SETTING AND ALLOCATING
THE CHESAPEAKE BAY
BASIN NUTRIENT AND SEDIMENT LOADS
The Collaborative Process, Technical Tools
and Innovative Approaches
PRINCIPAL AUTHORS
Robert Koroncai
U.S. Environmental Protection Agency
Region III
Philadelphia, PA
Lewis Linker
U.S. Environmental Protection Agency
Chesapeake Bay Program Office
Annapolis, Maryland
Jeff Sweeney
University of Maryland
Chesapeake Bay Program
Annapolis, Maryland
Richard Batiuk
U.S. Environmental Protection Agency
Chesapeake Bay Program Office
Annapolis, Maryland
U.S. Environmental Protection Agency
Region III
Chesapeake Bay Program Office
Annapolis, Maryland
DECEMBER 2003
-------
1
chapter |
Background
For the past twenty years, the Chesapeake Bay Program partners have been committed
to achieving and maintaining water quality conditions necessary to support living
resources throughout the Chesapeake Bay ecosystem. The 1983 Chesapeake Bay
Agreement set the stage for the collaborative multi-state and federal partnership, and
the 1987 Chesapeake Bay Agreement set the first quantitative nutrient reduction goals
(Chesapeake Executive Council 1983, 1987). With the signing of the Chesapeake
2000 agreement (Chesapeake Executive Council 2000), the Chesapeake Bay Program
partners committed to:
Defining the water quality conditions necessary to protect aquatic living
resources and then assigning load reductions for nitrogen and
phosphorus to each major tributary; and
Using a process parallel to that established for nutrients, determining the
sediment load reductions necessary to achieve the water quality con-
ditions that protect aquatic living resources, and assigning load
reductions for sediment to each major tributary.
Through a six-state memorandum of understanding, the headwater states of
Delaware, West Virginia and New York joined Maryland, Virginia, Pennsylvania, the
District of Columbia, the U.S. Environmental Protection Agency (EPA) and the
Chesapeake Bay Commission in committing to restore Chesapeake Bay and river
water quality through the adoption of new cap load allocations for nitrogen, phos-
phorus and sediment (Chesapeake Bay Watershed Partners 2001). All the watershed
partners understood that these allocations represented loading caps that must be
achieved and maintained, even in the face of increasing anthropogenic activities in
the watershed.
Using the best scientific information available, Chesapeake Bay Program partners
have agreed to nutrient and sediment cap loading allocations. On March 21, 2003
and April 15, 2003, the Chesapeake Bay Program Principals' Staff Committee and
representatives of the headwater states convened to adopt the nutrient and sediment
cap load allocations and submerged aquatic vegetation (SAV) restoration goals for
the Chesapeake Bay (Appendix A). The cap loads, allocated by major tributary basin
chapter i • Background
-------
2
and by state jurisdiction, will serve as a basis for each state's tributary strategies that,
when completed by April 2004, will describe local implementation actions necessary
to meet the Chesapeake 2000 nutrient and sediment cap load allocations by 2010.
This document describes the scientific and technical information and policy agree-
ments that formed the basis for the important, comprehensive agreements that the
Chesapeake Bay Program partners made with regard to cap load allocations for
nitrogen, phosphorus and sediments, as well as new baywide and local SAV restora-
tion goals. The assessment tools and techniques evolved significantly over the
allocation decision-making process, therefore, it should be noted that this document
is based on the most recent information and procedures used in support of the cap
load allocation decisions that were made.
FUNDAMENTALS OF DEVELOPING
CAP LOAD ALLOCATIONS
Cap load allocations can be defined as cumulative pollutant loadings for all point and
non-point sources established and assigned to different tributary basins within a larger
watershed that, when achieved, will allow the receiving water body to attain the
prescribed water quality goals. With the accelerated development of total maximum
daily loads (TMDLs) over the recent years, the development of loading caps has
become commonplace, but the size and complexity of the Chesapeake Bay watershed
has made allocation of the nutrient and sediment cap loads similarly complex.
Typically, water quality goals are prescribed in state water quality standards.
However, current state water quality standards addressing nutrient- and sediment-
related impairments for the Chesapeake Bay and its tidal tributaries, which are based
on national criteria first published in the 1960s for freshwater systems, only address
dissolved oxygen. For this reason, the EPA, in direct consultation with the watershed
states, developed comprehensive, Chesapeake Bay regional water quality criteria for
dissolved oxygen, chlorophyll a and clarity, along with SAV restoration goals for
each segment of the Chesapeake Bay and its tidal tributaries (U.S. EPA 2003a,
2003b). While at the time of publication of this document these criteria had not yet
been adopted into state water quality standards, they were used as the water quality
basis for setting and allocating the nutrient and sediment cap loads for the Chesa-
peake Bay watershed.
To determine the appropriate cap loads and allocate them to individual tributary
basins, the pollutant sources must be related to impacts on water quality. It is impor-
tant to quantify the loadings from all significant sources and to track the fate and
transport of those pollutants from the source to the Bay's tidal waters. In the case of
nutrients and sediments, the fate and transport mechanisms can be quite complex.
A complementary suite of models was employed to simulate the sources, transport,
fate and ultimate impact on tidal Bay water quality conditions of nutrient and
sediment loads. The airshed model was used to track air sources from the 350,000-
chapter i • Background
-------
3
square-mile Chesapeake Bay airshed and the transport and deposition of atmos-
pheric nitrogen loads to the Chesapeake Bay watershed and directly to tidal surface
waters. The watershed model tracked all sources—point, non-point and air deposi-
tion—within the watershed and simulated the fate of those pollutants as they were
transported through the free-flowing river systems of the watershed and delivered to
the tidal Bay waters. The water quality model, which is actually a compilation of
several models, then simulated the water quality impacts of those pollutants on the
water quality of the Chesapeake Bay and its tidal tributaries.
Knowing the water quality goals through the water quality criteria as applied within
the refined tidal-water designated uses and the reduced pollutant loading effects on
water quality through the models, it was possible to develop defensible, equitable cap
load allocations. However, good science was not enough to derive the cap load allo-
cations. It was also important to blend the scientific understanding with policy input
to derive cap load allocations that not only could achieve the stated water quality
goals but also could gain considerable support from local stakeholders ultimately
responsible for taking the actions necessary to reduce nutrient and sediment loadings.
Policy input to setting the cap load allocations was most important in determining an
appropriate distribution of the allowable pollutant loads by major tributary basin and
jurisdiction. 'Fair and equitable' were the basic principles used by the Chesapeake
Bay Program partners in allocating the cap loads. Such subjective qualities do not
readily lend themselves to technically based solutions without significant policy
direction on how to achieve this desired result. Once the policy direction was estab-
lished on distributing the cap loads 'fairly and equitably', a technical construct
supporting these policy principles was developed.
KEY PLAYERS IN DEVELOPING THE ALLOCATIONS
The Chesapeake Bay Program carries out its restoration and protection functions
through an extensive committee structure led by the original Chesapeake Bay agree-
ment signatories of Pennsylvania, Maryland, Virginia, the District of Columbia, the
EPA and the Chesapeake Bay Commission (Figure 1-1). For the development of
water quality criteria, refined tidal-water designated use and cap load allocations,
more than 500 individuals representing state, federal, regional and local government
agencies, academic institutions, businesses, conservation organizations, community
watershed organizations, many other nongovernmental organizations, as well as the
headwater states of New York, West Virginia and Delaware joined as fall partners.
Point source representatives and environmental groups also were well-represented
on the committees during this effort. An overview of the roles of each group and the
interplay between groups is described below and illustrated in figures 1-1 and 1-2.
A brief review of the primary groups is provided below.
WATER QUALITY TECHNICAL WORKGROUP
This workgroup consisted of technical staff and mid-level managers from the states,
the EPA and stakeholders from point source and environmental group interests and
chapter i • Background
-------
4
Citizens Advisory
Committee
Local Government
Advisory Committee
Scientific & Technical
Advisory Committee
Chesapeake Executive Council
Principals' Staff Committee
Implementation Committee
Fisheries Steering
Committee
Water Quality Steering
Committee
Water Quality Technical
Workgroup
Federal Agencies
Committee
Budget Steering
Committee
Nutrient
Subcommittees
Information
Management
Toxics
Monitoring
&
Assessment
Modeling
Living
Resources
Land, Growth
&
Stewardship
Communication
&
Education
Figure 1-1. Chesapeake Bay Program organizational structure.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
was expanded to include many of the modeling experts. Based on general policy
direction given by the Water Quality Steering Committee, the Water Quality Tech-
nical Workgroup assessed modeling results, explored options, developed the
allocation methodology and made recommendations to the Water Quality Steering
Committee on technical issues with regard to the allocations. The workgroup's
efforts were supported by several other groups:
• The Modeling Subcommittee maintained and updated the watershed and water
quality models used in the allocation effort and provided for all modeling
analyses, including an assessment of the relative impact of pollutant loadings
from the major basins on Bay water quality; the impact of nitrogen versus phos-
phorus versus sediment inputs on Bay water quality; and all sensitivity and cap
load allocation production runs leading up to the cap load allocations.
• The Nutrient Subcommittee developed the tiered scenarios and conducted an
assessment of sediment reduction efficiencies for near shore sediment reduction
best management practices.
chapter i • Background
-------
5
Principals' Staff
Committee and
Headwater State
Representatives
Monitoring and
Analysis
Subcommittee
Living Resources
Subcommittee
Use
Attainability
Analysis
Workgroup
Water Quality
Steering Committee
Water Quality
Technical
Workgroup
Dissolved
Oxygen
Criteria
Team
Nutrient
Subcommittee
Modeling
Subcommittee
Water
Clarity
Criteria
Team
Chlorophyll
Criteria
Team
Water Quality
Standards
Coordinators
Team
Figure 1-2. Chesapeake Bay Program partner's organizational structure supporting the
development and adoption of the Chesapeake Bay nutrient and sediment cap load
allocations.
• The Living resources Subcommittee developed the baywide and local SAV
restoration goals.
• The Monitoring and Analysis Subcommittee provided technical input and recom-
mendations on monitoring-related issues, including using a three-year averaging
period for all integrated monitoring and modeling results to determine attainability.
• The Dissolved Oxygen Criteria, Water Clarity Criteria, Chlorophyll Criteria and
Water Quality Standards Coordinators teams derived the water quality criteria and
refined tidal-water designated uses that were as the basis for setting and allocating
the cap loads and developed the cumulative frequency distribution biological
reference curve approach to determining criteria attainment.
• The Use Attainability Analysis Workgroup provided input on where to apply the
criteria throughout the Bay tidal waters and provided input on feasibility and cost
of options.
WATER QUALITY STEERING COMMITTEE
This committee consisted of senior water program managers from all states in the
Bay watershed, EPA Headquarters and regions II and III, the Chesapeake Bay
Commission, the Susquehanna River Basin Commission and the Potomac River
chapter i • Background
-------
6
Basin Commission. In addition, representatives from the point source and environ-
mental group interests attended the meetings. The committee provided critical
direction to the Water Quality Technical Workgroup, which explored policy and
technical issues related to the restoring Bay water quality initiative. The issues
explored included the derivation of the Bay water quality criteria, the refinement of
the tidal-water designated uses, analysis of the attainability of current and the refined
designated uses and the establishment and allocation of nutrient and sediment cap
loads. The committee selected the baywide nutrient cap loads from various options
that the workgroup forwarded. The Water Quality Steering Committee ultimately
forwarded a full package of nutrient and sediment cap load allocation recommenda-
tions to the Principals' Staff Committee for review and formal adoption.
PRINCIPALS' STAFF COMMITTEE
The Principals' Staff Committee (PSC) consists of the secretaries of the appropriate
natural resource, agricultural, and regulatory pollution control agencies for the
original signatory states of Pennsylvania, Maryland, Virginia, the District of
Columbia, the Regional Administrator of EPA Region III and the Executive Director
of the Chesapeake Bay Commission. While the headwater states of Delaware, New
York and West Virginia were not members of the committee, representatives of these
states attended PSC meetings and were directly involved in all decisions related to
the cap load allocations. The committee was responsible for approving the alloca-
tions, but the PSC's involvement went well beyond approving the package
recommended by the Water Quality Steering Committee. Since the recommendation
of the Water Quality Steering Committee did not fully allocate the agreed-upon
basinwide cap loads, the PSC and the headwater state representatives were called
upon to negotiate the allocation of the additional 12 milion pounds per year of
nitrogen reduction and 1 million pounds per year of phosphorus reduction necessary
to achieve the baywide loading caps.
REEVALUATING THE ALLOCATIONS
The nutrient and sediment cap load allocations adopted by the seven watershed juris-
dictions and EPA are the best scientific estimates of the annual load reductions
needed to attain proposed water quality criteria and tidal-water designated uses
described in the Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity
and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (Regional
Criteria Guidance) published by the EPA (U.S. EPA 2003a). Over the next two
years, Maryland, Virginia, Delaware and the District of Columbia will promulgate
new water quality standards based on the regional guidance published by EPA.
Although the public process for adopting water quality standards varies among the
states, each state's process will provide opportunities for considering and acquiring
new information at the local level. States may choose to explore a number of issues
chapter i • Background
-------
7
during their adoption process, such as the economic impact of water quality stan-
dards and specific designated use boundaries.
While the allocations adopted at this time will provide the basis for tributary strate-
gies, these allocations may need to be adjusted to reflect final state water quality
standards. Furthermore, planned Bay model refinements, designed to estimate water
quality benefits from filter feeding resources (such as oysters and menhaden) and
improve understanding of the sources and effects of sediments, will increase the
partners' understanding of the relationship between nutrient and sediment reductions
and living resource responses in the Chesapeake Bay. For these reasons, the states
and EPA agreed to a reevaluation of these cap load allocations by no later than 2007.
As partners, the jurisdictions committed to correcting the nutrient- and sediment-
related problems in the Chesapeake Bay and its tidal tributaries enough to remove
them from the list of impaired waters by 2010 under the Clean Water Act. The states
recognize, however, that it will be difficult to meet projected water quality standards
in all parts of the Chesapeake Bay tidal waters by that time. A key reason for this dif-
ficulty is that once nutrient and sediment reduction practices are installed and
implemented, it may be years or even decades before the Chesapeake Bay benefits
from these reductions. The jurisdictions intend to have programs in place and func-
tioning by 2010. The Chesapeake Bay and its tidal tributaries are expected to become
to be eligible for delisting when nutrient and sediment programs are fully imple-
mented in the basin.
SUPPORTING DOCUMENTS
In addition to recognizing the need for cap load allocations for nutrients and sediments,
Chesapeake 2000 also acknowledged the need for the development of scientifically
sound water quality criteria for the protection of the Chesapeake Bay's living resources
from nutrient- and sediment-related impacts. Through extensive scientific research,
partner involvement and stakeholder and scientific review, the EPA has published
regional water quality criteria for the Chesapeake Bay and its tidal tributaries for
dissolved oxygen, water clarity and chlorophyll a. A full description of these water
quality criteria can be found in the Regional Criteria Guidance (U.S. EPA 2003a).
To support the Regional Criteria Guidance, the EPA has published the Technical
Support Document for the Identification of Chesapeake Bay Designated Uses and
Attainability (Technical Support Document) (U.S. EPA 2003b). The purpose of the
Technical Support Document is to identify new refined tidal habitat zones, or desig-
nated uses, to which the Chesapeake Bay criteria will apply. In addition, SAV
restoration goals have been established by the Chesapeake Bay Program partners for
segments throughout the Chesapeake Bay tidal waters. The Technical Support Docu-
ment also delineates the boundaries of these designated uses and assesses their
technological attainability. The EPA also has published a companion document
entitled Economic Analysis and Impacts of Nutrient and Sediment Reduction Actions
chapter i • Background
-------
8
to Restore Chesapeake Bay Water Quality, which provides information on costs and
impacts of various levels of nutrient and sediment technology and best management
practices controls across the Chesapeake Bay watershed that may be necessary to
meet the new criteria and designated uses (U.S. EPA 2003c).
Collectively these three documents support the establishment of cap load allocations
for nutrients and sediments by identifying attainable water quality and resource
restoration goals for all habitats within the Chesapeake Bay and its tidal tributaries.
A memorandum from Secretary Tayloe Murphy (2003), Virginia Natural Resources
Secretary, to the Principals' Staff Committee members and representatives of the
Chesapeake Bay headwater states formally summarized the decisions regarding the
nutrient and sediment cap load allocations and the new submerged aquatic vegeta-
tion restoration goals.
A memorandum from Secretary Tayloe Murphy (2003), Virginia Natural Resources
Secretariate, to the Principals' Staff Committee members and representatives of the
Chesapeake Bay headwater states formally summarized the decisions regarding the
nutrient and sediment cap load allocations and the new submerged aquatic vegeta-
tion restoration goals.
ORGANIZATION OF THE ALLOCATIONS DOCUMENT
The cap load allocations were based largely on a scientific understanding of what
affects the water quality of the Chesapeake Bay and its tidal tributaries. Therefore,
much of this document is dedicated to presenting the scientific tools and issues that
were important to the development of the allocations. Accordingly, Chapter II
reviews the primary tools used in developing the cap load allocations, including the
loading scenarios. These scenarios were used to estimate the nutrient and sediment
loads associated with increased levels of pollution control measures and to gain
insight into the source loadings and associated impacts on water quality. In addition,
this chapter provides a brief technical review of the various models used to simulate
the source loads and their impact on the Bay's tidal water quality.
Chapter III reviews the major technical difficulties that arose and documents the
innovative solutions created by the partners' technical staff. Included in this chapter
are issues related to developing the methodology for determining attainment of the
water quality criteria (e.g., applying biological reference curves), results of assess-
ments on the impact of each major basin on the Bay's tidal water quality, results of
assessments on the water quality impact from nitrogen versus phosphorus inputs to
the Bay (e.g., analyzing relative effectiveness) and a brief technical review of the
attainment simulations for the SAV acreage goals established for the Bay.
However, significant policy guidance was vital in order to arrive at cap load alloca-
tions with the highest probability of 'buy-in' and, therefore, the greatest assurance of
implementation. Chapter IV describes how science informed the policy decisions
chapter i • Background
-------
9
applied during the cap load allocation process. It provides a detailed review of the
methodologies, model results and policy decisions used to derive the cap load alloca-
tions for nutrients and sediments. Specifically, it presents the principles applied and
approaches taken to derive baywide loading caps for nutrients and sediment and the
two separate methodologies used to distribute the cap loads to the major tributary
basins and then to jurisdictions within the Bay watershed for nutrients and sediments.
Finally, appendices A through F provide extensive model results and analyses in
support of the allocations.
LITERATURE CITED
Chesapeake Bay Watershed Partners. 2001.
Chesapeake Bay Executive Council. 2000. Chesapeake 2000 agreement. Annapolis, Maryland.
Chesapeake Bay Executive Council. 1987. Chesapeake Bay Agreement. Annapolis, Maryland.
Chesapeake Bay Executive Council. 1983. Chesapeake Bay Agreement. Annapolis, Maryland.
Secretary Tayloe Murphy. 2003. "Summary of Decisions Regarding Nutrient and Sediment
Load Allocations and New Submerged Aquatic Vegetation (SAV) Restoration Goals." April
25, 2003, Memorandum to the Principals' Staff Committee members and representatives of
the Chesapeake Bay headwater states. Virginia Office of the Governor, Natural Resources
Secretariate, Richmond, Virginia.
U.S. EPA. 2003a. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and
Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. EPA 903-R-03-002. Chesa-
peake Bay Program Office, Annapolis, Maryland.
U.S. EPA. 2003b. Technical Support Document for the Identification of Chesapeake Bay
Designated Uses and Attainability. EPA 903-R-03-004. Chesapeake Bay Program Office,
Annapolis, Maryland.
U.S. EPA. 2003c. Economic Analysis and Impacts of Nutrient and Sediment Reduction
Actions to Restore Chesapeake Bay Water Quality. Chesapeake Bay Program Office,
Annapolis, Maryland, http://www.chesapeakebay.net/ecoanalyses.htm.
chapter i • Background
-------
Contents
Acknowledgments vii
Executive Summary xi
CHAPTER I
Background 1
Fundamentals of Developing Cap Load Allocations 2
Key Players in Developing the Allocations 3
Water Quality Technical Workgroup 3
Water Quality Steering Committee 5
Principals' Staff Committee 6
Reevaluating the Allocations 6
Supporting Documents 7
Organization of the Allocations Document 8
Literature Cited 9
CHAPTER II
Overview of the Technical Tools 11
Tiered Management Implementation Scenarios 11
Development of the Tiered Scenarios 13
Tiered Scenario Estimated Nutrient and Sediment Loads 15
Chesapeake Bay Program Environmental Models 17
Chesapeake Bay Airshed Model and Atmospheric Deposition ... 19
Chesapeake Bay Watershed Model 23
Chesapeake Bay Water Quality Model 29
Hydrodynamic Model 29
Water Quality Model 31
Adjustment of Model Dissolved Oxygen, Water Clarity
and Chlorophyll a Estimates 33
Management Application of Model Outputs 36
Literature Cited 39
Contents
-------
iv
CHAPTER III
Technical and Modeling Considerations in Setting the Allocations .. 43
Refining Estimates of Pycnocline Depths 43
Averaging Period for Determining Criteria Attainment 44
Assessing Monitoring Data 44
Assessing Modeling Data 44
Defining Allowable Frequency and Duration of
Criteria Exceedances 46
Establishing the Geographic Influence of the Loads
on Tidal Water Quality 48
Focusing on Mainstem Segments CB3MH, CB4MH
and CB5MH 48
Comparing Absolute Versus Relative Effectiveness 48
Normalizing for the Combined Nitrogen and Phosphorus Load . . 49
General Findings from the Geographic Isolation Runs 51
Establishing Wetland Influence on Tidal-Water
Dissolved Oxygen Concentrations 54
Water Quality Model Runs Isolating Individual
Pollutant Effects on Water Quality 54
Surface Analysis Plots 54
Surface Analysis Utility 56
Influence of Sedimentation on Chesapeake Bay
Dissolved Oxygen 56
Establishing and Assessing the New SAV Restoration Goals 60
Developing the 185,000-Acre SAV Restoration Goal 61
Water Clarity and SAV 65
Sediment Loads: Local Effects 67
Calibrating the Water Quality Model for Clarity 68
Relating SAV Biomass to Acreage 70
Spatial Analysis of Effective Shoreline Load Reductions 74
Monitoring Approach 78
Sediment Cap Load Allocation Principles 78
Literature Cited 78
Contents
-------
V
CHAPTER IV
Setting the Nutrient and Sediment Allocations 81
Establishing Nutrient Cap Load Allocations 82
Geographic Location and Criterion Driving the Allocation 82
Baywide Cap Loading Options 83
Distributing Basinwide Allocations to the
Major Basins and Jurisdictions 91
The PSC Completes the Allocation Process 99
Cap Load Allocations to Achieve the Chlorophyll a Criteria .... 99
Additional Nutrient Cap Load Allocation Considerations 103
Establishing Sediment Cap Load Allocations 103
SAV Restoration as the Goal 103
Land-Based (Upland) Sediment Allocation 104
Establishing Near-Shore Sediment Allocation 105
SAV-Based Sediment Cap Load Allocations 106
Summary of Nutrient and Sediment Cap Load Allocations 106
Literature Cited 110
APPENDICES
Appendix A: Summary of Decisions Regarding Nutrient and
Sediment Load Allocations and New Submerged
Aquatic Vegetation (SAV) Restoration Goals—
Memorandum from W. Tayloe Murphy Jr., Chair,
Chesapeake Bay Program Principals' Staff Committee,
to the Principals' Staff Committee Members and
Representatives of Chesapeake Bay "Headwater" States A1
Appendix B: Summary of Water Quality Criteria and Use
Boundaries Used in Setting the Allocations B1
Appendix C: Summary of Watershed Model Results
for All Loading Scenarios CI
Appendix D: Summary of Key Attainment Scenarios D1
Contents
-------
-------
vii
Acknowledgments
Development of the nutrient and sediment allocations for the Chesapeake Bay
involved sifting through a wealth of scientific data and information, constructing
a technically sound decision making process and factoring in an array of policy con-
siderations. The collaborative efforts, collective knowledge and applied expertise of
the following committees, subcommittees, workgroups, and headwater representa-
tives were contributed to the success of the process.
Development of the technical recommendations that met the diverse needs of the
Chesapeake Bay Program partners would not have been possible without the under-
standing of water quality condition needs of the Bay, energy and enthusiasm, which
was provided by members of and staff to the Chesapeake Bay Program Water
Quality Technical Workgroup: Alan Pollock, Chair, Virginia Department of
Environmental Quality; Richard Batiuk, U.S. EPA Chesapeake Bay Program Office;
Victor Biennan, Jr., LimoTech Inc.; Michael Bowman, Virginia Department of
Conservation & Recreation; Charles Lunsford, Virginia Department of Conservation
& Recreation; William Brown, Pennsylvania Department of Environmental
Protection; Arthur Butt, Virginia Department of Environmental Quality; John
Kennedy, Virginia Department of Environmental Quality; James Collier, District of
Columbia Department of Health; Carol Young, Pennsylvania Department of
Environmental Protection; Richard Draper, New York State Department of
Environmental Conservation; Richard Eskin, Maryland Department of Environment;
Dave Montali, West Virginia Department of Environmental Protection; Will Hunley,
Hampton Roads Sanitation District; Maggie Kerchner, NOAA Chesapeake Bay
Office; Wendy Jastremski, U.S. EPA Chesapeake Bay Program Office; Robert
Koroncai, U.S. EPA Chesapeake Bay Program Office; Norm LeBlanc, Hampton
Roads Sanitation District; Lewis Linker, U.S. EPA Chesapeake Bay Program Office;
Russel Mader, National Resources Conservation Service; Robert Magnien,
Maryland Department of Natural Resources; Lee McDonnell, Pennsylvania
Department of Environmental Protection; Mark Morris, U.S. EPA Office of Water;
Scott Phillips, U.S. Geological Survey; Ana Pomales, U.S. EPA Region III;
Christopher Pomeroy, AquaLaw PLC; John Schneider, Delaware Department of
Natural Resources & Environmental Control; Gary Shenk, U.S. EPA Chesapeake
Bay Program Office; Tom Simpson, University of Maryland; Tanya Spano,
Metropolitan Washington Council of Governments; Peter Tango, Maryland
Department of Natural Resources; Lyle Varnell, Virginia Institute of Marine Science;
Lauren Wenzel, Maryland Department of Natural Resources; Allison Wiedeman,
U.S. EPA Chesapeake Bay Program Office; Clyde Wilbur, Greeley & Hansen; and
Kyle Zieba, U.S. EPA Chesapeake Bay Program Office.
Acknowledgments
-------
viii
Development of the nutrient and sediment cap load allocations would not have been
possible without the ability to understand the water quality and living resource
responses to pollutant loadings in the Bay Such understanding is made possible
through the Chesapeake Bay Airshed, Watershed and Water Quality models, which
are ably managed, maintained, and continually enhanced by members of the
Chesapeake Bay Program's Modeling Subcommittee: James Collier, Chair, District
of Columbia Department of Health; Lowell Bahner, National Oceanic & Atmos-
pheric Administration; Mark Bennett, U.S. Geological Survey; Peter Bergstrom,
U.S. Fish & Wildlife Service; Michael Bowman, Virginia Department of
Conservation & Recreation; William Brown, Pennsylvania Department of En-
vironmental Protection; Arthur Butt, Virginia Department of Environmental Quality;
Robin Dennis, National Oceanographic and Atmospheric Administration; Lewis
Linker, U.S. EPA Chesapeake Bay Program Office; Charles Lunsford, Virginia
Department of Conservation & Recreation; Robert Magnien, Maryland Department
of Natural Resources; Ross Mandel, Interstate Commission on the Potomac River
Basin; Timothy Murphy, Metropolitan Washington Council of Governments;
Narendra Panday, Maryland Department of Environment; Kenn Pattison,
Pennsylvania Department of Environmental Protection; Jeff Raffensperger, U.S.
Geological Survey-Baltimore; Helen Stewart, Maryland Department of Natural
Resources; Peter Tango, Maryland Department of Natural Resources; and Harry
Wang, Virginia Institute of Marine Science.
While all of the Modeling Subcommittee members made important contributions,
special recognition is appropriately due to Lewis Linker (EPA), Gary Shenk (EPA)
and Jeff Sweeney (University of Maryland) for pioneering efforts in creating new
approaches to difficult problems through relentless dedication to the task at hand.
Special thanks and recognition to Ping Wang (University of Maryland) for his skill,
expertise, and dedication in scenario operation and development on The National
Environmental Super Computer Center, and to Kate Hopkins (University Of
Maryland) for her expert application of GIS modeling support to the allocation
analyses.
The sediment allocation recommendations were driven by the new Submerged
Aquatic Vegetation (SAV) restoration goal. Without the close coordination between
the Chesapeake Bay Program's SAV Workgroup and the Water Quality Technical
Workgroup, linking the SAV resource to the sediment cap load allocations would not
have been possible. Mike Naylor (Maryland Department of Natural Resources), Ken
Moore (Virginia Institute of Marine Science), Frank Dawson (Maryland Department
of Natural Resources) and Mike Fritz (EPA) in particular, led the effort to assure
integration of the SAV restoration goal with efforts to derive water clarity criteria,
set shallow-water designated use boundaries and establish the sediment cap load
allocations.
The Chesapeake Bay Program's Scientific and Technical Advisory Committee
(STAC) provided timely and important input to the allocation process during a crit-
ical juncture in the deliberations. Special thanks to Scott Phillips for his leadership
in facilitating communication between STAC and the Water Quality Technical
Workgroup.
Cap load allocations, especially as complex as that for the Chesapeake Bay, are a
unique blend of science and policy. The Chesapeake Bay Program's Water Quality
Steering Committee provided much needed direction to the Water Quality
Acknowledgements
-------
ix
Technical Workgroup on difficult matters of equity and process. Furthermore, it was
the Water Quality Steering Committee that forwarded the cap load allocations to
the Principals' Staff Committee for approval. The members were: Jon Capacasa,
co-chair, U.S. EPA Region III; Rebecca Hanmer, co-chair, U.S. EPA Chesapeake
Bay Program; Russell Baxter, Chesapeake Bay Commission; Jerusalem Bekele,
District of Columbia Department of Health; Michael Bowman, Virginia Department
of Conservation & Recreation; Edward Brezina, Pennsylvania Department
of Environmental Protection; Patricia Buckley, Pennsylvania Department of
Environmental Protection; William Brannon, West Virginia Department
of Environmental Protection; James Collier, District of Columbia Department of
Health; Melanie Davenport, Chesapeake Bay Commission; Kevin Donnelly,
Delaware Department of Natural Resource and Environmental Control; Richard
Draper, New York State Department of Environmental Conservation; Phillip M.
DeGaetano, New York State Department of Environmental Conservation; Mario
DelVicario, U.S. EPA Region II; Diana Esher, U.S. EPA Chesapeake Bay Program
Office; Richard Eskin, Maryland Department of the Environment; Jack Frye,
Virginia Department of Conservation and Recreation; Stuart Gansell, Pennsylvania
Department of Environmental Protection; Carlton Haywood, Interstate Commission
on the Potomac River Basin; David Heicher, Susquehanna River Basin Commission;
James Keating, U.S. EPA Office of Water, Office of Science and Technology; Felix
Locicero, U.S. EPA Region II; Steve Luckman, Maryland Department of the
Environment; Robert Magnien, Maryland Department of Natural Resources; Chris
Miller, U.S. EPA Office of Water, Office of Science and Technology; Matthew
Monroe, West Virginia Department of Agriculture; Kenn Pattison, Pennsylvania
Department of Environmental Protection; Alan Pollock, Virginia Department of
Environmental Quality; John Schneider, Delaware Department of Natural Resources
and Environmental Control; Thomas Simpson, University of Maryland; Robert
Summers, Maryland Department of Environment; Ann Swanson, Chesapeake Bay
Commission; Robert Yowell, Pennsylvania Department of Environmental
Protection; and Robert Zimmerman, Delaware Department of Natural Resources and
Environmental Control.
Without a unified commitment to restoring the Chesapeake Bay, agreement on allo-
cating the last 12 million pounds of nitrogen and 1 million pounds of phosphorus
that is necessary to achieve the basinwide cap loads would not have been possible.
The Chesapeake Bay Program Principals' Staff Committee along with its new part-
ner states of Delaware, New York, and West Virginia, provided the leadership that
was necessary to approve the allocation recommendations and to allocate farther
remaining loads.
Principals' Staff Committee
W. Tayloe Murphy, Jr., Secretary of Natural Resources, Virginia, Office of
Governor (Chair)
Joseph Maroon, Director, Virginia Department of Conservation and Recreation
Robert G. Burnley, Director, Virginia Department of Environmental Quality
Theodore J. Gordon, Chief Operating Officer, District of Columbia Department of
Health
Elizabeth Berry, Special Assistant, Executive Office of Mayor, District of
Columbia
Acknowledgments
-------
X
Lewis R. Riley, Secretary, Maryland Department of Agriculture
Lynn Y. Buhl, Acting Secretary, Maryland Department of the Environment
C. Ronald Franks, Secretary, Maryland Department of Natural Resources
Audrey E. Scott, Secretary, Maryland Department of Planning
Kathleen A. McGinty, Secretary, Pennsylvania Department of Environmental
Protection
Michael DiBerardinis, Secretary, Pennsylvania Department of Conservation &
Natural Resources
Richard G. Sprenkle, Deputy Secretary, Pennsylvania Department of Conservation
and Natural Resources
Ann Swanson, Executive Director, Chesapeake Bay Commission
Donald S. Welsh, Regional Administrator, U.S. EPA Region III
Rebecca W. Hanmer, Director, U.S. EPA Chesapeake Bay Program Office
Headwater State Representatives
William Brannon, West Virginia Department of Environmental Protection
Matthew Monroe, West Virginia Department of Agriculture
Richard Draper, New York State Department of Environmental Conservation
Kevin Donnelly, Delaware Department of Natural Resources and Environmental
Conservation
Acknowledgments
-------
xi
Executive Summary
The Chesapeake 2000 agreement has been guiding Maryland, Pennsylvania,
Virginia, the District of Columbia, the Chesapeake Bay Commission and the
U.S. Environmental Protection Agency (EPA) in their combined efforts to restore
and protect the Chesapeake Bay. It defined the goal to "achieve and maintain the
water quality necessary to support the aquatic living resources of the Bay and its trib-
utaries and to protect human health." Subsequently, Delaware, New York and West
Virginia signed a Memorandum of Understanding committing to implement the
Water Quality Protection and Restoration section of the agreement.
Chesapeake 2000 committed its signatories to:
continue efforts to achieve and maintain the 40percent nutrient reduction
goal agreed to in 1987 and 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 by 2010.
Defining science-based loading caps for nutrients and sediment and allocating
responsibility by major tributary basin to the jurisdictions were critical steps to
fulfilling the water quality commitments. This document presents the collaborative
process, technical tools and innovative approaches that made possible the successful
allocation of nutrient and sediment cap loads to each jurisdiction by major tributary
basin.
NUTRIENT CAP LOAD ALLOCATIONS
Excessive nutrients in the Chesapeake Bay and its tidal tributaries promote a number
of undesirable water quality conditions such as excessive algal growth, low dissolved
oxygen and reduced water clarity. The effect of nutrient loads on water quality and
living resources tends to vary considerably by season and region. Low dissolved
oxygen problems tend to be more pronounced in the deeper parts of the upper bay
region during the summer months. The allocations for nutrients were developed
primarily to address this problem.
As a result, New York, Pennsylvania, Maryland, Delaware, Virginia, West Virginia,
the District of Columbia and the U.S. Environmental Protection Agency agreed to
cap annual nitrogen loads delivered to the Bay's tidal waters at 175 million pounds
Executive Summary
-------
xii
and annual phosphorus loads at 12.8 million pounds. It is estimated that these allo-
cations will require reductions, from 2000 levels, in nitrogen pollution by 110
million pounds and phosphorus pollution by 6.3 million pounds.
The Chesapeake Bay Program partners agreed to these load reductions based upon
Chesapeake Bay Water Quality Model projections of attainment of published Bay
dissolved oxygen criteria applied to the refined tidal water designated uses. The
model projects these load reductions will significantly reduce the persistent summer
anoxic conditions in the deep bottom waters of the Chesapeake Bay and restore suit-
able habitat quality conditions throughout the tidal tributaries. Furthermore, these
reductions are projected to eliminate excessive, sometimes harmful, algae conditions
(measured as chlorophyll a) throughout the Chesapeake Bay and its tidal tributaries.
The jurisdictions agreed to distribute the basinwide cap loads for nitrogen and phos-
phorus by major tributary basin (Table 1) and jurisdiction (Table 2). This distribution
of responsibility for load reductions was based on three basic principles:
1. Tributary basins with the highest impact on Chesapeake Bay tidal water quality
would be allocated the highest reductions of nutrients.
2. States without tidal waters—Pennsylvania, New York and West Virginia—
would be provided some relief from Principle 1 since they benefit less directly
from improved water quality in the Chesapeake Bay and its tidal tributaries.
3. Nutrient reductions prior to 2000 would be credited towards achievement of the
cap load allocations.
The nine major tributary basins were separated into three categories based upon their
impact on Bay tidal water quality. Each basin within an individual category was
assigned the same percent reduction of anthropogenic, or human-caused, load.
Consequently, basins with the highest impact on tidal water quality were assigned
the highest percentage reduction of anthropogenic load.
After completing the above calculations and applying Principle 2, New York, Penn-
sylvania and West Virginia allocations were set at the 'Tier 3' scenario nutrient load
levels. The Tier 3 scenario is one of several tiers representing different implementa-
tion scenarios of nutrient reduction measures for the Chesapeake Bay watershed
developed by the Chesapeake Bay Program partners. The Tier 3 scenario represented
nutrient and sediment loads of 181 million pounds of nitrogen per year, 13.4 million
pounds of phosphorus per year, 4.14 million tons of land-based sediment per year
and included a 20 percent reduction in tidal shoreline erosion sediment loads. Addi-
tionally, allocations for Virginia's York and James River basins were set at previously
established tributary strategy nutrient cap load levels since these two basins have a
minimal impact on mainstem Bay water quality conditions, and their influence on
tidal water quality is predominantly local.
Application of these rules resulted in shortfalls of 12 million pounds of nitrogen and
1 million pounds of phosphorus above the basinwide cap loads. However, the EPA
committed to pursue the Clear Skies initiative, which is estimated to reduce the
nitrogen load to Bay tidal waters by 8 million pounds per year. Furthermore, the Bay
watershed states agreed to take responsibility for the remaining 4 million pounds of
nitrogen and 1 million pounds of phosphorus. The nutrient cap load allocations in
tables 1 and 2 reflect these agreements.
Executive Summary
-------
The cap load allocations for nitrogen and phosphorus were adopted as 'nitrogen
equivalents'. Included was a commitment to explore how actions beyond traditional
best management practices (BMPs) might help meet the Chesapeake Bay water
quality restoration goals. A nitrogen equivalent is an action that results in the same
water quality benefit as removing nitrogen. The Chesapeake Bay Program partners
will evaluate how tidal water quality benefits from continued and expanded living
resource restoration, such as oysters and menhaden, can be accounted for in offset-
ting the reductions of watershed-based nutrient and sediment loads. Seasonal
fluctuations in implementation of biological nutrient removal, nutrient reduction
from shoreline erosion control, implementation of enhanced nutrient removal tech-
nologies at large wastewater treatment plants, and trade-offs between nitrogen and
phosphorus will also be evaluated.
Also, while the allocations adopted at this time will provide the basis for tributary
strategies, these allocations may need to be adjusted to reflect final state water
quality standards. If the final adopted state water quality standards are different than
the criteria and designated use used to establish these cap load allocations, then the
cap load allocations will need to be amended accordingly.
SEDIMENT CAP LOAD ALLOCATIONS
Sediments suspended in the water column reduce the amount of light available to
support healthy and extensive submerged aquatic vegetation (SAV), or underwater
bay grass, communities. The relative contribution of suspended sediment and algae
that cause poor light conditions varies with location in the Bay tidal waters. The
Chesapeake Bay Program partners agreed that a primary reason for reducing sediment
loads to the Bay tidal waters is to provide suitable habitat for restoring SAV. As a
result, the cap load allocations for sediments are linked to the recommended water
clarity criteria and the new SAV restoration goals and recognize that sediment load
reductions are essential to SAV restoration. The jurisdictions also agreed that nutrient
load reductions are critical for restoring SAV as well as improving oxygen levels.
To support the sediment cap load allocations, it became clear that updated SAV
restoration goals were needed. The partners explored various methodologies for
developing a baywide SAV acreage restoration target using the available historical
record. The methodology selected used aerial photography from the 1930s to present
to identify the best year of record (in terms of acres of SAV) for each Chesapeake
Bay Program segment. The acreage determined to be the best year of record was
designated as the SAV acreage goal for that segment. In aggregating all of the single
best year results for each segment, a baywide SAV acreage restoration goal for the
entire Bay of 185,000 acres was established. Table 3 provides the SAV acreage goal
for each Bay segment while Table 4 provides the SAV acreage goal for each major
tributary basin in the Chesapeake Bay watershed adopted by the Chesapeake Bay
Program partners.
Unlike nutrients, where loads from virtually the entire Chesapeake Bay watershed
affect mainstem Chesapeake Bay water quality, impacts from sediments are pre-
dominantly localized. For this reason, local, segment-specific SAV acreage goals
have been established and the sediment cap load allocations are targeted towards
achieving those restoration goals.
-------
xiv
The partners recognize that the current understanding of sediment sources and their
impact on the Chesapeake Bay is not yet complete. Currently understanding of land-
based sediments that are carried into local waterways through stream bank erosion
and runoff is still basic. Knowledge about nearshore sediments that enter the Bay and
its tidal rivers directly through shoreline erosion or shallow-water suspension is even
more limited. Consequently the sediment cap load allocations are currently focused
on land-based sediment cap loads by major tributary basin (Table 1) and jurisdiction
(Table 2).
Most land-based best management practices, which reduce nonpoint sources of
phosphorus, will also reduce sediment runoff. Therefore, the partners agreed to land-
based sediment allocations that represent the sediment load reductions likely to
result from implementing management actions required for the allocated phosphorus
reductions.
The sediment cap load allocations were set at the tier level for the phosphorus cap
load allocation for each jurisdiction-basin. This designation is referred to as the 'phos-
phorus equivalent' land-based sediment reduction. If the 'phosphorus equivalent'
land-based sediment reductions were found to be more than that which are necessary
to achieve the local S AV restoration goals, then the land-based sediment cap load allo-
cations were lowered to that level necessary to achieve the SAV restoration goal. The
tidal-fresh Susquehanna Flats and tidal-fresh Potomac River are two examples where
this modified approach was applied. If, in the development of their tributary strate-
gies, tributary teams conclude that the land-based sediment allocations need
revisions, the tributary teams may identify an alternate land-based allocation. For
example, a jurisdiction may select different nonpoint source management actions than
those prescribed in the tier approach to reach the phosphorus goal; the jurisdiction
may adjust the sediment cap load allocation accordingly so long as SAV restoration
and protection is not compromised. The tributary teams must work with all the juris-
dictions within the affected basin in revising the sediment cap load allocations.
It is likely that reductions in nutrients and land-based sediments alone will not be
sufficient to achieve the local SAV restoration goals for many areas of the Chesa-
peake Bay and its tidal tributaries. In these areas, tributary teams will be asked to
further assess varied and innovative methods to achieve SAV establishment and
growth. Such methods may include, but are not limited to SAV planting, offshore
breakwaters, shore erosion controls, beach nourishment, establishment of oyster
bars, and other actions as appropriate.
Executive Summary
-------
XV
Table 1. Chesapeake Bay watershed nitrogen, phosphorus and sediment cap load allocations
by major basin.
Nitrogen
Phosphorus
Upland Sediment
Cap Load Allocation
Cap Load Allocation
Cap Load Allocation
Basin/Jurisdiction (million pounds/year)
(million pounds/year)
(million tons/year)
SUSQUEHANNA
PA
67.58
1.90
0.793
NY
12.58
0.59
0.131
MD
0.83
0.03
0.037
SUSQUEHANNA Total
80.99
2.52
0.962
EASTERN SHORE - MD
MD
10.89
0.81
0.116
DE
2.88
0.30
0.042
PA
0.27
0.03
0.004
VA
0.06
0.01
0.001
EASTERN SHORE - MD Total
14.10
1.14
0.163
WESTERN SHORE
MD
11.27
0.84
0.100
PA
0.02
0.00
0.001
WESTERN SHORE Total
11.29
0.84
0.100
PATUXENT
MD
2.46
0.21
0.095
PATUXENT Total
2.46
0.21
0.095
POTOMAC
VA
12.84
1.40
0.617
MD
11.81
1.04
0.364
WV
4.71
0.36
0.311
PA
4.02
0.33
0.197
DC
2.40
0.34
0.006
POTOMAC Total
35.78
3.48
1.494
RAPPAHANNOCK
VA
5.24
0.62
0.288
RAPPAHANNOCK Total
5.24
0.62
0.288
YORK
VA
5.70
0.48
0.103
YORK Total
5.70
0.48
0.103
JAMES
VA
26.40
3.41
0.925
WV
0.03
0.01
0.010
JAMES Total
26.43
3.42
0.935
EASTERN SHORE - VA
VA
1.16
0.08
0.008
EASTERN SHORE - VA Total
1.16
0.08
0.008
SUBTOTAL
183
12.8
4.15
CLEAR SKIES REDUCTION -8
BASINWIDE TOTAL
175
12.8
4.15
Executive Summary
-------
xvi
Table 2. Chesapeake Bay watershed nitrogen, phosphorus and sediment cap load allocations
by jurisdiction.
Nitrogen
Phosphorus
Upland Sediment
Cap Load Allocation
Cap Load Allocation
Cap Load Allocation
Jurisdiction/Basin
(million pounds/year)
(million pounds/year)
(million tons/year)
PENNSYLVANIA
Susquehanna
67.58
1.90
0.793
Potomac
4.02
0.33
0.197
Western Shore
0.02
0.00
0.001
Eastern Shore - MD
0.27
0.03
0.004
PA Total
71.90
2.26
0.995
MARYLAND
Susquehanna
0.83
0.03
0.037
Patuxent
2.46
0.21
0.095
Potomac
11.81
1.04
0.364
Western Shore
11.27
0.84
0.100
Eastern Shore - MD
10.89
0.81
0.116
MD Total
37.25
2.92
0.712
VIRGINIA
Potomac
12.84
1.40
0.617
Rappahannock
5.24
0.62
0.288
York
5.70
0.48
0.103
James
26.40
3.41
0.925
Eastern Shore - MD
0.06
0.01
0.001
Eastern Shore - VA
1.16
0.08
0.008
VA Total
51.40
6.00
1.941
DISTRICT OF COLUMBIA
Potomac
2.40
0.34
0.006
DC Total
2.40
0.34
0.006
NEW YORK
Susquehanna
12.58
0.59
0.131
NY Total
12.58
0.59
0.131
DELAWARE
Eastern Shore - MD
2.88
0.30
0.042
DE Total
2.88
0.30
0.042
WEST VIRGINIA
Potomac
4.71
0.36
0.311
James
0.03
0.01
0.010
WV Total
4.75
0.37
0.320
SUBTOTAL
183
12.8
4.15
CLEAR SKIES REDUCTION -8
BASINWIDE TOTAL
175
12.8
4.15
Executive Summary
-------
xvii
Table 3. Chesapeake Bay submerged aquatic vegetation (SAV)
restoration goal acreage by Chesapeake Bay Program (CBP) segment
based on the single best year of record from 1930 to present.
CBP Segment Name
Segment
Acres
Northern Chesapeake Bay
CB1TF
12,908
Upper Chesapeake Bay
CB20H
302
Upper Central Chesapeake Bay
CB3MH
943
Middle Central Chesapeake Bay
CB4MH
2,511
Lower Central Chesapeake Bay
CB5MH
14,961
Western Lower Chesapeake Bay
CB6PH
980
Eastern Lower Chesapeake Bay
CB7PH
14,620
Mouth of the Chesapeake Bay
CB8PH
6
Bush River
BSHOH
158
Gunpowder River
GUNOH
2,254
Middle River
MIDOH
838
Back River
BACOH
0
Patapsco River
PATMH
298
Magothy River
MAGMH
545
Severn River
SEVMH
329
South River
SOUMH
459
Rhode River
RHDMH
48
West River
WSTMH
214
Upper Patuxent River
PAXTF
5
Western Branch (Patuxent River)
WBRTF
0
Middle Patuxent River
PAXOH
68
Lower Patuxent River
PAXMH
1,325
Upper Potomac River
POTTF
4,368
Anacostia River
ANATF
6
Piscataway Creek
PISTF
783
Mattawoman Creek
MATTF
276
Middle Potomac River
POTOH
3,721
Lower Potomac River
POTMH
10,173
Upper Rappahannock River
RPPTF
20
Middle Rappahannock River
RPPOH
0
Lower Rappahannock River
RPPMH
5,380
Corrotoman River
CRRMH
516
Piankatank River
PIAMH
3,256
Upper Mattaponi River
MPNTF
75
Lower Mattaponi River
MPNOH
0
Upper Pamunkey River
PMKTF
155
Lower Pamunkey River
PMKOH
0
Middle York River
YRKMH
176
Lower York River
YRKPH
2,272
Mobjack Bay
MOBPH
15,096
continued
Executive Summary
-------
xviii
Table 3. Chesapeake Bay submerged aquatic vegetation (SAV)
restoration goal acreage by Chesapeake Bay Program (CBP) segment
based on the single best year of record from 1930 to present (cont.).
CBP Segment Name
Segment
Acres
Upper James River
JMSTF
1,600
Appomattox River
APPTF
319
Middle James River
JMSOH
7
Chickahominy River
CHKOH
348
Lower James River
JMSMH
531
Mouth of the James River
JMSPH
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
69
Northeast River
NORTF
88
C&D Canal
C&DOH
0
Bohemia River
BOHOH
97
Elk River
ELKOH
1,648
Sassafras River
SASOH
764
Upper Chester River
CHSTF
0
Middle Chester River
CHSOH
63
Lower Chester River
CHSMH
2,724
Eastern Bay
EASMH
6,108
Upper Choptank River
CHOTF
0
Middle Choptank River
CHOOH
63
Lower Choptank River
CHOMH2
1,499
Mouth of the Choptank River
CHOMH1
8,044
Little Choptank River
LCHMH
3,950
Honga River
HNGMH
7,686
Fishing Bay
FSBMH
193
Upper Nanticoke River
NANTF
0
Middle Nanticoke River
NANOH
3
Lower Nanticoke River
NANMH
3
Wicomico River
WICMH
3
Manokin River
MANMH
4,359
Big Annemessex River
BIGMH
2,014
Upper Pocomoke River
POCTF
0
Middle Pocomoke River
POCOH
0
Lower Pocomoke River
POCMH
4,092
Tangier Sound
TANMH
37,965
Total acres
184,889
Executive Summary
-------
Table 4. Chesapeake Bay submerged aquatic vegetation
(SAV) restoration goal acreage by major basin by jurisdiction.
Basin/Jurisdiction
SAV Restoration Goal (Acres)
SUSQUEHANNA
12,856
EASTERN SHORE - MD
76,193
WESTERN SHORE - MD
5,651
PATUXENT
1,420
POTOMAC1
MD
12,747
VA
6,320
DC
384
RAPPAHANNOCK
12,798
YORK
21,823
JAMES
3,483
EASTERN SHORE - VA
31,215
TOTAL
184,889
1 Breakdown of Potomac SAV restoration goals by jurisdictions are draft, pending
confirmation of split between Maryland, Virginia and the District of Columbia
along jurisdictional lines. Due to ongoing refinement, some numbers in this table
differ from the April 25, 2003 version included in Appendix A and previous model
estimates presented in tables III-3 and III-4.
-------
11
chapter |
Overview of Technical Tools
Pollutant loading allocations must be based on credible science. It is important to
understand and simulate the source loadings, as well as their impact on the water
quality of the receiving water body. Because the Chesapeake Bay nutrient and
sediment dynamics are so complex, establishing the scientific basis required the
application of several coupled models of the Chesapeake Bay ecosystem:
• The Chesapeake Bay Airshed Model provided simulations of air sources of
nutrients and air deposition onto the Chesapeake Bay watershed and the tidal
surface waters;
• The Chesapeake Bay Watershed Model tracked loadings from all sources of
nutrients and sediments in the watershed and simulated pollutant transport down
to the Chesapeake Bay and its tidal tributaries;
• The Chesapeake Bay Water Quality Model is an aggregate of several models—
hydrodynamic, water quality, bottom sediment, benthic community and SAV
community—which combined effectively, simulated the effects of nutrient and
sediment pollutant loadings on the water quality of the Chesapeake Bay and its
tidal tributaries.
A brief review of these important tools is provided below. In addition, a description
is provided of the development of management control scenarios, called 'tiers',
which played a critical role in the process of developing allocations.
TIERED MANAGEMENT IMPLEMENTATION SCENARIOS
A series of watershed model scenarios were designed to estimate the nutrient and
sediment loads associated with increased implementation levels of best management
practices (BMPs), wastewater treatment upgrades and/or other point or non-point
control technologies. The resultant watershed model outputs—various combinations
of nitrogen, phosphorus and sediment delivered loads to tidal Bay waters—were
used as inputs to the Chesapeake Bay Water Quality Model to evaluate the relative
response of key tidal water quality parameters (i.e. dissolved oxygen, water clarity
and chlorophyll a concentrations) to these watershed loading levels. The range of
chapter ii • Overview of Technical Tools
-------
12
water quality responses, in turn, helped define cause (nutrient and sediment load-
ings) and effect (tidal water quality) relationships and were used in assessing the
attainability of current and refined designated uses (see Tiered Scenario Estimated
Nutrient and Sediment Loads).
These tiered scenarios do not prescribe control measures necessary for the watershed
jurisdictions to meet the Chesapeake 2000 nutrient and sediment cap load alloca-
tions. Again, they were developed as a tool to assess relative water quality impacts
from a range of load reductions. The scenarios are theoretical constructs of tech-
nological levels of effort and do not represent actual programs that jurisdictions must
implement or required combinations of region-specific BMPs. Cost effective combi-
nations of BMPs will be evaluated by the jurisdictions working directly with their
tributary strategy teams, who will address real issues such as physical limitations and
any potential adverse economic impacts from implementation.
The tiered scenarios characterize the Chesapeake Bay watershed's nutrient and sedi-
ment reduction potential in terms of types of BMPs, extent of implementation and
performance of BMPs for both point and nonpoint sources (Appendix B). Tier defi-
nitions were designed to ensure each Tier went beyond the nutrient and sediment load
reductions of the previous tier and, therefore, imply a 'level of effort'. The scenarios
range from the Tier 1 scenario, representing extensions of current implementation
rates throughout the watershed plus regulatory requirements in place by 2010, to
everything, everywhere by everybody (E3 scenario), which goes beyond any previous
Chesapeake Bay Program definition of 'limit of technology' (LOT). Two intermediate
levels of implementation, the Tier 2 and Tier 3 scenarios, were also developed.
If the only objective of developing the tier scenarios was to relate tidal water quality
response to nutrient and sediment load reductions, it would not have been necessary
to define the scenarios in terms of increased implementation levels of BMPs and
control technologies. This objective could have been accomplished by setting incre-
mental loading reductions from all tributary basins in the Bay watershed. However,
assessments of attainability of the current and refined tidal water designated uses
required the association of load reductions to specific implementation levels of
BMPs or control technologies, their nutrient and sediment reduction efficiencies, and
their feasibility of implementation.
Important Note: Tiers are artificial constructs of technological levels of effort
and were not meant to represent actual programs the jurisdictions will eventu-
ally implement to meet water quality standards. In addition, the tiers do not
denote combinations of region-specific BMPs that would best reach the
nitrogen, phosphorus and sediment cap loads allocated to each jurisdiction
within each tributary. They were developed as an assessment tool to determine
relative water quality impacts from a range of load reductions. Tier definitions
were designed to ensure each Tier went beyond the nutrient and sediment load
reductions of the previous Tier.
Appendix A of the Technical Support Document describes the development of
the tier scenarios and the pollutant control technologies represented in each tier
(U.S. EPA 2003a). Both Appendix A and Chapter V of this document present the
chapter ii • Overview of Technical Tools
-------
13
Chesapeake Bay watershed model estimates of the nitrogen, phosphorus and sedi-
ment load reductions associated with each of the tier scenarios.
The tier scenarios were based primarily on BMPs and control technologies directed
toward reductions in nitrogen and phosphorus loads. The model-simulated sediment
reductions were incidental responses to the implementation of nutrient reduction
BMPs. Other sediment reduction management practices are available and may if
implemented along with nutrient reduction efforts, afford additional water quality
improvements (see Chapter III). This is especially true for BMPs applied in the near
shore areas of the tidal Bay.
DEVELOPMENT OF THE TIERED SCENARIOS
The tiered BMP implementation levels were initially defined by the 'source' work-
groups of the Chesapeake Bay Program Nutrient Subcommittee. The Agricultural
Nutrient Reduction, Forestry, Point Source and Urban Stonnwater workgroups,
which is comprised of representatives of Bay watershed jurisdictions and other tech-
nical experts, contributed expertise and information for their assigned 'source'. In
some cases, the Nutrient Subcommittee's Tributary Strategy Workgroup edited the
tier scenario definitions so that necessary input decks for the watershed model,
which captured the essence of the definitions, could be developed.
Projected 2010 Conditions
All tier scenarios were based on 2010 projections of land uses, human populations,
agricultural animal populations, point source flows, and septic systems, as well as
2007/2010 or 2020 air emissions. Land use and human and animal population
projections were 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 (Hopkins et al. 2000).
Agricultural land uses were projected from agricultural census county information
(1982, 1987, 1992 and 1997) according to methodologies chosen by individual states.
The projected animal populations were also based on county agricultural census
trends and information provided by state environmental and agricultural agencies.
Urban land uses for 2010 were projected from a methodology involving human
population changes, as determined by the U.S. Census Bureau for 1990 and 2000, as
well as by some individual state agencies. The population changes were related to
1990 high-resolution satellite imagery of the Chesapeake Bay watershed, which is
the root source of urban and forest land acreages. In the case of Maryland, urban
growth from 2000 to 2010 was determined by Maryland Department of Natural
Resources and Maryland Department of Planning.
With urban and agricultural land use acreages fixed for 2010, the remaining land was
divided between forest and mixed open in the same proportion that existed in 1990
for New York, Pennsylvania, Delaware, West Virginia, and the District of Columbia.
The 2010 forest acreage was fixed for Maryland and Virginia following methodolo-
gies or data submitted by those states with the remaining acreage being mixed open.
chapter ii • Overview of Technical Tools
-------
14
Tier Scenario Components
Point Source
A multi-stakeholder Nutrient Reduction Technology Cost Task Force, which
consisted of federal, state and local representatives as well as municipal authority
representatives and expert consultants, was formed as a temporary extension of the
Nutrient Subcommittee's Point Source Workgroup. The Task Force defined what
would be logical tiers (break points) for incremental levels of point source control
technology implementation (U.S. EPA 2002). Using wastewater flows projected for
the year 2010, the tier scenarios range from the current (year 2000) treatment levels
to the E3 scenario.
Future flow projections were developed either from population projections or infor-
mation obtained directly from the municipal facility operators. The tier and E3
scenario flows for industrial dischargers remained at 2000 levels because these flows
are not necessarily subject to population growth. The point source facilities analyzed
in this effort include all significant facilities (including industrial) as defined by
New York, Pennsylvania, Maryland, Virginia, Delaware, West Virginia and the
District of Columbia.
Nonpoint Source: Agriculture
In the Tier 1 scenario, nonpoint source agricultural BMP implementation rates
between 1997 and 2000 were continued to the year 2010 with certain limitations.
Since historic BMP data were not available from New York, Delaware and West
Virginia, 2010 Tier 1 projections were determined from watershed-wide implemen-
tation rates from states that employed and tracked similar practices from 1997
through 2000.
The Tier 2 and Tier 3 scenario BMP implementation levels were generally deter-
mined by increasing BMP implementation by a fixed percentage of the remaining
acreage between Tier 1 and E3 levels. The percentages were specific for each BMP
and applied watershed-wide.
Nonpoint Source: Urban
The Tier 1 scenario represents voluntary and regulatory storm water management
programs that are or will be in place by 2010. These include both federal programs,
such as the EPA's National Pollutant Discharge Elimination System Phase I and II
storm water regulations, and state erosion control/storm water management
programs. The Tier 2 and 3 scenarios represent progressively increasing levels of
urban nonpoint source BMP implementation beyond Tier 1.
Atmospheric Deposition
The Chesapeake Bay Program modeled four different nitrogen oxide (NOx) emis-
sion reduction scenarios to estimate changes in atmospheric nitrate deposition and
loading to the Chesapeake Bay watershed (U.S. EPA 2003a). The NOx emission
reductions associated with Tier 1 and 2 scenarios are based on Clean Air Act
regulations. In the Tier 3 and E3 scenarios, NOx emission reductions go beyond
current regulations and include aggressive voluntary controls. All scenarios involve
chapter ii • Overview of Technical Tools
-------
15
the combined NOx emission reductions from 37 states within the Chesapeake Bay
airshed, well beyond the Chesapeake Bay watershed jurisdictions' boundaries.
E3 Scenario
To estimate non-attainment caused by human-caused conditions that cannot be
remedied, a boundary scenario had to be defined. In the past, the Chesapeake Bay
Program partners defined this as the 'limit of technology'. The BMP levels and
control technologies in the E3 scenario are believed by the Chesapeake Bay Program
partners to be beyond feasible. Cost, physical limitations and social/economic
impacts were not taken into account in order to eliminate subjectivity as much as
possible from the E3 definitions.
The E3 scenario represents the maximum theoretical implementation of the best
combination of BMPs or control technologies available to a land use or situation. It
is assumed that nutrient and sediment reductions beyond this level represent
"human-caused conditions that cannot be remedied." Generally, these are the best
nutrient and sediment reductions possible with current technologies at maximum
BMP implementation levels and include new technologies and management prac-
tices that are not currently part of jurisdictional pollutant control strategies or
federal, state or local cost-share programs. Appendix A of the Technical Support
Document details the assumptions and methodologies used to develop each control
technology and BMP-based implementation level in the E3 scenario for all nutrient
and sediment source categories and land uses (U.S. EPA 2003a).
TIERED SCENARIO ESTIMATED NUTRIENT AND SEDIMENT LOADS
The estimated Watershed Model loads for nitrogen, phosphorus and sediment loads
from simulated implementation of the tiered and E3 scenarios are described below
and graphically summarized in figures II-1, II-2 and II-3, respectively.
These load estimates are compared with modeled 2000 Progress loads of 285 million
pounds of nitrogen per year, 19 million pounds of phosphorus per year, and 5.04
million tons per year of land-based sediment.
Tier 1
The nutrient and sediment loads associated with the Tier 1 scenario are 261 million
pounds of nitrogen per year, 19.1 million pounds of phosphorus per year, and 4.64
million tons of land-based sediment per year. This represents an 8 percent reduction
in nitrogen, a 1 percent reduction in phosphorus, and an 8 percent reduction in sedi-
ment loads to the Chesapeake Bay from 2000 progress levels.
Tier 2
The nutrient and sediment loads associated with the Tier 2 scenario are 221 million
pounds of nitrogen per year, 16.4 million pounds of phosphorus per year, and
4.14 million tons of land-based sediment per year. Compared to 2000 progress
estimated loads, this represents a 22 percent reduction in nitrogen, a 14 percent
reduction in phosphorus, and an 18 percent reduction in sediment loads.
chapter ii • Overview of Technical Tools
-------
16
300
250
<0
a>
« ^ 200
15 o>
§ o.
_J <0
g 1 150
o> o
2 a.
z .2 100
50
284.76
260.93
221.26
180.76
175
2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3 2010 E3
ZII Chesapeake Bay Watershed ^^2010 Cap Load Allocation
Figure 11-1. Nitrogen loads delivered to the Chesapeake Bay and its tidal tributaries under the
watershed model-simulated 2000 Progress, tiered and E3 scenarios.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
25
<5 20
a>
>.
15
?i
0) «
O 3
Q- Q. 10
<0
5 O
Q- =
E 5
19.12
18.96
16.41
13.38
12.8
10.10
2000 Progress
2010 Tier 1
2010 Tier 2
2010 Tier 3
2010 E3
] Chesapeake Bay Watershed
¦2010 Cap Load Allocation
Figure II-2. Phosphorus loads delivered to the Chesapeake Bay and its tidal tributaries under the
watershed model-simulated 2000 Progress, tiered and E3 scenarios.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • Overview of Technical Tools
-------
17
6
5.04
4.64
4.14
3.62
2.95
4.15
E
0
2000 Progress 2010 Tier 1
2010 Tier 2
2010 Tier 3
2010 E3
i 1 Chesapeake Bay Watershed ^^2010 Cap Load Allocation
Figure II-3. Land-based sediment loads delivered to the Chesapeake Bay and its tidal tributaries
under the watershed model-simulated 2000 Progress, tiered and E3 scenarios.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
The nutrient and sediment loads associated with the Tier 3 scenario are 181 million
pounds of nitrogen per year, 13.4 million pounds of phosphorus per year, and
3.62 million tons of land-based sediment per year. This represents a 37 percent
reduction in nitrogen, a 30 percent reduction in phosphorus, and a 28 percent reduc-
tion in sediment loads from 2000 levels.
The combination of aggressive land and air nutrient controls resulted in E3 scenario
loads of about 116 million pounds of nitrogen per year, 10.1 million pounds of phos-
phorus per year, and 2.95 million tons of land-based sediment per year. Compared to
2000 progress loads, this represents a 59 percent reduction in nitrogen, a 47 percent
reduction in phosphorus, and a 41 percent reduction in land-based sediment loads.
The Chesapeake Bay Program partners use a series of environmental models to
project changes in the complex Bay ecosystem due to management actions. The
Chesapeake Bay Program has developed what have become standard large water-
shed estuarine modeling tools, including an airshed model or Regional Acid
Deposition Model (RADM) (Shin and Carmichael 1992; Appleton 1995, 1996), a
watershed model (Donigian et al. 1994; Linker 1996; Linker et al. 2000), an estu-
arine hydrodynamic model (Wang and Johnson 2000), an estuarine water quality
Tier 3
E3
CHESAPEAKE BAY PROGRAM
ENVIRONMENTAL MODELS
chapter ii • Overview of Technical Tools
-------
18
model (Cerco and Cole 1993, 1995a, 1995b; Thomann et al. 1994; Cerco and
Meyers 2000; Cerco 2000; Cerco and Moore 2001; Cerco et al. 2002a), and an
estuarine sediment diagenesis model (Di Toro and Fitzpatrick 2001). The Chesa-
peake Bay Program has used these environmental models for more than 18 years and
has refined and upgraded each of the models several times. Figure II-4 portrays the
interconnections among these cross-media models.
Results from the integrated airshed, watershed and estuarine models are used to
elucidate complexities like eutrophication of the Chesapeake Bay or to closely
examine sediment sources to assess their impacts on water quality and living
resources in tidal waters. Together, these linked simulations provide a system to
estimate dissolved oxygen, water clarity and chlorophyll a conditions in 35 major
segments of the Chesapeake Bay and its tidal tributaries. The same criteria
attainment assessment process applied to observed data is applied to integrated
modeling/monitoring 'scenario' data to determine likely criteria attainment under
management loading scenarios (U.S. EPA 2003b, Linker et al. 2002).
The watershed and airshed models are loading models. As such, they provide esti-
mates of the impacts of management actions through air emission controls,
agricultural and urban best management practices, and point source technologies
Regional Acid Deposition Model
~
Chesapeake Bay Watershed Model
*
Submerged Aquatic
|
Sediment Benthic
Vegetation
1
Model
Water Quality Model
Chesapeake Bay O Estuary Model
Hydrodynamic Model
of the Bay, Tributaries, and Continental Shelf
Figure 11-4. Cross-media models of the Chesapeake Bay airshed, watershed and estuary.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net.
chapter ii • Overview of Technical Tools
-------
19
that will reduce nutrient or sediment loads to the Chesapeake Bay tidal waters. The
advantage of using loading models is that the full simulation through different
hydrology periods (i.e., wet, dry and average) can be simulated on existing or hypo-
thetical land use patterns. All of the Chesapeake Bay Program models used in this
system simulate the same 10-year period from 1985 to 1994 (Linker et al. 2000).
The models are linked together so that the output of one simulation provides input
data for another model. For example, the nitrogen output from RADM affects the
nitrogen input from atmospheric deposition to the Watershed Model. The Watershed
Model, in turn, transports the total nutrient and sediment loads, including the contri-
butions from atmospheric deposition, to the Chesapeake Bay and its tidal tributaries
through the boundary of the watershed and estuarine domains. The Water Quality
Model examines the effects of the loads generated by the Watershed Model, as well
as the effects of direct atmospheric deposition, on Bay water quality and living
resources.
The models used by the Chesapeake Bay Program focus on quantifiable outcomes,
such as reductions in estimated nutrient and sediment loads resulting from integrated
point source, nonpoint source and air emission management actions, rather than a
pollutant reduction strategy based on a single medium. For Chesapeake Bay
Program decision-makers, model results are options to be examined, analyzed and
further developed through an iterative process with the model practitioners. This was
the process involved in determining cap load allocations (see section above titled
Tiered Management Implementation Scenarios).
The models produce estimates, not perfect forecasts. Hence, they reduce, but do not
eliminate, uncertainty in environmental decision making. Used properly, the models
assist in developing nutrient and sediment reductions that are most protective of the
environment, while being equitable and achievable.
CHESAPEAKE BAY AIRSHED MODEL AND
ATMOSPHERIC DEPOSITION
Regional Acid Deposition Model
The Regional Acid Deposition Model, or RADM, is designed to provide estimates
of atmospheric nitrogen deposition resulting from changes in precursor air emissions
due to management actions or growth, and to predict the influence of source loads
from one region on deposition in other regions (Chang et al. 1987). The current
version of RADM, RADM 2.61, encompasses a geographic domain of 2,800 kilo-
meters by 3,040 kilometers (Dennis 1996). Longitudinal coverage in the eastern
United States is central Texas to Bermuda while latitudinal coverage is from south
of James Bay, Canada to Florida, inclusive (Figure II-5). Grid cells are 80 kilometer
by 80 kilometer with 15 vertically layered cells placed from ground level to the top
of the troposphere, which equals an altitude of 16 kilometers. The total number of
cells in the model domain is 19,950 (Chang et al. 1990). As shown in Figure II-5,
over the regions of the mid-Atlantic states and the Chesapeake Bay watershed, the
RADM contains a finer grid of 20 kilometer by 20 kilometer cells nested into the
larger grid, allowing finer spatial distribution of nitrogen deposition.
chapter ii • Overview of Technical Tools
-------
Figure 11-5. Regional Acid Deposition Model domain grid and fine-scale nested grid for
the Chesapeake Bay watershed.
Source: Dennis 1996.
The RADM has been used to estimate the area where nitrogen emission sources have
the greatest potential in depositing nitrogen, both wet and dry, to a watershed. The
area encompassing these sources is referred to as the 'principal airshed'. Figure II-6
shows the boundaries of the Chesapeake Bay watershed juxtaposed with the
principle airsheds for both reduced (ammonia) and oxidized (NOx) nitrogen. The
Chesapeake Bay's ammonia airshed is about 688,000 square kilometers (266,000
square miles) in size. This is four times larger than the Chesapeake Bay's watershed
and two-thirds the size oftheNOx airshed which is 418,000 square miles (1,081,600
square kilometers) (Paerl et al. 2002).
Airsheds are not as firmly defined as watersheds in that there are no clear boundaries
to the flow of chemicals in the atmosphere as there are for the flow of surface and
ground waters in watersheds. The absolute influence that an emission source has on
deposition to an area continuously diminishes with distance. Operationally, modelers
chapter ii • Overview of Technical Tools
-------
21
REDUCED
OXIDIZED
Figure II-6. Principle nitrogen airsheds for the Chesapeake Bay and its watershed.
Source: Chesapeake Bay Program website http://www.chesapeakebay.net/wqcmodeling.htm.
have found that a good distance of demarcation for setting the airshed boundary is
the 65 percent contour of the normalized range of influence of a source region.
It is important to understand this concept of airsheds because the relationships
between emissions and deposition, and subsequently atmospheric loadings into a
water body, are not equal. For example, if 100 pounds of nitrogen were released into
the air from a source, it will not all be deposited at once nor in one area. The annual
deposition will be distributed over space and will be unevenly distributed in time.
Just as emissions and deposition are not in a 1:1 ratio, neither are deposition and
loadings to a water body. The terrestrial landscape will retain much of the deposited
chapter ii • Overview of Technical Tools
-------
22
nitrogen. For example, current belief is that approximately 10 percent of nitrogen
deposited to a typical forest ecosystem will be transported into receiving waters.
The three-dimensional RADM solves a series of conservation equations and
considers a complex range of physical and chemical processes and their interactions.
It is an Eulerian model in which the concentrations of gaseous and particulate
species are calculated for the specific grid cells as a function of time. The calcula-
tion depends on emission input rates, as well as three-dimensional advective
transport, dry deposition rates, turbulent transport, chemical transformations, scav-
enging and precipitation.
Meteorological fields used for advective transport and meteorological conditions for
RADM chemistry are from the Pennsylvania State University National Center for
Atmospheric Research Mesoscale Model (MM4). The MM4 is a weather model used
to recreate detailed meteorology (Dennis et al. 1990; Brook et al. 1995a, b).
The chemistry that is simulated by the model consists of 140 reactions among 60
species. Photolysis and oxidant photochemistry is included in the simulation as are
aqueous phase reactions which occur in clouds. Forty-one of the longer-lived chem-
ical species are transported between model cells.
The key nitrogen species that are simulated and are of concern to coastal watersheds
are: 1) particulate nitrate (pNCV), nitric acid gas (HNO3) and nitrate (N03) in
precipitation, which all originate from NOx emissions; 2) particulate ammonium
(NH4+), ammonia gas (NHr) and ammonium in precipitation, which all originate
from ammonia emissions; and 3) dissolved organic nitrogen (DON). Although the
sources of DON are not well identified, it is believed to be a small fraction of the
total nitrogen deposition.
The nitrogen oxide emissions that are accounted for in the RADM include those
from anthropogenic fuel combustion, soil biological processes and ammonia. These
emissions are input to the completely mixed grid cells of the model on an hourly
time step. The simulation uses dynamically determined time steps of seconds to
minutes to generate model output of wet and dry deposition on an hourly basis for
each surface cell.
Determination of Atmospheric Flux
While the RADM provides estimates of atmospheric deposition due to growth or
management of atmospheric emissions, a base data set of atmospheric deposition is
needed to provide a continuous 10-year time series of daily atmospheric deposition
loads to the watershed and estuary models. This base condition of deposition estab-
lishes a reference to which other atmospheric deposition reduction scenarios are
compared, quantifying the effects of managed reductions in emissions. The reduc-
tion scenarios are rooted in RADM results, represent changing levels of both
regulatory and voluntary controls, and are simulated from utility, industrial and
mobile sources.
Since precipitation is the primary forcing function in the Chesapeake Bay Watershed
Model, great care is taken in developing the time-variable atmospheric flux. A data
chapter ii • Overview of Technical Tools
-------
23
set of wet deposition of nitrate and ammonia is formed through concentration data
from a regression model and precipitation data from gauging stations that are
weighted according to a Thiessen polygon method.
The regression model uses National Atmospheric Deposition Program/National
Trends Network data from monitoring stations in the Chesapeake watershed area to
determine wet inorganic nitrogen concentrations. The regression calculates concen-
trations from measured precipitation amounts, the month of the year, and latitude.
The concentrations are then applied to the volume of precipitation, for each model
segment, to establish daily deposition of wet nitrate, ammonia, and organic nitrogen
for the 10-year simulation period of the Watershed Model. A rate of dry deposition
of nitrate is determined for each model segment from average proportions of wet-to-
dry deposition calculated by RADM.
When used for scenarios that have reduced emissions and subsequent deposition in
the Chesapeake watershed, RADM information on nitrogen emission reductions is
applied to the Watershed Model through a proportioning method. It is assumed that
the RADM reference inputs are the same as the calculated atmospheric flux. Frac-
tional changes to the RADM reference deposition are related to the deposition
database for each chemical species and both spatially and temporally. The results are
revised fluxes to the watershed, tidal waters and their respective models that are
used, in part, to determine the effects of emission controls on nutrient loads, water
quality and living resources.
CHESAPEAKE BAY WATERSHED MODEL
The Chesapeake Bay Watershed Model estimates the delivery of nutrients and sedi-
ment from all areas of the watershed to tidal waters under different management
scenarios (Donigian et al. 1994; Linker et al. 1996; Linker 1996). The continuous,
deterministic model has been in operation at the Chesapeake Bay Program since
1982. Since that time, many refinements to the simulation and data used in it have
been made. Phase 4.3 of the Watershed Model, in conjunction with the airshed and
estuarine models, was employed in the development of the nutrient and sediment cap
load allocations.
The Chesapeake Bay Program's Watershed Model is based on a slightly modified
version of Hydrologic Simulation Program-Fortran (HSPF) release 11 (Bicknell et
al.1996), a widely used public domain model supported by the U.S. Environmental
Protection Agency, U.S. Geological Survey, and U.S. Army Corps of Engineers. The
system is run on personal computers with the Linux operating system. All supporting
programs as well as HSPF are open source and written primarily in Fortran 77.
Nutrient simulation modules in the Watershed Model are detailed and flexible, and
thus can be used to simulate a variety of land use types with associated applications
of chemical fertilizers and animal manure. The model also takes into account loads
from point sources, atmospheric deposition and onsite wastewater management
systems. In addition, the simulation considers nutrient and sediment reductions due
to BMP implementation as well as attenuation of chemical species as they travel
through the river reaches to tidal waters of the Chesapeake Bay. The Watershed
chapter ii • Overview of Technical Tools
-------
24
Model simulates a period of ten years (1985-1994) on a one-hour time step and
results are aggregated into daily loads and flows, to be used as input to the estuary
model or into reported 10-year average loads for comparison among scenarios.
Watershed Model Segmentation
To simulate the delivery of nutrients and sediment to the Chesapeake Bay the 64,000
square mile Chesapeake Bay watershed is divided into 94 major hydrologic model
segments that have an average segment area of 680 square miles (177,000 hectares)
(Figure II-7). At the interface of the Watershed Model and Water Quality Model
domains, below-fall-line model segments are further divided into sub-segments to
deliver flow and nutrient and sediment loads to appropriate areas of the tidal waters
(Hopkins et al. 2000).
Segmentation partitions the watershed into regions of similar characteristics based
on criteria such as topographic areas with similar soil characteristics and slopes, or
Major Tributaries of the Chesapeake Bay
~ EASTERN SHORE MARYLAND
~ EASTERN SHORE VIRGINIA
~ JAMES RIVER BASIN
| M PATUXENT RIVER BASIN
POTOMAC RIVER BASIN
~ RAPPAHANNOCK RIVER BASIN
~ SUSQUEHANNA RIVER BASIN
~ WESTERN SHORE MARYLAND
I I YORK RIVER BASIN
Figure 11-7. Chesapeake Bay Watershed Model segmentation and major tributary basins.
Source: Linker et al. 2000.
chapter ii • Overview of Technical Tools
-------
25
similar travel times in river reaches (Hartigan 1983). Another consideration in
defining model segments is the location of reservoirs or monitoring stations. Model
segments are located so that segment outlets are as close as possible to monitoring
stations that collect water quality and discharge data (Langland et al. 1995).
The proximity of monitoring stations to the outlet of model segments is important
because the model is calibrated at the segment level. It is imperative to have the most
accurate calibration of nutrient and total suspended sediment concentrations and
flows in the river reaches so that the output loads of one segment accurately input
the adjacent downstream segment.
Overall, the right size for segmentation weighs two factors. If a segment is too large,
meaningful differences of many of the simulation parameters are missed. If a
segment is too small, it could be difficult to acquire all the data for the simulation at
that level, or the computing capacity of the model could be limited.
Watershed Model Calibration
The Chesapeake Bay Program calibrates the Watershed Model over all available data
and then uses the calibrated model to test management scenarios. In the Phase 4.3
version of the model, flow and water quality data from 1984-1997 were used for
calibration. The calibration was reviewed and approved by Chesapeake Bay Program
Modeling Subcommittee. The subcommittee members and quarterly review par-
ticipants are recognized academic experts in the field of modeling and
representatives from all Chesapeake Bay Agreement signatory jurisdictions—
Pennsylvania, Maryland, Virginia and the District of Columbia.
For the calibration of land uses, simulated exports from land uses are compared to
literature values and an analysis of the inputs. For example, the calibration of crop-
land considers the growth and nutrient uptake of estimated crop types—taking into
account drought, heat stress, and the growing season—as well as considerations of
the estimated nutrient inputs. The simulated cropland exports are, in turn, compared
to export values published in peer-reviewed scientific literature and relevant model
parameters are adjusted, if necessary, to achieve the best match.
For the calibration of river reaches, simulated results for stream flows, nutrient and
sediment concentrations and loads, as well as other water quality parameters, are
compared to observed data from in-stream monitoring sites. Results for the
hydrology calibration of the Phase 4.3 Watershed Model can be found on the
Chesapeake Bay Program Web site at http://www.chesapeakebay.net/pubs/113.pdf
while water quality calibration information can be accessed at: http://www.
chesapeakebay.net/pubs/238.pdf.
Calibration results are presented as plots and statistical tables of model information
and monitoring data from calibration stations for the following parameters: flow,
temperature, dissolved oxygen, total suspended sediment, total phosphorus, organic
and particulate phosphorus, phosphate, total nitrogen, nitrate, total ammonia and
organic nitrogen.
chapter ii • Overview of Technical Tools
-------
26
Watershed Model Data Sources
Since precipitation, in a large part, drives loads to the tidal Bay water, much effort is
spent developing this data base. For the 10-year simulation period of the Watershed
Model, rainfall data from 147 monitoring stations are used. Typically, about six
stations are used to develop the precipitation record for a model segment through a
Thiessen polygon method for spatial distribution. In addition, temperature, solar
radiation, wind speed, snow pack and dew-point temperature data are collected for
the simulation from seven primary meteorological stations in the watershed (Wang
et al. 1997).
A consistent land use dataset is compiled for the entire Chesapeake basin using a
LANSAT-derived GIS land cover as a base (U.S. EPA 1994). The land cover is
enhanced with detailed information on agricultural lands at the county level from the
U.S. Census Bureau series, Census of Agriculture for 1982, 1987, 1992 and 1997
(Volume 1, Geographic Area Series). County tillage information is acquired for the
conventional and conservation cropland distribution from the Conservation Tech-
nology Information Center (Palace et al. 1998). The land or source categories
simulated in the Watershed Model are as follows:
• Conventional-tilled cropland;
• Conservation-tilled cropland;
• Cropland in hay;
• Pasture;
• Animal waste areas;
• Forest;
• Pervious urban;
• Impervious urban land;
• Non-agricultural herbaceous or mixed-open land; and
• Atmospheric deposition directly to water surfaces.
Calculations and allocations of the agricultural land categories follow methods
described in Chesapeake Bay Watershed Model Land Use and Model Linkages to the
Airshed and Estuarine Models (Hopkins et al. 2000). The non-agricultural land use
classifications of 'forest', 'pervious' and 'impervious urban', 'mixed-open' and
'water' are generally developed through comparisons of the agricultural land acreage
and the GIS land cover database and projections or interpolations of these. Hopkins
et al. (2000) describes these calculations and allocations in detail.
For crop land, state agricultural engineers provide chemical fertilizer and manure
application rates and timing of applications as well as information on crop rotations
and the timing of field operations. The information on manure applications to
cropland is part of a time-varying mass balance of manure nutrients developed
through the Agricultural Census' animal populations and predominant manure
handling practices (Palace et al. 1998).
chapter ii • Overview of Technical Tools
-------
27
Soil characteristics for both nutrient interactions and hydrology are obtained from the
Soil Conservation Service Soil Interpretation Records (USDA 1984) with information
on soil types and land slope from the National Resources Institute (NRI). Delivery of
sediment from each land use is calibrated to the NRI estimates of annual edge-of-field
sediment loads calculated by the Universal Soil Loss Equation (USLE).
For animal waste areas, the designation of a 'manure acre' allows for the simulation
of high nutrient content runoff from animal operations. Manure acres are based on
the population of different animal types in the watershed as given in Agricultural
Census data. The animal types include beef and dairy cattle, swine and three cate-
gories of poultry (layers, broilers and turkeys). Nutrient export from animal waste
storage areas is simulated as a concentration applied to the calculated runoff where
the surface area of animal waste storages, or manure acres, changes with the number
of animals and implementation of animal waste management systems.
Loads from point sources, combined sewer overflows (CSOs), and septic systems are
input directly to river reaches. Point source inputs from municipal and industrial
sources are developed from state National Pollution Discharge Elimination System
(NPDES) records. If no state NPDES data are available, state and year-specific
default data are calculated for each missing parameter and annual estimates of loads
are based on flow from the wastewater treatment plant.
Several cities in the watershed have a sewer system with CSOs, including Wash-
ington, D.C., Richmond, Virginia and Harrisburg, Pennsylvania. Estimates of the
average annual discharge from CSOs are only available for Washington, D.C. and the
annual discharge is evenly distributed over the simulation period of the model.
Loads from septic systems are calculated using U.S. Census Bureau data of waste
disposal systems associated with households, along with a methodology suggested
in Maizel et al. (1995) where standard engineering assumptions of per capita
nitrogen waste and attenuation of nitrogen are applied. Septic system loads are simu-
lated as nitrate loads discharged to the river reaches.
Watershed Model Simulation
Each Watershed Model segment contains information generated by a hydrologic
sub-model, a nonpoint source sub-model, and a river or transport sub-model. The
hydrologic sub-model uses rainfall, evaporation and meteorological data to calculate
runoff and subsurface flow for land uses in each model segment.
The surface and subsurface flows ultimately drive the nonpoint source sub-model,
which simulates soil erosion and pollutant loads from the land to the rivers using, in
part, input data for atmospheric deposition, land use areas, nutrient applications, and
BMP implementation and reduction efficiencies. A river sub-model routes flow and
associated pollutant loads from the land through lakes, rivers and reservoirs to the
Chesapeake Bay.
For nitrogen and phosphorus, the simulation represents a mass balance in the basin,
so that the ultimate fate of the input nutrients is 1) incorporation into crops, forests,
or other vegetation, 2) incorporation into soil, or 3) loss through river runoff or
chapter ii • Overview of Technical Tools
-------
28
discharge directly to the Chesapeake Bay. Fate of nitrogen may also include
volatilization to the atmosphere and denitrification.
Much of the nutrient simulation for pervious lands considers cycling and storages in
the soil and plant mass as well as movement between the storages, thereby making
these land use simulations sensitive to nutrient inputs. Crops are specifically
modeled through a yield-based nutrient uptake algorithm allowing for the direct
simulation of nutrient management practices since exports rely heavily on the
nutrient levels above crop need. Nutrient exports from impervious urban land depend
on storage, which accumulates by a factor equal to atmospheric deposition. Rainfall
washes off this storage and the intensity of the rainfall determines how much is
washed off.
Sediment is modeled as eroded material washed off pervious land surface, eroded
from stream banks and transported to the tidal Bay waters. This simulation is
performed through a module, which represents sediment export as a function of the
amount of detached sediment and the runoff intensity.
The lumped-parameter HSPF model simulates each land use as an average for the
entire segment. For example, conventionally-tilled cropland is modeled as an
average crop rotation of corn, soybeans, and small grains in a segment with an
average model-segment input of chemical fertilizer and manure loads, and with
average slope, soil conditions, and nutrient cycling characteristics. The simulated
single-acre land use, in turn, is multiplied by the acres of each land use draining to
each river segment.
Each Watershed Model river reach is simulated as completely mixed waters with all
land uses considered in direct hydrologic contact. Of the 44 reaches modeled, the
average length is 106 miles (170 kilometers), the average drainage area is 730 square
miles (1,900 square kilometers), and the average time of travel is one day. Seven of
the reaches are impounded by reservoirs and are simulated as such.
The riverine simulation includes HSPF modules that consider, in part, sediment
transport, oxygen transformations, ammonification, nitrification, and modeling of
periphyton and phytoplankton. For areas close to the Chesapeake Bay and its tidal
tributaries with a time of travel less than one day, a river reach is not modeled and
terrestrial nutrient and sediment loads are directly loaded to the tidal estuary.
For all nutrient and sediment reduction scenarios, the Watershed Model is run for a 10-
year hydrologic period, representing 1985 to 1994, inclusive. This time frame matches
the years simulated in the Chesapeake Bay Estuary Model and provides a consistent
10-year hydrology, including wet, dry, and average periods of flow in each basin.
Nutrient and sediment loads from the Watershed Model are reported as the average
annual load over this 10-year period to make comparisons among model scenarios
without the influence of variable hydrology on loads. For example, any 2010
scenario has land uses, human and animal populations, point source discharges, and
land management projected to the year 2010 but modeled using the same 1985-1994
hydrology used for all other Watershed Model scenarios. Assessing loads for an
average-hydrology year shows how anthropogenic factors, such as changes in land
use and management practice implementation, change average annual nutrient and
sediment loads to the Chesapeake Bay over decadal periods of time.
chapter ii • Overview of Technical Tools
-------
29
CHESAPEAKE BAY WATER QUALITY MODEL
The Chesapeake Bay Water Quality Model used to assist in developing the
Chesapeake 2000 nutrient and sediment cap load allocations is a linked hydrody-
namic and water quality model which is coupled to a sediment processes, benthic
infaunal community and submerged aquatic vegetation (SAV) model. The Chesa-
peake Bay water quality model is a 'third generation' model with two major
refinements since its debut in 1992 when it was first used to develop the original
nutrient cap load allocations committed to in the 1987 Chesapeake Bay Agreement
(Chesapeake Executive Council 1987; Thomann et al. 1994; Cerco and Cole 1993;
Cerco et al. 2002a, 2002b). In 1998, the model grid was refined in the lower Virginia
tidal tributaries and lower Chesapeake Bay mainstem with the new benthic infauna
and SAV model. In 2002, the upper Chesapeake Bay mainstem and tidal tributaries
grid was refined along with significant enhancements in the model simulation of
primary productivity (Cerco et al. 2002a). During the 2002 model refinements,
particular emphasis was placed on the calibration and analysis of dissolved oxygen,
sediment, water clarity, SAV and chlorophyll a.
HYDRODYNAMIC MODEL
The Chesapeake Bay Hydrodynamic, or CH3D (Curvilinear Hydrodynamics in 3
Dimensions), Model provides advective transport for dissolved and particulate mate-
rial simulated in the Water Quality Model. The model grid covers the entire
Chesapeake Bay, tidal tributaries and the adjacent ocean boundary with about 13,000
computation model cells.
The complex movement of water within the Chesapeake Bay, particularly the density
driven vertical estuarine stratification, is simulated with a Chesapeake Bay
hydrodynamic model of more than 13,000 cells (Wang and Johnson 2000). Three-
dimensional equations of the intertidal physical system, including equations of
continuity, momentum, salt balance and heat balance, are employed to provide the
correct simulation of the movement, or the barriers to movement, of the water quality
constituents of dissolved oxygen, water clarity and chlorophyll a. Correct formula-
tion of vertical mixing, including the simulation of vertical eddy diffusion
coefficients in the hydrodynamic model is particularly important for the dissolved
oxygen criteria as the principal barrier to vertical movement of dissolved oxygen
from surface waters to the deep water is the pycnocline simulated by the hydro-
dynamic model.
The Hydrodynamic Model was applied to generate a 10-year record of hydrody-
namic transport for the Water Quality Model. The years that were simulated
(1985-94) cover a wide hydrologic range. The years 1985, 1988 and 1992 are
considered dry years; 1986, 1987, 1990 and 1991 are considered average years; and
1989, 1993 and 1994 are considered wet years. Although 1985 is considered a dry
year overall, in November of that year the track of hurricane Juan swept over the
upper Potomac and James basins and generated hundred-year-storm flows at the fall
lines of these rivers.
chapter ii • Overview of Technical Tools
-------
30
As its name implies, the Hydrodynamic Model makes computations on a generalized
curvilinear, or boundary-fitted, horizontal grid, i.e., the grid from the planar view
follows the shape of the Bay's shoreline. However, to ensure that long-term stratifi-
cation in the deep channels is maintained, the vertical grid, corresponding to depth,
is Cartesian. Boundary-fitted grids in the horizontal plane allow for a better repre-
sentation of the shoreline boundaries of the Chesapeake Bay, as well as internal
features such as channels and islands (Figure II-8).
Mathematical simulations of all physical processes influencing circulation and
mixing in water bodies such as Chesapeake Bay are included in the Hydrodynamic
Model. These include freshwater inflows, tides, wind forcing, Coriolis forces,
Figure 11-8. Plan view of the Chesapeake Bay Hydrodynamic or CH3D Model boundary
fitted grid.
Source: Cerco and Meyers 2000.
chapter ii • Overview of Technical Tools
-------
31
surface heat exchange and turbulence. The vertical turbulence closure model
computes the eddy viscosity and diffusivity from the kinetic energy and dissipation
of the turbulence. This type of closure model is known as a 'k-e turbulence model'.
Turbulence is produced by wind stress at the surface, velocity shear in the water
column and bottom friction. Density effects due to salinity and temperature are fully
coupled with the developing flow field. Thus, advection/diffusion equations for the
salinity and temperature are solved along with the conservation of mass and
momentum equations for the flow field.
Complete documentation of the Hydrodynamic Model can be found in "Chapter 2:
Validation and Application of the Second Generation Three-Dimensional Hydrody-
namic Model of Chesapeake Bay" of Tributary Refinements of the Chesapeake Bay
Model (Cerco et al. 2002a) available at: http://www.chesapeakebay.net/modsc.htm
under the Documentation tab.
WATER QUALITY MODEL
The Water Quality Model, based on the CE-QUAL-ICM code, is a three-
dimensional, time-variable model of eutrophication processes in the water column
and bottom sediments. As applied to the Chesapeake Bay and its tidal tributaries, the
model is part of a package that includes the Chesapeake Bay Watershed Model and
the Chesapeake Bay Airshed Model described previously.
The water quality model is linked to the hydrodynamic model and uses complex
nonlinear equations describing 26 state variables relevant to the simulation of
dissolved oxygen, water clarity and chlorophyll a (Cerco and Cole 1995a, 1995b,
2000; Thomann et al. 1994; Cerco and Meyers 2000). The state variables include the
full suite of nitrogen parameters (ammonia, nitrate, total nitrogen, dissolved labile
organic nitrogen, dissolved refractory organic nitrogen, particulate labile organic
nitrogen and particulate refractory organic nitrogen) and the equivalent set of
phosphorus and carbon parameters. Dissolved oxygen is simulated as the mass
balance calculation of reaeration at the surface, respiration of algae, benthos and
underwater bay grasses; photosynthesis of algae, benthic algae and underwater bay
grasses; and the diagenesis, or decay of organics, by microbial processes in the water
column and sediment. This mass balance calculation is made for each model cell and
for associated sediment cells at each hourly time step, providing an estimate of
dissolved oxygen from nutrient loads from the watershed and airshed to the waters
of the 35 major segments of the Chesapeake Bay and its tidal tributaries. Water
clarity is estimated from the daily input loads of sediment from the watershed and
shoreline acted on by regionally-calibrated settling rates, as well as estimated advec-
tion due to hydrodynamics. Chlorophyll a is estimated based on Monod calculations
of algal growth given resource constraints of light, nitrogen, phosphorous or silica.
Also, three basic phytoplankton groups, including greens, blue-greens and diatoms,
are simulated. Algal limitation is simulated by Michaelis-Menton kinetics, with the
resource in least supply providing the limitation to growth. Complete diagenesis is
simulated between the water column and sediment as organics settle to the bottom,
are incorporated in the sediment, undergo decomposition, and are ultimately simu-
lated as a return flux of nutrients to the water column, or as deep burial (DiToro and
chapter ii • Overview of Technical Tools
-------
32
Fitzpatrick 1993). Lastly, simulation of SAV in shallow waters is coupled with the
model (Cerco and Moore 2001).
Complete documentation of the Water Quality Model can be found in "Chapter 3:
Tributary Refinements to the Chesapeake Bay Model" and "Chapter 4: Phyto-
plankton Kinetics in the Chesapeake Bay Eutrophication Model" of Tributary
Refinements of the Chesapeake Bay Model (Cerco et al. 2002a) available at:
http://www.chesapeakebay.net/modsc.htm under the Documentation tab. Further
information on the model can be found at the same web site in the document Three-
Dimensional Eutrophication Model of the Chesapeake Bay (Cerco and Cole 1994).
Additional detailed documentation of this model is currently being developed and
will be available at the above web site in Spring 2004.
Wetland Sediment Oxygen Demand
During the most recent refinement and recalibration of the Water Quality Model,
processes simulating the incorporation of oxygen demand by wetland sediment were
built in. In some regions of the Chesapeake Bay tidal tributaries surface waters, a
natural oxygen deficit below saturation levels is typically observed in the summer.
These regions are found adjacent to extensive wetlands and contain comparatively
small volumes of water. The tidal fresh and oligohaline regions of the Mattaponi
(segments MPNTF and MPNOH) and Pamunkey (segments PMKTF and PMKOH)
rivers, respectively, are two specific examples. On the other hand, regions of the Bay
tidal waters where there are extensive tidal wetlands but are bordered by relatively
large bodies of water, such as the Tangier Sound, have sufficient water volumes and
mixing to mask the natural oxygen demand of adjacent wetland sediments.
In the segments with extensive tidal wetlands and small volumes of water, oxygen
demand from wetland sediments is thought to influence surface water dissolved
oxygen concentrations. Recent studies estimate wetland sediment oxygen demand to
range from 1 - 5.3 g 02/m2-day (Neubauer et al. 2000; Cai et al. 1999). In the model,
a uniform oxygen demand of 2g 02/m2-day was used. The wetland sediment oxygen
demand is universally applied in the model based on GIS estimates of tidal wetland
area (Cerco and Noel 2003).
SAV Model
Three components are required for a systemwide SAV model. The first is a unit-level
model of a plant. The second is a Water Quality Model (described above) that
provides light, temperature, nutrient concentrations and other forcing functions to
the plant component. The third is a coupling algorithm that links the systemwide
environmental model to the local-scale plant model.
The unit-level plant model incorporates three state variables: shoots (above-ground
biomass), roots (below-ground biomass), and epiphytes (attached growth).
Epiphytes and shoots exchange nutrients with the water-column component of the
eutrophication model while roots exchange nutrients with the diagenetic sediment
component (DiToro and Fitzpatrick 1993). Light available to the shoots and
epiphytes is computed via a series of sequential attenuations by color,
chapter ii • Overview of Technical Tools
-------
33
fixed and organic solids in the water column, and self-shading of shoots and
epiphytes. The selection of state variables and basic principles of the model were
based on principles established by Wetzel and Neckles (1986) and Madden et al.
(1996).
To improve the simulation of SAV, the computation model cell grid was extended
into shallow, littoral zones of depth from 0-2 meters. Following Moore et al. 2000,
three primary SAV communities were simulated: a freshwater community, a meso-
haline Riippia community, and a polyhaline Zostera community. The SAV
simulation was further refined by adding an additional 'Tidal Fresh Potomac SAV'
group to simulate the canopy-forming (as opposed to meadow-forming) SAV
community of hydrilla (Hydrilla verticillata) and eurasian watennilfoil (Myrio-
phyllum spicatum) in the tidal fresh Potomac (Cerco et al. 2002a).
Additional documentation of the SAV simulation can be found in "Chapter 5:
Systemwide Submerged Aquatic Vegetation Model for Chesapeake Bay" of Tribu-
laiy Refinements of the Chesapeake Bay Model (Cerco et al. 2002a) available at:
http://www.chesapeakebay.net/modsc.htm under the Documentation tab.
As a part of the 26 state variables that the Water Quality Model simulates by compu-
tational model cell, estimates of dissolved oxygen, chlorophyll a, and water clarity
are generated in ten minute time steps. To summarize model information into a
manageable form, the standard output for dissolved oxygen, water clarity and
chlorophyll a is presented as monthly averages for each designated use within each
Chesapeake Bay Program segment. The percent attainment of the parameters is
determined from the adjusted model output.
ADJUSTMENT OF MODEL DISSOLVED OXYGEN, WATER CLARITY
AND CHLOROPHYLLS ESTIMATES
To generate the modified data set for a particular scenario (e.g., 2010 Clean Air Act),
the EPA compared the frequency distribution output from a scenario was compared
with the frequency distribution output of the model calibration. Data were compared
on a month-by-month basis. For example, Figure II-9 illustrates the hypothetical
frequency distribution for dissolved oxygen concentration data in the deep-channel
of Chesapeake Bay mainstem segment CB5MH. The deep-channel dissolved oxygen
criterion is applied May 1 through September 30. From this graph one could infer
that the model was estimating the observed data fairly well, since model-simulated
output matches the mean, approximates the range and has the same characteristic
shape as the frequency distribution of the observed data. However, despite the
acceptable calibration, if the criterion had been set as 'dissolved oxygen concentra-
tion of < 2 mg liter1 no more than 10 percent of the time', the model would indicate
a 'pass' while the observed data would indicate a 'fail'.
For each point along the frequency distribution where an observation exists during
the 1985-1994 period, a mathematical relationship between the model scenario and
the model calibration was established by regressing the 30 or so daily values for the
month when the observation occurred in the water quality model cell that contains
the observation. Figure 11-10 compares the hypothetical output of a Water Quality
chapter ii • Overview of Technical Tools
-------
34
c
o
'-4—'
cc
&_
-I—'
c
CD
O
c
o
O
CD 5
CD —
05 D5 J
>< E 4
>*
O
¦o
CD
>
o
V)
V)
Observed Data
Model Calibration
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Cumulative Frequency of Occurence
Figure II-9. Frequency distribution of hypothetical observed data and model calibration
for a designated use.
Source: Linker et al. 2002.
CD
c
o
-4—'
CO
-I—'
c
CD
O
c
o
O
c _
CD —
O) U)
T3
CD
>
O
w
w
Observed Data
•Model Calibration
Model Scenario
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Cumulative Frequency of Occurence
Figure 11-10. Frequency distribution of hypothetical observed data, model calibration
and model scenario for a designated use.
Source: Linker et al. 2002.
chapter ii • Overview of Technical Tools
-------
35
Model scenario based on a given load reduction to the Water Quality Model output
calibration. These are shown on a frequency plot so that changes in the prediction of
attainment can be seen along with the blue line of the observed data.
Figure 11-11 shows the relationship between the calibration and scenario Water
Quality Model output in more detail. By regressing the scenario output against the
calibration output, one can find a relationship that can be used to transform the
observed data set. The regression generates a unique equation for each point and
month that transforms a calibration value to a scenario value. This relationship is
then applied to the monitored observation as an estimate of what would have been
observed had the Chesapeake Bay watershed been under the scenario management
rather than the management that existed during 1985-1994.
Once the relationship between the calibration and any particular scenario is estab-
lished, this relationship (applied as a regression equation illustrated in Figure 11-12)
is used to generate a 'scenario-modified' observed data set for the scenario. The
'scenario-modified' values represent an estimate of an observed data set under the
conditions of nutrient and sediment management represented by the scenario. Each
observed value for dissolved oxygen, chlorophyll a and light extinction in the 1985-
1994 data set is replaced with a 'scenario-modified' value.
For a full discussion of this procedure, see A Comparison of Chesapeake Bay
Estuary> Model Calibration With 1985-1994 Obsen'ed Data and Method of
Application to Water Quality Criteria (Linker et al. 2002) available at:
http://www.chesapeakebay. net/modsc.htm under the 'Documentation' tab.
Calibration
Figure 11-11. Example of a regression between model calibration and scenario data.
Source: Linker et al. 2002.
chapter ii • Overview of Technical Tools
-------
36
Figure 11-1 2. Example of the regression equation applied to the observed.
Source: Linker et al. 2002.
MANAGEMENT APPLICATION OF MODEL OUTPUTS
Apart from the adjusted model output that is used for assessing attainment of the
three criteria, it is useful to examine the degree of model calibration in each desig-
nated use within each Chesapeake Bay Program segment where the water quality
model will be applied to assess the quality/accuracy of the model calibration. For
this purpose, a strict one-to-one comparison is made between the observed and simu-
lated data. The comparisons are made for the same time (observed and simulated)
and space (real and virtual).
A set of empirical decision rules were developed for the purpose of assessing the
quality of the calibration for each Chesapeake Bay Program segment designated uses
(Table II-l). The relative performance of the predicted metric (e.g., dissolved oxygen
concentration) compared to the observed metric under the decision rules was rated
as 'high certainty', 'moderate certainty', or 'low certainty' (Linker et al. 2002).
One comparison that was made was the central tendency, the mean or median, of the
data. Another was the dispersion, or standard deviation. Range comparisons of the
minimum or maximum were also employed, as well as examination of the frequency
and scatter plots. A relative confidence estimate of model calibration was determined
from the summary statistics and statistical plots of all the comparisons. Best profes-
sional judgement was used in cases where most, but not all, of the criteria were met.
While the open-water dissolved oxygen criteria apply year-round, emphasis was on
the periods critical for the living resources protected by the criteria. Evaluation of the
migratory spawning and nursery dissolved oxygen criteria focused on the late winter
chapter ii • Overview of Technical Tools
-------
37
Table 11-1. The relative confidence in model calibration findings were used directly by the Water
Quality Technical Workgroup and Water Quality Steering Committee in making judgements as to
exactly where the water quality model outputs could be used for setting the cap load allocations
R2
Mean Difference
Standard
Deviation
Best
Professional
Judgement
Dissolved Oxygen
>0.5 desirable
1.0 mg liter1 (or roughly 10%);
minimum concentrations do not
differ by more than 2.0 mg liter1
Do not differ by
more than 0.5
Yes
Chlorophyll a
>0.2 desirable
Not greater than two times the
concentration; maximum
concentration do not differ
more than 20.0 mg liter1
Do not differ by more
than three times the
observed standard
deviation
Yes
Water Clarity
>0.2 desirable
Not greater than two times the
concentration; maximum
concentration do not differ
by more than two times Ke
Do not differ by more
than two standard
deviations
Yes
Source: Linker et al. 2002.
to late spring period, while evaluation of the open-water, deep-water and deep-
channel dissolved oxygen criteria focused on June through September.
A summary of the relative confidence in model calibration by Chesapeake Bay
Program segment by designated use is provided in Table II-2. More detailed
information on the Chesapeake Bay water quality model calibration is available
at: http://www.chesapeakebay.net/modsc.htm under the publications tab and within
the report A Comparison of Chesapeake Bay Estuary> Model Calibration With
1985-1994 Obsen'ed Data and Method of Application to Water Quality Criteria
(Linker et al. 2002).
chapter ii • Overview of Technical Tools
-------
38
Table 11-2. Relative confidence in Chesapeake Bay water quality model calibration for 35 Chesapeake Bay
Program segments for the three Chesapeake Bay water quality criteria by tidal water designated use.
Dissolved Oxygen Chlorophyll a
Chesapeake Bay
Program Segment
Migratory
Feb-June
Open Water
All Year
Deep
Water
Deep
Channel
Spring
Summer
Water
Clarity
CB1TF
a
NA
NA
NA
b
b
a
CB20H
a
NA
b
NA
a
b
a
CB3MH
a
NA
b
a
a
c
a
CB4MH
NA
a
b
b
b
a
a
CB5MH
NA
a
c
c
a
b
a
CB6PH
NA
a
c
NA
b
b
a
CB7PH
NA
a
a
NA
b
a
a
CB8PH
NA
a
NA
NA
a
a
a
PAXTF
b
NA
NA
NA
a
c
b
PAXOH
b
NA
NA
NA
c
c
b
PAXMH
a
b
b
NA
a
b
a
POTTF
b
NA
NA
NA
a
b
b
POTOH
b
NA
NA
NA
b
c
a
POTMH
a
a
b
a
a
b
a
RPPTF
a
NA
NA
NA
c
c
a
RPPOH
b
NA
NA
NA
c
b
b
RPPMH
b
a
a
NA
b
a
b
MPNTF
c
NA
NA
NA
b
a
b
MPNOH
b
NA
NA
NA
a
b
b
PMKTF
a
NA
NA
NA
b
a
c
PMKOH
b
NA
NA
NA
b
c
b
YRKMH
a
a
NA
NA
a
b
a
YRKPH
NA
a
a
NA
b
a
a
PIAMH
NA
a
NA
NA
a
a
a
MOBPH
NA
a
a
NA
a
a
a
JMSTF
b
NA
NA
NA
a
b
b
JMSOH
a
NA
NA
NA
a
c
a
JMSMH
a
a
NA
NA
c
c
a
JMSPH
NA
a
NA
NA
b
a
a
EASMH
NA
a
a
NA
b
c
a
CHOOH
c
NA
NA
NA
b
c
a
CHOMH2
a
NA
NA
NA
c
c
b
CHOMH1
NA
a
NA
NA
b
b
a
TANMH
NA
b
NA
NA
a
a
a
POCMH
NA
a
NA
NA
b
a
b
Key: a = High Certainty
b = Moderate Certainty
c = Low Certainty
Source: Linker et al. 2002.
chapter ii • Overview of Technical Tools
-------
39
LITERATURE CITED
Appleton, E. L., 1995. A cross-media approach to saving the Chesapeake Bay. Environmental
Science and Technology 29(12): 550-555.
Appleton, E. L., 1996. Air quality modeling's brave new world: A new generation of software
systems is set to tackle regional and multipollutant air quality issues. Environmental Science
and Technology 30(5) pp 200A-204A.
Bicknell, B., J. Imhoff, J. Kittle, A. Donigian, R. Johanson and T. Barnwell. 1996. Hydro-
logic Simulation Program - Fortran user's manual for release 11. U.S. Environmental
Protection Agency Environmental Research Laboratory, Athens, Georgia.
Brook, J., R Samson and S. Sillman. 1995a. Aggregation of selected three-day periods to esti-
mate annual and seasonal wet deposition totals for sulfate, nitrate, and acidity. Part I: a
synoptic and chemical climatology for eastern North America. Journal of Applied Meteo-
rology 34:297-325.
Brook, J., P. Samson and S. Sillman. 1995b. Aggregation of selected three-day periods to esti-
mate annual and seasonal wet deposition totals for sulfate, nitrate, and acidity. Part II:
selection of events, deposition totals, and source-receptor relationships. Journal of Applied
Meteorology 34:326-339.
Cai, W. J., L. R. Pomery, M. A. Moran and Y. Wang. 1999. Oxygen and carbon dioxide mass
balance for the estuarine-intertidal marsh complex of five rivers in the southeastern U.S.
Limnology and Oceanography 44(3):639-649.
Cerco, C. F. 2000. Phytoplankton kinetics in the Chesapeake Bay Eutrophication Model.
Water Quality and Ecosystem Modeling l(l-4):5-49.
Cerco, C. F. 1995a. Response of Chesapeake Bay to nutrient load reductions. Journal of
Environmental Engineering 121(8): 549-55 6.
Cerco, C. F. 1995b. Simulation of long term trends in Chesapeake Bay eutrophication.
Journal of Environmental Engineering 121(4) 298-310.
Cerco, C.F. and T. Cole. 2003. The 2002 Chesapeake Bay Eutrophication Model. EL-03-XX.
[in preparation] U.S. Army Engineering Research and Development Center, Vicksburg,
Mississippi.
Cerco, C. F. and K. Moore. 2001. System-wide submerged aquatic vegetation model for
Chesapeake Bay. Estuaries 24(4):522-534.
Cerco, C. F. and M. Meyers. 2000. Tributary Refinements to Chesapeake Bay Model. Journal
of Environmental Engineering 126(2): 164-174.
Cerco, C. F. and T. M. Cole. 1994. Three-Dimensional Eutrophication Model of the Chesa-
peake Bay Volume 1: Main Report. U.S. Army Corps of Engineers Waterways Experiment
Station, Vicksburg, Mississippi.
Cerco, C. F. and T. M. Cole. 1993. Three-dimensional eutrophication model of Chesapeake
Bay .Journal of Environmental Engineering 119(6): 1006-1025.
Cerco, C. F., B. H. Johnson and H. V. Wang. 2002a. Tributary Refinements to the Chesapeake
Bay Model. Final Report ERDC TR-02-4. U.S. Army Corps of Engineers, Washington, D.C.
chapter ii • Overview of Technical Tools
-------
40
Cerco, C. F., L. Linker, J. Sweeney, G. Shenk and J. Butt. 2002b. Nutrient and solids controls
in Virginia's Chesapeake Bay tributaries. Journal of Water Resources Planning and Manage-
ment May/June: 179-189.
Chang, J., P. Middleton, W. Stockwell, C. Walcek, J. Pleim, H. Lansford, S. Madronich, F.
Binkowski, N. Seaman and D. Stauffer. 1990. The Regional Acid Deposition Model and
Engineering Model, NAPAP SOS/T Report 4. In: National Acid Precipitation Assessment
Program : State of Science and Technology,', Volume 1. National Acid Precipitation Assess-
ment Program, Washington, D.C.
Chang J., R. Brost, I. Isaksen, S. Madronich, P. Middleton, W. Stockwell and C. Walcek.
1987. A three-dimensional eulerian acid deposition model-physical concepts and formula-
tion. Journal of Geophysical Research 92:14681-14700.
Chesapeake Executive Council. 1987. Chesapeake Bay Agreement. Annapolis, Maryland.
Chi, W., L. Pomeroy, M. Moran and Y. Wang. 1999. Oxygen and carbon mass balance for the
estuarine-intertidal march complex of five rivers in the southeastern U.S. Limnology and
Oceanography 44:3, 639-649.
Dennis, R. L. 1996. Using the Regional Acid Deposition Model to determine the nitrogen
deposition airshed of the Chesapeake Bay watershed. In: Joel Baker (ed.). Atmospheric
Deposition to the Great Lakes and Coastal Waters. Society of Environmental Toxicology and
Chemistry.
Dennis, R., F. Binkowski, T. Clark, J. McHenry, S. Reynolds and S. Seilkop. 1990. Selected
applications of the Regional Acid Deposition Model and Engineering Model, Appendix 5F
(Part 2) of NAPAP SOS/T Report 5. In National Acid Precipitation Assessment Program:
State of Science and Technology Volume 1. National Acid Precipitation Assessment Program,
Washington, D.C.
DiToro, D. M. and J. J. Fitzpatrick. 1993. Chesapeake Bay Sediment Flux Model. Report EL-
93-2. U.S. Army Corps of Engineers Waterways Experiment Station and U.S. Environmental
Protection Agency Chesapeake Bay Program Office. Pp. 198.
Donigian, Jr., A., B. Bicknell, A. Patwardhan, L. Linker, C. Chang, C. and R. Reynolds. 1994.
Chesapeake Bay Program Watershed Model application to calculate bay nutrient, loadings.
Report for the U.S. Environmental Protection Agency, Chesapeake Bay Program Office,
Annapolis, Maryland.
Hartigan, J. 1983. Chesapeake Bay basin model-final report. Report for the U.S. Environ-
mental Protection Agency Chesapeake Bay Program, Annapolis, Maryland.
Hopkins, K., B. Brown, L. Linker and R. Mader. 2000. Chesapeake Bay Watershed Model
land use and model linkages to the airshed and estuarine models. U.S. EPA Chesapeake Bay
Program, Annapolis, Maryland, http://www.chesapeakebay.net/pubs/1127.pdf.
Langland, M., P. Lietman and S. Hoffman. 1995. Synthesis of nutrient and sediment data for
watersheds within the Chesapeake Bay drainage basin. Report 95-4233. USGS Water-
Resources Investigations.
Linker, L. 1996. Models of the Chesapeake Bay. Sea Technology 37(9):49-55.
Linker, L., G. Shenk, P. Wang, C. Cerco, A. Butt, P. Tango and R. Savidge. 2002. A Compar-
ison of Chesapeake Bay Estuary Model Calibration With 1985-1994 Observed Data and
Method of Application to Water Quality Criteria. Chesapeake Bay Program Modeling
Subcommittee Report. Chesapeake Bay Program Office, Annnapolis, Maryland.
chapter ii • Overview of Technical Tools
-------
41
Linker, L., G. Shenk, R. Dennis and J. Sweeney. 2000. Cross-media models of the Chesa-
peake Bay watershed and airshed. Water Quality and Ecosystem Modeling 1(1-4):91-122.
Linker, L., C. Stigall, C. Chang and A. Donigian, Jr. 1996. Aquatic accounting: Chesapeake Bay
Watershed Model quantifies nutrient loads. Water Environment and Technology' 8(l):48-52.
Madden, C. J., M. Kemp and W. Michael. 1996. Ecosystem model of an estuarine submersed
plant community: calibration and simulation of eutrophication responses. Estuaries
19(2B):457-474.
Maizel, M., G. Muehlbach, P. Baynham, J. Zoerker, D. Monds, T. Iivari, P. Welle, J. Robbin
and J. Wiles. 1995. The potential for nutrient loadings from septic systems to ground and
surface water resources and the Chesapeake Bay. Report for Chesapeake Bay Program
Office, Annapolis, Maryland.
Moore, K. A., D. J. Wilcox and R. J. Orth. 2000. Analysis of the abundance of submersed
aquatic vegetation communities in the Chesapeake Bay. Estuaries 23(1): 115-127.
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.
Paerl, H. W., R. L. Dennis and D. R. Whitall, 2002. Atmospheric Deposition of Nitrogen:
Implications for Nutrient Over-enrichment of Coastal Waters. Estuaries 25(4B):677-693.
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.
In: Chesapeake Bay Watershed Model application and calculation of nutrient and sediment
loadings. EPA 903-R-98-009, CBP/TRS 201/98. Chesapeake Bay Program Office,
Annapolis, Maryland.
Shin, W. C. and G. R. Carmichael. 1992. Sensitivity of acid production/deposition to emis-
sion reductions. Environmental Science and Technology 26:4 pp 715-725.
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. Technology Transfer Report
CBP/TRS 101/94 (April, 1994) Chesapeake Bay Program Office Annapolis, MD.
USDA. 1984. Soil Conservation Service Soil Interpretation Records. Statistical Laboratory,
Iowa State University, Ames, Iowa.
U.S. EPA. 2003a. Technical Support Document for Identification of Chesapeake Bay Desig-
nated uses and Attainability. EPA 903-R-03-004. Chesapeake Bay Program Office,
Annapolis, Maryland.
U.S. EPA 2003b. Ambiant Water Quality Criteria for Dissolved Oxygen, Water Clarity and
Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. EPA 903-R-03-002. Chesa-
peake Bay Program Office, Annapolis, Maryland.
U.S. EPA. 2002. Nutrient Reduction Technology Cost Estimations for Point Sources in the
Chesapeake Bay Watershed. Nutrient Reduction Technology Cost Task Force. Chesapeake
Bay Program, Annapolis, Maryland.
U.S. EPA. 1994. Chesapeake Bay watershed pilot project. EPA/620/R-94. Environmental
Monitoring and Assessment Program Center, Research Triangle Park, NC.
Wang, H. V. and B. H. Johnson, 2000. Validation and application of the second generation
three dimensional hydrodynamic model of Chesapeake Bay. Water Quality and Ecosystem
Modeling 1(1-4)51-90.
chapter ii • Overview of Technical Tools
-------
42
Wang, P., L. Linker and J. Storrick. 1997. Appendix D: precipitation and meteorological data
development and atmospheric nutrient deposition. In: Chesapeake Bay Watershed Model
application and calculation of nutrient and sediment loadings—Phase IV Chesapeake Bay
Watershed Model. EPA 903-R-97-022, CBP/TRS 181/97. Chesapeake Bay Program Office,
Annapolis, Maryland.
Wetzel, R. and H. A. Neckles. 1986. A model of Zostera marina L. photosynthesis and
growth: simulated effects of selected physical-chemical variables and biological interactions.
Aquatic Botany 26:307-323.
chapter ii • Overview of Technical Tools
-------
43
chapter hi
Technical and Modeling
Considerations for Setting
the Cap Load Allocations
In calculating attainability under various loading scenarios using the Water Quality
Model, it is necessary to apply innovative approaches to address various technical
issues. The most important of these issues are described in this chapter, as follows:
refining estimates of pycnocline depths; setting averaging periods for determining
criteria attainment; defining allowable frequency and duration of criteria exceedances;
establishing the geographic influence of loads on tidal water quality; establishing the
tidal wetland influence on tidal-water dissolved oxygen; analysis of the isolation of
individual pollutant effects on water quality; influence of sediment loads on dissolved
oxygen; and the establishment and assessment of SAY restoration goals.
REFINING ESTIMATES OF PYCNOCLINE DEPTHS
The pycnocline is usually characterized by strong gradients in chemical and biolog-
ical properties and separates the deep, saltier waters from the less saline, well-mixed
surface waters. In the Chesapeake Bay, another well-mixed layer forms on the
bottom of the estuary due to bottom shear from estuary currents. Vertical stratifica-
tion of the Chesapeake Bay has implications for use designations and, therefore,
accurate estimates of the pycnocline are important for assessing attainment. The
method for assessing upper and lower mixed layer depths is based on Fisher et al.
(2003). This method differs from the standard field method in that it uses a measured
density gradient based on salinity and temperature rather than on the surrogate,
conductivity. Generally, the upper pycnocline depth is the shallowest occurrence of
a density gradient of 0.1 kg/m4 or greater and a lower mixed layer depth is the
deepest occurrence of a density gradient of 0.2 kg/m4, if a lower mixed layer exists.
Since pycnocline delineation is based on hydrodynamics and not bathymetry, the
depth of the pycnocline and hence the boundaries of the designated uses changes on
a monthly basis. Details are presented in Appendix D of the Technical Support Docu-
ment (U.S. EPA 2003b). Since monitoring data is used to adjust model output as
described previously in Chapter II, the upper and lower pycnocline boundary depths
are determined on a monthly average period usually formed from two water quality
monitoring sampling cruises each month over the assessment period. Consequently,
only monthly average water quality criteria were assessed.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
44
AVERAGING PERIOD FOR DETERMINING
CRITERIA ATTAINMENT
The method for determining attainment of the Chesapeake Bay dissolved oxygen,
clarity and chlorophyll a criteria became an issue. Chesapeake Bay Program partners
decided that the Bay modeling tools would be used to assist in allocating the nutrient
and sediment cap loads, and the ambient tidal water quality monitoring data would
be used to ultimately determine criteria attainment for listing and delisting purposes.
This course of action required greater coordination between monitoring data and
modeling output assessments and decisions on the method for analyzing monitoring
data.
ASSESSING MONITORING DATA
Monitoring criteria attainment requires reconciliation of dichotomous needs. Long
averaging periods are needed to obtain the best assessment of criteria attainment
through wet, dry and average years. Data from multiple years averages out other
interannual variability, such as the timing of high flow and load events. The large
nutrient and sediment load reductions called for in the Chesapeake 2000 cap load
allocations will occur in different places and at different rates, thereby adding
more variability to interannual measurements of dissolved oxygen, clarity and
chlorophyll a. All of these factors address assessing attainment with the longest
monitoring period practicable.
On the other hand, responsive water quality management requires a reasonable
assessment period, which requires a compromise on the quality of assessment. To
best address the disparate needs of quality and responsiveness, a three-year aver-
aging period was chosen. See Chapter 6 in the Regional Criteria Guidance for a
detailed justification for the selection of this averaging period (U.S. EPA 2003a).
ASSESSING MODELING DATA
Currently, Chesapeake Bay Water Quality Model output is available for 10 simulated
years (1985-1994), which provides eight three-year running averages (1985-1987,
1986-1988, 1987-1989, etc.). To compare the standard 10-year assessment of the
model outputs for dissolved oxygen, clarity and chlorophyll a to the three-year
assessment of monitoring data, the model output was modified to provide estimates
of the highest attainment of the eight three-year assessments, the lowest attainment
of the eight three-year assessment and the average of the eight three-year running
assessments. The modification allows for assessment of model estimated 'best' and
'worst' cases of attainment using a running three-year assessment period.
The deep waters of the middle mainstem Chesapeake Bay segments CB3MH,
CB4MH and CB5MH, along with the deep waters of the lower Potomac River
(POTMH) and Eastern Bay (EASMH) form a large contiguous region of deep water
in close contact with the often anoxic waters of the deep channel. Attainment of the
dissolved oxygen criteria for these deep waters is difficult, as Figure III-l illustrates.
Seven scenarios are shown: 1985-94 Observed, 2000 Progress, Tier 1, Tier 2, Tier 3,
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
45
DO Deep
CB3MH
^ CB4MH
POTMH
o
Pn <& N O v> v> .# # <.N O v> v> .# «P <.N O v> v> .# «P <.N O & v> .# & c$ <.N O O v> .#
d3 <•£ d3 <•£ d3 <•£ d3 <•£ d3 <•£
-High
— Low
1
T
— 10-yr avg
-Total 3-yr avg
-
K
Tt
T
i—i
—i
**1
i
H
c
-------
46
Given the findings that 10-year and 3-year averaging periods for determining attain-
ment were very close at loading levels approaching the basinwide cap loads, the
Chesapeake Bay Program partners decided the 10-year averaged modeling output
could be used in making cap load allocation decisions.
DEFINING ALLOWABLE FREQUENCY AND DURATION
OF CRITERIA EXCEEDANCES
Water quality criteria are established as 'safe' levels necessary for the protection of
aquatic life. Continued attainment of these levels should result in a healthy aquatic
community. Typically the EPA's national water quality criteria are further defined by
magnitude, maximum duration and frequency of exceedances. Although it is well-
established that exceedances of water quality criteria within limits still support a
healthy aquatic community, the Chesapeake Bay Program identified the need to go
beyond the simple time metrics of frequency and duration that are usually applied. An
innovative approach was adopted based on allowable exceedances of time (percent of
time exceeded with the criteria application period) and space (percent volume or
surface area of the designated use within a Chesapeake Bay Program segment).
Monitoring for criteria attainment requires collection of data that are as fully repre-
sentative as possible of the extent of space and time over which the assessment is to
be performed, but resource limitations inevitably limit data collection. Therefore, an
analytical framework is used to evaluate spatial and temporal criteria exceedance
based on limited data.
As the monitoring program was being designed for criteria assessment, the scientists
involved developed an analytical framework based on a cumulative frequency
diagram (CFD) approach. Monitoring data collected at a limited number of locations
were interpolated over a fixed three-dimensional grid. Criteria values were defined
for each grid cell and combined with the data interpolation to provide a cell-by-cell
estimate of criteria exceedance. Then, for each monitoring event, those grid-cell esti-
mates were aggregated to provide a segment-wide estimate of 'percent of space'
exceeding the criteria. Multiple monitoring events conducted over an assessment
period provided a temporally defined collection of estimates of 'percent of space'
exceeding the criteria. Those values were then plotted as a CFD using standard
statistical procedures. The CFD generated using this approach reflects criteria in
both space and time since 'percent of space' is represented on the horizontal axis and
'temporal frequency' is represented on the vertical axis (Figure III-2; see Chapter 6
of the Regional Criteria Guidance for more details) (U.S. EPA 2003a).
As the CFD approach was developed, it was recognized that some spatial and
temporal criteria exceedance could occur at the same time that the overall segment
was achieving its designated use. For example, some small tidal tributaries might
chronically exceed the criteria simply because they are naturally poorly flushed. It
was decided that these exceedances should be considered 'allowable' and should be
accounted for in the CFD analytical framework.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
47
o
CD TO
100
O CD
20
CD <
S5*-
iS o
10
0
CD
CL
0 10 20 30 40 50 60 70 80 90 100
Percentage of Area/Volume Exceeding the Criteria
Figure III-2. Non-allowable exceedance illustrated in dark blue.
Source: U.S. EPA 2003a.
To account for 'allowable exceedances' in the CFD approach, multiple options were
considered. Initially 10-percent of time and/or space was considered to be the best
approach because it was consistent with past EPA guidance. However, strict adher-
ence to a 10-percent rule almost always resulted in a violation because CFDs tend to
exceed 10-percent of time or space at some location on the figure, even when there
are few measured violations. A curved line is more consistent with the CFD and so
a mathematically defined hyperbolic line was developed that encompassed 10-
percent of the CFD plot area. This approach appeared to function well, but was
considered arbitrary because it had no scientific basis with regard to actual achieve-
ment of a designated use. As a result, a third option was considered where a CFD
was developed based on data from areas that were already achieving their designated
use. That CFD was defined as a 'reference curve' that would be used as a benchmark
against which other CFD assessment curves could be compared. The biologically-
defined 'reference curve' was selected as the best alternative of those considered and
adopted for routine use in criteria assessment (see Chapter 6 of the Regional Criteria
Guidance for more details; U.S. EPA 2003a).
Exceedances in time and space for model were determined with cumulative frequency
distributions (CFDs) and biological reference curves. As described in Chapter II, each
model scenario was used to create a modified data set for that scenario. These results
were then interpolated and used to create CFDs of spatial and temporal criteria
exceedance for each segment and designated use. The CFD for the segment and
scenario was compared to the appropriate biological reference curve that defines the
biologically acceptable and protective combinations of frequency and spatial extent
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
48
of criteria exceedances. The total area below the CFD for a segment, but above the
biological reference curve represents the unallowable exceedance for that segment
and scenario (Figure III-2). These calculations were automatically carried out by a
system of computer programs available from the Chesapeake Bay Program Office.
The development and application of CFDs is described in greater detail in Chapter 6
of the Regional Criteria Guidance (U.S. EPA 2003a).
ESTABLISHING THE GEOGRAPHIC INFLUENCE
OF LOADS ON TIDAL WATER QUALITY
In developing the cap load allocations, it was key to understand each major tribu-
tary's influence on tidal Bay water quality. To assist the Water Quality Steering
Committee in isolating the effects of each of the nine major basins, the Chesapeake
Bay Program ran a series of geographic isolation runs with the Water Quality Model.
The model runs helped establish estimates of the influence of loads from each of the
nine major tributary basins on water quality in each segment of the Bay's tidal
waters. Specifically, isolation scenarios, in which the management controls were set
at Tier 3 levels for the isolated basin and held at year 2000 levels for the rest of the
watershed, were performed for each major basin. Issues in identifying the most
affected segments and estimating the absolute and relative effects were addressed.
Absolute effects were defined as the total effect of a basin on water quality, including
loads, either large or small, and the geographic influence of a basin's position in the
estuary (i.e., the Susquehanna, with the largest loads and a position at the head of the
estuary, always had the highest estimated absolute effect). Relative loads were an
estimate of the geographic effect alone, irrespective of the amount of the load, so that
for upper Bay regions, the Western Shore and Patuxent were estimated to have about
the same relative effect as the Susquehanna. The cap load allocation assessments
took estimates of both the absolute and relative effects into account.
FOCUSING ON MAINSTEM SEGMENTS
CB3MH, CB4MH AND CB5MH
As described above, the Bay tidal-water area that requires the highest level of
nutrient reduction to attain dissolved oxygen criteria is the deep-water and deep-
channel designated use in the middle and central Chesapeake Bay (segment
CB4MH). Hence, all other tidal Bay habitats that are not currently in attainment for
dissolved oxygen would come into attainment before the CB4MH deep-water and
deep-channel designated uses were fully in attainment. For this reason, the Water
Quality Technical Workgroup focused on segment CB4MH when comparing the
influence of different basins. This focus was later broadened to include segment
CB3MH and segment CB5MH, respectively, since they were near segment CB4MH
and also required higher levels of nutrient reduction to reach attainment.
COMPARING ABSOLUTE VERSUS RELATIVE EFFECTIVENESS
Absolute effectiveness gives an indication of the total effectiveness of a particular
basin in reducing nonattainment in a given segment by taking into account geog-
raphy and total load, while relative effectiveness takes into account only geography.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
49
Absolute effectiveness is the change in criteria nonattainment that results from a
single basin changing from year 2000 level management to Tier 3 management. It is
expressed in the same units as the CFD, which is percentage of space and time in
nonattainment. For example, if the lower Potomac River segment POTMH moves
from 35 percent nonattainment to 30 percent nonattainment from the implementation
of Tier 3 in the Potomac basin, then the absolute effectiveness is 5 percent.
Comparing the absolute effectiveness among basins helps to identify basins that can
have the greatest total effect in correcting nonattainment. Figure III-3 shows the
absolute effectiveness of each basin on reducing the deep-water dissolved oxygen
criteria nonattainment in middle central Chesapeake Bay segment CB4MH.
Relative effectiveness is the absolute effectiveness divided by the total load reduction
necessary to gain that water quality response. For example, if the load reduction in the
Potomac basin was 5 million pounds of pollutant to get that 5 percent change in
nonattainment, the relative effectiveness is 1 percent per million pounds. The relative
effectiveness calculation is an attempt to isolate the effect of geography by normal-
izing by load. Comparing the relative effectiveness among basins shows the resulting
gain in attainment from performing equal reductions among the nine major basins.
3.50
3.00
¦*-> O)
g O 2.50
E
Z S 1.50
.E g
® ® 1.00
J= "O
o ®
E- 0.50
0.00
" ~ Susquehanna
~ MD Western Shore
~ Patuxent
" ~ Potomac
¦ Rappahannock
~ York
" ~ James
~ MD Eastern Shore
~ VA Eastern Shore
Major Tributary Basins
Figure III-3. Absolute effect of load reductions from the nine major basins on segment
CB4MH deep-water dissolved oxygen concentrations.
NORMALIZING FOR THE COMBINED NITROGEN
AND PHOSPHORUS LOAD
Since the reductions that cause the absolute effect are taken across the board from
nitrogen, phosphorus and sediment loads, one must determine the pollutant load type
responsible for the increased attainment. The Chesapeake Bay is both nitrogen- and
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
50
phosphorus-limited in different regions and seasons (D'Elia et al. 1986; Fisher et al.
1992, 1994, 1999, 2001; Boynton et al. 1995; Malone et al. 1996; Conley 1999). The
spring algal bloom near the tidal-fresh and oligohaline regions is generally
controlled by phosphorus. The summer algal bloom, primarily in the mesohaline
regions, is controlled more by nitrogen. Low dissolved oxygen conditions in deep
waters are caused by a combination of these seasonal blooms. Suspended sediment
also has an effect on dissolved oxygen, but its effect is less than the nutrient effect
(see Influence of Sediment on Chesapeake Bay Dissolved Oxygen below).
Since the effects of nitrogen and phosphorus are inherently connected in the Chesa-
peake Bay management control scenarios and cannot easily be isolated by separate
management practices, the Water Quality Technical Workgroup agreed that the most
appropriate divisor to convert absolute effectiveness to relative effectiveness is a
combination of the two nutrients. Since nutrients are taken up by algae in roughly a
10:1 N:P ratio (by weight), this ratio was also used in the metric. Therefore, an algal
unit is defined as 1 unit mass of phosphorus and 10 units mass of nitrogen.
Figure III-4 shows the relative effectiveness of the nine different major basins on
deep water in segment CB4MH, normalized by algal units.
To test if the water quality response was further separable by basin, the Susquehanna
River basin was run with a reduction in phosphorus only, since the tidal-fresh waters
that it empties into are typically phosphorus-limited. Figure III-5 shows the results
of this test in the three mid-Bay segments. From this graph, it is clear that both
nitrogen and phosphorus coming from the Susquehanna River basin both have large
effects on water quality in the mid-Bay region.
1.20
— w
c o
0) ~
E <»
I C
1 £
c £.
£ ?
4-1
.E §
a> "
Ui Q)
s °-
_c ^
a>
oc
O
1.00-
0.80-
0.60
0.40-
0.20
0.00
~ Susquehanna
~ MD Western Shore "
~ Patuxent
~ Potomac
¦ Rappahannock
~ York
~ James
~ MD Eastern Shore
~ VA Eastern Shore
1
Major Tributary Basins
Figure 111-4. Relative effect of load reductions from the nine major basins on segment
CB4MH deep-water dissolved oxygen concentrations normalized by algal units.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
51
3.5-
3.0-
¦p (0
c o
z i3
.E S
»> 2
G)
-------
52
H
1.00
0.90
C 0.80
H
^ W
c o
a> —
£ £
c c
'<0 "o
^ Q-
5 a>
-7 ®
.£ <1>
a> "
o> J>
c Q.
j="°
m
Oir
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00 J
_~ Susquehanna
~ MD Western Shore
_ ~ Patuxent
~ Potomac
_ ¦ Rappahannock
¦ York
_ ~ James
~ MD Eastern Shore
_ ¦ VA Eastern Shore
Major Tributary Basins
0.35
** (0
c o
a> —
E £
c c
'<0 'o
C a.
« a,
o 5>
-7 ®
.£
a> H
o> J>
c Q.
j="°
m
Oir
0.30
0.25
0.20
0.15
0.10
0.05
0.00
~ Susquehanna
~ MD Western Shore
~ Patuxent
" ~ Potomac
¦ Rappahannock
¦ York
~ James
~ MD Eastern Shore
¦ VA Eastern Shore
a
Major Tributary Basins
Figure III-6. Absolute (a, c) and relative (b, c) effect on mainstem Chesapeake Bay segments CB3MH and
CB5MH deep water dissolved oxygen concentrations, respectively.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
53
0
1.60
1.40
C- 1.20
** (0
c o
a> —
E £
c c
'<0 'o
C o.
o
1.00
= s
a> "
o>a>
c Q-
«u
m
Off
0.80
O)
(0
0.60
0.40
0.20
0.00J
~ Susquehanna
~ MD Western Shore
~ Patuxent
~ Potomac
¦ Rappahannock
¦ York
~ James
~ MD Eastern Shore
¦ VA Eastern Shore
Maior Tributarv Basins
0.70
¦H- —
E <2
E .E
"
o
0.60
= S
a> "
c o-
«u
m
Off
0.50
0.40
U)
(0
0.30
0.20
0.10
0.00
¦ VA Es
lo
~ Susquehanna
~ MD Western Shore
~ Patuxent
~ Potomac
¦ Rappahannock
¦ York
~ James
~ MD Eastern Shore
¦ VA Eastern Shore
Major Tributary Basins
Figure III-6. (continued)
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
54
ESTABLISHING WETLAND INFLUENCE ON TIDAL-
WATER DISSOLVED OXYGEN CONCENTRATIONS
In some regions of the Chesapeake tidal tributaries in the surface waters in the
summer, an oxygen deficit of several mg/L 02 is typically observed. These regions
are found adjacent to extensive tidal wetlands and contain comparatively small
volumes of tidal waters. The tidal-fresh and oligohaline regions of the upper tidal
York River is an example of relatively small volumes of waters fringed by extensive
wetlands—Mattaponi (MPNTF, MPNOH) and Pammkey (PMKTF. PMKOH) rivers.
In these segments, oxygen demand from tidal wetland sediments is thought to influ-
ence surface water dissolved oxygen concentrations. Recent studies estimate
wetland sediment oxygen demand to range from 1 - 5.3 g 02/m2-day (Neubauer et
al. 2000; Cai et al. 1999). In the Chesapeake Bay Water Quality Model, a uniform
oxygen demand of 2 g 02/m2-day was used as described in Chapter II. Regions of
the Bay tidal waters where there are extensive tidal wetlands, but border relatively
large bodies of water, such as in the Tangier Sound have sufficient volume and
mixing to mask the oxygen demand of adjacent wetland sediments.
WATER QUALITY MODEL RUNS ISOLATING
INDIVIDUAL POLLUTANT EFFECTS ON WATER QUALITY
Allocations were developed for nitrogen, phosphorus and sediment loads for each
basin. To achieve the water quality criteria, some reduction of each of the three loads
is needed. Within limits, however, the mix of nitrogen, phosphorus and sediment
load reductions can be altered and still achieve attainment of the criteria; for
example, relatively fewer nitrogen reductions could be played against relatively
more sediment reductions to achieve the same result. To examine these trade-offs, an
analysis tool called a 'surface analysis' was used. While this tool was useful to
examine the tradeoffs between reducing nitrogen, phosphorus and sediment loads,
ultimately it will be most useful for tributary strategy development, where different
load strategies that achieve the same level of water quality protection can
be examined.
SURFACE ANALYSIS PLOTS
In order to examine a particular water quality parameter, such as dissolved oxygen,
with respect to different load inputs of nitrogen, phosphorus and sediment, a surface
analysis was applied. Surface analysis is a statistical method that uses Water Quality
Model output from multiple scenarios and produces three-dimensional plots called
response surface plots. A response surface plot may be produced as a concentration
of dissolved oxygen, or as the percent attainment of a dissolved oxygen criteria for
a particular Chesapeake Bay Program segment or designated use over a particular
attainment period (i.e., June through September for the segment CB4MH deep-water
designated use). Response surface plots facilitate the understanding of interactions
among nutrient and sediment loads in the Chesapeake Bay's ecosystem and in
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
55
developing effective nutrient and sediment management strategies for improving
water quality.
Figure III-7 examines the influence of nitrogen and phosphorus loads on the segment
CB4MH deep-water dissolved oxygen concentrations. Note that the nutrient loads
are expressed as a portion between 0.4 and 1.0 of the 2000 Progress Scenario loads
for nitrogen and phosphorus. A 40 percent reduction in nitrogen and phosphorus
loads, therefore, is represented by the grid position corresponding to 0.6 TN and 0.6
TP. The surface analysis estimate of the dissolved oxygen response in segment
CB4MH deep water shows that a 40 percent reduction in either nitrogen or phos-
phorus alone would improve dissolved oxygen conditions, but reducing both
nitrogen and phosphorus would bring about greater improvements.
In using this tool, it is important to examine the surface responses with respect to all
the criteria—dissolved oxygen, water clarity and chlorophyll a—and in all regions
or designated uses of the Chesapeake Bay and its tidal tributaries, while keeping in
mind that the surface response plots are a statistical estimate of a series of model
scenarios, which are also estimates of Chesapeake water quality.
CB4MH Deep Water Dissolved Oxygen vs. TN and TP Loads
to the whole Bay (10-year average).
Range of TN & TP: 100% to 40% of 2000 Pregress Scenario
Figure III-7. Surface response of deep-water dissolved oxygen concentrations to nitrogen and
phosphorus loads in segment CB4MH.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
56
SURFACE ANALYSIS UTILITY
Despite the fact that surface analysis is an 'estimate of an estimate' and the esoteric
nature of three-dimensional regression plots, it remains a valuable tool. The utility
of surface analysis is threefold. First, one can gain insight from the relative response
of dissolved oxygen, clarity, SAV, chlorophyll a or any other water quality param-
eter, to any combination of nitrogen, phosphorus and sediment loads. Second, by
interpolating scenario runs, the surface analysis provides an initial estimate of a
water quality response without the need for exhaustive generation of numerous water
quality scenarios. Third, and most important, surface analysis enables the tributary
teams that are developing detailed implementation plans to achieve the nutrient and
sediment cap load allocations to examine possible tradeoffs between nitrogen, phos-
phorus and sediment cap loads.
INFLUENCE OF SEDIMENT ON CHESAPEAKE BAY
DISSOLVED OXYGEN
In the Water Quality Model, decreases in sediment loads were accompanied by
increases in water clarity, which resulted in simulated increases in shallow-water
algae, benthic algae and SAV. Further examination of dissolved oxygen responses to
sediment loads uncovered what initially seemed to be unusual simulation results. As
sediment loads were decreased, deep-water dissolved oxygen concentration
increased slightly. Further examination was necessary to explain this response.
Shallow waters of the Chesapeake Bay and its tidal tributaries occupy a region at the
interface of the land and estuary. Higher sediment concentrations are generally
observed in the shallow-water regions than in deeper open waters due to local water-
shed inputs, shore erosion and wave resuspension of sediment. As Figure III-8
illustrates, improved water clarity allows more processing of nutrients and organics
in shallow-water regions. Effective interception of nutrients by benthic algae, SAV
and phytoplankton in shallow, aerobic waters leads to nutrient diagenesis and loss in
sediment through denitrification and phosphorus sequestration.
Additional sensitivity runs provided insight into the cascading effect of reducing
sediment loads in shallow regions of the Chesapeake Bay on water quality in deep
waters (Figures III-9 and III-10a-b). Figure III-9 shows the benthic algae summer
biomass for the final calibration. The planar model grid shows benthic algae present
in many of the shallow regions, but rarely exceeding 2 grams meter2 biomass. Figure
III-10a is a sensitivity scenario that removes shoreline sediment loads and associated
nutrient loads (SENS 146). A related sensitivity scenario (SENS 147) removed only
the shoreline sediment loads, keeping the nutrients associated with the shoreline
sediment loads unchanged (Figure III- 10b). The pair of sensitivity scenarios (SENS
146 and 147) demonstrated that the reduced sediment load was the cause of the
benthic algae increase. In reality, complete elimination of shoreline sediment loads
is extreme and infeasible. However, reduced sediment loads will have a relative
effect on nutrients and, ultimately, on dissolved oxygen concentrations.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
57
Shallow waters are usually aerobic, as
they are located above the pycnoclirie.
When sediment is reduced in shallow
waters, light limitation of algae is reduced,
allowing more shallow water algal growth,
particularly benthic algae, and more SAV
growth. Overall more nutrients are either
sequestered into the sediments of shallow
waters or dentrified.
algae
aerobic waters
SAV
settling
of algae
benthic algae
nitrification and
2 dentrification at
water-sediment
interface
binding of P04 into
iron phosphate
at water-sediment
interface
decay
So diffusion to
4 + PO4 the surface
If shallow waters have algae sediment
loads, there is greater light limitation of
algae, benthic algae, and SAV. Then
nutrients no longer effectively sequestered
by processes in the shallow waters, fuel
algal growth in the deeper waters of the
Bay where the presence of a pycnocline
results in low to no dissolved oxygen
waters and ammonia and phosphate
flux out of the sediment.
algae
settling
of algae
anaerobic waters
N
ammonia
released to
Bay waters
••• •
P04
phosphate
released to
Bay waters
decay
~lj diffusion to
NH4 + 1 O4 the sediment
surface
anaerobic sediment
Figure 111 -8. Illustration of the influence sediment load has on shallow-water water quality and living resources.
Figure 111 -9 Final calibration summer biomass of benthic algae. The units are in grams
biomass meter2.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
Figure 111-1 Oa. Sensitivity scenario of benthic algae summer biomass with no shoreline
sediment or associated nutrient loads. The units are in grams biomass meter2.
Figure 111-1 Ob. Sensitivity scenario of benthic algae summer biomass with no shoreline
sediment, but associated shoreline sediment nutrient loads included. The units are in
grams biomass meter2.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
59
A modeling study of the Delaware inland bays demonstrated the importance of
benthic algae on sediment diagenesis in shallow waters. Figure III-ll shows the
simulated effect of the presence and absence of benthic algae on nutrient and oxygen
(C. Cerco, unpublished data). The presence of benthic algae results in greater varia-
tion in nutrient and oxygen flux from the sediment (positive values out of the
sediment, negative values into the sediment) but an overall net decrease of dissolved
inorganic phosphorus and dissolved inorganic nitrogen flux out of the sediments.
Model findings were substantiated by observed flux of oxygen and nutrients in
Delaware Inland Bay sediments (S. Seitzinger, unpublished data), i.e., shallow
waters with sufficient light for the growth of benthic algae demonstrated greater
retention of nutrients.
In addition, researchers have shown the role of improved clarity on decreased level
of nutrients. Using a STELLA modeling analysis, Kemp et al. (1994) explained that
the interception of nutrients by "enhanced suspension feeding in the shallow waters
of the Bay ... effect greater improvements for bottom oxygen than comparable action
at deep sites". The interception of nutrients and increased nutrient processing was
further examined by Newell et al. (2002), who described the potential for greater
denitrification and sequestering of nutrients in aerobic shallow-water sediment.
While these researchers specifically examined shallow-water oyster beds as the
agent for greater interception and processing of nutrients in aerobic shallow waters,
With Algae —
No Algae
o
o
Dissolved Oxygen Flux
2
1 -
0-
-1
-2
1
YEARS
D.
o
Phosphate Flux
15 n
10
5
o -
-5
-10
1
1 I ¦ I I I I I I I I I I 11
2 3
YEARS
O
Ammonium Flux
150
125
100
75
50
25
0
-25
-50'
I | I I I I I I I I I I I | I I
2 3
YEARS
Nitrate Flux
Q
251
CM
-
1
o.
Z
25 "
o
-50 -
2
-75 "
-100
i i i i i i i i i i i | i i i i i i i i i i i 11 i i i i i i i i i i |
12 3 4
YEARS
Figure 11-11. Delaware Inland Bay study showing relative range of nutrient and dissolved
oxygen flux resulting from the presence or absence of benthic algae.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
60
decreased light attenuation was the principal factor in increasing nutrient intercep-
tion in the model simulations.
Estimates of the influence that sediment loads, particularly to shallow waters, have on
dissolved oxygen indicate an interesting synergy among nutrient/sediment loads and
living resources, but care should be taken not to over-interpret these results. The
current sediment simulation is the most refined model estimate of sediment loads, fate
and effects, and considerable time was spent with the calibration. However, shoreline
loads were approximated everywhere as a daily baywide average input, and sediment
transport and wave resuspension were not simulated. Overall the influence of sedi-
ment loads on dissolved oxygen was found to be reasonable and consistent with
current understanding of shallow-water processes, but also proved slight in its effect.
A reduction of 20 percent of the loads from shoreline erosion and resuspension had
the equivalent reduction in deep water dissolved oxygen as about a five million pound
reduction in nitrogen. A 2003 review by the Chesapeake Bay Program's Scientific and
Technical Advisory Committee (STAC) found that the ". . . mechanisms linking
shoreline erosion reduction to improvements in deep-water dissolved oxygen through
improved water clarity and increased shallow-water microphytobenthos production
were plausible, but unproven" (STAC 2003). One concern the STAC review raised is
the inability of the model structure and mechanisms to scour benthic algae, which
may, after transport of organics to deep water, contribute, to deep-water oxygen
demand.
The Water Quality Model is now being refined with a sediment transport simulation,
refined spatial and temporal inputs of shoreline erosion loads and a simulation of
wave resuspension with enhanced feedbacks between SAV and resuspended sedi-
ment. The influence of sediment load reductions on deep-water dissolved oxygen
concentrations will be reexamined during the reevaluation of the nutrient and sedi-
ment allocations, which is planned for 2007.
ESTABLISHING AND ASSESSING
NEW SAV RESTORATION GOALS
During the development of the water clarity criteria, the shallow-water designated use
and the associated sediment cap load allocations, the partners agreed to the alignment
of the Chesapeake 2000 commitment to establishing a new SAV restoration goal with
the commitment to reducing sediment loads to "achieve the water quality conditions
that protect living resources." Chesapeake 2000 called for a recommitment to the
long-standing 114,000-acre SAV goal and further called for more ambitious "SAV
restoration goals and strategies to reflect historic abundance, measured as acreage and
density from the 1930s to the present" including the specific levels of water clarity
needed (Chesapeake Executive Council 2000).
Ultimately the SAV goal established to meet the Chesapeake 2000 commitment was
a 185,000-acre restoration goal, specified as baywide, tributary basin, and segment-
specific restoration goals (Appendix A; Secretary Tayloe Murphy 2003). The
sediment load allocation is closely aligned to this goal.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
61
DEVELOPING THE 185,000-ACRE SAV RESTORATION GOAL
The Chesapeake Bay Program has long committed to protecting and restoring SAV.
In 2001, there were 85,415 acres of SAV in the Chesapeake Bay and its tributaries.
The total potential shallow-water habitat available for SAV in the Chesapeake Bay
out to 2-meters is 640,000 acres. SAV never covers 100 percent of the available
habitat, but on average covers approximately 35 percent of it (U.S. EPA 2003b). On
April 15, 2003, the Chesapeake Bay Program's Principals' Staff Committee and
representatives of the headwater states approved the new Bay grass restoration goal
of 185,000 acres by 2010. The partner states of the Bay Program have adopted the
new goal, meeting the Chesapeake 2000 commitment to:
"By 2002, revise SAV restoration goals and strategies to reflect historic
abundance, measured as acreage and density from the 1930s to the
present. The revised goals will include specific levels of water clarity
that are to be met in 2010. Strategies to achieve these goals will
address specific levels of water clarity, water quality and bottom
disturbance."
The following principles guided the development of the recommended new SAV
goal:
• Use the best available data;
• Establish a direct link between the new goal and the new water quality criteria;
• Recognize that SAV should not be expected to cover all available shallow-water
habitat;
• Areas expected to contribute to the goal should only include those that have
demonstrated some minimal level of abundance or persistence in the past; and
• Provide segment-specific acreage goals for use by the tributary strategy teams.
The SAV abundance and distribution record includes interpreted historical aerial
photography from the late 1930s to the 1960s, as well as the annual baywide aerial
survey data from 1978 and 1984-2000. The single best year of SAV growth observed
in each CBP segment from the entire record of aerial photographs (1938-2000) is the
best available data on SAV occurrence over the long term. These same data were
used to define, within each Chesapeake Bay segment, the depth to which the
shallow-water Bay grass designated use should be considered. That depth is the
maximum depth at which water clarity criteria would apply in the context of state
water quality standards, and is, therefore, referred to as the 'application depth' for
each segment (U.S. EPA 2003b). Table III-l contains the derived segment-specific
application depths.
As the first step to setting the SAV goal acreage out to the specific application depth
was determined through bathymetry data and aerial photographs used to slice the
single-best-year SAV acreage in each segment into three depth zones: 0-0.5 meters,
0.5-1.0 meters and 1-2 meters; and aerial photographs used to determine the depth
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
62
to which SAV grew in each segment with either a minimum abundance or minimum
persistence.
Next, the SAV goal for a segment is the portion of the single-best-year acreage that
falls within this determined depth range, which, in turn, was established as follows:
In all segments, the 0-0.5 meter depth interval will be designated for
shallow-water Bay grass use. In addition, the shallow-water Bay grass use
will be designated for deeper depths within a segment if either:
• The single-best-year SAV distribution covered at least 20 percent of the
potential habitat in a deeper depth zone; or
• The single-best-year SAV covered at least 10 percent of the potential
habitat in the segment-depth interval, and at least three of the four five-
year periods of the record (1978-2000) show at least 10 percent SAV
coverage of potential habitat in the segment-depth interval.
SAV restoration goals have been established in a manner consistent with the single-
best-year method used to determine the application depths. Within each segment, the
2010 restoration goal for designated use attainment purposes is equal to the acreage
of the single best year on record within the segment's application depth (U.S. EPA
2003b). These segment-specific SAV restoration goals are listed in Table III-l. New
SAV acreage goals have been established on a segment-specific basis, a baywide
basis and, between those two, a major tributary basin-specific basis (e.g., Potomac
River; see Table III-2).
The new baywide SAV goal, 185,000 acres, is the sum of acreage targets for each of
the 78 Chesapeake Bay segments based on the single-best-year acreage on record for
each segment. The achievement of the baywide goal, as well as the local tributary
basin and segment-specific restoration goals, will be based on the single-best-year
SAV acreage within the most recent three-year record of survey results (U.S. EPA
2003a).
The Chesapeake Bay Program partners reached the following agreements on the
implementation of the SAV restoration goals:
1. The tidal states of Delaware, Maryland and Virginia and the District of Columbia
will adopt numerical water clarity criteria and consider the adoption of the SAV
acreage restoration goals for each Chesapeake Bay Program segment into their
Water Quality Standards.
2. The SAV acreage restoration goals will be used as the primary metric in the
development and implementation of the tributary strategies with regard to sedi-
ment controls. If the SAV acreage restoration goal is achieved in a given segment,
and if the state water quality standards allow, that segment will be considered as
having achieved the shallow-water bay grass designated use even if the sediment
loading caps were not met.
3. Virginia and Maryland will develop comprehensive SAV restoration strategies to
meet the new SAV restoration goal.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
63
Table 111-1. The new Chesapeake Bay SAV acreage goal and current SAV acreages by
Chesapeake Bay Program segment.
Chesapeake Bay Program Shallow-water SAV
Segment Name Application Depth
2001 SAV
Acreage Out to
Application Depth
SAV
Restoration
Goal
Northern Chesapeake Bay
2
7,979
12,908
Upper Chesapeake Bay
0.5
203
302
Upper Central Chesapeake Bay
0.5
1
943
Middle Central Chesapeake Bay
2
112
2,511
Lower Central Chesapeake Bay
2
4,487
14,961
Western Lower Chesapeake Bay
1
715
980
Eastern Lower Chesapeake Bay
2
9,168
14,620
Mouth of the Chesapeake Bay
0.5
8
6
Bush River
0.5
3
158
Gunpowder River
2
*
2,254
Middle River
2
*
838
Back River
0.5
*
0
Patapsco River
1
*
298
Magothy River
1
*
545
Severn River
1
120
329
South River
1
27
459
Rhode River
0.5
*
48
West River
0.5
*
214
Upper Patuxent River
0.5
205
5
Western Branch (Patuxent River)
0.5
*
0
Middle Patuxent River
0.5
104
68
Lower Patuxent River
1
22
1,325
Upper Potomac River
2
1,964
4,368
Anacostia River
0.5
4
6
Piscataway Creek
2
*
783
Mattawoman Creek
1
*
276
Middle Potomac River
2
3,070
3,721
Lower Potomac River
1
1,739
10,173
Upper Rappahannock River
0.5
66
20
Middle Rappahannock River
0.5
*
0
Lower Rappahannock River
1
478
5,380
Corrotoman River
1
389
516
Piankatank River
2
539
3,256
Upper Mattaponi River
0.5
*
75
Lower Mattaponi River
0.5
*
0
Upper Pamunkey River
0.5
140
155
Lower Pamunkey River
0.5
*
0
Middle York River
0.5
*
176
Lower York River
1
801
2,272
Mobjack Bay
2
9,508
15,096
Upper James River
0.5
95
1,600
Appomattox River
0.5
*
319
Middle James River
0.5
15
7
continued
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
64
Table III-1. (continued)
Chesapeake Bay Program Shallow-water SAV
Segment Name Application Depth
2001 SAV
Acreage Out to
Application Depth
SAV
Restoration
Goal
Chickahominy River
0.5
268
348
Lower James River
0.5
2
531
Mouth of the James River
1
232
604
Western Branch Elizabeth River
*
*
0
Southern Branch Elizabeth River
*
*
0
Eastern Branch Elizabeth River
*
*
0
Lafayette River
*
*
0
Mouth of the Elizabeth River
*
*
0
Lynnhaven River
0.5
43
69
Northeast River
0.5
*
88
C&D Canal
0.5
7
0
Bohemia River
0.5
354
97
Elk River
2
2,034
1,648
Sassafras River
1
1,169
764
Upper Chester River
0.5
*
0
Middle Chester River
0.5
*
63
Lower Chester River
1
205
2,724
Eastern Bay
2
2,886
6,108
Upper Choptank River
*
*
0
Middle Choptank River
0.5
*
63
Lower Choptank River
1
148
1,499
Mouth of the Choptank River
2
5,257
8,044
Little Choptank River
2
2,377
3,950
Honga River
2
4,945
7,686
Fishing Bay
0.5
6
193
Upper Nanticoke River
*
*
0
Middle Nanticoke River
0.5
*
3
Lower Nanticoke River
0.5
*
3
Wicomico River
0.5
*
3
Manokin River
2
404
4,359
Big Annemessex River
2
721
2,014
Upper Pocomoke River
*
*
0
Middle Pocomoke River
0.5
*
0
Lower Pocomoke River
1
1,528
4,092
Tangier Sound
2
13,310
37,965
Totals
77,858
184,889
+7,561 acres of
SAV not included in
the survey due to
heightened security
85,419
*Denotes no data available or no SAV present.
Source: U.S. EPA 2003b.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
65
Jurisdiction-Basin
SAV Restoration
Goal (acres)
Susquehanna
12,856
Eastern Shore - MD
76,193
Western Shore - MD
5,651
Patuxent
1,420
Potomac
19,450
Rappahannock
12,798
York
21,823
James
3,483
Eastern Shore - VA
31,215
TOTAL
184,894
Table 111-2. Chesapeake Bay SAV restoration WATER CLARITY AND SAV
goals by major tributary basin.
The water quality criteria distin-
guish two types of SAV
communities with respect to light
requirements (Batiuk et al. 2000;
U.S. EPA 2003a). The tidal-fresh
and oligohaline communities are
estimated to require greater than 13
percent light-through-water while
the more light-sensitive SAV
communities of the mesohaline and
polyhaline areas are estimated to
require 22 percent light-through-
water. These light requirements can
also be expressed as light attenua-
tion (variously symbolized as Kd or
Ke), which represents the rate of
light lost through the water column.
Representing the equivalent light needs for the tidal-fresh/oligohaline and the meso-
haline/polyhaline communities, Figure 111-12 graphs the tradeoffs between light
attenuation and depth. Light attenuation is a rate of light lost by passage through a
water column, either by scattering through sediment, absorption by algal chloro-
phyll, or loss through absorption by dissolved organic material or water. For
tidal-fresh or oligohaline SAV communities, a Kd of 2.0 meter1 is equivalent to the
13 percent light-through-water light requirement at a 1-meter depth. As depth
increases the light path, less light attenuation (greater water clarity) is required to
achieve the same 13 percent light-through-water, so that at a 2 meter depth, light
attenuation of no less than 1 meter1 is required to support SAV. At decreased depths
more light attenuation is allowable for SAV, so that at 0.5 meters depth, a Kd of 4.0
meter1 is still supportive of SAV growth.
To achieve the water clarity levels to support SAV, reductions in light attenuation by
any of the various components (sediment, algae or color) may achieve the light
requirements supportive of SAV, but for much of the Bay's tidal waters, reductions
solely in nutrients and ultimately chlorophyll and epiphytic growth, are insufficient.
A light attenuation model developed by Gallegos (2001) provides insight into the
various components of light attenuation (see http://www.chesapeakebay.net/cims/
index.htm under "Factors Contributing to Water-Column Light Attenuation: A Diag-
nostic Tool"). This model is applicable to any monitoring station data for any period
of time. Figure 111-13 represents estimated seasonal average light attenuation from
the various components with color and attenuation due to water combined at the
monitoring station EE3.2 in the Tangier Sound for the SAV season of April to
October. At a 1-meter depth plotted here, only an estimated 1 year in 10 provides, on
a seasonal average basis, the light required for a mesohaline SAV community of 22
percent light-through-water (Kd of 1.5 meter1).
Reductions in light attenuation due to dissolved organic material and the base light
attenuation rate of water are here depicted as 'Kd color' and are not possible as they
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
66
Application Depth vs allowable Kd
Application Depth (meters)
Figure 111-12. Plots of equivalent 13 percent light-through-water for tidal-fresh (TF) and oligohaline
(OH) SAV communities and 22 percent light-through-water for mesohaline (MH) and polyhaline (PH)
SAV communities at depths between 0.3 and 2.0 meters expressed as light attenuation coefficient, or Kd.
3.50
3.00
2.50
2.00
^ 1.50
1.00
0.50
0.00
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
2.50
2.61
1.52
1.36
1.14
0.87
0.10
0.37
0.14
0,16
0.37
0.19
0.37
0.16
0.37
0.10
0.37
I I Kj Sediment
I I Kj Chlorophyll
~ ^ Color
1.79
1.68
1.47
0.16
0.37
2.28
0.15
0.37
Figure 111-13. Estimated average components of light attenuation (Kd) for the Tangier Sound monitoring
station EE3.2 for the clarity criteria season (April-October) using a light attenuation model developed by
Gallegos (2001).
Source: Chesapeake Bay water quality output http://www.chesapeakebay.net.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
67
are natural conditions. Management reductions in reducing algal nutrients will
reduce light attenuation from phytoplankton and epiphytes, but in Tangier Sound, as
in many regions of the Bay's tidal waters, reductions in nutrients are estimated to be
insufficient to improve water clarity to levels necessary to support SAV growth.
SEDIMENT LOADS: LOCAL EFFECTS
Sediment loads and allocations are different from nutrient loads and allocations
previously done by the Chesapeake Bay Program partners in that sediments are more
local in their effect. Nutrient loads affect large regions of the Bay's tidal waters, as
discussed above. Sediment loads in this water quality model simulation have a
higher settling rate than organic material and, without simulated sediment transport,
do not resuspend from the bottom.
Figure III-14 illustrates the local effect of sediment model behavior through the use
of a simulated sediment load in a particular surface water quality model cell (#1720)
in the Eastern Bay of the Chesapeake Bay. The simulated sediment tracer concentra-
tion was highest in the cell into which the tracer was loaded, with the concentration
quickly dropping in adjacent cells. At a distance of 10 cells from the cell into which
the tracer was loaded (about 10 kilometers), the tracer was no longer detectable.
These findings are consistent with monitoring and research findings of sediment
behavior, with one important difference. With the current lack of a sediment
transport model in the water quality simulation, once suspended sediment reaches
2.50
2.00
C
_ 1.50
u>
E
1.00
0.50
0.00
Down-Bay from Cell 1720
Up-Bay from Cell 1720
1690 1700 1710 1720 1730 1740
Water Quality Model Cell Numbers
1750
1760
Figure 111-14. Local effect of a conservative sediment tracer loaded to a single shoreline
surface model cell (#1720) in Eastern Bay.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
68
the bottom of the water column and is incorporated into the bottom sediments, it is
lost from the system, as no resuspension is simulated. Work is under way to incor-
porate sediment transport into the simulation. A complete description of the
Chesapeake Bay Water Quality Model's sediment simulation can be found in Cerco
and Noel (2003).
CALIBRATING THE WATER QUALITY MODEL FOR CLARITY
To support the development of the sediment cap load allocation, much attention was
given to calibrating various components of light attenuation in the Water Quality
Model. In the absence of a full sediment transport model, calibration entailed recon-
ciling the daily Chesapeake Bay Watershed Model (Phase 4.3) sediment input loads
with monitoring program estimates of suspended sediment concentrations by region-
ally adjusting the sediment settling rates. Further adjustment of the sediment
concentrations, particularly useful for the calibration of sediment in bottom waters
and in turbidity maximum zones, used differential settling rates in the water column
and in the sediment bed. The settling rate of sediment in the water column was set
at a higher rate than that of sediment bed incorporation to factor in the potential for
resuspension of accumulated sediment in the bottom model cells. Figure III-15 is an
example of the resulting calibration in upper Chesapeake Bay mainstem segment
CB20H surface waters and is representative of a single monitoring station calibra-
tion in comparison with model estimates of the few associated model cells at the
monitoring station CB2.2 location. Full calibration results for sediment, chlorophyll
and light attenuation are documented in Cerco and Noel (2003) and further docu-
mented in http://www.chesapeakebay.net/modsc.htm.
SENS134 ON NEW GRID
Figure 111-1 5. Time series plot of model simulated light attenuation (solid line) and model-
ing program observed (circles) for a single monitoring station, CB2.2, compared to a single
surface model cell. The time series extends from January 1985 to December 1994.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
69
While calibration of light attenuation was necessarily at the location of the long-term
monitoring stations, these stations are typically located in deeper waters and away
from shallow-water SAV habitats. Shallow regions, located at the interface of the
watershed and the tidal Bay, are at the 'point of discharge' of all sediment loads from
the adjacent watershed, shore erosion and shallow-water resuspension and generally
have less clarity than that found in the traditional deep-water monitoring stations.
Figure III-16 shows the relative difference of Kd model estimates for the shallows
and deep waters of the Chesapeake Bay. Typically, the simulation estimates that the
Legend
Kd (1/m)
~ 0.00000 - 0.50000
~ 0.50001 -1.50000
]] 1.50001 -2.50000
| 2.50001 - 3.50000
I >3.5
Figure 111-16. Chesapeake Bay Water Quality Model estimated light attenuation (Kd)
showing greater light attenuation in the shallows than in the deeper waters of the
Chesapeake Bay and its tidal tributaries due to the local influence of sediment loads
from the adjacent watershed and shoreline (units are meter"1).
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
70
shallows have an attenuation rate two times greater than that of deeper waters, a
finding consistent with monitoring program observations.
To address the difference between light attenuation estimates in shallow and deep
waters, the monitoring program initiated a long-term shallow-water monitoring
assessment in 2003. With information from new and existing monitoring assess-
ments and research into sediment processes and transport, the Water Quality Model
will be refined with an explicit sediment transport simulation by 2007, in time to
support the reevaluation of the nutrient and sediment allocations.
RELATING SAV BIOMASS TO ACREAGE
SAV abundance has been assessed by aerial surveys from 1984-2000, usually flown
once annually at the time of estimated peak abundance (Moore et al. 2000). Area is
related to abundance of SAV through density and biomass, that is, the area of SAV
coverage increases as either density deceases or biomass increases, all else being the
same. Further, changes in area may not be linear with changes in biomass. For these
reasons, biomass has been described as a better measure of abundance than area, and
biomass is the key SAV metric simulated by the Chesapeake Bay Water Quality
Model. On the other hand, aerial surveys of SAV area are cost-effective, and the
public goal of SAV restoration to an established acreage is a straightforward message
to communicate to the public. For these reasons alone the aerial surveys of SAV have
been, and will continue to be, the basis for abundance estimates of SAV in the Chesa-
peake Bay, augmented by associated estimates of SAV biomass.
The model structure of simulating a 'unit plant' of SAV within the larger water
quality context of the Water Quality Model (Cerco et al. 2002; Cerco and Moore
2001) generates biomass estimates of SAV. Obviously, the first step in relating the
SAV restoration goal and the sediment cap load allocations estimated in the model
is the reconciliation of the acreage and biomass estimates. Fundamental to this
reconciliation is the work done by Moore et al. (2000). Building on this approach,
the Chesapeake Bay Program partners used the Water Quality Model estimates of
SAV biomass to derive SAV acreage estimates (Cerco et al. 2003). The essence of
using the model estimates of biomass relies on the simple assumption that SAV
density does not change in the model scenarios. Then model estimates of SAV area
can be determined by the simple relationship:
SAV Acres = (SAV biomass scenario/SAV biomass calibration) * acres SAV observed 1985-1994
As the calibration relates the SAV biomass to estimated SAV area over the 10-year
period of 1985-1994, and further as the scenarios relate a relative change in SAV due
to changes in nutrient or sediment loads, the relationship above provides a reason-
able estimate of SAV area for any scenario.
SAV biomass varies over the growing season as shown in figures III-17 through
III-19. Aerial estimates of SAV abundance are taken once during the year at about the
time of peak biomass, generally in the late summer for oligohaline and mesohaline
regions, and in the late spring or early summer for the polyhaline regions (Moore et al.
2000). To coordinate the observed peak abundance estimates with model-simulated
estimates of SAV, July averaged simulated SAV biomass was used throughout, except
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
71
freshwater community
• observed
month
Figure 111-17. Modeled (mean [solid line] and interval encompassing 95 percent of com-
putations [dashed line]) and observed (mean [dot] and 95 percent confidence interval
[vertical line through dot]) freshwater SAV community (above ground shoot biomass
only). Observations from Moore et al. (2000). Model simulation from the Susquehanna
Flats (Segment CB1TF) using the 10,000-cell 1998 version of the Water Quality Model.
Source: Cerco et al. 2002.
for tidal-fresh regions, which use a September averaged biomass. The monthly peak
average is typically about three times higher than the annual average biomass.
In relating the SAV restoration goal to the sediment cap load allocations, two factors
needed to be considered in determining the scale at which SAV estimates will be
made. In assessing SAV biomass: 1) sediment cap loads, like nutrients, are allocated
at the major basin level; and 2) sediment is not transported far from its discharge
point, which is usually a fall line or shoreline, due to relatively rapid settling.
Accordingly, the tidal Bay shorelines and adjacent shallow-water habitats were
apportioned into SAV regions associated with major tributary basins—the Susque-
hanna, Patuxent, Potomac, Rappahannock, York, James, Western Shore, Eastern
Shore Maryland/Delaware and Eastern Shore Virginia. The Potomac basin was
further divided into Maryland, Virginia and the District of Columbia. A major
portion of the Susquehanna Flats (CB1TF) was assigned to the Susquehanna basin,
which is considered the primary influence. The Northeast, Elk, Bohemia and
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
72
ruppia community
• observed
month
Figure 111-18. Modeled (mean [solid line] and interval encompassing 95 percent of
computations [dashed line]) and observed (mean [dot] and 95 percent confidence interval
[vertical line through dot]) mesohaline SAV community (Ruppia, above ground shoot
biomass only). Observations from Moore et al. (2000). Model simulation from Eastern
Bay using the 10,000-celI 1998 version of the Chesapeake Bay Water Quality Model.
Source: Cerco et al. 2002.
Sassafras rivers, though part of CB1TF, were assigned to the Eastern Shore Mary-
land/Delaware basin (Figure 111-20).
Model estimates of the SAV response under different management scenarios were
estimated with two metrics, an SAV single-best-year estimate and an SAV running-
three-year, single-best-year mean estimate. The single-best-year estimate is an
estimate of the highest annual SAV biomass throughout the simulated hydrology
period of the 1985-1994. The single-best-year estimate most closely resembles the
new SAV restoration, in that the highest annual biomass is used for the entire simu-
lation period. The SAV running-three-year, single-best-year mean estimate is a mean
of the best year estimates of the eight three-year periods that the 1985-1994
simulation can be parsed into (1985-1987, 1986-1988, 1987-1989, etc.) The SAV
running-three-year, single-best-year mean and standard deviation is the best a priori
estimate of SAV biomass that will be ultimately be assessed through the monitoring
program as described below. Taken together these two estimates provide an estimate
of the greatest SAV response over a 10-year simulated hydrology and the estimated
variation in SAV biomass over the period (tables III-3 and III-4). To further differ-
entiate the SAV response in the major basins, the major fall line load regions where
split into a tidal-fresh (TF) and a lower tidal river region. The Susquehanna SAV
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
73
zostera community
• observed
month
Figure 111-19. Modeled (mean [solid line] and interval encompassing 95 percent of
computations [dashed line]) and observed (mean [dot] and 95 percent confidence interval
[vertical line through dot]) polyhaline SAV community (Zostera above ground shoot biomass
only). Observations from Moore et al. (2000). Model simulation from the Mobjack Bay
(segment MOBPH, formerly WE4) using the 10,000-cell 1998 version of the Chesapeake Bay
Water Quality Model.
Source: Cerco et al. 2002.
response is represented as the SAV response of the Susquehanna Flats in the upper
tidal-fresh Chesapeake Bay.
Under all scenarios, the lower Rappahannock and the tidal-fresh James rivers did not
meet the C2K SAV acreage restoration goal, as the simulated SAV area in response
to the scenario load reductions was much less than the estimates of SAV historic
acreage that forms the basis of the 185,000-acre SAV restoration goal. The Patuxent
and Rappahannock tidal-fresh estimates of SAV area show an initial drop in SAV
acreage between the 2000 Progress and Tier 3 scenarios. In both cases this counter-
intuitive response is due to a decrease in sediment loads causing an increase in light
through the water column, resulting in greater algal biomass and a simulated poorer
habitat for SAV. Further reductions past Tier 3 show increasing SAV response to
decreasing loads. The standard deviation is in many cases greater than the mean,
particularly in regions of the Bay where SAV acreage is sparse, indicating the high
variability in year-to-year SAV area.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
74
SAV Region
~ James River
| | Eastern Shore MD/DE
~ Western Shore MD
| Patuxent River
Potomac
| | Rappahannock River
| | Susquehanna
~ Eastern Shore VA
I | York River
Figure 111-20. SAV regions associated with the major Chesapeake Bay tributary basins.
SPATIAL ANALYSIS OF EFFECTIVE SHORELINE LOAD REDUCTIONS
Sediment reductions from the watershed alone are estimated to be insufficient for fall
SAV recovery to the 185,000-acre SAV restoration goal. Additional reductions in
shoreline loads including shoreline erosion loads and resuspension were simulated for
key scenarios. In tables III-3 and III-4, two scenarios are simulated with an additional
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
75
Table 111-3. Single-best-year estimate of SAV area under key management scenarios. Meets CBP goal =
the original 1992 SAV restoration goal of 113,000 acres. Meets Chesapeake 2000 goal = the new SAV
restoration goal of 185,000 acres.
SAV Acreage
2000 Progress
Tier 3
Tier 3 +20%
Scenario 175
CBP Goal
C2K Goal
Susquehanna
13171
20400
20400
20400
7620
12856
Western Shore MD
4522
4978
6453
6418
3710
5652
Patuxent TF
142
85
88
198
14
5
Patuxent Lower
209
276
745
772
451
1420
Potomac TF
6278
8768
12618
12842
7374
5438
Potomac Lower
7611
7976
10072
9751
5244
14017
Rappahannock TF
48
29
45
45
0
20
Rappahannock Lower
2927
3203
3539
3527
5376
12778
York TF
1734
2173
4298
4857
0
231
York Lower
15995
17848
20726
20408
18347
21592
James TF
136
313
580
552
0
1944
James Lower
656
746
983
838
441
1593
Eastern Shore MD/DE
33765
40970
54819
54475
42280
77706
Eastern Shore VA
21281
22747
26267
28518
22818
29702
108475
130512
161633
163601
113675
Scenario 175 = nutrient and sediment cap load allocations
I I Scenario 175 meets original 1992 CBP SAV restoration goal
I I Scenario 175 meets Chesapeake 2000 (C2K) SAV restoration goal
20 percent reduction in the base shoreline loads representing BMPs, which reduce
shoreline erosion or sediment resuspension1. In many regions of the Chesapeake Bay,
particularly those with extensive shorelines, the 20 percent shoreline load reduction
resulted in a significant improvement in shallow-water water clarity and in SAV.
To farther refine where the shoreline loads should be applied, an analysis was
conducted to determine where any historical SAV occurred and map the adjacent
shoreline. The identified shoreline was considered to be that where shoreline reduc-
tions would be effective for improving SAV habitat. An arbitrary 0.5-kilometer buffer
was extended along the shoreline beyond the SAV areas as a farther protection of SAV
habitat. The combined shoreline adjacent to any historical SAV occurrence and the
0.5-kilometer buffer of shoreline was called the 'effective shoreline'.
The percent of effective shoreline varied from basin to basin ranging from a low of 16
percent in the James River to an effective shoreline of 73 percent in the Potomac River
'information was presented to the partners that a 20 percent reduction in base shoreline loads may be
beyond present technical feasibility. However, sufficient information was not available to reach a
definitive conclusion at that time.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
Table 111-4. Mean and standard deviation of the estimated running-three-year, single-best-year SAV area under key management
scenarios. Meets CBP goal = the original 1992 SAV restoration goal of 113,000 acres. Meets Chesapeake 2000 goal = the new
SAV restoration goal of 185,000 acres.
SAV Acreage Calculation Using Running-Three-Year SBY Mean and Standard Deviation
2000 Progress Tier 3 T3+20% Scenario 175 Goals
Mean
Std. Dev.
Mean
Std. Dev.
Mean
Std. Dev.
Mean
Std. Dev.
CBP
C2K
Susquehanna
10,149
1,546
20,400
4,777
20,400
5,348
20,400
5,507
7,620
12,856
Western Shore MD
1,375
1,509
1,514
1,661
1,962
2,153
1,951
2,141
3,710
5,652
Patuxent TF
66
65
40
39
41
40
92
91
14
5
Patuxent Lower
104
67
137
89
369
240
382
249
451
1,420
Potomac TF
4,750
1,197
6,633
1,672
9,546
2,406
9,716
2,449
7,374
5,438
Potomac Lower
5,027
1,697
5,268
1,778
6,652
2,245
6,440
2,173
5,244
14,017
Rappahannock TF
8
16
5
10
8
15
8
16
-
19.7
Rappahannock Lower
2,469
470
2,702
514
2,986
568
2,975
566
5,376
12,778
York TF
372
739
466
925
921
1,830
1,041
2,068
0
231
York Lower
14,271
1,902
15,925
2,122
18,493
2,465
18,209
2,427
18,347
21,592
James TF
29
58
67
133
124
247
118
235
0
1,943.60
James Lower
245
227
279
258
368
340
313
290
441
1,593
Eastern Shore MD/DE
28,284
4,304
34,320
5,222
45,921
6,988
45,633
6,944
42,280
77,706
Eastern Shore VA
18,667
1,951
19,953
2,085
23,041
2,408
25,015
2,614
22,818
29,702
TOTAL
85,816
107,709
130,832
132,293
113,675
184,953
Scenario 175 = nutrient and sediment cap load allocations
| | Scenario 175 meets original 1992 CBP SAV restoration goal
| | Scenario 175 meets Chesapeake 2000 (C2K) SAV restoration goal
-------
77
(Figure 111-21). In scenarios in which reductions in the base shoreline loads were
reduced, these reductions were universally applied to all base shoreline loads. Using
the estimated effective shoreline estimates, the shoreline length to be considered for
BMPs is considerably reduced (Figure 111-22).
0.00
West Shore Potomac York ESMD/DE
Patuxent Rappahannock James ESVA
Figure 111-21. Estimated effective shoreline for the major Chesapeake Bay basins.
Comprehensive
SAV Location &
Selection of
Target Shoreline
i I XIWrVIN
Figure III-22. Effective shoreline regions of the James, York and lower Rappahannock basins.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
78
MONITORING APPROACH
The Chesapeake Bay Program partners agreed to measure the achievement of the
SAV restoration goal at the segment scale based on the single best year of a running
three-year assessment to account for year-to-year fluctuations in water clarity due to
changing hydrology and loads (U.S. EPA 2003a). To ensure consistency between
metrics used to derive the cap load allocations and measure attainment, model-
simulated SAV acreages were assessed using the single best year of a running
three-year assessment period. The model estimates from the 10-year average esti-
mate were matched with running three-year single-best-year estimates and formed
the basis of the final model estimates of SAV under the different scenario assump-
tions as shown in tables III-3 and III-4.
SEDIMENT CAP LOAD ALLOCATION PRINCIPLES
The principles applied in developing the sediment cap load allocations were as
follows:
1. SAV habitat and the sediment allocation are linked and the primary reason for
reducing sediment loads is to provide suitable habitat for SAV;
2. Sediment impacts, unlike those of nutrients, are local in their influence; and
3. The analysis and effects of nutrients on dissolved oxygen is well developed and
understood, but the analysis of sediment loads and water quality effects is in-
complete.
With these principals in mind, the Chesapeake Bay Program partners agreed to include
the SAV goals into water quality standards. The local nature of the effects of sediment
loads is reflected in the assignment of SAV goals to each Chesapeake Bay Program
segment. It was decided that either the SAV acreage goal or the clarity goal would be
used to assess attainment, through detailed monitoring assessments. If the SAV goal
is not achieved with the nutrient and sediment allocations in place, additional innova-
tive methods to achieve SAV regrowth, such as SAV planting, offshore breakwaters,
shore erosion controls and other methods will be applied. The incomplete under-
standing of shoreline loads from shoreline erosion and resuspension led the partners
to decide to allocate sediment load reductions to the land-based sediment loads.
LITERATURE CITED
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, J. Naylor, D. Wilcox, K. A.
Moore, S. Ailstock and M. Teichberg. 2000. Chesapeake Bay Submerged Aquatic Vegetation
Water Quality and Habitat-Based Requirements and Restoration Targets: A Second Technical
Synthesis. CBP/TRS 245/00 EPA 903-R-00-014. U. S. EPA Chesapeake Bay Program,
Annapolis, Maryland.
Boynton, R. W., J. H. Garber, R. Summers and W. M. Kemp. 1995. Inputs, transformations,
and transport of nitrogen and phosphorus in Chesapeake Bay and selected tributaries.
Estuaries 18(1B):285-314.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
79
Cai, W. J., L. R. Pomeroy, M. A. Moran and Y. Wang. 1999. Oxygen and carbon dioxide mass
balance for the estuarine-intertidal marsh complex of five rivers in the southeastern U.S.
Limnology and Oceanography 44(3):639-649.
Cerco, C. F. and M. Noel. In preparation, 2003. The 2002 Chesapeake Bay Eutrophication
Model. EL-03-XX. U.S. Army Engineering Research and Development Center, Vicksburg,
Mississippi.
Cerco, C. F. and K. Moore. 2001. System-wide submerged aquatic vegetation model for
Chesapeake Bay. Estuaries 24(4):522-534.
Cerco, C. F., M. R. Noel and L. C. Linker. In press, 2003. Managing for water clarity in
Chesapeake Bay. Journal of Environmental Engineering
Cerco, C. F., B. H. Johnson and H. V. Wang. 2002. Tributary Refinements to the Chesapeake
Bay Model. Final Report. U.S. Army Corps of Engineers, Washington, D.C. ERDC TR-02-
4. 201 pp.
Conley, D. J. 1999. Biogeochemical nutrient cycles and nutrient management strategies
Hydrobiologia 410:87-96.
D'Elia, C. F., J. G. Sanders and W. R. Boynton. 1986. Nutrient growth studies in a coastal
plain estuary: Phytoplankton growth in large-scale, continuous cultures. Canadian Journal of
Fisheries and Aquatic Science 43:397-406.
Fisher, T. R., A. B. Gustafson, H. L. Berndt, L. Walstad, L. W. Haas and S. Maclntyre. In
review, 2003. The upper mixed layer of Chesapeake Bay, USA. Estuaries.
Fisher, T. R. and A. B. Gustafson. 2001. Draft report on Bay-wide bioassays to assess P limi-
tation and N distribution in spring. Report to Maryland Department of Natural Resources,
Annapolis, Maryland.
Fisher, T. R., A.B. Gustafson, K. Seiner, R. Lacouture, L. W. Haas, R. L. Wetzel, R. Magnien,
D. Everitt, B. Michaels and R. Karrh. 1999. Spatial and temporal variation of resource limi-
tation in Chesapeake Bay. Marine Biology 133:763-778.
Fisher, T. R. and A. J. Butt. 1994. The role of nitrogen and phosphorus in Chesapeake Bay
anoxia. STAC Literature Synthesis. Scientific and Technical Advisory Committee, Chesa-
peake Research Consortium Edgewater, Maryland.
Fisher, T. R. E. R. Peele, J. W. Ammerman and L. W. Harding Jr. 1992. Nutrient limitation of
phytoplankton in Chesapeake Bay. Marine Ecology Progress Series 82:51-63.
Gallegos, C. L. 2001. Calculating optical water quality targets to restore and protect
submersed aquatic vegetation: Overcoming problems in partitioning the diffuse attenuation
coefficient for photosynthetically active radiation. Estuaries 24:381-397.
Kemp, W. M., S. B. Brandt, W. R Boynton, C. J. Madden, J. Luo, J. Hagy and R. Bartleson.
1994. Benthic filtration, nutrient inputs, and hypoxia in mesohaline Chesapeake Bay. In:
Ecosystem Models of the Patuxent River Estuary. Maryland Department of Natural
Resources, Annapolis, Maryland. CBRM-GRF-94-2. Pp. 57-72.
Malone, T. C. D. J. Conley, T. R. Fisher, P. M. Gilbert, L. W. Harding, K. Seiner and J. Kevin.
1996. Scales of nutrient-limited phytoplankton productivity in Chesapeake Bay. Estuaries
19 (2B): 3 71 -3 8 5.
Moore, K. A., D. J. Wilcox and R. J. Orth. 2000. Analysis of the abundance of submersed
aquatic vegetation communities in the Chesapeake Bay. Estuaries 23(1): 115-127.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
80
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
Newell, R. I. E., J. C. Cornwell and M. S. Owens. 2002. Influence of simulated bivalve biode-
position and microphytobenthos on sediment nitrogen dynamics: A laboratory study.
Limnology and Oceanography 47(5): 1367-1379.
Secretary Tayloe Murphy. 2003. "Summary of Decisions Regarding Nutrient and Sediment
Load Allocations and New Submerged Aquatic Vegetation (SAV) Restoration Goals." April
25, 2003 memorandum to the Principals' Staff Committee members and representatives of
the Chesapeake Bay headwater states. Virginia Office of the Governor, Natural Resources
Secretariate, Richmond, Virginia.
STAC. 2003. Shoreline Erosion and Chesapeake Bay Water Quality: A Scientific Evaluation
of Prediction Uncertainty, Potential for Improvement, and Management Implications. Scien-
tific and Technical Advisory Committee, Chesapeake Research Consortium. Edgewater,
Maryland.
U.S. EPA. 2003a. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and
Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. EPA 903-R-03-002.
Chesapeake Bay Program Office, Annapolis, Maryland.
U.S. EPA. 2003b. Technical Support Document for the Identification of Chesapeake Bay
Designated Uses and Attainability. EPA 903-R-03-004. Chesapeake Bay Program Office,
Annapolis, Maryland.
chapter iii • Technical and Modeling Considerations for Setting the Cap Load Allocations
-------
81
chapter IV
Setting Nutrient and
Sediment Allocations
This chapter describes the specific processes involved in deriving and allocating the
cap loads for nutrients and sediments. While many alternative processes were
explored, only the process ultimately agreed to and followed by the partners is
described. The processes for deriving sediment and nutrient cap load allocations are
distinct and are described separately in this chapter.
To establish cap load allocations for nutrients, the following steps were taken:
• A basinwide loading cap was established, which required identifying a baywide
load that would meet the dissolved oxygen criteria throughout the Bay. The
sections Geographic Location and Criterion Driving the Allocation and Baywide
Cap Loading Options below, respectively, identifies the parts of the Bay's tidal
waters and the criteria that were most critical to establishing a baywide allocation
and presents the cap options that the Chesapeake Bay Water Quality Steering
Committee explored.
• The baywide nutrient cap loads were distributed among the basins and juris-
dictions. The section Distributing Basinwide Allocations to Major Basins
and Jurisdictions below (page 91) describes the principles, decision rules and
processes used to distribute the cap loading to the basins and jurisdictions.
• The initial process did not result in sufficient nutrient reductions to achieve the
baywide cap loads. As described in the section The PSC Completes the Allocation
Process below (page 99), it was necessary to have input from the Principals' Staff
Committee and headwater state representatives to complete the allocations.
• The dissolved oxygen-based nutrient allocations were examined to ensure that
they resolved any remaining chlorophyll a problems. The brief section Cap Load
Allocations to Achieve the Chlorophyll a Criteria below (page 99) reviews the
results of this analysis.
To establish allocations for sediments, the following steps were taken:
• SAV restoration goals were set and used to derive the sediment cap load alloca-
tions. The section SAV Restoration as the Goal below (page 103) explains why the
SAV restoration goals were used in the sediment cap load allocation process.
• Sediment loadings were divided into two major source categories: upland loads
(page 104) and near-shore loads (page 105).
• Sediment allocations were set. The section SAV-Based Sediment Allocations
below (page 106) describes the scientific and policy bases for that process.
chapter iv • Setting Nutrient and Sediment Allocations
-------
82
The mathematical models described in Chapter II were used to identify the sources
of pollutant loadings and relate reductions in those loading sources to attainment of
the Chesapeake Bay water quality criteria and restoration of underwater bay grasses,
or SAV. While these models provided a good understanding of projected water
quality effects from pollutant source reductions, policy decisions were necessary to
derive an equitable distribution of the allocated load.
Chapter III describes many of the technical issues that had to be resolved before the
allocations could be derived. The technical methods and policy decisions that led to
the nutrient cap load allocations are discussed below. Because these methods and
decisions differed from those used to develop sediment allocations, the processes for
deriving each are described in separate sections.
ESTABLISHING NUTRIENT CAP LOAD ALLOCATIONS
Three steps were involved in setting and allocating allowable caps on nutrient loads
throughout the Chesapeake Bay watershed that, collectively, would restore Chesa-
peake Bay and tidal tributary water quality:
1. The basinwide caps on nitrogen and phosphorus loads necessary to attain the Bay
criteria for dissolved oxygen through all tidal Bay habitats were determined;
2. The loading caps were distributed among the major tributary basins by jurisdic-
tion; and
3. Care was taken to ensure that the dissolved oxygen-based nutrient cap load allo-
cations would also bring the Chesapeake Bay and its tidal tributaries into
attainment with the chlorophyll a criteria.
GEOGRAPHIC LOCATION AND CRITERION
DRIVING THE ALLOCATIONS
Early in the process of developing nutrient allocations, there was a question as to
whether there was a geographic location in the Chesapeake Bay tidal waters and a
criterion (dissolved oxygen or chlorophyll a) that would drive the nutrient cap load
allocations. If such factors converged, then analyses could be focused on that loca-
tion and that criterion in deriving nutrient cap load allocations. Also, if the cap load
allocations eliminated the water quality impairment at that point, then they would
likely eliminate all other impairments related to nutrients across all other tidal water
habitats. To explore this issue, the modeled water quality predictions were reviewed
(see Appendix D for modeled water quality results of various loading scenarios).
The water quality results from 'Tier 3 plus 20 percent near-shore reductions' were
used in this analysis because they constituted the likeliest allocation scenario. The
following observations can be made:
• For dissolved oxygen, the migratory spawning and nursery and open-water
criteria have a high level of attainment under current observed conditions.
• For dissolved oxygen, significant nonattainment is shown for the Pamunkey and
Mattaponi rivers. This nonattainment is observed under all loading scenarios
chapter iv • Setting Nutrient and Sediment Allocations
-------
83
because it is due to natural conditions (extensive tidal wetlands resulting in natural
oxygen consuming processes) and for this reason is not considered in establishing
the allocations for nutrients. Chapter 5 of the Technical Support Document (U.S.
EPA 2003b) addresses this issue in greater detail.
• For dissolved oxygen, nonattainment of the water quality criteria was highest in
the deep-water portions of the middle Chesapeake Bay mainstem (segments
CB3MH, CB4MH and CB5MH). It should be noted that the deep-water criteria
only apply in summer, from June through September.
• For chlorophyll a, the Chesapeake Bay and its tidal tributaries achieve a set of
numerical target concentrations except for a limited set of local areas.
These observations suggested that if the nutrient allocations were established to
achieve the dissolved oxygen criteria in the deep-water portions of segments
CB3MH, CB4MH and CB5MH, then all other impairments for dissolved oxygen
and chlorophyll a would most likely be corrected (see Chapter III for details).
BAYWIDE CAP LOADING OPTIONS
Having established the importance of correcting dissolved oxygen nonattainment in
the deep-water portions of segments CB3MH, CB4MH and CB5MH, it was consid-
ered important to explore various baywide nutrient cap load options and their water
quality effects on these segments.
Chapter III discusses the development of various management control scenarios, or
tiers, that were used for deriving the cap load allocations. The tier scenarios were
based on increasing point and nonpoint source controls throughout the Chesapeake
Bay watershed. The loads delivered to tidal waters as a result of each of these control
scenarios were then derived through the watershed model. This control scenario
approach was considered superior to a straight percent reduction approach because:
• The tier scenarios provide a sense of the actual point and nonpoint technology
necessary to achieve the loadings; and
• Costs for tier scenarios can be estimated for use in use attainability analyses.
Five Options Explored
Ultimately, five bay nutrient cap load options, based largely on the tier approach, were
explored. These options, and the model projections of the water quality response to
them, are explained below and are further described in tables IV-1 and IV-2.
Option 1: Nitrogen load capped at 160 million pounds per year, phosphorus load
capped at 12.8 million pounds per year. This option was actually a model simula-
tion that had been run and resulted in full attainment of the bay dissolved oxygen
criteria.1 Therefore it represented the lowest end of basinwide cap loads under
consideration. While this option resulted in attainment, it was unknown at the time
whether higher loading options would also result in attainment.
'The final water quality model results for Option 1 showed a small degree of nonattainment due to
changes (agreed to by the partners) in how the deep-water and deep-channel dissolved oxygen criteria
would be applied.
chapter iv • Setting Nutrient and Sediment Allocations
-------
84
Option 2: Nitrogen load capped at 175 million pounds per year, phosphorus load
capped at 12.6 million pounds per year. This option, which considers all but the
deep-water portion of segment CB4MH, was developed acknowledging that
attainment of the dissolved oxygen criteria in deep-water portion of segment CB4MH
is difficult. While the total loading under this option is not much different from
Option 3 (5 million pounds nitrogen and 0.8 million pounds phosphorus less), the
critical difference is the geographic distribution of the cap loadings. The cap loads for
Option 3, compared with this Option, are higher for the northern tributaries (where
additional reductions improve the Bay's water quality) with lower cap loads in the
southern tributaries (where the impact of loads on Bay water quality is much less).
Option 3: Nitrogen load capped at 181 million pounds per year, phosphorus load
capped at 13.4 million pounds per year. This option represented the application of
the Tier 3 level of controls across all major tributary basins. It was considered viable
because it was perceived at the time as an equitable (all basins at Tier 3) and feasible
allocation by the Water Quality Technical Workgroup and the Water Quality Steering
Committee.
Option 4: Nitrogen load capped at 188 million pounds per year, phosphorus load
capped at 13.3 million pounds per year. This option was created as an alternative to
Option 3, after recognizing that Virginia's lower western shore tidal tributary basins
had a much lower effect on the dissolved oxygen depletion in the middle mainstem
Chesapeake Bay than the Potomac, eastern shore and northern western shore tidal
tributary basins. The nutrient cap loads for the Rappahannock, York and James
basins were set to their existing tributary strategy levels of nutrient reductions. This
option was established to determine if similar water quality results to Option 3 can
be gained, despite the higher loading, at a lower cost to the lower western shore
Virginia tributaries.
Option 5: Nitrogen load capped at 198 million pounds per year, phosphorus load
capped at 15.7 million pounds per year. Like Option 4, Option 5 is predominantly
based on Tier 3 levels. However, the three lower Virginia western shore tributary
basins' cap loads were increased to year 2000 progress levels. Again, this option was
explored because it was known from previous Bay water quality model scenarios
that these three tributary basins had less impact on the water quality of the Chesa-
peake Bay than the eastern shore and northern western shore tributaries. Like Option
4, the partners wanted to explore whether Option 5 would provide water quality
results similar to Option 3, despite the higher loading, at less cost for the lower
western shore Virginia tributaries.
Although the five options focused on assessing the effects of nutrient reductions on
the Chesapeake Bay and its tidal tributaries, it was necessary for them to be appli-
cable to subsequent sediment allocations as well. Therefore, each option included a
20 percent reduction in near-shore sediment loads.
The five options were intended to derive a basinwide loading cap for nutrients. At
the same time, these options not only consisted of different basinwide cap loadings
but also different geographical distributions of those nutrient cap loadings to the
major tributary basins. For distributing the loading to individual basins, however, a
more deliberate approach was necessary. Discussed later in this chapter, the
approach was based on three underlying principles that sought to assure that the allo-
cation process was both equitable and feasible.
chapter iv • Setting Nutrient and Sediment Allocations
-------
85
Table IV-1. Basinwide nitrogen cap load options (million pounds per year) developed by the
Water Quality Technical Workgroup, broken down by major tributary basin.
Basin
Option 1
Option 2
Option 3
Option 4
Option 5
Susquehanna
69.2 (T3.5)
75.9 (T3.25)
82.6 (T3)
82.6 (T3)
82.6 (T3)
Eastern Shore—MD/DE
10.6 (T3.5)
11.9 (T3.25)
13.2 (T3)
13.2 (T3)
13.2 (T3)
Western Shore—MD
8.0 (T3.5)
9.25 (T3.25)
10.5 (T3)
10.5 (T3)
10.5 (T3)
Patuxent
2.5 (T3.5)
2.8 (T3.25)
3.1 (T3)
3.1 (T3)
3.1 (T3)
Potomac
30.5 (T3.5)
34.2 (T3.25)
37.9 (T3)
37.9 (T3)
37.9 (T3)
Rappahannock
5.0 (T3)
5.0 (T3)
5.0 (T3)
5.0 (T3)
5.0 (T3)
York
5.7 (TS)
5.7 (TS)
5.1 (T3)
5.7 (TS)
8.0 (2000)
James
28.1 (TS)
28.1 (TS)
22.3 (T3)
28.1 (TS)
35.6 (2000)
Eastern Shore—VA
0.7 (T3.5)
1.9 (TS)
0.9 (T3)
1.9 (TS)
2.1 (2000)
Total
160.4
174.8
180.8
188
198.1
Key: T3—Tier 3 scenario loading; T3.25—loading one quarter of the way between the Tier 3 and E3 scenarios;
T3.5—loading halfway between Tier 3 and E3 scenarios; TS—tributary strategy loading; 2000—2000 progress
scenario loading.
Table IV-2. Basinwide phosphorus cap load options (million pounds per year) developed by
the Water Quality Technical Workgroup, broken down by major tributary basin.
Basin
Option 1
Option 2
Option 3
Option 4
Option 5
Susquehanna
2.54 (T3.5)
2.69 (T3.25)
2.83 (T3)
2.83 (T3)
2.83 (T3)
Eastern Shore—MD/DE
1.29 (T3)
1.2 (T3.25)
1.29 (T3)
1.29 (T3)
1.29 (T3)
Western Shore—MD
0.62 (T3.5)
0.7 (T3.25)
0.77 (T3)
0.77 (T3)
0.77 (T3)
Patuxent
0.20 (T3.5)
0.22 (T3.25)
0.24 (T3)
0.24 (T3)
0.24 (T3)
Potomac
3.18 (T.3)
2.86 (T3.25)
3.18 (T3)
3.18 (T3)
3.18 (T3)
Rappahannock
0.66 (T3)
0.66 (T3)
0.66 (T3)
0.66 (T3)
0.66 (T3)
York
0.48 (TS)
0.48 (TS)
0.54 (T3)
0.48 (TS)
0.79 (2000)
James
3.71 (TS)
3.71 (TS)
3.77 (T3)
3.71 (TS)
5.70 (2000)
Eastern Shore—VA
0.10 (T3.5)
0.09 (TS)
0.10 (T3)
0.09 (TS)
0.22 (2000)
Total
12.78
12.61
13.38
13.25
15.68
Key: T3—Tier 3 scenario loading; T3.25—loading one quarter of the way between the Tier 3 and E3 scenarios;
T3.5—loading halfway between Tier 3 and E3 scenarios; TS—tributary strategy loading; 2000—2000 progress
scenario loading.
chapter iv • Setting Nutrient and Sediment Allocations
-------
86
Factors for Selecting the Basinwide Nutrient Cap Loads
In selecting the most appropriate basinwide cap loads from the five options consid-
ered above, the Water Quality Steering Committee considered three factors:
1. Basinwide nutrient cap loads should protect the living resources in the Chesa-
peake Bay and its tidal tributaries. The purpose of the allocation is to identify the
cap loads necessary to achieve water quality standards that conform to the Chesa-
peake Bay criteria and refined tidal-water designated uses. This goal of protecting
living resources by determining the necessary cap loads to do so is an important
concept to keep in mind during the state-specific development and adoption of
water quality standards.
2. Basinwide nutrient cap loads should be feasible to achieve. The Water Quality
Steering Committee agreed that the Tier 3 loading levels were feasible to achieve
while achieving the E3 loadings were infeasible. The water quality model results
suggested that loads somewhere between the Tier 3 and E3 levels were necessary
to protect the living resources of the Chesapeake Bay. Obviously, the closer the
loading caps come to E3, the more concern exists as to their feasibility. As states
work toward adopting water quality standards, the issue of feasibility will likely
be subjected to further analysis and may become an important factor requiring
further consideration.
3. Any nonattainment less than 1 percent is not considered significant. It is impor-
tant to remember that the results reported here are model-simulated results and
already factor in a defined level of allowable nonattainment. The Water Quality
Steering Committee considered less than 1 percent nonattainment to be an artifact
of the attainment determination methodology and, therefore, insignificant. This
factor did not favor one of the options. Rather it was an important screening
device to identify significant nonattainment in the complex and voluminous set
of modeling results reviewed throughout the cap load allocation decision
making process.
Predicted Water Quality Response to the
Five Basinwide Cap Load Options
Appendix D contains the predicted water quality response for the Chesapeake Bay
and its tidal tributaries for many loading scenarios, including each of these options
(presented as 'percent nonattainment'). Table IV-3 and figures IV-1 through IV-4,
below, present the relevant information from Appendix D. Again, the nonattainment
for dissolved oxygen in the Pamunkey and the Mattaponi rivers is not included
because it is due to natural conditions (see Chapter II for details).
Table IV-3 provides an overview of the five options that were considered as possible
baywide nutrient loading caps and a summary of water quality responses to each of
the loading cap options.
As Table VI-3 indicates:
• The results of the various control options confirm that the nutrient loads of the
Rappahannock York and James basins do not have as significant an effect on the
chapter iv • Setting Nutrient and Sediment Allocations
-------
87
Table IV-3. Modeled water quality responses to the five basinwide nutrient cap load options.1
Modeled Responses
Option 1
Option 2
Option 3
Option 4
Option 5
Nitrogen Loading
(million pounds per year)
160
175
181
188
198
Phosphorus Loading
(million pounds per year)
12.8
12.6
13.4
13.3
15.7
Potomac and north, Eastern
Shore Tributary Basins
Tier 3.5
Tier 3.25
Tier 3
Tier 3
Tier 3
Rappahannock, York and
James Basins
Tributary
Strategy
Tributary
Strategy
Tier 3
Tributary
Strategy
2000
Progress
Number of segments with >1%
dissolved oxygen nonattainment
(percent time volume)
1
1
3
4
11
CB4MH deep-water nonattainment
(percent time volume)
3.9
6.0
7.6
7.9
3.84
Area of Bay bottom with dissolved
oxygen concentrations <1 mg/L
(percent bay bottom surface area)
4
4
15
15
19
Volume of bay in nonattainment
for dissolved oxygen
(percent bay volume)
4
7
15
19
19
Bay water surface area not meeting
target chlorophyll a concentrations
(percent surface area)
1
15
23
24
25
'The dissolved oxygen response for these options includes a 20 percent reduction of shoreline erosion sediment loads.
The dissolved oxygen nonattainment results do not include results from the tidal Mattaponi and Pamunkey rivers since
the lower dissolved oxygen concentrations is a natural condition that was not remedied with nutrient loading reductions.
dissolved oxygen conditions of the mainstem Chesapeake Bay as the Potomac and
Virginia Eastern Shore basins. Therefore, for all options but Option 3, the Potomac,
western shore tributaries north of the Potomac and Eastern Shore basins have higher
levels of nutrient load reductions than the Rappahannock, York and James basins.
• Water quality improves with each increasing level of baywide loading reduction.
• The bay water quality is good for most metrics below under options 1 and 2 but
declines rapidly under options 3 through 5.
• Nonattainment of water quality criteria in the middle central Chesapeake Bay
(segment CB4MH) does increase with increased loading but not dramatically so.
• The number of segments in nonattainment is less under options 1 and 2 (one
segment impaired) than under the other options. However, note that only the deep-
water portion of CB4MH is impaired under Option 1, while both the deep-water
and the deep-channel portion of CB4MH is impaired under Option 2 (although the
deep-channel impairment is marginal) (Table IV-3).
Figure IV-1 illustrates the percent of the Chesapeake Bay and its tidal tributaries in
which the Bay bottom surface area is below 1 mg/L dissolved oxygen for various
loading scenarios, including the five cap load allocation options. A low percentage
of bottom surface area with less than 1 mg/L dissolved oxygen is a good indicator of
chapter iv • Setting Nutrient and Sediment Allocations
-------
88
60
Observed 2000 Tier 1 Tier 2 Option 5 Option 4 Option 3 Option 2 Option 1
Progress
(336/26.5) (285/19.1) (261/19.0) (221/16.4) (198/15.7) (188/13.3) (181/13.4) (175/12.6) (160/12.8)
Scenario
(Nitrogen Load/Phosphorus Load in million pounds per year)
Figure IV-1. Nitrogen and phosphorus load versus percent of the Bay bottom surface area
with dissolved oxygen concentrations less than 1 mg/L.
the extent to which the Bay may be habitable for bottom sediment dwelling worms
and clams. Further, since phosphorus, and to some extent, nitrogen, are released
from bottom sediments predominantly at dissolved oxygen levels below 1 mg/L,
this analysis also indicates the potential for nutrient release from these sediments.
Figure IV-1 shows that:
• Loading reductions represented by the observed through Tier 2 scenarios achieve
little reduction in the percentage of the Bay bottom area that has dissolved oxygen
concentrations of less than 1 mg/L. However, reductions beyond the Tier 2
scenario cause a dramatic reduction in the bottom area with dissolved oxygen
concentrations of less than 1 mg/L.
• Implementation of options lor 2 achieve dramatic improvement in low dissolved
oxygen concentrations along the Bay bottom in comparison to Option 3. This
improvement is due to the further nutrient reductions realized in the Potomac,
northern western shore tidal tributaries and along the Eastern Shore. These basins
are the ones that have the most impact on the dissolved oxygen levels of the
Chesapeake Bay. Dissolved oxygen concentrations of less than 1 mg/L are almost
eliminated with both options 1 and 2.
Figure IV-2 identifies the model-simulated volume of the Chesapeake Bay and its
tidal tributaries, integrated over the 10-year simulation period, that do not attain the
chapter iv • Setting Nutrient and Sediment Allocations
-------
89
¦s «r 60
Q) t
E ~
C T5
Observed 2000 Tier 1 Tier 2 Option 5 Option 4 Option 3 Option 2 Option 1
Progress
(336/26.5) (285/19.1) (261/19.0) (221/16.4) (198/15.7) (188/13.3) (181/13.4) (175/12.6) (160/12.8)
Scenario
(Nitrogen Load/Phosphorus Load in million pounds per year)
Figure IV-2. Percent volume of the Chesapeake Bay and its tidal tributaries in nonattainment for
applicable dissolved oxygen criteria.
applicable dissolved oxygen criteria for numerous loading scenarios, including the
five cap load allocation options. This metric shows the fraction of the water column
that provides suitable habitat for living resources with respect to dissolved oxygen.
Figure IV-2 shows that:
• Improvements in water column attainment of the dissolved oxygen criteria are not
dramatic until loading reductions exceed Tier 2 levels. While water quality is
improving with all loading reductions, these necessary nutrient reductions are not
enough to bring many parts of the Chesapeake Bay and its tidal tributaries back
into attainment.
• There is a dramatic improvement in attainment through all five basinwide cap
load allocations stepwise from options 5 through 1.
• While the improvement in attainment of Option 1 over Option 2 looks significant,
further review of the modeling results gives a better perspective. Nonattainment
in the deep-channel portion of segment CB4MH for Option 2 is 1.02 percent, just
barely over the established 1 percent threshold. It is this deep-channel nonattain-
ment that brings the total water column volume nonattainment for Option 2 to 7
percent. Without this deep-channel nonattainment, Option 2 would have the same
water column volume nonattainment as Option 1 (4 percent).
chapter iv • Setting Nutrient and Sediment Allocations
-------
90
Figure IV-3 shows the model-simulated water surface area of the Chesapeake Bay and
its tidal tributaries that do not meet a set of target chlorophyll a concentrations in
spring (Appendix C). Spring algae concentrations and the timing of the spring
algal blooms are closely linked to summer low dissolved oxygen levels. Figure IV-3
shows that:
• There are dramatic improvements in the water surface area of chlorophyll a
achievement of target concentrations through the entire range of load reductions,
from 2000 progress through to Option 1.
• The dramatic improvement in the water surface area of the Chesapeake Bay and
its tidal tributaries in achieving the target chlorophyll a concentrations between
options 2 and 3 requires closer review. That is, under Option 3, the lower Potomac
estuary level of nonattainment is 1.53 percent, while it is less than 1 percent under
Option 2. This small change in the level of achievement of the target concentra-
tions in the Potomac River accounts for the difference in the baywide water
surface area of nonattainment between options 2 and 3.
• The dramatic improvement between options 1 and 2 also needs closer review.
That is, under Option 2, segment CB7PH is 1.52 percent, while it is less than
1 percent under Option 1. This small change in attainment accounts for the differ-
ence in baywide nonattainment between options 1 and 2.
80
70
60
-S 50
40
30
20
10
3
£
0)
c
t—
O
a
a
T3
c
i-
a
(0
o
c
~u
c
o
o
-o
E
a
<0
>*
a
>
"O
c
m
.c
a.
a
a
o
o
j*:
a
0
E
o
a.
a
.c
o
1
(0
o
o
c
.c
u>
o
O
a
o
h-
a
o
a
O)
c
Q.
£
>
<
a
o
!c
o
o
a
<
3
o
CO
z
o
a
5
Observed
Tier 1
Tier 2
Option 5 Option 4 Option 3 Option 2
2000
Progress
(336/26.5) (285/19.1) (261/19.0) (221/16.4) (198/15.7) (188/13.3) (181/13.4) (175/12.6)
Scenario
(Nitrogen Load/Phosphorus Load in million pounds per year)
Option 1
(160/12.8)
Figure IV-3. Percent of water surface area of the Chesapeake Bay and its tidal tributaries
achieving target chlorophyll a concentrations in spring.
chapter iv • Setting Nutrient and Sediment Allocations
-------
91
The Water Quality Steering Committee debated these five cap load allocation
options at length and concluded that:
• Options 1 and 2 provide high protection against low (< 1 mg/L) dissolved oxygen
waters along the Bay bottom and provide significantly better protection from
these effects than options 3 through 5.
• Options 1 and 2 offer a similar level of water quality protection with respect to
dissolved oxygen criteria, superior to that achieved under options 3 through 5.
Although the Water Quality Model did not simulate full criteria attainment, and
since the criteria and designated use will be subject to public review during the
states' water quality standards adoption process, the marginal level of nonattain-
ment remaining with these options was considered acceptable.
• As characterized by the target concentrations, model-simulated chlorophyll a-
related water quality effects were largely addressed with the application of Tier 2
???? loading reductions. While the chlorophyll a improvement through the five
cap load allocation options is significant in Figure IV-2, caution should be taken
not to overestimate the actual improvement, given the localized nature of algal-
related impairments.
• Although the water quality response of Option 1 is similar to that for Option 2,
Option 2 costs less and is more feasible.
Based on this information, the Water Quality Steering Committee recommended
basinwide cap loadings of 175 million pounds of nitrogen per year and 12.8 million
pounds of phosphorus per year. These cap loads combined the best Bay water quality
and living resource protection and feasibility of all the potential options.
DISTRIBUTING BASINWIDE ALLOCATIONS TO MAJOR BASINS
AND JURISDICTIONS
Once these basinwide cap loads were identified, they needed to be allocated to the
20 major basins, by jurisdiction, in the watershed. To enable states and local stake-
holders to develop tributary strategies, it was necessary to divide the basinwide
nitrogen and phosphorus loads into cap loads for each of these 20 areas of the Bay
watershed for which tributary strategies will be developed. States and local stake-
holders will identify the actions necessary to achieve the nutrient and sediment cap
load allocations.
Figure IV-4 delineates each of the major basins in the watershed and identifies the
various jurisdictions for each major basin. In some cases (for example, the Sus-
quehanna River Basin in Pennsylvania), states have chosen to further subdivide their
allocated cap load into smaller watersheds for which tributary strategies will be
developed.
Guiding Principles of Allocation Decisions
The discussions and analyses of options for equitable allocation of the basinwide cap
loads were extensive. The policy decisions for allocating the basinwide cap loads
were driven by an overall desire for equity and achievability. Achieving equity is a
complex and somewhat subjective undertaking. In addition to equity, the Chesapeake
chapter iv • Setting Nutrient and Sediment Allocations
-------
92
Chesapeake Bay Basins
| | EASTERN SHORE MARYLAND/DELAWARE
I I EASTERN SHORE VIRGINIA
| | JAMES RIVER BASIN
PATUXENT RIVER BASIN
POTOMAC RIVER BASIN
RAPPAHANNOCK RIVER BASIN
SUSQUEHANNA RIVER BASIN
Figure IV-4. The major tributary basins and jurisdictions in the Chesapeake Bay watershed.
chapter iv • Setting Nutrient and Sediment Allocations
-------
93
Bay Program partners factored in the feasibility of achieving reductions when
distributing the cap loadings. All the partners agreed that the E3 scenario was not
feasible. Similarly the partners agreed that Tier 3 was feasible. Hence, the Chesa-
peake Bay Program partners limited allocations options to below E3.
The Chesapeake Bay Program partners succeeded in framing an equitable and
feasible approach by applying three underlying principles to the allocation process.
The specific process that was used to distribute the allocation based upon these prin-
ciples is provided later in this chapter. The underlying principles were:
1. Basins that contribute the most to the problem must do the most to resolve the
problem. The Chesapeake Bay water quality model allowed the partners to
determine the relative impact of each tributary basin on the dissolved oxygen
problems experienced in the middle mainstem Bay and lower tidal Potomac River.
Figure IV-5 shows the relative influence from each basin. Basins that have the
greatest influence on the Bay water quality will generally be required to achieve
the highest percent reduction of nutrient loads.2
2. States that benefit most from the Chesapeake Bay recovery> must do more. States
that encompass the Chesapeake Bay and its tidal tributaries in its state boundaries,
e.g., Maryland, Virginia, Delaware and the District of Columbia, will realize
greater benefits, such as tourism dollars, than others. This principle was applied
by capping the reductions for nontidal states (New York, Pennsylvania and West
Virginia) at a lower level than reduction targets suggested through application of
Principle 1.
3. All reductions in nutrient loads are credited toward achieving final assigned
loads. This principle was adopted to avoid penalizing states that have achieved
significant nutrient reductions. It was applied by establishing a 'baseline' load
using 2010 land use and population, but no point or nonpoint source treatment in
place (2010 anthropogenic load). Since all reductions were from this baseline, all
past and existing best management practices and treatment upgrades were cred-
ited toward the needed reductions.
The above principles guided the Water Quality Technical Workgroup in allocating
the loadings among the major tributary basins, but a more detailed approach was
needed in order to divide the load among the major basins by jurisdiction. After
exploring alternatives to allocating the basinwide cap loads based on these prin-
ciples, the Water Quality Technical Workgroup recommended a more detailed
approach to the Water Quality Steering Committee. The Chesapeake Bay Program
partners agreed to the following decision rules for dividing the cap load allocation:
1. Basins with the greatest impact on the Bay must achieve the highest controls.
Although segment CB4MH was considered the critical area of focus relative to
dissolved oxygen in establishing the basinwide nutrient cap loads, a broader look
at water quality effects than the original focus on CB4MH was preferred for deter-
mining which tributary basins has the greatest impact on the Bay water quality. To
2Earlier modeling studies indicated ocean inputs were responsible for 29 to 36 percent of the total nitro-
gen loading (approximately 131 million pounds per year) to the Chesapeake Bay (Thomann et al.
1994). These ocean loads were a constant factor in the model-based analysis of relative impact on
water illustrated in Figure IV-5.
chapter iv • Setting Nutrient and Sediment Allocations
-------
94
avoid an overly narrow assessment, basin impacts on water quality conditions in
segments CB3MH, CB4MH and CB5MH were assessed.
'Relative impact' (i.e., comparative water quality impact of the major basins) was
used to determine the impact on the Bay (see Chapter III for more details). To
derive the 'relative impact' of each basin the water quality model was run with all
basins but one (isolated) basin set at their existing loading (2000 progress). The
isolated basin was set at the Tier 3 level of controls. The water quality model was
run nine times, thereby 'isolating' each of the nine major basins. In this way, the
water quality improvement from reductions from each basin could be modeled.
'Relative impact' was chosen over 'absolute impact' because the latter, which
measures the impact of the total loading and the hydrologic proximity of the basin
with the depressed dissolved oxygen concentrations in the middle Bay, was deter-
mined to be arbitrary and unfair to the larger basins and subsequently dismissed.
To calculate 'relative impact', 'absolute impact' was 'normalized' by dividing it
by the nitrogen and phosphorus loading for each basin. Hence, the approach
measures the impact from each basin for each unit of nutrient load delivered to the
Bay's tidal waters and approximates only the hydrologic proximity of each basin.
Figure IV-5 shows the relative influence, determined from a 'normalized' impact
assessment, of each basin on the dissolved oxygen concentrations of Bay
segments CB3MH through CB5MH.
Using the Chesapeake Bay water quality model, basins were grouped based on
their relative influence (per pound nutrient loading) on the dissolved oxygen
concentration in the identified segments of the mainstem Chesapeake Bay. In this
analysis, the Chesapeake Bay Program partners decided to assess the combined
nitrogen and phosphorus load impacts on the middle mainstem Chesapeake Bay
(CB3MH through CB5MH). These loads were 'normalized' by assuming that 10
pounds of nitrogen had the impact of 1 pound of phosphorus. The potential load
impacts from both nitrogen and phosphorus were thus combined into the term
'algal units' (see Chapter III for more details).
Finally, basins were grouped based on their influence on improving the dissolved
oxygen concentrations in segments CB3MH through CB5MH (Figure IV-6). The
Virginia Eastern Shore, Susquehanna River, Patuxent River and Maryland
Western Shore were found to have the greatest influence on the dissolved oxygen
levels of the middle mainstem Chesapeake Bay and, therefore, grouped as basins
having high impact on the Bay tidal water quality. The Potomac River and the
Maryland/Delaware Eastern Shore basins were found to have moderate impact on
the middle mainstem Chesapeake Bay water quality. The Rappahannock, York
and James river basins were found to have a low impact on the middle mainstem
Chesapake Bay water quality.
2. An 'equalpercent reduction 'of the 2010 'anthropogenic load'would be used as a
baseline. Using the grouping of basins identified above, the Chesapeake Bay
Program partners agreed that load reductions would be based on an equal percent
reduction of anthropogenic load for all basins within a single group.
Using 2010 population and land use estimates and assuming no point or nonpoint
controls in place, watershed model runs were conducted to calculate the total
loading delivered to Bay tidal waters from each basin. The watershed model was
chapter iv • Setting Nutrient and Sediment Allocations
-------
95
Relative Impact
I I High
~ Medium
Low
EASTERN SHORE
VIRGINIA
RAPPAHANNOCK
RIVER BASIN
POTOMAC RIVER
BASIN
PATUXENT RIVER
BASIN
WESTERN SHORE
MARYLAND
EASTERN SHORE
MARYLAND
YORK RIVER BASIN
Figure IV-5. Relative impact of major tributary basins on the dissolved oxygen concentration
in the mainstem Chesapeake Bay that was considered when allocating the basinwide nutrient
cap loads.
chapter iv • Setting Nutrient and Sediment Allocations
-------
96
CO
c
o
Q_
£
"E
c
3
o
TO
o>
o>
£
CO
O
T3
O
<0
CO
Q
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
<1)
o
-C
GO
C
03
c
c
c
-------
97
To achieve the basinwide target load of 175 million pounds of nitrogen and 12.8
million pounds of phosphorus, the 3-percent difference needed to be translated
into actual percent reduction for each jurisdictional basin. The resulting percent
reductions for nitrogen and phosphorus are shown in Figure IV-6.
Based on application of the "basins with the greatest impact on the Bay need to
achieve the highest controls" and the "equal percent reduction" decision rules
above, preliminary allocations were developed using the equation:
Preliminary _ 2010 Anthropogenic Load *
Load Allocation ~~ [(100 - basin group percent reduction)/100] + Forest Land
Table IV-4 summarizes the results of this analysis.
The above decision rules were applicable to principles 1 and 3. The Chesapeake Bay
Program partners agreed that further decision rules were necessary to better address
Principle 1 and Principle 2. After applying the above decision rules, the Bay partners
agreed to the following additional decision rules.
3. The Virginia tributary basins of the York and James rivers would be set at their
current tributary strategy cap loads. The York River and James River tributary
strategies called for loading targets that were slightly higher for nitrogen and
slightly lower for phosphorus than the cap loads proposed in Table IV-4. Because
the differences are small and offset each other, the Bay Program partners agreed
that the current tributary strategy cap load goals for nitrogen and phosphorus for
the York River and the James River basins would be applied in the proposed cap
load allocations.
4. All nontidal states with nitrogen or phosphorus reductions greater than Tier 3 from
decision rules 1 and 2 above would be adjusted to a Tier 3 levels. As further expres-
sion of equity, the Chesapeake Bay Program partners agreed that the states that
benefited most directly from the recovery of the Bay would take on a greater burden
for the cleanup. Obviously, the jurisdictions with Bay tidal waters benefit most from
nutrient reductions directed toward Bay water quality restoration. Hence, they
agreed to limit the loading reductions of the nontidal states—New York Pennsyl-
vania and West Virginia—to Tier 3 levels for nitrogen and phosphorus.
5. For phosphorus, any tidal jurisdiction with an allocation of reductions greater
than Tier 3.4 would be adjusted to a Tier 3.4 level. When decision rules 1 and 2
were applied for phosphorus, the resultant cap loads allocated to several basins—
Eastern Shore (VA), Susquehanna (MD), Eastern Shore (MD) and Rappahannock
(VA)—were at or beyond E3 levels. The partners expressed concern that such
high levels of controls were not achievable. Therefore, the allocations for these
basins would be set at a Tier 3.4 level, which is a loading equal to Tier 3 plus 40
percent (0.4) of the difference between the Tier 3 and the E3 loadings. In this way
the tidal states were 'capped' at a greater loading reduction (Tier 3.4) than the
nontidal states (Tier 3), thus requiring greater reductions for those states that
benefit more from the reductions.
chapter iv • Setting Nutrient and Sediment Allocations
-------
Table IV-4. Preliminary nitrogen and phosphorus cap load allocations based on the application of decision rules 1 and 2 with
jurisdictional-basins grouped according to their relative influence on rnainstem Chesapeake Bay water quality.
NITROGEN PHOSPHORUS
(Million pounds per year) (Million pounds per year)
Jurisdiction-Basin
2010
No BMPs
2010
All-Forest
2010
Anthropogenic
Preliminary
Load
Distribution
2010
No BMPs
2010
All-Forest
2010
Anthropogenic
Preliminary
Load
Distribution
Eastern Shore YA - VA
2.84
0.24
2.61
1.16
0.29
0.01
0.29
0.08
Susquehanna - MD
0.00295
1.80
0.32
1.48
0.85
0.1021
0.0046
0.0975
Susquehanna - PA
117.19
30.35
86.85
61.06
4.89
0.28
4.62
1.46
Susquehanna - NY
16.99
7.64
9.35
10.95
0.91
0.08
0.83
0.29
Western Shore MD - MD
30.52
1.05
29.47
11.47
3.61
0.02
3.59
0.94
Western Shore MD - PA
0.05
0.00
0.04
0.02
0.00
0.00
0.00
0.00
Patuxent - MD
6.07
0.55
5.53
2.50
0.84
0.02
0.82
0.23
HIGH IMPACT BASINS LOADING
175.47
40.14
135.32
88.00
10.64
0.41
10.24
3.03
Eastern Shore MD - MD
24.86
2.45
22.41
11.05
2.96
0.05
2.90
0.88
Eastern Shore MD - VA
0.14
0.02
0.12
0.06
0.02
0.00
0.02
0.01
Eastern Shore MD - DE
6.64
0.53
6.11
2.88
1.20
0.01
1.19
0.35
Eastern Shore MD - PA
0.54
0.05
0.49
0.24
0.05
0.00
0.05
0.01
Potomac - D.C.
7.22
0.05
7.18
2.80
1.38
0.00
1.37
0.39
Potomac - MD
27.63
2.26
25.37
11.99
3.79
0.08
3.71
1.14
Potomac - VA
28.68
2.98
25.69
12.84
4.64
0.10
4.54
1.4
Potomac - PA
8.09
1.02
7.08
3.73
0.66
0.04
0.62
0.21
Potomac - WV
7.97
1.83
6.14
4.18
0.63
0.09
0.54
0.24
MODERATE IMPACT BASINS LOADING
111.77
11.18
100.60
49.77
15.32
0.38
14.94
4.65
Rappahannock - VA
9.87
1.98
7.89
5.24
1.40
0.05
1.34
0.48
York - VA
10.16
1.66
8.50
5.18
2.03
0.05
1.98
0.6791
James - VA
56.83
5.59
51.24
26.79
11.89
0.25
11.64
3.9228
James - WV
0.04
0.02
0.01
0.03
0.01
0.00
0.01
0.0055
LOW IMPACT BASINS LOADING
76.90
9.26
67.64
37.23
15.33
0.36
14.97
5.08
BASINWIDE TOTAL
364.13
60.58
303.56
175.00
41.29
1.14
40.15
12.76
Notes: 2010 No BMPs = 2010 land use, no BMPs or wastewater treatment controls; 2010 All-Forest = fully forested Watershed; 2010 Anthropogenic = 2010 All-Forest -
2010 No BMPs.
-------
99
The preliminary allocations presented in Table IV-4 were modified to reflect deci-
sion rules 3 through 5. Table IV-5 shows the allocations that the Water Quality
Steering Committee presented to the Chesapeake Bay Program's Principals Staff
Committee and headwater state representatives. Note that the basinwide cap loads of
187 million pounds for nitrogen and 13.8 million pounds for phosphorus after rules
3 through 5 were applied. Specifically, the Water Quality Steering Committee's
cap load allocations fell short of the agreed upon basinwide cap loads of 175 and
12.8 million pounds by 12 million pounds of nitrogen and 1 million pounds of phos-
phorus, respectively. These shortfalls were called 'orphaned loads'.
THE PSC COMPLETES THE ALLOCATION PROCESS
In the spring of 2003, the Principals' Staff Committee and the headwater state repre-
sentatives promptly approved the basinwide cap loadings of 175 million pounds per
year of nitrogen and 12.8 million pounds per year of phosphorus, which the Water
Quality Steering Committee had recommended. However, as Table IV-5 shows,
recommended jurisdiction-basin allocations fell short of the nutrient reductions
needed. Twelve million pounds of nitrogen reductions and 1 million pounds of phos-
phorus reductions still needed to be assigned to the jurisdiction-basins. The
Principals' Staff Committee and headwater state representatives succeeded in
addressing the 'orphaned loads' by sharing the burden. The EPA committed to the
pursuit of adopting the proposed Clear Skies initiative, which is estimated to bring
about an 8 million pound reduction of nitrogen loads delivered to the Chesapeake
Bay and its tidal tributaries per year beyond the Clean Air Act controls. In a genuine
gesture of partnership to restore Bay water quality, Pennsylvania, Virginia, Mary-
land, Delaware and the District of Columbia promptly accepted further reductions in
their respective nitrogen and/or phosphorus cap loads. These additional reductions in
individual basin/jurisdiction cap loads were sufficient to achieve the nutrient basin-
wide cap loads. These cap load allocations are presented in Table IV-6 by major
tributary basin by jurisdiction and in Table IV-7 by jurisdiction.
CAP LOAD ALLOCATIONS TO ACHIEVE
THE CHLOROPHYLLS CRITERIA
As the previous discussion demonstrates, nutrients not only depress the amount of
dissolved oxygen in the water but also promote excessive algae growth. Therefore,
along with numeric criteria for dissolved oxygen for the Chesapeake Bay, the EPA
also recommended narrative chlorophyll a criteria to protect against excessive algal
growth (U.S. EPA 2003a). Early in the process of developing the cap load alloca-
tions, it appeared likely that nutrient controls designed to achieve the dissolved
oxygen criteria would also be adequate to achieve the chlorophyll a criteria. There-
fore, the analysis of nutrient allocations for chlorophyll a was secondary to that of
nutrient allocations for dissolved oxygen.
After developing the nutrient cap load allocations, the resulting chlorophyll a
concentrations were assessed to determine if further reductions were necessary. After
reviewing the model-simulated chlorophyll a concentrations under the cap load
allocation scenario (see Appendix C), further adjustments to the nutrient cap load
allocations were deemed unnecessary.
chapter iv • Setting Nutrient and Sediment Allocations
-------
Table IV-5, The revised draft nitrogen and phosphorus cap load allocations based on application of decision rules 1 through 5 that the
Water Quality Steering Committee presented to the Principals' Staff Committee and headwater state representatives.
NITROGEN PHOSPORUS
(Million pounds per year) (Million pounds per year)
J urisdiction-Basin
Preliminary
Load
Distribution
(from Table IV-4)
Allocation
Percent
Reduction of
Anthropogenic
Load
Tiers
Preliminary
Load
Distribution
(from Table IV-4)
Allocation
Percent
Reduction of
Anthropogenic
Load
1 it'Is
Eastern Shore VA - VA
1.16
1.16
64.6
2.40
0.08
0.08
74.42
3.40
Susquehanna - MD
0.85
0.85
64.6
3.30
0.0295
0.03
74.42
3.40
Susquehanna - PA
61.06
69.08
55.4
3.00
1.46
2.20
58.25
3.00
Susquehanna - NY
10.95
12.58
47.2
3.00
0.29
0.59
39.11
3.00
Western Shore MD - MD
11.47
11.47
64.6
2.90
0.94
0.94
74.42
2.40
Western Shore MD - PA
0.02
0.0192
64.6
n/a
0.00
0.0000
n/a
n/a
Patuxent - MD
2.50
2.50
64.6
3.55
0.23
0.23
74.42
3.10
TOTAL BASIN LOADING
88.00
97.65
-
-
3.03
4.06
-
-
Eastern Shore MD - MD
11.05
11.05
61.6
2.60
0.88
0.88
71.42
3.40
Eastern Shore MD - VA
0.06
0.0642
61.6
3.10
0.01
0.0100
71.42
3.10
Eastern Shore MD - DE
2.88
2.88
61.6
3.00
0.35
0.35
71.42
1.00
Eastern Shore MD - PA
0.24
0.27
54.5
3.00
0.01
0.03
49.93
3.00
Potomac - D.C.
2.80
2.80
61.6
2.90
0.39
0.39
71.42
2000 Progress
Potomac - MD
11.99
11.99
61.6
3.20
1.14
1.14
71.42
1.90
Potomac - VA
12.84
12.84
61.6
3.20
1.40
1.40
71.42
3.00
Potomac - PA
3.73
4.02
57.5
3.00
0.21
0.33
52.80
3.00
Potomac - WV
4.18
4.71
53.0
3.00
0.24
0.36
49.29
3.00
TOTAL BASIN LOADING
49.77
50.62
_>
—
4.65
4.90
—
Rappahannock - VA
5.24
5.24
58.6
2.70
0.48
0.62
57.79
3.40
York - VA
5.18
5.70
52.5
TS/2.4
0.6791
0.48
78.47
TS/3.5
James - VA
26.79
27.90
56.5
TS/2.0
3.9228
3.71
70.25
TS/3.0
James - WV
0.03
0.03
31.1
3.00
0.0055
0.01
n/a
n/a
TOTAL BASIN LOADING
37.23
38.87
-
-
5.08
4.82
-
-
BASINWIDE TOTAL
175.00
187.15
_
_
12.76
13.78
—
Note: Bolded numbers in this table resulted from application of decision rules 3 through 5 to Table IV-4.
-------
Table IV-6 The final Chesapeake 2000 nitrogen and phosphorus cap load allocations by major tributary basin and jurisdiction.
NITROGEN PHOSPGRUS
(Million pounds per year) (Million pounds per year)
WQSC
PSC
Cap
Clear Sides
Delivered
WQSC
PSC
Cap
Jurisdiction-Basin Recommendation
Reduction
Load
To 2010
Load
Recommendation
Reduction
Load
Eastern Shore VA - VA
1.16
0.00
1.16
0.05
1.11
0.08
0.00
0.08
Susquehanna - MD
0.85
0.02
0.83
0.03
0.80
0.03
0.00
0.03
Susquehanna - PA
69.08
1.50
67.58
3.91
63.67
2.20
0.30
1.90
Susquehanna - NY
12.58
0.00
12.58
0.80
11.78
0.59
0.00
0.59
Western Shore MD - MD
11.47
0.20
11.27
0.19
11.08
0.94
0.10
0.84
Western Shore MD - PA
0.02
0.00
0.02
0.00
0.02
0.00
0.00
0.00
Patuxent - MD
2.50
0.04
2.46
0.09
2.38
0.23
0.02
0.21
TOTAL BASIN LOADING
97.7
1.8
95.9
5.1
90.8
4.1
0.4
3.6
Eastern Shore MD - MD
11.05
0.16
10.89
0.30
10.58
0.88
0.08
0.81
Eastern Shore MD - VA
0.06
0.00
0.06
0.00
0.06
0.01
0.00
0.01
Eastern Shore MD - DE
2.88
0.00
2.88
0.11
2.77
0.35
0.05
0.30
Eastern Shore MD - PA
0.27
0.00
0.27
0.01
0.27
0.03
0.00
0.03
Potomac - D.C.
2.80
0.40
2.40
0.02
2.38
0.39
0.05
0.34
Potomac - MD
11.99
0.18
11.81
0.38
11.42
1.14
0.10
1.04
Potomac - VA
12.84
0.00
12.84
0.52
12.32
1.40
0.00
1.40
Potomac - PA
4.02
0.00
4.02
0.19
3.83
0.33
0.00
0.33
Potomac - WV
4.71
0.00
4.71
0.35
4.37
0.36
0.00
0.36
TOTAL BASIN LOADING
50.6
0.7
49.9
1.9
48.0
4.9
0.3
4.6
Rappahannock - VA
5.24
0.00
5.24
0.19
5.05
0.62
0.00
0.62
York - VA
5.70
0.00
5.70
0.19
5.51
0.48
0.00
0.48
James - VA
27.90
1.50
26.40
0.69
25.71
3.71
0.30
3.41
James - WV
0.03
0.00
0.03
0.00
0.03
0.01
0.00
0.01
TOTAL BASIN LOADING
38.9
1.5
37.4
1.1
36.3
4.8
0.3
4.5
BASIN WIDE TOTAL
187
4
183
8
175
13.8
1.0
12.8
Target Load
175
175
175
12.8
12.8
Orphaned Load
12
8
0
1.0
0.0
WQSC - Water Quality Steering Committee; PSG - Principals' Staff Committee.
-------
Table IV-7. The final Chesapeake 2000 nitrogen and phosphorus cap load allocations by jurisdiction.
NITROGEN PHOSPORUS
(Million pounds per year) (Million pounds per year)
J urisdiction- Basin
WQSC
Recommendation
PSC
Reduction
Cap
Load
Clear Skies
To 2010
Delivered
Load
WQSC
Recommendation
PSC
Reduction
Cap
Load
Pennsylvania
73.40
1.50
71.90
4.10
67.79
2.56
0.30
2.26
Maryland
37.85
0.60
37.25
0.99
36.26
3.22
0.30
2.92
Virginia
52.90
1.50
51.40
1.64
49.76
6.30
0.30
6.00
District of Columbia
2.80
0.40
2.40
0.02
2.38
0.39
0.05
0.34
New York
12.58
0.00
12.58
0.80
11.78
0.59
0.00
0.59
Delaware
2.88
0.00
2.88
0.11
2.77
0.35
0.05
0.30
West Virginia
4.75
0.00
4.75
0.35
4.40
0.37
0.00
0.37
TOTAL
187
4
183
8
175
13.8
1.0
12.8
WQSCS—Water Quality Steering Committee; PSC—Principals' Staff Committee,
-------
103
Target concentrations of chlorophyll a by season and salinity regime were drawn
from the technical information published in the Regional Criteria Guidance (U.S.
EPA 2003a) (see Appendix C). Comparing these target chlorophyll a concentrations
with the cap load allocations 'confirmation' scenario simulated chlorophyll a
concentration yielded the following findings:
• Chlorophyll a levels relative to the target concentrations were very similar
between the 'confirmation' scenario and Option 1, indicating additional nutrient
reductions down to the Option 1 level would not yield large chlorophyll a concen-
tration reductions at the Chesapeake Bay Program-wide segment scale.
• Only in very localized tidal habitats were the target chlorophyll a concentrations
not achieved under the 'confirmation' scenario.
ADDITIONAL ALLOCATION CONSIDERATIONS
Recognizing that nutrient effects could be lessened either by reducing nitrogen or
phosphorus, or by other management controls that would alleviate low dissolved
oxygen concentrations in the Bay's tidal waters, the Chesapeake Bay Program part-
ners agreed to keep the nutrient allocations flexible (Secretary Tayloe Murphy 2003).
Any jurisdiction can exchange loading for a nutrient from one major tributary basin
to another as long as the basins were in the same grouping of relative effectiveness
(see Figure IV-6).
A jurisdiction may exchange or credit nitrogen reductions for phosphorus reduc-
tions. It is important to note that both nitrogen and phosphorus have an adverse, but
exchangeable, effect on the water quality of the Chesapeake Bay, so the nutrient allo-
cations could be viewed as 'nitrogen equivalents'. 'Nitrogen equivalent' means any
management action (e.g., phosphorus control, oyster or underwater bay grass
restoration, etc.) that has the similar water quality effect of reducing a known quan-
tity of nitrogen loading.
ESTABLISHING SEDIMENT CAP LOAD ALLOCATIONS
SAV RESTORATION AS THE GOAL
The cap load allocation process for sediments originally focused on achieving the
water clarity water quality criteria. However, good reasons existed for focusing
management plans and even the establishment of the sediment cap load allocations
on the recovery of the underwater bay grass or SAV beds. This was a positive shift
in emphasis, for the following reasons:
• It directly measures the health of the underwater bay grass living resource;
• Annual aerial surveys enable the partners to record and measure the SAV beds,
whereas, sparse water clarity data exists for Bay tidal- and shallow-water habitats;
• The Chesapeake Bay water quality model cannot at present reliably simulate
reductions in sediment loads or water clarity responses in Bay tidal- and shallow-
water habitats at the desired geographic scale with sufficient accuracy; and
• It accommodates the transient nature of SAV growth, which the historical record
clearly documents, whereas water clarity criteria necessitated rigid boundaries.
chapter iv • Setting Nutrient and Sediment Allocations
-------
104
While acres of SAV have become the dominant measure to direct management
controls of sediment within the tributary strategies, water clarity still plays an impor-
tant role. The EPA has published water clarity criteria for the protection of the SAV
in the Regional Criteria Guidance (U.S. EPA 2003a). In the Technical Support
Document the EPA also identified SAV restoration goals for the Chesapeake Bay and
its tidal tributaries (U.S. EPA 2003b). Currently, sediments are discharged into the
Bay's tidal waters in quantities that cause exceedance of the water clarity criteria and
prevent achievement of the SAV restoration goals. In response, sediment cap load
allocations have been developed along with the SAV restoration goals for each trib-
utary basin. Sediment loads that affect water clarity and SAV growth in the Bay and
its tidal tributaries come from two major areas:
1. Land-based loads originate from land erosion, are discharged in runoff and
include stream bank erosion; and
2. Near-shore erosion is attributable to tidal shoreline erosion and includes resus-
pension of sediment material from the shoreline.
Model results have indicated that sediments tend to affect areas in the Chesapeake
Bay and its tidal tributaries close to where they are introduced (see Chapter III for
details). For this reason, the Bay and its tidal tributaries were divided into discrete
sections representing areas affected by the local sediment loads that had little to no
impact on other areas (see Figure 111-20). These areas roughly correspond with the
nine major tributary basins of the Bay.
LAND-BASED (UPLAND) SEDIMENT ALLOCATION
As the previous section points out, the Water Quality Model is not capable of
providing a reliable understanding of the sediment loads' effect on water clarity.
Therefore, it was necessary to derive and agree on reasonable sediment cap load
allocations without a similar level of quantitative support from the Water Quality
Model as was used in establishing the nutrient cap load allocations.
Since no reliable modeling tool existed, neither water clarity criteria attainment nor
SAV-based sediment cap load allocations could be developed. Sediment cap load
allocations, therefore, were based on sediment loads (reductions) that would likely
result from implementing the land-based phosphorus controls necessary to achieve
the dissolved oxygen-based phosphorus cap load allocations.
It is well-known that for nonpoint sources, most BMPs that reduce phosphorus do so
by reducing the sediment that carries the phosphorus to the stream. Thus, phosphorus
and sediment controls for nonpoint sources are closely related. Figure IV-7 illus-
trates the strong correlation between phosphorus and sediment load reductions
from BMPs.
The methodology used to determine the 'phosphorus equivalent' sediment loads was
relatively straightforward. Since increasing control scenarios were already defined
(e.g., Tier 1 through E3), the first step involved identifying the tier level represented
by the phosphorus cap load allocations already established to achieve the dissolved
oxygen and chlorophyll a criteria for each major tributary basin. If the phosphorus
cap load allocation was between two loading levels (i.e., two tiers), the exact tier was
chapter iv • Setting Nutrient and Sediment Allocations
-------
105
Figure IV-7. Chesapeake Bay Watershed Model simulated relationship between sediment and
nonpoint source phosphorus loads.
interpolated. Once the tier for the phosphorus allocation was identified, the sediment
cap load allocation was determined by calculating the corresponding sediment load
for that tier. It is important to recognize the tentative nature of these allocations,
which are driven by the anticipated sediment loads after the phosphorus controls are
in place. The tributary teams were, therefore, given latitude in identifying alternate
land-based sediment allocations if it could be shown to be more appropriate for
achieving the SAV restoration goals for that particular tributary basin.
After the 'phosphorus equivalent' sediment loads were established, these land-based
sediment cap load allocations were modified for several major tributary basins (e.g.,
Potomac tidal-fresh and Susquehanna) because the Chesapeake Bay Water Quality
Model and existing data suggested the previously determined land-based sediment
allocations were greater than necessary to achieve the SAV restoration goal for that
particular major tributary basin. For these basins, the sediment cap load allocations
were relaxed to levels estimated to be appropriate for that basin. Table IV-8 provides
the resulting allocations.
ESTABLISHING THE NEAR-SHORE SEDIMENT ALLOCATION
Due to an insufficient technical understanding of near-shore sediment fate and
transport, no specific recommendation for near-shore sediment load reductions was
recommended when the land-based sediment cap load allocations were established.
Tributary teams should acquire local knowledge of near-shore erosion problem areas
and make specific recommendations on reductions in those sediment loadings.
chapter iv • Setting Nutrient and Sediment Allocations
-------
106
SAV-BASED SEDIMENT CAP LOAD ALLOCATIONS
Scientific understanding of the quantitative relationship between sediment reduc-
tions and SAV recovery is less broad than the current understanding of the
relationship between nutrient loads and dissolved oxygen on Bay tidal waters. Thus,
the tributary teams should note the following when establishing their sediment/SAV
related components of the tributary strategies:
1. The local SAV goal should serve as the primary goal in establishing sediment
control measures by the tributary teams. Attaining more SAV acreage is the most
direct measure of the status of this living resource and can be measured directly
Therefore, if all management actions prescribed in the tributary strategy are taken,
yet the SAV restoration goal is not attained, further measures should be employed.
Conversely, if the SAV restoration goal is achieved, yet all sediment reduction
measures have not been implemented, then further management actions may not
be necessary.
2. Based on a comprehensive SAV recovery plan by the tributary teams, revisions
to the upland sediment cap load allocations may be recommended to the Prin-
cipals ' Staff Committee, where appropriate. As noted, the 'upland' allocations
are tentative. That is, the sediment cap load allocations represent the sediment
load likely to result from implementing the phosphorus cap load allocations that
have been established by the Principals' Staff Committee and headwater state
partners. Obviously, these upland sediment loads have only a qualitative relation-
ship to SAV recovery. Thus, these upland sediment allocations should be used as
a basis for sediment controls unless the tributary teams, based on the tributary
strategy development process, conclude that the recommended upland sediment
controls are not appropriate. In such cases, the tributary team shall identify the
upland sediment cap load allocations that are appropriate and also identify the
management actions necessary to achieve those allocations.
3. The tributary teams should explore a comprehensive suite of management actions
to achieve the local SAV restoration goal. It is apparent that upland sediment
controls alone will be insufficient to achieve the local SAV restoration goals in some
areas. The tributary teams should assess varied and innovative methods to achieve
SAV regrowth in such areas. Methods could include, but not be limited to, stream-
bank stabilization, SAV planting and near-shore erosion control, where appropriate.
SUMMARY OF NUTRIENT AND SEDIMENT
CAP LOAD ALLOCATIONS
Through extensive modeling and an intricate interplay of technical and policy deci-
sions, the Chesapeake Bay Program partners agreed to load allocations for nitrogen,
phosphorus and sediment for each of the 20 areas of the Chesapeake Bay watershed
delineated by major basin and jurisdiction. These nutrient and sediment cap load allo-
cations are based on achieving the Chesapeake Bay water quality criteria for dissolved
oxygen, chlorophyll a and water clarity, and the baywide and local SAV acreage
restoration goals. Tables IV-9 and IV-10 provide a full tabulation of the nutrient and
sediment cap load allocations by major tributary basin and jurisdiction, respectively.
chapter iv • Setting Nutrient and Sediment Allocations
-------
107
Table IV-8. Land-based 'phosphorus equivalent' sediment cap load allocation by
major tributary basin, by jurisdiction.
Land-Based Sediment
Allocation
Basin
Jurisdiction
(Million tons per year)*
SUSQUEHANNA
PA
0.793
NY
0.131
MD
0.037
Basin Total
0.962
EASTERN SHORE - MD
MD
0.116
DE
0.042
PA
0.004
VA
0.001
Basin Total
0.163
WESTERN SHORE
MD
0.100
PA
0.001
Basin Total
0.100
PATUXENT
MD
0.095
Basin Total
0.095
POTOMAC
VA
0.617
MD
0.364
WV
0.311
PA
0.197
DC
0.006
Basin Total
1.494
RAPPAHANNOCK
VA
0.288
Basin Total
0.288
YORK
VA
0.103
Basin Total
0.103
JAMES
VA
0.925
WV
0.010
Basin Total
0.935
EASTERN SHORE - VA
VA
0.008
Basin Total
0.008
SUBTOTAL
4.15
BASINWIDE TOTAL
4.15
*The tributary teams will assess these upland sediment allocations and, if necessary, revise them as
part of a comprehensive strategy of management actions necessary to achieve the local SAV
restoration goals.
chapter iv • Setting Nutrient and Sediment Allocations
-------
108
Table IV-9. Chesapeake Bay watershed nitrogen, phosphorus and sediment cap load allocations by
major tributary basin.
Nitrogen
Phosphorus
Upland Sediment
Cap Load Allocation
Cap Load Allocation
Cap Load Allocation
Basin/Jurisdiction (million pounds/year)
(million pounds/year)
(million tons/year)
SUSQUEHANNA
PA
67.58
1.90
0.793
NY
12.58
0.59
0.131
MD
0.83
0.03
0.037
SUSQUEHANNA Total
80.99
2.52
0.962
EASTERN SHORE - MD
MD
10.89
0.81
0.116
DE
2.88
0.30
0.042
PA
0.27
0.03
0.004
VA
0.06
0.01
0.001
EASTERN SHORE - MD Total
14.10
1.14
0.163
WESTERN SHORE
MD
11.27
0.84
0.100
PA
0.02
0.00
0.001
WESTERN SHORE Total
11.29
0.84
0.100
PATUXENT
MD
2.46
0.21
0.095
PATUXENT Total
2.46
0.21
0.095
POTOMAC
VA
12.84
1.40
0.617
MD
11.81
1.04
0.364
WV
4.71
0.36
0.311
PA
4.02
0.33
0.197
DC
2.40
0.34
0.006
POTOMAC Total
35.78
3.48
1.494
RAPPAHANNOCK
VA
5.24
0.62
0.288
RAPPAHANNOCK Total
5.24
0.62
0.288
YORK
VA
5.70
0.48
0.103
YORK Total
5.70
0.48
0.103
JAMES
VA
26.40
3.41
0.925
WV
0.03
0.01
0.010
JAMES Total
26.43
3.42
0.935
EASTERN SHORE - VA
VA
1.16
0.08
0.008
EASTERN SHORE - VA Total
1.16
0.08
0.008
SUBTOTAL
183
12.8
4.15
CLEAR SKIES REDUCTION -8
BASINWIDE TOTAL
175
12.8
4.15
chapter iv • Setting Nutrient and Sediment Allocations
-------
109
Table IV-10. Chesapeake Bay watershed nitrogen, phosphorus and sediment cap load allocations by
jurisdiction.
Nitrogen
Phosphorus
Upland Sediment
Cap Load Allocation
Cap Load Allocation
Cap Load Allocation
Jurisdiction/Basin
(million pounds/year)
(million pounds/year)
(million tons/year)
PENNSYLVANIA
Susquehanna
67.58
1.90
0.793
Potomac
4.02
0.33
0.197
Western Shore
0.02
0.00
0.001
Eastern Shore - MD
0.27
0.03
0.004
PA Total
71.90
2.26
0.995
MARYLAND
Susquehanna
0.83
0.03
0.037
Patuxent
2.46
0.21
0.095
Potomac
11.81
1.04
0.364
Western Shore
11.27
0.84
0.100
Eastern Shore - MD
10.89
0.81
0.116
MD Total
37.25
2.92
0.712
VIRGINIA
Potomac
12.84
1.40
0.617
Rappahannock
5.24
0.62
0.288
York
5.70
0.48
0.103
James
26.40
3.41
0.925
Eastern Shore - MD
0.06
0.01
0.001
Eastern Shore - VA
1.16
0.08
0.008
VA Total
51.40
6.00
1.941
DISTRICT OF COLUMBIA
Potomac
2.40
0.34
0.006
DC Total
2.40
0.34
0.006
NEW YORK
Susquehanna
12.58
0.59
0.131
NY Total
12.58
0.59
0.131
DELAWARE
Eastern Shore - MD
2.88
0.30
0.042
DE Total
2.88
0.30
0.042
WEST VIRGINIA
Potomac
4.71
0.36
0.311
James
0.03
0.01
0.010
WV Total
4.75
0.37
0.320
SUBTOTAL
183
12.8
4.15
CLEAR SKIES REDUCTION -8
BASINWIDE TOTAL
175
12.8
4.15
chapter iv • Setting Nutrient and Sediment Allocations
-------
110
Nutrient and sediment cap load allocations were established based on the EPA's
recently published Regional Criteria Guidance (U.S. EPA 2003a), which is specific
to the Chesapeake Bay. Therefore, the states will be modifying their water quality
standards based upon the published Bay criteria as well as the refined tidal-water
designated uses. If the final adopted state water quality standards do not rely on the
criteria and designated uses employed to establish these cap load allocations, then
the allocations will need to be amended accordingly.
It will be difficult to achieve these cap load allocations. States will develop tributary
strategies for each of the 20 areas by April 30, 2004. Some states may choose further
to subdivide their tributaries into smaller watershed for the development of tributary
strategies. These tributary strategies will identify specific actions needed to achieve
the cap load nutrient and sediment cap load allocations.
LITERATURE CITED
Secretary Tayloe Murphy, 2003. "Summary of Decisions Regarding Nutrient and Sediment
Load Allocations and New Submerged Aquatic Vegetation (SAV) Restoration Goals."
April 25, 2003, memorandum to the Principals' Staff Committee members and representa-
tives of the Chesapeake Bay headwater states. Virginia Office of the Governor, Natural
Resources Secretariate, Richmond, Virginia.
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.
EPA 903-R-03-002. Chesapeake Bay Program Office, Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003b. Technical Support Document for Identifica-
tion of Chesapeake Bay Designated Uses and Attainability. EPA 903-R-03-004. Chesapeake
Bay Program Office, Annapolis, Maryland.
chapter iv • Setting Nutrient and Sediment Allocations
-------
A1
Summary of Decisions
Regarding Nutrient and Sediment Load
Allocations and New Submerged Aquatic
Vegetation (SAV) Restoration Goals
Memorandum from W. Tayloe Murphy, Jr.f
Chair, Chesapeake Bay Program Principals' Staff Committee,
to the Principals' Staff Committee Members and
Representatives of Chesapeake Bay "Headwater" States
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A2
COMMONWEALTH of VIRQINIA
Office of the Governor
P.O. Box 1475 (804) 786-0044
Richmond, Virginia 23218 Fax: (804) 371-8333
TTY: (804) 786-7765
W. Tayloe Murphy, Jr.
Secretary of Natural Resources
To: Principal Staff Committee Members and Representatives of Chesapeake Bay
"Headwater" States
From: W. Tayloe Murphy, Jr., Chair
Chesapeake Bay Program Principals' Staff Committee
Date: April 28, 2003
Subject: Summary of Decisions Regarding Nutrient and Sediment Load Allocations and
New Submersed Aauatic Vegetation (SAV1 Restoration Goals
For the past twenty years, the Chesapeake Bay partners have been committed to
achieving and maintaining water quality conditions necessary to support living resources
throughout the Chesapeake Bay ecosystem. In the past month, Chesapeake Bay Program
partners (Maryland, Virginia, Pennsylvania, the District of Columbia, the Environmental
Protection Agency and the Chesapeake Bay Commission) have expanded our efforts by
working with the headwater states of Delaware, West Virginia and New York to adopt
new cap load allocations for nitrogen, phosphorus and sediment.
Using the best scientific information available, Bay Program partners have agreed to
allocations that are intended to meet the needs of the plants and animals that call the
Chesapeake home. The allocations will serve as a basis for each state's tributary
strategies that, when completed by April 2004, will describe local implementation actions
necessary to meet the Chesapeake 2000 nutrient and sediment loading goals by 2010.
This memorandum summarizes the important, comprehensive agreements made by Bay
watershed partners with regard to cap load allocations for nitrogen, phosphorus and
sediments, as well as new baywide and local SAV restoration goals.
Nutrient Allocations
Excessive nutrients in the Chesapeake Bay and its tidal tributaries promote undesirable
algal growth, and thereby, prohibit light from reaching underwater bay grasses
(submerged aquatic vegetation or SAV) and depress the dissolved oxygen levels of the
deener waters of the Bav.
¦ i *
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A3
As a result, Bay watershed states and the District of Columbia, with the concurrence of
FPA aorpprl tn ran annual nitrndpn loads delivered to the Bav's tidal waters at 175
— "C? ~ " "ST - - „
million pounds and annual phosphorus loads at 12.8 million pounds. It is estimated that
these allocations will require a reduction, from 2000 levels, of nitrogen pollution by 110
1U,
pviuiuo U11U jJllV/apliVJlUO JJWll L411WJ1 uj \J.~f 1111U1VK ^/V .
The partners agreed upon these load reductions based upon Bay Water Quality Model
projections of attainment of proposed water quality criteria for dissolved oxygen. The
model projects these load reductions will eliminate the persistent summer anoxic
conditions in the deep bottom waters of the Bay. Furthermore, these reductions are
projected to eliminate excessive algae conditions (measured as chlorophyll a) throughout
the Bay and its tidal tributaries.
The jurisdictions agreed to distribute the baywide cap load for nitrogen and phosphorus
by major tributary basin (Table 1) and jurisdiction (Table 2). This distribution of
responsibility for load reductions was based on three basic principles:
1. Tributary basins with the highest impact on Bay water quality would have the
highest reductions of nutrients.
2. States without tidal waters - Pennsylvania, New York and West Virginia -
Uq provided some relief from Principle 1 since they do tint benefit as
directly from improved water quality in the Bay and its tidal tributaries.
niifmnnt V»q r
-------
A4
The allocations for nitrogen and phosphorus were adopted with the concept of "nitrogen
equivalents" and a commitment to explore how actions beyond traditional best
management practices might help meet Bay restoration goals. A nitrogen equivalent is an
action that results in the same water quality benefit as removing nitrogen. The
Chesapeake Bay Program will evaluate how to account for tidal water quality benefits
from continued and expanded living resource restoration, such as oysters and menhaden,
to offset the reductions of watershed based nutrient and sediment loads. Seasonal
frvr Kinlnrnfcil nnfrtAtif tpmrtval 1 mtllPtYlPTltfltlf\t1 TllltTlftnt rfiHllCtlOTl VlftflftfltS
ilUVVWMUVUt; iVi • «-¦- ""f y
from shoreline erosion reductions, implementation of enhanced nutrient removal at large
wastewater treatment plants, and trade-offs between nitrogen and phosphorus will also be
evaluated.
BaywideSAVRestoration Goal
To set new SAV restoration goals, scientists and resource managers from state and
federal agencies agreed to use data from the single best year of observed SAV growth to
estimate the historical longterm bay grass coverage in Chesapeake Bay. Data were
collected from aerial photographs taken between 1938 and 2000. From 3-4 years in the
1938 -1964 period, and more than 20 years of data since 1978, new baywide SAV
restoration goal acreage was determined by totaling the single best year acreage from
each Chesapeake Bay Program segment.
The states have adopted 185,000 acres as the new baywide SAV restoration goal to be
achieved by 2010 - consistent with the goals of Chesapeake 2000. The achievement of
the baywide goal, as well as the local tributary basin and segment specific restoration
goals summarized in Table 3, will be based on the single best year SAV acreage within
the most recent three-year record of survey results. This new acreage goal has been
aJ4a4 fVi#* i-itwfnr* ar\A A"PS* A\/
O.V1UVJ IV 1111/ IVVVllUj ttuvpww dviwvvgj VW WWVW4V* —
in the Chesapeake Bay; and Maryland and Virginia have agreed to develop an
implementation plan for this strategy by April 2004.
Sediment Allocations
Sediments suspended in the water column reduce the amount of light available to support
healthy and extensive SAV communities. With regard to the sediment allocations, the
partners agreed that a primary reason for reducing sediment loads to the Bay is to provide
suitable habitat for restoring SAV. The jurisdictions also agreed that nutrient load
reductions are critical for SAV restoration as well as improving oxygen levels. As a
result, the states linked the establishment of sediment cap load allocations to the proposed
water clarity criteria and to the new SAV restoration goals.
Unlike nutrients - where loads from virtually all parts of the Bay watershed affect Bay
mainstem water quality - impacts from sediments are predominantly seen at the local
level. For this reason, local SAV acreage goals have been established and sediment
olln^-jtinnc arp iaroptpA tnwarHs achieving those restoration eoals.
UilVVWklUllkl VM- V w .. — Q c
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A5
The partners recognize that the current understanding of sediment sources and their
impact on the Bay is not yet complete. We have only a basic understanding of land-
based sediments that are carried into local waterways through stream bank erosion and
runoff, but a more limited knowledge about near shore sediments that enter the Bay and
its tidal rivers directly through shoreline erosion or shallowwatcr rcsuspension.
Consequently, sediment allocations are currently focused on land-based sediment cap
loads by major tributary basin (Table 1) and jurisdiction (Table 2).
Most land-based best management practices which reduce nonpoint sources of
phosphorus will also reduce sediment runoff. Therefore, the jurisdictions agreed to land-
based sediment allocations that represent the sediment loading likely to result from
implementation management actions required to achieve the phosphorus cap load
allocations.
The sediment allocation was set equal to the tier level for phosphorus allocation for each
jurisdictionbasin. This is referred to as the 'phosphorus equivalent' land-based sediment
reduction. If the 'phosphorus equivalent' land-based sediment reductions were found to
be more than necessary to achieve the local SAV acreage goals, then the land-based
sediment allocations were raised to that necessary to achieve the SAV goal. The tidal
fresh Susquehanna Flats and tidal fresh Potomac River are two examples where this
modified approach was applied. If, in the development of their tributary strategies,
tributary teams conclude that the land-hased sediment allocations need revisions, the
tributary teams may identify an alternate land-based allocation working with all the
jurisdictions within the effected basin. For example, a jurisdiction may select different
nonpoint source management actions than those prescribed in the tier approach to reach
the phosphorus goal; the jurisdiction may adjust the sediment goal accordingly so long as
SAV restoration and protection is not compromised.
It is likely that reduction in nutrients and land-based sediments alone will not be
sufficient to achieve the local SAV goals for many areas of the Bay. In these areas,
tributary teams will be asked to further assess varied and innovative methods to achieve
SAV re-growth. Such methods may include, but are not limited to SAV planting,
offshore breakwaters, shore erosion controls, beach nourishment, establishment of oyster
bars, and other actions as appropriate.
Support to State Tributary Strategies
The partners have agreed to complete their nutrient and sediment reduction strategies by
April 2004. To assist in the development of tributary strategies, the Chesapeake Bay
Program Office will provide an array of technical analyses, water quality and watershed
modeling, cost-effectiveness and economic assessment support to the tributary strategy
teams through the states.
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A6
The jurisdictions agreed that it is critical to work together to assure the aggregate of
control actions recommended within the nutrient and sediment strategies yield the load
reductions and the Bay and tidal tributary water quality improvements desired.
Reevaluation of the Allocations
The nutrient and sediment cap load allocations adopted by the jurisdictions are the best
scientific estimates of what will be needed to attain proposed water quality criteria and
tidal watex* designated uses described m guidsncv publishsd x?p a Over the next two
years, Maryland, Virginia, Delaware and the District of Columbia will promulgate new
water quality standards based on the guidance published by EPA. Although the public
process for adopting water quality standards vanes among the states, each state's process
will provide opportunities for considering and acquiring new information at the local
level. States may choose to explore a number of issues during their adoption process,
such as the economic impact of water quality standards and specific designated use
boundaries.
While the allocations adopted at this time will provide the basis for tributary strategies,
these allocations may need to be adjusted to reflect final state water quality standards.
Furthermore, planned Bay model refinements - directed towards estimating water quality
benefits from filter feeding resources (e.g., oysters and menhaden) and better
understanding the sources and effects of sediments - will increase our understanding of
the relationship between nutrient and sediment reductions and living resource responses
in the Bay. For these reasons, the states agreed to a reevaluation of these allocations no
later than 2007.
As partners, the jurisdictions committed to correcting the nutrient and sediment related
problems in the Bay and its tidal tributaries sufficiently to remove them from the list of
1 tv* nai rc±r\ tirflfofp WT A /if A Uli/vimli ~
iMywiivu wimviu hMXVAWA. U1V 1V4U1 »T UIVI L 1VV. U1V OldllsO dgl VVU IV/ UU lllt/il
utmost to remove the Bay from the federal list of impaired waters by 2010, they
recognize that it will be difficult to meet projected water quality standards in all parts of
the Bay by thai time. A key reason for this difficulty is that once nutrient reduction
practices are installed, it may be years or even decades before the Bay benefits from these
reductions. The jurisdictions intend to have programs in place and functioning by 2010
such that when fully implemented all parts of the Bay are expected to become eligible for
delisting.
I would like to express my appreciation to all the partners in this effort for their hard
work and commitment to restoration of the Chesapeake Bay. We have agreed to nutrient
and sediment reductions which will result in profound improvements in the water quality,
habitat and living resources of the Bay.
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A7
Table A-1. Chesapeake Bay watershed nitrogen, phosphorus and sediment cap load allocations by
major basin.
Nitrogen
Phosphorus
Upland Sediment
Cap Load Allocation
Cap Load Allocation
Cap Load Allocation
Basin/Jurisdiction (million pounds/year)
(million pounds/year)
(million tons/year)
SUSQUEHANNA
PA
67.58
1.90
0.793
NY
12.58
0.59
0.131
MD
0.83
0.03
0.037
SUSQUEHANNA Total
80.99
2.52
0.962
EASTERN SHORE - MD
MD
10.89
0.81
0.116
DE
2.88
0.30
0.042
PA
0.27
0.03
0.004
VA
0.06
0.01
0.001
EASTERN SHORE - MD Total
14.10
1.14
0.163
WESTERN SHORE
MD
11.27
0.84
0.100
PA
0.02
0.00
0.001
WESTERN SHORE Total
11.29
0.84
0.100
PATUXENT
MD
2.46
0.21
0.095
PATUXENT Total
2.46
0.21
0.095
POTOMAC
VA
12.84
1.40
0.617
MD
11.81
1.04
0.364
WV
4.71
0.36
0.311
PA
4.02
0.33
0.197
DC
2.40
0.34
0.006
POTOMAC Total
35.78
3.48
1.494
RAPPAHANNOCK
VA
5.24
0.62
0.288
RAPPAHANNOCK Total
5.24
0.62
0.288
YORK
VA
5.70
0.48
0.103
YORK Total
5.70
0.48
0.103
JAMES
VA
26.40
3.41
0.925
WV
0.03
0.01
0.010
JAMES Total
26.43
3.42
0.935
EASTERN SHORE - VA
VA
1.16
0.08
0.008
EASTERN SHORE - VA Total
1.16
0.08
0.008
SUBTOTAL
183
12.8
4.15
CLEAR SKIES REDUCTION -8
BASINWIDE TOTAL
175
12.8
4.15
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A8
Table A-2. Chesapeake Bay watershed nitrogen, phosphorus and sediment cap load allocations by
jurisdiction.
Nitrogen
Phosphorus
Upland Sediment
Cap Load Allocation
Cap Load Allocation
Cap Load Allocation
Jurisdiction/Basin
(million pounds/year)
(million pounds/year)
(million tons/year)
PENNSYLVANIA
Susquehanna
67.58
1.90
0.793
Potomac
4.02
0.33
0.197
Western Shore
0.02
0.00
0.001
Eastern Shore - MD
0.27
0.03
0.004
PA Total
71.90
2.26
0.995
MARYLAND
Susquehanna
0.83
0.03
0.037
Patuxent
2.46
0.21
0.095
Potomac
11.81
1.04
0.364
Western Shore
11.27
0.84
0.100
Eastern Shore - MD
10.89
0.81
0.116
MD Total
37.25
2.92
0.712
VIRGINIA
Potomac
12.84
1.40
0.617
Rappahannock
5.24
0.62
0.288
York
5.70
0.48
0.103
James
26.40
3.41
0.925
Eastern Shore - MD
0.06
0.01
0.001
Eastern Shore - VA
1.16
0.08
0.008
VA Total
51.40
6.00
1.941
DISTRICT OF COLUMBIA
Potomac
2.40
0.34
0.006
DC Total
2.40
0.34
0.006
NEW YORK
Susquehanna
12.58
0.59
0.131
NY Total
12.58
0.59
0.131
DELAWARE
Eastern Shore - MD
2.88
0.30
0.042
DE Total
2.88
0.30
0.042
WEST VIRGINIA
Potomac
4.71
0.36
0.311
James
0.03
0.01
0.010
WV Total
4.75
0.37
0.320
SUBTOTAL
183
12.8
4.15
CLEAR SKIES REDUCTION -8
BASINWIDE TOTAL
175
12.8
4.15
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A9
Table A-3. Chesapeake Bay submerged aquatic (SAV) restoration
goal acreage by Chesapeake Bay Program (CBP) segment based on
the single best year of record from 1930 to present.
Segment Name
Segment
Acres
Northern Chesapeake Bay
CB1TF
12,908
Upper Chesapeake Bay
CB20H
302
Upper Central Chesapeake Bay
CB3MH
943
Middle Central Chesapeake Bay
CB4MH
2,511
Lower Central Chesapeake Bay
CB5MH
14,961
Western Lower Chesapeake Bay
CB6PH
980
Eastern Lower Chesapeake Bay
CB7PH
14,620
Mouth of the Chesapeake Bay
CB8PH
6
Bush River
BSHOH
158
Gunpowder River
GUNOH
2,254
Middle River
MIDOH
838
Back River
BACOH
0
Patapsco River
PATMH
298
Magothy River
MAGMH
545
Severn River
SEVMH
329
South River
SOUMH
459
Rhode River
RHDMH
48
West River
WSTMH
214
Upper Patuxent River
PAXTF
5
Western Branch (Patuxent River)
WBRTF
0
Middle Patuxent River
PAXOH
68
Lower Patuxent River
PAXMH
1,325
Upper Potomac River
POTTF
4,368
Anacostia River
ANATF
6
Piscataway Creek
PISTF
783
Mattawoman Creek
MATTF
276
Middle Potomac River
POTOH
3,721
Lower Potomac River
POTMH
10,173
Upper Rappahannock River
RPPTF
20
Middle Rappahannock River
RPPOH
0
Lower Rappahannock River
RPPMH
5,380
Corrotoman River
CRRMH
516
Piankatank River
PIAMH
3,256
Upper Mattaponi River
MPNTF
75
Lower Mattaponi River
MPNOH
0
Upper Pamunkey River
PMKTF
155
Lower Pamunkey River
PMKOH
0
Middle York River
YRKMH
176
Lower York River
YRKPH
2,272
Mobjack Bay
MOBPH
15,096
continued
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A10
Table A-3. Chesapeake Bay submerged aquatic (SAV) restoration goal
acreage by Chesapeake Bay Program (CBP) segment based on the single
best year of record from 1930 to present, (cont.).
Segment Name
Segment
Acres
Upper James River
JMSTF
1,600
Appomattox River
APPTF
319
Middle James River
JMSOH
7
Chickahominy River
CHKOH
348
Lower James River
JMSMH
531
Mouth of the James River
JMSPH
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
69
Northeast River
NORTF
88
C&D Canal
C&DOH
0
Bohemia River
BOHOH
97
Elk River
ELKOH
1,648
Sassafras River
SASOH
764
Upper Chester River
CHSTF
0
Middle Chester River
CHSOH
63
Lower Chester River
CHSMH
2,724
Eastern Bay
EASMH
6,108
Upper Choptank River
CHOTF
0
Middle Choptank River
CHOOH
63
Lower Choptank River
CHOMH2
1,499
Mouth of the Choptank River
CHOMH1
8,044
Little Choptank River
LCHMH
3,950
Honga River
HNGMH
7,686
Fishing Bay
FSBMH
193
Upper Nanticoke River
NANTF
0
Middle Nanticoke River
NANOH
3
Lower Nanticoke River
NANMH
3
Wicomico River
WICMH
3
Manokin River
MANMH
4,359
Big Annemessex River
BIGMH
2,014
Upper Pocomoke River
POCTF
0
Middle Pocomoke River
POCOH
0
Lower Pocomoke River
POCMH
4,092
Tangier Sound
TANMH
37,965
Total acres
184,889
'Breakdown of Potomac SAV restoration goals by jurisdictions are draft, pending confirmation of split
between Maryland, Virginia and the District of Columbia along jurisdictional lines. Due to ongoing
refinement, some numbers in this table differ from the April 25, 2003, version included in Appendix A
and previous model estimates presented in tables III-3 and III-4.
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
A11
Table A-4. Chesapeake Bay submerged aquatic vegetation
(SAV) restoration goal acreage by major basin by jurisdiction.
Basin/Jurisdiction
SAV Restoration Goal (Acres)
SUSQUEHANNA
12,856
EASTERN SHORE - MD
76,193
WESTERN SHORE - MD
5,651
PATUXENT
1,420
POTOMAC1
MD
12,747
VA
6,320
DC
384
RAPPAHANNOCK
12,798
YORK
21,823
JAMES
3,483
EASTERN SHORE - VA
31,215
TOTAL
184,889
'Breakdown of Potomac SAV restoration goals by jurisdictions are draft, pending
confirmation of split between Maryland, Virginia and the District of Columbia along
jurisdictional lines. Due to ongoing refinement, some numbers in this table differ
from the April 25, 2003, version included in Appendix A and previous model
estimates presented in tables III-3 and III-4.
appendix A • Decisions Regarding Nutrient & Sediment Load Allocations and New SAV Restoration Goals
-------
B1
a ppend ix B
Chesapeake Bay Living Resource-Based
Refined Designated Uses and Water
Quality Criteria for Dissolved Oxygen,
Water Clarity and Chlorophyll a
To better reflect the desired and attainable Chesapeake Bay water quality conditions
called for in the Chesapeake 2000 agreement, Chesapeake Bay Program watershed
partners determined that the underlying tidal-water designated uses needed to be
refined. The Chesapeake Bay watershed partners, thus, proposed five refined sub-
categories of the current broad aquatic life designated uses contained in the existing
state water quality standards of the four jurisdictions bordering directly on Chesa-
peake Bay and its tidal tributaries.
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, is a
seasonal overlay on that part of the year-round open-water use which borders the
land along the tidal portions of the Chesapeake Bay and its tributaries.
Table B-1 provides general descriptions of the five designated uses and the aquatic
communities they were established to protect1, while Table B-2 provides the
proposed designated uses for each Chesapeake Bay Program segment. See the Tech-
nical Support Document for Identification of Chesapeake Bay Designated uses and
Attainability (U.S. EPA 2003b) for more detailed explanation of the five refined
designated uses.
'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.
appendix B • Living Resource-Based Refined Designated Uses and Water Quality Criteria
-------
B2
Table B-1. 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 Bay Grass Designated Use: Designed to protect underwater bay grasses and the
many fish and crab species that depend on the shallow-water habitat provided by grass beds.
Open-Water Fish and Shellfish Designated Use: Designed to protect water quality in the
surface water habitats within tidal creeks, rivers, embayments and the mainstem Chesapeake
Bay year-round. This use aims to protect diverse populations of sportfish, including striped
bass, bluefish, mackerel and seatrout, 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.
Source: U.S. EPA 2003b.
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. See
Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chloro-
phyll a for the Chesapeake Bay and Its Tidal Tributaries for more detailed
explanation of the Chesapeake Bay water quality criteria (U.S. EPA 2003a). As
presented in Table B-3, the Chesapeake Bay dissolved oxygen criteria have been
defined for each of the five designated uses. Table B-4 presents the water clarity
criteria applicable to the shallow-water designated use. The narrative chlorophyll a
criteria, which is recommended for all Chesapeake Bay and tidal tributaries, is
presented in Table B-5.
appendix B • Living Resource-Based Refined Designated Uses and Water Quality Criteria
-------
B3
Table B-2. Recommended tidal-water designated uses by Chesapeake Bay Program segment.
Chesapeake Bay Program (CBP)
Segment Name
CBP
Segment
Migratory
Spawning
and Nursery
(2/1-5/31)
Open-Water
(Year-Round)
Deep-Water Deep-Channel Shallow-Water
(6/1-9/30) (6/1-9/30) (4/1-10/30)
Northern Chesapeake Bay
CB1TF
X
X
X
Upper Chesapeake Bay
CB20H
X
X
X
Upper Central Chesapeake Bay
CB3MH
X
X
XXX
Middle Central Chesapeake Bay
CB4MH
X
X
XXX
Lower Central Chesapeake Bay
CB5MH
X
XXX
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
XXX
Upper Rappahannock River
RPPTF
X
X
X
Middle Rappahannock River
RPPOH
X
X
X
Lower Rappahannock River
RPPMH
X
X
XXX
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
appendix B • Living Resource-Based Refined Designated Uses and Water Quality Criteria
-------
B4
Table B-2. Recommended tidal-water designated uses by Chesapeake Bay Program segment (cont.).
Chesapeake Bay Program (CBP)
Segment Name
CBP
Segment
Migratory
Spawning
and Nursery
(2/1-5/31)
Op en-Water
(Year-Round)
Deep-Water
(6/1-9/30)
D eep-Chan n el S li allow-Water
(6/1-9/30) (4/1-10/30)
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
Lafayette River
LAFMH
X
Mouth to mid-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
Source: U.S. EPA 2003b.
appendix B • Living Resource-Based Refined Designated Uses and Water Quality Criteria
-------
Table B-3. Chesapeake Bay dissolved oxygen criteria.
Designated Use
Criteria Concentration/Duration
Protection Provided
Temporal Application
Migratory fish
spawning
and
nursery use
7-day mean > 6 mg liter"1
(tidal habitats with 0-0.5 ppt salinity)
Survival/growth of larval/juvenile tidal-fresh resident
fish; protective.pf threatened/endangered species.
February 1 - May 31
Instantaneous minimum > 5 mg liter"1
Survival and growth of larval/juvenile migratory fish;
protective of threatened/endangered species.
Open-water fish and shellfish designated use criteria apply
June 1 - January 31
Shallow-water bay
grass use
Open-water fish and shellfish designated use criteria apply
Year-round
Open-water fish
and shellfish use
30-day mean > 5.5 mg liter"1
(tidal habitats with 0-0.5 ppt salinity)
Growth of tidal-fresh juvenile and adult fish; protective of
threatened/endangered species.
Year-round
30-day mean > 5 mg liter"1
(tidal habitats with >0.5 ppt salinity)
Growth of larval, juvenile and adult fish and shellfish;
protective_of threatened/endangered species.
7-day mean > 4 mg liter'1
Survival of open-water fish larvae.
Instantaneous minimum > 3.2 mg liter"
Survival of threatened/endangered sturgeon species.1
Deep-water
seasonal fish and
shellfish use
30-day mean > 3 mg liter"1
Survival and recruitment of bay anchovy eggs and
larvae.
June 1 - September 30
1-day mean > 2.3 mg liter"1
Survival of open-water juvenile and adult fish.
Instantaneous minimum >1.7 mg liter"1
Survival of bay anchovy eggs and larvae.
Open-water fish and shellfish designated-use criteria apply
October 1 - May 31
Deep-channel
seasonal refuge
use
Instantaneous minimum > 1 mg liter"1
Survival of bottom-dwelling worms and clams.
June 1 - September 30
Open-water fish and shellfish designated use criteria apply
October 1 - May 31
n
r—(¦
CO
a>'
1 At temperatures considered stressful to shortnose sturgeon (>29°C), dissolved oxygen concentrations above an instantaneous minimum 4.3 mg liter"1 will protect survival of this listed sturgeon species.
Source: U.S. EPA 2003a.
00
U1
-------
B6
Table B-4. Summary of Chesapeake Bay water clarity criteria for application to shallow-water bay
grass designated use habitats.
Salinity
Regime
Water Clarity
Criteria as
Percent Light-
through-Water
(PLW)
Water Clarity Criteria as Secchi Depth1
Temporal
Application
Water Clarity Criteria Application Depths
0.25
0.5
0.75
1.0
1.25
1.5
1.75
2.0
Secchi Depth (meters) for Above Criteria Application
Depth
Tidal fresh
13%
0.2
0.4
0.5
0.7
0.9
1.1
1.2
1.4
April 1 - October 31
Oligohaline
13%
0.2
0.4
0.5
0.7
0.9
1.1
1.2
1.4
April 1 - October 31
Mesohaline
22%
0.2
0.5
0.7
1.0
1.2
1.4
1.7
1.9
April 1 - October 31
Polyhaline
22%
0.2
0.5
0.7
1.0
1.2
1.4
1.7
1.9
March 1 - May 31,
September 1 - November 30
'Based on application of the equation, PLW = 100exp(-K,jZ), the appropriate PLW criterion value and the selected application depth are
inserted and the equation is solved for Kd. The generated Kd value is then converted to Secchi depth (in meters) using the conversion
factor Kd = 1.45/Secchi depth.
Source: U.S. EPA 2003a.
Table B-5. Recommended Chesapeake Bay chlorophyll a narrative criteria.
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, proliferation of species deemed potentially harmful to aquatic life or humans or aesthetically
objectionable conditions—or otherwise render tidal waters unsuitable for designated uses.
Source: U.S. EPA 2003b.
LITERATURE CITED
U.S. Environmental Protection Agency. 2003a. Ambient Water Quality Criteria for Dissolved
Oxygen, Water Clarity, and Chlorophyll a for Chesapeake Bay and its Tidal Tributaries. EPA
903-R-03-002. Chesapeake Bay Program Office, Annapolis, Maryland.
U.S. EPA. 2003b. Technical Support Document for Identification of Chesapeake Bay Desig-
nated Uses and Attainability. EPA 903-R-03-004. Chesapeake Bay Program Office,
Annapolis, Maryland.
appendix B • Living Resource-Based Refined Designated Uses and Water Quality Criteria
-------
C1
Summary of
Watershed Model Results
for All Loading Scenarios
This appendix describes general assumptions and methodologies applied for several
model scenario used in the cap load allocation process including the 2010 Tiers,
2010 "Everything, Everywhere, by Everyone" (E3), 2010 No-BMPs and All-Forest
scenarios.
LEVEL-OF-EFFORT AND E3 SCENARIOS
As described in Chapter 4, the Tier and E3 scenarios were developed by the Chesa-
peake Bay Program Nutrient Subcommittee's Workgroups to provide reference
points of increasing load reductions of nutrients and sediment that could be associ-
ated with increasing levels of BMP implementation for both point and non-point
sources in the Chesapeake Bay watershed.
The series of ranging scenarios were simulated by the Chesapeake Bay Program's
Phase 4.3 Watershed Model and the resultant loads for nitrogen, phosphorus and sedi-
ment were used as inputs to the Chesapeake Bay Estuary Model. Evaluation of water
clarity, dissolved oxygen and chlorophyll a concentrations from the Estuary Model,
in turn, provided a sense of the response of key water quality parameters to the various
loading levels. For the Tier and E3 scenarios, best management practices (BMP)
implementation levels, the resultant 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.
Implementation levels in all of the Tiers and E3 scenarios are not cost effective. The
most cost effective combinations of BMPs will be evaluated by jurisdictions and
their tributary or watershed teams as their tributary strategies are developed. In addi-
tion, and as noted in Chapter 4, E3 levels of BMP implementation are theoretical
since the scenario, generally, did not account for physical limitations or participation
levels in its design.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C2
The Tier and E3 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 juris-
dictions and Chesapeake Bay Program Office personnel. The specific workgroups that
decided BMP implementation levels included the Agricultural Nutrient Reduction
Workgroup, the Forestry Workgroup, the Point Source Workgroup and the Urban
Stonnwater Workgroup. The Tributary Strategy Workgroup and Nutrient Subcom-
mittee finalized the E3 scenario definitions after review and further deliberation.
To conform to Chesapeake 2000 goals, all of the Tier and E3 scenarios were rooted
in 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 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 (CBPO,
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
• Mixed Open
2010 agricultural landuses were projected from Agricultural Census information
(1982, 1987, 1992 and 1997) by county and according to methodologies chosen by
individual states. Projected animal populations, to estimate manure applications,
were rooted in county Agricultural Census trends and information from state envi-
ronmental and agricultural agencies.
2010 urban landuses were mostly projected from a methodology 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 root
source of urban and forest acreage. In the case of Maryland, urban growth from 2000
to 2010 was determined by Maryland Department of Natural Resources and the
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.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C3
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 included: 1) significant municipal
wastewater treatment facilities—discharging flows greater than or equal to 0.5 mil-
lion gallon per day; 2) significant industrial facilities—discharging flows greater
than or equal to 0.5 million gallon per day; and 3) non-significant municipal waste-
water 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.
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 facilities located in all jurisdictions of the Chesapeake Bay water-
shed. These future flows were developed mostly from population projections. Tier
and E3 scenario flows for industrial dischargers remained at 2000 levels.
Treatment technologies for municipal facilities varied among the Tier scenarios to
reach and maintain concentrations defined under each Tier scenario description. The
treatment technologies included 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.
Atmospheric deposition to the Chesapeake Bay watershed and tidal surface waters
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 Progress model runs.
2010 TIER 1 SCENARIO
2010 Tier 1 BMP implementation levels were generally determined by continuing
current levels of effort and cost-share in each Chesapeake Bay watershed jurisdic-
tion. In addition, expected regulatory measures, jurisdictional programs and
construction schedules between 2000 and 2010 were included.
2010 TIER 1 NON-POINT SOURCE BMPs
For most non-point source BMPs, implementation rates between 1997 and 2000
were continued to the year 2010 with limits that levels could not exceed the avail-
able or E3 land area to apply the BMPs to. The scale of the calculations is a
county-segment or the intersection of a county political boundary and a Chesapeake
Bay watershed model hydrologic segment. This is the same scale that most jurisdic-
tions report BMP implementation levels to the 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 was not available from New York,
Delaware and West Virginia, 2010 Tier 1 projections were determined from water-
shed-wide implementation rates in states which employ and track the practice.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C4
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 land, 2010 Tier 1 crop land 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 individually, 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. These practices are tracked by some
jurisdictions and credited in the Watershed Model for progress scenarios, but are not
part of the Tiers and E3. For forest harvesting practices and erosion and sediment
control, the watershed 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 is included in Tier 1
for pasture as forest buffers since this BMP is also part of the Tier scenarios and E3
and pasture tree planting and pasture buffers are treated the same in the model.
Table C-1 shows Tier 1 watershed-wide BMP implementation levels for all nonpoint
source BMPs. The table designates the unit of measure for each BMP and the rele-
vant model landuses that BMPs are applied to by four major categories: agricultural,
urban and mixed open, forestry and septic. As references, 2000 nonpoint source
BMP implementation levels are listed as well.
2010 TIER 1 POINT SOURCE TREATMENT TECHNOLOGIES
• Tier 1 significant municipal wastewater treatment facilities
0 Nitrogen—Existing municipal facilities with nutrient-removal technologies
(NRT) and those planned to go to NRT by 2010 are at 2010 projected flows and
8 mg/L total nitrogen effluent concentrations (annual average). All remaining
significant facilities are at 2010 projected flows and 2000 total nitrogen effluent
concentrations.
0 Phosphorus—2010 projected flows and 2000 total phosphorus effluent concen-
trations except those targeted in VA which are at 1.5 mg/L total phosphorus
effluent concentrations (annual average).
• Tier 1 significant industrial dischargers
0 2000 flows and 2000 levels of effluent concentrations for total nitrogen and
total phosphorus or the permit limit effluent concentration, whichever is less.
• Tier 1 Non-significant municipal wastewater treatment facilities
0 2000 total nitrogen and total phosphorus effluent concentrations applied to 2010
projected flows.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
Table C-1. Chesapeake Bay watershed-wide nonpoint source best management practice implementation levels for 2000, Tier and E3.
Unit of
Measure
Applicable
Landuse
2000
Progress
2010
Tier 1
2010
Tier 2
2010
Tier 3
2010
E3
0)
"0
15
n>
3
a
x'
n
oo
c
CD
O
:>
CD
i—(¦
05
ro
Q_
O
Q_
rD_
ro
O
2>
O
CD
Q_
zj'
UD
on
n
ro
13
CD
o
AGRICULTURAL BMPs
Conservation Tillage
Acres
Low-Till
1,994,745
1,962,824
2,340,908
2,300,093
2,312,209
Riparian Forest Buffers
Acres
Row Crop, Hay
9,054
30,588
133,772
206,663
494,450
Riparian Forest Buffers 1-side stream miles,
100 foot width
Row Crop, Hay
747
2,524
11,036
17,050
40,792
Wetland Restoration
Acres
Row Crop, Hay
1,277
2,862
10,260
17,659
25,282
Land Retirement
Acres
Row Crop, Hay
87,488
128,510
500,452
742,695
1,090,540
Grass Buffers
Acres
Row Crop
4,294
15,036
71,985
113,800
0
Tree Planting
Acres
Row Crop, Pasture
8,568
4,142
0
0
0
Riparian Forest Buffers
Acres
Pasture
0
0
46,732
63,851
184,081
Riparian Forest Buffers 1 side stream miles,
100 foot width
Pasture
0
0
3,855
5,268
15,187
Carbon Sequestration/
Bio Energy
Acres
Row Crop
0
0
0
509,431
770,736
Standard Nutrient Management
Plan Implementation
Acres
Row Crop, Hay
2,283,426
3,023,742
3,850,244
2,967,870
0
Yield Reserve Implementation
Acres
Row Crop, Hay
0
0
0
1,271,944
4,830,817
Total Nutrient Management
Plan Implementation
Acres
Row Crop, Hay
2,283,426
3,023,742
3,850,244
4,239,814
4,830,817
Farm Plans
Acres
Agriculture
3,666,165
5,075,549
5,860,003
6,854,953
7,202,280
Cover Crops
Acres
Row Crop
220,134
152,766
1,544,635
2,203,196
2,312,209
Stream Protection With Fencing
Acres
Pasture
40,744
69,257
171,739
580,365
712,302
Stream Protection Without Fencing Acres
Pasture
26,166
27,979
83,584
63,583
0
Grazing Land Protection
Acres
Pasture
134,327
304,868
853,863
1,394,909
2,371,463
Animal Waste Management
Acres
Manure Acres
4,886
6,425
6,953
7,692
8,537
Animal Units
Manure Acres
708,498
931,677
1,008,208
1,115,351
1,237,801
Manure Excess Wet Tons As Excreted
N/A
1,270,139
1,927,899
2,145,277
1,870,085
8,856,825
continued
-------
Table C-1. Chesapeake Bay watershed-wide nonpoint source best management practice implementation levels for 2000, Tier and E3. (cont)
Unit of
Measure
Applicable
Land use
2000
Progress
2010
Tier 1
2010
Tier 2
2010
Tier 3
2010
E3
URBAN AND MIXED OPEN BMPs
Abandoned Mine Reclamation
Acres
Urban/Exposed
6,062
0
0
0
0
Urban Growth Reduction
Acres
Urban
38,787
0
26,096
52,192
78,288
Riparian Forest Buffers
Acres
Pervious Urban
0
364
9,808
28,522
93,643
1 side stream miles,
50 foot width
Pervious Urban
0
60
1,618
4,706
15,451
Grass Buffers
Acres
Pervious Urban
0
95,022
84,997
65,702
0
Storm Water Management
on New Development
Acres
Urban
0
153,157
207,705
183,440
159,560
Storm Water Management
on Recent Development
Acres
Urban
165,040
374,357
373,817
373,236
0
Storm Water Management on
Recent and Old Development
Acres
Urban
0
29,959
187,185
748,488
3,740,806
Total Storm Water Management Acres
Urban
165,040
557,474
768,707
1,305,164
3,900,366
Erosion and Sediment Control
Acres
Urban
25,911
0
0
0
0
Urban Nutrient Management
Acres
Pervious Urban
6,608
28,630
1,055,077
1,964,784
2,601,733
Tree Planting
Acres
Mixed Open
22,596
44,280
0
0
0
Riparian Forest Buffers
Acres
Mixed Open
0
0
54,702
73,757
413,922
1 side stream miles,
100 ft. width
Mixed Open
0
0
4,513
6,085
34,149
Mixed Open Nutrient
Acres
Mixed Open
0
60,791
1,997,497
3,870,252
4,950,621
continued
-------
Table C-1. Chesapeake Bay watershed-wide nonpoint source best management practice implementation levels for 2000, Tier and E3. (cont)
Unit of
Applicable
2000
2010
2010
2010
2010
Measure
Landuse
Progress
Tier 1
Tier 2
Tier 3
E3
FORESTRY BMPs
Forest Harvesting Practices
Acres
Forest
67,448
0
0
0
0
l SEPTIC BMPs
Septic Connections
Systems
Septic
31,514
31,514
31,514
31,514
31,514
Septic Pumping
Systems
Septic
2,954
N/A
N/A
N/A
N/A
Septic Denitrification
Systems
Septic
312
312
N/A
N/A
N/A
Septic Denitrification/Pumping
Systems
Septic
N/A
N/A
8,305
93,014
1,357,026
on New and Existing Systems
-------
C8
2010 TIER 1 ATMOSPHERIC DEPOSITION SOURCE CONTROLS
Tier 1 atmospheric deposition assumes implementation of the 1990 Clean Air
Act projected for the year 2010 with existing regulations. Air emission source
controls for the Tier 1 scenario include the following:
• 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 nitrogen oxides (NOx) state implementation plan (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 indi-
vidual landuse source categories, i.e., agriculture, urban, mixed open, forest and
non-tidal surface waters). The reported Chesapeake Bay Watershed Model loads;
however, usually do not include contributions from atmospheric deposition to tidal
waters although the water quality responses, as measured by the Chesapeake Bay
Estuary Model, account for this source at levels prescribed by Tier 1.
2010 TIER 2 SCENARIO
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 generally described below for each of
the major source category.
2010 TIER 2 NON-POINT SOURCE BMPs
2010 Tier 2 BMP implementation levels for non-point sources were generally deter-
mined by increasing levels above Tier 1 by a percentage of the difference between
Tier 1 and E3 levels for each BMP with the percentages being lower than those used
in Tier 3. These percentages were mostly prescribed by individual source work-
groups in the Chesapeake Bay Program Nutrient Subcommittee and were applied
watershed-wide by county-segments or the intersections of county political bound-
aries and the Watershed Model's segments.
Table C-1 shows Tier 2 watershed-wide BMP implementation levels for all nonpoint
source BMPs. The table designates the unit of measure for each BMP, the relevant
model landuses BMPs are applied to by four major categories: agricultural, urban
and mixed open, forestry and septic.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C9
2010 TIER 2 POINT SOURCE TREATMENT TECHNOLOGIES
For Tier 2 point source municipal facilities, technologies to achieve 8 mg/L total
nitrogen effluent concentration included extended aeration processes and denitrifica-
tion zones, along with chemical addition to achieve a total phosphorus effluent
concentration of 1.0 mg/L where facilities are not already achieving these levels.
• Tier 2 significant municipal wastewater treatment facilities
0 Nitrogen—All significant municipal facilities are at 2010 projected flows and
reach and maintain effluent concentrations of 8 mg/L (annual average)
including those facilities that planned to go to NRT by 2010.
0 Phosphorus—All significant municipal facilities are at 2010 projected flows
and reach and maintain total phosphorus effluent concentrations of 1.0 mg/L
(annual average) or the permit limit, whichever is less.
• Tier 2 significant industrial dischargers
0 2000 flows and generally maintain total nitrogen and phosphorus effluent
concentrations that are 50 percent less than those in Tier 1 or the permit limit,
whichever is less.
• Tier 2 non-significant municipal wastewater treatment facilities
0 2000 total nitrogen and total phosphorus effluent concentrations are applied to
2010 projected flows.
2010 TIER 2 ATMOSPHERIC DEPOSITION SOURCE CONTROLS
Tier 2 atmospheric deposition assumes implementation of the 1990 Clean Air Act
projected for the year 2020 with mobile source controls beyond those in Tier 1. Air
emission source controls for the Tier 2 scenario include the following:
• 2020 non-utility (industrial) point source and area source emissions with no addi-
tional controls than Tier 1.
• 2020 mobile source emissions with 2020 mobile source emissions with Tier II tail
pipe standards on light duty vehicles that are more effective than those in the Tier 1
scenario, as well as 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 Tier 2 emissions and resultant atmospheric deposition to the Chesa-
peake Bay watershed's land area and non-tidal waters 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 Chesapeake Bay
Watershed Model loads, however, usually do not include contributions from atmos-
pheric deposition to tidal waters although the water quality responses, as measured
by the Chesapeake Bay Estuary Model, account for this source at levels prescribed
by Tier 2.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C10
2010 TIER 3 SCENARIO
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 are
considered technically possible and are generally described below for each of the
major source categories.
2010 TIER 3 NON-POINT SOURCE BMPs
2010 Tier 3 BMP implementation levels for non-point sources were generally deter-
mined by increasing levels above Tier 1 by a percentage of the difference between
Tier 1 and E3 levels with the percentages being higher than those used in Tier 2. As
with Tier 2, the levels of nonpoint source control were applied watershed-wide by
county-segments or the intersections of county political boundaries and the Chesa-
peake Bay Watershed Model's segments.
Table C-1 shows Tier 3 watershed-wide BMP implementation levels for all nonpoint
source BMPs. The table designates the unit of measure for each BMP, the relevant
model landuses BMPs are applied to by four major categories: agricultural, urban
and mixed open, forestry and septic.
2010 TIER 3 POINT SOURCE TREATMENT TECHNOLOGIES
For Tier 3 municipal point source facilities, treatment technologies to achieve
5 mg/L total nitrogen effluent concentration included extended aeration processes
beyond those in Tier 2, a secondary anoxic zone plus methanol addition, additional
clarification tanks and additional chemicals to achieve a phosphorus effluent concen-
tration of 0.5 mg/L total phosphorus.
• Tier 3 significant municipal wastewater treatment facilities
0 Nitrogen—All significant municipal facilities are at 2010 projected flows and
reach and maintain effluent concentrations of 5 mg/L total nitrogen (annual
average) including those facilities that planned to go to NRT by 2010.
0 Phosphorus—All significant municipal facilities are at 2010 projected flows
and reach and maintain effluent concentrations of 0.5 mg/L total phosphorus
effluent concentration (annual average) or the permit limit, whichever is less.
• Tier 3 significant industrial dischargers
0 2000 flows and generally maintain total nitrogen and phosphorus effluent
concentrations that are 80 percent less than those in Tier 1 or the permit limit,
whichever is less.
• Tier 3 non-significant municipal wastewater treatment facilities
0 2000 total nitrogen and total phosphorus effluent concentrations are applied to
2010 projected flows.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C11
2010 TIER 3 ATMOSPHERIC DEPOSITION SOURCE CONTROLS
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 E3 SCENARIO
BMP implementation levels in the Tier scenarios were bounded by levels of E3,
which is specifically designed to take out most of the subjectivity surrounding what
can or cannot be achieved in control measures. The particular definitions of E3 BMP
implementation levels are, in part, rooted in earlier work of the Chesapeake Bay
Program when a limit-of-technology condition was assessed by the Tributary
Strategy Workgroup. However, E3 is less subjective than the previous limit-of-
technology scenarios in its determinations of maximum implementation levels.
The BMP levels in E3 are theoretical. There are no cost and few physical limitations
to implementing BMPs for point and non-point sources. As discussed in Chapter 4,
E3 implementation levels and their associated reductions in nutrients and sediment
could not be achieved for many BMPs when considering physical limitations and
participation levels. However, there are some control measures in E3 that physically
could be more aggressive. The E3 conditions for these BMPs were established
because a theoretical maximum implementation level would have been entirely
subjective. Finally, E3 includes new BMP technologies and programs that are not
currently part of jurisdictional pollutant control strategies. BMP implementation
levels for the E3 scenario are generally described below for nonpoint and point
source categories.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C12
2010 E3 NON-POINT SOURCE BMPs
For most non-point source BMPs, it is assumed that the load from every available
acre of the relevant land area is 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 yields. Table
C-l shows E3 watershed-wide BMP implementation levels for all nonpoint source
BMPs. The table designates the unit of measure for each BMP and the relevant
model landuses that BMPs are applied to by four major categories: agricultural,
urban and mixed open, forestry and septic.
2010 E3 POINT SOURCE TREATMENT TECHNOLOGIES
For point sources in E3, municipal wastewater treatment facilities reach and main-
tain effluent concentrations of 3 mg/L total nitrogen and at least 0.1 mg/L total
phosphorus through technologies such as deep bed denitrification filters and
micro-filtration.
• E3 significant municipal wastewater treatment facilities
0 Nitrogen—Significant municipal facilities are at 2010 projected flows and
reach and maintain total nitrogen effluent concentrations of 3 mg/L (annual
average) including those facilities that planned to go to NRT by 2010.
0 Phosphorus—Significant municipal facilities are at 2010 projected flows and
reach and maintain total phosphorus effluent concentrations of 0.1 mg/L
(annual average).
• E3 significant industrial dischargers
0 Nitrogen—2000 flows and total nitrogen effluent concentrations of 3 mg/L
(annual average).
0 Phosphorus—2000 flows and total phosphorus effluent concentrations of
0.1 mg/L (annual average) or the permit limit, whichever is less.
• E3 non-significant municipal wastewater treatment facilities
0 Nitrogen—Non-significant municipal facilities are at 2010 projected flows and
reach and maintain total nitrogen effluent concentrations of 8 mg/L (annual
average).
0 Phosphorus—Non-significant municipal facilities are at 2010 projected flows
and reach and maintain total phosphorus effluent concentrations of 2.0 mg/L
(annual average) or 2000 concentrations, whichever is less.
2010 E3 ATMOSPHERIC DEPOSITION SOURCE CONTROLS
E3 atmospheric deposition assumes implementation of the 1990 Clean Air Act
projected for the year 2020 with aggressive controls on utilities, industry and mobile
sources. Air emission source controls for the E3 scenario include the following:
• 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 Tiers 1-3.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C13
• 2020 mobile source emissions assuming super ultra-low emissions for light duty
vehicles and heavy duty diesel standards to further reduce NOx emissions 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 E3 emissions and resultant 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, i.e., agriculture, urban, mixed open,
forest and non-tidal surface waters. The reported Chesapeake Bay Watershed Model
loads, however, usually do not include contributions from atmospheric deposition to
tidal waters although the water quality responses, as measured by the Chesapeake
Bay Estuary Model, account for this source at levels prescribed by E3.
BASINWIDE LOADS FOR 2000, TIERS 1-3 AND E3
Figures C-l through C-3 depict Chesapeake Bay watershed modeled basinwide
nutrient and sediment loads delivered to the Chesapeake Bay and its tidal tributaries
by major source category for each of the Tier scenarios as well as E3. As references,
the model estimated loads for the year 2000 are also portrayed.
330
¦ Non-Tidal
Water
Atmospheric
Deposition
~ Septic
~ Mixed Open
~ Urban
I Forest
~ Point Source
~ Agriculture
2000 Progress 2010 Tier 1
2010 Tier 2
2010 Tier 3
2010 E3
Figure C-1. Chesapeake Bay Watershed Model-estimated nitrogen loads delivered to the Chesapeake Bay
and its tidal tributaries by source.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C14
TJ O
ra a>
o >»
o o
So
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
2.89
¦ 0.351
3.72
6.71
0.18
2.52
2.59
¦ 0.341
2.21
5.54
0.19
2.07
3.74
I Non-Tidal
Water
Atmospheric
Deposition
~ Mixed Open
~ Urban
I Forest
~ Point Source
~ Agriculture
2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3
2010 E3
Figure C-2. Chesapeake Bay Watershed Model-estimated phosphorus loads delivered to the Chesapeake Bay
and its tidal tributaries by source.
<0
u
ca
ra
a>
o
.5*
_i
(0
c
c
o
0)
E
c
T3
o
d>
—
(O
E
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
1.000
2.714
0.494
0.461
2.179
0.522
0.414
1.020
1.669
0.507
1.067
~ Mixed Open
I Urban
~ Forest
~ Agriculture
2000 Progress 2010 Tier 1 2010 Tier 2 2010 Tier 3
2010 E3
Figure C-3. Chesapeake Bay Watershed Model-estimated land-based sediment loads delivered to the
Chesapeake Bay and its tidal tributaries by source.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C15
As is common for reporting purposes, the model-estimated delivered loads are a
yearly average of loads simulated over a 10-year period (1985-1994). This 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 E3 show the impact of most point and non-point
source BMPs employed in the design of the scenarios. For nonpoint sources, the
influence of generally increasing BMPs listed in Table C-1 is depicted in the nutrient
and sediment load reductions for the three relevant source categories: agriculture,
urban and mixed open and septic. For point sources, the impact of lower effluent
concentrations through the Tier to E3 yields the point source reductions shown in
Figures C-l and C-2.
Atmospheric deposition to the Chesapeake Bay watershed's land area and non-tidal
surface waters are part of the reported loads but the loads do not include contribu-
tions from atmospheric deposition direct to tidal surface waters. In addition, the
reported loads do not reflect shoreline erosion controls employed in the scenarios.
The water quality responses as measured by the Chesapeake Bay Estuary Model,
however, account for both atmospheric deposition to tidal waters and shoreline
erosion at levels prescribed for the Tiers and E3.
It is important to note that landuses and animal populations change considerably
between 2000 Progress and the Tiers and E3, which are rooted in 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 phosphorus loads increase
from 2000 to 2010 Tier 1 because of increases in municipal facility flows which,
unlike nitrogen, are not offset by technologies to reduce this nutrient in effluents.
In addition to changes between 2000 and the 2010 Tier and E3 scenarios, it is imper-
ative to consider landuse changes among the Tiers and E3 due to increasing
non-point source BMP implementation levels. For example, sediment loads from
forested land increase through the Tiers to E3 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 AIR 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 surface waters are part of
the reported nutrient loads from the individual landuse source categories in the Tiers
and E3, i.e., agriculture, urban, mixed open, forest and non-tidal surface waters. As
mentioned previously, the reported loads; however, usually do not include contribu-
tions from atmospheric deposition to tidal surface waters although the water quality
responses account for this source.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C16
To estimate the effects of only the Tier and E3 emission controls, i.e., without the
influences of other point and non-point source BMPs, the histograms in Figure C-4
show changes in atmospheric deposition of nitrogen to the watershed's land area and
non-tidal surface waters and the response in delivered loads. In this model study, all
landuses, fertilizer applications, point sources, septic loads and BMP implementation
levels were held constant at 2000 conditions. Only atmospheric deposition varied.
What the deposition scenarios say, for example, is "If projected emission and depo-
sition reductions associated with the Tiers and E3 were realized today (2000), loads
to the Chesapeake Bay and its tidal tributaries are estimated to be the following." For
references, reported Tier 1 and Tier 2 loads from the watershed are also shown in the
graphics.
As can be seen in Figure C-4, atmospheric deposition to the watershed progressively
declines from 2000 through the Tiers to E3 as more air emission controls are
included in the model simulation. Loads from the watershed land area and non-tidal
surface 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 deposition falls
on forests. Among landuses, forests have the greatest potential to uptake nitrogen as,
generally, forests in the Bay basin are not nitrogen-sensitive.
] 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 C-4. Chesapeake Bay Watershed Model-estimated nitrogen deposition versus delivered loads—
2000 baseline with Tier and E3 emission controls.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
C17
It is the impacts of emission controls on delivered loads that are important in the
establishment of tributary strategies—rather than the contribution to loads from
atmospheric deposition. Understanding the loading responses to changes in deposi-
tion 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 because of both variable air emission controls and changes
in landuses that the atmospheric flux is deposited to.
In the most dramatic case, atmospheric deposition of nitrogen to the watershed
decreases 171 million lbs/year from 2000 to 2010 E3. If this reduction in deposition
were realized today, (i.e., deposition was to 2000 landuses with all other present
conditions), nitrogen loads to the Chesapeake Bay and its tidal tributaries would
decrease 21 million lbs/year or would be at levels associated with the Tier 1 scenario.
It is important to note that E3 levels of emission controls are considered to be the
current limits of technology with aggressive controls on all major sources of tech-
nology with aggressive controls on all major sources utilities, mobile and industrial.
E3 emission controls are voluntary, as opposed to regulatory and follow the format
of defining other E3 point and nonpoint source BMPs in that implementation levels
did not consider physical limitations, participation rates and costs. As has been
described previously, the intent of the Tiers is not to establish what can and cannot
be done through management actions, either regulatory or voluntary, as this is the
responsibility of Bay watershed jurisdictions.
LITERATURE CITED
Chesapeake Bay Program Office (CBPO). 2000. Chesapeake Bay Watershed Model Land
Use and Model Linkages to the Airshed and Estuarine Models. Prepared by the Chesapeake
Bay Program Modeling Subcommittee. Annapolis, Maryland.
appendix C • Summary of Watershed Model Results for All Loading Scenarios
-------
D1
appendix D
Summary of
Key Water Quality
Attainment Scenarios
Table D-1. Key scenario descriptions.
Observed 1984-1994 Chesapeake Bay water quality monitored conditions.
Progress 2000 Model estimated conditions resulting from implementation of BMPs and treatment technologies
in place in 2000
Tier 1 Model estimated conditions resulting from implementation of Tier 1 BMPs and treatment
technology implementation levels.
Tier 2 Model estimated conditions resulting from implementation of Tier 2 BMPs and treatment
technology implementation levels.
Tier 3 Model estimated conditions resulting from implementation of Tier 3 BMPs and treatment
technology implementation levels; same as Option 3 cap load allocation.
Tier 3 + 20% Tier 3 model estimated conditions plus a 20 percent reduction in shoreline/nearshore
sediment loads.
Tier 3 + 50% Tier 3 model estimated conditions plus a 50 percent reduction in shoreline/nearshore
sediment loads.
Option 4 Option 4 cap load allocation model estimated conditions.
Confirm Confirmation of agreed to nutrient and sediment cap load allocations model estimated
conditions.
Confirm + 10 Confirmation scenario model estimated conditions plus a 10 percent reduction in
shoreline/nearshore sediment loads.
Confirm + 20 Confirmation scenario model estimated conditions plus a 20 percent reduction in
shoreline/nearshore sediment loads.
Allocation Selected cap load allocation option (175 million pounds nitrogen/12.8 million pounds
phosphorus) model estimated conditions.
Option 1 Option 1 cap load allocation model estimated conditions.
Option 5 Option 5 cap load allocation model estimated conditions.
E3 E3 scenario model estimated conditions.
All Forest All forested watershed scenario model estimated conditions.
Pristine Pristine watershed scenario model estimated conditions.
appendix D • Summary of Key Water Quality Attainment Scenarios
-------
0)
"0
15
fD
3
Q-
X'
~
Ifl
C
OJ
'<
O
I 1
£
CD
r-1*
CO
a
c
cd_
i—h
>
m
n
cv>
Z3
cu
5'
Table D-2. Key scenario summary of dissolved oxygen criteria attainment/
o
nj
Progress
Tier 3
Tier 3
Tier 3
Opt4
Confirm
Confirm
Confirm
Allocation
Qpt1
Opt5
Segment
DU
Observed
2000
Tier 1
Tier 2
(181)
+ 20%
+ 50%
(188)
(175)
+ 10
+ 20
(175)
(160)
(198)
E3
All Forest
Pristine
Mainstem Upper Bay (CB1TF)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Upper Bay (CB20H)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
1.92
0.88
0.68
0.43
0.17
0.13
0.07
0.14
0.12
0.10
0.10
0.08
0.04
0.14
A
A
A
Mainstem Upper Bay (CB3MH)
MIG
0.19
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
DW
4.18
2.52
2.24
1.61
0.73
0.54
0.37
0.61
0.54
0.44
0.40
0.38
0.17
0.67
A,
A
A
DC
13.52
8.16
7.21
5.03
1.84
1.24
0.11
1.46
0.67
0.31
0.22
0.12
A
1.68
A
A
A
Mainstem Mid-Bay (CB4MH)
OW
0.05
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
DW
19.64
15.28
14.28
12.05
8.51
7.57
5.62
7.89
7.08
6.68
6.32
5.96
3.90
8.24
0.69
A
A
DC
45.19
32.75
28.94
18.81
3.93
2.69
1.00
3.17
1.79
1.44
1.24
1.02
0.33
3.84
A
A
A
Mainstem Mid-Bay (CB5MH)
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
DW
6.16
4.38
3.75
2.58
1.08
1.00
0.72
1.10
0.82
0.80
0.76
0.72
0.31
1.17
A
A
A
DC
13.79
7.76
6.00
2.59
0.15
0.14
0.11
0.24
0.09
0.09
0.09
0.08
0.01
0.32
A
A
A
Mainstem Lower Bay (CB6PH)
OW
5.87
4.26
3.68
2.71
1.30
1.23
0.99
1.39
1.07
1.05
1.01
0.97
0.51
1.58
0.01
A
A
DW
0.36
0.01
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB7PH)
OW
4.55
3.31
2.81
1.82
0.74
0.66
0.49
0.78
0.57
0.55
0.52
0.50
0.22
0.93
A
A
A
DW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB8PH)
OW
A
A
A
A
A
A,
A
A
A
A
A
A
A
A
A,
A
A
Patuxent Tidai Fresh (PAXTF)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
0.01
0.03
OW
A
A
A
A
A
A,
A
A
A
A
A
A
A
A
0.38
15.14
19.13
Patuxent Mid-Estuary (PAXOH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
9.79
1.56
1.84
1.62
0.86
0.36
0.11
0.36
0.06
0.05
0.03
0.09
0.01
0.38
A
A
0.15
Patuxent Lower Estuary (PAXMH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
AA
OW
7.40
1.59
1.69
1.04
0.01
A
A
A
A
A
A
A
A
A
A
A
A
DW
5.52
0.85
0.82
0.50
0.07
0.02
A
0.02
A
A
A
A
A
0.03
A
A
A
Potomac Tidal Fresh (POTTF)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Potomac Mid-Estuary (POTOH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
2.10
1.36
1.08
0.63
0.31
0.30
0.25
0.31
0.24
0.17
0.15
0.18
0.08
0.32
0.01
A
A
Potomac Lower Estuary (POTMH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
0.78
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
DW
6.90
5.03
4.53
3.11
1.12
0.70
0.15
0.87
0.67
0.40
0.33
0.26
A
0.95
A,
A
A
DC
18.89
11.39
8.64
5.07
0.19
0.17
0.16
0.17
0.17
0.17
0.17
0.16
0.11
0.17
A
A
A
Rappahannock Tidai Fresh (RPPTF)
MIG
A
A
A
A
A
A,
A
A
A
A
A
A
A
A
A,
A
A
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Rappahannock Mid-Estuary (RPPOH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Rappahanock Lower Estuary (RPPMH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
0.44
0.27
0.10
A
A
A
A
A
A
A
A
A
A
A
A
A
A
DW
5.58
2.61
1.09
0.01
A
A
A
A
A
A
A
A
A
A
A
A
A
DC
6.39
5.20
3.38
1.65
A
A
A
A
A
A
A
A
A
A
A
A
A
continued
-------
a)
"0
"0
fl>
J
Q.
X'
~
«
c
cu
—1
O
I 1
£
(-(¦
CO
a
c
Qj_
r—(¦
>
00
r
CD
13
CU
5"
Progress
Tier 3
Tier 3
Tier 3
Opt4
Confirm
Confirm
Confirm
Allocation
Qpt1
Opt5
Segment
DU
Observed
2000
Tier 1
Tier 2
(181)
+ 20%
+ 50%
(188)
(175)
+ 10
+ 20
(175)
(160)
(198)
E3
All Forest
Pristine
York Lower Estuary Piankatank (PIAMH) OW
0.12
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Tidai Fresh Mattaponi (MPNTF)
MIG
A
A
A
A
A
A,
A
A
A
A
A
A
A
A
A,
A
A
OW
33.26
27.37
25.87
27.23
33.73
32.44
30.50
34.44
40.58
39.64
36.53
34.44
34.44
22.51
52.14
63.65
64.72
York Mid-Estuary Mattaponi (MPNOH)MIG
A
A
A
1.72
2.78
2.40
1.79
1.34
2.34
2.34
2.34
1.34
1.34
A
6.08
4.77
3.98
OW
46.88
31,00
28.95
31.86
28.99
26.88
19.11
24.25
29.83
29.85
29.36
24.17
23.72
22.63
48.11
56.07
58.52
York Tidal Fresh Pamunkey (PMKTF)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
0.10
4.28
4.28
OW
62.25
49.53
42.07
30.35
32.94
21.16
10.32
21.77
36.67
29.48
25.80
21.77
21.77
28.81
54.50
81.08
80.84
York Mid-Estuary Pamunkey (PMKOH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
42.15
15.22
12.66
13.86
10.32
4.52
1.06
4.96
11.32
10.21
9.73
4.92
4.88
6.21
11.39
24.27
32.26
York Lower Estuary (YRKMH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
18.08
4.85
3.31
2.32
0.42
0.23
0.03
0.42
0.21
0.20
0.20
0.15
A
0.29
A
A
A
York Lower Estuary (YRKPH)
OW
1.48
0.01
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
DW
0.01
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Lower Estuary Mobjack (MOBPH) OW
2.30
1.78
1.60
1.10
0.34
0.29
0.23
0.38
0.27
0.26
0.25
0.25
0.16
0.56
A
A
A
James Tidal Fresh (JMSTF)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
0.66
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Mid-Estuary (JMSOH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Lower Estuary (JMSMH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Lower Estuary (JMSPH)
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Eastern Bay (EASMH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
DW
3.26
2.18
2.00
0.90
0.36
0.32
0.20
0.32
0.29
0.27
0.28
0.27
0.14
0.34
A
A
A
DC
20.23
12.87
11.26
6.49
0.67
0.10
0.01
0.18
0.20
0.08
0.02
0.02
A
0.22
A,
A
A
Choptank Mid-Estuary (CHOOH)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
0.14
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Choptank Lower Estuary (CH0MH1)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
2.27
1.83
1.78
1.51
1.08
0.92
0.74
0.97
0.94
0.88
0.83
0.78
0.65
1.00
0.43
A
A
Choptank Lower Estuary (CH0MH2)
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
0.33
A
A
A
A
A
A
A
A
A
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
0.33
0.31
0.29
0.29
0.31
0.28
0.35
0.22
0.20
0.35
Pocomoke (POCMH)
OW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Chester Lower (CHSMH)**
MIG
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
OW
5.67
4.71
4.56
3.56
2.54
2.42
1.69
2.42
2.13
2.06
1.90
1.74
1.42
2.42
0.86
A
A
DW
0.85
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
DC
11.80
3.98
2.89
0.85
A
A
A
A
A
A
A
A
A
A
A
A
A
Elizabeth River (ELIPH)**
OW
3.05
A
A
A
A
A
A
A
A
A
A
A
A
A
A
2.22
6.48
DW
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
South Branch Elizabeth (SBEMH)**
OW
59.51
58.86
58.67
60.37
57.71
56.71
56.39
56.81
58.67
58.58
58.47
56.80
56.80
60.73
56.20
50.31
53.63
* 4/1/03, Version 15 — Changes since version 12: SAV Re-calibration, Wetlands Oxygen Demand, No Seasonal Anoxic Zone
** for information purposes only, model not sufficiently calibrated for these areas
-------
0)
"0
15
fD
3
Q-
X'
~
*
c
OJ
'<
O
I 1
£
CD
r-1*
CO
a
c
cd_
i—h
>
m
n
cv>
Z3
cu
5'
Table D-3. Key scenario summary of chlorophyll a criteria attainment.51
a
-e*
Progress
Tier 3
Tier 3
Tier 3
Opt4
Confirm
Confirm
Confirm
Allocation
Opt1
Segment
Season
Observed
2000
Tier 1
Tier 2
(181)
+ 20%
+ 50%
(188)
(175)
+ 10
+ 20
(175)
(160)
E3
Pristine
Mainstem Upper Bay (CB1TF)
Spring
2.51
0.88
0.21/
N
A
A
A
A
A
A
A
A
A
A
A
Summer
0.39
0.36
0.39
0.37
0.35
0.37
0.41
0.37
0.38
0.40
0.40
0.36
0.30
A
A
Mainstem Upper Bay (CB20H)
Spring
0.70
0.54
0.57
0.51
0.29
0.02
A
0.02
0.23
0.10
0.01
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Upper Bay (CB3MH)
Spring
1.13
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
5.71
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Mid-Bay (CB4MH)
Spring
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
3.09
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Mid-Bay (CB5MH)
Spring
4.35
0.16
0.13
0.07
A
A
A
A
A
A
A
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB6PH)
Spring
10.38
6.97
5.50
3.18
0.40
0.22
A
0.30
0.31
0.24
0.14
A
A
A
A
Summer
0.47
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB7PH)
Spring
7.81
6.62
5.31
3.31
2.06
1.79
0.18
1.94
1.87
1.75
1.62
1.52
0.03
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB8PH)
Spring
9.28
4.16
3.45
0.01
A
A
A
A
A
A
A
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Patuxent Tidal Fresh (PAXTF)
Spring
3.61
3.35
3.15
3.78
3.84
4.26
3.62
4.26
3.35
3.57
3.59
4.01
3.62
0.73
A
Summer
47.01
42.60
42.90
46.93
44.09
48.26
47.20
48.26
44.06
45.93
47.55
47.02
45.49
29.78
A
Patuxent Mid-Estuary (PAXOH)
Spring
0.43
0.93
1.57
1.17
0.92
1.55
0.35
1.56
0.24
0.46
0.63
1.10
0.48
0.09
A
Summer
18.49
20.92
20.98
21.32
20.12
23.88
22.04
23.90
19.51
20 74
21.56
22.88
22.15
12.98
A
Patuxent Lower Estuary (PAXMH)
Spring
2.93
0.17
0.57
0.21
A
A
A
A
A
A
A
A
A
A
A
Summer
11.79
5.36
5.24
2.60
1.06
0.20
A
0.22
A
A
A
A
A
A
A
Potomac Tidal Fresh (POTTF)
Spring
0.55
0.54
0.55
0.56
0.55
0.54
0.53
0.54
0.55
0.55
0.55
0.53
0.53
A
A
Summer
16.76
11.41
8.76
7.11
1.76
A
A
A
10.87
5.14
1.82
A
A
0.97
A
Potomac Mid-Estuary (POTOH)
Spring
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
0.09
0.04
0.07
0.05
A
A
A
A
0.01
0.01
A
A
A
A
A
Potomac Lower Estuary (POTMH)
Spring
7.96
4.20
4.12
3.14
1.53
1.53
0.58
1.53
0.70
0.66
0.62
0.65
A
A
A
Summer
3.11
1.58
0.49
0.06
A
A
A
A
A
A
A
A
A
A
A
Rappahannock Tidai Fresh (RPPTF)
Spring
0.66
0.54
0.07
0.12
0.24
0.22
0.10
0.22
0.25
0.25
0.25
0.22
0.22
A
A
Summer
36.03
16.06
11.04
2.73
A
A
A
A
A
A
A
A
A
A
A
Rappahannock Mid-Estuary (RPPOH) Spring
0.61
A
A
A
A
A
A
A
A
A
A
A
A
A
0.43
Summer
2.01
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Rappahanock Lower Estuary (RPPMH) Spring
0.70
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Lower Estuary Piankatank (PIAMH) Spring
4.72
0.49
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
2.37
0.49
A
A
A
A
A
A
A
A
A
A
A
A
A
York Tidal Fresh Mattaponi (MPNTF) Spring
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
0.49
A
A
A
A
A
A
A
A
A
A
A
A
A
A
continued
-------
a)
"0
"0
fl>
J
Q.
X'
~
«
c
cu
—1
O
I 1
£
(-(¦
CO
a
c
Qj_
r—(¦
>
Progress
Tier 3
Tier 3
Tier 3
Opt4
Confirm
Confirm
Confirm
Allocation
Opt1
Segment
Season
Observed
2000
Tier 1
Tier 2
(181)
+ 20%
+ 50%
(188)
(175)
+ 10
+ 20
(175)
(160)
E3
Pristine
York Mid-Estuary Mattaponi (MPNOH) Spring
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Tidal Fresh Pamunkey (PMKTF) Spring
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Mid-Estuary Pamunkey (PMKOH) Spring
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Lower Estuary (YRKMH)
Spring
1.99
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
2.06
0.50
0.14
A
A
A
A
A
A
A
A
A
A
A
A
York Lower Estuary (YRKPH)
Spring
12.36
2.05
0.70
0.32
0.01
A
A
0.04
0.06
0.03
0.01
0.01
0.01
A
A
Summer
A
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
York Lower Estuar/ Mobjack (M08PH) Spring
4.86
2.29
0.96
0.03
A
A
A
A
A
A
A
A
A
A
A
Summer
0.17
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
James Tidal Fresh (JMSTF)
Spring
18.40
4.28
5.03
1.37
A
A
A
0.25
0.06
0.03
0.02
0.25
0.25
A
A
Summer
44.31
19.80
28.86
8.88
A
A
A
3.40
1.45
0.90
0.38
3.40
3.40
A
A
James Mid-Estuary (JMSOH)
Spring
10.13
0.54
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
0.33
0.38
0.39
0.31
A
A
A
0.24
0.19
0.18
0.18
0.24
0.24
AA
James Lower Estuary (JMSMH)
Spring
5.20
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Lower Estuary (JMSPH)
Spring
26.27
18.87
16.83
8.55
0.07
A
A
5.89
2.25
1.92
1.58
2.78
2.67
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Eastern Bay (EASMH)
Spring
A
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
Summer
9.37
0.71
0.43
0.17
0.05
A
A
A
A
A
A
A
A
A
A
Choptank Mid-Estuary (CHOOH)
Spring
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
14.34
13.91
11.88
9.30
7.54
7.62
3.21
7.71
7.52
7.43
7.27
6.13
4.87
1.94
A
Choptank Lower Estuary (CH0MH2) Spring
1.01
0.03
0.01
A
A
A
A
A
A
A
A
A
A
A
A
Summer
9.56
3.02
0.40
0.13
A
A
A
A
A
A
A
A
A
A
A
Choptank Lower Estuary (CH0MH1) Spring
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
0.30
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Tangier Sound (TANMH)
Spring
2.05
0.03
0.02
A
A
A
A
A
A
A
A
A
A
A
A
Summer
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Pocomoke (POCMH)
Spring
0.23
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Summer
3.15
0.30
0.18
A
A
A
A
A
A
A
A
A
A
A
A
* 4/1/03, Version 15 — Changes since version 12: SAV Re-calibration, Wetlands Oxygen Demand, No Seasonal Anoxic Zone
oo
r
CD
13
CU
O
-------
0)
"0
15
fD
3
Q-
X'
~
*
c
OJ
'<
O
I 1
£
CD
r-1*
CO
a
c
cd_
i—h
>
m
n
cv>
Z3
cu
5'
Table D-4 Key scenario summary of water clarity criteria attainment at maximum depths.1
o
CTl
Progress
Tier 3
Tier 3
Tier 3
Opt4
Confirm
Confirm
Confirm
Allocation
Opt1
Segment
Observed
2000
Tier 1
Tier 2
(181)
+ 20%
+ 50%
(188)
(175)
+ 10
+ 20
(175)
(160)
E3
Pristine
Mainstem Upper Bay (CB1TF)
75.37
75.32
75.31
74.18
65.08
54.87
41.09
54.87
73.19
68.43
64.05
52.58
50.16
58.05
0.07
Mainstem Upper Bay (CB20H)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Upper Bay (CB3MH)
0.01
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Mid-Bay (CB4MH)
72.64
57.26
54.58
49.45
40.38
26.26
6.86
26.37
42.45
35.89
29.94
23.20
19.97
25.98
A
Mainstem Mid-Bay (CB5MHJ
60.81
39.64
37.34
31.81
24.69
11.18
0.01
11.26
24.18
17.57
11.67
9.18
6.91
11.33
A
Mainstem Lower Bay (CB6PH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB7PI-I)
43.87
36.46
35.13
32.23
29.06
12.08
0.10
10.97
28.52
20.83
14.03
10.13
11.12
24.44
A
Mainstem Lower Bay (CB8PH)
A
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
Patuxent Tidal Fresh (PAXTF)
25.77
11.04
14.33
26.15
9.94
2.00
A
2.00
11.66
6.71
2.56
1.13
0.64
4.21
A
Patuxent Mid-Estuary (PAXOH)
20.51
7.41
7.18
7.19
6.15
A
A
A
6.67
2.97
A
A
A
5.02
A
Patuxent Lower Estuary (PAXMH)
36.87
30.29
29.03
27.16
25.57
18.81
6.78
18.87
25.19
21.75
18.60
18.39
17.86
22.20
A
Potomac Tidal Fresh (POTTF)
75.37
75.29
75.29
74.79
71.30
46.62
18.54
46.61
75.28
74.80
70.29
44.25
53.46
65.17
0.01
Potomac Mid-Estuary (POTOH)
75.37
74.42
74.20
73.22
72.46
53.29
30.86
53.25
74.89
73.36
68.84
53.43
62.23
75.20
5.13
Potomac Lower Estuary (POTMH)
21.31
10.49
9.84
6.62
6.21
2.13
0.42
2.13
8.09
4.89
3.67
2.10
2.85
7.92
A
Rappahannock Tidal Fresh (RPPTF)
1.59
0.02
0.02
0.01
0.01
A
A
A
0.01
0.01
0.01
A
A
A
A
Rappahannock Mid-Estuary (RPPOH)
8.66
0.69
0.69
0.19
0.04
0.02
A
0.02
0.08
0.04
0.04
0.02
0.02
0.03
A
Rappahanock Lower Estuary (RPPMH)
39.74
34.67
33.49
32.44
31.11
24.62
7.85
24.67
30.94
29.75
28.07
24.48
24.30
28.82
A
York Lower Estuary Piankatank (PIAMI-I)
70.67
45.30
39.33
20.78
13.17
6.76
2.60
7.72
10.88
8.73
6.76
5.83
4.10
1.35 A
York Tidal Fresh Mattaponi (MPNTF)
A
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
York Mid-Estuary Mattaponi (MPNOH)
11.34
0.77
0.26
0.26
0.14
0.02
A
0.02
0.26
0.26
0.26
0.02
0.02
0.08
A
York Tidal Fresh Pamunkey (PMKTF)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Mid-Estuary Pamunkey (PMKOH)
17.63
3.48
2.67
1.94
0.96
A
A
A
2.20
1.39
0.67
A
A
0.30
A
York Lower Estuary (YRKMH)
17.09
7.60
6.54
5.42
3.57
A
A
A
4.32
2.92
1.83
A
A
1.60
A
York Lower Estuary (YRKPH)
9.10
4.06
3.37
2.69
2.11
0.01
A
0.05
2.31
1.70
1.23
0.03
0.02
1.22
A
York Lower Estuary Mobjack (MOBPH)
62.96
53.25
51.58
48.73
45.18
33.89
10.62
34.31
45.02
40.19
35.19
33.55
32.61
40.34
A
James Tidal Fresh (JMSTF)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Mid-Estuary (JMSOH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Lower Estuary (JMSMH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Lower Estuary (JMSPH)
4.95
0.70
0.36
0.02
A
A
A
A
A
A
A
A
A
A
A
Eastern Bay (EASMH)
65.24
35.47
32.16
25.01
9.70
2.03
0,42
2.03
9.43
3.79
2.10
1.96
1.84
2.87
A
Choptank Mid-Estuary (CHOOH)
5.47
2.27
2.18
1.92
1.63
0.15
A
0.15
1.63
1.28
1.03
0.15
0.15
1.22
A
Choptank Lower Estuary (CH0MH2)
33.64
8.53
5.10
1.46
A
A
A
A
A
A
A
A
A
A
A
Choptank Lower Estuary (CHOMI-11)
67.17
49.00
45.46
39.17
32.68
14.89
1.33
15.13
33.24
26.34
16.45
12.04
9.25
17.62
A
Tangier Sound (TANMH)
74.55
71.19
70.37
68.17
65.11
46.54
3.44
46.06
64.80
58.65
49.61
45.20
45.08
60.55
A
Pocomoke (POCMH)
41.96
22.15
20.19
14.46
10.02
0.02
A
0.01
9.25
1.43
0.35
0.01
0.02
20.24
A
* 4/1/03, Version 15 — Changes since version 12: SAV Re-caiibration, Wetlands Oxygen Demand, No Seasonal Anoxic Zone
-------
Table D-5 Key scenario summary of water clarity criteria attainment at mid depths.*
Segment Observed 2000 Tier 1 Tier 2 (181) +20% +50% (188) (175) + 10 + 20 (175) (160) E3 Pristine
Mainstem Upper Bay (CB1TF) 71.62 55.46 50.88 40.18 23.13 16.03 10.03 16.03 35.95 31.08 26.85 14.43 12.69 13.42 0.01
Mainstem Upper Bay (CB20H) AAAAAA A AAA AAAAA
Mainstem Upper Bay (CB3MH) AAAAA, A AAA A AAAAA
Mainstem Mid-Bay (CB4MH) 37.20 16.20 12.48 7.19 2.78 0.30 0.01 032 3.78 2.15 1.08 0.04 001 0.38 A
Mainstem Mid-Bay (CB5MH) 16J37 0.01 0_01 AAA A AAA AAAAA
Mainrtem Lower Bay (CB6PH) AAAAA A A AAA AAAAA
Mainstem Lower Bay (CB7PH) 8.13 1.99 1.33 0.09 0.01 AAA O01 0.01 A A A A A
Mainrtem Lower Bay_(CB8PH) A A A A A A A A A A AAAAA
Patuxent Tidai FreshJPAXTF) 0.20 AAA A A A A A A A A A A A
Patuxent Mid-Estuary (PAXOH) AAAAA A A AAA AAAAA
CD Patuxent Lower Estuary (PAXMH) 17.55 13.63 13.46 12.88 1 1.77 5.55 A 5.56 11.01 8.58 5.26 4.80 3.69 8.71 A
Potomac Tidal Fresh_(POTTF) 74.97 73_J_5 73.03 68.56 55.27 25.35 1.25 25.35 72.82 68.13 50.02 23.35 29.40 4239 A
ft! Potomac Mid-Estuary (POTOH) 73^1 64.27 63.04 54.36 49.75 31.74 19.24 31.70 65.41 52.99 40.17 31.81 35.88 67.30 A
q_ Potomac Lower Estuary (POTMH) 4.53 1.02 0.98 0.23 0.09 0.09 A 0.09 0.61 0.09 0.09 0.03 0.03 0.20 A
Rappahannocl^Tida! Fresh (RPPTF) AAAAAA A AAA A AAAA
~ Rappahannock Mid-Estuary (RPPOH) 0.03 0.01 0.01 AAA AAAA AAAAA
Rappahanock Lower EstuaryjRPPMH) 27.17 17.92 16.50 15.60 14.41 6.64 A 6.69 14.43 13.30 12.22 6.60 6.49 12.79 A
York Lower Estuary Piankatank (PIAMH) 29.01 9.78 3.33 0.87 0.20 0.20 0.06 0.20 0.20 0.20 0.20 0.20 0.06 0.06 A
c York Tidal Fresh Mattaponi (MPNTF)_ A A A A A A A A A A AAAAA
York Mid-Estuary MattaponijMPNOH) 0.02 AAAAA AAAA AAA _0.01 A
5 York Tidal Fresh Pamunkey (PMKTF) AAAAA A A AAA AAAAA
York Mid-Estuary Pamunkey (PMKOH) AAAAAA AAAA AAAAA
S, York Lower EstuaryJYRKMH) AAAAAA AAAA AAAAA
York Lower EstuaryJYRKPH) 0.61 AAAA A AAAA AAAAA
York Lower Estuary MobjackjMOBPH) 32.89 17 42 14.74 12.07 8.83 0.34 A 0.41 8.18 3.74 0.70 0.27 022 3.30 A
£' James Tidal fresh (JMSTfj A A A A A A A A A A A A A A A
James_Mid-Estuary (JMSOH) AAAAAA AAAA AAAAA
O James_Lower Estuary (JMSMI-I) AAAAAA AAAA AAAAA
limes. Lower Estuary (JMSPH) AAAAAA AAAA AAAAA
¦i? Eastern Bay (EASMH) 24.96 2.61 1.91 0.54 A 001 0.01 O01 0_07 0.01 O01 0.01 O01 0.01 A
> Choptank Mid-EstuaryjCHOOH) AAAAAA AAAA AAAAA
a Choptank Lower Estuary (CHOMH2) 0.24 A A A A A A A A A AAAAA
Choptank Lower Estuary (CHOMH1) 30.84 11_80 8.79 2.58 0.07 001 0.01 O01 057 0.01 O01 0.01 O01 0.01 A
re Tangier Sound (TANMH) 49.18 38.38 36.38 32.93 28.44 11.18 A 1 1.27 28.34 20.62 13.23 1 1.03 10.45 23.04 A
Pocomoke (POCMH) 7.41 0.43 0.18 AAA AAAA AAAAA
00 — — —
CD * 4/1/03, Version 15 — Changes since version 12: SAV Re-calibration, Wetlands Oxygen Demand, No Seasonal Anoxic Zone
CD
5"
in
-------
0)
"0
15
fD
3
Q-
X'
~
*
c
OJ
'<
O
I 1
£
CD
r-1*
CO
a
c
cd_
i—h
>
m
n
cv>
Z3
cu
5'
Table D-6. Key scenario summary of water clarity criteria attainment at low depths."
u
oo
Progress
Tier 3
Tier 3
Tier 3
Opt4
Confirm
Confirm
Confirm
Allocation
Opt1
Segment
Observed
2000
Tier 1
Tier 2
(181)
+ 20%
+ 50%
(188)
(175)
+ 10
+ 20
(175)
(160)
E3
Pristine
Mainstem Upper Bay (CB1TF)
21.88
11.93
8.43
1.74
0.04
0.04
0.04
0.04
0.70
0.16
0.07
0.03
0.02
0.01
A
Mainstem Upper Bay (CB20H)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Upper Bay (CB3MH)
A
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
Mainstem Mid-Bay (CB4MHJ
0.07
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Mid-Bay (CB5MH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB6PI-I)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB7PH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Mainstem Lower Bay (CB8PH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Patuxent Tidal Fresh (PAXTF)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Patuxent Mid-Estuary (PAXOH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Patuxent Lower Estuary (PAXMH)
0.02
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Potomac Tidal Fresh (POTTFj
54.15
30.87
29.00
11.69
3.97
0.01
0.01
0.01
18.35
6.17
2.39
0.01
0.01
0.02
A
Potomac Mid-Estuary (POTOH)
40.89
26.46
25.09
20.64
17.30
8.73
2.07
8.75
23.85
17.83
10.82
6.64
7.97
14.73
A
Potomac Lower Estuary (POTMH)
A
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
Rappahannock Tidal Fresh (RPPTF)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Rappahannock Mid-Estuary (RPPOH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Rappahanock Lower Estuary (RPPMI-I)
2.98
0.13
A
A
A
A
A
A
A
A
A
A
A
A
A
York Lower Estuary Piankatank (PiAMH)
0.87
0.01
0.01
0.01
0.01
A
A
A
A
A
A
A
A
A
A
York Tidal Fresh Mattaponi (MPNTF)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Mid-Estuary Mattaponi (MPNOH}
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Tidal Fresh Pamunkey (PMKTF)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Mid-Estuary Pamunkey (PMKOH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Lower Estuary (YRK.MH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Lower Estuary (YRKPH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
York Lower Estuary Mobjack (MOBPH)
A
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
James Tidal Fresh (JMSTF)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Mid-Estuary (JMSOH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Lower Estuary (JMSMI-I)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
James Lower Estuary (JMSPH)
A
A
A
A
A,
A
A
A
A
A
A
A
A
A
A
Eastern Bay (EASMH)
0.06
0.01
A
A
A
A
A
A
A
A
A
A
A
A
A
Choptank Mid-Estuary (CHOOH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Choptank Lower Estuary (CH0MH2)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Choptank Lower Estuary (CH0MH1)
0.01
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Tangier Sound (TANMH)
4.53
1.86
1.32
0.59
0.41
A
A
A
0.41
A
A
A
A
A
A
Pocomoke (POCMH)
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
* 4/1/03, Version 15 — Changes since version 12: SAV Re-calibration, Wetlands Oxygen Demand, No Seasonal Anoxic Zone
------- |