and nursery
habitats will continue to be protected.
SHALLOW-WATER EXISTING USE
In delineating the shallow-water use, the single best year of underwater bay grass
distribution mapped since the 1930s was used to define a shallow-water designated
use depth, underwater bay grass restoration goal and a corresponding shallow-water
habitat acreage to support achievement of the restoration goal for each respective
Chesapeake Bay Program segment. Most of the segment-specific restoration goal
acreage is higher than the established existing use underwater bay grass acreage
derived from the single best year of the 1978-2001 data record out to the maximum
depth of abundant/persistent underwater plant growth (see Table IV-15). In those
cases where the existing use acreage is higher than the restoration goal, the existing
use acreage will drive the shallow-water designated use boundary. As most of the
chapter iv • Refined Designated Uses for the Chesapeake Bay and Tidal Tributaries
-------
129
single best years were based on historical underwater bay grass distributions (1930s
through the early 1970s), the shallow-water bay grass uses existing since 1975 will
continue to be protected.
OPEN-WATER EXISTING USE
The application of the open-water fish and shellfish designated use dissolved oxygen
criteria will provide an equal level of protection to the same tidal waters as current
state water quality standards. The combined set of 5 mg/1 30-day mean, 4 mg/1 7-day
mean, and 3 mg/1 instantaneous minimum have been documented to protect all life
stages of open-water habitat species in the Chesapeake Bay and its tidal waters (U.S.
EPA 2003). Existing uses within the open-water habitats will continue to be protected.
DEEP-WATER AND DEEP-CHANNEL EXISTING USES
The application of the deep-water seasonal fish and shellfish designated use and the
deep-channel seasonal refuge designated use and their respective oxygen criteria will
result in improvements to existing water quality conditions that currently do not
attain the applicable criteria (see Chapter V). Given that trends in dissolved oxygen
conditions have been generally degrading since the early 1970s (see Chapter III;
Hagy 2002), improvements to these conditions will ensure that existing uses within
the deep-water and deep-channel habitats will continue to be protected.
LITERATURE CITED
Alldredge, A. L., T. J. Cowles, S. Maclntyre, J. E.B. Rines, P. L. Donaghay, C. F. Greenlaw,
D. V. Holliday, M. M. Dekshenieks, J. M. Sullivan, J. Ronald, V. Zaneveld. 2002. "Occur-
rence and mechanisms of formation of a dramatic thin layer of marine snow in a shallow
Pacific fjord." Mar. Ecol. Prog. Ser. In Press.
Austin, H.M., A.D. Estes and D.M. Seaver. 2000. Estimation of juvenile striped bass: rela-
tive abundance in the Virginia portion of Chesapeake Bay. Annual Report 1999. Virginia
Institute of Marine Science, Gloucester Point, Virginia.
Batiuk, R.A., P. Bergstrom, M. Kemp, E. Koch, L. Murray, J.C. Stevenson, R. Bartleson, V.
Carter, N.B. Rybicki, J.M. Landwehr, C. Gallegos, L. Karrh, M. Naylor, D. Wilcox, K.A.
Moore, S. Ailstock and M. Teichberg. 2000. Chesapeake Bay submerged aquatic vegetation
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chapter\/
Technological Attainability
of the Refined Recommended
Tidal-Water Designated Uses
BACKGROUND
Chapter IV presented the rationale for delineating the refined tidal-water designated
uses and their boundaries on the basis of physical conditions, bathymetric features
and insights into natural conditions versus anthropogenic influences through the
analysis of Chesapeake Bay water quality monitoring data. The next step is to deter-
mine whether the water quality criteria protecting each of these designated uses can
be achieved throughout each use's proposed boundaries strictly on the basis of tech-
nological implementation of nutrient and sediment controls, or on the basis of the
historical presence of underwater bay grasses.
*
A use attainability analysis (UAA) is not required to justify refined designated uses,
particularly in areas where they will be more stringent than they are at present.
However, the Chesapeake Bay watershed partners agreed that it was as important to
document the future attainability of the refined tidal-water designated uses as it was
to show why current designated uses could not be achieved in some tidal habitats.
For dissolved oxygen, the criteria that apply throughout the designated use bound-
aries were compared to model-simulated dissolved oxygen concentrations under a
range of technological scenarios. These scenarios, or tiers, estimate the nutrient and
sediment reductions resulting from the implementation of various best management
practices (BMPs) and control technologies. The tier scenarios were run through the
Chesapeake Bay Program's Phase 4,3 Watershed Model, and the resulting nitrogen,
phosphorus and sediment loads delivered to tidal waters were entered into the Chesa-
peake Bay Water Quality Model. The water quality model-simulated ambient
dissolved oxygen concentrations were assessed, based on comparisons with the
applicable criteria in each refined designated use. Finally, water quality responses
resulting from the load reductions represented by each tier were arrayed and
compared. A series of 'attainability tables* illustrates these comparisons and indi-
cates where the dissolved oxygen criteria, per each refined designated use, were and
were not attained in the Chesapeake Bay and its major tidal tributaries.
The Chesapeake Bay Program partners performed these attainability analyses with
respect to the monthly dissolved oxygen criteria proposed for each designated use.
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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Sufficient data providing the basis for the other averaging periods (e.g., weekly, daily
or instantaneous minimum) do not currently exist.
For the shallow-water designated use, the Chesapeake Bay Program partners
assessed attainability by evaluating past and present abundance and distribution of
underwater bay grasses. While water clarity is the water quality criteria applicable to
protecting this designated use, implementation of these criteria will be coupled with
regional and local scale underwater bay grass acreage data for attainment assess-
ment. Rather than assessing attainability based on water clarity, it is appropriate to
base attainability relative to the resource requiring restoration. The Chesapeake Bay
Program partners determined that the historic and recent records showing the
unequivocal presence of underwater bay grasses to be sufficient documentation to
justify the attainability of their presence in the future.
The Technical Support Document does not address attainability for chlorophyll a
because this criteria is expressed in narrative terms and does not include numeric
values at the baywide scale around which to perform attainability analyses (U.S.
EPA 2003). As the four jurisdictions with Chesapeake Bay tidal waters derive
specific numerical values for chlorophyll a criteria for application to local tidal
waters where algal-related impairments are expected to persist after the dissolved
oxygen and water clarity criteria have been attained, it will be up to those jurisdic-
tions to assess attainability based on those concentrations.
DEFINING AND DETERMINING TECHNOLOGICAL
ATTAINABILITY FOR DISSOLVED OXYGEN
The nutrient and sediment reduction tier scenarios are described in terms of their
respective BMP and control technologies and the resulting load reductions. The
water quality response realized by the theoretical implementation of each tier is esti-
mated and an assessment is made of whether this response is sufficient to attain the
dissolved oxygen criteria applicable to each of the refined designated uses.
DEVELOPMENT OF LEVEL-OF-EFFORT SCENARIOS
The Chesapeake Bay Program partners developed a series of level-of-effort scenarios
to represent the potential for reducing nutrient and sediment loads from the Chesa-
peake Bay watershed in terms of the types, extent of implementation and performance
of BMPs, wastewater treatment technologies and storm water controls. These
scenarios range from Tier 1, which represents the current level of implementation
throughout the watershed plus existing regulatory requirements implemented through
the year 2010, up to a limit of existing technologies scenario referred to as 'every-
thing, everywhere by everybody', or the E3 scenario, which is acknowledged by Bay
Program partners not to be physically possible. Two intermediate levels of im-
plementation also were developed, Tier 2 and Tier 3. Each tier has associated with it
a given nitrogen, phosphorus and sediment load reduction resulting from model-
simulated implementation of the different technologies assigned to the tier.
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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As the introduction to the Technical Support Document stresses, these tiers are arti-
ficial constructs of technological levels of effort and do not represent actual
programs that the Chesapeake Bay watershed jurisdictions will eventually imple-
ment to meet the wqter quality standards. Rather, the tiers were developed as an
assessment tool to determine potential load reductions achievable by various levels
of technological effort yielding different tidal-water quality responses-
Water quality responses yielding attainment of the Chesapeake Bay criteria were
simulated by the Chesapeake Bay Water Quality Model under the nutrient and sedi-
ment reductions represented by the E3 scenario and, to a great extent, by Tier 3. The
technologies and their performance capabilities are known to be available; however,
the technological and physical feasibility of their implementation has not been
proven. Additionally, the tiers were constructed on a basinwide scale, distinct from
local circumstances. The partners agree that the E3-level nutrient and sediment
reductions are not physically plausible and that the load reductions represented by
Tier 3 are technologically achievable. However, the mix of technologies employed
to achieve the load reductions at Tier 3 will be up to the jurisdictions as they consider
local situations, capabilities and the cost-effectiveness of reduction practices within
their specific tributary basins.
The Chesapeake Bay Program partners developed the tiers primarily on the basis of
the amount of nutrient (nitrogen and phosphorus) reductions afforded by the various
practices and technologies described in each. Upland sediment load reductions were
estimated as resulting from implementation of BMPs directed toward reducing
nutrient loads. Other sediment reduction practices are available, and may, if imple-
mented along with nutrient reduction efforts, afford additional water quality
improvements. The primary benefit from sediment load reductions is increased light
for the restoration of underwater bay grasses (see "Measures to Attain the Shallow-
Water Designated Use," below).
The Chesapeake Bay Program Nutrient Subcommittee's 'source' workgroups
defined the tiered scenarios. Representatives of the Chesapeake Bay watershed
jurisdictions and Chesapeake Bay Program office personnel comprise these work-
groups. The workgroups that decided BMP and technology implementation levels
included the Agricultural Nutrient Reduction Workgroup, the Forestry Workgroup,
the Point Source Workgroup and the Urban Storm Water Workgroup. The Tributary
Strategy Workgroup and Nutrient Subcommittee finalized the E3 scenario defini-
tions after review and further deliberation. The tiers were developed for the
following source categories:
• Point sources;
• Onsite treatment systems;
• Nonpoint source agriculture;
• Nonpoint source urban; and
• Nonpoint source forests.
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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The following sections summarize the technologies that will enable progressively
higher levels of reductions by tier according to the source categories listed above.
Appendix A describes the development of these tiers and the technologies represented
by each, along with Chesapeake Bay Watershed Model-simulated nitrogen, phos-
phorus and sediment load reductions resulting from the implementation of the tiers.
POINT SOURCES
A multistakeholder Nutrient Removal Technology (NRT) Cost Task Force,
consisting of federal, state and local governments as well as municipal authority
representatives and consultants, was formed as a temporary extension of the Chesa-
peake Bay Program's Nutrient Subcommittee Point Source Workgroup. The task
force defined logical tiers (or different nutrient reduction levels) for point sources
(U.S. EPA 2002). Using flows estimated or projected for the year 2010, the tiers
range from the current year 2000 treatment levels to the levels of existing control
technologies.
The point sources analyzed in this effort include facilities located in the Chesapeake
Bay watershed (including Pennsylvania, Maryland, Virginia, Delaware, West
Virginia, New York and the District of Columbia), which the watershed jurisdictions
have determined discharge significant amounts of nitrogen and phosphorus
(Table V-l), These point sources were divided into several categories for the purpose
of this UAA.
* Significant municipal facilities, usually municipal wastewater treatment plants,
that discharge flows of equal to or greater than 0.5 million gallons per day
(MGD);
• Significant industrial facilities that discharge equivalent to or greater quantities
of nutrients than that discharged by a municipal wastewater treatment plant
(0.5 MGD);
* Nonsignificant municipal facilities with discharge flows smaller than 0.5
MGD, limited to facilities in Maryland and Virginia due to the availability of
data; and
• Combined Sewer Overflows (CSOs), which, for this assessment, include the
CSO for the District of Colombia (the only CSO for which the Chesapeake Bay
Program has nutrient load data).
For municipal facilities, the technologies for each tier varied depending on the tiers'
nutrient reduction levels. For Tier 2, technologies to achieve 8 mg/1 total nitrogen
include extended aeration processes and denitrification zones, along with chemical
addition to achieve a total phosphorus discharge of 1.0 mg/1 where facilities are not
already achieving these levels. For Tier 3, technologies to achieve 5.0 mg/1 total
nitrogen include additional aeration, a secondary anoxic zone plus methanol
addition, additional clarification tankage and additional chemical to achieve a
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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Table V-1. Point source tiered scenario descriptions.*
Point Source
Category
Tier 1
Tier 2
Tier 3
E3
Significant
Municipals
TN = 8 for publically-owned
treatment works (POTWs)
operating (or planned)
NRT TN for remainder =
2000 concentrations.
TP = 2000 concentrations,
except TP = 1.5 in those
targeted by VA.
TN = 8;
TP= 1.0 or
permit limit if less
TN = 5;
TP = 0.5 or
permit limit if less
TN = 3.0;
TP = 0.1
Significant
Industrials
TN and TP = 2000
concentrations or
permit limit if less
Generally a 50%
reduction from Tier 1
(2000 concentrations)
or permit conditions
if less
Generally an 80%
reduction from Tier 1
(2000 concentrations)
or permit conditions
if less
TN = 3.0; TP =
0.1 or permit
conditions
if less
Nonsignificant
Municipals
TN and TP =
2000 concentrations
TN and TP =
2000 concentrations
TN and TP =
2000 concentrations
TN = 8; TP =
20 or 2000
concentrations
if less
Combined Sewer 43% reduction for tiers 1-3 Zero overflow
Overflows
•Note that all flows are in terms of those projected by 2010, and concentrations of total nitrogen (TN) and total phosphorus (TP) are presented
as annual averages in mg/1.
total phosphorus discharge of 0.5 mg/1. For the E3 scenario, technologies to achieve
3.0 mg/1 total nitrogen include deep bed denitrification filters and microfiltration to
achieve a phosphorus discharge of 0.1 mg/1. Due to seasonal fluctuation, the
effluent/discharge levels for each tier were defined as an annual average.
For industries, site-specific information on reductions by facility was obtained via
phone or site visits. Tier 1 represents current conditions or plans for reductions that
already are in progress. Tiers 2 and 3 generally reflect levels of reduction of
50 percent and 80 percent from Tier 1, respectively, unless permit conditions are less
than this or site-specific information provides alternate data. The E3 scenario reflects
total nitrogen and total phosphorus concentrations of 3.0 and 0.1 mg/1, respectively,
unless permit conditions or actual 2000 concentrations are less than this level. For
the E3 scenario, some industrial facilities would be incapable of achieving the
discharge concentration/level.
The only combined sewer overflow included in the tiers was the District of Columbia
because it is the only one for which the Chesapeake Bay Program has data on
resulting nutrient loads. According to the District of Columbia Water and Sewer
Authority, overall nutrient loads are expected to be reduced by 43 percent from 2000
levels over the next eight years, and Tier 1 reflects this reduction, which also is
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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carried over into Tier 2 and Tier 3. For the purpose of estimating limits of tech-
nology, zero overflows were assumed for the E3 scenario, although the D.C. Water
and Sewer Authority stresses that no overflow is not physically possible.
ONSITE TREATMENT SYSTEMS
The Chesapeake Bay Program's Point Source Workgroup developed the tiers for
onsite treatment systems, or septic systems. Tier 1 involved maintaining current
septic concentrations/loads per system equivalent to 36 mg/1 total nitrogen. Tier 2
includes 10 percent of new treatment systems installing nutrient reduction
technologies to obtain an edge-of-drainage field total nitrogen concentration of
10 mg/1 per system. Tier 2 for existing systems remains the same as Tier 1. Total
phosphorus levels are not addressed in the septic system tiers because septic systems
are not considered a significant source of phosphorus. Tier 3 involves 100 percent of
new treatment systems installing nutrient reduction technologies to obtain an edge-
of-drainage field total nitrogen concentration of 10 mg/1 per system, and upgrades
1 percent of existing systems to this level of treatment as well. Note that the Point
Source Workgroup members believe it is unlikely that existing systems could be
retrofitted due to the high cost, thus only 1 percent of existing systems were included
in the Tier 3 scenario for retrofit. For the E3 scenario, 100 percent retrofits and
upgrades are defined for existing as well as new septic systems.
NONPOINT SOURCE AGRICULTURE
Estimated load reductions for agricultural practices are a function of the definition
and assumed efficiency of the BMPs being investigated. For the purposes of this
document, all definitions and efficiencies of BMPs assumed for the reduction tiers
and included in the model scenarios are described in Appendix H of the Chesapeake
Bay Watershed Model Phase 4.3 documentation (Palace et al. 1998). The Chesa-
peake Bay Program's Nutrient Subcommittee is updating several BMP definitions
and efficiencies. The Chesapeake Bay Program will publish these revisions in 2003
in a revised Appendix H watershed model documentation. The Chesapeake Bay
Program encourages the jurisdictions to use the most recent information on BMPs
when developing their tributary strategies and adopting their water quality standards.
For most nonpoint source agricultural BMPs, implementation rates between 1997
and 2000 were continued to the year 2010, however, levels could not exceed the
available or the E3 scenario land area on which to apply the BMPs (Table V-2). The
scale of calculations was by county segment or by the intersection of a county polit-
ical boundary and a Chesapeake Bay Watershed Model hydrologic segment. This is
the same scale that most jurisdictions use to report BMP implementation levels to
the Chesapeake Bay Program.
The 2010 Tier 1 BMPs were extrapolated from recent implementation rates by the
landuse types submitted by the states for each BMP. For example, if a jurisdiction
submits data for nutrient management on crops, 2010 Tier 1 cropland and was
chapter v - Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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Table V-2. Examples of the increasing levels of agricultural nonpoint source BMP implementation by tier.
Agricultural
BMP
Tier 1
Tier 2
Tier 3
E3
Conservation
Tillage
Continue current level
of implementation
Applied to 30% of
remaining cropland
beyond Tier 1
Applied to 60% of
remaining cropland
beyond Tier I
Conservation tillage
on 100% of cropland
Cover Crops
Continue current level
of implementation
Applied to 40% of
remaining cropland
beyond Tier 1
Applied to 75% of
remaining cropland
beyond Tier 1
Applied to 100%
of cropland
Stream
Protection
w/Fencing
Continue current level
of implementation
Applied to 15% of
remaining stream
reaches within pasture
land beyond Tier 1
Applied to 75% of
remaining stream
reaches within pasture
land beyond Tier 1
Streambank protection
on all unprotected
stream miles (each
side) associated
with pasture
projected and then split among high-till, low-till and hay, according to relative
percentages. If a jurisdiction submits data as nutrient management on high-till, low-
till and hay individually, projections were done for each of these land use categories.
The 2010 Tier 1 scenario does not include tree planting on tilled land, forest conser-
vation and forest harvesting practices, because these BMPs are not part of the tiers
and the E3 scenario. For forest harvesting practices and erosion and sediment
control, the model simulation does not account for additional loads from disturbed
forest and construction areas, respectively. For forest conservation, planting above
what is removed during development is accounted for in the 2010 urban and forest
projections. Tree planting on agricultural land was included in Tier 1 for pasture as
forest buffers since this BMP is also part of the tiers and the E3 scenario and pasture
tree planting and pasture buffers are treated the same in the model.
The 2010 Tier 2 and Tier 3 BMP implementation levels for nonpoint sources were
generally determined by increasing levels above Tier 1 by a percentage of the differ- '
ence between Tier 1 and the E3 scenario levels for each BMP. These percentages
were mostly prescribed by individual source workgroups under the Chesapeake Bay
Program Nutrient Subcommittee and were applied watershed-wide by county
segments or the intersections of county political boundaries and the Chesapeake Bay
Watershed Model's hydrologic segmentation.
The BMP levels in the E3 scenario are believed to be the maximum extent feasible.
There are no cost and few physical limitations to implementing BMPs for both point
and nonpoint sources. In addition, the E3 scenario includes new BMP technologies
and programs that are not currently part of jurisdictional pollutant control strategies.
Riparian forest buffers are particular BMPs under agricultural and urban sources that
can be estimated in terms of acres or stream miles. Table A-2 in Appendix A illus-
trates that riparian forest buffers estimates exist in hay and pasture land uses under
chapter v - Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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142
w
agriculture and in pervious and mixed open landuses under urban sources. Chesa-
peake 2000 includes a goal to conserve existing forest along all streams and
shorelines and to restore riparian forest on 2,010 miles of stream and shoreline in the
watershed by 2010. Between 1996 and 2002, 2,283 miles of riparian forest buffers
were actually planted in the Chesapeake Bay watershed, surpassing the 2010 goal.
The tiers also include estimates of projected riparian forest buffers, and their total
one-sided stream miles with 50-feet width are listed below (which can be calculated
by adding the total stream miles listed in Appendix A, Table A-2, per tier): Tier 1 -
2,584; Tier 2 - 21,022; Tier 3 - 33,109; and the E3 scenario - 105,579 miles.
NONPOINT SOURCE URBAN
Tier 1 represents voluntary and regulatory storm water management programs that
will be in place between 2000 and 2010, including EPA National Pollutant Discharge
Elimination System (NPDES) Phase I and II storm water regulations, the construc-
tion and effluent development guidelines and state storm water management
programs (Table V-3). Tiers 2 and 3 represent progressively increased levels of
voluntary BMP implementation measures beyond Tier 1. the E3 scenario represents
the Nutrient Subcommittee's Urban Storm Water Workgroup's understanding of the
highest levels of urban BMP protection achievable.
Table V-3. Examples of the increasing levels of urban nonpoint source BMP implementation by tier.
Urban
BMP
Tier 1
Tier 2
Tier 3
E3
Storm Water Management—
recent development
(1986-2000)
60% of recent
development has
storm water
management
Same as Tier 1
Same as Tier 1
See below for
'recent and old
development'
Storm Water Management—
new development
(2001-2010)
60% of recent
development has
storm water
management
75% of new
development has
storm water
management;
25% of new
development has
LID*
50% of new
development has
storm water
management;
50% of new
development has
LID*
100% of new
development
has LID*
Storm Water Management—
recent and old development
(pre-1986)
0.8% of recent
and old
development
is retrofitted
5% of recent
and old
development
is retrofitted
20% of recent
and old
development
is retrofitted
100% of recent
and old
development
is retrofitted
"Low Impact Development
chapter v
Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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143
NONPOINT SOURCE FORESTRY
The forestry BMP levels defined in the tiers are the same throughout the four levels.
The tiers reflect an assumption that forestry BMPs are designed to minimize the
environmental impacts from timber harvesting such as road building and cutting-
and-thinning operations, and are properly installed on all harvested lands with no
measurable increase in nutrient and sediment discharge. The assumption is based on
maintaining the state of forest loads as measured during the calibration of the Chesa-
peake Bay Phase 4.3 Watershed Model.
ATMOSPHERIC DEPOSITION
The Chesapeake Bay Program modeled four different nitrogen oxide (NOx) emission
reduction scenarios to estimate changes in atmospheric nitrate deposition and loads
to the Chesapeake Bay and its watershed (Table V-4). The first two scenarios
describe Clean Air Act (CAA) regulations; the third and fourth scenarios include
these existing regulations, as well as emissions controls that are not tied to existing
or proposed regulations. All scenarios involve NOx emissions reductions made by 37
states contained in the EPA Regional Acid Deposition Model (RADM) domain
based on the national 1990 NOx emissions inventory. All the tiered scenarios summa-
rized in Table V-4 include the full array of emission controls described for the
preceding tier.
Table V-4. Atmospheric deposition tiered scenario descriptions and NOx reduction assumptions.
Tier 1
Tier 2
Tier 3
E3
NOx state implementation
plans (SIPs), assuming
implementation by
2007/2010
Tier I controls, plus
heavy-duty diesel vehicle
(HDDV) regulations,
assuming implementation
by 2020
Tier 1 and 2 controls, plus
'what if* aggressive utility
controls, assuming imple-
mentation by 2020
Tier 1-3 controls, plus
'what if industry and
mobile source controls,
assuming implementation
by 2020
2007 non-utility and area
source emissions
2020 non-utility and area
source emission standards
2020 non-utility and area
source emission standards
2020 non-utility and area
source emissions
2007 mobile source-
Tier 2 tailpipe standards
on Light Duty Vehicles
(LDVs) (cars and trucks)
2020 Tier 2 tailpipe
standards on LDVs
2020 Tier 2 tailpipe stan-
dards on LDVs
Industry (non-utility)
emissions at almost 50%
for both S02 and NOx
2010 utility emissions—
Title IV (acid rain) fully
implemented and Title I
20-state NOx SIP call
seasonal (May-September)
ozone controls
2020 Title V and Title I
NOx SIP
HDDV Regulations
2020 Title V and Title I
NOx SIP greater emissions
reductions from utility
sector- annual controls
2020 Title V and Title I
SIP greater emissions
reductions from utility
sector-annual controls
Super ultra-low emission
vehicle assumed for LDVs
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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144
The effects of emission controls and the resulting lower atmospheric deposition to
the Chesapeake Bay watershed's land area and nontidal waters are part of the
reported nutrient loads from the individual land use source categories in the tiers and
the E3 scenario (i.e., agriculture, urban, mixed open, forest and nontidal surface
waters). The reported loads, however, usually do not include contributions from
atmospheric deposition directly to'surface tidal waters, although the model-simu-
lated water quality responses account for this source.
LOAD REDUCTIONS BY TIER
The Chesapeake Bay Program's Phase 4.3 Watershed Model simulated the tier and
E3 scenarios, and the resulting loads for nitrogen, phosphorus and sediment were
used as inputs to the Chesapeake Bay Water Quality Model. Evaluation of the simu-
lated water clarity, dissolved oxygen and chlorophyll a concentrations from the
Water Quality Model, in turn, provided a sense of the response of these key water
quality parameters to the various loading levels.
For the tiers, BMP implementation levels, the resulting modeled loads and the
measured responses in tidal-water quality are informational. They are not intended
to prescribe control measures to meet Chesapeake 2000 nutrient and sediment
loading caps.
Relating BMP implementation levels in the tier scenarios to water quality responses
only provides examples of what levels of effort achieve the reported loads and what
the water quality responses are to those loading levels. Reported E3 loads from the
Chesapeake Bay's basin, however, can imply measurable theoretical minimums that
would be extremely difficult, if not impossible, to remedy at this time.
Figures V-l to V-3 illustrate modeled nitrogen, phosphorus and sediment loads,
respectively, delivered to the Chesapeake Bay and its tidal tributaries for the four
tiered scenarios, excluding atmospheric deposition to tidal waters and shoreline
erosion loads. The model-simulated load estimates for the year 2000 and pristine
scenario (see Chapter HI) are provided as reference points.
DEVELOPMENT OF THE CRITERIA ATTAINABILITY TABLES
A series of coupled Chesapeake Bay airshed, watershed and water quality model
scenarios were run to determine the water quality response to the reduction actions
represented in each tiered scenario described above. The results of these analyses are
presented in a series of technological 'attainability tables' which show, on a Chesa-
peake Bay Program segment-by-segment basis, the level of attainment of the
applicable Chesapeake Bay criteria by designated use and tiered scenario. The
model-simulated percent criteria attainment, illustrated in the attainability tables that
follow, are based on an integrated evaluation of Chesapeake Bay model-simulated
output and water quality monitoring observed data. For a full discussion of this inte-
gration procedure, see A Comparison of Chesapeake Bay Estuary Model Calibration
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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116.4
284.8
2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3 2010 E3 Pristine
Figure V-1. Model-simulated nitrogen loads delivered to the Chesapeake Bay and its
tidal tributaries under the four tiered scenarios.
Source: Chesapeake Bay Program website httpVAvww.chesapeakebay.net.
2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3 2010 E3
Pristine
Figure V-2. Model-simulated phosphorus loads delivered to the Chesapeake Bay arid its tidal
tributaries under the four tiered scenarios.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter v • Technological Attainability of the Refined Recommended Tidaf-Water Designated Uses
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146
2000 Progress 2010 Tier 1 20X0 Tier 2 2010 Tier 3 2010 E3 Pristine
Figure V-3. Model-simulated sediment loads delivered to the Chesapeake Bay and its tidal
tributaries under the four tiered scenarios.
Source; Chesapeake Bay Program website http^/www, Chesapeake bay. net
with 1985-1994 Observed Data and Method of Application to Water Quality Criteria
(Linker et al. 2002). Results are presented for the 35 major Chesapeake Bay Program
segments where management-applicable model results are available.
These attainability tables were developed using a comprehensive set of criteria
attainment determination procedures described in detail in the EPA's Ambient Water
Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the
Chesapeake Bay and Its Tidal Tributaries (U.S. EPA 2003). In general, modeled
dissolved oxygen water quality observations were compared to proposed criteria, on
a segment-by-segment basis (see Figure IV-30 and Table IV-11 for a map and listing
of the Chesapeake Bay Program monitoring segments) to determine the spatial and
temporal extent of nonattainment.14 The criteria used to conduct these comparisons
were the 30-day mean dissolved oxygen concentrations of 6 mg/1 for the migratory
and spawning use, 5 mg/1 for the open-water use, 3 mg/1 for the deep-water use and
1 mg/1 for the deep-channel use. The attainability tables do not reflect assessment of
the 7-day mean, 1-day mean or instantaneous minimum criteria.
l4Note: The term 'nonattainment' is used within the context of comparing dissolved oxygen water
quality modeled response to reduction measures with the EPA published Chesapeake Bay water
quality criteria. The term is not used here to imply nonattainment with respect to CWA 303(d) lists.
chapter v * Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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147
The dissolved oxygen criteria have several different durations: 30-day mean. 7-day
mean. I-day mean (deep water only) and instantaneous minimum. A state's ability
to assess these criteria and to have certainty in the results depends on ilie time scnie
of available data and the capacity of models to estimate conditions at those time
scales. At present, long-term, fixed-station, midchannel water quality monitoring in
the Chesapeake Bay and its tidal tributaries provides dissolved oxygen measure-
ments twice monthly at most or approximately every 15 days between April and
August, Proposed enhancements to the tidal-water quality monitoring program
include shallow-water monitoring, as well as high-resolution spatial and temporal
monitoring in selected locations. However, these new components are only in the
planning and early implementation stages at this point, and because of financial
constraints or limitations to current technology, direct monitoring at the scales of the
criteria may not be possible in the foreseeable future across all tidal waters. There-
fore. the direct assessment of attainment for some geographic regions and for some
short-term criteria elements (e.g.. instantaneous minimum. 1-day mean and 7-day
meant must be waived for the time being or based on statistical methods that esti-
mate probable attainment fU.S. EPA 20031.
ASSESSING CRITERIA EXCEEDANCE THROUGH
THE CUMULATIVE FREQUENCY DISTRIBUTIONS
Cumulative Frequency Diagrams (CFDs) are the foundation for deriving the attain-
ability tables. Tliesc curves were used to assess water-quality criteria "exceedanee' (or
nonattainment based on the monthly average dissolved oxygen concentrations speci-
fied by designated use) in Chesapeake Bay tidal waters. Some observed spatial and
temporal criteria excecdances do not have serious effects on ecological health or
designated uses. Such excecdances arc referred to as 'allowable excecdances.' Even
w hen water quality is restored in the Chesapeake Bay and its tidal tributaries, certain
areas will exceed the Chesapeake Bay water quality criteria, either due to poor
flushing {chlorophyll a\. a strong stratification event (dissolved oxygen), a wind
resuspension event (water clarity) or some other natural phenomenon. A reference
curve should reflect expected excecdances that occur naturally when the biological
community is not impaired by the stressors ) the criteria were designed to limit. Tradi-
tional regulatory assessments take 10 percent of the samples collected at a point and
consider this amount to be 'allowable excecdances' that have limited impact on the
designated use (U.S. EPA 19071. The 10 percent principle is not applicable in the
context of the CFD methodology used herein for defining criteria attainment because
U was designed for samples collected at one location and only reflects time variations.
CFDs offer the advantage of allowing the evaluation of both spatial and temporal
variations in criteria cxcecdance. Methods currently used for assessing criteria
attainment arc based only on the frequency of excecdances because measurements
arc usually evaluated only at individual locations. In a water body the size of the
Chesapeake Bay, accounting for spatial variation can be important and in that
respect, the CFD approach represents a significant improvement over past methods.
chapter v • Techndogical Attainability of the Refined Recommended Tidal-Water Designated Uses
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148
Developing a CFD is accomplished first by quantifying the spatial extent of criteria
exccedancc for every monitoring event during the assessment (>criod. The compila-
tion of estimates of spatial cxceedanee through time provides the capability to
account for both spatial and temporal variation in criteria exccedancc. Assessments
arc performed within spatial units defined by the intersection of monitoring
segments and designated uses, and temporal units of three-year periods. Thus indi-
vidual CFDs arc developed for each spatial unit over three-year assessment periods.
Details of the development of CFDs arc described in the EPA's Ambient Hitter
Quality Criteria for Dissolved Oxygen. Hater Clarity- and Chlorophyll a for Clwsih
peike liar a ml Its Tidal Tributaries (U.S. EPA 200?).
The CFD is a graphical summary of criteria cxceedanee created by plotting temporal
frequency on the vertical axis and spatial extent on the horizontal axis (Figure V-4).
The resulting figure can be used to draw conclusions about the extent and pattern of
criteria attainment or cxccedancc. The area under the curve represents a spatial and
temporal composite index of criteria cxceedanee that is biologically acceptable and
is used as the basis for defining criteria attainment for all Chesapeake Bay segments
and designated uses.
Criteria Exceedartce
Reference Curve
Figure V-4. Light area reflects amount of 'allowable' criteria exceedanee defined as
the area under the reference curve {light line). Dark area reflects the amount of 'non-
allowable' criteria exceeds nee defined as the area between the attainment curve
(black line) and the reference curve.
Attainment Curve
Area of 'Non-Allowable'
Criteria Exceedance
O)
ro j±>
TD
a> d)
O O
CP X
50
O.LU
w a>
Area of 'Allowable'
Percentage of AreaA/olume Exceeding the Criteria
chapter v * Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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149
A more appropriate approach for defining 'allowable exceedances' in the CFD
context is to develop a reference curve, described above, that identifies the amount
of spatial and temporal criteria exceedance that can occur without causing ecolog-
ical degradation. Such curves are based on biological indicators of ecological health
that are separate from the criteria measures and thus more closely reflect the needs
of the Chesapeake Bay's living resources. Biological indicators are used to identify
areas of the Bay that have healthy ecological conditions. CFDs developed for those
areas would reflect an extent and pattern of criteria exceedance that did not have
ecological impact. In that way the reference curve approach takes the development
of criteria levels beyond those developed in a laboratory setting and provides actual
environmental context (U.S. EPA 2003).
The use of the reference curve and the interpretation of criteria attainment using the
CFD is illustrated in Figure V-4. The dark blue (or bottom) line in the figure illus-
trates a possible reference curve, below which a certain amount of spatial or
temporal exceedance is allowed. The black (or upper) line is an attainment curve,
which is developed over every assessment period during which monitoring data are
collected. The attainment curve is the assessment of the condition in the segment and
it is compared to the reference curve, which serves as the benchmark. The area above
the reference curve and below the attainment curve is the measure of criteria attain-
ment and is referred to as 'nonallowable exceedances.'
As the states adopt the Chesapeake Bay water quality criteria and concomitant
implementation procedures into their water quality standards, they may decide to:
1) allow for no criteria exceedance, 2) select the normal distribution curve repre-
senting approximately 10 percent allowable criteria exceedance or 3) apply a
biological reference curve. The first two options are likely to be more restrictive than
the biological reference curve approach.
APPLYING THE KOLMOGOROV-SMIRNOV TEST FOR
CRITERIA ATTAINABILITY USING THE CFD
The use of the Kolmogorov-Smirnov (KS) test had been considered early on to
enhance the designated use attainability analyses for dissolved oxygen. However, the
Chesapeake Bay Program partners determined that this test is really designed to
assist decision making with regard to actual environmental attainment (U.S. EPA
2003). A statistical test is necessary because of limitations in the quantity of moni-
toring data that can be collected. Certainty will be a function of the amount of data
available for the assessment, and the KS test provides a mechanism for accounting
for different levels of certainty. The same situation does not exist for modeling infor-
mation, which is used to assess attainability in this Technical Support Document.
Models provide simulated data that have error characteristics that are inherently
different than data collected in the field. As a result, application of a statistical test
to model output would not necessarily provide results that are comparable to the
same application to monitoring data. Thus, the application of the KS test for
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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ISO
assessing attainability using model information is not appropriate. Models are used
as a guide, not as a strict determination of attainability. The goal in using models for
determining attainability and for defining allocations should be to achieve conditions
where there are no non-allowable criteria exceedances. Therefore, the KS test is not
used for the purpose of assessing attainability in this Technical Support Document.
However, for assessing attainment of water quality criteria, once these designated
uses have been incorporated into state standards, using the KS test may be appro-
priate with environmental monitoring data to detect significant differences between
the reference and assessment curves. The purpose in this case will be to account for
differences in the certainty of either curve, which could result from differences in
sampling rate or intensity. The test will provide a basis for distinguishing between a
curve (reference or assessment) that is developed based on limited information and
one that is based on detailed information.
The KS test was selected because it was developed for comparing two cumulative
distribution functions such as the reference and assessment curves. The KS test is
commonly used to detect significant deviations between two curves including those
above and those below a reference curve (i.e., it is used as a 'two-sided* test). To
assess Chesapeake Bay water quality criteria attainment, only deviations above the
reference curve (i.e., non-allowable exceedances) are of interest and the test is being
modified to detect only those deviations (i.e., to allow use as a 'one-sided* test).
Assessing criteria attainment will take place over specific units of space and time.
Spatial units have been defined according to Chesapeake Bay Program monitoring
segments and designated uses within each segment. Decisions regarding attainment
will be made independently for each spatial unit, and monitoring data will be
collected for three-year assessment periods in each spatial unit. Thus, separate CFDs
will be developed for each spatial unit based on three years of monitoring data, 2nd
the KS test will be applied to each CFD for making decisions regarding attainment,
USE OF THE '10 PERCENT DEFAULT REFERENCE CURVE'
VERSUS BIOLOGICAL REFERENCE CURVES
For most criteria components and designated uses, biologically-based reference
curves are the preferred benchmark for evaluating CFDs and for defining the extent
and pattern of allowable exceedances. However, biological information is not avail-
able in all cases and for those situations a default reference curve is needed. The
default reference curve was developed on the basis of two principles: 1) limiting the
amount of allowable exceedance to 10 percent of time and space combined; and
2) showing no preference for either spatial or temporal exceedance. The curve used
for this purpose is a simple inverse curve that is forced through the 100 percent levels
of temporal and spatial exceedance. In most cases, the biological references curves
that have been developed are very similar to the default curve and it is considered to
be a reasonable approach on that basis. However, actual biologically-based reference
curves are the preferred approach and are used wherever possible (U.S. EPA 2003).
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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151
CONSIDERATION OF DIFFERENT HYDROLOGY PERIODS
Currently, the CFD curves are generated from 10 years (1985-1994) of data and
model output to assess attainment and nonattainment of criteria in model scenarios.
However, compliance monitoring of the criteria adopted by the states may be
performed using a more traditional three-year hydrology (U.S. EPA 2003). Analyses
performed by the Chesapeake Bay Program staff and presented to the Chesapeake
Bay Water Quality Steering Committee illustrates that the 10-year CFD is a better
estimate of expected future attainment than any single 3-year period. Figure V-5
shows the 10-year attainability (blue dashes) versus the maximum, minimum, and
average (black dashes and gray dashes) 3-year attainability for the eight 3-year
periods between 1985-1994. The range between maximum and minimum decreases
as scenarios become closer to attainment for the 10-year period, and, in most cases,
attainment is achieved almost simultaneously for the 10-year and 3-year averages.
CB3MH
*
CB4MH
CB5MH
<*> <> ru /b o> 4
^ -O®
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152
TECHNOLOGICAL ATTAINABILITY OF THE OPEN-WATER,
DEEP-WATER AND DEEP-CHANNEL DESIGNATED USES
The results of the analyses of the technological attainability of the open-water, deep-
water and deep-channel designated uses are presented in a series of attainability
tables (tables V-5 and V-6). The 'Observed' column in each table represents current
conditions in the Chesapeake Bay and tidal tributaries derived from 1985-1994
Chesapeake Bay water quality monitoring program data. The data are aggregated by
month . and interpolated across all Chesapeake Bay tidal waters. The CFD is
constructed from violations in the interpolated data. The attainability of all other
scenarios is obtained by comparing the model scenario to the model calibration on a
point-by-p'. it and month-by-month basis. The change in the model predictions due
to the management actions in the scenario is applied to the observed 1985-1994 data.
This 'scenario-modified1 data set is then aggregated, interpolated, and used in the
CFD to determine the attainability results (see Chapter HI; Linker et al. 2002).
The letter 'A' in the tables denotes attainment (i.e., 0 percent nonattainment), and the
numbers represent percent nonattainment for each segment as determined using the
biological reference curves described above. Percent nonattainment values of less
than 1 percent were considered in attainment for purposes of these analyses by the
Chesapeake Bay Program partners. There are multiple examples where very small
percent nonattainment values (< 1 percent) were observed across scenarios spanning
large differences in nutrient reductions. These small, less than 1 percent nonattain-
ment values are an artifact of the overall CFD/reference criteria attainment
assessment methodology.
The analyses presented in this section will show that, with the exception of a few
segments in Chesapeake Bay tidal waters, the dissolved oxygen criteria protecting of
the designated uses are attained by reductions represented by the E3 scenario. For
Tier 3, these same analyses show that the dissolved oxygen criteria protecting desig-
nated uses in some segments, particularly for deep-water uses in certain mainstem
segments, do not achieve full attainment.
MIGRATORY FISH AND SPAWNING AND NURSERY
DESIGNATED USE ATTAINABILITY
The monthly average dissolved oxygen concentration of 6 mg/i applied to the migra-
tory and spawning designated use habitats shows attainment is achieved in all
segments where this use would apply in the Chesapeake Bay and its tidal tributaries
with one exception (Table V-5). There is a certain amount of nonattainment simu-
lated in the lower Mattaponi River segment (see Open-Water Use Attainability below
for an explanation). Recognizing the actual criteria protective of this use are 6 mg/!
7-day mean and 5 mg/1 instantaneous mean dissolved oxygen concentrations, the
migratory fish spawning and nursery designated use can essentially be attained under
current conditions and should not be an issue in the near future as long as respon-
sible pollution prevention and control measures are maintained.
chapter v - Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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153
Table V-5. Percent nonattainment of a monthly averaged 6 mg/l dissolved oxygen concentration
applied to migratory spawning and nursery designated uses.
Model Scenarios
Chesapeake Bay
Program Segment Observed
Progress
2000
Tier 1
Tier 2
Tier 3
Tier 3+
20%
Tier 3
+ 50%
E3
Northern Chesapeake Bay (CB1TF)
A
A
A
A
A
A
A
A
Upper Chesapeake Bay (CB20H)
A
A
A
A
A
A
A
A
Central Chesapeake Bay (CB3MH)
0.19
A
A
A
A
A
A
A
Upper Patuxent River (PAXTF)
A
A
A
A
A
A
A
A
Middle Patuxent River (PAXOH)
A
A
A
A
A
A
A
A
Lower Patuxent River (PAXMH)
A
A
A
A
A
A
A
A
Upper Potomac River (POTTF)
A
A
A
A
A
A
A
A
Middle Potomac River (POTOH)
A
A
A
A
A
A
A
A
Lower Potomac River (POTMH)
A
A
A
A
A
A
A
A
Upper Rappahannock River (RPPTF)
A
A
A
A
A
A
A
A
Middle Rappahannock River (RPPOH)
A
A
A
A
A
A
A
A
Lower Rappahannock River (RPPMH)
A
A
A
A
A
A
A
A
Upper Mattaponi River (MPNTF)
A
A
A
A
A
A
A
A
Lower Mattaponi River (MPNOH)
A
A
A
1.72
2.78
2.40
1.79
6.08
Upper Pamunkey River (PMKTF)
A
A
A
A
A
A
A
0.10
Lower Pamunkey River (PMKOH)
A
A
A
A
A
A
A
A
Middle York River (YRKMH)
A
A
A
A
A
A
A
A
Upper James River (JMSTF)
A
A
A
A
A
A
A
A
Middle James River (JMSOH)
A
A
A
A
A
A
A
A
Lower James River (JMSMH)
A
A
A
A
A
A
A
A
Eastern Bay (EASMH)
A
A
A
A
A
A
A
A
Middle Choptank River (CHOOH)
A
A
A
A
A
A
A
A
Lower Choptank River (CHOMH1)
A
A
A
A
A
A
A
A
Mouth of the Choptank River (CHOMH2)
A
A
A
A
A
A
A
A
A = attainment; the number provides an estimate of percent nonattainment.
Tier 3+ 20% = Tier 3 reductions plus 20 percent reduction in loads from tidal shoreline erosion.
Tier 3+ 50% = Tier 3 reductions plus 50 percent reduction in loads from tidal shoreline erosion.
OPEN-WATER FISH AND SHELLFISH
DESIGNATED USE ATTAINABILITY
Table V-6 presents the results of the attainability analyses for monthly average
dissolved oxygen concentrations of 5, 3- and 1 mg/l, respectively, applied to the
open-water, deep-water and deep- channel designated uses. Full attainment is rare
for the open-water use under observed conditions. However, at reduction levels
represented by Tier 3, attainment for most segments is achieved for this refined
chapter v - Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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154
Table V-6. Percent nonattainment of a monthly averaged 5, 3 and 1 mg/l dissolved oxygen concentration
applied to migratory spawning and nursery designated uses.
Model Scenarios
Chesapeake Bay
Progress
Tier 3+
Tier 3
Program Segment
DU
Observed
2000
Tier 1
Tier 2
Tier 3
20%
+ 50%
E3
Northern Chesapeake Bay (CB1TF)
ow
A
A
A
A
A
A
A
A
Upper Chesapeake Bay (CB20H)
ow
1.92
0.88
0,68
0.43
0.17
0.13
0.07
A
Upper Central Chesapeake Bay (CB3MH)
ow
A
A
A
A
A
A
A
A
DW
4.18
2.52
2.24
1.61
0.73
0.54
0.37
A
DC
13.52
8.16
7.21
5.03
1.84
1.24
0.11
A
Middle Central Chesapeake Bay (CB4MH)
OW
0.05
A
A
A
A
A
A
A
DW
19.64
15.28
14,28
12.05
8.51
7.57
5.62
0.69
DC
45.19
32.75
28.94
18.81
3.93
2.69
1.00
A
Lower Central Chesapeake Bay (CB5MH)
OW
A
A
A
A
A
A
A
A
DW
6.16
4.38
3.75
2.58
1.08
1.00
0.72
A
DC
13.79
7.76
6.00
.2.59
0.15
0.14
0.11
A
Western Lower Chesapeake Bay (CB6PH)
OW
5.87
4.26
3.68
2.71
1.30
1.23
0.99
0.0]
DW
0.36
0.01
A
A
A
A
'A
A
Eastern Lower Chesapeake Bay (CB7PH)
OW
4.55
3.31
2.81
1.82
0.74
0.66
0.49
A
DW
A
A
A
A
A
A
A
A
Mouth of the Chesapeake Bay (CB8PH)
OW
A
A
A
A
A
A
A
A
Upper Patuxent River (PAXTF)
ow
A
A
A
A
A
A
A
0.38
Middle Patuxent River (PAXOH)
ow
9.79
1.56
1.84
1.62
0.86
0.36
0.11
A
Lower Patuxent River (PAXMH)
ow
7.40
1.59
1.69
1.04
0.01
A
A
A
DW
5.52
0.85
0.82
0.50
0.07
0.02
A
A
Upper Potomac River (POTTF)
OW
A
A
A
A
A
A
A
A
Middle Potomac River (POTOH)
ow
2.10
1.36
1.08
0.63
0.31
0.30
0.25
0.01
Lower Potomac River (POTMH)
ow
0.78
A
A
A
A
A
A
A
DW
6.90
5.03
4.53
3.11
1.12
0.70
0.15
A
DC
18.89
11.39
8.64
5.07
0.19
0.17
0.16
A
Upper Rappahannock River (RPPTF)
OW
A
A
A
A
A
A
A
A
Middle Rappahannock River (RPPOH)
OW
A
A
A
A
A
A
A
A
Lower Rappahanock River (RPPMH)
OW
0.44
0.27
0.10
A
A
A
A
A
DW
5.58
2.61
1.09
0.01
A
A
A
A
DC
6.39
5.20
3.38
1.65
A
A
A
A
continued
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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155
Table V-6. Percent nonattainment of a monthly averaged 5, 3 and 1 mg/l dissolved oxygen concentration
applied to migratory spawning and nursery designated uses (corit.).
Model Scenarios
Chesapeake Bay
Program Segment
DU
Observed
Progress
2000
Tier 1
Tier 2
Tier 3
Tier 3+
20%
Tier 3
+ 50%
E3
Piankatank River (PIAMH)
ow
0.12
A
A
A
A
A
A
A
Upper Mattaponi River (MPNTF)
ow
33.26
27.37
25.87
27.23
33.73
32.44
30.50
52.14
Lower Mattaponi River (MPNOH)
ow
46.88
31.00
28.95
31.86
28.99
26.88
19.11
48.11
Upper Pamunkey River (PMKTF)
ow
62.25
49.53
42.07
30.35
32.94
21.16
10.32
54.50
Lower Pamunkey (PMKOH)
ow
42.15
15.22
12.66
13.86
10.32
4.52
1.06
11.39
Middle York River (YRKMH)
ow
18.08
4.85
3.31
2.32
0.42
0.23
0.03
A
Lower York River (YRKPH)
ow
DW
1.48
0.01
0.01
A
A
A
A
A
A
A
A
A
A
A
A
A
Mobjack Bay (MOBPH)
ow
2.30
1.78
1.60
1.10
0.34
0.29
0.23
A
Upper James River (JMSTF)
ow
0.66
A
A
A
A
A
A
A
Middle James River (JMSOH)
ow
A
A
A
A
A
A
A
A
Lower Jarnes River (JMSMH)
ow
A
A
A
A
A
A
A
A
Mouth of the James River (JMSPH)
ow
A
A
A
A
A
A
A
A
Eastern Bay (EASMH)
ow
DW
DC
A
3.26
20.23
A
2.18
12.87
A
2.00
11.26
A
0.90
6.49
A
0.36
0.67
A
0.32
0.10
A
0.20
0.01
A
A
A
Middle Choptank River (CHOOH)
OW
0,14
A
A
A
A
A
A
A
Lower Choptank River (CHOMH1)
ow
2.27
1.83
1.78
1.51
1.08
0.92
0.74
0.43
Mouth of the Choptank River (CHOMH2)
ow
0,33
A
A
A
A
A
A
A
Tangier Sound (TANMH)
ow
0.15
0.06
0.06
0.05
0.36
0.31
0.84
0.22
Lower Pocomoke River (POCMH)
ow
A
A
A
A
A
A
A
A
A = Attainament; the number provides an estimate of percent nonattainment.
Tier 3+ 20% - Tier 3 reductions plus 20 percent reduction in loads from tidal shoreline erosion.
Tier 3+ 50% - Tier 3 reductions plus SO percent reduction in loads from tidal shoreline erosion.
chapter v - iechnological Attainability of the Refined Recommended Tidal-Water Designated Uses
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156
designated use. Outside of the Mattaponi and Pamunkey rivers, only the Western
Lower Chesapeake Bay (1.3 percent) and the Lower Choptank River (1.1 percent)
segments had non-attainment levels above 1 percent at reduction levels represented
by Tier 3. The jurisdictions will need to determine the significance of any degree of
nonattainment during the development of their individual UAAs. Complete attain-
ment is generally observed in the open-water designated use habitats at reduction
levels equal to the E3 scenario. Natural lower dissolved oxygen conditions result
from the wetland areas of the Mattaponi and Pamunkey rivers in segments MPNTF,
MPNOH, PMKTF, and PMKOH (see Table V-6).
Extensive tidal wetlands lining most of the shorelines of the Mattaponi and
Pamunkey rivers cause a natural oxygen deficit in the tidal-fresh and oligohaline
areas. These areas consist of productive tidal wetlands which create extensive
amounts of biomass that consume vast quantities of oxygen as they decompose. In
these segments, the natural oxygen demand from wetland sediments directly influ-
ences dissolved oxygen criteria attainment. Recent studies estimate wetland
sediment oxygen demand to range from 1-5.3 grams oxygen meter"2-day (Neubauer
et al. 2000; Chi et al. 1999). The Chesapeake Bay Program Water Quality Model was
recalibrated to account for this phenomenon that occurs in relatively small bodies of
water such as the Mattaponi and Pamunkey rivers. In the model, a uniform oxygen
demand of 2 grams oxygen meter"2-day was used. The effect of this wetland sedi-
ment oxygen demand is most evident in the Chesapeake Bay Program segments
where there are extensive tidal wetlands which border relatively small bodies of
water, such as in the Mattaponi and Pamunkey rivers.
In the face of significant nutrient reductions up through the E3 scenario, there were
still high model-simulated percent nonattainment of the monthly average dissolved
oxygen in the Mattaponi and Pamunkey Rivers (Tables V-5 and V-6). These findings
reflect naturally reduced low dissolved oxygen conditions that cannot be remedied
by nutrient reductions.
DEEP-WATER SEASONAL FISH AND SHELLFISH
DESIGNATED USE ATTAINABILITY
As Figure V-6 illustrates, the deep-water designated use (assessed with a monthly
dissolved oxygen concentration of 3 mg/1) is not currently attained in any Chesa-
peake Bay Program segments under observed conditions with the exception of the
eastern lower Chesapeake Bay (CB7PH). Some degree of attainment is seen at
reductions levels equivalent to Tier 2. At Tier 3, nonattainment persists in several
major segments. Attainment is achieved in all of the segments at reduction levels
represented by the E3 scenario.
DEEP-CHANNEL SEASONAL REFUGE DESIGNATED
USE ATTAINABILITY
The monthly average 1 mg/1 dissolved oxygen concentration, that applies to
deep-channel designated use habitats, is not attained under observed conditions
(Table V-6). However, the percent non-attainment decreases with increasing load
chapter v •
Technological Attainability of the Refined Recommended Tida.a/ater Designated Uses
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157
reductions, until attainment is achieved in all segments at reduction levels repre-
sented to the E3 scenario. Even at levels of reduction represented by Tier 3 almost
complete attainment is realized.
SEDIMENT REDUCTION AND ITS EFFECT
ON WATER QUALITY
Shoreline-erosion sediment reductions beyond the BMPs considered in the tiered
scenarios do not have a significant effect on the dissolved oxygen water quality
response. Tables V-5 and V-6 inciude model scenarios labeled 'Tier 3 + 20%' and
'Tier 3 + 50%.' These are scenarios where additional shoreline sediment loads (20
percent and 50 percent beyond year 2000 levels, respectively) have been reduced
beyond that which occurs in Tier 3. As shown in the attainability tables for dissolved
oxygen (Table V-5 and V-6), a 20 percent shoreline reduction in sediment beyond the
tiers (which is considered by the Chesapeake Bay Program partners to be difficult,
at best, to achieve) results in a less than 1 percent improvement in, for example,
segment CB4MH deep-water use. Even a 50 percent reduction in shoreline erosion
(considered not feasible to achieve by the Chesapeake Bay Program partners) results
in a less than 3 percent improvement in attainment of the dissolved oxygen criteria
for that same segment. While shoreline sediment load reductions may not signifi-
cantly improve dissolved oxygen conditions in the deep-water and deep-channel
monitoring segments, it can have positive effects on water clarity in shallow-water
areas. Reduction of sediment loads remains a critical component to the restoration of
underwater bay grasses.
Work is continuing to examine the degree and cause of the model-simulated sediment
reduction and resultant water quality responses (dissolved oxygen, water clarity and
chlorophyll a). Greater sequestering and retention of nutrients in the shallows may be
due to increased underwater bay grass and benthic algae in the shallows (caused by
improved light conditions resulting from reduced sediment). Decreases in shoreline
sediment loads in the shallows would also have a positive effect on benthic filter
feeders, which may also cause greater nutrient retention in shallow sediment. Simu-
lated shoreline sediment loads are associated with soil phosphorus loads as well as
negligible nitrogen loads, and the contributing effect of these nutrient reductions asso-
ciated with shoreline sediment reductions needs to be assessed as well. For these
reasons, sediment reduction will be targeted more for underwater bay grass restoration
than for dissolved oxygen improvement. The Chesapeake Bay Program partners are
evaluating the value of targeting sediment reduction to specific underwater bay grass
sensitive areas for more effective restoration results.
ATTAINABILITY OF THE SHALLOW-WATER
DESIGNATED USE
ATTAINING THE SHALLOW-WATER BAY GRASS DESIGNATED USE
While water clarity is the criteria that will be applicable to the shallow-water desig-
nated use (U.S. EPA 2003), attainability is not being assessed on the basis of this
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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158
parameter, as is the case for the dissolved oxygen criteria for the other designated
uses. The Chesapeake Bay Watershed and Water Quality Models have been exten-
sively refined over many years to accurately measure water quality responses of
nutrient reduction practices in terms of improvements in ambient dissolved oxygen
concentrations (see Table 131-3). Chesapeake Bay watershed modeling of sediment
sources and transport and Bay water quality modeling of water sediment transport
and resuspension has not yet reached this level of sophistication. Thus, the Chesa-
peake Bay Program partners agreed to assess attainability for the shallow-water
designated use based on the presence of underwater bay grasses which offers the
added advantage of providing a more direct measure of Bay restoration.
Because attainment with water quality standards will ultimately be based, in part, on
the acreage of underwater bay grasses per segment, the measurement of attainability,
for purposes of this Technical Support Document, will also be based on underwater
bay grasses. The attainability of the shallow-water designated use has been assessed
based on the following concepts:
• The restoration goal was based on the historical and recent presence of under-
water bay grasses;
• The methodology for setting the acreage restoration goal is conservative;
• The natural coverage of underwater bay grasses is potentially greater than the
restoration goal;
• Reasonable time frames within which to assess attainment of the underwater
bay grass goal are incorporated into the criteria implementation recommenda-
tions; and
• Implementation of the shallow-water designated use allows for a flexible
approach to determine use attainability.
Because the restoration target for the shallow-water designated use is 185,000 acres
of underwater bay grasses based on their actual presence in the recent and historical
past (see Chapter IV), this use is considered to be attainable. There is compelling
evidence that such conditions once existed and can exist again, especially after states
have completed their tributary strategies, adopted new water quality standards and
have begun to implement restoration measures.
The methodology for setting the acreage goal is conservative in that a set of decision
rules (described in Chapter IV) were applied to ensure that the goal did not require
restoring underwater bay grasses to areas deeper than the amount of light was
expected to reach the Bay bottom in each segment by 2010. To do this, it was
required that at least 20 percent of each depth zone (0-0.5, 0.5-1 or 1-2 meters) be
covered by underwater bay grass in that single best year (an acute presence
threshold), or 10 percent of that area be covered at some time during three of four
five-year intervals (a chronic presence threshold) in order for those underwater bay
chapter v * Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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159
grasses to be included in the total (i.e., all underwater bay grass growing deeper than
these areas was not included).
Additionally, the restoration goal of 185,000 is actually less than the potential under-
water bay grasses natural coverage. The total shallow-water habitat available for
underwater bay grasses in the Chesapeake Bay from the shoreline to a depth of 2
meters is just over 640,000 acres. On average, underwater bay grasses cover approx-
imately 35 percent of the available shallow-water habitat (see Chapter IV).
Therefore, at any given time in the past it is likely that the Chesapeake Bay had as
much as 225,000 acres of underwater bay grasses (based on 35 percent occupation
of the 640,000 acreages of potential bay grass habitat). Within the application depths
set by the shallow-water designated uses, there are just under 496,000 acres of
habitat. Given the occupation rate described above, provided that light levels reach
the proposed segment-specific depths, it is reasonable to assume that a goal of
185,000 acres is attainable (37 percent of 496,000 acres of shallow-water habitat).
It is important to note that weather plays a key role in annual underwater bay grass
abundance. An untimely hurricane or algae bloom may suppress underwater bay
grass growth despite management actions. It is thus unreasonable to expect that
underwater bay grass goals will be reached consistently, each year. The EPA
Regional Criteria makes accommodations for the need to identify a reasonable time
frame for assessing attainment by recommending that achievement of the underwater
bay grass goal be determined on the basis of the single best year during a three-year
period (U.S. EPA 2003).
Finally, as summarized in Chapter IV and described in EPA 2003, states have options
for defining attainment of the shallow-water designated use that allows for meeting
either the water clarity criteria out to a segment-specific depth, the recommended
underwater bay grass acreage by segment or the water clarity criteria over the
established acreage of shallow-water habitat required to support meeting the restora-
tion goal.
MEASURES TO ATTAIN THE SHALLOW-WATER
DESIGNATED USE
The restoration of underwater bay grasses and the achievement of the water clarity
criteria will depend on reductions in sediment across the watershed. Sediment
reductions associated with the tiers are those that are achieved in the process of
conducting BMPs to remove nutrients. Additional sediment reduction measures may
be implemented, especially in nearshore areas closer to the tidal Bay waters, which
have not been captured in the tier scenario reductions. In February 2003 the Chesa-
peake Bay Program conducted a workshop to explore additional sediment reduction
opportunities. This workshop yielded a menu listing the various types and efficien-
cies of sediment BMPs available to assist in achievement of the Bay sediment
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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160
reduction goals (Chesapeake Bay Program 2003). The menu includes the following
BMPs for consideration by the jurisdictions in developing their tributary strategies:
Stream/Riverine BMPs
• Riparian buffers
• Stream restoration
• Urban storm water management
Shoreline BMPs
• Structural shoreline erosion controls
• Offshore breakwaters
• Breakwater systems (includes structures/beach nourishment/marsh)
• Headland control
In-Water BMPs
• Bay grass planting
• Oyster reef restoration and oyster aquaculture
Where available, the report provides information on each BMP's definition, impact,
sediment and nutrient reduction efficiencies, potential problems, costs estimates and
possible funding sources.
The report concludes that based on initial reviews of efficiencies and reasonable
application, current sediment BMPs are likely to reduce shoreline and nearshore
sediment inputs/resuspension by about 10 to 20 percent overall. Generally, shoreline
and nearshore practices can provide local clarity improvements. However, these
practices tend to be costly. A targeted approach is recommended that focuses on
reducing cc -.trollable sources near the most critical living underwater bay grass areas
in order to extract the most efficient cost per water quality improvement.
LITERATURE CITED
Chi, W., L. Pomeroy, M. Moran, and Y. Wang. 1999. Oxygen and carbon mass balance for
the estuarine-intertidal marsh complex of five rivers in the southeastern U.S. Limnology and
Oceanography 44:3, 639-649.
Linker, L.C., G.W. Shenk, P. Wang, C.F. Cerco, A.J. Butt, P.J. Tango, and R.W. Savidge.
2002. A Comparison of Chesapeake Bay Estuary Model Calibration with 1985-1994
Observed Data and Method of Application to Water Quality Criteria. Modeling Subcom-
mittee, Chesapeake Bay Program Office, Annapolis, Maryland.
Neubauer, S., W. Miller and I. Anderson. 2000. Carbon cycling in a tidal freshwater marsh
ecosystem: a carbon gas flux study. Marine Ecology Progress Series 199:13-30.
Palace, M., J. Hannawald, L. Linker, G. Shenk, J. Storrick and M. Clipper. 1998. Appendix
H: tracking best management practice nutrient reductions in the Chesapeake Bay Program.
chapter v - Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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161
In Chesapeake Bay Watershed Model application and calculation of nutrient and sediment
loadings. EPA 9Q3-R-98-009, CBP/TRS 201/98. Chesapeake Bay Program Office,
Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003. Ambient Water Quality Criteria for Dissolved
Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
EPA 903-R-G3-002. Chesapeake Bay Program Office, Annapolis, Maryland.
U.S. Environmental Protection Agency (EPA). 1997. Guidelines for Preparation of the
Comprehensive State Water Quality Assessments (305 [b] Reports) and Electronic Updates.
Assessment and Watershed Protection Division, Office of Wetlands, Oceans and Watersheds,
Office of Water, U.S. EPA, Washington, D.C.
chapter v • Technological Attainability of the Refined Recommended Tidal-Water Designated Uses
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chapte VI
Summary and
Economic Analyses
In developing revised water quality criteria, designated uses and boundaries for those
uses in the Chesapeake Bay and its tidal tributaries, the Chesapeake Bay Program
used tiered scenarios of pollution controls to model water quality responses to
varying levels of technology-based implementation. Although these scenarios do not
represent actual management strategies that will be employed by states in achieving
water quality standards (states are likely to find more cost-effective mixes of controls
for achieving target reductions), the Chesapeake Bay Program partners sought to
provide the public with information on the potential costs and effects associated with
these different levels of effort.
This chapter summarizes three economic analyses that the Chesapeake Bay Program
has performed—estimated costs, screening-level and economic impacts and bene-
fits—which are documented in Economic Analyses Associated with the Identification
of Chesapeake Bay Designated Uses and Attainability (U.S. EPA 2003). In particular,
Part I of the Economic Analyses provides estimates of the total annual cost of
achieving the three levels of controls (the Tier 1 through 3 scenarios presented in
Chapter V) based on the costs of best management practices (BMPs) to remove
nitrogen and phosphorus loads to the Chesapeake Bay. This cost information includes
total capital cost requirements, and to the extent that information could be compiled,
estimates of how these costs may be shared between the public and private sectors.
It is important to note, however, that the Chesapeake Bay Program partners did not
use these economic analyses to show why the current designated uses to protect
aquatic life in the Chesapeake Bay tidal waters are not attainable (Chapter III); to
define the refined designated uses and boundaries presented in Chapter IV; or to
assess attainability of the refined designated uses (Chapter V). Rather, the analyses
are intended to provide information to assist the jurisdictions during their tributary
strategy and water quality standards development processes.
chapter vi • Summary and Economic Analyses
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164
ESTIMATED COSTS
The Chesapeake Bay Program estimated the costs of implementing three levels of
controls captured in the Tier 1 through 3 scenarios. These are just three scenarios in
what could be an infinite number of combinations of reduction actions. The Chesa-
peake Bay Program developed them by layering available reduction technologies
and not by combining the most cost-effective mix of controls. Therefore, the costs
may represent a near-worst case estimate of what will actually be incurred to meet
the dissolved oxygen criteria. Not only are the types and combinations of nutrient
reduction measures artificial, but when nutrient reduction costs will be incurred or
how these reduction measures will be funded also is unknown. The Chesapeake Bay
Program did not estimate costs for the E3 scenario because the reduction measures
in this scenario are not physically plausible in all cases.
Implementation of sediment-related BMPs likely to be necessary to meet the water
clarity criteria for underwater bay grass protection were not included in the tier
scenarios, and thus their costs are not estimated, beyond what is inherently removed
through nutrient reduction measures. Costs to meet the chlorophyll a criteria also are
not included beyond those actions included in the tiers because these were published
as narrative criteria, which provide no single value around which to determine reduc-
tion requirements or costs. In the process of setting the new nutrient and sediment
cap load allocations, the Chesapeake Bay Program partners determined that, for the
most part, reduction actions to meet the dissolved oxygen criteria defined by the tiers
will be sufficient to meet anticipated region-specific numerical chlorophyll a criteria,
except in certain local situations that will require individual state evaluations.
The tier scenarios include controls on publicly-owned treatment works, industrial
facilities, forestry, agriculture, municipal storm water and onsite waste management
systems sources of nitrogen and phosphorus to the Chesapeake Bay. Costs for
publicly-owned treatment works and industrial sources (more than 330 combined
sources) were based on facility-provided estimates and engineering calculations
based on methods developed by the Chesapeake Bay Program's Nutrient Removal
Technology Task Force and documented in Nutrient Reduction Technology> Cost
Estimations for Point Sources in the Chesapeake Bay Watershed (Chesapeake Bay
Program 2003). The Nutrient Removal Technology Task Force generally accepted
estimates provided by facilities 'as is' during the development of point source costs.
Some documentation of the cost estimates, particularly for the largest facilities, is
provided in the appendix to the report. Further review and refinement of these costs
is left to states should they pursue additional economic analyses associated with
revised adoption of water quality standards for the Chesapeake Bay tidal waters.
Costs for urban, agriculture, forestry and onsite system BMPs are based on the units
(e.g., acres) of BMP implementation in each tier scenario and BMP-specific esti-
mates of capital and operation and maintenance costs. The Chesapeake Bay Program
performed an extensive literature search to estimate such costs. To estimate the costs
chapter vi • Summary and Economic Analyses
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165
for the onsite system denitrification BMP, the Chesapeake Bay Program collected
data from manufacturers of such technology. The Chesapeake Bay Program gave
preference to well-documented sources and studies in or near the Chesapeake Bay
watershed and typically used a simple average of the estimated costs from
appropriate sources.
Aside from controls specified in Tier 1 for the District of Columbia, the tier
scenarios do not include controls on combined sewer overflows (CSOs) and sanitary
sewer overflows (SSOs) because these sources are regulated separately, and costs are
associated with the protection of human health parameters such as fecal colifonn
reduction. However, the Chesapeake Bay Program partners recognize that Bay
watershed municipalities required to implement CSO and SSO measures will bear
the burden of the additional cost, and such information will be relevant to the juris-
dictions in assessing the total costs that certain cities may incur. Furthermore, it is
recognized that there must be priority funding decisions to accommodate CSO/SSO
and nutrient removal technology improvements at the federal, state and local levels
of government. The appendices to the separately published Economic Analyses
document (U.S. EPA 2003) include additional information on potential CSO and
SSO costs.
Table VI-1 summarizes the total capital and annual operating and maintenance costs
associated with the tier scenarios. The estimates for each tier are cumulative costs
beyond what has already been expended up to the year 2000 (including already
funded publically-owned treatment works upgrades). The estimates include costs to
businesses and households as well as federal and state governments that provide
funding for nutrient controls through cost-share programs, with existing cost-share
programs alone possibly accounting for almost one-third of annual costs. Total
capital costs represent total initial expenditures to achieve the level of control or
degree of BMP implementation specified for each scenario. However, these costs
will not be incurred in any single year but will be spread across many years though
gradual implementation and financing. Similarly, total annual costs represent those
Table VI-1. Estimated cumulative costs and pollutant loading reductions.
Scenario
Total Nitrogen/Total
Phosphorus Reduction
from Levels in 2000
(millions of pounds per year)1
Total Capital Costs
(in millions of 2001 dollars)2
Total Annual Costs
(in millions of 2001 dollars)3
Tier 1
23.9
$1,442
$198
Tier 2
63.5
$3,644
$555
Tier 3
104.0
$7,975
$1,138
1. Loadings based on Phase 4.3 of the Chesapeake Bay Program's Watershed Model.
2. Costs include those paid by private-sector businesses and households in addition to those paid by public entities
that provide cost-share funding for nutrient reduction controls and BMPs.
3. Total annual costs include amortized capital costs plus operating and maintenance costs.
chapter vi • Summary and Economic Analyses
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166
at fall implementation of the scenarios. Therefore, actual annual costs in the years
prior to meeting the fall implementation goals are expected to be lower.
A number of limitations and uncertainties are associated with the estimated costs.
These considerations are described in detail in the separately published Economic
Analyses document (U.S. EPA 2003). In addition, as noted above, the tier scenarios
are not likely representative of any actual tributary strategy that states will adopt, nor
do they represent the most cost-effective mix of controls possible.
SCREENING-LEVEL IMPACT ANALYSIS
One of the factors that states may consider in evaluating use attainability is whether
controls more stringent than those required by sections 301(b)( 1)(A) and (B) and 306
of the Clean Water Act would result in substantial and widespread economic and
social impacts. The EPA's Interim Economic Guidelines for Water Quality Standards
Workbook (U.S. EPA 1995) provides detailed worksheets and guidance for evalu-
ating whether meeting water quality standards would result in such impacts. Before
embarking on the analysis of widespread impacts, the Chesapeake Bay Program did
not implement this guidance for the tier scenarios because of the tremendous amount
of data and resources required to do so. However, the Chesapeake Bay Program's
UAA Workgroup performed a screening analysis to rule out areas that would not
experience such negative effects. The screening analysis is based on the cost of each
tier, although the tier scenarios likely do not represent the actual control strategies
that will be employed by states, and the Chesapeake Bay Program's estimated costs
of these scenarios are not precise values.
The Chesapeake Bay Program partners decided not to draw conclusions regarding
affordability based on the screening analysis for several reasons. First, the analyses
are screening-level, and do not represent the type required to support a claim of
substantial and widespread economic and social impacts.14 Second, the tier scenarios
do not necessarily reflect a cost-effective mix of controls, which would be necessary
to support a claim of substantial and widespread economic and social impacts.
Finally, as discussed above, the estimated costs do not accurately reflect when costs
will be incurred, or how such reduction measures will be funded. On a regional, state
or large watershed scale, economic impacts can be mitigated by cost-share, loans and
new federal or state funding programs. Therefore, the screening analyses may not
indicate the actual potential for impacts. Analysis of the socioeconomic impacts
associated with meeting water quality standards is best performed during the process
of establishing tributary strategies, with more accurate information on actual reduc-
tion measures and costs within the respective jurisdictions.
14The Economic Analyses Associated with the Identification of Chesapeake Bay Designated Uses and
Attainability (U.S. EPA 2003) provides information for jurisdictions on the types of information and
economic analyses they would need to conduct and submit as part of a UAA.
chapter vi • Summary and Economic Analyses
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167
The screening analysis does provide some comparative information at the county
level throughout the Chesapeake Bay watershed. This analysis consists of 12 county-
level variables or ratios designed to indicate whether either substantial or widespread
economic and social impacts would be likely (Table VI-2). For some sectors, the
ratios indicate when the estimated control costs are small relative to household
incomes and, therefore, substantial impacts are unlikely. For other sectors, the ratios
indicate whether the sector is small relative to the local economy and, therefore,
widespread impacts are unlikely. Because these screening variables cannot indicate
when substantial and widespread impacts would occur, the report also directs states
regarding the types of information and economic analyses that they would need to
conduct and submit to support such a claim.
The screening analysis provides information, in addition to the modeling results
described previously (see "Estimated Costs," above,), related to evaluating whether the
tier scenarios would result in substantial and widespread impacts. Although the
Table VI-2. Screening-level impact analysis variables.
Impact Condition
Sector
Substantial (Financial)
Widespread
POTWs
Current household sewer rate plus average
new household cost/median household income
None
Industrial
None
Percent of county earnings from
industrial sectors containing affected
facilities/total county earnings
Agriculture
• Average BMP costs/net cash return;
• Crop plus portion of hay BMP costs/
crop plus hay sales;
• Livestock plus portion of hay BMP costs/
livestock sales; and
• Average BMP costs/median household income.
Percent of county earnings from
agriculture, agriculture services,
food and kindred products, and
tobacco sectors/total county
earnings
Forestry
None
Percent of county earning from
forestry and logging/total county
earnings
Urban Average
BMP costs/median household income
None
POTWs and urban
Total sewer costs (current plus new) plus average
urban BMP cost/median household income
None
Onsite Treatment
Systems
Average BMP costs/median household income
Percent of households affected in
county
chapter vi • Summary and Economic Analyses
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168
Chesapeake Bay Program partners did not use this information to delineate boundaries
for the designated refined uses, this information may be useful for states as they
conduct their own UAAs. The information may also be valuable for determining where
additional funding, possibly in the form of government cost-shares or loans, would be
most useful, or in determining the most appropriate level of funding assistance.
ECONOMIC IMPACTS AND BENEFITS
As stated previously, when evaluating use attainability, states may consider whether
controls more stringent than those required by sections 301(b)(1)(A) and (B) and 306
of the Clean Water Act would result in substantial and widespread economic and
social impacts. The EPA's National Center for Environmental Economics (NCEE)
offers economic models that can estimate changes in the value of regional output or
goods produced, employment and wages and income, providing information on the
widespread socio-economic effects of pollution controls. Estimating potential
economic benefits also is integral to understanding the economic impacts of
improving water quality in the Chesapeake Bay and its tidal tributaries.
Using economic models allows the evaluation of baseline conditions in the future as
well as the direct and indirect effects of expenditures on pollution controls. Although
the tier scenarios likely do not represent the actual control strategies that will be
employed by states, and the Chesapeake Bay Program's estimated costs of these
scenarios are not precise values, the Chesapeake Bay Program wanted to provide
states with this type of information (such as baseline forecasts and direct and indi-
rect impacts). To provide this information, the NCEE used a regional forecasting
model developed by Regional Economic Modeling, Inc. (REMI), and an economic
impact model (IMPLAN) from the Minnesota IMPLAN Group. The NCEE used
IMPLAN to estimate the socio-economic changes resulting from the estimated
expenditures; the REMI model provides a baseline forecast (for one state) over the
next decades without tier scenario implementation.
The IMPLAN model indicates that the Tier 3 scenario would result in a net increase
in output, employment, and value-added in the six Chesapeake Bay watershed states
and the District of Columbia. In addition, the REMI model forecasts that gross
regional product in the State of Maryland will grow by 37 percent by 2010, corre-
sponding to 19 percent growth in employment and 17 percent growth in real
disposable personal income. This estimated growth is not accounted for in the
IMPLAN results (which are based on current economic conditions). The economic
stimulus from Tier 3 results from increased spending in high-wage industries (e.g.,
wastewater treatment technologies) as well as an influx of funds for pollution
controls (e.g., federal cost shares for agricultural BMPs); additional market benefits
likely to result from improved water quality (e.g., commercial and recreational
fishing industries) are not included. Therefore, the regional economy should expand
as a result of the tier scenarios.
chapter vi • Summary and Economic Analyses
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169
Some members of the Chesapeake Bay Program's UAA Workgroup raised the issue
of other potential social impacts stemming from limits on wastewater treatment
plants, as a result of water quality standards eventually imposed by the jurisdictions.
Their concern is that nutrient allocation caps on wastewater treatment plants will
promote urban sprawl. Most Chesapeake Bay Program partners contend that urban
sprawl is occurring now regardless of the nutrient reduction measures that may ulti-
mately be required, that it will not necessarily be affected by POTW caps and that not
all jurisdictions will be imposing such caps. They further contend that current policies
and growth trends, left unchecked (i.e., the baseline scenario), would result in greater
environmental impacts than the tier scenarios. However, deliberations on this issue
may be valuable on a watershed basis as sprawl is also an interstate issue. The Chesa-
peake Bay Program partners' concerns and deliberations to date also are provided in
the separately published Economic Analyses document referenced above.
Numerous goods and services are associated with the Chesapeake Bay's ecological
resources. Changes in water quality will lead to changes in ecological resources, and
corresponding values of related goods and services. Time and resource constraints
limited the ability of the Chesapeake Bay Program's UAA Workgroup to conduct
original research and estimate comprehensive benefit values. However, the
Economic Analyses document (U.S. EPA 2003) provides a brief summary of the
benefits provided by estuaries such as the Chesapeake Bay and existing studies
related to the value of these services.
The Chesapeake Bay Program expects that changes in water quality will affect many
different aspects of the Bay's ecology (e.g., underwater bay grasses, fish and shell-
fish populations, water clarity and aesthetics), all of which affect how the
Chesapeake Bay community, and society in general, will use and value the Chesa-
peake Bay. For example, ecological benefits will be derived from the increased size
of fish, shellfish and aquatic plant populations and the increased stability (i.e.,
reduced variability) of these populations, and how humans value these improve-
ments. Commercial fishery yields should improve, generating greater potential for
economic returns, and secondary benefits accrue as support industries (e.g., sales and
repair of harvest equipment, fuel) and value-added industry sectors (e.g., processing
and retail facilities) expand in response to increased catch. Both market and
nonmarket benefits should accrue from enhanced recreational opportunities,
including hunting, fishing, boating, ecotourism and photography. For example, the
increased value of recreational angling and support industries (e.g., gear, bait, charter
boats) may be significant, and increased numbers of anglers will generate increased
sales of fuel, lodging, and dining as the quality and number of fishing trips and
opportunities increase.
Although no comprehensive estimate of the benefits from nutrient and sediment
reduction actions in the Chesapeake Bay watershed is available, data suggest that the
Chesapeake Bay affects industries that generate approximately $20 billion and
340,000 jobs (including commercial fishing, boat building and repair and tourism).
Tourism, as a composite industry, represents the 14th largest source of output, and
chapter vi • Summary and Economic Analyses
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170
the 8th largest source of employment, in the Chesapeake Bay watershed. It is not
clear the extent to which each of these sectors relies on Chesapeake Bay water
quality; however, participation rates and expenditures on recreational fishing suggest
that a significant percentage of tourism output is likely linked to the quality of water
bodies such as the Chesapeake Bay For example, the U.S. Fish and Wildlife
Service's 2001 National Survey of Fishing, Hunting and Wildlife-Associated Recre-
ation reports annual expenditures by fishermen of $1,261 million, and 1,859,000
fishing participants, in the states of Maryland, Virginia and Delaware.
Available studies of benefits include Bockstael et al. (1989), which estimate the total
value of 20 percent improvement in nitrogen and phosphorous concentrations in the
Chesapeake Bay to be $17 million to $76 million in 1996 dollars. Similarly, Krup-
nick (1988) estimated the total value of a 40 percent improvement in nitrogen and
phosphorus concentrations at $43 million to $123 million (in 1996 dollars).
LITERATURE CITED
Bockstael, N., K. McConnell and I. Strand. 1989. Measuring the benefits of improvements in
water quality: The Chesapeake Bay. Marine Resource Economics 6:1-18.
Chesapeake Bay Program. 2003. Nutrient Reduction Technology Cost Estimations for Point-
Sources in the Chesapeake Bay Watershed. Chesapeake Bay Program Office, Annapolis,
Maryland.
Krupnick, A. 1988. Reducing bay nutrients: An economic perspective. Maryland Law Review
47(2):453-480.
U.S. Environmental Protection Agency. 2003. Economic Analyses Associated with the Iden-
tification of Chesapeake Bay Designated Uses and Attainability. Chesapeake Bay Program
Office, Annapolis, Maryland.
U.S. EPA. 1995. Interim Economic Guidance for Water Quality Standards, Workbook. Office
of Water, Washington, D.C.
chapter vi • Summary and Economic Analyses
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171
Glossary
Airshed. A geographical region that, due to topography, meteorology and climate,
shares the same air.
Anadromous. Fish that spend most of their lives in salt water but migrate into fresh-
water tributaries to spawn (such as shad and sturgeon).
Anoxia. A condition in which no oxygen is present. Much of the 'anoxic zone' is
anaerobic and contains no oxygen. In this condition toxic hydrogen sulfide gas is
emitted in the decomposition process.
Anthropogenic. Of human origin.
Bathymetry. The physical characteristics—including the depth, contour and
shape—of the bottom of a body of water.
Benthos. A group of organisms, often invertebrates, that live in or on the bottom in
aquatic habitats (such as clams that live in the sediments) and that are typically
immotile or have limited mobility or range.
Biomass. The quantity of living matter, expressed as a concentration or weight per
unit area.
Cap loads. The maximum pollutant load of nutrients and sediments that can be
allowed and still meet water quality criteria.
Chlorophyll a. A pigment contained in plants that converts light energy into food.
Chlorophyll a also gives plants their green color and is used to indicate the amount
of microscopic algae growing in a water body.
Designated use. An element of a water quality standard, expressed as a narrative
statement, describing an appropriate intended human or aquatic life objective for a
body of water. Designated uses for a water body may refer to recreation, shellfishing,
water supply and aquatic life habitat.
Glossary
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172
Dissolved oxygen. Microscopic bubbles of oxygen that are mixed in the water and
occur between water molecules. Dissolved oxygen is necessary for healthy lakes,
rivers, and estuaries. Most aquatic plants and animals need oxygen to survive. Fish
will drown in water when the dissolved oxygen levels become too low. The absence
of dissolved oxygen in water is a sign of possible pollution.
Epifaunal. Plants, animals and bacteria that are attached to the hard bottom or
substrate (for example, to rocks or debris); are capable of movement; or that live on
the sediment surface.
Epiphyte. Algae that grow on the surfaces of plants or other objects. The epiphyte
does not "eat" the plant on which it grows, but merely uses it for structural support
or as a means to enter the canopy environment. By encrusting leaf surfaces, they
reduce the light available to the plant leaves and lead to loss of underwater bay
grasses.
Estuarine species. A permanent resident of an estuary. Also called a resident
species.
Estuary. A semi-enclosed body of water, such as the Chesapeake Bay, that has a free
connection with the open sea and within which seawater from the ocean is diluted
measurably with freshwater derived from land drainage. Brackish estuarine waters
are decreasingly salty in the upstream direction, and vice versa. The ocean tides are
projected upstream to the fall lines.
Eutrophic. A condition of an aquatic system containing high nutrient concentra-
tions, which fuels algal growth. When the algae die off and decompose, the amount
of dissolved oxygen in the water is reduced.
Filter feeders. Organisms that filter food from the environment using a straining
mechanism, such as gills (e.g., barnacles, oysters and menhaden).
Hypoxia. A condition in which only very low levels of oxygen are present.
Light attenuation. The absorption, scattering or reflection of light by water, chloro-
phyll a, dissolved substances or particulate matter. Light attenuation reduces the
amount of light available to underwater bay grasses.
Mean Low Water. The average of all the low water heights observed over the
National Tidal Datum Epoch.
Mesohaline. Pertaining to moderately brackish water with low to middle range
salinities (from 5 to 18 parts per thousand)
Mesotrophic. A condition of an aquatic system containing medium nutrient concen-
trations and, therefore, is between eutrophic (nutrient enriched) and oligotrophic
(nutrient poor) conditions.
Mg liter"1. Concentration unit milligrams per liter.
Glossary
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173
Mixed open. Herbaceous land that is not agricultural.
Nitrogen saturated. A state in which the forest vegetation and soils have reached
their capacity to retain additional nitrogen. This state leads to greater leakage of
nitrogen to sub-surface or ground waters.
Nutrients. Compounds of nitrogen and phosphorus dissolved in water that are
essential to plants and animals. Too much nitrogen and phosphorus act as pollutants
and can lead to unwanted consequences—primarily algae blooms that cloud the
water and rob it of oxygen critical to most forms of aquatic life. Sewage treatment
plants, industries, vehicle exhaust, acid rain and runoff from agricultural, residential
and urban areas are sources of nutrients that enter the Bay.
Oligohaline. Pertaining to moderately brackish water with low range salinities (from
0.5 to 5 parts per thousand).
Percent-light-through-water. The amount of light reaching just above the canopy
of underwater bay grasses, expressed as a fraction of the light at the water surface.
Phosphorus. A key nutrient in the Bay's ecosystem, phosphorus occurs in dissolved
organic and inorganic forms, often attached to particles of sediment. This nutrient is
a vital component in the process of converting sunlight into usable energy forms for
the production of food and fiber. It is also essential to cellular growth and reproduc-
tion for organisms such as phytoplankton and bacteria. Phosphates, the inorganic
form, are preferred, but organisms will use other forms of phosphorus when phos-
phates are unavailable.
Phytoplankton. Microscopic plants, such as algae, that are capable of making food
via photosynthesis. They float and cannot move independent of water currents.
Polyhaline. Pertaining to waters with a higher range of salinities (18 to 30 parts per
thousand).
Ppt. Parts per thousand (used as a measurement of salinity).
Pycnocline. The portion of the water column where density changes rapidly because
of salinity and temperature. In an estuary the pycnocline is the zone separating deep,
more saline waters from the less saline, well-mixed surface layer waters.
Salinity. A measure of the salt concentration of water. Higher salinity means more
dissolved salts. Usually measured in parts per thousand (ppt).
Salinity regimes. A portion of an estuary distinguished by the amount of tidal influ-
ence and salinity of the water. The major salinity regimes are, from least saline to
most saline:
• Tidal fresh—Describes waters with salinity between 0 and 0.5 parts per thou-
sand (ppt). These areas are at the extreme reach of tidal influence.
Glossary
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174
• Oligohaline—Describes waters with salinity between 0.5 and 5 ppt. These
areas are typically in the upper portion of an estuary.
• Mesohaline—Describes waters with salinity between 5 and 18 ppt. These areas
are typically in the middle portion of an estuary.
• Polyhaline—Describes waters with salinity between 18 and 30 ppt. These areas
are typically in the lower portion of an estuary, where the ocean and estuary
meet.
Saturation. The state of a compound or solution that is fully saturated. For example,
a condition in which water at a specific temperature contains all the dissolved
oxygen it can hold. Dissolved oxygen percent saturation is an important measure-
ment of water quality. Cold water can hold more dissolved oxygen than warm water.
Also, high levels of bacteria from sewage pollution or large amounts of decomposing
plants can cause the percent saturation to decrease. This can cause large fluctuations
in dissolved oxygen levels throughout the day, which can affect the ability of plants
and animals to thrive.
Secchi depth. A measure of cloudiness or turbidity of surface water determined by
the depth at which the 'Secchi disk,' a flat black and white disk, cannot be seen any
more. It is the greatest depth to which light can penetrate underwater.
Seiching. Formation of standing waves in a water body due to wave formation and
subsequent reflections from the ends. These waves may be incited by earthquake
motions (similar to the motions caused by shaking a glass of water), impulsive winds
over the surface, or due to wave motions entering the basin. In the Chesapeake Bay,
sustained winds force bottom water onto the shallows through this physical process.
Sill. A submerged ridge at relatively shallow depth separating the basins of two
bodies of water.
Stratification. The formation, accumulation or deposition of materials in layers,
such as layers of fresh water overlying higher salinity water (salt water) in estuaries.
Submerged Aquatic Vegetation (SAV). Rooted vegetation that grows under water
in shallow zones where light penetrates. Also known as 'underwater bay grasses.'
Subpycnocline. Bottom mixed layer waters located below the pycnocline layer (see
definition for 'pycnocline').
Surficial. Of, relating to, or occurring on or near the surface of the sediment bottom.
Thermocline. A specific depth where the water temperature changes dramatically.
Warmer surface water is separated from the cooler deep water. This temperature
gradient results in the formation of a density barrier.
Total Suspended Solids (TSS). Solids in water that can be trapped by a filter
(usually with a pore size greater than 0.45 micrometer). TSS can include a wide
Glossary
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175
variety of material, such as silt, decaying plant and animal matter, industrial wastes
and sewage. High concentrations of suspended solids can cause many problems for
Chesapeake Bay health and aquatic life. For example, high TSS can block light from
reaching underwater bay grasses, increase surface water temperature, because the
suspended particles absorb heat from sunlight, and affect the ability of fish to see and
catch food.
Trophic level. Layer in the food chain in which one group of organisms serves as
the source of nutrition of another group of animals.
Turbidity. The decreased clarity in a body of water due to the suspension of silt or
sedimentary material.
Underwater bay grass. Submerged vascular plants often referenced in the scientific
literature as submerged aquatic vegetation or SAV, not to be confused with emergent
wetland plants.
Water clarity. Measurement of how far you can see through the water. The greater
the water clarity, the further you can see through the water.
Water column. The open-water environment, as distinct from the bed or shore,
which may be inhabited by swimming marine, estuarine or freshwater organisms.
Water-column light requirement. The amount of light just above the leaf surface
(estimated as the fraction of the light at the water surface) that is necessary for the
survival and growth of underwater bay grasses.
Water quality criteria. Numeric or narrative description of a water quality param-
eter that represent a quality of water that supports a particular designated use.
Adopted by states, along with designated uses, into water quality standards.
Water quality standards. A provision of State or Federal law consisting of a desig-
nated use or uses for a water body and a narrative or quantifiable criterion protective
of the use(s) describing the desired conditions of the subject waters or water body to
which they apply.
Watershed. A region bounded at the periphery by physical barriers that cause water
to part and ultimately drain to a particular body of water.
Young-of-the-year. All of the fish of a species younger than one year of age. Usually
scientists assign an arbitrary 'birth date' to all fish of a species hatched over a two or
three month period in one year. The fish are then assigned to Age 1 status on that
birth date. By convention, this is usually January 1.
Zooplankton. A community of floating, often microscopic animals that inhabit
aquatic environments. Unlike phytoplankton, zooplankton cannot produce their own
food, and so are consumers.
Glossary
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177
Acronyms
BMP
best management practice
mg/1
milligrams per liter
CAA
Clean Air Act
mniBtu
million British thermal unit
CFD
cumulative frequency
Nox
nitrogen oxides
distribution
nutrient reduction technology
NRT
CSO
combined sewer overflow
POTW
publically-owned treatment
CWA
Clean Water Act
works
E3
everything, everywhere
SAV
submerged aquatic vegetation
by everybody
SED
sediment
EPA
U.S. Environmental
Protection Agency
SIP
state implementation plan
ESD
environmental site design
so2
sulfur dioxide
km2
kilometers squared
TN
total nitrogen
lbs
pounds
TP
total phosphorus
LID
low impact development
TSS
total suspended solid
m
meter
Mg/1
micrograms per liter
MGD
million gallons per day
Acronyms
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append ix^
Development of the
Level-of-Effort Scenarios
Listed in this appendix are the assumptions and methods employed in determining
four best management BMP (including point source technologies) implementation
levels for the three tiers and 'everything, everywhere, by everybody' (E3) scenarios.
The scenarios were developed by the Chesapeake Bay Program's Nutrient Subcom-
mittee Workgroups to provide reference points for load reductions of nutrients and
sediment that could be associated with increasing levels of BMP implementation for
both point and nonpoint sources in the Chesapeake Bay watershed. The Use Attain-
ability Analysis (UAA) workgroup was provided with examples of the types of
BMPs and implementation levels to develop a defensible costing tool. These four
scenarios range from Tier 1, which represents the current level of implementation
throughout the watershed plus regulatory requirements implemented through the
year 2010, up to a limit of technology scenario referred to as the E3 scenario. Tier 2
and Tier 3 represent intermediate levels of implementation between Tier 1 and the
E3 scenario. Each tier has associated with it a given nitrogen, phosphorus and sedi-
ment load reduction effected by the different technologies assigned to the tier. The
nutrient and sediment sources were divided into the following categories for tier
development:
• point sources;
• nonpoint source agriculture;
• nonpoint source urban;
• nonpoint source forests;
• onsite treatment systems; and
• atmospheric deposition.
The Chesapeake Bay Program partners have acknowledged that the E3 scenario goes
beyond what is physically possible in some cases, and that the feasibility of imple-
menting certain reduction measures at Tier 3 are also questionable. These tiers are a
broad brush estimate of technological reduction measures that could be implemented
appendix A • Development of the Level-of-Effort Scenarios
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A2
at the bay watershed level without regard to physical limitations. Certainly there will
be local circumstances and conditions that make implementation of these tiers as
defined unreasonable. It will be up to the individual jurisdictions to tailor reduction
programs that fit their specific capabilities and needs. The series of ranging scenarios
were simulated using the Chesapeake Bay Program's Phase 4.3 Watershed Model,
and the resultant loads for nitrogen, phosphorus, and sediment were used as inputs
to the Chesapeake Bay Water Quality Model. Evaluation of dissolved oxygen, water
clarity and chlorophyll a concentrations from the Water Quality Model, in turn,
provided a sense of the response of key water quality parameters to the various
loading levels. For the tiered and the E3 scenario scenarios, the BMP implementa-
tion levels, the resultant modeled loads, and the measured responses in tidal water
quality are all informational. They are not intended to prescribe control measures the
jurisdictions must implement to meet Chesapeake 2000 nutrient and sediment cap
load allocations.
All above and below fall line nitrogen, phosphorus, and sediment loads are included
in the loadings for each tier. Shoreline erosion control sediment reductions at 2000
progress levels are assumed for all tiers.
The costs for specific management practices developed by the UAA Workgroup
could be used by Chesapeake Bay basin jurisdictions for their individual UAAs. The
Water Quality Steering Committee of the Chesapeake Bay Program believed it
would be useful to provide data to the jurisdictions to promote coordination and
consistency across all jurisdictions. It is a jurisdiction's prerogative to use the basin-
wide cost analyses in developing its individual UAA.
Implementation levels in all of the tiers and the E3 scenario are not the most cost
effective. More cost-effective combinations of BMPs will be evaluated by jurisdic-
tions and their tributary strategy watershed teams as their strategies are developed.
In addition, levels of BMP implementation for the E3 scenario are theoretical since,
generally, the scenario does not account for physical limitations or participation
levels in its design.
The tier and the E3 scenario BMP implementation levels were mostly deliberated
and set by the 'source' workgroups of the Chesapeake Bay Program's Nutrient
Subcommittee. These workgroups are made up of representatives of Chesapeake
Bay watershed jurisdictions and Chesapeake Bay Program Office personnel. The
specific workgroups that decided BMP implementation levels include the Agricul-
tural Nutrient Reduction Workgroup, the Forestry Workgroup, the Point Source
Workgroup, and the Urban Storm Water Workgroup. The Tributary Strategy Work-
group and Nutrient Subcommittee finalized the E3 scenario definitions after review
and further deliberation.
To conform to Chesapeake 2000 goals, all of the scenarios were based on 2010
projections of landuses, animals, point source flows, and septic systems as well as
2007/2010 or 2020 air emission controls. Landuses and animal populations in the
appendix A • Development of the Level-of-Effort Scenarios
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A3
Chesapeake Bay Program Watershed Model are developed from an array of national,
regional, and state databases as described in Chesapeake Bay Watershed Model Land
Use and Model Linkages to the Airshed and Estuarine Models (Chesapeake Bay
Program, 2000). The modeled landuses include the following categories:
• forest;
• conventional-tilled (high-till);
• conservation-tilled (low-till);
• hay;
• pasture;
• manure acres (model accounting of runoff from animal feeding operations);
• pervious urban;
• impervious urban; and
• mixed open.
The 2010 agricultural landuses were projected from 1982, 1987, 1992, and 1997
Agricultural Census information by county according to methods chosen by indi-
vidual states. Projected animal populations, to estimate manure applications, were
based on county Agricultural Census trends and information from state environ-
mental and agricultural agencies.
Implementation of Low Impact Development (LID) or Environmental Site Design
(ESD) in the tiered scenarios was used to reflect urban pollutant load reductions that
go above and beyond conventional storm water management practices. The tiered
scenarios reflect an ongoing shift from conventional storm water management to the
more innovative LID/ESD practices that address both storm water quantity (repli-
cating pre-development hydrology) and quality (reducing pollutant loads). The
LID/ESD approach encourages practices that promote groundwater recharge, stream
channel protection, flood protection, and improved water quality. The pollutant
removal efficiencies for LID/ESD were developed by the Urban Storm Water Work-
group, based on national and watershed studies and expert professional judgement.
The workgroup evaluated pollutant removal efficiencies for over 50 best manage-
ment practices from sources such as the American Society of Civil Engineers Best
Management Practices national database, the Center for Watershed Protection's
National Pollutant Removal Performance Database for Stonnwater Treatment Prac-
tices, the 2000 Maryland Stonnwater Design Manual, the Virginia Stonnwater
Handbook, and Prince George's County's Low Impact Development Design Strate-
gies manual. Maintenance costs of ESD/LID approaches were based on data
primarily from Maryland (which promotes ESD) and Prince George's County
(which promotes LID). There are several jurisdictions that are actively promoting
ESD (Maryland state stonn water regulations) and LID (Prince George's County,
District of Columbia, various municipalities in Virginia).
appendix A • Development of the Level-of-Effort Scenarios
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A4
The 2010 urban landuses were mostly projected from methods involving human
population changes as determined by the U.S. Census Bureau for 1990 and 2000,
and by individual state agencies for 2010. The population changes were related to
1990 high-resolution satellite imagery of the Chesapeake Bay watershed, which is
the primary source of urban and forest acreages. In the case of Maryland, urban
growth from 2000 to 2010 was determined by Maryland Department of Natural
Resources and the Maryland Department of Planning.
For all jurisdictions except Maryland and Virginia, 2010 forest and mixed open
landuses were determined by proportioning the net change between 2010 and 1990
agricultural and urban land to 1990 mixed open and 1990 forest. Maryland and
Virginia forest acreage changes followed methodologies or data submitted by these
states.
Each agricultural BMP in the tier scenarios is associated with research that identifies
the expected level of nutrient reduction. In many cases this could be viewed as the
best reduction one can expect from a BMP given optimal growing conditions and
expected annual maintenance. However, the yield reserve BMP is slightly different.
This BMP is not based solely on hydrologic conditions, but includes the known
response of a particular crop to nutrient availability. There is an additional amount or
cushion within universally recommended nutrient application rates to insure optimal
yield under ideal growing conditions. Real world observations have shown that
optimal growing conditions occur infrequently, and 'average' hydrologic conditions
may result in substantially less than optimal yield. By combining this management
practice with an insurance plan to protect against yield loss in suboptimal growth
years, potential nitrogen leaching and phosphorus runoff are reduced while providing
plant nutrient requirements seven or eight years out of every ten. The insurance
program protects producers in those two to three years of yield loss. Since this is the
reduction of a direct input based on plant response curves and not an estimate of
nutrient reduction efficiency, the potential benefits from a yield reserve program can
be fully modeled. Since yield is a function of rainfall and nutrient availability, the
benefits of this type of program can be seen best in years with less than average rain-
fall when yields drop, yet spring application rates were high.
Estimates of the number of septic systems in the watershed in 2010 were derived
from human population projections and people per septic system ratios from the
1990 U.S. Census Bureau survey.
Point sources were divided into categories which include 1) significant municipal
wastewater treatment facilities—generally discharging flows greater than or equal to
0.5 million gallon per day, 2) significant industrial facilities—discharging nutrient
loads of greater than or equivalent to municipal facilities with flows greater than or
equal to 0.5 million gallon per day, and 3) non-significant municipal wastewater
treatment facilities—discharging flows less than 0.5 million gallon per day, and
limited to facilities in Maryland and Virginia due to availability of data.
appendix A • Development of the Level-of-Effort Scenarios
-------
A5
Point source nitrogen and phosphorus loads from significant and non-significant
municipal wastewater treatment facilities were determined using flows projected for
the year 2010 for POTWs located in all jurisdictions of the Chesapeake Bay Water-
shed. These future flows were developed either from population projections or
information obtained directly from the municipal facility operators. The tier and E3
scenario flows for industrial dischargers remained at 2000 levels because industrial
flows are not necessarily subject to growth due to population.
Technologies in municipal facilities varied among the tiers depending on the nutrient
concentrations to be achieved under each tier description. The technologies include
extended aeration processes and denitrification zones, chemical additions, additional
clarification tanks, deep bed denitrification filters, and micro-filtration. For industrial
dischargers, site-specific information on reductions by facility was obtained via
phone contacts or site visits.
Estimation of atmospheric deposition to the Chesapeake Bay watershed for all tier
and E3 scenarios employed deposition data from the Regional Acid Deposition
Model (RADM) which also provides deposition estimates representing current
conditions used for 2000 Progress model runs. All of the air scenarios involve
nitrogen oxide emissions reductions made by roughly 37 states (the deposition
modeling domain). Air scenarios in Tiers 1 and 2 describe existing Clean Air Act
regulations that have passed; the Tier 3 and E3 air scenarios describe additional
voluntary control measures.
Table A-l provides a brief overview of the reduction measures in the tiers organized
by nutrient source. Table A-2 shows the implementation levels of the BMPs in the
tier scenarios in terms of landuse acres, or their appropriate unit of measurement
(Figures A-l through A-3). The text that follows provides a more detailed overview
of the reduction measures per source, organized by tier scenario.
In the listing of BMP levels in Table A-2, there are cases where implementation
levels may be lower in a higher tier, or may be lower for the 2010 scenarios, when
compared to 2000 Progress. It is important to note that landuses change from 2000
to 2010 and that these changes were based on trends specified by individual jurisdic-
tions with concurrence from the Chesapeake Bay Program Nutrient Subcommittee's
Tributary Strategy Workgroup. Also, landuses change through the 2010 tiers and the
E3 scenario depending on degrees of BMP implementation (i.e., riparian buffers,
wetland restoration, land retirement, carbon sequestration for agricultural land). In
other words, as landuses change, less land may be available to apply BMPs in a
higher level-of-effort scenario. Overall however, nutrient and sediment reductions
will increase through the tiers to the E3 scenario as the combined impact of nonpoint
source BMPs increases. Note that riparian buffer information is presented both in
terms of acres and 1-side stream miles.
appendix A • Development of the Level-of-Effort Scenarios
-------
A6
Table A-1. Description of the source reduction measures by tier scenario.
Nutrient
Reduction
Activity
Tier 1
Tier 2
Tier 3
E3
CROPLAND CONVERSIONS TO FOREST HAYLAND
Buffers—
pasture to forest
Continue current
level of
implementation
using average rate
of 1997-2000.
Note: Includes
fencing
Increase level of
implementation up
to a total of 20% of
the remaining
stream reaches in
pasture. Note:
Includes fencing
Increase level of
implementation up
to a total of 30% of
the remaining
stream reaches in
pasture. Note:
Includes fencing
Both sides of all
stream reaches
within pasture
receive 100 foot
forest buffers and
fencing.
Buffers—
cropland to forest
Continue current
level of
implementation
using average rate
of 1997-2000.
Increase level of
implementation up
to a total of 20% of
the remaining
stream reaches in
cropland.
Increase level of
implementation up
to a total of 30% of
the remaining
stream reaches in
cropland.
Both sides of all
stream reaches
within cropland
receive forest
buffers.
Buffers—
cropland to grass
Continue current
level of
implementation
using average rate
of 1997-2000.
25% of remaining
stream reaches
within cropland.
50% of remaining
stream reaches
within cropland.
Buffers—
hayland to forest
Continue current
level of
implementation
using average rate
of 1997-2000.
25% of remaining
stream reaches
within hayland over
Tier 1.
50% of remaining
stream reaches
within hayland over
Tier 1.
Both sides of all
stream reaches
within hayland
receive forest
buffers.
Wetland Reserve
(cropland to forest)
Continue current
level of
implementation
using average rate
of 1997-2000.
Increase level of
implementation up
to a total of 33% of
the remaining goal.
Increase level of
implementation up
to a total of 66% of
the remaining goal.
Wetland Reserve
equals 25,000 acres
in signatory
states (based on
Chesapeake 2000
goal).
CRP/CREP
(cropland to
mixed open)
Continue current
level of
implementation
using average rate
of 1997-2000.
CRP-CREP-
Wetland Reserve-
buffers (combined)
comprise 10% of
cropland within
each county.
CRP-CREP-
Wetland Reserve-
buffers (combined)
comprise 15% of
cropland within
each county.
CRP-CREP-
Wetland Reserve
buffers (combined)
comprise 25% of
cropland within
each county.
continued
appendix A • Development of the Level-of-Effort Scenarios
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A7
Table A-1. Description of the source reduction measures by tier scenario (cont.).
Nutrient
Reduction
Activity
Tier 1
Tier 2
Tier 3
E3
Carbon
Sequestration &
Bioenergy
Applied to 15% of
remaining the E3
scenario cropland
after land
conversion
programs applied.
Applied to 25% of
remaining cropland
after land
conversion
programs applied.
I AGRICULTURE NPS
Conservation
Tillage
Continue current
level of
implementation
using average rate
of 1997-2000.
Applied to 30% of
remaining cropland
beyond Tier 1.
Applied to 60% of
remaining cropland
beyond Tier 1.
Conservation
tillage on 100% of
cropland.
Farm Plans
Continue current
level of
implementation
using average rate
of 1997-2000.
Applied to 30% of
remaining
agricultural land
(crop, hay, pasture)
beyond Tier 1.
Applied to 70% of
remaining
agricultural land
(crop, hay, pasture)
beyond Tier 1.
Applied to 100% of
agricultural land
(crop, hay, pasture).
Cover Crops
Continue current
level of
implementation
using average rate
of 1997-2000.
Applied to 40% of
remaining cropland
beyond Tier 1.
Applied to 75% of
remaining cropland
beyond Tier 1.
Applied to 100% of
cropland
Nutrient
Management
Planning
MD & DE: 100%
cropland and
hayland under
nutrient
management. Other
basin states:
Continue current
level of
implementation
using average rate
of 1997-2000.
MD & DE: 100%
cropland and
hayland under
nutrient
management. Other
basin states:
Applied to 30% of
remaining cropland
and hayland
beyond Tier 1.
MD & DE: 100%
cropland and
hayland under
nutrient
management. Other
basin states:
Applied to 30% of
remaining cropland
and hayland
beyond Tier 2.
Applied to 100% of
cropland and
hayland.
Yield Reserve
Applied to 30% of
the cropland and
hayland under
nutrient manage-
ment. Replaces
nutrient application
component of
nutrient
management plan.
Applied to 100% of
cropland and
hayland. Replaces
nutrient application
component of
nutrient
management plan.
continued
appendix A • Development of the Level-of-Effort Scenarios
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A8
Table A-1. Description of the source reduction measures by tier scenario (cont.).
Nutrient
Reduction
Activity
Tier 1
Tier 2
Tier 3
E3
AGRICULTURE NPS (cont.) 1
Excess Nutrients
Assume alternative
use for excess
manure.
Assume alternative
use for excess
manure.
Assume alternative
use for excess
manure.
Assume alternative
use for excess
manure.
Agriculture Waste
Systems
Continue current
level of
implementation
using average rate
of 1997-2000.
Applied to 25% of
remaining confined
animal units
beyond Tier 1
(combines storage
system and
barnyard runoff
controls).
Applied to 60% of
remaining confined
animal units
beyond Tier 1
(combines storage
system and
barnyard runoff
controls).
Applied to 100% of
confined animal
units (combines
storage system and
barnyard runoff
controls).
Stream Protection
without fencing
Continue current
level of
implementation
using average rate
of 1997-2000.
Applied to 10% of
remaining stream
reaches within
pasture land
beyond Tier 1.
Applied to 25% of
remaining stream
reaches within
pasture land
beyond Tier 1.
N/A (see buffers-
forest-pasture)
Stream Protection
with fencing
Continue current
level of
implementation
using average rate
of 1997-2000.
Applied to 15% of
remaining stream
reaches within
pasture land
beyond Tier 1.
Applied to 75% of
remaining stream
reaches within
pasture land
beyond Tier 1.
N/A (see buffers-
forest-pasture)
Grazing Land
Protection
Continue current
level of
implementation
using average rate
of 1997-2000.
Applied to 25% of
remaining pasture
land beyond Tier 1.
Applied to 50% of
remaining pasture
land beyond Tier 1.
Applied to 100% of
pasture land.
1 URBAN NPS
Urban Land
Conversion (PA,
MD, VA and DC
only)
Full 2000-2010
urban land
conversion based
on 2010
population.
2000-2010 urban
conversion -
reduced 10% (acres
'returned' as 65%
forest, 20% mixed
open, 15%
agriculture).
2000-2010 urban
conversion -
reduced 20% (acres
'returned' as 65%
forest, 20% mixed
open, 15%
agriculture).
2000-2010 urban
conversion -
reduced 30% (acres
'returned' as 100%
forest).
continued
appendix A • Development of the Level-of-Effort Scenarios
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A9
Table A-1. Description of the source reduction measures by tier scenario (cont.).
Nutrient
Reduction
Activity
Tier 1
Tier 2
Tier 3
E3
Storm water
66% of new
75% of new
50% of new
100% of new
management &
development has
development has
development has
development
LID—New
storm water
storm water man-
storm water man-
employs
Development
management.
agement. 25% of
agement. 50% of
environmental site
(2001-2010)
(TN=35, TP=45,
new development
new development
design and low-
TSS=80)
employs environ-
employs environ-
impact develop-
mental site design
mental site design
ment techniques
and low-impact
and low-impact
(TN=50, TP=60,
development tech-
development tech-
TSS=90).
niques. Efficiencies
niques. Efficiencies
represent a
represent a
75%/25% weighted
50%/50% weighted
average reduction.
average reduction.
(TN=40, TP=55,
(TN=45, TP=57,
TSS=85)
TSS=87)
Stormwater
60% of recent
60% of recent
60% of recent
management—
development has
development has
development has
Recent
storm water
storm water
storm water
Development
management.
management.
management.
(1986-2000)
(TN=27,
(TN=27,
(TN=27,
TP=40,TSS=65)
TP=40,TSS=65)
TP=40,TSS=65)
Retrofits—Recent
0.8% of recent and
5% of recent and
20% of recent and
100% of recent and
(1986-2000) & Old
old (pre-1986)
old (pre-1986)
old (pre-1986)
old (pre-1986)
(pre 1986)
development is
development is
development is
development is
Development
retrofitted (TN=20,
retrofitted (TN=20,
retrofitted (TN=20,
retrofitted (TN=40,
TP=30,TSS=65)
TP=30,TSS=65)
TP=30,TSS=65)
TP=40, TSS=80).
Urban Nutrient
Continue to
40% of urban
75% of urban
No fertilizer is
Management
implement BMP at
pervious and mixed
pervious and mixed
applied to urban
average annual rate
open lands are
open lands are
pervious or mixed
through 2010,
under nutrient
under nutrient
open land.
using average of
management.
management.
1997-2000.
(TN=17%,
(TN=17%,
(TN=17%,
TP=22%)
TP=22%)
TP=22%)
Buffers—
All urban stream
Reduce grass
Reduce grass
Grass (existing)
reaches are assumed
buffers by 10%
buffers by 30%
to have either grass
below Tier 1 level.
below Tier 1 level.
or tree buffers.
(conversion to
(conversion to
Where urban
forest buffers)
forest buffers)
disturbance has
altered a stream
reach beyond
repair/restoration, it
is not included as a
potential buffer area.
continued
appendix A • Development of the Level-of-Effort Scenarios
-------
A10
Table A-1. Description of the source reduction measures by tier scenario (cont.).
Nutrient
Reduction
Activity
Tier 1
Tier 2
Tier 3
E3
URBAN NPS (cont.) 1
Buffers—
Grass to Forest
Increase forest
buffer acreage by
the same amount of
'reduced' grass
buffer acreage.
Increase forest
buffer acreage by
the same amount of
'reduced' grass
buffer acreage.
50-foot forest
buffer on both sides
of stream reaches
in urban pervious
areas. No credit
given on upstream
effects, land
conservation only.
Buffers—
Mixed Open
to Forest
Continue current
level of implemen-
tation using
average rate of
1997-2000.
Increase forest
buffer acreage by
the same amount as
forest buffers on
urban pervious.
Increase forest
buffer acreage by
the same amount as
forest buffers on
urban pervious.
100-foot forest
buffer on mixed
open. No credit
given on upstream
effects, land
conservation only.
1 ONSITE TREATMENT SYSTEMS
New Systems
(post-2000)
Maintain current
concentration/load
per system.
10% of new
treatment systems
will meet an edge
of drainage field
concentration for
nitrogen of 10
mg/L TN per
system. Remaining
systems meet
existing concen-
tration/load levels.
100% of new
treatment systems
will meet an edge
of drainage field
concentration for
nitrogen of
10 mg/L TN
per system.
100% of new
treatment systems
will meet an edge
of drainage field
concentration of
nitrogen of
10 mg/L TN
per system.
Existing Systems
(pre-2001)
Maintain current
concentration/load
per system.
Maintain current
concentration/load
per system.
1% of existing (per
year) treatment
systems will meet
an edge of drainage
field concentration
for nitrogen of
10 mg/L TN per
system. (1%
100% of existing
treatment systems
will meet an edge
of drainage field
concentration of
nitrogen of
10 mg/L TN
per system.
represents failed
systems and
opportunities for
upgrades.) Re-
maining systems
maintain existing
concentrations/
loads.
continued
appendix A • Development of the Level-of-Effort Scenarios
-------
A11
Table A-1. Description of the source reduction measures by tier scenario (cont.).
Nutrient
Reduction
Activity
Tier 1
Tier 2
Tier 3
E3
I POINT SOURCES I
Municipal
Existing NRT and
Reach and maintain
Reach and maintain
Reach and maintain
Wastewater
those planned to go
8.0 mg/1 TN and
5.0 mg/1 TN and
3.0 mg/1 TN and
Treatment
to NRT by 2010:
1.0 mg/1 TP
0.5 mg/1 TP
0.10 mg/1 TP
(Significant
2010 flow at 8.0
concentrations at
concentrations at
concentrations at
Facilities as of
mg/1 TN and 2000
2010 flows at all
2010 flows at all
2010 flows at all
2000)
concentrations for
facilities.
facilities.
facilities.
TR For all
(Phosphorus
(Phosphorus
(Phosphorus
remaining facilities
concentration is 1.0
concentration is 0.5
concentration is 0.1
without NRT ex-
mg/1 or permit
mg/1 or permit
mg/1 or permit
isting or planned:
limit, whichever is
limit, whichever is
limit, whichever is
2000 TN & TR For
lower).
lower.)
lower).
certain VA facilities
in lower VA tribu-
taries TP=1.5 mg/1
Industrial
Maintain current
Generally a 50%
Generally an 80%
II
jo
Wastewater
levels.
reduction from
reduction from
TP = 0.1 or
Treatment
Tier 1 (2000
Tier 1 (2000
permit conditions
(Significant
concentrations)
concentrations)
if less.
Facilities as
or permit
or permit
of 2000)
conditions if less.
conditions if less.
Municipal
Maintain current
Maintain current
Maintain current
Maintain 8.0 mg/L
Wastewater
TN/TP
TN/TP
TN/TP
nitrogen and 2.0
Treatment (Non-
concentrations with
concentrations with
concentrations with
mg/L phosphorus
significant
2010 flows.
2010 flows.
2010 flows.
concentrations or
Facilities as of
2000 concentra-
2000)
tions if less with
2010 flows.
C-SO Control (DC)
43% reduction in
43% reduction in
43% reduction in
Zero discharge
CSOs.
CSOs.
CSOs.
from DC CSOs.
continued
appendix A • Development of the Level-of-Effort Scenarios
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A12
Table A-1. Description of the source reduction measures by tier scenario (cont.).
Nutrient
Reduction
Activity Tier 1 Tier 2 Tier 3 E3
FOREST NPS
Forest Harvest
BMPs
Forestry BMPs are
properly installed
on 80% of all
harvested lands.
Forestry BMPs are
properly installed
on 90% of all
harvested lands.
Forestry BMPs are
properly installed
on 100% of all
harvested lands
with no measurable
increase in nutrient
and sediment
discharge.
Forestry BMPs are
properly installed
on 100% of all
harvested lands
with no measurable
increase in nutrient
and sediment
discharge.
Air Controls (NOx
only)
2007/2010 Base
with NOx SIP.
AIR EMISSIONS
2020 CAA with
Tier 2 and heavy
duty diesel
regulations.
2020 CAA with
aggressive utility
controls.
2020 CAA
aggressive utility
controls and
industry-point and
mobile controls.
appendix A • Development of the Level-of-Effort Scenarios
-------
A13
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-------
A15
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appendix A • Development of the Level-of-Effort Scenarios
-------
A16
2010 TIER 1 SCENARIO
2010 Tier 1 BMP implementation levels were generally determined by continuing
current levels-of-effort and cost-share in the Chesapeake Bay watershed. In addition,
expected regulatory measures, jurisdictional programs, and construction schedules
between 2000 and 2010 were included.
2010 TIER 1 SCENARIO NONPOINT SOURCE BMPs
For most nonpoint source BMPs, implementation rates between 1997 and 2000 were
continued to the year 2010 with limits that levels could not exceed the available or
the E3 scenario land area to which BMPs levels could be applied. The scale of the
calculations was a county segment, or the intersection of a county political boundary
and a model hydrologic segment. This is the same scale on which most jurisdictions
report BMP implementation levels to the Chesapeake Bay Program Office.
Every effort was made to include BMPs submitted by the jurisdictions for progress
model runs into Tier 1. Since historic BMP data were not available from New York
Delaware, and West Virginia, 2010 Tier 1 projections were determined from watershed-
wide implementation rates in the states which employ and track the practice.
2010 Tier 1 BMPs were extrapolated from recent implementation rates by the
landuse types submitted by the states for each BMP. For example, if a jurisdiction
submits data for nutrient management on crop, 2010 Tier 1 crop was projected and
then split among high-till, low-till, and hay according to relative percentages. If a
jurisdiction submits data as nutrient management on high-till, low-till, and hay indi-
vidually, projections were done for each of these landuse categories.
The 2010 Tier 1 scenario does not include tree planting on tilled land, forest conser-
vation, and forest harvesting practices as these BMPs are not part of the tier and E3
scenarios. For forest harvesting practices and erosion and sediment control, the
model simulation does not account for additional loads from disturbed forest and
construction areas, respectively. For forest conservation, planting above what is
removed during development is accounted for in the 2010 urban and forest projec-
tions. Tree planting on agricultural land was included in Tier 1 for pasture as forest
buffers since this BMP is also part of the tier and E3 scenarios and pasture tree
planting and pasture buffers are treated the same in the model.
2010 TIER 1 SCENARIO AGRICULTURAL BMPs
• Tier 1 Conservation tillage
-Continue 1997-2000 implementation rates of conservation-tillage.
-Low-till acres cannot be below 2000 levels or greater than 75 percent of the
available cropland by county-segment.
-Landuse conversion of high-till to low-till.
appendix A • Development of the Level-of-Effort Scenarios
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• Tier 1 Riparian forest buffers on agriculture
-Continue 1997-2000 implementation rates of riparian forest buffers on cropland
and hay to the year 2010.
-Continue 1997-2000 implementation rates of tree planting on pasture to the year
2010.
-Tier 1 implementation levels cannot exceed the available or E3 scenario land
area to which BMPs could be applied.
-The E3 scenario assumes 100-foot forest buffers on un-buffered stream miles
(each side) associated with crop, hay and pasture.
-Landuse conversion of crop, hay, and pasture to forest.
-For every acre of crop and hay converted, two upland acres of crop and hay
receive a reduction of 57 percent (TN), 70 percent (TP), and 70 percent (SED).
-There is no upland benefit associated with forest buffers on pasture.
• Tier 1 Wetland restoration
-Continue 1997-2000 implementation rates of wetland restoration on cropland
and hay to the year 2010.
-Landuse conversion of crop and hay to forest.
• Tier 1 Agricultural land retirement
-Continue 1997-2000 implementation rates of cropland and hay retirement to the
year 2010.
-The sum of the acreage in Tier 1 riparian forest buffers, wetland restoration, and
land retirement cannot exceed 25 percent of the total crop and hay in a county-
segment.
-Landuse conversions of crop and hay to mixed open.
• Tier 1 Riparian grass buffers on cropland
-Continue 1997-2000 implementation rates of riparian grass buffers on cropland
to the year 2010 with limits that levels cannot exceed the available or the E3
scenario land area to apply the BMPs to.
-The E3 scenario levels are revised following the same methodologies but
account for previously applied BMPs that involve landuse changes.
-The E3 scenario assumes 100-foot buffers on un-buffered stream miles (each
side) associated with agricultural land.
-Landuse conversions of crop to mixed open.
-For every acre of cropland converted, two upland acres of crop receive a reduc-
tion of 43 percent (TN), 53 percent (TP), and 53 percent (SED).
appendix A • Development of the Level-of-Effort Scenarios
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• Tier 1 Nutrient Management Plan Implementation
-Continue 1997-2000 rates of nutrient management plan implementation on crop
and hay to the year 2010 in all jurisdictions except MD and DE where all crop
and hay acres are fully implementing nutrient management plans.
-Nutrient management plan implementation levels cannot exceed the available
land area to apply the BMPs to.
-Under nutrient management plans, crop and hay acres do not receive more than
130 percent of their TN and TP need.
• Tier 1 Manure excess
-Excess nutrients resulting from the differences between manure generated and
conforming to nutrient management rules and losses in agricultural land are
reported.
-It is assumed that all of the excess manure has alternative uses that do not affect
loads to the Chesapeake Bay tidal waters.
• Tier 1 Animal waste management/runoff control
-Continue 1997-2000 implementation rates of animal waste management on
'manure acres' to the year 2010 with limits that levels cannot exceed the avail-
able area to apply the BMPs to.
-Manure acres are the model's accounting of runoff from animal feeding opera-
tions based on the number of animal units.
-The BMP combines storage systems and barnyard runoff controls and reduction
factors of 75 percent (TN and TP) are applied to protected manure acres.
• Tier 1 Farm Plans (non-nutrient management)
-Continue 1997-2000 rates of Farm Plan implementation on agricultural land
(crop, hay, and pasture) to the year 2010 with limits that levels cannot exceed the
available land area to apply the BMPs to.
-Nutrient and sediment reduction factors for Farm Plans on high-till are 10
percent (TN) and 40 percent (TP and SED). Low-till and hay reduction factors
are 4 percent (TN) and 8 percent (TP and SED) while the reduction factors for
Farm Plans on pasture are 20 percent (TN) and 14 percent (TP and SED).
• Tier 1 Cover crops
-Since cover crop acreage varies annually or is not cumulative, cover crop imple-
mentation is determined as the average of 1997-2000 implementation acreage
(or years in that period where data exists from the jurisdictions) with limits that
levels cannot exceed the available land area to apply the BMPs to.
-BMP reduction factors of 35 percent (TN) and 15 percent (TP and SED) are
applied to cover crop acres.
appendix A • Development of the Level-of-Effort Scenarios
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• Tier 1 Streambank protection with fencing
-Continue 1997-2000 implementation rates of streambank protection with
fencing on pasture to the year 2010 with limits that levels cannot exceed the
available of the E3 scenario land area to apply the BMPs to.
-The E3 scenario levels are revised following the same methodologies but
account for previously applied BMPs that involve landuse changes.
-The E3 scenario assumes for every stream mile protected, 51 upland acres of
pasture receive a reduction benefit.
-BMP reduction factors of 75 percent for TN, TP, and SED are applied to pasture
acres protected.
• Tier 1 Streambank protection without fencing
-Continue 1997-2000 implementation rates of streambank protection without
fencing on pasture to the year 2010 with limits that levels cannot exceed the
available pasture land area to apply the BMPs to.
-BMP reduction factors of 40 percent for TN, TP, and SED are applied to pasture
acres protected.
• Tier 1 Grazing land protection
-Continue 1997-2000 implementation rates of rotational grazing on pasture to the
year 2010 with limits that levels cannot exceed the available land area to apply
the BMPs to.
-BMP reduction factors of 50 percent (TN) and 25 percent (TP) are applied to
protected pasture acres.
2010 TIER 1 URBAN AND MIXED OPEN BMPs
• Tier 1 Storm Water Management on new development
-Storm water management applied to 66 percent of new development between
2000 and 2010.
-Storm water management practices are designed to reduce TN by 35 percent,
TP by 45 percent, and SED by 80 percent.
• Tier 1 Storm Water Management on recent development
-60 percent of recent development (1986-2000) is has storm water management
that are designed to reduce nutrients and sediment in storm water runoff by
27 percent (TN), 40 percent (TP), and 65 percent (SED).
• Tier 1 Storm Water retrofits on old and recent development
-0.8 percent of pre-1986 urban land and 1986-2000 recent development is retro-
fitted with a suite of practices that reduce nutrients and sediment in runoff by
20 percent (TN), 30 percent (TP), and 65 percent (SED).
appendix A • Development of the Level-of-Effort Scenarios
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• Tier 1 Riparian forest and grass buffers on urban
-It is assumed that all urban stream reaches have either forest or grass riparian
buffers except where urban disturbance has altered a stream reach beyond
repair/restoration (i.e., impervious surface).
-50-foot buffers on all un-buffered stream miles (each side) associated with
pervious urban.
-Landuse conversion of pervious urban to mixed open (grass buffers) or forest
(forest buffers).
-There is no upland benefit associated with forest and grass buffers on urban.
• Tier 1 Riparian forest buffers on mixed open
-Continue 1997-2000 implementation rates of tree planting on mixed open to the
year 2010 with limits that levels can not exceed the available or the E3 scenario
land area to which BMPs could be applied.
-100-foot forest buffers on all un-buffered stream miles (each side) associated
with mixed open.
-Landuse conversion of mixed open to forest.
-There is no upland benefit associated with forest buffers on mixed open.
• Tier 1 Nutrient management on urban and mixed open
-Continue 1997-2000 implementation rates of nutrient management on pervious
urban and mixed open to the year 2010 with limits that levels cannot exceed the
available land area to which BMPs could be applied.
-BMP reduction factors of 17 percent (TN) and 22 percent (TP) are applied to
acres under nutrient management.
2010 TIER 1 FOREST HARVEST BMPs
• It is assumed that forestry BMPs designed to minimize the environmental impacts
from timber harvesting, such as road building and cutting/thinning operations, are
properly installed on all harvested lands with no measurable increase in nutrient
and sediment discharge.
• The assumption is based on maintaining the state of forest loads as measured
during the calibration of the Chesapeake Bay Watershed Model.
2010 TIER 1 SEPTIC BMPs
• Current edge-of-septic-field concentrations and flows per system are maintained.
• The number of systems varies according to population projections from 2000 to
2010.
• Septic BMPs incorporate submissions from the Chesapeake Bay-basin juris-
dictions on the current number of systems employing denitrification technologies
appendix A • Development of the Level-of-Effort Scenarios
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(50 percent TN reduction) and those with regular maintenance through pumping
(5 percent TN reduction).
2010 TIER 1 POINT SOURCE BMPs
• Tier 1 Significant municipal wastewater treatment facilities
-Nitrogen - POTWs with existing nutrient-removal technologies (NRT) and
those planned to go to NRT by 2010 are at 2010 projected flows and 8 mg TN/L
effluent concentrations (annual average). All remaining significant facilities are
at 2010 projected flows and 2000 TN effluent concentrations.
-Phosphorus - 2010 projected flows and 2000 TP/L effluent concentrations
except those targeted in VA which are at 1.5 mg TP/L (annual average).
• Tier 1 Significant industrial dischargers
-2000 flows and maintain current (2000) levels of effluent concentrations for TN
and TP or the permit limit, whichever is less.
• Tier 1 Non-significant municipal wastewater treatment facilities
-2000 TN and TP effluent concentrations applied to 2010 projected flows.
2010 TIER 1 COMBINED SEWER OVERFLOW BMPs
• There is a 43 percent reduction in the current discharge from DC combined sewer
overflows, the only CSO loads among all jurisdictions for which the Chesapeake
Bay Program has nutrient load data specifically quantified in the model simula-
tion.
• The reduction from 2000 loads is what is expected by the District to be achieved
by 2010.
2010 TIER 1 ATMOSPHERIC DEPOSITION BMPs
Tier 1 atmospheric deposition assumes implementation of the 1990 Clean Air Act
projected for the year 2010 with nitrogen oxide emissions regulations for ground-
level ozone and acid rain that have passed. Estimated changes in deposition for the
Tier 1 scenario includes the following controls on nitrogen oxide emissions:
• 2007 non-utility (industrial) point source and area source emissions.
• 2007 mobile source emissions with 'Tier II' tail pipe standards on light duty
vehicles.
• 2010 utility emissions with Title IV (Acid Rain Program) fully implemented and
20-state NOx SIP call reductions at 0.15 lbs/MMbtu during the May to September
ozone season only.
The impacts of Tier 1 emissions and deposition to the Chesapeake Bay watershed's
land area and non-tidal waters are part of the reported nutrient loads from the
appendix A • Development of the Level-of-Effort Scenarios
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A22
individual landuse source categories (i.e., agriculture, urban, mixed open, forest, and
non-tidal surface waters). The reported Watershed Model loads, however, usually do
not include contributions from atmospheric deposition to tidal waters although the
water quality responses, as measured by the Water Quality Model, account for this
source at levels prescribed by Tier 1.
2010 TIER 1 SHORELINE EROSION BMPs
• Tier 1 shoreline erosion controls include structural and non-structural practices at
2000 levels.
The impacts of Tier 1 shoreline erosion controls are not included in the reported
Watershed Model loads although the water quality responses, as measured by the
Model, account for this source at BMP levels prescribed by Tier 1.
2010 TIER 2 SCENARIO
2010 Tier 2 BMP implementation levels for nonpoint sources were generally deter-
mined by increasing levels above Tier 1 by a percentage of the difference between
the Tier 1 and the E3 scenario levels for each BMP. These percentages were mostly
recommended by individual source workgroups under the Chesapeake Bay Program
Nutrient Subcommittee, and were applied watershed-wide by county segments, or
the intersections of county political boundaries and the Watershed Model's hydro-
logic segmentation.
For Tier 2 point source municipal facilities, technologies to achieve 8 mg TN/L
include extended aeration processes and denitrification zones, along with chemical
addition to achieve a phosphorus discharge of 1.0 mg/1 where facilities are not
already achieving these levels.
In the design of the Tier 2 scenario, considerations of the costs of BMP implemen-
tation, participation levels, and physical limitations are very limited. Tier 2 BMP
levels are considered technically possible, and are listed below for each of the major
source categories.
2010 TIER 2 SCENARIO AGRICULTURAL BMPs
• Tier 2 Conservation tillage
-Applied to 'Tier 1' levels plus 30 percent of the available crop acres between
'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-Landuse conversion of high-till to low-till.
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A23
• Tier 2 Riparian forest buffers on agriculture
-Applied to 'Tier 1' levels plus 20 percent of the available stream reaches in crop-
land and pasture and 25 percent of the remaining stream reaches in hay between
'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-The E3 scenario assumes 100-foot forest buffers on un-buffered stream miles
(each side) associated with crop, hay and pasture.
-Tier 1 forest buffers on pasture are rooted in agricultural tree planting from juris-
dictional BMP reporting.
-Landuse conversions of crop, hay, and pasture to forest.
-For every acre of crop and hay converted, two upland acres of crop and hay
receive a reduction of 57 percent (TN), 70 percent (TP), and 70 percent (SED).
-There is no upland benefit associated with forest buffers on pasture.
• Tier 2 Wetland restoration
-Applied to 'Tier 1' levels plus 33 percent of the available crop and hay acres in
PA, MD, and VA between 'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-Landuse conversion of crop and hay to forest.
• Tier 2 Agricultural land retirement
-The remainder of 10 percent of the total crop and hay acres and those acres
converted through forest buffers and wetland restoration is retired to a grass
condition.
-Landuse conversions of crop and hay to mixed open.
• Tier 2 Riparian grass buffers on cropland
-Applied to 'Tier 1' levels plus 25 percent of the available stream reaches in crop-
land between 'Tier 1' and the 'E3' scenario levels and after forest buffer planting.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-The E3 scenario assumes 100-foot buffers on un-buffered stream miles (each
side) associated with agricultural land.
-Landuse conversions of crop to mixed open.
-For every acre of cropland converted, two upland acres of crop receive a reduc-
tion of 43 percent (TN), 53 percent (TP), and 53 percent (SED).
• Tier 2 Nutrient Management Plan Implementation
-Applied to 'Tier 1' levels plus 30 percent of the available crop and hay acres
between 'Tier 1' and the 'E3' scenario levels in PA, VA, NY, and WV.
appendix A • Development of the Level-of-Effort Scenarios
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A24
-All crop and hay acres in MD and DE are fully implementing nutrient manage-
ment plans.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-Under nutrient management plans, crop and hay acres do not receive more than
130 percent of their TN and TP need.
• Tier 2 Manure excess
-Excess nutrients resulting from the differences between manure generated and
conforming to nutrient management rules and losses in agricultural land are
reported.
-It is assumed that all of the excess manure has alternative uses that do not affect
loads to the Chesapeake Bay tidal waters.
• Tier 2 Animal waste management/runoff control
-Applied to 'Tier 1' levels plus 25 percent of the available manure acres between
'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-BMP reduction factors of 75 percent (TN and TP) are applied to protected
manure acres.
• Tier 2 Farm Plans (non-nutrient management)
-Applied to 'Tier 1' levels plus 30 percent of the available agricultural acres (crop,
hay, and pasture) between 'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-Nutrient and sediment reduction factors for Farm Plans on high-till are 10
percent (TN) and 40 percent (TP and SED). Low-till and hay reduction factors
are 4 percent (TN) and 8 percent (TP and SED) while the reduction factors for
Farm Plans on pasture are 20 percent (TN) and 14 percent (TP and SED).
• Tier 2 Cover crops
-Applied to 'Tier 1' levels plus 40 percent of the available cropland between 'Tier
1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-BMP reduction factors of 35 percent (TN) and 15 percent (TP and SED) are
applied to cover crop acres.
• Tier 2 Streambank protection with fencing
-Applied to 'Tier 1' levels plus 15 percent of the available pasture land that can
be protected between 'Tier 1' and the 'E3' scenario levels.
appendix A • Development of the Level-of-Effort Scenarios
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A25
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-BMP reduction factors of 75 percent for TN, TP, and SED are applied to pasture
acres protected.
• Tier 2 Streambank protection without fencing
-Applied to 'Tier 1' levels plus 10 percent of the available pasture land area to
apply the BMPs to accounting for the acres protected by fencing.
-Tier 1 levels are revised following the same methodologies but account for previ-
ously applied BMPs that involve landuse changes and streambank protection
with fencing.
-BMP reduction factors of 40 percent for TN, TP, and SED are applied to pasture
acres protected.
• Tier 2 Grazing land protection
-Applied to 'Tier 1' levels plus 25 percent of the available pasture land between
'Tier 1' and the 'E3' scenario' levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-BMP reduction factors of 50 percent (TN) and 25 percent (TP) are applied to
protected pasture acres.
2010 TIER 2 URBAN AND MIXED OPEN BMPs
• Tier 2 Reduction in 2000-2010 urban growth
-10 percent of the projected pervious and impervious urban growth in PA, MD,
VA, and DC between 2000 and 2010 is not developed.
-It is assumed that 65 percent of the reduction in projected urban growth is
retained in forest, 20 percent in mixed open, and 15 percent in agriculture.
-Landuse conversions of pervious and impervious urban to forest, mixed open,
and agriculture (crop, hay, and pasture).
• Tier 2 Storm Water Management and environmental site design/low-impact devel-
opment on new development
-Storm water management applied to 75% of new development between 2000 and
2010.
-Environmental site design/low-impact development practices applied to 25% of
new development between 2000 and 2010.
-Efficiencies of storm water management and environmental site design and low-
impact development practices represent a 75%/25% weighted average reduction
of 40% for TN, 55% for TP, and 85% for TSS.
appendix A • Development of the Level-of-Effort Scenarios
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A26
• Tier 2 Storm Water Management on recent development
-60 percent of recent development (1986-2000) has storm water management
practices that are designed to reduce nutrients and sediment in storm water
runoff by 27 percent (TN), 40 percent (TP), and 65 percent (SED).
• Tier 2 Storm Water retrofits on old and recent development
-5 percent of pre-1986 urban land and 1986-2000 recent development has storm
water management practices that reduce nutrients and sediment in runoff by 20
percent (TN), 30 percent (TP), and 65 percent (SED).
• Tier 2 Riparian grass buffers on urban lands
-Urban grass buffer acreage is reduced 10 percent below 'Tier 1' levels and is
converted to urban forest buffers.
-Tier 1 levels are revised following the same methodology but account for previ-
ously applied BMPs that involve landuse changes.
-The assumption is maintained that all urban stream reaches have 50-foot riparian
buffers in either forest or grass except where urban disturbance has altered a
stream reach beyond repair/restoration (i.e., impervious surface).
-There is no upland benefit associated with grass buffers on urban.
• Tier 2 Riparian forest buffers on urban lands
-Urban forest buffer acreage is increased by the same amount as the reduction in
urban grass buffers.
-The assumption is maintained that all urban stream reaches have 50-foot riparian
buffers in either forest or grass except where urban disturbance has altered a
stream reach beyond repair/restoration (i.e., impervious surface).
-There is no upland benefit associated with forest buffers on urban.
• Tier 2 Riparian forest buffers on mixed open lands
-Mixed open forest buffer acreage is increased from 'Tier 1' levels by the same
amount as the increase in urban forest buffers between 'Tier 1' and Tier 2.
-Tier 1 levels are revised following the same methodology but account for previ-
ously applied BMPs that involve landuse changes.
-Landuse conversion of mixed open to forest.
-There is no upland benefit associated with forest buffers on mixed open.
• Tier 2 Nutrient management on urban and mixed open lands
-It is assumed that 40 percent of pervious urban and 40 percent of mixed open
land are under nutrient management.
-BMP reduction factors of 17 percent (TN) and 22 percent (TP) are applied to
acres under nutrient management.
appendix A • Development of the Level-of-Effort Scenarios
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A27
2010 TIER 2 FOREST HARVEST BMPs
• It is assumed that forestry BMPs designed to minimize the environmental impacts
from timber harvesting, such as road building and cutting/thinning operations, are
properly installed on all harvested lands with no measurable increase in nutrient
and sediment discharge.
• The assumption is based on maintaining the state of forest loads as measured
during the calibration of the Chesapeake Bay Watershed Model.
2010 TIER 2 SEPTIC BMPs
• 10 percent of new treatment systems between 2000 and 2010 employ denitrifica-
tion technologies and are maintained through regular pumping to meet an edge of
septic field TN concentration of 10 mg/1 or 2.3 lbs TN per person-year.
• Remaining new and existing systems are at current edge of septic field concentra-
tions and flows per system.
• Septic BMPs incorporate submissions from the Chesapeake Bay basin jur-
isdictions of the current number of systems employing denitrification
technologies (50 percent TN reduction) and those with regular maintenance
through pumping (5 percent TN reduction).
2010 TIER 2 POINT SOURCE BMPs
• Tier 2 Significant municipal wastewater treatment facilities
-Nitrogen - All significant POTWs are at 2010 projected flows and reach and
maintain effluent concentrations of 8 mg TN/L (annual average) including those
facilities that planned to go to NRT by 2010.
-Phosphorus - POTWs are at 2010 projected flows and reach and maintain
effluent concentrations of 1.0 mg TP/L (annual average) or the permit limit,
whichever is less.
• Tier 2 Significant industrial dischargers
-2000 flows and generally maintain effluent concentrations that are 50 percent
less that those in Tier 1 or the permit limit, whichever is less.
• Tier 2 Non-significant municipal wastewater treatment facilities
-2000 TN and TP effluent concentrations applied to 2010 projected flows.
2010 TIER 2 COMBINED SEWER OVERFLOW BMPs
• There is a 43 percent reduction in the current discharge from District of Columbia
combined sewer overflows, the only CSO loads among all jurisdictions for which
the Chesapeake Bay Program has nutrient load data specifically quantified in the
model simulation.
appendix A • Development of the Level-of-Effort Scenarios
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A28
• The reduction from 2000 loads is what is expected by the District of Columbia to
be achieved by 2010.
2010 TIER 2 ATMOSPHERIC DEPOSITION BMPs
Atmospheric deposition under Tier 2 reflects implementation of the 1990 Clean Air
Act projected for the year 2020 with nitrogen oxide emissions regulations described
in Tier 1 plus heavy-duty diesel regulations that have passed. Estimated changes in
deposition for the Tier 2 scenario reflects the following controls on nitrogen oxide
emissions:
• 2020 non-utility (industrial) point source and area source emissions with no addi-
tional controls beyond Tier 1.
• 2020 mobile source emissions with the effect of the Tier II tail pipe standards on
light duty vehicles being felt, and the implementation of the heavy-duty diesel
standards to further reduce NOx emissions.
• 2020 utility emissions with Title IV (Acid Rain Program) fully implemented and
20-state NOx SIP call reductions at 0.15 lbs/MMbtu during the May to September
ozone season only—Same as Tier 1 controls.
The impacts of emissions and deposition to the Chesapeake Bay watershed's land
area and non-tidal waters under Tier 2 are part of the reported nutrient loads from the
individual landuse source categories (i.e., agriculture, urban, mixed open, forest, and
non-tidal surface waters). The reported Watershed Model loads, however, usually do
not include contributions from atmospheric deposition to tidal waters although the
water quality responses, as measured by the Water Quality Model, account for this
source at levels prescribed by Tier 2.
2010 TIER 2 SHORELINE EROSION BMPs
• Tier 2 shoreline erosion controls include structural and non-structural practices at
2000 levels.
The impacts of Tier 2 shoreline erosion controls are not included in the reported
Watershed Model loads although the water quality responses, as measured by the
Water Quality Model, account for this source at BMP levels prescribed by Tier 2.
2010 TIER 3 SCENARIO
The 2010 Tier 3 BMP implementation levels for nonpoint sources were generally
determined by increasing levels above the Tier 1 scenario by a percentage of the
difference between the Tier 1 and the E3 scenario levels, with the percentages being
higher than those used in the Tier 2 scenario. As with the Tier 2 scenario, the levels
of nonpoint source control were applied watershed-wide by county segments, or the
intersections of county political boundaries and the Watershed Model's hydrologic
segmentation.
appendix A • Development of the Level-of-Effort Scenarios
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A29
For Tier 3 municipal point source facilities, technologies to achieve 5 mg TN/L
include extended aeration processes beyond those in the Tier 2 scenario, a secondary
anoxic zone plus methanol addition, additional clarification tanks, and additional
chemicals to achieve a phosphorus discharge of 0.5 mg TP/L.
In the Tier 3 scenario, considerations of the costs of BMP implementation, partici-
pation levels, and physical limitations are very limited. Tier 3 BMP levels,
considered technically possible, are listed below for each of the major source
categories.
2010 TIER 3 AGRICULTURAL BMPs
• Tier 3 Conservation tillage
-Applied to 'Tier 1' levels plus 60 percent of the available crop acres between
'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-Landuse conversion of high-till to low-till.
• Tier 3 Riparian forest buffers on agriculture
-Applied to 'Tier 1' levels plus 30 percent of the available stream reaches in crop-
land and pasture and 50 percent of the remaining stream reaches in hay between
'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-The E3 scenario assumes 100-foot forest buffers on un-buffered stream miles
(each side) associated with crop, hay, and pasture.
-Tier 1 forest buffers on pasture are rooted in agricultural tree planting from juris-
dictional BMP reporting.
-Landuse conversions of crop, hay, and pasture to forest.
-For every acre of crop and hay converted, two upland acres of crop and hay
receive a reduction of 57 percent (TN), 70 percent (TP), and 70 percent (SED).
-There is no upland benefit associated with forest buffers on pasture.
• Tier 3 Wetland restoration
-Applied to 'Tier 1' levels plus 66 percent of the available crop and hay acres in
PA, MD, and VA between 'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-Landuse conversion of crop and hay to forest.
appendix A • Development of the Level-of-Effort Scenarios
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A30
• Tier 3 Agricultural land retirement
-The remainder of 15 percent of the total crop and hay acres and those acres
converted through forest buffers and wetland restoration is retired to a grass
condition.
-Landuse conversions of crop and hay to mixed open.
• Tier 3 Carbon sequestration/bio-energy
-15 percent of crop acres (after BMP landuse conversions) are replaced with long-
term grasses that serve as a carbon bank and could be converted to energy
through combustion.
-Landuse conversion of low-till to hay.
• Tier 3 Riparian grass buffers on cropland
-Applied to 'Tier 1' levels plus 50 percent of the available stream reaches in crop-
land between 'Tier 1' and the 'E3' scenario levels and after forest buffer planting.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-The E3 scenario assumes 100-foot buffers on un-buffered stream miles (each
side) associated with agricultural land.
-Landuse conversions of crop to mixed open.
-For every acre of cropland converted, two upland acres of crop receive a reduc-
tion of 43 percent (TN), 53 percent (TP), and 53 percent (SED).
• Tier 3 Nutrient Management Plan Implementation (standard and yield reserve
program)
-Nutrient management is applied to 'Tier 2' levels plus 30 percent of the available
crop and hay acres between 'Tier 2' and the 'E3' scenario levels in PA, VA, NY,
and WV.
-Tier 2 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-All crop and hay acres in MD and DE are fully implementing nutrient manage-
ment plans.
-Of the crop and hay acres available for nutrient management, 30 percent
conforms to a yield reserve program where the land receives 25 percent less TN
and TP than standard nutrient management applications - Do not receive more
than 98 percent of TN and TP need.
-Yield reserve program assumes farmer insurance for yield losses.
-The remaining 70 percent of land available for nutrient management follows
standard rules where crop and hay acres do not receive more than 130 percent of
their TN and TP need.
appendix A • Development of the Level-of-Effort Scenarios
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A31
• Tier 3 Manure excess
-Excess nutrients resulting from the differences between manure generated and
conforming to nutrient management rules and losses in agricultural land are
reported.
-It is assumed that all of the excess manure has alternative uses that do not affect
loads to the Chesapeake Bay tidal waters.
• Tier 3 Animal waste management/runoff control
-Applied to 'Tier 1' levels plus 60 percent of the available manure acres between
'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-BMP reduction factors of 75 percent (TN and TP) are applied to protected
manure acres.
• Tier 3 Farm Plans (non-nutrient management)
-Applied to 'Tier 1' levels plus 70 percent of the available agricultural acres (crop,
hay and pasture) between 'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-Nutrient and sediment reduction factors for Farm Plans on high-till are 10
percent (TN) and 40 percent (TP and SED). Low-till and hay reduction factors
are 4 percent (TN) and 8 percent (TP and SED) while the reduction factors for
Farm Plans on pasture are 20 percent (TN) and 14 percent (TP and SED).
• Tier 3 Cover crops
-Applied to 'Tier 1' levels plus 75 percent of the available cropland between 'Tier
1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-BMP reduction factors of 35 percent (TN) and 15 percent (TP and SED) are
applied to cover crop acres.
• Tier 3 Streambank protection with fencing
-Applied to 'Tier 1' levels plus 75 percent of the available pasture land that can
be protected between 'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-BMP reduction factors of 75 percent for TN, TP, and SED are applied to pasture
acres protected.
appendix A • Development of the Level-of-Effort Scenarios
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A3 2
• Tier 3 Streambank protection without fencing
-Applied to 'Tier 1' levels plus 25 percent of the available pasture land area to
apply the BMPs to accounting for the acres protected by fencing.
-Tier 1 levels are revised following the same methodologies but account for previ-
ously applied BMPs that involve landuse changes and streambank protection
with fencing.
-BMP reduction factors of 40 percent for TN, TP, and SED are applied to pasture
acres protected.
• Tier 3 Grazing land protection
-Applied to 'Tier 1' levels plus 50 percent of the available pasture land between
'Tier 1' and the 'E3' scenario levels.
-Tier 1 and the E3 scenario levels are revised following the same methodologies
but account for previously applied BMPs that involve landuse changes.
-BMP reduction factors of 50 percent (TN) and 25 percent (TP) are applied to
protected pasture acres.
2010 TIER 3 URBAN AND MIXED OPEN BMPs
• Tier 3 Reduction in 2000-2010 urban growth
-20 percent of the projected pervious and impervious urban growth in PA, MD,
VA, and DC between 2000 and 2010 is not developed.
-It is assumed that 65 percent of the reduction in projected urban growth is
retained in forest, 20 percent in mixed open, and 15 percent in agriculture.
-Landuse conversions of pervious and impervious urban to forest, mixed open,
and agriculture (crop, hay, and pasture).
• Tier 3 Storm Water Management and environmental site design/low-impact devel-
opment on new development
-Storm water management applied to 50 percent of new development between
2000 and 2010.
-Environmental site design/low-impact development practices applied to 50
percent of new development between 2000 and 2010.
-Efficiencies of storm water management and environmental site design and low-
impact development practices represent a 50%/50% weighted average reduction
of 45% for TN, 57% for TP, and 87% for TSS.
• Tier 3 Storm Water Management on recent development
-60 percent of recent development (1986-2000) has storm water management
practices that are designed to reduce nutrients and sediment in stonnwater runoff
by 27 percent (TN), 40 percent (TP), and 65 percent (SED).
• Tier 3 Storm Water retrofits on old and recent development
-20 percent of pre-1986 urban land and 1986-2000 recent development has storm
water management practices that reduce nutrients and sediment in runoff by
20 percent (TN), 30 percent (TP), and 65 percent (SED).
appendix A • Development of the Level-of-Effort Scenarios
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A3 3
• Tier 3 Riparian grass buffers on urban lands
-Urban grass buffer acreage is reduced 30 percent below 'Tier 1' levels and is
converted to urban forest buffers.
-Tier 1 levels are revised following the same methodology but account for previ-
ously applied BMPs that involve landuse changes.
-The assumption is maintained that all urban stream reaches have 50-foot riparian
buffers in either forest or grass except where urban disturbance has altered a
stream reach beyond repair/restoration (i.e., impervious surface).
-There is no upland benefit associated with grass buffers on urban.
• Tier 3 Riparian forest buffers on urban lands
-Urban forest buffer acreage is increased by the same amount as the reduction in
urban grass buffers.
-The assumption is maintained that all urban stream reaches have 50-foot riparian
buffers in either forest or grass except where urban disturbance has altered a
stream reach beyond repair/restoration (i.e., impervious surface).
-There is no upland benefit associated with forest buffers on urban.
• Tier 3 Riparian forest buffers on mixed open lands
-Mixed open forest buffer acreage is increased from 'Tier 1' levels by the same
amount as the increase in urban forest buffers between 'Tier 1' and Tier 3.
-Tier 1 levels are revised following the same methodology but account for previ-
ously applied BMPs that involve landuse changes.
-Landuse conversion of mixed open to forest.
-There is no upland benefit associated with forest buffers on mixed open.
• Tier 3 Nutrient management on urban and mixed open lands
-It is assumed that 75 percent of pervious urban and 75 percent of mixed open
land are under nutrient management.
-BMP reduction factors of 17 percent (TN) and 22 percent (TP) are applied to
acres under nutrient management.
2010 TIER 3 FOREST HARVEST BMPs
• It is assumed that forestry BMPs designed to minimize the environmental impacts
from timber harvesting, such as road building and cutting/thinning operations, are
properly installed on all harvested lands with no measurable increase in nutrient
and sediment discharge.
• The assumption is based on maintaining the state of forest loads as measured
during the calibration of the Chesapeake Bay Watershed Model.
appendix A • Development of the Level-of-Effort Scenarios
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A34
2010 TIER 3 SEPTIC BMPs
• 100 percent of new treatment systems between 2000 and 2010 and 1 percent of
existing systems employ denitrification technologies and are maintained through
regular pumping to meet an edge-of-septic-field TN concentration of 10 mg/L or
2.3 lbs TN per person-year.
• The 1 percent of existing systems represents failed systems and opportunities for
upgrades.
• The remaining existing systems are at current edge of septic field concentrations
and flows per system.
• Septic BMPs incorporate submissions from the Chesapeake Bay basin juris-
dictions of the current number of systems employing denitrification technologies
(50 percent TN reduction) and those with regular maintenance through pumping
(5 percent TN reduction).
2010 TIER 3 POINT SOURCE BMPs
• Tier 3 Significant municipal wastewater treatment facilities
-Nitrogen - All significant POTWs are at 2010 projected flows and reach and
maintain effluent concentrations of 5 mg TN/L (annual average) including those
facilities that planned to go to NRT by 2010.
-Phosphorus - POTWs are at 2010 projected flows and reach and maintain
effluent concentrations of 0.5 mg TP/L (annual average) or the permit limit,
whichever is less.
• Tier 3 Significant industrial dischargers
-2000 flows and generally maintain effluent concentrations that are 80 percent
less that those in Tier 1 or the permit limit, whichever is less.
• Tier 3 Non-significant municipal wastewater treatment facilities
-2000 TN and TP effluent concentrations applied to 2010 projected flows.
2010 TIER 3 COMBINED SEWER OVERFLOW BMPs
• There is a 43 percent reduction in the current discharge from District of Columbia
combined sewer overflows, the only CSO loads among all jurisdictions for which
the Chesapeake Bay Program has nutrient load data specifically quantified in the
model simulation.
• The reduction from 2000 loads is what is expected by the District of Columbia to
be achieved by 2010.
appendix A • Development of the Level-of-Effort Scenarios
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A3 5
2010 TIER 3 ATMOSPHERIC DEPOSITION BMPs
Atmospheric deposition under the Tier 3 scenario reflects existing regulatory
nitrogen oxide emissions controls under the 1990 Clean Air Act, as well as more
aggressive but voluntary emissions controls on the utility sector, projected for the
year 2020. Estimated changes in deposition for the Tier 3 scenario reflect the
following controls on nitrogen oxide emissions:
• 2020 non-utility (industrial) point source and area source emissions with no addi-
tional controls than Tiers 1 and 2.
• 2020 mobile source emissions with the effect of the Tier II tail pipe standards on
light duty vehicles being felt, and the implementation of the heavy duty diesel
standards to further reduce NOx emissions. Same as Tier 2 controls.
• 2020 utility emissions with major (90 percent) reductions in S02 and aggressive
20-state NOx SIP call reductions through utilities going to 0.10 lbs/MMbtu for the
entire year—no longer just seasonal.
The impacts of emissions and deposition to the Chesapeake Bay watershed's land
area and non-tidal waters under the Tier 3 scenario are part of the reported nutrient
loads from the individual landuse source categories (i.e., agriculture, urban, mixed
open, forest, and non-tidal surface waters). The reported loads, however, usually do
not include contributions from atmospheric deposition to tidal waters although the
water quality responses, as measured by the Water Quality Model, account for this
source at levels prescribed by the Tier 3 scenario.
2010 TIER 3 SHORELINE EROSION BMPs
• Tier 3 shoreline erosion controls include structural and non-structural practices at
2000 levels.
The impacts of Tier 3 shoreline erosion controls are not included in the reported
Watershed Model loads although the water quality responses, as measured by the
Water Quality Model, account for this source at BMP levels prescribed by the Tier 3
scenario.
2010 E3 SCENARIO
BMP implementation levels in the tier scenarios were bounded by the E3 scenario.
The E3 scenario was specifically designed to take out most of the subjectivity
surrounding what can or cannot be achieved in control measures. The E3 scenario
BMP implementation levels were, in part, based on earlier work of the Chesapeake
Bay Program partners when a 'limit-of-technology' condition was assessed by the
Tributary Strategy Workgroup. However, the E3 scenario is less subjective than the
limit-of-technology scenario in terms of maximum implementation levels. The BMP
appendix A • Development of the Level-of-Effort Scenarios
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A3 6
levels in the E3 scenario are theoretical: there are no cost and few physical limita-
tions to implementing BMPs for point and nonpoint sources. In addition, the E3
scenario includes new BMP technologies and programs that are not currently part of
jurisdictional pollutant control strategies.
For most nonpoint source BMPs, the workgroups assumed that the load from every
available acre of the relevant land area was being controlled by a full suite of existing
or innovative practices. In addition, management programs convert landuses from
those with high-yielding nutrient and sediment loads to those with lower. For point
sources in the E3 scenario, municipal wastewater treatment facilities reach and main-
tain effluent concentrations of 3 mg TN/L, and at least 0.1 mg TP/L, through
technologies such as deep-bed denitrification filters and micro-filtration.
The E3 scenario implementation levels and their associated reductions in nutrients
and sediment were developed without consideration of site specific physical
constraints, costs, or even plausible BMP program participation levels. The Chesa-
peake Bay Program partners acknowledge that if these factors are considered,
several aspects of the E3 scenario could not be achieved. On the other hand, there
are some control measures in the E3 scenario that physically could be more aggres-
sive. The E3 scenario conditions for these BMPs were established because a
theoretical maximum implementation level would have been entirely subjective.
BMP implementation levels for the E3 scenario are described in detail below for the
major source categories—agriculture, urban and mixed open, point sources, septic,
and atmospheric deposition.
PHYSICAL LIMITATIONS TO THE E3 SCENARIO
In all appropriate circumstances, BMP implementation levels in the E3 scenario
were applied to all relevant landuse areas or current limits-of-technology. In many
cases and to remove the subjectivity in determining human-caused conditions that
cannot be remedied, there were no physical limitations to employing the practices or
programs.
For many BMPs, the E3 scenario implementation levels could not be physically
achieved. For example, space may not be available for 50-foot riparian buffers in
urban areas, or certain developed lands may not allow for retrofitting with practices
that attain pollutant reduction efficiencies used in the E3 scenario. As other exam-
ples, certain crop types cannot be conservation-tilled, and it may be physically
impossible to completely eliminate runoff from animal feeding operations.
It is also unlikely that every homeowner and farmer would efficiently apply fertil-
izers so that only the needs of the vegetation are met and that water-front property
owners would plant 50-foot buffers even if it were physically possible. As a whole,
'feasible' participation levels are not built into the E3 scenario. All of the above-
mentioned instances are examples of where the E3 scenario may overestimate
reductions.
appendix A • Development of the Level-of-Effort Scenarios
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A3 7
UNDERESTIMATIONS OF LOAD REDUCTIONS
UNDER THE E3 SCENARIO
Contrarily, there are assumptions in the E3 scenario where BMP implementation
levels could physically be even higher than those currently defined in the E3
scenario. For example, it is physically possible that more than 25,000 acres of crop-
land and hay in Chesapeake Bay watershed could be restored to wetlands. This limit
on wetland acres restored in the E3 scenario in Pennsylvania, Maryland and Virginia
was used to reflect the Chesapeake 2000 goal since a theoretical maximum imple-
mentation level for wetlands restoration would be entirely subjective.
As an other example, 25 percent of cropland was replaced with long-term grasses
that serve as a carbon bank and could be converted to energy through combustion.
Benefits of a carbon sequestration program, in terms of lower pollutant loads, would
increase as more agricultural land is converted. Conversion of more than 25 percent
of cropland is physically possible. In addition, the 30 percent reduction in urban
sprawl over a decade could be physically set at a higher level. This rate was
employed in the E3 scenario to adhere to a Chesapeake 2000 goal.
The E3 scenario only includes shoreline erosion controls at current levels for lack of
a 'maximum' limit that would not be entirely subjective. It has been demonstrated
through modeling efforts that additional controls of shoreline erosion can signifi-
cantly improve tidal water quality. In general, much opportunity exists for reducing
sediment and nutrient loads from eroding shorelines that would not be reflected in
the E3 scenario water quality model results.
If greater BMP implementation levels than those designated in the E3 scenario could
be physically achieved for any BMPs, pollutant loadings would decrease and the
there would be corresponding improved responses in water quality. For the most
part, however, the E3 scenario does not include real physical limitations to BMP
implementation or participation levels.
2010 E3 AGRICULTURAL BMPs
• The E3 scenario conservation tillage
-All cropland (high-till and low-till) is conservation-tilled.
-Landuse conversion of high-till to low-till.
• The E3 scenario riparian forest buffers on agriculture
-100-foot forest buffers on all un-buffered stream miles (each side) associated
with crop, hay, and pasture.
-Landuse conversion of low-till, hay, and pasture to forest.
-For every acre of low-till and hay converted, two upland acres of low-till and hay
receive a reduction of 57 percent (TN), 70 percent (TP), and 70 percent (SED).
-There is no upland benefit associated with forest buffers on pasture.
appendix A • Development of the Level-of-Effort Scenarios
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A3 8
• The E3 scenario wetland restoration
-In accordance with the Chesapeake 2000 agreement, 25,000 acres of crop and
hay in PA, MD, and VA are converted to and simulated as forest.
-The 25,000 acre restoration goal is allocated among these states as follows to
conform to agreements subsequent to Chesapeake 2000: PA = 4,250 acres, MD
= 15,000 acres, and VA = 5,750 acres.
• The E3 scenario agricultural land retirement
-The remainder of 25 percent of the total crop and hay acres and those acres
converted through forest buffers and wetland restoration is retired to a grass
condition.
-Landuse conversions of low-till and hay to mixed open.
• The E3 scenario carbon sequestration/bio-energy
-25 percent of crop acres (after BMP landuse conversions) are replaced with long-
term grasses that serve as a carbon bank and could be converted to energy
through combustion.
-Landuse conversion of low-till to hay.
• The E3 scenario yield reserve program
-All crop and hay acres (after BMP landuse conversions) receive 25 percent less
TN and TP than normal nutrient management applications; do not receive more
than 98 percent of TN and TP need.
-Yield reserve program assumes farmer insurance for yield losses.
• The E3 scenario manure excess
-Excess nutrients resulting from the differences between manure generated and
conforming to yield reserve (nutrient management) rules and losses in agricul-
tural land are reported.
-It is assumed that all of the excess manure has alternative uses that do not affect
loads to the Chesapeake Bay tidal waters.
• The E3 scenario animal waste management/runoff control
-There is no runoff from manure in animal feeding operations.
-Modeled landuse acres that account for runoff from animal feeding operations
are converted to pasture.
-Landuse conversion of manure acres to pasture.
• The E3 scenario Farm Plans (non-nutrient management)
-Farm Plans are fully implemented on all agricultural land (crop, hay, and
pasture).
-Nutrient and sediment reduction factors for Farm Plans on low-till and hay are 4
percent (TN) and 8 percent (TP and SED). Pasture reduction factors are 20
percent (TN) and 14 percent (TP and SED).
appendix A • Development of the Level-of-Effort Scenarios
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A3 9
• The E3 scenario cover crops
-All crop landuses have cover crops.
-BMP reduction factors of 35 percent (TN) and 15 percent (TP and SED) are
applied to all low-till.
• The E3 scenario streambank protection with fencing
-Streambank protection with fencing on all unprotected stream miles (each side)
associated with pasture.
-For every stream mile protected, 51 upland acres of pasture receive a reduction
of 75 percent for TN, TP and SED.
• The E3 scenario grazing land protection
-All pasture land is protected through rotational grazing.
-BMP reduction factors of 50 percent (TN) and 25 percent (TP) are applied.
2010 E3 SCENARIO URBAN AND MIXED OPEN BMPs
• The E3 scenario reduction in 2000-2010 urban growth
-30 percent of the projected pervious and impervious urban growth in PA, MD,
VA, and DC between 2000 and 2010 remains in forest to conform to the Chesa-
peake 2000 agreement.
-It is assumed that the reduction in projected urban growth in PA, MD, VA, and
DC over the decade is retained or planted in forest.
-Landuse conversions of pervious and impervious urban to forest.
• The E3 scenario environmental site design/low-impact development on new
development
-Environmental site design/low-impact development practices applied to all
urban growth between 2000 and 2010.
-Environmental site design and low-impact development practices are designed to
reduce TN by 50 percent, TP by 60 percent, and SED by 90 percent.
• The E3 scenario storm water retrofits on existing urban
-All pre-2001 urban areas are retrofitted with a suite of practices to reduce nutri-
ents and sediment in storm water runoff by 40 percent (TN), 40 percent (TP), and
80 percent (SED).
• The E3 scenario riparian forest buffers on urban
-50-foot forest buffers on all un-buffered stream miles (each side) associated with
pervious urban.
-Landuse conversion of pervious urban to forest.
-There is no upland benefit associated with forest buffers on urban.
appendix A • Development of the Level-of-Effort Scenarios
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A40
• The E3 scenario riparian forest buffers on mixed open
-100-foot forest buffers on all un-buffered stream miles (each side) associated
with mixed open.
-Landuse conversion of mixed open to forest.
-There is no upland benefit associated with forest buffers on mixed open.
• The E3 scenario nutrient management on urban and mixed open
-All pervious urban and mixed open acres do not receive nutrient applications
from chemical fertilizers.
2010 E3 SCENARIO FOREST HARVEST BMPs
• It is assumed that forestry BMPs designed to minimize the environmental impacts
from timber harvesting, such as road building and cutting/thinning operations, are
properly installed on all harvested lands with no measurable increase in nutrient
and sediment discharge.
• The assumption is based on maintaining the state of forest loads as measured
during the calibration of the Chesapeake Bay Program Watershed Model.
2010 E3 SCENARIO SEPTIC BMPs
• All septic systems employ denitrification technologies and are maintained
through regular pumping to meet an edge-of-septic-field TN concentration of 10
mg/L or 2.3 lbs TN per person-year.
2010 E3 SCENARIO POINT SOURCE BMPs
• The E3 scenario significant municipal wastewater treatment facilities
-Nitrogen - POTWs are at 2010 projected flows and reach and maintain effluent
concentrations of 3 mg TN/L (annual average).
-Phosphorus - POTWs are at 2010 projected flows and reach and maintain
effluent concentrations of 0.1 mg TP/L (annual average).
• The E3 scenario significant industrial dischargers
-Nitrogen - 2000 flows and effluent concentrations of 3.0 mg TN/L
average) or the permit limit, whichever is less.
-Phosphorus - 2000 flows and effluent concentrations of 0.1 mg TP/L
average) or the permit limit, whichever is less.
• The E3 scenario non-significant municipal wastewater treatment facilities
-Nitrogen - POTWs are at 2010 projected flows and reach and maintain effluent
concentrations of 8 mg TN/L (annual average).
(annual
(annual
appendix A • Development of the Level-of-Effort Scenarios
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A41
-Phosphorus - POTWs are at 2010 projected flows and reach and maintain
effluent concentrations of 2.0 mg TP/L (annual average) or 2000 concentrations,
whichever is less.
2010 E3 SCENARIO COMBINED SEWER OVERFLOW BMPs
• There is no discharge from DC combined sewer overflows, the only CSO loads
among all jurisdictions for which the Chesapeake Bay Program has nutrient load
data specifically quantified in the model simulation.
2010 E3 SCENARIO ATMOSPHERIC DEPOSITION BMPs
Levels of atmospheric deposition in the E3 scenario reflect existing regulatory
nitrogen oxide emissions controls under the 1990 Clean Air Act, as well as more
aggressive but voluntary emissions controls on the utility, industrial, and mobile
source sectors, projected for the year 2020. Estimated changes in deposition for the
E3 scenario reflects the following controls on nitrogen oxide emissions:
• 2020 non-utility (industrial) point source emissions cut almost in half for both
S02 and NOx.
• 2020 area source emissions that are the same as the Tier 1-3 scenarios.
• 2020 mobile source emissions assuming super ultra-low emissions for light duty
vehicles and heavy duty diesel standards to further reduce NOx emission beyond
Tier 2 and Tier 3.
• 2020 utility emissions with major (90 percent) reductions in S02 and aggressive
20-state NOx SIP call reductions through utilities going to 0.10 lbs/MMbtu for the
entire year—same as Tier 3 controls.
The impacts of emissions and deposition to the Chesapeake Bay watershed's land
area and non-tidal waters under the E3 scenario are part of the reported nutrient loads
from the individual landuse source categories (i.e., agriculture, urban, mixed open,
forest, and non-tidal surface waters). The reported Watershed Model loads, however,
usually do not include contributions from atmospheric deposition to tidal waters
although the water quality responses, as measured by the Water Quality Model,
account for this source at levels prescribed by the E3 scenario.
2010 E3 SCENARIO SHORELINE EROSION BMPs
• The E3 scenario shoreline erosion controls include structural and non-structural
practices at 2000 levels.
The impacts of the E3 scenario shoreline erosion controls are not included in the
reported Watershed Model loads although the water quality responses, as measured
by the Water Quality Model, account for this source at BMP levels prescribed by the
E3 scenario.
appendix A • Development of the Level-of-Effort Scenarios
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A42
BAY-WIDE LOADS FOR 2000,
TIERS 1 TO 3, AND E3 SCENARIO
Figures A-l through A-3 depict modeled Chesapeake Bay-wide nutrient and sedi-
ment loads delivered to the Chesapeake Bay and its tidal tributaries by major source
category for each of the tier scenarios as well as the E3 scenario. As references, the
estimated loads for the year 2000 are also portrayed.
The delivered loads are a yearly average of loads simulated over a 10-year period
(1985-1994). This convention removes considerations of the effects of variable
precipitation levels or flows on loads. Also, nutrient loads are reported in units of
million pounds per year while sediment fluxes are in million tons per year.
Load reductions through the tiers to the E3 scenario show the impact of most point
and nonpoint source BMPs in the scenarios as described previously in this Appendix.
Atmospheric deposition to the Chesapeake Bay watershed's land area and non-tidal
waters are part of the reported loads, but the loads do not include contributions from
atmospheric deposition to tidal waters. In addition, the reported loads do not reflect
330
300
§, 120 -
60
30 +-
116.3
101.1
o « 180
76.0
— 55.5 —
18.3
25.3
¦ Non-Tidal
Water
Deposition
~ Septic
~ Mixed Open
~ Urban Runoff
I Forest
~ Point Source
~ Agriculture
2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3
2010 E3
Figure A-1. Nitrogen loads delivered to the Chesapeake Bay and its tidal tributaries by source,
appendix A • Development of the Level-of-Effort Scenarios
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A43
TJ O
ra o
o >»
o o
5.2
22
20
18
16
14
12
10
0.16
0.16
2.18
3.12
10.411
4.26
8.99
2.51
3.13
10.361
5.10
7.69
0.17
2.57
6.71
0.18
5.54
2.07
3.74
I Non-Tidal
Water
Deposition
~ Mixed Open
~ Urban
Runoff
I Forest
~ Point
Source
~ Agriculture
2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3 2010 E3
Figure A-2. Phosphorus loads delivered to the Chesapeake Bay and its tidal tributaries by source.
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o
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c
o
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E
c
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o
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(O
I
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.386
0.475
3.188
0.451
2.714
0.494
2.179
0.522
0.414
1.020
1.669
0.507
1.067
~ Mixed Open
I Urban
Runoff
~ Forest
~ Agriculture
2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3
2010 E3
Figure A-3. Sediment loads delivered to the Chesapeake Bay and its tidal tributaries by source.
appendix A • Development of the Level-of-Effort Scenarios
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A44
shoreline erosion controls employed in the scenarios. The water quality responses as
measured by the Watershed Model, however, account for both atmospheric deposi-
tion to tidal waters and shoreline erosion at levels prescribed by the tier and E3
scenarios.
It is important to note that landuses and animal populations change considerably
between 2000 Progress and the tier and E3 scenarios, which are based on projected
2010 landuses and populations. Therefore, nutrient applications to agricultural land
change considerably over the decade. Also, the number of septic systems and the
flows from municipal wastewater treatment facilities shift dramatically from 2000 to
2010 based on an increasing population. For example, point source phosphorous
loads increase from 2000 to 2010 Tier 1 because of increases in POTW flows which,
unlike nitrogen, are not offset by technologies to reduce this nutrient in effluents.
In addition to changes between 2000 and 2010 tier and E3 scenarios, it is imperative
to consider landuse changes among the tier and E3 scenarios due to increasing non-
point source BMP implementation levels. For example, sediment loads from forested
land increase through the tier to E3 scenarios because the land area increases as, for
example, more and more riparian buffers are planted on agricultural and urban land.
In addition, increases in loads from mixed open land is attributable to greater acreage
in this category as, for example, agricultural land is retired.
INFLUENCE OF EMISSION CONTROLS AND
ATMOSPHERIC DEPOSITION ON LOADS
The impacts of emission controls and the resultant lower atmospheric deposition to
the Chesapeake Bay watershed's land area and non-tidal waters are part of the
reported nutrient loads from the individual landuse source categories in the tier and
E3 scenarios (i.e., agriculture, urban, mixed open, forest, and non-tidal surface
waters). As mentioned previously, the reported loads however, usually do not include
contributions from atmospheric deposition to tidal waters although the model simu-
lated tidal Bay water quality responses account for this source.
To estimate the effects of only the tier and E3 scenarios air emission controls—
without the influences of other point and non-point source BMPs—the following
histogram (Figure A-4) show changes in atmospheric deposition of nitrogen to the
watershed's land area and non-tidal waters, and the response in delivered loads. In
these model simulations, all land uses, fertilizer applications, point sources, septic
loads, and BMP implementation levels were held constant at 2000 conditions; only
atmospheric deposition varied.
What these scenarios say is that "If projected emission and deposition reductions
associated with the tiers and E3 scenarios were realized today (2000), loads to the
Chesapeake Bay and its tidal tributaries are estimated to be the following." As
references, Tier 1 and Tier 2 scenario loads delivered from the watershed are shown
in the graphics.
appendix A • Development of the Level-of-Effort Scenarios
-------
A45
As can be seen in Figure A-4, atmospheric deposition to the watershed progressively
declines from 2000 through the tier to E3 scenarios as more emission controls are
included in the model simulation. But note how the loads from the watershed's land
area and non-tidal waters respond to these progressive emission and deposition
reductions, but to a much smaller degree.
The most significant reason for the dampened response is that the Chesapeake Bay
watershed is about 57 percent forested—or 57 percent of atmospheric nitrogen
deposits on forests—and among landuses, forests have the greatest potential to
uptake nitrogen. Generally forests in the Chesapeake Bay basin are not nitrogen-
saturated—whereby they leak nitrogen to sub-surface or ground water.
The largest single source of nitrogen loads to the Chesapeake Bay is agriculture
where nitrogen-based commercial fertilizers and animal manure applied to agricul-
tural land are currently eight times the input of nitrogen to agricultural land from
atmospheric deposition.
It is the impacts of emission controls on loads that are important in evaluating water
quality responses, the development of a cost estimating tool, and the establishment
of tributary strategies—rather than the contribution to loads from atmospheric
] Atmospheric Deposition i i DaiivaraH Load
¦Tier 1 Load
"Tier 2 Load
500
450
400
350
300
250
200
150
100
50
0
442.2
(0
a>
n
c
o
369.3
284.8
328.2
276.5
295.7
270.7
270.9
265.0
261.1
2000 Progress 2000 Base w/ 2000 Base w/ 2000 Base w/ 2000 Base w/ E3
(Baseline) Tier 1 Deposition Tier 2 Deposition Tier 3 Deposition Deposition
Figure A-4. Nitrogen deposits versus delivered loads.
appendix A • Development of the Level-of-Effort Scenarios
-------
A46
deposition. Understanding the loading responses to changes in deposition better
addresses to what degree the loads can be controlled. The proportion of the loads
attributed to atmospheric deposition changes dramatically from 2000 through the
tiers and E3 scenarios because of both variable emission controls and changes in
landuses to which the atmospheric nitrogen is deposited.
In the most dramatic case, deposition of nitrogen to the watershed decreases
171 million pounds/year from the 2000 Progress to 2010 E3 scenarios. If this reduc-
tion in deposition were realized today (i.e., deposition was to 2000 landuses with all
other present conditions), nitrogen loads to the Chesapeake Bay would decrease
21 million pounds/year or would be at levels associated with the Tier 1 scenario.
It is important to note that the E3 scenario levels of emission controls are considered
to be the current limits of technology with aggressive controls on all major sources
—utilities, mobile, and industrial—and follow the format of defining the E3 scenario
BMPs. It is not important that these emission controls would be voluntary, as
opposed to regulatory, as the E3 scenario implementation levels for almost all other
point and nonpoint source BMPs did not consider physical limitations, participation
rates, and costs. In other words, the tier scenarios are not intended to establish what
can and cannot be done through management actions—either regulatory or voluntary
—as this is the responsibility of Chesapeake Bay watershed jurisdictions. However,
the air scenarios involve actions taken by 37 states not just the Chesapeake Bay
watershed states.
appendix A • Development of the Level-of-Effort Scenarios
-------
B1
a ppend ix t3
Data Supporting Determination
of the Shallow-Water
Designated Use Depths and
Underwater Bay Grasses
Restoration Goals
Table B-1. Potential underwater bay grass habitat acreage by depth contour interval by Chesapeake
Bay Program segment.
Chesapeake Bay Program Segment
0-0.5 Meter Depth
0.5-1 Meter Depth
1-2 Meter Depth
Northern Chesapeake Bay (CBITF)
5,893
7,828
7,185
Northern Chesapeake Bay (CBITF)
5,893
7,828
7,185
Upper Chesapeake Bay (CB20H)
2,406
2,496
3,885
Upper Central Chesapeake Bay (CB3MH)
2,011
1,702
957
Middle Central Chesapeake Bay (CB4MH)
3,252
2,688
4,689
Lower Central Chesapeake Bay (CB5MH)
9,223
6,184
14,693
Western Lower Chesapeake Bay (CB6PH)
2,324.4
1,614
1,630
Eastern Lower Chesapeake Bay (CB7PH)
17,308
11,154
5,623
Mouth of the Chesapeake Bay (CB8PH)
381
314
355
Bush River (BSHOH)
1,136
932
2,536
Gunpowder River (GUNOH)
1,393
1,402
4,564
Middle River (MIDOH)
938
491
1,050
Back River (BACOH)
850
451
1,558
Patapsco River (PATMH)
1,042
766
1,610
Magothy River (MAGMH)
838
540
677
Severn River (SEVMH)
775
572
761
South River (SOUMH)
840
592
804
Rhode River (RHDMH)
267
162
281
West River (WSTMH)
542
491
435
continued
appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals
-------
B2
Table B-1. Potential underwater bay grass habitat acreage by depth contour interval by Chesapeake
Bay Program segment (cont.).
Chesapeake Bay Program Segment
0-0.5 Meter Depth
0.5-1 Meter Depth
1-2 Meter Depth
Upper Patuxent River (PAXTF)
24
10
20
Western Branch Patuxent River (WBRTF)
0
0
0
Middle Patuxent River (PAXOH )
1,072
362
638
Lower Patuxent River (PAXMH)
3,376
1,745
3,672
Upper Potomac River (POTTF)
4,751
2,944
9,807
Anacostia River (ANATF)
85
99
137
Piscataway Creek (PISTF)
241
347
326
Mattawoman Creek (MATTF)
397
298
693
Middle Potomac River (POTOH)
3,148
4,038
8,008
Lower Potomac River (POTMH)
15,964
10,111
19,729
Upper Rappahannock River (RPPTF)
2,175
1,012
1,324
Middle Rappahannock River (RPPOH)
1,226
427
857
Lower Rappanhannock River (RPPMH)
12,282
7,511
10,315
Corrotoman River (CRRMH)
1,279
540
792
Piankatank River (PIAMH)
3,237
2,429
2,348
Upper Mattaponi River (MPNTF)
835
203
371
Lower Mattaponi River (MPNOH)
323
80
151
Upper Pamunkey River (PMKTF)
1,860
327
465
Lower Pamunkey River (PMKOH)
420
129
258
Middle York River (YRKMH)
4,728
3,703
4,285
Lower York River (YRKPH )
3,332
1,617
2,049
Mobjack Bay (MOBPH)
14,207
8,761
11,022
Upper James River (JMSTF)
8,249
2,149
2,438
Appomattox River (APPTF)
1,084
221
298
Middle James River (JMSOH)
3,179
3,289
4,476
Chickahominy River (CHKOH)
3,283
222
996
Lower James River (JMSMH)
9,618
5,455
11,525
Mouth of the James River (JMSPH)
1,037
578
786
Western Branch Elizabeth River (WBEMH)
0
0
0
Southern Branch Elizabeth River (SBEMH)
0
0
0
Eastern Branch Elizabeth River (EBEMH)
0
0
0
Lafayette River (LAFMH)
0
0
0
Mouth to Mid-Elizabeth River (ELIPH)
0
0
0
Lynnhaven River (LYNPH)
2,476
807
658
continued
appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals
-------
B3
Table B-1. Potential underwater bay grass habitat acreage by depth contour interval by Chesapeake
Bay Program segment (cont.).
Chesapeake Bay Program Segment
0-0.5 Meter Depth
0.5-1 Meter Depth
1-2 Meter Depth
Northeast River (NORTF)
456
476
1,810
C & D Canal (C&DOH)
99
24
48
Bohemia River (BOHOH)
735
397
772
Elk River (ELKOH)
1,595
1,186
2,244
Sassafrass River (SASOH)
1,644
971
1,096
Upper Chester River (CHSTF)
574
192
104
Middle Chester River (CHSOH)
926
736
646
Lower Chester River (CHSMH)
4,183
2,798
4,520
Eastern Bay (EASMH)
7,423
5,659
7,723
Upper Choptank River (CHOTF)
0
0
0
Middle Choptank River (CHOOH)
592
260
432
Lower Choptank River (CHOMH2)
2,264
1,507
3,062
Mouth of the Choptank River (CHOMHl )
8,101
4,861
7,895
Little Choptank River (LCHMH)
5,012
3,011
4,344
Honga River (HNGMH)
6,117
4,513
5,826
Fishing Bay (FSBMH)
2,467
4,461
6,714
Upper Nanticoke River (NANTF)
0
0
0
Middle Nanticoke River (NANOH)
1,141
380
531
Lower Nanticoke River (NANMH)
1,583
1,605
4,524
Wicomico River (WICMH)
1,514
1,525
2,872
Manokin River (MANMH)
3,590
3,132
3,979
Big Annemessex River (BIGMH)
1,994
1,199
1,872
Upper Pocomoke River (POCTF)
0
0
0
Middle Pocomoke River (POCOH)
289
58
111
Lower Pocomoke River (POCMH)
3,915
6,090
4,412
Tangier Sound (TANMH)
20,101
18,720
31,052
appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals
-------
B4
2000
7,619
640
tr-
2,998
682
8,107
r-
187
2,281
698
m
OO
123
V©
O
00
3,670
O
309
1999
6,209
1 1
v©
23
out
635
8,006
c-~
235
87
09
433
V©
OS
3,106
OO
1998
5,529
272
665
1,496
734
8,675
o
2,029
93
m
167
376
50
OO
38
72
2,537
»/"S
304
1997
OO
o
o
242
832
46
1,685
859
9,474
1 |
79
1,463
269
»/"s
V©
293
37
67
m
1,259
OO
296
1996
5,185
47
827
1,629
933
9,223
ii
88
819
67
V©
79
262
20
44
58
OO
OO
m
1995
5,087
0\
799
1,611
1,023
8,569
o
148
o
74
123
»/"S
23
l/"S
»/"S
OO
V©
in
78
1994
6,614
OO
767
1,758
1,070
9,676
172
56
1—1
42
77
34
2,186
m
73
1993
4,360
C\
767
2,958
1,208
10,729
62
32
3,186
m
33
1992
OO
v©
OO
412
r-
3,909
o
o
9,986
220
102
3,154
V©
1991
4,161
Os
40
»/"s
1,976
932
OO
V©
oC
091
4,466
265
1990
4,378
V©
74
2,987
888
7,960
203
V©
3,663
o
137
1989
4,798
205
2,430
843
7,825
t—
2,988
o
22
1987
5,461
199
532
Os
2,064
583
7,115
35
c-~
87
1—1
o
3,032
o
783
1986
5,774
m
420
CN
OO
V©
o
ILL
7,273
o
34
3,144
»/"s
753
1985
5,033
277
808
62
1,255
796
7,036
25
o
193
OO
»/"S
o
108
2,797
OO
520
1984
5,338
887
650
748
6,875
23
24
1,134
o
341
1981
316
542
5,627
1980
73
433
4,446
1979
527
42
905
OO
952
326
442
»/"s
427
303
1978
2,057
V©
1,296
176
857
692
5,973
1—1
464
236
Tl-
319
318
47
901
56
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3
13,124
985
834
2,803
16,121
1,232
14,753
227
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OO
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870
494
682
341
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98
313
44
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CB5MH
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CB7PH
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GUNOH
MIDOH
BACOH*
PATMH
MAGMH
SEVMH
SOUMH
RHDMH
WSTMH
PAXTF*
WBRTF*
PAXOH
PAXMH
POTTF
ANATF
PISTF
appendix B
Shallow-Water Designated Use
Depths and Underwater Bay Grasses Restoration Goals
-------
B5
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-------
B6
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Underwater Bay Grasses Restoration Goals
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-------
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appendix B • Shallow-Water Designated Use Depths and Underwater Bay Grasses Restoration Goals
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a ppend ix(
Underwater Bay Grasses
No-Grow Zones Acreage
Table C-1. Underwater bay grasses no-grow zones acreage by Chesapeake Bay
Program segment.
Chesapeake Bay Program
Segment
CBP
Segment
Acres in
No Grow Zones
Reason
Northern Chesapeake Bay
CB1TF
679
1
Upper Chesapeake Bay
CB20H
1,564
1
Upper Central Chesapeake Bay
CB3MH
4,537
1
Middle Central Chesapeake Bay
CB4MH
14,590
1
Lower Central Chesapeake Bay
CB5MH
5,061
1
Western Lower Chesapeake Bay
CB6PH
3,684
1
Eastern Lower Chesapeake Bay
CB7PH
8,339
1
Mouth of the Chesapeake Bay
CB8PH
1,186
1
Patapsco River
PATMH
5,701
Magothy River
MAGMH
199
1
South River
SOUMH
102
1
Rhode River
RHDMH
375
1
West River
WSTMH
132
1
Lower Potomac River
POTMH
19
1
Lower Rappahannock River
RPPMH
395
1
Piankatank River
PIAMH
105
1
Mobjack Bay
MOBPH
635
1
Lower James River
JMSMH
4,312
1
Mouth of the James River
JMSPH
619
1
Western Branch Elizabeth River
WBELI
1,484
2
Southern Branch Elizabeth River
SBELI
2,073
2
Eastern Branch Elizabeth River
EBELI
1,426
2
Lafayette River
LAFMH
1,421
2
Mouth of the Elizabeth River
ELIPH
20,626
2
continued
appendix C • Underwater Bay Grasses No-Grow Zones Acreage
-------
C2
Table C-1. Underwater bay grasses no-grow zones acreage by Chesapeake Bay
Program segment (cont.).
Chesapeake Bay Program
Segment
CBP
Segment
Acres in
No Grow Zones
Reason
Northeast River
NORTF
<1
1
Sassafras River
SASOH
2
1
Eastern Bay
EASMH
134
1
Upper Choptank River
CHOTF
2,200
4
Middle Choptank River
CHOOH
984
4
Mouth of the Choptank River
CHOMH1
37
1
Little Choptank River
LCHMH
6
1
Upper Nanticoke River
NANTF
1,138
3
Wicomico River
WICMH
708
3
Big Annemessex River
BIGMH
4
1
Upper Pocomoke River
POCTF
988
3
Middle Pocomoke River
POCOH
2,466
1
Lower Pocomoke River
POCMH
13,293
1
Tangier Sound
TANMH
6,198
1
Reason Codes:
1 - Extreme physical wave energy.
2 - Permanent physical alteration to near-shore habitat.
3 - Natural, extreme coloration of the water.
4 - Natural river channelization.
appendix C • Underwater Bay Grasses No-Grow Zones Acreage
-------
D1
appendix u
Vertical Stratification
and the Pycnodine
The pycnodine has a functional role in defining designated use boundaries. The defi-
nitions of the designated use boundaries take into account the types and needs of the
living resources that inhabit different parts of the Chesapeake Bay, as well as the
bathymetry, hydrology, physical features, and natural stratification of the Chesa-
peake Bay waters as described in Chapter IV.
STRATIFICATION
Vertical stratification is foremost among the physical factors affecting dissolved
oxygen concentrations in some parts of Chesapeake Bay and its tidal tributaries.
Stratification arises from differences in water density within the water column due
to vertical differences in the salinity and temperature of the source waters feeding
into Chesapeake Bay tidal waters. The water coming into Chesapeake Bay and its
tidal tributaries from the land via the tributaries is fresh while water from the ocean
is saline. In the summer period, the water coming from the land is also warmer than
ocean water. Colder water is more dense than warmer water, and saline water is more
dense than fresh. The simple model is that the less dense freshwater moves seaward
over the layer of more dense seawater moving from the mouth of Chesapeake Bay
northward. An idealized example is shown in Figure D-l. To the extent that the two
(or more) layers remain self-contained and poorly mixed, the waters are stratified. If
the density discontinuity is great enough to prevent mixing of the layers and con-
stitutes a vertical barrier to diffusion of dissolved oxygen, then a pycnodine is said
to exist.
When physical features like channels, holes and sills inhibit lateral exchange of
waters and a pycnodine inhibits vertical exchange, oxygen that is consumed in
biological respiration or other oxygen-consuming processes in the imprisoned
subpycnocline waters cannot be replenished. When there is no barrier to lateral
exchange, the effect of the pycnodine on lower layer oxygen levels may be amelio-
rated. For this reason, the extent of isolation caused by a pycnodine, as well as the
frequency of formation and the depth of the pycnodine when present are factors to
be considered in defining designated use boundaries.
appendix D • Vertical Stratification and the Pycnodine
-------
D2
density
DO
A upper pyc
y lower pyc
-5 -
w
-------
D3
pycnocline depths were not overly sensitive to the threshold value chosen, since
mixed layer gradients tend to be much less than 0.1 kg/m4 and inter-pycnocline
gradients tend to be much greater than 0.1 kg/m4.
Using similar methods, the value of 0.2 kg/m4 was chosen as the lower pycnocline
depth gradient by the monitoring data analysis team at the Chesapeake Bay Program.
Vertical density and dissolved oxygen concentration plots from around the Chesa-
peake Bay and its tidal tributaries were examined to determine the threshold value
that was most representative of the density gradient defining the upper boundary of
the lower mixed layer, when and where it existed. The upper layer density threshold
of 0.1 kg/m4 was judged to be too low as it sometimes placed the lower pycnocline
depth at levels that did not have a large effect on the dissolved oxygen concentration.
PYCNOCLINE CALCULATION METHODOLOGIES
The Chesapeake Bay Program Water Quality Monitoring Program collects vertical
profiles of temperature, salinity and conductivity measurements (among other
parameters) at 1 to 2 meter intervals at each of its sampling stations. From these
measurements, there are at least two approaches for determining a pycnocline.
Vertical Density Profile
The upper and lower pycnocline depths can be determined by constructing a vertical
density (sigma_t) profile and applying an absolute density change threshold. This is
the method used for all pycnocline calculations in this document and is recom-
mended for application by the states in defining designated use boundaries. For a
detailed explanation of the derivation of this method see Fisher et al. (2003).
1) Calculate density using the following equations:
temp c = water temperature in degrees Celsius
sigo = -0.069+((1.47808*((salinity-0.03)/1.805))
(0.00157*(((salinityB0.03)/1.805)**2))
+0.0000398*(((salinityB0.03)/1.805)**3)));
tsum = (-l*(((tempc-3.98)**2)/503.57))*
((tempc+283)/(tempc+67.26));
sa = (10**-3)*tempc)*(4.7867-
(0.098185*tempc)+(0.0010843*(tempc**2)));
sb = ((10**-6)*tempc)*( 18.030-
(0.8164*tempc)+(0.01667*(tempc**2)));
Sigma_t = tsum+((sigo+0.1324)*(l-sa+sb*(sigo-0.1324)));
appendix D • Vertical Stratification and the Pycnocline
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D4
2) Apply the following rules to the density profile:
i) From the water surface, the first density slope observation that is greater
than 0.1 kg/m4 is designated as the upper pycnocline depth provided that:
a) That observation is not the first observation in the water column; and
b) The next density slope observation below is positive.
ii) From the bottom, the first density slope observation that is greater than
0.2 kg/m4 is designated as the lower pycnocline depth provided that:
a) An upper pycnocline depth exists;
b) There is a bottom mixed layer, defined by the first or second density
slope observation from the bottom being less than 0.2 kg/m4; and
c) The next density slope observation above is positive.
Vertical Differences in Conductivity
A 'working' pycnocline depth can be calculated using vertical differences in conduc-
tivity. The following is the Chesapeake Bay Water Quality Monitoring Program field
method applied during water quality monitoring sampling cruises for determining
the presence of a pycnocline and, if one or more exist, the depth of the upper and
lower boundary and, therefore, depths at which to collect water samples for chem-
ical analysis in the laboratory.
1) Find the average rate of change from surface to bottom: i.e., subtract surface
conductivity from bottom conductivity and divide by the depth.
2) Multiply the average rate of change by 2. This product is called the threshold.
3) If the threshold is less than 500, then it is determined that no pycnocline exists
at the site.
4) It the threshold is 500 or greater, then each interval from surface to bottom is
checked to determine if the difference from one meter to the next is greater than
or equal to the threshold. The upper pycnocline is defined as the first encounter
of a difference that exceeds the threshold and the upper pycnocline depth is set
at one-half the depth interval distance. For example, if the threshold is first
exceeded between 4 and 5 meters, then the pycnocline is set at 4.5 meters.
5) Then the process is reversed and each interval from bottom to surface is checked.
If the threshold is exceeded at a depth more than 1.5 meters from the upper pycn-
ocline, then a second pycnocline is said to exist and the lower pycnocline depth
is set at one-half the depth interval distance, as before.
Table D-l provides some statistics on the frequency of occurrence, depth of pycno-
clines, and the distance between upper and lower pycnoclines in spring and summer
at locations throughout the Chesapeake Bay and its tidal tributaries. The statistics are
for each Chesapeake Bay Water Quality Monitoring Program station over the period
analyzed for the allocations process 1985-1994. (See the Chesapeake Bay Program
website at http://www.chesapeakebay.net for a map of these stations.)
appendix D • Vertical Stratification and the Pycnocline
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D5
Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and
percent occurrence: 1985-1994.
Upper
Interpyc
Lower
Upper
Lower
Station
Depth
Depth
Depth
Depth
Percent
Percent
CB1.1
6.1
-
-
-
0%
0%
CB2.1
6.0
2.3
-
-
17%
0%
CB2.2
12.1
4.0
2.8
6.9
68%
20%
CB3.1
12.8
2.9
5.0
7.9
99%
76%
CB3.2
11.7
2.9
4.2
7.1
93%
57%
CB3.3C
23.7
4.2
10.6
14.8
100%
88%
CB3.3E
8.2
2.6
1.6
4.2
80%
18%
CB3.3W
9.0
2.7
2.3
5.0
77%
13%
CB4.1C
31.8
5.6
11.7
17.3
100%
96%
CB4.1E
23.1
6.5
7.8
14.3
99%
84%
CB4.1W
9.1
3.4
2.6
5.9
56%
19%
CB4.2C
26.8
6.9
9.6
16.5
100%
98%
CB4.2E
9.3
4.1
2.1
6.2
65%
13%
CB4.2W
9.3
4.3
1.2
5.5
46%
11%
CB4.3C
25.9
6.5
8.6
15.2
100%
94%
CB4.3E
22.1
7.1
7.8
14.8
97%
86%
CB4.3W
9.7
4.4
1.2
5.6
51%
10%
CB4.4
29.4
6.6
10.3
16.9
100%
100%
CB5.1
33.3
6.4
8.6
15.0
100%
99%
CB5.1W
9.1
4.4
-
-
24%
0%
CB5.2
29.5
7.5
9.0
16.6
100%
100%
CB5.3
26.2
6.1
7.2
13.2
100%
96%
CB5.4
32.6
5.3
12.8
18.1
100%
97%
CB5.4W
5.3
2.5
1.0
3.5
29%
3%
CB5.5
19.5
4.7
8.4
13.1
99%
79%
CB6.1
13.1
4.5
4.3
8.7
100%
80%
CB6.2
11.2
4.3
3.3
7.6
96%
76%
CB6.3
12.8
3.7
4.5
8.1
97%
87%
continued
appendix D • Vertical Stratification and the Pycnocline
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D6
Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and
percent occurrence: 1985-1994 (cont.).
Upper
Interpyc
Lower
Upper
Lower
Station
Depth
Depth
Depth
Depth
Percent
Percent
CB6.4
10.3
3.3
3.3
6.6
90%
54%
CB7.1
25.2
4.8
9.7
14.5
85%
65%
CB7.1N
31.7
5.9
12.5
18.4
69%
35%
CB7.1S
16.1
3.8
5.5
9.3
96%
87%
CB7.2
22.1
3.4
9.0
12.4
97%
95%
CB7.2E
13.4
3.2
3.7
6.9
88%
72%
CB7.3
13.8
3.3
5.8
9.1
96%
81%
CB7.3E
17.8
4.1
6.1
10.2
93%
73%
CB7.4
13.9
3.2
5.3
8.5
95%
79%
CB7.4N
12.9
3.3
3.9
7.3
74%
44%
CB8.1
9.8
3.5
3.7
7.2
95%
38%
CB8.1E
17.9
4.3
6.2
10.5
96%
82%
EBE1
8.4
3.2
1.8
5.0
61%
9%
EBE2
9.0
2.5
-
-
100%
0%
EE1.1
12.3
6.6
2.6
9.2
74%
31%
EE2.1
7.8
3.3
1.4
4.7
53%
12%
EE2.2
13.1
5.0
3.6
8.6
72%
49%
EE3.0
7.1
2.8
-
-
12%
0%
EE3.1
13.2
4.1
2.5
6.6
60%
16%
EE3.2
26.8
6.9
10.7
17.6
42%
9%
EE3.3
3.9
1.5
-
-
19%
0%
EE3.4
4.7
2.0
0.5
2.5
26%
4%
EE3.5
27.3
7.0
8.7
15.7
41%
19%
ELI1
8.0
3.5
-
-
100%
0%
ELI2
13.5
5.9
4.9
10.8
87%
30%
ELI3
12.0
3.5
6.0
9.5
100%
100%
ET1.1
2.9
-
-
-
0%
0%
ET10.1
5.2
-
-
-
0%
0%
continued
appendix D • Vertical Stratification and the Pycnocline
-------
D7
Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and
percent occurrence: 1985-1994 (cont.).
Upper
Interpyc
Lower
Upper
Lower
Station
Depth
Depth
Depth
Depth
Percent
Percent
ET2.1
13.2
4.0
-
-
3%
0%
ET2.2
2.9
-
-
-
0%
0%
ET2.3
12.3
4.5
-
-
8%
0%
ET3.1
5.3
-
-
-
0%
0%
ET4.1
5.4
1.8
-
-
5%
0%
ET4.2
13.9
5.4
4.4
9.8
70%
43%
ET5.1
5.7
2.0
-
-
8%
0%
ET5.2
11.8
3.7
3.4
7.1
76%
20%
ET6.1
5.0
1.5
-
-
3%
0%
ET6.2
3.8
1.5
-
-
49%
0%
ET7.1
7.7
2.3
0.6
2.9
71%
14%
ET8.1
5.1
1.7
2.8
4.5
31%
3%
ET9.1
4.8
1.5
1.0
2.5
11%
6%
LAF1
5.2
2.5
-
-
40%
0%
LE1.1
12.1
4.8
2.7
7.5
75%
25%
LEI.2
17.1
5.7
3.9
9.6
68%
16%
LEI.3
23.3
7.3
5.3
12.6
43%
9%
LEI.4
14.9
7.5
3.0
10.5
44%
4%
LE2.2
11.2
3.4
3.7
7.1
91%
64%
LE2.3
19.7
5.7
7.4
13.1
95%
77%
LE3.1
5.5
4.0
-
-
34%
0%
LE3.2
12.2
6.2
2.2
8.4
73%
43%
LE3.3
4.1
4.0
-
-
3%
0%
LE3.4
11.3
6.6
3.7
10.2
72%
23%
LE3.6
9.9
3.9
2.5
6.4
81%
30%
LE3.7
7.4
3.7
1.3
5.0
52%
8%
LE4.1
7.5
4.3
1.7
6.0
60%
6%
LE4.2
11.6
4.8
3.0
7.8
51%
17%
continued
appendix D • Vertical Stratification and the Pycnocline
-------
D8
Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and
percent occurrence: 1985-1994 (cont.).
Upper
Interpyc
Lower
Upper
Lower
Station
Depth
Depth
Depth
Depth
Percent
Percent
LE4.3
14.3
7.0
5.1
12.1
66%
39%
LE5.1
6.6
4.7
1.3
6.0
24%
1%
LE5.2
7.6
4.2
2.0
6.3
79%
10%
LE5.3
6.3
4.0
2.0
6.0
68%
3%
LE5.4
13.7
5.4
6.6
12.0
44%
13%
LE5.5
21.2
5.1
10.5
15.6
96%
73%
LE5.6
13.7
7.0
5.0
12.0
71%
16%
MAT0016
6.8
-
-
-
0%
0%
MAT0078
1.0
-
-
-
0%
0%
PIS0033
1.0
-
-
-
0%
0%
RET1.1
11.1
4.7
2.8
7.5
64%
9%
RET2.1
7.3
-
-
-
0%
0%
RET2.2
9.8
5.1
1.9
7.0
22%
2%
RET2.3
9.2
-
-
-
0%
0%
RET2.4
15.7
5.4
5.4
10.8
79%
33%
RET3.1
5.2
4.0
-
-
12%
0%
RET3.2
4.0
-
-
-
0%
0%
RET4.1
4.5
4.0
-
-
1%
0%
RET4.2
10.9
7.1
0.9
8.0
18%
1%
RET4.3
4.7
4.0
-
-
4%
0%
RET5.1
1.1
-
-
-
0%
0%
RET5.1A
2.8
-
-
-
0%
0%
RET5.2
7.5
4.9
-
-
15%
0%
SBE1
14.0
3.5
-
-
100%
0%
SBE2
12.5
4.4
4.9
9.3
83%
43%
SBE3
11.0
2.5
5.0
7.5
100%
100%
SBE4
12.0
2.5
-
-
100%
0%
SBE5
11.0
3.6
3.5
7.1
100%
70%
continued
appendix D • Vertical Stratification and the Pycnocline
-------
D9
Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and
percent occurrence: 1985-1994 (cont.).
Station
Depth
Upper Interpyc Lower Upper
Depth Depth Depth Percent
Lower
Percent
TF1.2
1.0
0%
0%
TF1.3
1.0
0%
0%
TF1.4
1.2
0%
0%
TF1.5
10.5
0%
0%
TF1.6
6.0
0%
0%
TF1.7
2.9
1.8 - - 5%
0%
TF2.1
19.0
0%
0%
TF2.2
8.3
0%
0%
TF2.3
12.8
0%
0%
TF2.4
8.9
0%
0%
TF3.1A
2.9
0%
0%
TF3.1B
2.9
0%
0%
TF3.1C
4.0
0%
0%
TF3.1D
2.7
0%
0%
TF3.1E
2.8
0%
0%
TF3.2
6.1
0%
0%
TF3.2A
4.0
0%
0%
TF3.3
5.7
4.2 - - 14%
0%
TF4.1A
5.8
0%
0%
TF4.2
5.9
0%
0%
TF4.4
2.7
0%
0%
TF4.4A
6.3
0%
0%
TF5.2
1.0
0%
0%
TF5.2A
7.0
0%
0%
TF5.3
9.8
0%
0%
TF5.4
5.8
0%
0%
TF5.5
8.2
0%
0%
TF5.5A
7.4
0%
0%
continued
appendix D • Vertical Stratification and the Pycnocline
-------
D10
Table D-1. Chesapeake Bay Water Quality Monitoring Program stations median pycnocline depths and
percent occurrence: 1985-1994 (cont.).
Upper
Interpyc
Lower
Upper
Lower
Station
Depth
Depth
Depth
Depth
Percent
Percent
TF5.6
8.5
6.0
-
-
1%
0%
TF5.6A
7.8
-
-
-
0%
0%
WBE1
4.7
2.8
-
-
17%
0%
WE4.1
6.1
2.9
0.7
3.6
35%
9%
WE4.2
14.5
6.3
4.2
10.5
86%
35%
WE4.3
6.0
2.8
0.8
3.5
20%
1%
WE4.4
7.6
2.3
1.5
3.8
19%
4%
WT1.1
2.3
-
-
-
0%
0%
WT2.1
2.0
-
-
-
0%
0%
WT3.1
3.3
1.5
-
-
5%
0%
WT4.1
1.8
-
-
-
0%
0%
WT5.1
14.5
3.6
7.7
11.3
100%
69%
WT6.1
5.4
2.5
1.0
3.5
57%
5%
WT7.1
8.6
3.1
2.4
5.4
87%
31%
WT8.1
8.6
2.2
1.7
3.8
91%
58%
WT8.2
2.9
1.5
-
-
2%
0%
WT8.3
3.3
1.5
-
-
15%
0%
WXT0001
1.1
-
-
-
0%
0%
XFB1986
1.5
-
-
-
0%
0%
XGG8251
5.5
2.5
-
-
8%
0%
Literature Cited: Fisher, T.R., A.B. Gustafson, H.L. Berndt, L. Walstad, L.W. Haas, and S. Maclntyre, "The upper mixed layer of
Chesapeake Bay, USA." Submitted to Estuaries, 2003.
appendix D • Vertical Stratification and the Pycnocline
------- |