903R83012
United States
Environmental Protection
Agency
Region 3
Sixth and Walnut Streets
Philadelphia, PA 19106
September
CHESAPEAKE BAY: A PROFILE
OF ENVIRONMENTAL CHANGE
&EPA
r
Region 111 Library
Environmental Protection Agency
I'T)
225
.C5A
J54
vol. 1
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Regional Center for Environmental Information
US EPA Region 111
1650 Arch St.
Philadelphia, PA 19103
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Co
CHESAPEAKE BAY: A PROFILE
OF ENVIRONMENTAL CHANGE
Technical Coordinators
David A. Flemer1
Gail B. Mackiernan2
Willa Nehlsen3
Virginia K. Tippie1
Contributing Authors
Robert B. Biggs4
Dewey Blaylock5
Ned H. Burger2
Linda C. Davidson1
Daniel Haberman2
Kent S. Price4
Jay L. Taft8
'U.S. Environmental Protection Agency,
Chesapeake Bay Program,
2083 West Street, Annapolis, MD 21401.
2University of West Florida,
Chesapeake Bay Program,
2083 West Street, Annapolis, MD 21401.
3CREST, P.O. Box 175,
Astoria, OR 97103.
4College of Marine Studies,
University of Delaware, Lewes, DE 19960.
department of Natural Resources
Office of Environmental Affairs,
Water Pollution Control Division
P.O. Box 44-66, Baton Rouge, LA 70804-4066.
6Department of Organismic and Evolutionary Biology
Harvard University
22 Divinity Avenue, Cambridge, MA 02138.
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DISCLAIMER
This document has been reviewed in ac-
cordance with the U.S. Environmental Protection
Agency policy and approved for publication. Men-
tion of trade names or commercial products does
not constitute endorsement or recommendation
for use.
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FOREWORD
Chesapeake Bay has experienced significant
changes in recent years. Concern for this national
resource prompted the U.S. Congress in 1976 to
direct the U.S. Environmental Protection Agency
(EPA) to conduct a study of the Bay's resources
and water quality, and to develop appropriate
management strategies. This document, Chesa-
peake Bay: A Profile of Environmental Change,
is the third of four final reports developed by the
EPA's Chesapeake Bay Program (CBP). It pro-
vides a characterization of the health of the Bay
and its tributaries. The project was initiated by
the former director, Tudor T. Davies, and the
deputy director, Thomas B. DeMoss. Their vision
and encouragement resulted in the establishment
of a comprehensive data base that permitted Bay-
wide analysis of water quality and resource trends
over time. This analysis would not have been
possible without the many years of effort by Bay
scientists. The CBP gratefully acknowledges their
contribution to our understanding of Chesapeake
Bay.
This characterization of the Bay makes a sig-
nificant step forward by attempting to link water
quality trends to Bay resource trends, thus, mak-
ing science useful to managers and citizens. Such
a retrospective approach is imperfect because
large gaps in the data base and necessary assump-
tions limit our ability to make strong scientific
causal inferences. Yet, similar approaches suffer-
ing from similar imperfections, such as the efforts
in the Great Lakes and in the Thames River in
England, have yielded interpretations used di-
rectly to restore the ecosystem. Without doubt,
some of our water quality-ecosystem linkages are
strong; others are more tenuous — none are incor-
rect. Nonetheless, what we now have, for the first
time, is a comprehensive assessment of the state
of the Bay, and it clearly suggests the need for ac-
tion. The CBP hopes that the findings of this
report will assist managers in developing strategies
that will modify the Bay's water quality and im-
prove the ecosystem.
SK<
, V
\
Virginia K. Tippie
Director,
Chesapeake Bay Program
David A. Flemer
Senior Science Advisor
Chesapeake Bay Program
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CREDITS and ACKNOWLEDGEMENTS
Editors
Elizabeth Giles Macalaster
Debra Allender Barker
Mary Wilkes Kasper
Statistical Analysis and
Data Management
Jerry Oglesby
L. David Lively
Vicky Mabry
Dewey Blaylock
Bill Allen
Paul Mowery
Jackie Wheeler
Production
Dorothy Szepesi
Marion Manganello
Diane Pawlowicz
Art, Design, and Composition
Elaine Kasmer and
Fisher gate Publishing Co., Inc.
Staff support for this project was provided
through a cooperative agreement (X-003264) with
The University of West Florida under the super-
vision of Dr. Jerry Oglesby, Project Manager.
Over the years, many EPA, The University of
West Florida, and GEOMET Technologies, Inc.
personnel have been involved in this massive ef-
fort. We extend special thanks to Mary Barrow,
William Cook, Elise Christenson, Ian Gillelan,
Mike Keller, John Klein, Jan Kuzava, James
Smullen, Charles Strobel, Duane Wilding, and
Maryann Wohlgemuth for their assistance with
this project.
In addition, the Chesapeake Bay Foundation;
Citizens Program for Chesapeake Bay; District of
Columbia Department of Environmental Services;
Maryland Department of Health and Mental
Hygiene, Office of Environmental Programs;
State of Maryland Department of Natural
Resources; Commonwealth of Pennsylvania
Department of Environmental Resources; Sus-
quehanna River Basin Commission; Virginia
Council on the Environment; and the Virginia
State Water Control Board are gratefully
acknowledged for their cooperation, active sup-
port, and sustained interest in the Chesapeake Bay
Program.
IV
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EXECUTIVE SUMMARY
INTRODUCTION
The Chesapeake Bay Program (GBP)
characterization report, Chesapeake Bay: A Pro-
file of Environmental Change, describes trends
in water and sediment quality, and in the living
resources of Chesapeake Bay. The water quality
parameters evaluated include nutrients, dissolved
oxygen, organic chemical compounds, and heavy
metals. The living resources that were assessed
include phytoplankton, submerged aquatic
vegetation (SAV), benthic organisms (including
shellfish), and finfish. Trends in water and sedi-
ment quality, and in living resources, including
the interrelationships among these factors, were
used to characterize the current state of the Bay.
The GBP's characterization of Chesapeake Bay is
based on a ranking of specific areas, or segments,
of the Bay with regard to selected nutrient and
toxicant variables, and to the diversity and abun-
dance of the living components.
WATER AND SEDIMENT QUALITY
The quality of the Bay's water and sediments
reflects both the natural physical and chemical
characteristics, and the impact of human ac-
tivities. Over 150 tributaries drain the 64,000
square rnile (16.6 x 104 square kilometers) water-
shed. Along with fresh water, the rivers bring
other materials into the Bay: nutrients, sediments,
and toxic substances. Although the Bay has the
ability to assimilate much of this material, most
remains within the estuary. Human activities have
greatly contributed to the input of nutrients, sedi-
ment, and a variety of synthetic chemicals, heavy
metals, and other potential toxicants into
Chesapeake Bay.
Chesapeake Bay has changed greatly since the
time of the first settlers. The delivery of nutrients
to the Bay has increased, reflected by increases
in runoff containing suspended sediment and fer-
tilizers, and sewage effluents. The amount of toxic
materials —heavy metals and organic chemi-
cals—has similarly increased as industrialization
has progressed. Many of these changes occurred
before the first scientific surveys of the Bay. For
that reason, it is sometimes difficult to show strong
recent trends, as the bulk of the change had al-
ready taken place before any data were collected.
Nutrient Enrichment
Nutrients, such as nitrogen and phosphorus,
are essential for plant growth and, thus, for
primary productivity in the estuary. However, in
excess, these nutrients can cause problems, in-
cluding blooms of undesirable algae, reduction in
dissolved oxygen (DO), and decreased water
clarity. Currently, the northern Bay and upper
portions of the tributaries have relatively high
nutrient concentrations; the mid-Bay, lower por-
tions of the tributaries, and eastern embayments
have moderate concentrations of nutrients; and
the lower Bay (where sufficient data exist) appears
to be not enriched. When data from 1950 to 1980
are analyzed, they indicate that, in most areas,
water quality is degrading; that is, nutrient levels
are increasing. Total nitrogen concentrations are
declining in the Patapsco, lower Potomac, and up-
per James Rivers; total phosphorus concentrations
are declining in the upper Potomac River and
throughout the James River. Elsewhere, trends are
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vi Executive Summary
increasing (or stable) for most forms of nutrients,
particularly in the upper and mid-Bay main stem
and larger tributaries.
Dissolved Oxygen Trends
To assess the management implications for
resources of these nutrient trends, it is valuable
to examine a related parameter, dissolved oxygen.
As nutrient levels increase, phytoplankton (algal)
growth is encouraged and more organic matter
is produced. Decay of this organic matter con-
sumes oxygen. If more oxygen is used than is sup-
plied by reaeration or photosynthesis, as often oc-
curs in deep water, the water becomes anoxic (no
oxygen) and devoid of most forms of life except
anaerobic bacteria. This process occurs naturally
in some Bay areas during the summer; however,
high nutrient loads can increase its severity.
Both the chlorophyll a, an indicator of algal
biomass, and the DO trends suggest that the dura-
tion and extent of anoxia have been accelerated
in the Bay in recent years. There were no anoxic
waters and only limited areas of low DO in the
main stem of the Bay during July of 1950. In July
1980, however, a very large area of the main stem
of the Bay was experiencing anoxic conditions. It
is estimated that the volume of water with DO
concentrations equal to or less than 0.7 mg L"1
was 15 times greater in 1980 than in 1950. The
duration of oxygen depletion has also increased.
It was sporadic during the mid-1950's; occurred
from mid-June to mid-August during the 1960's;
and, in 1980, began during the first week in May
and continued into September. This increase in
the spatial and temporal extent of low DO levels
reduces the area of the Bay that can support nor-
mal finfish and shellfish populations.
Organic Compounds in Water and Sediments
Organic compounds can occur naturally; the
ones of major concern are synthetically produced.
The distribution of organic compounds, such as
hydrocarbons, pesticides, and herbicides, in the
bottom sediments and the water column of the
main Bay, and an analysis of limited tributary
data, suggest that organic compounds concentrate
near sources, at river mouths, and in maximum
turbidity areas. The highest concentrations of
organic chemicals in the sediments were found in
the Patapsco and Elizabeth Rivers, exceeding 100
parts per million (ppm) at several locations. In
the main Bay, highest concentrations of organic
substances occur in the northern half. Most
observed sediment concentrations range from 0
to 10 ppm; however, in the upper Bay, some sta-
tions had levels of total organics over 50 ppm.
These general trends suggest that many of the
problem organic compounds in the Bay tend to
adsorb to suspended sediments, and then ac-
cumulate in areas dominated by fine-grained
sediments.
Metal Contamination
Metals are chemical elements which occur
naturally in the environment; however, in excess,
they can become toxic to organisms. Many areas
of the Bay show metal concentrations that are
significantly higher than natural background
levels. The Contamination Index (Cj) was
developed by comparing present concentrations
of cadmium (Cd), copper (Cu), chromium (Cr),
nickel (Ni), lead (Pb), and zinc (Zn) in the Bay's
surface sediments to predicted natural levels from
the weathering of rock in the Bay watershed and
measured pre-colonial levels from sediment cores.
If the present concentration of a given metal ex-
ceeded these natural Chesapeake Bay background
levels, it was considered to be anthropogenically
enriched. The most contaminated sediments are
located in the Patapsco and Elizabeth Rivers, both
heavily industrialized tributaries. Metal concen-
trations up to 100 times greater than natural
background levels were found in these areas. High
levels of metal contamination (Q > 14) were also
found in the upper Potomac, upper James, small
sections of the Rappahannock and York Rivers,
and the upper mid-Bay. Moderate contamination
occurs in the Susquehanna Flats and off the mouth
of the Potomac River. These trends suggest that
higher concentrations are found near industrial
sources and in areas where fine sediments ac-
cumulate, such as in the deep shipping channel
of the upper Bay. In general, there is little move-
ment of metals out of the most contaminated
areas, except when physically transported, as
might occur through movement or disposal of con-
taminated dredge material.
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Executive Summary vii
Significant levels of particulate and dissolved
metals occur in the water column. Concentrations
of particulate Cd, Cr, Cu, Ni, and Zn are greatest
in the upper Bay and near the turbidity maxi-
mum; actual values vary greatly with the tidal
cycle arid the amount of suspended sediment.
High dissolved values, some exceeding EPA water
quality criteria, have been observed, particularly
for Cd, Cu, Ni, and Zn. These high values are
most frequent in areas near industrial sources, and
near upper reaches of the main Bay and western
shore tributaries.
LIVING RESOURCES
Major changes in Bay resources can be iden-
tified, including shifts in the relative abundance
of species or the types of biological communities
found in certain areas. The CBP focussed on in-
dividual living resource groups (e.g., submerged
aquatic vegetation, finfish), describing the
documented trends, and comparing present con-
ditions with the potential status.
Phytoplankton in Two Well-Documented Areas
The upper Bay (above the Bay Bridge) and up-
per Potomac River (tidal-fresh reach) have shown
increased dominance by a single species of phy-
toplankton and increased biomass. Such changes
are considered to be indicative of eutrophication
and, in fact, have paralleled changes in nutrient
enrichment in these areas. These two areas are
those for which the best data are available; similar
changes may be occurring elsewhere, or could be
expected to occur if nutrient enrichment
continues.
The Potomac River's tidal-fresh reach was
characterized in the 1960's and 1970's by massive
blue-green algal blooms, indicators of excess
nutrients. Increased phosphorus control in the
watershed appears to have been beneficial. In
1979, algal populations were diverse, with blue-
greens composing only 25 percent of the total.
Total cell counts (biomass) for 1979 and 1980 were
also considerably lower than in the past.
Trends in nutrient enrichment of the upper
Bay tributaries have closely paralleled those of the
upper Potomac during the 1960's. Massive algal
blooms have been frequently reported in the up-
per main Bay (above the Bay Bridge), with ele-
vated chlorophyll levels caused by increasing
numbers of blue-green algae. By comparison, ob-
servers of this area from 1965 to 1966 reported
only an occasional occurrence of blue-green algae.
It is estimated that cell numbers in this area have
increased approximately 250-fold since 1955.
Decline of Submerged Aquatic Vegetation
Since the late 1960's, a dramatic, Bay-wide
decline has occurred in the distribution and abun-
dance of submerged aquatic vegetation. Loss has
moved progressively down-estuary. Submerged
aquatic vegetation now occupies a significantly
more restricted habitat than at any time during
the past. The role of SAV in the ecosystem has
been reduced; its ability to recover from this cur-
rent status is uncertain. Changes in the distribu-
tion and abundance of Bay waterfowl, which feed
on SAV, have paralleled these vegetation changes.
Annual surveys of SAV conducted by the
Maryland Department of Natural Resources and
the U.S. Fish and Wildlife Service Migratory Bird
and Habitat Research Laboratory have shown
that the number of vegetated stations in Maryland
dropped from 28.5 percent in 1971 to 4.5 percent
in 1982. Species diversity also declined signifi-
cantly. Comparison of the habitat filled in 1978
with the expected habitat shows that the areas of
greatest loss (upper Bay, western shore tributaries,
and upper Eastern Shore tributaries) correspond
with areas of greatest nutrient enrichment.
Changes in Benthic Invertebrates
Benthic animals are considered good indicators
of pollution because most are relatively immobile
and cannot readily escape unfavorable conditions.
Changes in benthic biomass, community struc-
ture, and diversity can indicate a variety of
stressful conditions. Where sufficient data exist,
spatial comparisons were made of current condi-
tions, particularly in the main Bay and in certain
tributaries. Trends in diversity and the relative
abundance of pollution-tolerant annelids were in-
vestigated. In the main Bay, benthic abundance
and diversity seem to be related to physical aspects
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viii Executive Summary
of the environment (i.e., salinity and sediment
type). Highest diversity occurs in the lower Bay.
In some polluted tributaries, especially the Patap-
sco and Elizabeth Rivers, significant declines in
species diversity and enhancement of pollution-
tolerant annelids, relative to molluscs or Crustacea,
are observed. These changes are characteristic of
stressed communities.
Trends in Commercial Shellfish
The density of annual oyster spat set is a
measure of the success of oyster reproduction and
recruitment, and is a reasonable predictor of
oyster harvest. Comparison of the average oyster
spat set for the past ten years with the previous
ten to thirty years shows significant declines in the
upper main Chesapeake Bay and the Chester,
James, Nanticoke, Patuxent, Pocomoke, Potomac,
Rappahannock, and Wicomico Rivers, Eastern
Bay, Fishing Bay, and Pocomoke Sound. In gen-
eral, 1980 was a good year for spat fall, particu-
larly in Eastern Shore tributaries; this fact is
related to high salinities during the spawning
period. Spat set in the upper Chesapeake and its
western tributaries was generally light even in this
good year.
The harvest of oysters for Chesapeake Bay has
declined since 1880, but has remained relatively
stable since 1960 to 1965. This is in part due to
management practices, such as shell and seed
planting. The harvest for the western shore has
decreased significantly during the period from
1962 to 1980; the harvest for the Eastern Shore
increased significantly. This is consistent with the
Eastern Shore's consistently better spat set. For
the Chesapeake Bay as a whole, declines in oyster
harvest have been somewhat offset by an increased
harvest of blue crabs. As a result, the Bay-wide
landings of shellfish have not changed greatly
from 1962 to 1970 and 1970 to 1980. However,
overall shellfish harvest for the western shore has
decreased significantly during this period.
Shifts in Finfish Harvest
The CBP examined trends in harvest and other
indicators (young-of-the-year surveys) for the ma-
jor commercial species historically landed in Ches-
apeake Bay. These include freshwater spawners
such as striped bass, white perch, yellow perch,
catfish, shad, and alewife; marine spawners such
as menhaden, croaker, spot, bluefish, and weak-
fish; and three estuarine forage fish, Bay anchovy,
mummichog, and Atlantic silverside.
The Maryland juvenile index provides consis-
tent data since 1958 for the upper Bay, and the
Nanticoke, Choptank, and Potomac Rivers. Ju-
venile indices of most anadromous and freshwater
species show declines in recent years, with the ex-
ception of the Potomac River where white perch
and yellow perch have increased. Information for
Virginia waters is not directly comparable, be-
cause of differences in methodology and target
species (sciaenids). However, trends in marine-
spawning fish were similar in both data sets.
Marine spawners show general overall increases
in all basins, although some species show declines
in the most recent surveys. In Maryland, mum-
michog shows an increasing pattern similar to that
of marine spawners, while the Bay anchovy and
Atlantic silverside show declines. However, the
anchovy has been increasing in Virginia tributar-
ies surveyed during the same period. This may
reflect differences in water quality or habitat (par-
ticularly the availability of SAV, used as shelter
by this species) between the two states.
Harvests of anadromous and freshwater spe-
cies have declined in Chesapeake Bay. The down-
ward trend in American shad has been continuous
since 1900, while declines in river herring and
striped bass landings have been more recent.
Landings of alewife, shad, and yellow perch are
now at unprecedented low levels. Harvests of
marine spawners, on the other hand, have in-
creased in most areas. Menhaden landings have
risen steadily since 1955; the increase in bluefish
landings has been more recent. The increased
yield of marine spawners and decreased yield of
freshwater spawners represent a major shift in the
proportion of the finfishery accounted for by each
group: during 1881 to 1890 marine spawners ac-
counted for about 75 percent of the fishery; dur-
ing 1971 to 1980 they accounted for 96 percent.
Because freshwater-spawning fish and
estuarine-spawning shellfish spend all or most of
their sensitive life stages in the Bay, their well-
being may be considered as an indication of the
health of the estuary. Thus, the simultaneous
declines in most of these species is reason for
concern.
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Executive Summary
RELATIONSHIPS BETWEEN WATER
AND SEDIMENT QUALITY,
AND LIVING RESOURCES
Organisms respond directly to changes in their
habitat, food supply, competitors, or predators.
Major factors which affect the Bay's living
resources include natural variables such as
freshwater inflow, temperature, or other organ-
isms, as well as human-induced stress such as
nutrient and toxicant enrichment. Distinguishing
between effects triggered by anthropogenic, as op-
posed to natural, causes is often difficult because
of the natural variability of organism distribution
and abundance. Although the CBP was unable
to pinpoint causes for specific resource changes,
the similarity in patterns and the overlap in the
distribution of water or sediment quality and liv-
ing resource trends in the Bay should be consid-
ered as more than a striking coincidence.
Submerged Aquatic Vegetation
The Chesapeake Bay Program supported a
major research effort to identify the causes of the
recent SAV decline. Investigators focussed on two
main hypotheses: (1) the use of toxic agricultural
materials, particularly herbicides, has increased
in recent years. Runoff of these substances from
agricultural areas may be reducing or eliminating
SAV. (2) Reduction in the light available to the
plants because of an increase in water column tur-
bidity or increased growth of epiphytes (or both)
may be causing the decline. Nutrient enrichment
was considered a major factor affecting both tur-
bidity and epiphyte growth. Research sponsored
by the CBP implicated light limitation as the most
important factor regulating the Bay-wide SAV
loss. Herbicides could be important locally, or
close to sources (although areas affected may
represent significant habitat).
The GBP's research conclusions are supported
by field observations. Comparison of a map of
current SAV status to Bay nutrient conditions
reveals that vegetation now occurs primarily in
areas that are not enriched or only moderately
enriched. Statistical analysis (rank correlation)
shows a significant correlation between declines
in SAV and increased nutrient concentrations in
many areas. The major nutrient which appears
to correlate with SAV abundance is nitrogen. A
negative response to maximum chlorophyll a
values, an analog of both nutrient loading and tur-
bidity, was also found. These analyses support ex-
perimental results linking the recent loss of Bay
vegetation to increases ia nutrient loadings and
ultimately to light stress caused by increasing phy-
toplankton biomass and epiphytic growth.
Benthic Organisms
Major anthropogenic factors which could ad-
versely affect benthic organisms in Chesapeake
Bay are toxic materials, either in bed sediments
or in the overlying water column, and nutrients.
Toxicants can produce either acute (elimination
of susceptible species) or sublethal (accumulation
in body tissues) effects. Nutrient enrichment can
alter the Bay's benthic community structure by
stimulating phytoplankton production. Excessive
production of organic material has been linked to
the increased duration and extent of low DO
values in Chesapeake Bay, decreasing available
benthic habitat.
Episodes of low DO have been cited as the ma-
jor factor limiting benthic distribution in deeper
waters of the upper and mid-main Bay. The doc-
umented increase in extent of anoxic water in the
mid-Bay can be related to complete loss of ben-
thic habitat or replacement with ephemeral as-
semblages. This may have secondary impacts on
bottom-feeding predators such as crabs or fish,
which can be stressed by food limitation and
reduction of habitat. Recent changes in the mid-
Bay blue crab fishery, especially the necessity to
set pots in shallower water, may be a direct result
of these anoxic episodes.
Changes in benthic diversity, abundance, and
community structure could be related to toxic con-
tamination of sediments only in areas recognized
as "impacted" (e.g., the Patapsco River and the
Elizabeth River). These areas are characterized
by low benthic diversity and abundance, and
dominance by pollution-tolerant annelids, in com-
parison to non-polluted reference areas. Else-
where, other factors, primarily physical or bio-
logical, are apparently controlling benthic distrib-
utions. However, bioaccumulation of certain me-
tals in tissues of shellfish could be correlated with
enrichment of those metals in the bed sediments,
even in the main Bay.
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Executive Summary
Oysters
Oysters (and other shellfish) are benthic organ-
isms, but because of their commercial importance,
oysters are treated separately here. Factors affect-
ing benthic communities in general (i.e., low DO
water, toxicants in sediments or water column)
will impact oysters as well. In addition, oysters
are potentialy vulnerable to shifts in phytoplank-
ton species brought about by nutrient enrichment.
Phytoplankton species usable as food can be re-
placed by undesirable or inedible forms. Compar-
ison of EPA water quality criteria to measured and
estimated concentrations of toxicants in the water
column revealed a number of violations in the
areas of oyster habitat; these were chiefly for
heavy metals. Although the duration or extent of
high toxicant concentrations is unknown, the ob-
servations may be significant. Some populations
may be more vulnerable than others to diseases
such as MSX or "Dermo." The impact of these pro-
tozoan parasites has increased in recent years
because of higher salinities resulting from drought
conditions.
In addition, oyster habitat may be adversely
impacted by the increased rate of sedimentation
in Chesapeake Bay. Beds may be buried, or spat
set impeded, by deposition of sediment. Loss of
once productive oyster bars in the upper Bay is
probably due in part to sedimentation over the
past 100 years.
Fishery Landings and Juvenile Index
Although total fishery landings have increased
since 1920, the distribution of landings among
species has changed significantly. Anadromous
and other freshwater-spawning fish such as shad
and striped bass have declined greatly; marine
spawners have remained stable or increased. The
finfish juvenile index, a measure of recruitment
success, reflects these changes as well.
Several causes of this change in distribution
have been suggested: (1) nutrient enrichment may
lead to food web shifts, as suggested by changes
in phytoplankton species, primarily affecting early
life stages; (2) the level of toxicants, particularly
heavy metals, pesticides, and chlorine, in major
spawning areas are elevated and, in fact, have ex-
ceeded EPA criteria in some spawning and nursery
areas used by anadromous fish; (3) habitat is be-
ing lost because of increased area of low DO
water; (4) adverse climatic conditions (freshwater
inflow, temperature, etc.) have reduced the
spawning success of anadromous species; (5) over-
fishing is affecting stock sizes; (6) construction of
dams represents a physical obstruction that im-
pedes spawning success of shad and other ana-
dromous species; and (7) modifications of
upstream spawning and nursery habitat, such as
wetlands destruction and stream channelization,
further stresses fishery stocks. It is possible that
all of these factors are contributing to the changes
observed in Chesapeake Bay resources.
STATE OF THE BAY
The Chesapeake Bay Program developed a
numerical ranking system to assess status of cer-
tain water quality and living resource variables
to provide a snapshot of the state of the Bay.
Nutrients, toxic materials, and submerged aquatic
vegetation were used as the primary classification
variables because of their importance and the
completeness of data. Variables were ranked
numerically by Bay segment. Nutrient and toxi-
cant (metal contamination) ranks were summed
to give water and sediment quality status Bay-
wide. Similarly, resource ranks were summed to
assess status according to living resources.
When ranks for water and sediment quality
are aggregated, the following assessment can be
made: the poorest water and sediment quality
now occurs in the upper Bay, upper reaches of
the Potomac and James Rivers, and the Patuxent
River. The lower Potomac and James Rivers, the
mid-Bay, and most of the York and Rappahan-
nock Rivers, and the Eastern Shore tributaries ex-
hibit moderate water and sediment quality. The
lower Bay main stem, Mobjack Bay, Pocomoke
Sound, lower Choptank River, and Eastern Bay
currently have the best water and sediment
quality.
In terms of resource quality, the following
assessment is made: The western shore shows a
general pattern of decline in certain resources. In
fact, the upper Patuxent, lower James, and
Patapsco and Middle Rivers showed poor ranks.
Tangier Sound and the lower and mid-Bay display
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Executive Summary xi
moderate resource quality. The Eastern Shore
generally appears to be the most productive region
of the Bay system. This conclusion is supported
by the regional comparison; Eastern Bay, and the
Choptank and Chester Rivers ranked most
favorably.
When one compares the rank of water qual-
ity to the ranks of living resources, it is evident
that areas with the best resource quality corres-
pond to areas with the best water and sediment
quality (eg., eastern embayments). This suggests
that, to improve the quality of life in the Bay,
water and sediment pollution must be reduced.
Achieving this goal will require the concerted ef-
fort of everyone.
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CONTENTS
Foreword iii
Executive Summary v
Figures xv
Tables ixx
Technical Symbols, Glossary xxi
Introduction 1
Chapter 1: Water and Sediment Quality:
Current Conditions and
Trends 7
Introduction 9
Nutrient Levels and Dissolved
Oxygen 13
Sediment: Sources, Transport, and
Trapping 37
Fecal Coliform Trend Assessment 41
Organic Compounds in the Water
and Sediments 45
Metals in the Water and Sediments 51
Metals and Pesticides in Oysters 61
Summary by Geographic Areas 73
Ranking Chesapeake Bay Program
Segments According to Current
Water Quality Conditions 77
Chapter 2: Living Resources: A History
of Biological Change 81
Introduction 83
Changes in Biomass and Species
Composition of Phytoplankton in
Two Well-Documented Areas . . .
89
The Decline of Submerged Aquatic
Vegetation (SAV) 91
Spatial Trends in Benthic Organisms
99
The Shellfishery: Changes in Oysters
and Crabs 103
Changes in the Finfishery Ill
Synthesis: A Geographical
Assessment 127
Chapter 3: Belationship Between Water
and Sediment Quality, and
Living Resource Trends 131
Introduction 133
Potential Relationships Between
Water Quality and Living Resources 137
Submerged Aquatic Vegetation and
Water Quality 141
Benthic Organisms and Water and
Sediment Quality 151
Oysters and Water and Sediment
Quality 163
Finfish and Water Quality 169
Summary 185
Literature Cited 187
Notes 201
xm
-------
FIGURES
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Rank of Chesapeake Bay
segments according to
concentrations of total
nitrogen
(a) Rank of Chesapeake Bay
segments according to
concentrations of total
phosphorus
22
23
(b) Annual average of total
phosphorus (depth-averaged)
for 1977 to 1980, displayed
by USGS
7 1/2-minute quadrangles . .
Trends in total phosphorus
(IFF and TP) occurring in
any season or annually ....
Trends in total nitrogen or
any other nitrogen form
seasonally or annually ....
Trends in levels of nitrogen
and phosphorus seasonally
or annually
(a) Trends in total phos-
phorus and its inorganic
filterable fraction (IFF) ....
(b) Seasonal trends in total
phosphorus and its inorganic
filterable fraction
Annual trends in total
nitrogen
Annual trends in nitrate
and nitrite nitrogen
Annual and seasonal trends
in chlorophyll a
25
26
27
28
30
30
31
32
33
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Concentrations of bottom
dissolved oxygen for two
years with similar spring
flow
Volume of water in
Chesapeake Bay with low
levels of dissolved oxygen,
1950 to 1980
Shellfish closure areas and
POTW flow (MGD) in
Chesapeake Bay
Concentration of organic
compounds in the Bay's
sediments
34
36
44
46
Annual trends of Kepone
concentrations in bed
sediments compared to the
Kepone production
record
Zinc and chromium concen-
trations down-core com-
pared to natural
background levels
Copper, cadmium, and zinc
enrichment in the Bay
based on the contamination
factor (Cf)
Degree of metal contami-
nation in the Bay based
on the Contamination
Index (Cr)
Average particulate metal
concentrations from five
cruises, March to
September 1979, 1982 . . .
50
54
55
57
58
xv
-------
xvi Figures
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23
Figure 24.
Figure 25.
Figure 26.
Figure 27.
(a) Dissolved metals that
have violated EPA Criteria
(before 1971 to 1975) ............ 59
(b) Dissolved metals that
have violated EPA
criteria since 1975
59
(a) Mean levels of
chromium (mg kg'1) in
oyster tissue .................... 66
(b) Mean levels of arsenic
(mg/kg) in oyster tissue .......... 67
(c) Mean levels of lead
(mg/kg) in oyster tissue .......... 68
(d) Mean levels of mercury
(mg/kg) in oyster tissue .......... 69
(e) Mean levels of zinc
(mg/kg) in oyster tissue .......... 70
(f) Mean levels of copper
(mg/kg) in oyster tissue .......... 71
(g) Mean levels of cadmium
(mg/kg) in oyster tissue .......... 72
Rank of Chesapeake Bay
segments according to
nutrient status .................. 80
NOAA National Marine
Fisheries Service (NMFS)
basins used in living
resources analysis ............... 84
Feeding relationships of
fish in Chesapeake Bay .......... 86
Area of SAV distribution,
1965 and 1980 93
Percent of SAV sampling
locations in Maryland with
vegetation, 1971 to 1981 . .
94
Percent of expected SAV
habitat occupied in 1978 for
aggregated sampling areas 96
Number of specimens of
benthos in Chester River
reference stations and in
three environmental zones
of Baltimore Harbor 100
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39.
Figure 40.
Diversity index of benthic
communities in the Patapsco
and Rhode Rivers
Historical pounds of
shucked oyster meat for
Chesapeake Bay, 1880
to 1981
102
105
Geographic distribution of
spat set on natural oyster
bars in the Maryland por-
tion of Chesapeake Bay in
the fall of 1980
Oyster spat settlement on
natural cultch in the
Potomac River, 1939 to
1980
Historical landings of blue
crabs for Chesapeake
Bay, 1880 to 1981
Historical landings of
menhaden for Chesapeake
Bay, 1880 to 1981
Historical landings of
bluefish for Chesapeake
Bay, 1880 to 1981
Historical landings of
croaker for Chesapeake
Bay, 1880 to 1981
Historical landings of
weakfish for Chesapeake
Bay, 1880 to 1981
Historical changes in the
juvenile index for bluefish
in Chesapeake Bay
Historical landings of
American shad for
Chesapeake Bay, 1880
to 1981
Historical landings of yellow
perch for Chesapeake
Bay, 1880 to 1981
Historical landings of
alewife for Chesapeake
Bay, 1880 to 1981
107
109
110
117
117
118
118
121
122
122
123
-------
Figures xvii
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Historical landings of white
perch for Chesapeake
Bay, 1880 to 1981
Historical landings of
striped bass for Chesapeake
Bay, 1880 to 1981
123
124
Historical changes in the
juvenile index for striped
bass in Northern Chesa-
peake Bay, and the
Potomac, Choptank, and
Nanticoke Rivers
Simplified trophic diagram
showing a pathway from
phytoplankton to finfish . .
(a) General area of SAV
distribution in 1965 . . . .
(b) General area of SAV
distribution in 1980
Current status of nutrients
in Chesapeake Bay
(a) Percent total vegetation
compared with mean total
nitrate in the Susquehanna
Flats, CB-1
(b) Percent total vegetation
compared with mean
chlorophyll a of previous
year in EE-1, 1971 to 1981
(c) SAV and Nutrients
125
134
144
144
145
146
146
150
Figure 48.
Figure 49.
Figure 50.
Figure 51.
Figure 52.
Figure 53.
Figure 54.
Diversity index (d) of
benthic communities in the
Patapsco and Rhode Rivers .
Contamination of Patapsco
River and Baltimore Harbor
sediments with heavy metals
and organic chemicals
Density of Leptochierus
plumulosus in Patapsco
and Rhode Rivers
154
155
156
Percent survivorship of the
amphipod, Rhepoxynium
abronius compared with the
contamination factor for
nickel
Historical pounds of
shucked oyster meat for
Chesapeake Bay, 1980 to
1981
Extent of anoxic bottom
water in the main stem of
Chesapeake Bay in
1950 and 1980
157
164
174
Observed and predicted
juvenile indices for (a)
striped bass in the Potomac
River and (b) spot in the
Choptank River base on
models derived from mul-
tiple regression analysis . . .
180
-------
TABLES
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Sources and Effects of
Pollutants
Relation between Organic
Material, Nutrients, and
Potential Oxygen Demand . . .
Comparison of DO Concen-
trations over Depth at CBI
Station 848E, March 20, 1980
to May 21, 1980
Classification of Chesapeake
Bay Water Using Total
Nitrogen and Total
Phosphorus
10
16
17
18
Depth-Averaged Four-Year
Means of All Years From 1977
to 1980 of Total Nitrogen and
Total Phosphorus for All Bay
Segments Meeting Minimum
Data C riteria
19
Mean Values of Total
Nitrogen and Total
Phosphorus in Bay Segments
Where Insufficient Recent
Data Exist to Compute
Annual Means
Ranking of Bay Segments
According to Nutrient
Concentrations
Relationship Between Capa-
city and Inflow Ratio, and
Percent Sediment Trapped
Sediment Trapping Efficiency
of Chesapeake Bay Tributaries
20
21
38
39
Tables 10 Student Newman-Keuls Test
through of Mean Fecal Coliform
12. Levels (MPN) for Western
and Eastern Shore Tributaries .
Table 13. Seasonal Kepone Water
Column Concentrations in
James River, 1976 to 1978 . . .
Table 14. Comparison of Mean Dis-
solved Metal Content in
Susquehanna River Water,
Bay Water, and Ocean Water
42, 43
49
Table 15.
Table 16.
FDA Action Levels for
Shellfish and Finfish .
53
62
Classification of Mean Metal
Concentrations (mg/kg) in
Oyster Tissues Based on
Cluster Analysis
Table 17. Ranking GBP Segments
According to Selected Present
Water Quality Conditions . . .
Table 18.
Table 19.
Major Species of SAV in
Chesapeake Bay
63, 64
78, 79
...91
Range of Annelid.-Mollusc
Values for Chesapeake Bay
Segments
100
Table 20. Species Diversity, Redun-
dancy, Annelid: Moll use, and
Annelid:Crustacean Ratios
Along a Gradient of Pollution
in the Patapsco River
Table 21. Oyster Harvest for 1962 to
1970 and 1971 to 1980,
Annual Mean
101
104
-------
xx Tables
Table 22. Trends in Means of Oyster
Spat Set for the Period 1938
to 1980, Comparing Past to
Pre-1970 Spat Set
Table 23. Crab Harvest for 1962 to
1970 and 1971 to 1980,
Annual Mean
Table 24.
Table 25.
Principal Commercial Finfish
Species in Chesapeake Bay
Unit Area Finfish Landings
for Chesapeake Bay, 1881 to
1980, Annual Mean by Decade
Table 26. Correspondence of Finfish
Juvenile Index and Finfish
Landings for Chesapeake Bay
(1958 to 1980)
106
108
111
Table 27. Landings for Marine-
Spawning Finfish, Annual
Average for 1962 to 1970 and
1971 to 1980
Table 28. Comparison of 1971 to 1981
Annual Mean Juvenile Indices
with 1958 to 1970 Annual
Means
Table 29. Landings for Freshwater-
Spawning Finfish, Annual
Average for 1962 to 1970 and
1971 to 1980
Table 30. Summary of Segment Ranks .
Table 31. Results of Linear Regression
Analysis of Water Quality
Variables Against Submerged
Aquatic Vegetation
116
119
120
126
129
147
Table 32. Spearman Rank Correlation
Coefficient Results for
Submerged Aquatic Vegeta-
tion Against Water Quality
Variables
Table 33. Diversity, Redundancy, and
Species Number for Patapsco
and Rhode River Stations . . .
Table 34. Area of Chesapeake Bay Bot-
tom Affected by Low DO
Waters in Summer
115 Table 35.
Mixture of Contaminants
Causing Lethal and Sublethal
Effects in Larval Striped Bass
Suggested Levels of Protection
for Selected Groups of Finfish
Summary of Oxygen
Tolerance Data Involving
Principal Chesapeake Bay
Species
Table 36.
Table 37.
Table 38. Volume of Water Affected by
Reduced Oxygen Concentrations
Table 39. Period of Utilization of Deep
Water by Ecologically and
Commercially Important
Species of Finfish and Blue
Crabs
Table 40. Result of Linear Regression
Analysis of Juvenile Finfish
Index Against Air
Temperature
149
158
161
170
172
173
175
Table 41.
Relationship Between Juvenile
Index and Freshwater Flow . .
176
178
179
-------
TECHNICAL SYMBOLS and GLOSSARY
Ag silver
Al aluminum
As arsenic
ATP adenosine triphosphate
Cd cadmium
Co cobalt
Cr chromium
Cu copper
DO dissolved oxygen
Fe iron
Hg mercury
IFF inorganic filterable fraction
JTU Jackson turbidity unit
m meter
mg milligram
MGD millions of gallons per day
ug L"1 microgram per liter
ml L"1 milliliter per liter
mg L"1 milligram per liter
Mn manganese
Mo molybdenum
MPN most probable number
MSX Minchinia nelsoni, a sporozoan, also
name given to disease in oysters caused
by this sporozoan
ng nanogram (one billionth of one gram)
NHa ammonia
Ni nickel
NO2 nitrite
NOs nitrate
PAH polynuclear aromatic hydrocarbon
PAR photosynthetically active radiation
Pb lead
PCB polychlorinated biphenyl
POTW publicly owned treatment work
ppb parts per billion
ppm parts per million
SAV submerged aquatic vegetation
Sc scandium
Si silicon
TKN total Kjeldahl nitrogen
TN total nitrogen
TP total phosphorus
U uranium
Zn zinc
arenacious
bioturbation
calcareous
depth averaged
diagenesis
hypoxia
isopleth
oxycline
210Pb profiles
planimetry
sciaenid
having shell or test constructed of
sand grains, as of foraminifera
the disturbance of the environ-
ment (i.e., bottom sediments)
through biologic activity
of, like, or containing calcium
carbonate, calcium, or lime
arithmetic average of two or
more samples taken at different
depths
physical and chemical changes
occurring to sediments during
and after the period of decom-
position up until the time of
consolidation
containing low levels of oxygen,
as in water or body tissues
the line connecting points on a
graph or map that have equal
values with regard to certain
variables
region of relatively rapid change
in dissolved oxygen concentration
with depth, usually dividing up-
per well-oxygenated waters from
lower poorly oxygenated waters
radioactivity of the lead 210
isotope in sediments, with depth
the measuring of the areas of
plane forms
any of a family of mostly
saltwater fishes, including drums
and croakers, that make drum-
ming or rumbling sounds
xxi
-------
INTRODUCTION
Characterizing an environment, that is, pull-
ing together data in a way that identifies func-
tional relationships between various components
of an ecosystem, is a management tool used by
many resource managers. The concept stems from
a growing knowledge that man's utilization of the
environment brings about major, yet often subtle,
changes in how the system works. An extensive
series of coastal characterizations is presently be-
ing done by the U.S. Fish and Wildlife Service.
Other groups that have used this approach with
great success include the International Joint Com-
mission on the Great Lakes and the Thames Water
Authority in Great Britain. Several partial
assessments have been done on Chesapeake Bay
(Croniri 1983, Lippson 1979, McErlean et al.
1972, Mackiernan et al. 1982, Mihursky et al.,
1981, Shea et al. 1980, U.S. Army Corps of
Engineers 1973, U.S. Army Corps of Engineers
1975). Although these studies begin to describe
ecological interactions within the Bay, the picture
is incomplete. An important tool for expanding
the existing ecological information on the Bay is
an assessment of trends in water quality and of
how living resources have changed over time.
Characterizing the quality of the Chesapeake
Bay water and sediment, and changes in re-
sources, began as a response to the Chesapeake
Bay Program's (GBP) 1976 Congressional direc-
tive. According to the mandate, principal factors
altering the Bay's quality were to be addressed.
As part of this assessment, a set of analyses was
used allowing a description of the Bay's water
quality and living resources and how these have
changed over the past 25 years to be developed.
This characterization provides more than a
description and synthesis of information, however;
it also tries to link changes occurring in the Bay
to potential causes. For example, one analysis at-
tempts to relate nutrient concentrations in various
areas to the abundance of Bay grasses living there.
Making such potential linkages will help us bet-
ter understand resource changes that may occur
in water receiving nutrients or other pollutants.
Effective strategies to control pollutants can then
be developed.
Characterization has produced additional
benefits for water quality managers. Segmenta-
tion, the division of the Bay into regions with
similar features, allows data to be logically
assembled, mapped, and classified. It allows us
to assess past and present conditions and to com-
pare trends in various regions (Appendix A). In
addition, the understanding we have gained of
water quality processes and their relationships to
resources will help shape the program's recom-
mended monitoring strategies. Finally, character-
ization has identified gaps in information and,
thus, points to methods for improving future data
collection.
The Program tried to approach characteriza-
tion from a viewpoint that stresses the understand-
ing of the Bay as an ecosystem. The Chesapeake
ecosystem possesses many individual components
linked through a variety of physical, chemical,
and biological processes. Benthic communities, for
example, are closely linked to the sediment en-
vironment and processes while anadromous fish
depend on tidal freshwater spawning areas. Be-
cause of these interrelationships, the individual
components can complement one another to
maintain functioning of this ecological system.
However, these links also allow effects of pertur-
bations, such as pollution, to be proliferated
through the system.
Although this ecosystem view tells us not to
-------
Introduction
Segments of Chesapeake Bay and Their Principal Characteristics
Segment
Tidal-fresh reaches
Ches Bay N, (CB-1)
Up PatuxentfTF-1)
Up Potomac (TF-2)
Up. Rapp (TF-3)
Up. York (TF-4)
Up James (TF-5)
Transition zones
Up Bay (CB-2)
Patuxent(RET-l)
Potomac (RET-2)
Rapp (RET-3)
York (RET-4)
James (RET-5)
Characteristics
• dominated by freshwater inflow
of the river system
• spawning areas for anadromous
and semi-anadromous fish
• resident habitat for freshwater
fish
• dominated by freshwater plank-
ton and aquatic vegetation
• slight salinity (3-9 ppt, mean)
influence
• zones of maximum turbidity
where suspended sediment
causes light limitation of
phytoplankton production
most of the year
• areas are valuable sediment
traps, concentrating material
associated with sediments in-
cluding absorbed toxic
chemicals
Lower estuarine reaches
Up C. Bay (CB-3)
L Patuxent(LE-l)
L Potomac (LE-2)
L Rapp, (LE-3)
L York (LE-4)
L James (LE-5)
Sec W Tnbu (WT-1-
E S Tnbu (ET-1-10)
Lower Main Bay
Chesapeake Bay
Lower Central
(CB-4)
Chesapeake Bay
South (CB-5)
Chesapeake Bay
General West (CB-6)
Chesapeake Bay
General East [CB-7)
Chesapeake Bay
Mouth (CB-8)
• upstream limit of deep water
anoxia
• moderate salinity (7-13 ppt,
mean)
• two-layer, estuarine circulation
driven primarily by freshwater
inflow
• weaker estuarine circulation
characterized by limited
flow/flushing characteristics
• water quality controlled by the
density structure of the main
stem of the Bay at the tributary
mouth
• water deeper than 30' usually
experiences oxygen depletion
in summer—can be toxic to fish,
crabs, shellfish and benthic
animals
• mean salinity of 9 to 14 ppt
• rich in nutrients
• influenced by inflow from
Potomac and Patuxent and rich
in nutrients
• mean salinity of 10 to 17 ppt
• subject to summer anoxia and
contains most of the deeper Bay
waters
• net southward flow
• mean salinity of 14 to 21 ppt
• net northward flow
• mean salinity ot 19 to 24 ppt
• net southeastward flow
• mean salinity of 19 to 23 ppt
Embayments
E Bay (EE-1)
L Chopfank (EE-2)
Tangier Sound (EE-3)
Mobjack Bay (WE-4)
p have salinities similar to
adjacent Bay waters
• shallow enough to permit light
penetration for submerged
aquatic vegetation growth
' influenced strongly by wind
patterns
Estuaries have a capacity to assimilate waste before
experiencing significant ecological damage, but, this
ability can vary dramatically from one area to another To
assess water quality of areas with similar characteristics
the CBP divided the Bay into regions, or segments using
natural processes such as circulation and salinity These 45
segments were used as a framework to map and
evaluate past and present conditions of Chesapeake Bay
-------
Introduction
ignore the many other components while assess-
ing the condition of one, certain assumptions were
made to approach the task practically. First, it
was assumed that areas with similar physical and
chemical characteristics will behave similarly.
This allowed a comparison of trends and responses
in similar segments. It was also assumed that in-
formation gained from simple systems, such as
laboratory microcosms, can be related to the
natural environments of the Bay (with proper cau-
tion) . Furthermore, the limitations of available
data were recognized and, consequently, so were
uncertainties of some of the analyses. Sometimes,
data were compared that were not collected at
the same time or place, or for the same purposes.
Nor were the effects of human intervention always
separated from natural variability in the analyses.
In interpreting results, only statements from
a narrow historical standpoint —a slash of the
Bay's history —can be made. As the chart shows,
many aspects of the Bay's environment had
already been altered significantly by the time
scientific monitoring and research began. The
metal supply to Chesapeake Bay, for example,
began to increase considerably about the time of
the Civil War, peaking shortly after World War
II. This suggests that some benthic communities
have been exposed to higher-than-natural levels
of certain metals for over 50 years or more.
Changes in land-use, including clearing of forest
for farmland, had been significant by the
mid-1800's. Sedimentation rate had increased
greatly over the same time span. Increased sedi-
ment and nutrient loads caused alterations in
species dominance, abundance of diatoms, and
in submerged aquatic vegetation (SAV). A reduc-
tion in clean-water diatom populations in the
1800's was the first clear signal that nutrient
enrichment of the upper Bay was occurring.
Recognizing the sense of the ecosystem
perspective as well as the limitations imposed by
practicality, the Program set out to determine pre-
sent conditions and trends in about 45 areas of the
Bay. The CBP tried to assess what had created
those conditions. A great deal of present and
historical data were collected for statistical
analysis (Appendix A contains a summary of
statistical analyses). From that point, current con-
ditions and trends in each segment, or groups of
segments, were looked at, and hypotheses link-
ing the trends in water quality to those observed
in resources were set forth. Where enough infor-
mation was available, some cause-and-effect rela-
tionships in the Bay are explained, and others sug-
gested. Where possible, the portion of the cause
that is most likely human-related is shown.
The following report is organized into three
main chapters with several appendices contain-
ing most of the support material used in the
characterization process. The first chapter
characterizes the Bay's water and sediment quality
using nutrients, dissolved oxygen, fecal coliform
levels, metals, and organic compounds. The se-
cond chapter looks at changes in abundance of the
Bay's major resources, including phytoplankton,
submerged aquatic vegetation, benthic inverte-
brates, shellfish, and finfish. The final chapter
shows what linkages exist between the water
quality parameters and resoures, particularly of
submerged vegetation, benthic organisms, and
shellfish.
In overview, this report provides a framework
for the widest application of Program results. A
list of all of the products and their relationship
to the characterization report includes:
• Forty final reports on individual research
projects with summaries of each report
(listed in Appendix A).
• Chesapeake Bay: Introduction to an
Ecosystem explains important ecological
relationships and serves as a reference for
the synthesis report, the characterization
report, and the CBP management
alternatives.
• Chesapeake Bay Program Technical
Studies: A Synthesis summarizes and ex-
plains the technical knowledge gained from
the research projects funded by this pro-
gram in the areas of nutrient enrichment,
toxic substances, and submerged aquatic
vegetation. It provides an understanding of
the processes that affect the quality of
Chesapeake Bay.
• Chesapeake Bay: A Framework for Action
identifies control alternatives for
agriculture, sewage treatment plants, in-
dustry, urban runoff, and construction;
estimates costs and effectiveness of different
approaches to remedy environmental
problems.
-------
Introduction
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-------
Introduction 5
For scientists, resource managers, and inter- and the management report. Just as the synthesis
ested public, Chesapeake Bay Program: A Profile papers provide a sound technical foundation for
of Environmental Change bridges the gap be- the GBP's characterization process, this volume
tween the technical, scientific results as presented provides information from which to develop man-
in the 40 final reports and the synthesis papers, agement options as presented in the final report.
-------
CHAPTER 1
WATER AND SEDIMENT QUALITY:
CURRENT CONDITIONS
AND TRENDS
-------
SECTION 1
INTRODUCTION
CHARACTERIZING WATER
AND SEDIMENT QUALITY
Water quality can be described as the extent
to which water can support aquatic life and meet
standards for various human uses. Water quality
depends in part on the individual capability of a
body of water to assimilate various pollutants. For
an estuary such as the Chesapeake, assimilative
capacity depends on the types and amounts of
riverine pollutants (Table 1), and on biogeo-
chemical processes in the Bay. When the Bay's
assimilative capacity is stressed or exceeded, water
and sediment quality can deteriorate. Aquatic life
and man's use of the Bay can, in turn, be affected.
Rivers and streams entering the Bay carry both
life-supporting materials and pollutants. They
carry direct-waste discharges as well as nutrients
and other chemicals draining from urban and
agricultural lands of the watershed. Many of the
chemicals brought into the Bay are necessary to
biological processes; however, in excess they cause
problems. For example, nutrients such as nitrogen
and phosphorus are needed by aquatic plants, but
if they occur in high concentrations, noxious algal
blooms may occur. Populations of useful plankton
species and submerged aquatic vegetation may be
reduced as a consequence. As the algae decay,
they consume oxygen in the water. If more ox-
ygen is consumed than biologically produced by
photosynthesis or made available through reaera-
tion arid mixing, the water becomes anoxic and
devoid of most forms of life. In addition to
nutrients, disease-carrying agents or pathogens
may be associated with land runoff and sewage
treatment plant discharges. Organic chemicals,
heavy metals, and other toxicants from point
source discharges, land runoff, and atmospheric
pollution eventually enter the Bay. Once in the
estuary, these substances follow a variety of fates,
including entrapment in the sediments and up-
take by estuarine organisms.
Two major objectives of the Chesapeake Bay
Program (CBP) were to characterize the present
(1980) water quality in Chesapeake Bay system
and to identify long-term water quality trends in
the historical data base. In the sections that
follow, present conditions and trends in nutrients,
dissolved oxygen, fecal coliforms, organic com-
pounds, and metals, and how these factors may
affect the quality of the Bay's waters and sedi-
ments are discussed. The Program is cautious,
however, in some of the interpretations expressed,
especially changes noted in many of the small
tributaries and embayments where data are few,
concentrated in short time intervals, or do not
cover enough years to establish a firm trend. Ad-
ditionally, various sorts of water quality data were
rarely collected at the same time or place. Thus,
present conditions and trends are based on data
integrated within segment boundaries. For more
than one-half of the segments, the 1980 data were
inadequate so that 'present conditions' were deter-
mined using information from 1977 to 1980.
These difficulties are compounded when the
historical (1950 to 1980) data are analyzed for
trends. First, some analytical methods have
changed over time, usually resulting in greater
sensitivity and reliability in recent years. Few in-
vestigators have actually compared current and
past methods to quantify the differences in results
that each gives. Second, few, if any, laboratories
have cross-calibrated their analytical and sample-
handling procedures to determine that all obtain
the same numerical results on the same samples.
Third, the temporal and spatial distribution of
-------
10 Chapter 1: Water and Sediment Quality
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Introduction
11
data are quite patchy during the 30-year period
considered by the GBP. Even in years where data
density is generally high, the cold months are
usually poorly represented. Annual means are thus
skewed toward the warmer months, and processes
that allow nutrients to accumulate in the water
during winter for utilization in spring cannot be
clearly identified. Fourth, it is difficult and
sometimes impossible to apply the most desirable
statistical analyses to identify trends (e.g., time-
series analysis). These shortcomings not with-
standing, an attempt at trend analysis yielded
some interesting and useful results for analyses
done in larger areas of the Bay.
-------
SECTION 2
NUTRIENT LEVELS AND DISSOLVED OXYGEN
INTRODUCTION
This section presents data on seasonal and
spatial trends in a number of water quality
variables over time. Ten water quality parameters
were considered in this assessment: orthophos-
phate, total phosphorus, total Kjeldahl nitrogen
(TKN), nitrate (NOs), nitrite (NO2), ammonium,
total nitrogen (TN), chlorophyll a, (uncorrected
for phaeophytin), dissolved oxygen (DO), and tur-
bidity. The uncorrected chlorophyll a data were
used because numerically they dominate the
chlorophyll a data base, particularly in earlier
years. Annual and seasonal trends in each variable
were evaluated. Some of the nutrients, notably
orthophosphate, NO2, NOs, and ammonium,
usually exist at very low concentrations in the
water column because of uptake by microbial
organisms (including bacteria, phytoplankton,
and small heterotrophic forms). For this reason,
total phosphorus (TP) and TN concentrations
(which include amounts present in phytoplankton)
are often better indicators of trophic conditions
than the somewhat ephemeral soluble nutrient
concentrations. Exceptions exist for NOs, especi-
ally in spring, and for the other nutrients in areas
of the Bay system near the fall line or near major
point sources. Total Kjeldahl nitrogen measures
most, but not all, organic nitrogen and includes
virtually all of the living and detrital particulate
nitrogen as well as the soluble ammonium nitro-
gen. A general discussion of nutrient processes and
effects can be found in Chesapeake Bay: Introduc-
tion to an Ecosystem (U.S. EPA 1982a).
In this section, present conditions and histor-
ical trends in nutrients and other water quality
parameters are defined in terms of concentrations.
Measured concentrations are actually the net
result of several interacting factors, including
basin topography, freshwater inflow, water cir-
culation patterns (which influence residence
time), nutrient and sediment loading rates, and
many biological and chemical processes. The con-
centration changes measured over time are related
to the dynamic balance among these interacting
components. If a particular trend in nutrient con-
centrations suggests that the system is changing,
then the processes influencing the concentrations
in each segment should be evaluated when con-
trols are considered. These processes (input rates,
recycling, settling, flow) are discussed in detail
in the series of synthesis papers produced by the
Chesapeake Bay Program (U.S. EPA 1982b).
DATA ANALYSIS AND TREND ASSESSMENT
The present condition of the Bay was deter-
mined using an average of the annual means of
the four most recent years —1977 through 1980.
The following criteria were applied in calculating
these means: at least three observations of each
parameter were needed in each month of each
year to calculate a monthly mean; a minimum of
two monthly means were necessary to calculate
a seasonal mean; and two seasonal means were
needed to produce an annual mean. This pro-
cedure ensures at least a minimum adequacy of
data before characterizing each segment of the
Bay. Also, by averaging over a period of four years
where data are available, the effect of year to year
variability of freshwater inflow is reduced.
Trends were established by use of Pearson's
correlation of each parameter over time that in-
cluded all data in the CBP computer data base.
The data were determined to have a significant
13
-------
14 Chapter 1: Water and Sediment Quality
trend if the coefficient (r) was associated with an
alpha level equal to, or less than 0.05. Analysis
employed the same criteria as described above for
current conditions.
Only statistically significant relationships were
used in the assessment of water quality trends in
each segment. For this evaluation, we considered
in an initial screen that if any one nutrient showed
increasing concentrations over time, the overall
water quality of that Bay segment should be ex-
amined further. A more thorough assessment re-
quires a measure of total nutrient content (i.e.,
TN and TP). Based on present nutrient status (i.e.,
TN and TP), as well as potential oxygen demand,
Bay segments were ranked to determine present
conditions Bay-wide. The results of these assess-
ments are summarized below.
In addition to nutrients, the problem of in-
creased phytoplankton biomass (as reflected in
chlorophyll a values) and decreased DO in deeper
waters of the estuary is addressed. Both these
parameters can be related to nutrient enrichment,
and both have implications for the integrity of the
Bay ecosystem.
The data concerning current conditions and
historical trends for nutrients and dissolved oxygen
are tabluated and discussed further in Appendix B.
Nutrients and Phytoplankton
When the amount of nutrients delivered to a
water body increases, the first and most obvious
response is often an increase in phytoplankton
biomass. This is frequently observed in lakes; in
flowing-water systems, physical dispersion may
prevent build up of phytoplankton standing crop.
Grazing by herbivores may also reduce algal bio-
mass, as long as dominant phytoplankton species
remain usable by consumers. In freshwater areas,
proliferation of inedible blue-green algae has led
to serious water quality problems. Buildup of
organic material — either from algal biomass or in-
directly through deposition of zooplankton fecal
material —produces an oxygen demand in affected
water. Areas with high photoplankton biomass
(i.e., high chlorophyll a values) sometimes exhibit
elevated amounts of diurnal DO from algal photo-
synthesis, followed by extremely low nighttime
DO levels (Clark and Roesch 1978). Reduction in
oxygen results from algal respiration and bacterial
oxidation of organic material.
Growth of phytoplankton and potential bio-
mass depends on the availability of certain
chemical nutrients —primarily phosphorus and
nitrogen, but sometimes silica or carbon — as well
as light, temperature, and other physical vari-
ables. Nutrients are utilized in certain (atom to
atom) ratios that reflect the chemical composition
of the organic material produced. If one of the
nutrients is missing, or is in short supply, or if light
levels or temperature are at sub-optimum levels,
then phytoplankton growth is limited by that
factor —even if the remaining factors are abun-
dant or favorable.
The concept that a single nutrient usually
limits phytoplankton standing crop (biomass) is
commonly used in water quality management.
This is useful because it simplifies the application
of nutrient controls. In fresh waters, phosphorus
is most often the limiting nutrient (that is, the
nutrient in shortest supply), so management strat-
egies can conveniently focus on phosphorus con-
trol. However, this management concept may not
apply to the Bay system as a whole. In the oceans,
nitrogen is usually considered the most limiting
nutrient, but as yet there is little concern over
managing nutrient inputs to the ocean.
The Chesapeake Bay estuary lies between
freshwater and the ocean, so we might expect it
to have characteristics of both environments. In-
deed, it appears that when and where riverine
influence dominates, the Bay tends to be
phosphorus-limited. When and where the oceanic
influence dominates, the Bay is nitrogen-limited.
In addition, low light and temperature may over-
ride the influence of nutrients in winter. In the
upper reaches of the Bay and tributaries during
the summer, turbidity can produce light-limited
conditions.
Estimates of annual nitrogen and phosphorus
inputs were compared with annual phytoplankton
production in a variety of estuarine systems (which
included data from mid-Chesapeake Bay and the
Patuxent River) (Boynton et al. 1982). A rea-
sonable relationship was identified between
loading and production for nitrogen (r2 = 0.60) but
not for phosphorus (r2 = 0.08). Boynton et al. con-
cluded that nitrogen dynamics are more impor-
tant than those of phosphorus in regulating
estuarine phytoplankton production.
-------
Nutrient Levels and Dissolved Oxygen 15
At an October 1982 GBP workshop on limiting
factors in the Bay, scientists generally agreed on
the following points:
• The best assessment is that phosphorus con-
trols phytoplankton biomass yield in tidal-
freshwater and low-salinity areas
throughout the warm season; nitrogen con-
trols phytoplankton biomass yield during
the summer in higher-salinity waters. The
controlling influence is probably not
uniform over all higher-salinity areas of the
Bay and tidal tributaries. In cold months,
light and temperature are often limiting.
Light is also important in turbid areas.
• Low soluble and particulate nitrogen to
phosphorus (N to P) ratios suggest poten-
tial nitrogen limitation; these are typically
observed during the summer in mesohaline
reaches.
• In the Calvert Cliffs area, an approximate
linear relationship exists between nitrogen
loading from the Susquehanna River and
both primary productivity and chlorophyll
a., the same relationship does not occur with
phosphorus (Boynton et al. 1982).
• Phosphorus, in particular, and probably
nitrogen, play a minor role in controlling
the specific growth rate of phytoplankton
(as opposed to potential biomass). Impor-
tant here are species-specific nutrient up-
take characteristics in relation to ambient
nutrient conditions or production of en-
zymes such as alkaline phosphatase or
nitrate reductase; this has been determined
from dose-response experiments and field
observations.
• Physical dispersion influences biomass yield
in the Bay. Where dispersion is high,
biomass does not accumulate, although pro-
duction of organic material may be large.
• The decrease in magnitude of the spring
bloom and increase in the temporal extent
of the summer bloom in the upper Bay in-
dicate a shift from nutrient limitation to
nutrient saturation of phytoplankton in
Jiummer.
• Denitrification and nitrification may be im-
portant cycling and loss mechanisms for
nitrogen in the upper estuary (Kemp et al.
1982d, Seitzinger et al. 1980).
Upstream processes can affect the transport of
nutrients downstream and their concentration
there. Particularly in spring, when freshwater in-
flow is high, residence time of water in the upper
Bay is short. Nutrients delivered there are not used
completely, but are passed through to downstream
areas. This "pulse" of spring nutrients, primarily
NOa, can be detected well into the mesohaline
reaches of the estuary (D'Elia 1982, Taft et al.
1982). Results from both modeling and field
studies indicate that reducing phosphorus inputs
to tidal freshwater regions may allow propor-
tionally more nitrogen to pass through the tidal-
fresh regions into the saline waters. This occurs
because as phosphorus is reduced, less phytoplank-
ton biomass is produced, and less nitrogen is re-
quired for growth. So, rather than settling out as
particulate organic material, the soluble nitrogen
(primarily NOs) continues downstream for poten-
tial utilization in the higher salinity reaches (Taft
et al. 1978). Although reduction in riverine
phosphorus loads could theoretically be offset by
rapid recycling of this nutrient within the upper
estuary, the short residence times would actually
allow much of the nitrogen to pass downstream.
In this way, the single nutrient strategy for
phosphorus removal may actually allow more
nitrogen delivery to downstream reaches that are
usually nitrogen-limited. Increased available in-
organic nitrogen will support increases in produc-
tion of organic nitrogen and carbon in the mid-
Bay. This in turn will result in larger biological
oxygen demands in these areas.
OXYGEN DEMAND AND NUTRIENTS
One principal result of nutrient enrichment
of concern to managers is the oxygen demand
created by increased production of organic
material. When organic matter is decomposed by
bacterial action, oxygen is used. Decomposition
of large amounts of organic matter can result in
loss of dissolved oxygen in the water (sometimes
complete anoxia occurs). Criteria describing the
current condition of the Chesapeake Bay system
are related to nutrient levels and corresponding
potential oxygen demand. For the simplest case,
planktonic organic material and its oxidation can
-------
16 Chapter 1: Water and Sediment Quality
be represented, after Richards (1965), by the
following formula:
(CH2O)io6 (NHsJie H3PO4 + 138 Oa =>
Organic Material
106 CO2 + 122 H2O + 16 HNOs + H3PO4
Remineralized Nutrients
The coefficients in this relationship are
multiplied by the atomic weights of the
elements to obtain the masses involved. That
is, for nitrogen, 16 times the atomic weight of
14 gives 224 mass units, and, for oxygen, 138
times 32 gives 4416 mass units. Converting to
milligrams (mg) shows that planktonic organic
material containing 0.224 mg nitrogen would
require 4.42 mg oxygen for complete degrada-
tion, giving a ratio of 19.7 mg oxygen used for
every 1 mg nitrogen oxidized.
This relation between organic material and
the oxygen required for its complete mineraliza-
tion was used to construct a table of potential ox-
ygen concentrations and organic material concen-
trations expressed in terms of carbon, nitrogen,
and phosphorus (Table 2). The table is entered
with a nutrient concentration value: for example,
0.035 mg P L'1 represents a potential oxygen de-
mand by organic material of 5 mg. Thus, a satura-
tion DO concentration of 7 mg L"1 would be
reduced by 5 mg to 2 mg L"1 if all of the organic
material associated with 0.035 mg P L"1 were
oxidized. The potential oxygen demand is ex-
pressed as mg rather than mg L"1 because, in some
cases, the potential demand is much greater than
the actual saturation oxygen concentration. Ox-
ygen demand in excess of available dissolved ox-
ygen will lead to the production of toxic hydrogen
sulfide (HsS).
If this approach is carried further, a total
nitrogen concentration of 0.75 mg L"1 and a total
phosphorus concentration of 0.105 mg L"1 would
have a potential oxygen demand of 15 mg oxygen
L"1. However, expected oxygen saturation values
at salinities and temperatures typical of upper Bay
deep waters are only 12.5 mg L"1 oxygen in March
and 9.5 mg L"1 in May. Thus, if total nitrogen
concentrations are maintained near 0.75 mg L"1
in the upper Bay, the potential oxygen demand
exceeds the available oxygen.
This simple approach relating nutrient levels
to oxygen demand does not account for either
reaeration of the water from the atmosphere or
TABLE 2.
RELATION BETWEEN ORGANIC MATERIAL,
NUTRIENTS, AND POTENTIAL OXYGEN DEMAND
0,28
1.40
2.80
4.20
5.60
7.00
8.40
9.80
11,20
12.60
Organic Material Oxidized
(mg L-1)
N
0.05
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2,00
2,25
0.007
0.035
0.070
0.105
0.140
0,175
0.210
0.245
0.280
0.315
Potential Oxygen Demand
(mg)
1
5
10
15
20
25
30
35
40
45
-------
Nutrient Levels and Dissolved Oxygen 17
steady accumulation of organic material in deep
water (which can increase oxygen demand). Re-
aeration of the water column is a function of both
diffusion and mixing; aeration of bottom water
is reduced when strong vertical stratification ex-
ists, as occurs during warm months in much of
the Bay. The net result of these interacting pro-
cesses can be seen in the 1980 data set for
Chesapeake Bay Institute (CBI) station 848E (off
the Rhode River), where deep-water oxygen con-
centrations were about 10 mg L"1 (7.0 ml L"1) in
March and zero in May 1980 at all sampled depths
below llm (Table 3). Of the total oxygen loss,
a decrease of 3 mg L"1 was caused by temperature
and salinity effects on oxygen solubility. Loss of
the remaining 7 mg L"1 was due to biological and
chemical oxidation reactions. If the above rela-
tionship is applied, this 7 mg L'1 oxygen loss is
due to the oxidation of organic material contain-
ing 0.35 mg L"1 nitrogen.
This concept relating nutrients, organic
material, and potential oxygen demand may be
extended into a classification scheme for
Chesapeake Bay and its tributaries. The classifica-
tion scheme helps define a range of uses that are
compatible with a given number of environmen-
tal factors. A relative ranking of the Bay segments
was developed based on nutrient concentrations
of TN and TP; using the above formula, the po-
tential oxygen demand for that level of nutrients
was also estimated. Table 4 assigns class 1 through
6 to total nitrogen and total phosphorus concen-
tration ranges observed in the Chesapeake Bay
Program data base. Class 1 is envisioned as a
relatively pristine situation (uninfluenced by
human intervention) and class 6 is the most
enriched.
The issue arises as to the appropriateness of
using nutrient trends to assess water quality, ver-
sus chlorophyll a or oxygen. In light of the rela-
tionship between nutrient loadings, plankton
growth, and dissolved oxygen levels, a Bay-wide
assessment using the nutrient data base was made.
This relationship is reinforced by observed trends
in deep-water DO concentrations at selected sta-
tions in the Bay, and in observed changes in phy-
toplankton biomass.
SEASONAL PATTERNS OF NUTRIENTS
AND DISSOLVED OXYGEN
When data from the last four years are com-
pared, seasonal nutrient concentrations for 1978
are generally the highest recorded; those for 1980
TABLE 3.
COMPARISON OF DO CONCENTRATIONS OVER DEPTH AT CBI STATION 848E
MARCH 20, 1980 TO MAY 21, 1980. (FROM CRONIN ET AL. 1982)
March 20, 1980
Depth
(m)
0.0
4.0
8.0
10,0
12,0
16.0
32,0
DO
mg L~1
8.52
8.29
8.19
7,00
5,65
Oxygen
saturation
percent
102.28
99.32
98.08
82.63
66.12
May 21, 1980
Depth
(m)
0.0
4.0
8.0
10.0
12.0
16.0
30.0
DO
mg L~1
5.65
5.39
4.44
0.59
0.00
0.00
0,00
Oxygen
saturation
percent
86.94
84.87
69.96
9.17
0.00
0.00
0,00
-------
18 Chapter 1: Water and Sediment Quality
TABLE 4.
CLASSIFICATION OF CHESAPEAKE BAY WATER USING TOTAL NITROGEN (TN)
AND TOTAL PHOSPHORUS (TP)
Class TN
mg L~1
1 0 -0,40
2 0.41-0,60
3 0,61-0,80
4 0.81-1,00
5 1.01-1.75
6 1.76 +
TP
mg L~1
0 -0.056
0.057-0.084
0.085-0.112
0.113-0.140
0.141-0.245
0.246 +
Potential
DO Demand
mg
8
12
16
20
35
36 +
are frequently the lowest (Appendix B, Section 8,
Table 38). This illustrates the importance of non-
point sources of nutrients and the impact of rain-
fall on nutrient loadings; 1978 was a wet year,
and 1980 a dry year.
When seasonal trends in nutrient concentra-
tions are examined, a general pattern results. In
the mid to upper Bay (CB-1-3), the tidal-fresh
reaches of the Potomac, Rappahannock, York,
and James Rivers (TF 1-5), and the mid-Potomac
(RET-2) (the segments chosen for this analysis),
total phosphorus concentrations usually increase
from spring to summer, then decrease through the
fall and winter. Reduced nonpoint source loads,
utilization of phosphorus by phytoplankton, and
losses of particulate P to the sediments may ac-
count for these reductions. Increase in concentra-
tions from spring to summer may be due to re-
mineralization of phosphorus from bottom
sediment.
Annual and seasonal nitrogen concentrations
are inversely related to phosphorus concentrations
in most areas: that is, increasing phosphorus con-
centrations are generally associated with decreas-
ing nitrogen concentrations; decreasing phos-
phorus concentrations are generally associated
with increasing nitrogen concentrations. For ex-
ample, distinct increases in phosphorus concen-
trations from spring to summer are associated with
decreases in nitrogen concentrations during the
same period. In CB-2, CB-3, and TF-2, for ex-
ample, low seasonal phosphorus concentrations
observed for 1980 are associated with relatively
high nitrogen concentrations for the same period.
The reasons for this phenomenon may be two-
fold: in tidal-fresh areas, this may reflect the
reduced uptake of nitrogen by phytoplankton that
occurs when the amount of the limiting nutrient
available (phosphorus) is decreased. Down-
estuary, large nitrogen concentrations associated
with a spring freshet may be reduced by phyto-
plankton uptake and decreased nonpoint source
loadings in summer. Concentrations increase
again in the fall when the photosynthetic demand
for nitrogen is reduced, and the nonpoint source
contribution of nitrogen increases with greater
runoff. The importance of losses of particulate
nitrogen to the sediments or of nitrification (and
loss to the atmosphere) are not known.
The greatest range in phosphorus concentra-
tions and the largest values generally occur in the
spring. This probably reflects varying intensity of
the spring freshet and the importance of nonpoint
sources. Total nitrogen concentrations are at their
lowest during summer. Low summer total
nitrogen concentrations may be attributed to an
increased demand for nitrogen coupled with a
decreased supply from nonpoint sources during
this time of increased primary productivity and
reduced rainfall. The pattern for NOs and NO2
differs from that of ammonium (NHs) and TKN.
Inorganic nitrogen (NOa and NOs) declines from
spring to summer, then increases through fall to
a high in winter, reflecting patterns of loading and
-------
Nutrient Levels and Dissolved Oxygen 19
decreased phytoplankton utilization. Concentra-
tions of NHa and TKN are low at all seasons and
show relatively little seasonal variablility.
Phytoplankton utilization probably accounts for
most of the use of NHs. The smallest range in
phosphorus concentrations generally occurs in the
fall. Reduced ranges in concentration during the
fall indicate more stable conditions. Influence of
erratic runoff from nonpoint sources in spring is
reduced, but steady point source load continues
in all seasons. The tidal-fresh areas of the upper
tributaries are where publicly owned treatment
works (POTWs) and industries are concentrated,
and they account for a significant portion of
phosphorus load (58 percent) to the Chesapeake
Bay tidal system (U.S. EPA 1983).
The Patuxent River is a special case; in all
seasons, highest nutrient concentrations are found
in the tidal-fresh portion of the river. There is a
direct (as opposed to inverse) relationship between
phosphorus and nitrogen concentrations; both in-
crease throughout the year and then decrease from
fall to winter. This reflects the importance of
POTW loadings in this river, particularly during
seasons when runoff is reduced.
In general, chlorophyll concentrations increase
from spring to summer, except in lower Bay areas.
Values in the fall are also often high, similar to
or slightly below that of summer. Not unexpected-
ly, chlorophyll a concentrations are lowest in
winter.
Dissolved oxygen shows a typical pattern,
reflecting effects of temperature, salinity, and
biological processes. Values are highest in winter,
declining through spring to summer lows, and
then increasing through fall to winter.
PRESENT STATUS AND TRENDS OF
NUTRIENTS AND DISSOLVED OXYGEN
Present Status
Depth-averaged means for TN and TP, for all
data from the years 1977 to 1980, are given in
Table 5 for all segments where data meet
TABLE 5.
DEPTH-AVERAGED MEANS OF ALL YEARS FROM 1977 to 1980 OF TOTAL NITROGEN (TN)
AND TOTAL PHOSPHORUS (TP) FOR ALL BAY SEGMENTS MEETING DATA MINIMUM CRITERIA.
NOTE: SOME MEANS REPRESENT FEWER THAN FOUR YEARS (rt = YEARS REPRESENTED IN MEANS)
Segment TN
CB-1
CB-2
CB-3
CB-4
CB-5
WT-2
n
TP
n
1.508
1240
1,261
0,923
0.970
1.456
2
4
4
3
3
1
0.094
0.109
0.095
0.078
0.065
0.062
3
4
4
4
3
1
WT-5
WT-6
WT-8
TF-'I
RET-1
LE-'I
TF-2
RET-2
LE-2
1.790
0.570
0.803
2.188
1,041
0,959
0.666
1.208
0.515
3
1
1
2
1
1
4
4
1
0,110
0.076
0.100
0.420
0.147
0.126
0.140
0.131
0.062
3
1
1
2
2
1
4
4
2
Segment TN
n
TP
n
TF-3
RET-3
LE-3
TF-4
RET-4
LE-4
TF-5
0.916
0.556
0.563
0.617
—
—
1.138
2
1
1
2
—
—
1
0.151
0.109
0.078
0.123
—
0.085
0.184
2
2
2
2
—
2
2
LE-5
ET-2
ET-4
ET-5
ET-6
ET-7
ET-10
EE-1
EE-3
0,624
1,229
0,909
1.09
1.066
1.440
0.942
0.589
0,696
2
1
2
2
1
1
1
1
1
0.101
0.101
0.178
0.106
0.081
0.132
0.090
0.091
0,064
2
A
2
2
1
1
1
1
1
-------
20 Chapter 1: Water and Sediment Quality
minimum criteria. Four-year annual and seasonal
means for all water quality variables are tabulated
and included in Appendix B, Section 8, Tables 35
to 38. It should be noted that some segments lack-
ing TN or TP information have data for other
forms of nitrogen or phosphorus. It was sometimes
necessary to use these data in assessing nutrient
trends in such areas. For comparative purposes,
TN and TP concentrations in segments with in-
complete data (i.e., not recent or not meeting
minimum criteria to compute annual means) are
included in Table 6.
When Bay segments are ranked on the basis
of TN and TP, according to the system discussed
previously, the following assessment can be made:
upper and mid-Bay, main stem, upper western
shore tributaries, tidal-fresh reaches, and some
riverine-estuarine transition zones of major
tributaries have total nitrogen concentrations that
are characteristic of class 5 or 6 water (Table 7
and Figure 1). Total phosphorus concentrations
characteristic of class 5 and 6 waters tend to oc-
cur in upper reaches of major western shore
tributaries. Water quality generally improves
down-estuary and down-tributary to class 3 or 4.
Eastern embayments (EE segments) and small
western shore tributaries south of the Patapsco
River also have relatively low ambient nutrient
concentrations, class 3 or 2 for both nitrogen and
phosphorus (Table 7 and Figure 2a). Insufficient
TN and TP data exist to rank the Virginia main
Bay segments (CB-6, 7, and 8); the few observa-
tions available, however, are low.
Chlorophyll concentrations, a measure of phy-
toplankton biomass, have a pattern similar to that
of nutrients: higher in the upper Bay, tidal-fresh,
and transition areas of major tributaries, and in
certain smaller western shore tributaries than in
TABLE 6.
MEAN VALUES OF TOTAL NITROGEN (TN) AND TOTAL PHOSPHORUS (TP) IN BAY SEGMENTS
WHERE INSUFFICIENT RECENT DATA EXIST TO COMPUTE ANNUAL MEANS.
YEAR AND MONTH(S) WHEN DATA WERE COLLECTED ARE INDICATED.
Segment
CB-7
EE-2
ET-1
ET-3
ET-8
ET-9
RET-4
RET-5
WE-4
WT-1
WT-4
WT-7
LE-4
TN
TP
Date
0.008
0,57
100
0.744
0.672
0.734
0.593
0.566
1015
1128
0.60
120
5.32
0.454
1347
0.568
0.064
0.07
0.070
0.091
0.081
0.051
0.172
0.114
0.106
0.119
0.06
0.066
0.050
0.368
0,069
0.077
0.084
1979, months 2, 8
1976, months 5, 6, 8
1976, mean of spring and summer
1977, months 6, 8
1979, summer
1976, month 7
1976 month 7
1979, months 3, 4, 6
1978, months 7, 8
1979, months 7, 9
1978, months 7, 8
1976, month 9
1977, months 4, 7
1978, month 5
1977, summer
1980, summer
1976, 1977, June mean
1977, summer
1978, winter
1978, months 7, 9
-------
Nutrient Levels and Dissolved Oxygen 21
TABLE 7.
PRESENT RANK OF CHESAPEAKE BAY SEGMENTS ACCORDING TO NUTRIENT CONCENTRATIONS
BASED ON DEPTH-AVERAGED MEANS OF 1977 TO 1980 (TABLE 4).
RANKS ASSIGNED ON THE BASIS OF INCOMPLETE DATA ARE INDICATED WITH AN ASTERISK (')
Segment
CB-1
CB-2
CB-3
CB-4
CB-5
CB-6
CB-7
CB-8
WT-1
WT-2
WT-3
WT-4
WT-5
WT-6
\VT-7
WT-8
EE-1
EE-2
EE-3
ET-1
ET-2
ET-3
ET-4
ET-5
TN
5
5
5
4
4
ND
1*
ND
5*
5
ND
6*
6
2
2
3
2
2*
3
4'
5
3*
4
5
TP
3
3
3
2
2
ND
ND
ND
2*
2
ND
6*
3
2
2*
3
3
2'
2
2*
3
2*
5
3
Segment
WE-4
TF-1
RET-1
LE-1
TF-2
RET-2
LE-2
TF-3
RET-3
LE-3
TF-4
RET-4
LE-4
TF-5
RET-5
LE-5
ET-6
ET-75
ET-8
ET-9
ET-10
TN
2*
6
5
4
5
5
2
4
2
2
3
2*
2*
5
5*
3
5
4
3*
3*
4
TP
2'
6
5
4
4
4
2
5
3
2
4
3
3
5
5*
3
2
2*
2*
3
the more saline regions (Appendix B, Section 8).
Summer chlorophyll levels are typically higher
than in spring, except in CB-4 and 5, which show
a pronounced spring bloom pattern. Data from
1979 show that the same cycle occurs in CB-7.
Heinle et al. (1980) suggest that it is useful to con-
sider three levels of chlorophyll a concentrations
in the Bay: <30 ug L'1 (low); 30 to 60 ug L'1
(medium); and >60 ug L"1 (high). There is in-
sufficient information in CB-6 and 8 to assess cur-
rent conditions or phytoplankton biomass cycles.
Analysis of measured spring and summer
Jackson turbidity unit (JTU) and Secchi disk mea-
surements taken since 1960 in the tidal-fresh and
lower estuarine portions of the major western
tributaries and main Bay segments CB-1 through
CB-4 does not reveal any trend in water clarity
from year to year. However, there does appear
to be a recent change in seasonal water clarity.
For the most part, pre-1972 JTU measurements
indicate that more turbid conditions exist in spring
than summer. More recent JTU measurements
-------
22 Chapter 1: Water and Sediment Quality
Lowest
Concentrations
Highest
Concentrations
Limited
Data
FIGURE 1.
Present rank of Chesapeake Bay
segments according to concentrations of
total nitrogen, based on depth-averaged
means of I977 to I980 (Table 4). Class I
represents lowest concentrations; class 6,
highest.
-------
Nutrient Levels and Dissolved Oxygen 23
Lowest
Concentrations
Highest
Concentrations
Limited Data
FIGURE 2a.
Present rank of Chesapeake Bay
segments according to concentrations of
lotal phosphorus, based on depth-
averaged means of I977 to I980 [Table 4).
Class 2 represents lowest concentrations
of TP; class 6, highest.
-------
24 Chapter 1: Water and Sediment Quality
and Secchi disk measurements, however, indicate
more turbid conditions in summer than spring.
The increased turbidity in summer waters may
reflect increased algal growth reducing water
clarity and light transmission.
Tidal-fresh areas are generally more turbid
than lower estuary areas. The tidal-fresh Patux-
ent was the most turbid; the lower Potomac was
the least turbid of all areas examined. There are
very little data in the Rappahannock and York
Rivers.
The present conditions of the Bay for nutrients
and chlorophyll a are assessed based on partial
spatial coverage within any segment. To provide
a better idea of the extent of spatial coverage, as
an example, a map of the depth-aver aged cover-
age of annual means (1977 to 1980) for total
phosphorus displayed by USGS 7 1/2-minute
quadrangle (Figure 2b) is shown. Maps of total
nitrogen (depth-aver aged) and surface concentra-
tions of chlorophyll a (i.e., < 10 m) are shown for
annual, spring, and summer means for 1977 to
1980 in Appendix B (Section 8).
Nutrient Trends
Nutrient trends were examined for increases
or decreases over the period of record. (Note: this
differs from current status that included data from
1977 to 1980.) Most data on nitrogen and phos-
phorus distribution began in 1964 with a few
studies occurring in the late 1930's (Newcombe
and Brust 1940, Newcombe and Lang 1939, Nash
1947). Chlorophyll a (uncorrected for decomposi-
tion products), an index of phytoplankton stand-
ing crop, is included in this assessment. Earliest
data on chlorophyll a were collected in the 1950s.
Trends in nitrogen and phosphorus were
evaluated to see if any form of these nutrients
showed a statistically significant change over time
at an alpha level equal to, or less than 0.05, using
Pearson correlation. Trends are summarized in
Appendix B (Tables 40 and 41). Sample sizes of
less than 5 were excluded in the analysis. This sim-
ple screening approach was judged to be a useful
starting point but, as discussed later, a more
meaningful assessment requires an estimate of the
total nutrients (i.e., TN and TP). A case can be
made for the inclusion of silica, a key constituent
of diatoms, in the trend assessment, but historical
data are poorly represented in the data base
(D'Elia et al. 1983).
Initially the data were examined for trends
occurring during any season or annually. For this
screening assessment, we described phosphorus by
both its inorganic filterable fraction (IFF) and TP;
the latter includes particulate and dissolved
organic fractions as well as IFF. In theory, the
IFF is immediately available to phytoplankton;
the organic forms can undergo remineralization
and eventually become available to phytoplank-
ton. Concentrations are averaged throughout the
water column because mixing can eventually
bring phosphorus at depth in contact with
phytoplankton. Several regions of the main Bay,
such as CB-1, 2, 3, and 5, Tangier Sound (EE-3),
and a few segments in some tributaries, showed
an increase in TP or IFF during one or more
seasons (Figure 3). Segments that showed only a
decreasing trend are also represented. The
decreasing trends in the James River estuary, the
upper tidal freshwater Potomac River, and mid-
Bay in Maryland (CB-4) are notable.
Similar to phosphorus, nitrogen was examined
in the screening mode; nitrogen is described in
terms of inorganic forms, NHs, NO2, NOs, and
TKN, which includes organic nitrogen and
ammonia-nitrogen. The sum of these components
is TN after accounting for the free ammonia in
the TKN component. Examination of nitrogen
trends in a screening mode showed an increasing
trend in either TN or in any form of nitrogen
seasonally in the following segments: CB 1-4,
ET-2, ET-4, ET-6, ET-7, TF-1, LE-1, TF-2,
RET-2, LE-2, and TF-4 (Figure 4). A decreasing
trend, not accompanied by any increasing trends,
occurred only in the Patapsco River (WT-5), the
Northeast River, and the James River estuary
(TF-5 and LE-5).
Trends in both nitrogen and phosphorus were
considered together, with any increasing trend in
any form taking precedence over a decreasing
trend. With that assessment, most segments show
an increasing trend in at least one nutrient type
(Figure 5).
However, an assessment based on trends in in-
dividual nutrient forms (e.g., IFF or NOs-
nitrogen) is not a straight-forward procedure. The
increase or decrease in IFF or NOs is not necessar-
ily a rigorous index of an improving or degrading
-------
Nutrient Levels and Dissolved Oxygen 25
TP< =0.042
0.042 0.245
Limited
data
FIGURE 2b
Annual average of total phosphorus
(depth-averaged) for I977 to I960
displayed by USGS 7 1/2-minute
quandrangles.
-------
26 Chapter 1: Water and Sediment Quality
FIGURE 3.
Trends in phosphorus (IPF and TP) occurr
ing in any season or annually.
-------
Nutrient Levels and Dissolved Oxygen 27
Increase
Decrease
No trend
Limited data
FIGURE 4.
Trends in TN or in any other nitrogen form
seasonally or annually.
-------
28 Chapter 1: Water and Sediment Quality
FIGURE 5.
Trends in levels of nitrogen and
phosphorus seasonally or annually
-------
Nutrient Levels and Dissolved Oxygen 29
water quality situation. Nitrate can increase as a
consequence of nitrification, a microbial process,
while the TN may remain unchanged. Organic
nitrogen can decrease in concentration through
natural remineralization processes or upgraded
sewage treatment processes with a subsequent in-
crease in NOs. However, depending on the
relative change, the total nitrogen concentration
may actually decrease. In a similar vein, organic
phosphorus may decrease while IFF shows an in-
crease. Thus, it is desirable to have a measure of
the total nutrient content (i.e., TN, TP) for an
ecological assessment. Unfortunately, the nutrient
data base in the Chesapeake Bay and tidal tribu-
taries is relatively poorly characterized in terms
of these total forms. This should be addressed in
future monitoring activities.
It is probably more biologically meaningful
to examine trends in individual nutrient fractions
because of differences in availability and
preference for phytoplankton. Individual trends
in total phosphorus and IFF are summarized in
Figure 6a. Annual changes (representing at least
two significant seasonal trends) show an increas-
ing trend in CB-1, CB-2, and CB-5 and a decreas-
ing trend in the tidal Potomac (TF-2). Note that
relatively few segments are represented, compared
to results from the less constrained screening ap-
proach. Quite a few segments showed no signifi-
cant trends, although samples were sufficient for
statistical analysis (Appendix B, Section 8).
Seasonal changes are shown in Figure 6b.
Eight segments show an increase in IFF for one
or more seasons: the lower Potomac (LE-2), mid-
Patuxent (RET-2), lower Rappahannock (LE-3),
mid-Rappahannock (RET-3), and several eastern
shore segments. Only in three cases were sig-
nificant increasing trends noted for TP and IFF
in the same segments (CB-1, 2, and 5). Segment
TF-2 showed a decreasing trend in both. Similar
relationships between TP and IFF may occur else-
where, but either the data were insufficient or
trends were not statistically significant. The
screening approach and results from the in-
dividual annual and seasonal trends compare
favorably when IFF and TP are given equal
weight (Figures 3 and 6). However, as pointed out
earlier, TP is believed to be a more reliable in-
dicator of phosphorus enrichment or reduction.
The lack of TN data limits a more thorough
assessment of trends in nitrogen. Figure 7 shows
an increasing annual trend in TN for ET-4, TF-1,
and LE-3; TN decreased in LE-2, TF-5, ET-1,
and ET-7. So few segments have sufficient TN
data, that little annual comparison can be made
among segments. Annually, NOs and NO2 showed
an increasing trend in CB-1, 2, and 3, ET-2, 4,
6 and 7, TF-1, 2, RET-2, and LE-2 (Figure 8).
Some of these segments showed a decreasing an-
nual trend in TKN and ammonia (Appendix B,
Section 8, Table 40) and increasing trends in NOs.
This may result from nitrification processes in use
at sewage treatment plants, i.e., the upper tidal
Potomac (TF-2). Seasonal trends in nitrogen are
spatially complex since both increasing and
decreasing trends were observed for the various
forms of nitrogen in some segments in different
seasons (Appendix B, Section 8, Table 40).
Figure 9 shows the combination of annual and
seasonal trends in chlorophyll a. Annual seasonal
trends were mapped, and a segment showing an
increasing trend took precedence over any
decreasing trends. This criterion showed that most
of the main Bay segments experience increasing
levels of chlorophyll a. There is a general correla-
tion between increasing trends in chlorophyll a
and segments showing an increasing trend in one
or more nutrients.
It has been known for many years that there
is an annual cycle of oxygen concentration in
many Bay waters deeper than 9 to 11 meters (Taft
et al. 1980). Low DO has been recorded from
Chesapeake Bay since 1917; in September 1912,
bottom water in the lower estuarine portion of the
Potomac River was less than 35 percent saturated
with oxygen (<2.0 ml L'1) (Sale and Skinner
1917). However, during the same period of time,
bottom water between Annapolis and Hampton
Roads was over 60 percent saturated. Off the
Patuxent, bottom water at 10 meters was 100 per-
cent saturated in late September 1912. Newcombe
et al. (1939) reported low dissolved oxygen in the
Patuxent River and also in the Bay main stem at
two deep stations, for 1937, and for parts of 1936
and 1939. In 1936 and 1937, dissolved oxygen
reached 0 ml L"1 in August, although it was over
1.0 ml L"1 for most of the year (Figure 10). When
compared to the oxygen regime for 1980, a year
with similar spring freshwater inflows of 1937, it
becomes apparent that presently the onset and
-------
30 Chapter 1: Water and Sediment Quality
DDDD
"D
D
00-
JC =-
Q-c
in k
O .2
—
DC O O
Fn D --
^2 O «
u_ co ±:
•o
c
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51
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c ^=
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DDDD
S^.9
^ a a
§ § 9>
O c o
-------
Nutrient Levels and Dissolved Oxygen 31
FIGURE 7,
Annual trends in total nitrogen
-------
32 Chapter 1: Water and Sediment Quality
FIGURE 8.
Annual trends in nitrate and nitrite
nitrogen.
-------
Nutrient Levels and Dissolved Oxygen 33
FIGURE 9.
Annual and seasonal trends in chlorophyll a
-------
34 Chapter 1: Water and Sediment Quality
;>
-
O
CO
0
^
O
u>
0
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c
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I
o
,,_•) |uu ue6Axo
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-------
Nutrient Levels and Dissolved Oxygen 35
duration of anoxia are much greater. These two
stations (station 1 of Newcombe, 818 P of CBI)
are very close together, and it is reasonable to
assume similar responses of DO at each.
During winter this lower layer is well oxygen-
ated, but the normal reduction in water mixing
rates, which occurs in spring and summer, results
in oxygen being used faster in the deep water than
it is replenished from the atmosphere. The result
is oxygen depletion to levels that will not support
typical Bay biota. There appears to be a change
in this normal cyclic behavior, based on oxygen
data collected by Chesapeake Bay Institute over
a period of 30 years. As indicated in Figure 11,
the volume of water with DO concentrations
equal to or less than 0.7 mg L"1 (0.5 ml L"1) was
15 times greater in 1980 than in 1950. On a Bay-
wide basis, oxygen depletion seems to be increas-
ing over time. In the mid-1950's, it was sporadic
in intensity and extent. In the 1960's, oxygen
depletion occurred from mid-June to mid-August
for each year recorded with relatively complete
data. During the 1970's, duration and extent of
low dissolved oxygen generally continued to in-
crease. In 1980, low DO began during the first
week in May and continued into September. In
addition, the presence of hydrogen sulfide, an in-
dicator of complete anoxia, has been observed
more frequently in the 1970's and 1980's than
previously. This trend could result from increas-
ed organic material in the deep layer available to
consume oxygen during its degradation, or from
lower DO concentrations in the surface layer that
influence the oxygen gradient, or from both. The
DO data shown in Figure 11 were examined to
see if the trend would likely result from antece-
dent conditions of wind and tides. The tentative
conclusion is that the observed concentrations of
DO and calculated volumes of water character-
ized by low DO levels are not related to the
antecedent conditions of wind and tide. It is now
inferred that the low levels of DO are related to
increasing nutrient loads. A more thorough an-
alysis of the dissolved oxygen trends is included
in Appendix B, Section 5.
-------
36 Chapter 1; Water and Sediment Quality
o
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-------
SECTION 3
SEDIMENT: SOURCES, TRANSPORT, AND TRAPPING
Sources and amounts of sediments to
Chesapeake Bay, where they are transported, and
how they are trapped, can affect the quality of
the estuary. Sediments are introduced into the Bay
by rivers, shore erosion, the sea and biological ac-
tivity. The patterns of erosion, deposition, and
sediment composition depend on circulation pat-
terns, water depth, erosion, and local conditions.
Additionally, agricultural and urban activities
have increased the susceptibility of the land to ero-
sion and contributed additional particulate mat-
ter. Physical and chemical processes of the Bay
prevent much of the sediment from leaving the
estuary, and many of the sub-estuaries become ef-
ficient sediment traps.
The physical and chemical characteristics of
bottom sediments and the patterns of erosion and
deposition have been measured and mapped by
the CBP for both the Maryland and Virginia por-
tions of the main Bay (Byrne et al. 1982, Kerhin
et al. 1982). The most northern part of the Bay
is composed of clayey silt and mixed sediment.
The remainder of the northern Bay is dominated
by sand along near-shore zones and by silty clay
in the deeper axial channel. Most researchers have
concluded that the prime source of this suspended
sediment is the Susquehanna River, especially dur-
ing storm conditions and flooding. Overall, the
southern Bay contains coarser sediments. Some
silty clays are contributed from the northern Bay,
but the influence of the Bay mouth is significantly
greater. The patterns of sand and clayey silt sug-
gest that the Bay mouth is the major source of the
larger sand and silt-sized material. Scouring of
geologically older sediments and shoreline erosion
are other minor sources of sandy material.
Major erosion and deposition zones have been
identified throughout the main stem of the Bay.
For example, there is an extensive area of Bay floor
erosion from Kent Island south to the mouth of
the Rappahannock River (segments CB-4, 5). Fur-
thermore, it can be seen that throughout the Bay,
at the confluence of major tributaries, the patterns
of erosion and deposition are highly variable. This
is due to the overall circulation patterns, mixing
effects, and density differences of the waters.
Once sediment enters the Bay, its distribution
is primarily influenced by the circulation pattern.
Bedload material brought in by the rivers moves
seaward with the freshwater discharge and is
deposited where reversing tidal currents are first
encountered. Thus, sediment tends to accumulate
between the upstream (flood) and downstream
(ebb) limit of salt intrusion (i.e., the landward-
flowing lower layer). Suspended material brought
into the Bay and its tributaries is carried seaward
in the upper layer until it either mixes or settles
downward into the lower layer that flows back
up the estuary. Because of this process and the
mixing that occurs between the upper and lower
layers, suspended sediments tend to accumulate
in an area between the tidal-fresh and lower-
estuarine segments of the Bay, producing a zone
of maximum turbidity. These riverine- estuarine-
transition areas are characterized by large salin-
ity ranges and high turbidities (low Secchi values)
as compared to the adjoining segments (Appen-
dix B, Section 1).
An understanding of the distribution of
suspended sediment in the Bay is critical to any
evaluation of the environmental quality of the
Bay. High levels of suspended material in the
water column inhibit the light penetration
necessary for the growth of aquatic plants. Fur-
37
-------
38 Chapter 1: Water and Sediment Quality
thermore, toxic substances tend to concentrate in
turbid areas for most metals, and organic com-
pounds tend to adsorb to the sediments in the
physical and chemical conditions typical of
estuaries. Under varying flow conditions, this
"suspended sediment front" will shift upstream or
downstream. For a further discussion of the pro-
cesses involved, see Chesapeake Bay Program
Technical Studies: A Synthesis (U.S. EPA 1982b).
In light of these physical and chemical pro-
cesses, it is improbable that much of the sediment
introduced into the Bay escapes to the sea. Fur-
thermore, studies have shown that several of the
Bay's sub-estuaries are efficient sediment traps.
Using a box model approach, Biggs (1970) deter-
mined that approximately 75 percent of the sedi-
ment introduced to northern Chesapeake Bay was
trapped between the Susquehanna River and the
Bay Bridge. Yarbro et al. (1981) have also used
the box model approach for the Choptank and
found that 89 percent of the total suspended solids
remain trapped in the Choptank River. Nichols
and Thompson (1973), using historical shoaling
rates for the Rappahannock, concluded that over
90 percent of the suspended sediment from runoff
was trapped in the upper reaches of the estuary.
These findings suggest that probably most of the
sub-estuaries of Chesapeake Bay trap sediment
very efficiently.
To develop a Bay-wide assessment of sediment
trapping efficiency, water resource engineers used
a technique to predict the useful life of a reser-
voir before it fills with sediment. Using field data
collected on various reservoirs, they have devel-
oped a curve depicting the relationship between
the percent sediment trapped and the ratio of the
TABLE 8.
RELATIONSHIP BETWEEN CAPACITY
AND INFLOW RATIO,
AND PERCENT SEDIMENT TRAPPED
Capacity and
Inflow Ratio
0.02
0.03
0.07
0.1
0,2
0,3
0.5-10
Percent
Sediment Trapped
60
70
80-85
85-90
90-95
95
95-100
reservoir volume to the inflow of water (Linsley
and Franzini 1972). The median curve for nor-
mal reservoirs indicates a general relationship
shown in Table 8 between the capacity and in-
flow ratio as well as the percent sediment trapped.
To apply this technique to Chesapeake Bay
tributaries, a tidewater volume to potential inflow
ratio was used for each of the tributaries (Table
9). This procedure established that the Pamunkey
and Mattaponi Rivers have the lowest sediment
trapping efficiency, and Eastern Bay and the
Honga River have the highest sediment trapping
efficiency. Based on these calculations, it is
reasonable to assume that all of the sub-estuaries
of Chesapeake Bay efficiently trap sediments and
their associated toxic compounds.
-------
Sediment: Sources, Transport, and Trapping 39
TABLE 9.
SEDIMENT TRAPPING EFFICIENCY OF
CHESAPEAKE BAY TRIBUTARIES
BASED ON THEIR TIDEWATER VOLUME TO
POTENTIAL INFLOW RATIO
(DATA FROM SEITZ 1971 AND CRONIN 1971)
Potential
Tributary Inflow Ratio
I. Tributaries with 80 to 85 percent trapping
efficiency:
Pamunky 0.07
Mattaponi 0.07
II. Tributaries with 90 to 95 percent trapping
efficiency:
Gunpowder 0,02
Sassafras 0.02
James 0.02
Northeast River 0.03
York 0.04
III. Tributaries with 95 to 100 percent trapping
efficiency:
Elk 1 *
Bush 0,5
Potomac* 0.5*
Rhode 0.6
Rappahannock* 0.7
Patuxent* 0,8
Patapsco 0.8
Back 1,0
South 1
West 1
Wicomico 1
Piankatank 1
Pocomoke Sound 1.5
Middle 15
Chester* 2
Magothy 2
Severn 2
Miles 2
Choptank* 2 *
Tangier Sound 2
Mobjack 3
Lower Choptank 3
Honga 5
Eastern Bay 6
"Sediment trapping efficiency has been cal-
culated associated with sediments.
-------
SECTION 4
FECAL COLIFORM TREND ASSESSMENT
INTRODUCTION
Microbiological indicators such as coliform
bacteria are used to estimate the potential
presence of viruses and pathogenic bacteria and,
thereby, the safety of water for contact recrea-
tion and shellfish harvesting. Thus, fecal coliform
concentrations are considered an indication of
microbiological water quality and can be used in
characterizing segments of the Bay. A major use
of fecal coliform data is in determining shellfish
closure; areas (discussed below). Some bacteria are
indigenous to natural waters; others gain access
from land, air, or human and animal wastes. Ma-
jor nonpoint sources of coliform bacteria are
decomposing organic materials and animal wastes
that are deposited on land or in feedlots and barn-
yards. Large concentrations of waterfowl may
also be an important source. Nonpoint source
runoff washes large numbers of these microbes
into the estuary from their natural habitats in soil
and on vegetation. Marginally treated and un-
treated sewage and liquid wastes from industries
such as dairies, canneries, frozen food processing,
meat-packing, tanning, textiles, and pulp and
paper plants may contribute large numbers of
micro-organisms directly to receiving waters
(Geldreich 1981).
Until the mid-1970's, the total coliform
measurement was universally used to express the
sanitary quality of water and waste effluents.
Fecal coliforms (found in feces of warm-blooded
animals) compose a portion of the total coliform
group; they may be distinguished from other col-
iform bacteria by various microbiological tests
(American Public Health Association 1976). Pres-
ent standards in Chesapeake Bay are based upon
fecal, rather than total, coliform levels because
they are more likely to assess the possible presence
of pathogens. It is recognized that the validity of
fecal coliform levels as indicators of water qual-
ity has been questioned, particularly in estuarine
and marine waters because levels are influenced
by dilution, tributary flow, light, temperature,
salinity, predators, and tidal variation. However,
we have not yet found a more appropriate indi-
cator. Fecal coliforms are included in this assess-
ment as an indicator of environmental trends, and
the results are not meant to imply public health
risk.
DATA BASES
The data base used for characterizing the
Maryland portion of the Bay was obtained from
the Maryland State Department of Environmen-
tal Health and Mental Hygiene and was reported
in median values of fecal coliforms for each sta-
tion. The Division of Technical Analysis in Mary-
land analyzes fecal coliform data collected at 1402
sampling stations within the Chesapeake Bay
area. Samples are collected once a month in most
areas and twice in selected areas. Fecal coliforms
are measured as a Most Probable Number (MPN)
per 100 milliliters. The fecal coliform data ana-
lyzed cover the 1975 to 1981 time period.
Data used for characterization of the Virginia
portion of the Bay were provided by the Virginia
State Department of Health, Bureau of Shellfish
Sanitation. The data are reported as median
values of fecal coliforms for each of 3 to 50 sampl-
ing stations in 98 shellfish growing areas. For this
analysis, data from 1975 to 1981 were used. It is
important to recognize when reviewing these data
that there is a significant difference between the
41
-------
42 Chapter 1: Water and Sediment Quality
Virginia and Maryland data bases in the represen-
tation of the areas restricted for shellfish
harvesting. The difference is that the State of
Maryland samples shellfish areas with the same
frequency throughout the year whereas the State
of Virginia will decrease the number of samples
taken within an area that is closed to shellfish
harvesting. For the statistical analysis, median
values were weighted in an effort to compensate
for this difference.
ANALYSIS OF
COLIFORM LEVELS
Mean fecal coliform levels from selected
tributaries of Chesapeake Bay were converted to
natural logs and were compared using analysis of
variance procedures followed by a Student-
Newman-Keuls test. Differences were considered
significant at the p<0.05 level. The natural logs
of the MPN means rather than the MPN means
were used because the distribution of MPN values
is logarithmically normal.
The first set of comparisons was made between
the James, Potomac, York, and Rappahannock
Rivers. The means were significantly different be-
tween groups and not significantly different
within groups. The following significantly dif-
ferent groups of means were distinguished (listed
in descending order): Group A —James River,
Group B — York River, and Group C — Potomac
and Rappahannock Rivers (Table 10). It should
be noted that data from several Maryland tribu-
taries were not included when the Potomac River
mean was calculated. The higher fecal coliform
levels in the James River are attributable to con-
centrations in the upstream portion of rivers and
creeks and reflect land-use patterns in these areas.
In Maryland, three western shore tributaries
were compared to three eastern shore tributaries
to determine if water quality in the more urban-
ized western shore rivers was significantly dif-
ferent from water quality in the eastern shore
rivers. Their means fell into three significantly dif-
ferent groups (Table 11) with the Tred Avon River
(Eastern Shore) having the highest values, and
Harris Creek (Eastern Shore) and the Severn River
(western shore) having the lowest values.
A third set of comparisons was made between
seven Maryland eastern shore tributaries. The
results showed five significantly different groups
that are listed in Table 12. The Great Wicomico
River had the highest values and was significant-
ly different from the other six rivers, while Fishing
Bay had the lowest values.
DETERMINATION OF SHELLFISH
CLOSURE AREAS
Shellfish are defined as all edible molluscan
species of oysters, clams, and mussels. The oyster,
Crassostrea virginica, is considered to be the most
economically important of these species in the
Chesapeake Bay area. The oyster's filter-feeding
process enables it to obtain nutrients from micro-
organisms, small detrital particles, and phyto-
plankton. However, this type of feeding may also
concentrate pollutants from the water column in
TABLE 10.
GROUPS OF MAJOR WESTERN SHORE TRIBUTARIES BASED ON STUDENT- NEUMAN-KEULS TEST OF Ln
FECAL COLIFORM LEVELS (LnMPN). MEANS ARE SIGNIFICANTLY DIFFERENT BETWEEN GROUPS BUT
NOT SIGNIFICANTLY DIFFERENT WITHIN GROUPS, AT p < 0.05
Basin
Ln(MPN)
n
Group
James
York
Potomac
Rappahannock
2.8374
2.1723
19689
19191
837
3084
2347
319
A
B
C
C
-------
Fecal Coliform Trend Assessment 43
TABLE 11.
GROUPS OF SMALLER TRIBUTARIES FROM EASTERN AND WESTERN SHORE BASED ON STUDENT-
NEUMAN-KEULS TEST OF Ln FECAL COLIFORM LEVELS (LnMPN). MEANS ARE SIGNIFICANTLY DIFFERENT
BETWEEN GROUPS BUT NOT SIGNIFICANTLY DIFFERENT WITHIN GROUPS, AT p<0.05
River
Ln(MPN)
n
Group
Tred Avon
West and Rhode
Broad Creek
Harris Creek
Severn
2,2229
1 .9439
1.7734
1.6357
1.6092
236
217
147
141
235
A
B
B&C
C
C
TABLE 12.
GROUPS OF EASTERN SHORE TRIBUTARIES BASED ON STUDENT-NEUMAN-KEULS TEST OF Ln FECAL COL-
IFORM LEVELS (LnMPN). MEANS ARE SIGNIFICANTLY DIFFERENT BETWEEN GROUPS BUT NOT
SIGNIFICANTLY DIFFERENT WITHIN GROUPS, AT p<0.05
River
Ln(MPN)
n
Group
Grt. Wicomico
Pocomoke Sound
Choptank
Nanticoke
Miles
Chester
Fishing Bay
2.8527
2,0948
1.9783
1.8275
1.6710
1,4742
1,3071
105
112
398
153
159
305
121
A
B&C
C&D
D& E
E
its tissues. Intensive monitoring of shellfish grow-
ing areas is necessary to ensure safety in the con-
sumption of these products. Fecal coliform bac-
terial levels are monitored by Maryland and
Virginia in all waters capable of propagating
shellfish (including public and leased beds). If the
bacteriological standard is violated, the area will
generally be closed to shellfish harvesting.
Harvesting can be resumed when the Virginia
Department of Health or the Maryland Depart-
ment of Health and Mental Hygiene determine
that the water quality has met the established
standards.
Other factors besides the bacteriological stan-
dards are considered in the closure of shellfish
harvesting waters. Areas in the Choptank River
have been closed to harvesting for the protection
and propagation of prime seed area. The closures
are instituted through the Maryland Department
of Natural Resources. Waters have been closed
based upon the possible threat of pollution from
point sources such as sewage treatment plants and
industries, upon the results of sanitary surveys on
dwelling units, and upon the consideration that
certain locations were sources of boat pollution
and animal waste pollution. Buffer zones are clo-
sure areas established around actual and poten-
tial sources of pollution. The source determines
the size of the buffer zone. The most common
source associated with buffer zones is wastewater
treatment plants. The effectiveness and reliabil-
ity of wastewater treatment, distances of
pollutants from shellfish areas, the effects of
winds, runoff, stream flow, and tidal currents are
important items to be considered when
establishing buffer zones. Figure 12 shows shellfish
closure areas (1981 for Virginia and 1982 for
Maryland) and the location of Publicly Owned
Treatment Works.
-------
44 Chapter 1: Water and Sediment Quality
+ 0. MGD
+ ) 100. MGD
300. MGD
x-—\
Closure area
FIGURE 12.
Chesapeake Bay shellfish closures as of
December I982 for Maryland and I98I for
Virginia; superimposed on locations and
flow (MGD) of publicly owned treatment
works.
-------
SECTION 5
ORGANIC COMPOUNDS
IN THE WATER AND SEDIMENTS
INTRODUCTION
Organic compounds are a broad class of
chemicals that include synthetic organic com-
pounds as well as naturally occurring compounds.
The groups of organic compounds most frequently
studied include pesticides, herbicides, polychlor-
inated biphenyls (PCBs), polynuclear aromatic
hydrocarbons (PAHs), phenols, substituted ben-
zenes, and halogenated aliphatics. Many have
been or are presently being discharged into the
waters of Chesapeake Bay and its tributaries.
Once introduced to Bay waters, organic com-
pounds can adsorb to sediment, dissolve in the
water column, and concentrate in the biota; or
they can be removed from and/or be destroyed
in the estuarine environment. Removal and
destruction processes can include photolysis,
hydrolysis, volatilization, and other chemical
reactions.
Some of the most frequently investigated or-
ganic compounds are those contained in the U.S.
Environmental Protection Agency Priority Pollu-
tant List (Appendix B). The dominant fates of the
priority pollutants are adsorption to sediment,
biological uptake, and chemical and physical
destruction. In general, the structural activity of
each compound usually determines its fate. Com-
pounds; that are hydrophilic (attracted to water)
will exist primarily in the water column and can
eventually leave the Bay through its exchange with
the ocean. However, hydrophobic (repelled by
water) compounds will adsorb rapidly to sediment
particles and, through sedimentation processes,
be trapped in the Bay environment. The chemical
properties of these compounds and the physical
and chemical conditions, such as salinity and pH,
determine the toxicity of the compounds to biota
and their bioavailability.
DATA ANALYSIS
The analytical capabilities for analysis of
organic compounds in an estuarine system have
been developed only recently. For many com-
pounds, the methodologies and detection capa-
bilities are still not sensitive enough to routinely
measure environmental concentrations at which
toxicity to biota may occur. In addition to the low
sensitivity, most analyses are restricted to search-
ing for a limited number of compounds; thus,
many organic compounds go undetected. These
problems have made it difficult to fully
"characterize" the organic compounds in the Bay
and its tributaries. Nonetheless, in segments where
sufficient data exist, an effort was made to
evaluate bottom sediment, water column, point
source discharge, and oyster tissue data collected
by GBP researchers and the States of Virginia and
Maryland. The data base that was created was
re-examined for quality and accuracy as described
in Section 6.
To develop a graphic assessment of the cur-
rent condition of the main Bay, we relied on GBP
research by Bieri et al. (1982b). Their analysis by
gas chromatography of sediment samples collected
in the spring and fall of 1979 revealed over 300
organic compounds in sufficient abundance to be
recognizable. The concentration sums of all iden-
tifiable compounds at given station locations are
shown in Figure 13. This figure shows that organic
compounds are most abundant in the upper Bay
sediments, decreasing seaward, and increasing
45
-------
46 Chapter 1: Water and Sediment Quality
14
9«
^^
&£
10
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
102
103
104
10s
106
FIGURE 13. Station locations and bar graphs representing concentration sums (ppb) of all
recognizable peaks for organic compounds after normalizing for silt and clay content.
(From Bieri et al. I982c).
-------
Organic Compounds in the Water and Sediments 47
again near mouths of lower Bay tributaries (Note:
concent rations are on a log scale). Additional sedi-
ment data retrieved from the GBP-compiled data
base revealed levels above EPA criteria in five
western tributaries and Pocomoke Sound.
Data on levels of toxic organic compounds in
the waters of the Bay and its tributaries are largely
limited to pesticides, PCBs, and to very spotty
data on volatile halogenated hydrocarbons and
phenols. There are relatively few observations
compared to the number for heavy metals in the
water column (Appendix B). To provide a frame-
work for assessing the water column data, ob-
served concentrations were compared to estab-
lished EPA water quality criteria levels for priority
pollutants. Aldrin and dieldrin criteria levels were
exceeded in Pocomoke Sound and portions of the
Potomac, Rappahannock, York, and James
Rivers. Five observations exceeded chronic levels
of dieldrin in the tidal-fresh portion of the James
River (TF-5), and two observations of endrin in
Pocomoke Sound (EE-3) exceeded acute values.
Chapter 3 discusses implications of these concen-
tration levels for the living resources of Chesa-
peake Bay.
Measured concentrations of total residual
chlorine? were elevated according to criteria from
a 1982 draft EPA document.2 Most of the 358
observations were in tidal freshwater, and 67 per-
cent exceeded the draft criteria. On the basis of
this data alone, it is difficult to assess the impact
of chlorination on Bay waters. It is likely that
analytical methods used in the past have not been
sensitive enough to accurately measure low am-
bient concentrations.
BAY-WIDE SUMMARY
Organic Compounds in the Sediments
The distribution of organic compounds in the
bottom sediments of the main Bay (Figure 13) and
an analysis of the limited tributary data gener-
ally suggest that organic compounds concentrate
at river mouths and in maximum turbidity areas.
This is apparently due to the tendency of organic
compounds to adsorb to suspended material
accumulating in these areas. It is interesting to
note that the higher concentrations also appear
to be associated with sediments of increasing
fineness. The highest concentration of organics in
the bed sediments were found in the tidal-fresh
portions of the Patapsco and Elizabeth Rivers.
Overall, 480 compounds were identified in sur-
face samples from the Patapsco estuary, and 310
compounds were identified in samples taken in the
Elizabeth estuary (Bieri et al. 1982c). In both
areas the sum of all organic compounds detected
exceeded 100 ppm at several locations. Concen-
trations of PAHs ranged from 1 to 90 ppm in Pa-
tapsco River sediments and from 1 to over 100
ppm in Elizabeth River sediments. In the Patapsco
River, levels of PCBs were as high as 8,000 ppb.
It is apparent that these unusually high levels are
due to industrial activities in these harbors. This
is further substantiated by the fact that core
analyses show that variation in both phthalate
esters and polynuclear aromatics correlate well
with historical rates of coal production and use
in the United States (Peterson 1982).
Organic Compounds in the Waters
Organic compounds in the waters of the Bay
and its tributaries appear most often associated
with anthropogenic point and nonpoint sources
located in industrialized areas (Bieri et al. 1982c).
Toxicants associated with suspended material do
not appear to migrate from these highly con-
taminated areas such as the Patapsco River
(Palmer 1974). This would be expected in light
of our understanding of the sediment trapping ef-
ficiency of the sub-tributaries of the Bay.
On a Bay-wide level, the primary organic
groups of concern are the pesticides and herbicides
because they are extensively used on agricultural
lands that comprise a large portion of the water-
shed. Chesapeake Bay Program research on two
major herbicides, atrazine and linuron, indicates
that ambient levels did not exceed 5.5 ppb in the
main stem of the Bay or 3.5 ppb in the western
tributaries between 1976 and 1980 (Kemp et al.
1982a). These levels are below the concentrations
that would begin to significantly inhibit the
growth of submerged aquatic plants (U.S. EPA
1982b). However, lethal levels of atrazine as high
as 140 ppb have been found in the Rhode River
following post-spraying rainfall events (Wu 1980).
Thus, in smaller tributaries near sources of her-
-------
48 Chapter 1: Water and Sediment Quality
bicides, biological effects may occur. Nonetheless,
pesticide levels throughout the Bay are generally
in the range of 1 ppb (generally considered safe),
except at riverine headwaters following applica-
tion and rainfall events. In such situations, the
observed levels of pesticides exceed EPA's water
quality criteria. Because of the way data were col-
lected, duration or extent of these high values is
not well known.
KEPONE IN THE JAMES RIVER -
AN EXAMPLE
The organic pesticide Kepone was discharged
into the James River at Hopewell, Virginia, un-
til 1975. This synthetic organic substance can be
easily bioconcentrated by organisms, from phy-
toplankton to fish. In fact, Nichols and Cutshall
(1981) found that the highest concentrations of
Kepone occurred in zooplankton, averaging 2.9
ppb, whereas the total (bulk) suspended material
averaged 0.09 ppb. Laboratory studies by Banner
et al.(1977) have further established that shellfish
and finfish are capable of bioconcentrating
Kepone to concentrations near or above the Food
and Drug Administration Action Level of 0.30
ppm, when exposed to water with total Kepone
residues as low as 0.022 ppb. Kepone was detected
at or above 0.022 ppb during 1976 to 1978 within
all reaches of the James estuary. Because of the
high levels of Kepone, much of the James River
was closed to fishing in 1975. Thus, the Kepone
incident became one of the major pollution events
in the Bay.
Kepone has been extensively studied as a result
of public concern. Through these efforts much has
been learned about the processes that affect the
movement of synthetic organics through the sys-
tem. Concentrations of dissolved Kepone have
ranged from as high as 45 ppb near the source
(Saleh and Lee 1978) to 1.0 to 9.8 ppb 75 km3
seaward from the source (Slone and Bender 1980).
The distribution generally indicates downstream
dilution and mixing away from the source. How-
ever, the bulk of Kepone in the water is associated
with particulate material, and Kepone is difficult
to remove from sediment particles over the range
of pH and salinity values occurring in the James
River (Huggett et al. 1980). It is, therefore, val-
uable to examine the concentrations in the sus-
pended sediment.
The Kepone content of suspended material
varies with distance from the source depending
on hydrologic conditions. At relatively low river
inflow, August 1977, concentrations ranged from
258 ppb near the source to less than 10 ppb at 118
km downstream. Additionally, the concentrations
are higher in surface water than near the bottom.
The relatively high surface values result from
locally high concentrations of organic matter as
indicated by relatively high concentrations of ATP
and a high percent organic carbon of the sus-
pended material.
At relatively high river inflow, April 29 to 30,
1978, when the inner limit of saline water was
restricted to the lower estuary and there was
substantial sediment influx, the Kepone content
of suspended material varied widely with time
and location. However, highest concentrations
generally were found near the source and near the
turbidity maximum. In fact, on April 25, 1978,
concentrations reached 420 ppb in the turbidity
maximum area, 80 to 100 km downstream from
the source. This zone contained high loads of
organic material, including up to 35 percent of
the total suspended material. Again, these high
Kepone concentrations appear to be related to bio-
accumulation of plankton. This has been con-
firmed by direct examination of filtered suspended
material as well as by corresponding analysis of
zooplankton populations (Jordan et al. 1979).
Temporal variations in the concentrations of
Kepone also appear to be related to the organic
matter in the water column. Over a tidal cycle,
there is generally a tendency for concentrations
to peak near slack water when organic matter
makes up relatively high percentages of the sus-
pended load (Nichols and Trotman 1979). Season-
al trends are marked by peak Kepone content in
summer, July to September, 1977 and 1978 (Table
13). During the summer, high Kepone content in
the water column is most likely caused by bio-
accumulation of plankton that proliferate more
in summer than in winter, making up a signifi-
cant portion of the suspended load (Lunsford
1981). This trend suggests that organisms are more
exposed during the summer than at other times.
An examination of vertical sediment core pro-
files of Kepone concentrations with depth shows
-------
Organic Compounds in the Water and Sediments 49
TABLE 13.
SEASONAL KEPONE WATER-COLUMN CONCENTRATIONS IN JAMES RIVER ESTUARY,
1976 TO 1978 (LUNSFORD ET AL. 1980)
Season
Winter
Spring
Summer
Fall
Season
Winter
Spring
Summer
Fall
Season
Winter
Spring
Summer
Fall
Sample Size
131
76
70
64
Sample Size
9
84
64
60
Sample Size
54
33
52
51
1976
Median
0.03
0.03
0.03
0.00
1977
Median
0.00
0,00
0.04
0.00
1978
Median
0,00
0.03
0.04
0.02
Mean
0,05
0.04
0.05
0.01
Mean
0.01
0.00
0.04
0.01
Mean
0.00
0,04
0.05
0.03
Range
ND1 - 0.95
ND - 120
ND2 - 0.97
ND -0.16
Range
ND -0.04
ND -0.05
ND -0.19
ND -0.07
Range
ND3-0.14
ND -0.15
ND -0,29
ND -0.30
1 Non-detectable; O.OIppb
2Non-detectable; 0.02 ppb
3Non-detectable; 0.02 ppb or 0.05 ppb.
the trends over the life span of Kepone contamina-
tion, 1966 to 1976 (Figure 14). Contamination of
sediments began shortly after production started
in 1966 and gradually increased to 1973. When
production increased markedly in 1974, contam-
ination also increased. Diminished Kepone con-
centrations after 1976 relate to the halt of pro-
duction. It is evident that general annual trends
recorded in the sediments vary with source input
and that the 1975 high levels of Kepone in the sed-
iments are gradually being removed from the sys-
tem by flushing or burial processes.
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50 Chapter 1: Water and Sediment Quality
0
10
E 20
o
£ 30
Q.
Q 40
50
60
Kepone, ppb
100 200 300
Kepone, kg x 10
200 400
1975
1970
Contamination
Record
1965
Kepone
Production
FIGURE 14, Annual trends of Kepone concentations in bed sediments compared to the
Kepone production record (Nichols and Cutshall I98I).
-------
SECTION 6
METALS IN THE WATER AND SEDIMENTS
INTRODUCTION
Metals are naturally-occurring chemical ele-
ments, but can be anthropogenically enriched.
Several of the metals, such as copper (Cu) and zinc
(Zn), are essential trace elements for most living
organisms. However, if organisms are exposed to
high concentrations of metals, they may suffer
chronic or lethal effects. High concentrations of
metals are generally found in industrialized areas,
coming largely from industrial plant discharges,
sewage treatment plants, runoff from urbanized
areas, a.nd atmospheric pollution. Once in the Bay
environment, physical, chemical, and biological
processes affect the ultimate fate of the metals.
(Maps showing station locations for metals in the
water and sediments are in Appendix B, Section
2.) A more complete discussion of these processes
can be found in Chesapeake Bay Program
Technical Studies: A Synthesis (U.S. EPA 1982b).
The metals found in Chesapeake Bay occur in
many forms. Some are chemically stable with
limited biological availability; other forms are
very unstable and available to biota. Metals can
be bound to organic or inorganic components, in
either dissolved or particulate phases. Some data
on melals in the water column are expressed as
total metals, and other data include the specific
dissolved or particulate components of the various
metals. From some of the investigations of water
column concentrations, particularly Nichols et al.
(1981), jt is evident that the range of metal con-
centrations at any given station can vary depend-
ing on various physical and chemical factors. For
some metals, the variability of particulate water-
column concentrations within one tidal cycle at
a particular station can be as great as the varia-
bility from Bay-wide sampling (Nichols, et al.
1982). For this reason and because more data are
available in sediments, the bottom-sediment data
base was used as the primary source to charac-
terize the Bay and tributary segments for levels
of metal contamination.
DATA BASES AND ANALYSIS
Data from the water column and bottom
sediments were assembled to provide as compre-
hensive a data base as possible. Temporal and
spatial trends were identified as well as the rela-
tionships and the interactions among toxic
chemical parameters. Chesapeake Bay Program
project data were the primary source for the main
Bay analysis. Dissolved and particulate metal data
from Kingston et al. (1982) and Nichols et al.
(1982) provided main Bay coverage for 1979 to
1980. The data cover 14 metals in solution and
11 to 14 metals in particulate form from surface
and near bottom waters. Metals data from sedi-
ment cores and surface samples (Helz 1981) were
used to characterize the main Bay sediments. Ad-
ditional data covering a larger temporal scale (ap-
proximately 1960 to present) and, also an ex-
panded geographical coverage into the tributary
segments, were obtained from STORET and from
Maryland and Virginia water quality data bases.
Additional data on bottom sediments in the trib-
utaries were collected and summarized by the staff
of the Maryland Department of Health and Men-
tal Hygiene. The Virginia State Water Control
Board staff also assisted in gathering and enter-
ing additional data. All laboratory analyses
followed EPA standards and included participa-
51
-------
52 Chapter 1: Water and Sediment Quality
tion in the EPA water quality assurance program.
The data were assumed to be log-normally dis-
tributed and were subjected to univariate statis-
tics. Tables summarizing the data are included
in Appendix B.
The data were analyzed to determine if the
metal concentrations were above natural back-
ground levels. In the bottom sediments, the six
most frequently sampled metals [cadmium (Cd),
Cu, chromium (Cr), nickel (Ni), lead (Pb), Zn]
were analyzed by comparing pre-colonial, natural
pristine levels as determined from cores, with cur-
rent levels. A full discussion of the methodology
used to determine this "Metal Contamination In-
dex" (Ci) and the values calculated for the dif-
ferent GBP segments are included in Appendix B.
For the water column analysis, the concentrations
of the various metals were normalized (propor-
tioned) to a reference metal [usually iron (Fe),
aluminum (Al), or scandium (Sc)] that occurs ubi-
quitously in the Bay, or compared with their
abundance in either shale or average crustal
material. A more complete discussion of this
methodology is included in Chesapeake Bay Pro-
gram Technical Studies: A Synthesis (U.S. EPA
1982b), and Kingston et al. (1982). These assess-
ments of metal enrichment above natural back-
ground levels give us some indication of the im-
pact of human activities. High levels of metal
enrichment warrant some concern; however, Bay
organisms will only be affected if the actual metal
concentrations exceed the species' levels of toler-
ance (Chapter 3 and Appendix D). To determine
if metal concentrations in Bay waters ever reached
levels that could threaten Bay organisms, data on
water column metals were screened against the
U.S. EPA's Water Quality Criteria. These criteria
and a discussion of the analysis are included in
Appendix B.
To assess the transport and fate of metals in
the Bay, water column data were also evaluated
along salinity gradients. The Bay is a site where
river water and seawater mix. If metals trans-
ported in solution by rivers undergo no biological
or chemical reactions, then the trends of concen-
tration are due solely to physical mixing processes
and dilution. This relationship, known as conser-
vative mixing, is a linear function of salinity whose
slope will be negative for a metal more concen-
trated in river water than in seawater. In theo-
retical conservative mixing, data lie close to a
straight line joining river and ocean end members;
concentrations would be highest (or lowest) in the
river water, lowest (or highest) in the ocean water.
Uranium (U) and molybdenum (Mo) behave con-
servatively. On the other hand, if the metal con-
centrations are affected by processes other than
dilution, then they behave nonconservatively;
they deviate from a straight line and lie above,
indicating addition to the Bay waters, or below,
indicating biological or chemical removal from
Bay waters. All of the remaining trace metals
behave nonconservatively in the Bay.
When the average dissolved metal concentra-
tion of the Susquehanna River, or alternately, the
average from world rivers, is compared with the
average metal content of the Bay (Kingston et al.
1982) and the average for seawater, it is evident
that the metal content of river water exceeds that
of Bay water and seawater for all metals except
Ni (Table 14). This trend indicates substantial
mixing and dilution of river-borne metals in the
Bay, or substantial removal of metals in the Bay
prior to their discharge to the ocean. For example,
data indicate that some metals such as Cd, Cu,
Pb are taken up by phytoplankton and zooplank-
ton and, thus, become incorporated into organic
matter. Depositing this organic material is one
path in which metals from the water column are
deposited in the sediments.
SUMMARY OF METALS IN BED SEDIMENTS
The GBP approach to assessing metal trends
in the bed sediment was to use cores that
documented changes over time. Sediment cores,
analyzed for trace metals and with an established
geochronology, can estimate trace metal inputs,
assuming no diagenetic migration of metals
through the length of the core. The cores were
carefully selected, because burrowing activities of
benthic organisms in aerobic environments could
disturb the sedimentary record, create an "ar-
tificial" 210Pb distribution and, thus, influence
trace metal patterns. Three cores with 210Pb pro-
files that showed a clear chronology and no
evidence of bioturbation were used for the
analysis. The change in sediment composition and
the associated metal concentrations over time was
taken into account by using a ratio of silicon (in-
-------
Metals in the Water and Sediments
53
TABLE 14.
COMPARISON OF MEAN DISSOLVED METAL CONTENT IN
SUSQUEHANNA RIVER WATER, BAY WATER, AND OCEAN WATER
Metal
Cadmium (Cd)
Cobalt (Co)
Copper (Cu)
Chiomium (Cr)
Lead (Pb]
Nickel (Ni)
Zinc (Zn)
River water1
ugL-1
0,8
1.0
180 (7)3
10.0
10
ND (0.3)3
26.0
Bay Water2
ugL-1
0,02
0.1
0.3
0.2
0,1
1.2
0.9
Ocean Water3
ugL-1
0.1
0.1
2.0
0.2
0,03
2.0
2.0
1Based on data ot Lang and Grason (1980).
2From data ot Kingston et al. (1982) tor summertime only.
3From data tor world rivers and natural concentrations of seawater. Turekian (1971)
ND is non-detectable.
dicative of sandy material) to aluminum (in-
dicative of clay material). A model was developed
to separate the sediments into classes based on
their metal content and their silicon to aluminum
(Si/Al) ratios (Appendix B, Section 6). By using
a statistical relation between the Si/Al ratio and
log-metal content of old pre-pollution sediments
in the Bay, a natural Chesapeake background con-
centration for the metal can be estimated. Then,
the predicted natural Chesapeake values can be
compared to the actual observed values and to
average levels world-wide. Details of this analysis
are in Appendix B, Section 6.
Metals analyzed by Helz (1981) include Cr,
Zn, Ni, Cu, Fe, Pb, Mn, Co, Al, and Cd. The
observed values for most of the metals are general-
ly higher than estimated natural Chesapeake
values, with the exception of Cr. Figure 15 il-
lustrates the changes in observed metal concen-
trations for Zn and Cr over time compared to
natural background levels. Zinc shows significant
increases in the late 1800's coincident with peak
land clearance from timbering and agriculture,
as well as from coal mining in the Susquehanna
drainage basin. Chromium shows no historic en-
richment in the cores. Using the model, we can
compute a contamination factor (Cf) for each
sample and each metal with an observed Si/Al
ratio, compared to pre-pollution samples from
deep in Bay sediments.
Contamination Factor (Cf) = C0 - Cp
where C0 = surface metal concentration
and Cp = predicted metal concentration
Thus, if the Cf equals 1.0, the sample contains
concentrations of that particular metal that ex-
ceed natural Chesapeake Bay sediment by 100
percent. If the Cf equals 0, then the sample con-
tains concentrations of that particular metal equal
to natural concentrations. If the Cf is negative,
then the sample contains concentrations of the
metal below expected natural concentrations.
Taking the sum of the individual contamination
factors for available metals, we can compute a
Contamination Index (Ci) for each sediment
sample:
Contamination Index (Cz) = Z Cf
n=l
Figure 16 shows the level of metal contamination
in the Bay based on Cfs for Cd, Cr, Cu, Pb, Ni,
and Zn.
The Contamination Index is a useful indicator
of potential problem areas in the Bay. It is ap-
-------
54 Chapter 1: Water and Sediment Quality
Core 4
Zn (ppm)
100 300
1800
1780
1880
Predicted from world-wide averages.
Predicted for Chespeake Bay sediments
Observed
Core 60
Zn (ppm)
100 300
1780
1680
Core 4
Cr(ppm)
100
Core 60
1880
1780
1880
1780
1680
Cr(ppm)
100
—
i
i
i
i
i
[1
i
1 1 1 1 i
f ,
FIGURE 15. Zinc and chromium concentrations down-core compared to natural
background levels.
-------
Metals in the Water and Sediments 55
r ^-H ^^^C^%^X«
^l ^L ~A>*7 j^^r^- - ^
AALJ^%T v-iV^ ^^.^
^
^
> ^~—***' y <7 YV? -.^f re2-V>
ODD
o
c
O
0
c
E
_D
O
O
O
O
OD
IDDD
c
"c
o
E
.c
o
o
15
C
D
"E
"D
D
O
0
Q.
a
o
u
o
-------
56 Chapter 1: Water and Sediment Quality
parent from Figure 17 that the most contaminated
areas are near industrialized parts of the Bay such
as Baltimore and Norfolk. For example, the Pa-
tapsco River contamination factors are Cd (64),
Cu (27), Pb (19), Zn (6), Cr (5), andNi (0.1). The
upper Potomac and upper James Rivers, upper-
mid Bay, and small sections of the Rappahannock
and York are moderately contaminated. Minor
contamination occurs in the Susquehanna Flats
and the lower Potomac River. Although these
trends are suggestive, it is important to evaluate
the metal levels in terms of their toxicity to ben-
thic organisms in the Bay. This will be discussed
in Chapter 3.
Actual concentrations of metals in the sedi-
ments are given in Appendix B, Tables 5, 8, and
12. Figures are in ug/g (or ppm). It is interesting
to note that mean concentrations of Cu, for ex-
ample, often exceed the level at which burrow-
ing activity of a west coast clam, Protothaca
staminea, is greatly reduced —33 ppm (Phelps, in
prep.). However, failure of Chelex-sorbed Cu to
affect burrowing rates indicates that tightly
bound, less bioavailable forms of the metal have
a much lower potential toxicity. Dissociation of
metals from the sediments and availability to biota
will determine potential biological impacts, more
than bulk concentrations per se.
SUMMARY OF METALS
IN THE WATER COLUMN
An evaluation of the dissolved metal concen-
trations at specific locations reveals significantly
measurable levels throughout the Bay (Kingston
1982). The dissolved content of mean Cd, Cr, Ni,
and Zn is higher in the upper Bay segments CB
1 to 3 than elsewhere. Concentrations decrease
seaward in more salty water, segments CB 6-
8. Cadmium exhibits the greatest seaward change,
whereas Zn displays the least change. The Bay-
wide decrease of Cr correlates with salinity, sug-
gesting that Cr comes from the Susquehanna
River. Its concentration partly results from dilu-
tion and conservative mixing of river water with
ocean water (Figure 18). The other metals, Cd,
Cu, Ni, and Zn, are affected by sedimentological
and biological processes, in addition to dilution
and mixing, that tend to remove them from solu-
tion. The Susquehanna River is a significant
source of metals to the Bay and follows the general
trend that rivers carry higher metal loads than
does seawater.
Particulate metal concentrations in the water
column are also quite variable. The concentra-
tions (ug L'1) tend to vary with changes in total
suspended material as it resuspends and settles to
the bed with changes in tidal-current strength.
However, general trends are apparent in the
average mean concentrations for the different
Chesapeake Bay segments. Figure 18 shows the
average particulate concentrations from five
cruises between March through September 1979
to 1980 (Nichols et al. 1982).
Mean concentrations of particulate Co, Cr,
Cu, Ni, Pb, and Zn per liter of water are greatest
in the upper Bay (CB 1-3), a zone near the Sus-
quehanna River that includes the turbidity max-
imum. Localized high concentrations occur in the
bottom water of CB-2, particularly where the con-
centrations of total suspended material are high.
Particulate metal concentrations vary widely in
CB-2 with time, ranging more than 8-fold within
three hours as a result of sediment resuspension
from the bed. An analysis of metal enrichment
based on Cd to Fe ratios indicates that Cd con-
centrations in mid-depth and surface waters of the
central (CB-5) and lower Bay segments (CB 6-8)
are 30 times greater than the background levels.
It seems likely that phytoplankton uptake of Cd
in these areas could be responsible for these
elevated levels (Nichols et al. 1982).
The metals data in the tributaries of the Bay
are primarily total metal concentrations (Mary-
land and Virginia "106" data). An assessment of
this data suggests that the western shore tributaries
of the lower Bay, such as the James River, have
elevated metal content of total Cu, Pb, and Zn
in their upper (TF) and lower (LE) segments, and
a lesser content in central segments (RET). Other
tributaries have localized concentrations of
various metals in either upper or lower segments,
except for the Rappahannock River which has
higher Pb and Zn per liter of water in the central
segment. Most of these trends reflect nearness to
industrial or wastewater pollution sources; how-
ever, concentrations of Pb and Zn per liter of
water in the central Rappahannock could be
-------
Metals in the Water and Sediments 57
FIGURE 17.
Degree of metal contamination in the Bay
based on the contamination index (C|).
No data exist near shore, and large local
increases could be expected close to
outfalls.
-------
58 Chapter 1: Water and Sediment Quality
RIVER
Pb
Cu
CdC
Zn
JO ug/L
FIGURE 18.
Average participate metal concentrations
trom five cruises, March 1979 to
September 1982 (Data from Nichols et al.
1982).
-0 ug/L
-------
Metals in the Water and Sediments 59
enhanced by a high content of suspended material
associated with the turbidity maximum.
In summary, the concentration of dissolved,
particulate, and total metals does not warrant
drastic action throughout the entire Bay basin.
However, the quantity of samples (taken both
before and after 1975) exceeding the EPA Water
Quality Criteria raises general concern (Figures
19a and 19b) (see Appendix, B Section 3).
It can be seen that these criteria "violations"
in the main Bay are concentrated in small tribu-
taries and along the shore. It is reasonable to
assume that the sampling distribution reflects
specific monitoring or research needs, not a
general coverage of the region. It should also be
noted that sampling does not give a good indica-
tion of duration of instances of high metals con-
centrations. Such information is needed to assess
potential biological impacts.
%^". y?.-:*
FIGURE 19a.
Areas, where
dissolved
meters violated
EPA criteria
before 1971 to
1975.
For the main Bay and lower estuarine zones
of the western tributaries, estimated dissolved Cu
and Ni exceed chronic and acute saltwater criter-
ia. The chronic criterion for Zn is exceeded in
Baltimore Harbor and the tidal-fresh portion of
the Potomac River. On the lower eastern shore,
the Pocomoke Sound region has significant
amounts of Cu above the chronic criterion.
The broad distribution of "dissolved" obser-
vations above criteria should increase the aware-
ness of the possible environmental effects of trace
metals. However, it should be viewed in the con-
text of the ecology of the Bay, the distribution of
sampling, and the general lack of information on
the form of the metal. This will be further discuss-
ed in the chapter on relationships between water
and sediment quality and living resources
(Chapter 3).
->
/-,' ,. f
FIGURE 19b.
Areas where
dissolved
metals violated
EPA criteria
after I975.
-------
SECTION 7
METALS AND PESTICIDES IN OYSTERS
INTRODUCTION
When sediments and water are enriched by
trace metals or pesticides, shellfish tend to bioac-
cumulate those substances in their tissue. The pro-
cess of concentrating toxicants in shellfish tissue
is known as magnification or biomagnification.
An analysis of metals and pesticides in shellfish
and finf ish tissues provides information on their
suitability for human consumption. Because the
organisms act as biomonitors, an assessment also
enables detection of excessive metal and pesticide
loadings in the environment and helps to charac-
terize the water quality of the Bay. It is well
known that certain metals and pesticides can cause
severe human health effects, such as neurological
disorders, muscle and bone deterioration, etc. To
protect public health, the Food and Drug Admin-
istration has established standards for some toxic
substances in the edible portions of finfish and
shellfish. These standards are called "FDA Action
Levels" and are summarized in Table 15. Unfor-
tunately, action levels have not yet been developed
for many of the metals and organic compounds
that are frequently found at elevated levels in the
Bay. Concentrations of toxic chemicals in finfish
and shellfish that appear to be above background
levels (i.e., two standard deviations above the
mean) should be investigated. Furthermore, an
evaluation of toxic chemical concentrations in
organisms allows a better understanding of the
water and sediment quality of the Bay. A more
detailed discussion of the ecological implications
of these concentrations is included in Chapter 3.
DATA ANALYSIS
The data on metal and pesticide levels in
oysters were compiled and analyzed by the
Maryland Department of Health and Mental
Hygiene (Eisenberg and Topping 1981) and the
Virginia State Water Control Board (Gilinsky and
Roland 1983). Data for the State of Maryland
cover the period 1976 to 1980. The data set for
Virginia includes data from the Virginia Bureau
of Shellfish Sanitation, the Virginia Institute of
Marine Science (VIMS), the Virginia State Water
Control Board, and other studies. It covers a time
span from 1967 to 1980 for metals and from 1964
to 1980 for pesticides. In both state-wide data
bases, tissue samples were analyzed for several
heavy metals including Cu, mercury (Hg), Zn, Pb,
Cd, Cr, and arsenic (As). The pesticide and poly-
chlorinated biphenyl concentrations included in
the data bases are DDT, DDD, DDE, chlordane,
dieldrin, and polychlorinated biphenyls (PCBs).
The sampling station locations are shown in Ap-
pendix B.
To characterize the current conditions and
trends, oyster data were analyzed by CBP seg-
ments and regions. Univariate statistics for each
year were calculated by river basin and/or
segments. The mean levels of pesticides, PCBs,
and metals in oysters are summarized in Appen-
dix B (Tables 15 to 21).
In Virginia waters, oyster tissue metal concen-
trations in the York and Rappahannock Rivers are
highest in the riverine-estuarine transition segment
(Appendix B, Section 7, Tables 15 through 18),
possibly reflecting predominately nonpoint source
fall line metal transport. In addition, there were
historical mining operations in the York River
basin. In the James River basin, metal tissue con-
centrations are highest in the Elizabeth River and
lower estuary segment (Appendix B, Section 7,
Tables 15 through 18). Pesticide concentrations
in oyster tissues are highest in the Elizabeth River,
61
-------
62
Chapter 1: Water and Sediment Quality
TABLE 15.
*FDA ACTION LEVELS FOR SHELLFISH AND FINFISH
Shellfish
Chlordane
DDT, DDE, ODD
Dieldrin
Heptachlor
Heptachlorepoxide
Kepone
Mercury
Mi rex
Polychlorinated Biphenyls
Toxaphene
0.3 ppm
5.0 ppm
0.3 ppm
0.3 ppm
0.3 ppm
0.3 ppm
1.0 ppm
5.0 ppm
Finfish
0.3 ppm
5.0 ppm
0.3 ppm
0.3 ppm
0.3 ppm
0.3 ppm
10 ppm
0.1 ppm
5.0 ppm
5.0 ppm
* United States Department of Health of Human Services Public Health Service, Food and
Drug Administration. 1980. Action Levels for Poisonous or Deleterious Substances in Human
Food and Animal Feed.
with the lower estuarine portions of the James and
York Rivers having similar tissue concentrations
(Gilinsky and Roland 1983).
In the Maryland tributaries, the metal con-
centrations in oysters were highest in the Patux-
ent River and the upper Bay. High levels of chlor-
dane and PCBs in oyster tissues were found in the
east Chesapeake (Kent Island) and the west
Chesapeake area from Baltimore Harbor to the
Rhode River (Eisenberg and Topping 1981).
There were not enough data for a detailed
analysis of metals and pesticides in fish tissues in
Maryland or Virginia. However, mean tissue
DDE and PCB concentrations were calculated for
several fish species having greater than twenty
data points for Virginia waters (Gilinsky and
Roland 1983). It appears that bluefish and chan-
nel catfish have higher DDE concentrations than
the other fish species, and that PCB concentra-
tions are highest in channel and white catfish. A
similar trend was noted for bluefish in Maryland
waters (Eisenberg and Topping 1981).
BAY-WIDE SUMMARY
Cluster Analysis of Metal Concentration
by Segment
Cluster analysis was used to delineate groups
of CBP segments with similar mean metal con-
centrations in oyster tissue. This provides a more
objective method for ranking segments based on
their relative level of metal contamination. Also,
it allows identification of segments where pro-
cesses are leading to high metal availability to
organisms. The means were based on from one
to 411 tissue samples per segment. The analysis
was carried out separately for each of the follow-
ing metals and chemicals: Cu, Cr, As, Pb, Hg,
and Zn. Clustering was carried out via the ag-
glomerative average linkage method in SAS (SAS
User's Guide, Statistics, 1982 Edition. SAS In-
stitute, Inc.). Clustering was halted at five groups.
These groups were then used to define the class
intervals shown in Figures 20a through g, and in
Table 16 (LC50 values are given in Appendix B).
The lower limit for each class was calculated as
the mid-point between the minimum mean con-
centration (i.e., data value) in each group and the
maximum mean concentration in the group with
the next lowest average concentration. The up-
per limit for each class was calculated as the mid-
point between the maximum mean concentration
in each group and the minimum mean concen-
tration in the group with the next highest average
concentration.
The metal levels in oyster tissues are different
throughout the Bay. Levels of metals in oyster
tissues vary among the segments depending on the
-------
Metals and Pesticides in Oysters 63
TABLE 16.
CLASSIFICATION OF MEAN METAL CONCENTRATIONS IN OYSTER TISSUES IN CHESAPEAKE BAY
BASED ON CLUSTER ANALYSIS
Class Zinc
200
I RET-5
WT-1
Class Zinc
200-747
II LE-2
LE-4
EE-1
RET-3
LE-3
CB-8
WE-4
EE-3
Copper
8.7
RET-5
WT-1
Copper
8.7-51.7
WT-5
ET-5
WT-8
LE-4
CB-8
LE-3
WE-2
WE-4
CB-5
RET-3
EE-2
ET-7
ET-6
ET-8
LE-1
EE-3
ET-4
CB-4
Concentrations
Mercury
0.015
EE-3
EE-1
WT-8
ET-4
RET-1
CB-3
CB-5
WT-7
ET-7
Concentrations
Mercury
0.016-0.03
EE-2
ET-5
LE-2
LE-1
CB-4
, mg/kg (ppm)
Arsenic Lead
0.023 0.05
ET-6 ET-7
ET-8 ET-8
WT-8 ET-5
WT-7 EE-2
CB-3 ET-6
WT-7
CB-3
WT-8
LE-2
RET-1
LE-1
ET-4
, mg/kg (ppm)
Arsenic Lead
0.023-0.06 0.05-0.115
EE-1 CB-4
ET-5 EE-3
Cadmium
0.32
WT-1
RET-5
Cadmium
0.32-0.86
LE-2
RET-3
EE-3
WE-4
LE-3
WT-5
ET-8
Chromium
0.40
WT-7
ET-7
WT-8
ET-6
CB-5
EE-1
EE-2
CB-4
ET-4
LE-2
RET-1
LE-1
CB-3
ET-8
Chromium
0.40-1.56
ET-5
EE-3
(continued)
-------
64 Chapter 1: Water and Sediment Quality
Table 16 (continued).
Concentrations, mg/kg (ppm)
Class Zinc
748-1381
111 WT-5
EE-2
LE-1
LE-5
RET-1
ET-6
WT-8
RET-4
ET-5
ET-7
ET-4
CB-5
CB-3
Copper Mercury Arsenic Lead
51.8-84.7 0.031-0.06 0.061-0.105 0.116-0.24
RET-1 WT-5 LE-2 EE-1
RET-4 ET-6 EE-3
WT-7 CB-4
CB-3 ET-7
ET-4
Cadmium
0.087-1.34
ET-4
EE-2
EE-1
ET-7
ET-5
CB-8
ET-6
CB-5
Chromium
1.57-2.98
CB-8
Concentrations, mg/kg (ppm)
Class Zinc
1382-2784
IV WT-5
ET-8
Copper Mercury Arsenic Lead
84.8-104.2 0.061-0.165 0.106-0.175 0.241-0.36
Eliz.R. ET-8 LE-1 CB-5
EE-2
RET-1
Cadmium
1.35-2.01
WT-8
LE-5
RET-4
CB-4
LE-4
Eliz. R.
Chromium
2.99-4.0
LE-4
RET-4
Eliz.R.
Concentrations, mg/kg (ppm)
Class Zinc
2764
V Eliz.R.
Copper Mercury Arsenic Lead
104.2 0.165 0.175 0.36
LE-5 WT-1 CB-5 WT-5
WT-5
Cadmium
2.01
RET-1
LE-1
CB-3
WT-7
Chromium
4.00
LE-5
RET-3
-------
Metals and Pesticides in Oysters 65
metal (Figures 20a to g). Highest levels of Cu
(Class 5) were found in the James River (LE-5)
and highest levels of Cr were in the James River
(LE-5) and the Rappahannock Rivers (RET-3).
Highest levels of Zn occur in oyster tissues in the
Elizabeth River. The Patuxent River (RET-1 and
LE-1), the Severn River (WT-6), and a main Bay
segment (CB-3) had the highest levels of Cd in
oyster tissues. Highest levels of As were found in
oysters in a main Bay segment (CB-5); highest
levels of Pb were in the Patapsco River (WT-5);
and highest levels of Hg were in the Bush River
(WT-1). In contrast, lowest concentrations (Class
1) tend 1o occur in smaller tributaries, but there
are many exceptions (Table 16).
Mean Cu and Zn levels in Bay oyster tissue cor-
relate with the corresponding contamination fac-
tors (Cf) in surface sediments indicating some
relationship between metal sediment enrichment
and metal concentration by oysters (Chapter 3).
Copper, Cd, and Zn levels in oyster tissue tend
to be higher near the more urbanized centers such
as the Patuxent River, the upper Bay, the lower
James River, and the Elizabeth River. They are
lower in the Potomac River, the tidal-fresh seg-
ment of the Rappahannock River, and Mobjack
Bay. However, trace metal levels in tissues are in-
fluenced by a number of environmental factors
which are discussed in Chapter 3. Furthermore,
it should be noted that concentrations of these
metals in the Chesapeake Bay are less than the
averages reported by a survey of corresponding
metal concentrations in oysters from Maine
through North Carolina (Pringle and Shuster
1967). Throughout the period of record, there was
little problem with shellfish or fish tissue metal
contamination that violated FDA action levels.
The levels of pesticides in oyster tissue do not
exceed FDA action levels and are similar to con-
centrations along the entire Atlantic Coast.
Pesticide concentrations are highest in the
Elizabeth River oyster tissues (Gilinsky and
Roland 1983). Levels of oyster contamination by
DDT in both states have decreased over time
because it has presumably not been introduced
into the system for several years and has broken
down to DDE and DDD. The by-products of
DDT are less toxic, and their levels are detectable,
but not known to be harmful at these concentra-
tions. Garreis and Pittman (1981) found levels of
some pesticides in Choptank River oysters directly
related to rainfall. This was in contrast to trace
metal concentrations, and probably represents the
nonpoint source of these pesticides.
-------
66 Chapter 1: Water and Sediment Quality
FIGURE 20a.
Mean levels of chromium (mg/kg) in oyster
tissue.
-------
Metals and Pesticides in Oysters 67
FIGURE 20b.
Mean levels of arsenic (mg/kg) in oyster
tissue.
-------
68 Chapter 1; Water and Sediment Quality
FIGURE 20c.
Mean levels of lead (mg/kg) in oyster
tissue.
-------
Metals and Pesticides in Oysters 69
FIGURE 20d.
Mean levels of mercury (mg/kg) in oyster
tissue.
-------
70 Chapter 1: Water and Sediment Quality
FIGURE 20e.
Mean levels of zinc (mg/kg) in oyster
tissue.
-------
Metals and Pesticides in Oysters 71
FIGURE 20f.
Mean levels of copper (mg/kg) in oyster
tissue.
-------
72 Chapter 1: Water and Sediment Quality
FIGURE 20g.
Mean levels of cadmium (mg/kg) in oyster
tissue.
-------
SECTION 8
SUMMARY BY GEOGRAPHIC AREAS
This section summarizes the current conditions
and trends by geographic area: main bay, Eastern
Shore, and western shore. Present status and cur-
rent trends are both described. These are, not
synonomous: an area may currently have high
levels cif nutrients, but nevertheless show a signifi-
cant decline over time, or vice-versa. Data tables
giving information on the basis for the following
assessment are in Appendix B, Section 8.
MAIN BAY (CB 1-8)
The main Bay is primarily influenced by the
Susquehanna River. The Susquehanna accounts
for approximately 50 percent of the freshwater in-
flow to the Bay (70 percent above the Potomac).
As a consequence, this river is the most significant
single source of nutrients and toxic chemicals to
the main Bay (U.S EPA 1982b). For this reason,
the upper Bay is enriched with nutrients (class 5)
(Figure 1) and metals in the water column (Figure
18). Moving down the Bay, concentrations begin
to decrease. Nutrient levels in the water column
are still high in the mid-Bay, but decrease to
background levels in the lower Bay. The metals
in the water column are relatively high in the
upper Bay (CB 1-3), drop to intermediate levels
off the Patuxent and Potomac (CB-5), and then
decrease to background levels in most parts of the
lower Bay.
The concentration of organic compounds and
the degree of metal contamination in the sediment
follow the same general pattern as the water-
column nutrients and metals. Because metals and
organic compounds tend to preferentially adsorb
to fine grain sediments, an effort was made to
"normalize" the organic compound and metal
values, so that they reflect comparative enrich-
ments. In Figure 13, it is apparent that the up-
per Bay is enriched with organic compounds.
Levels decrease down-Bay, then increase at sta-
tions off Hampton Roads. The degree of metal
contamination (Ci) in the sediment follows a
slightly different pattern (Figure 17). It is
moderate in the Susquehanna Flats, then increases
to high levels off Baltimore, probably from long-
term input from polluted Patapsco River sedi-
ments in this area. The Q then decreases down
the Bay to levels of minimal contamination, ex-
cept that very high values are found in the
Elizabeth River, Hampton Roads, and Lynnhaven
areas.
In terms of trends, one sees an increase in at
least one form of nitrogen or phosphorus in most
of the upper and mid-Bay (Figure 5). As was dis-
cussed in Section 2 of this chapter, this screening
assessment actually obscures some individual
nutrient trends. Some form of nitrogen is increas-
ing in CB 1-4; similarily, segments CB-1, 2, 3, and
5 show increases in some form of phosphorus.
Nitrate or nitrite-nitrogen show increases in CB-1,
2, and 3, while TKN and NH3 generally show no
trends or declines. Chlorophyll is increasing an-
nually or seasonally in every main Bay segment
where data exist: CB-1, 2, 3, 4, 5, and 7. These
trends may be contributing to the temporal and
spatial increases in summertime anoxic bottom
water in the upper and mid-Bay.
EASTERN SHORE (ET 1-10, EE 1-3)
The Eastern Shore tributaries and embay-
ments are shallow, highly productive waters.
Nutrient inputs from land runoff have long con-
73
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74 Chapter 1: Water and Sediment Quality
tributed to this productivity. However, assessment
of present status and trends shows a change in
nutrient enrichment in many of the eastern
tributaries, and in Tangier and Pocomoke Sounds.
All tributaries except the Sassafras, Manakin, and
Annamessex Rivers are class 4 or 5 waters, based
on nitrogen. We see an increase in at least one
form of nitrogen or phosphorus in all but the
above-mentioned rivers; the lower Choptank
River and Eastern Bay also show no nutrient
trends. Individual nutrient species trends are less
consistent. Again, when NOs or NO2 increase,
these trends are generally accompanied by
decreases in ammonia or TKN. Chlorophyll shows
annual or seasonal increases in ET-5, ET-10, and
EE-1. Data are relatively incomplete in much of
the Eastern Shore for chlorophyll; it is possible
that more complete information would reveal
trends in other tributaries.
Data are also few for toxicants in Eastern
Shore areas. An assessment of existing informa-
tion indicates that there are relatively few pro-
blems with toxic substances. Although the data
are very sporadic, they indicate no metal con-
tamination in the Eastern Shore sediments (Figure
17). There have been relatively few recorded
observations of water column metals and
pesticides that exceed EPA water quality criteria.
Toxic chemicals are apparently not a problem in
the Eastern Shore tributaries and embayments at
this time except for local situations. Agricultural
chemicals (pesticides and herbicides) might repre-
sent the major potential problem.
WESTERN SHORE (WT 1-8, TF 1-5,
RET 1-5, LE 1-5)
The western shore of Chesapeake Bay is char-
acterized by a series of small tributaries (WT 1-8)
and major tributaries (Patuxent, Potomac, Rap-
pahannock, York, and James Rivers). Most of the
Bay's major population centers are located along
these tributaries. It is, therefore, not surprising
that many sections of the western shore are
stressed with nutrients and toxic chemicals.
Western Shore Tributaries (WT 1-8)
Upper western shore tributaries are presently
class 5 or 6 waters when ranked on the basis of
TN or TP: .these include segments WT-1, 2, 4, and
5. Segments WT 6-8 are class 2 or 3. Although
there is a paucity of long-term data, it appears
that some segments are experiencing degrading
water quality. In fact, Back River (WT-4) in
Maryland has reached a state in which its DO
levels are decreasing from the presence of excessive
organic material in the water (chl a maximum is
200 ug L'1). Municipal sewage treatment plant
discharges, failing septic systems, and storm water
runoff all contribute to the problem.
Toxic chemicals are a problem primarily in the
Baltimore area. There have been many recorded
violations of organic compound and metal criteria
in the water column in Baltimore Harbor (WT-5)
and in the Back River (WT-4) areas. Also, the
degree of metal contamination is higher in the
Baltimore area than in any other area in Maryland
(Figure 17). On the basis of this analysis, it is ap-
parent that the Patapsco River is severely polluted.
Fortunately, much of this pollution appears to stay
in the harbor under average conditions due to the
circulation pattern. Thus, the Patapsco River
generally serves as a sink rather than a source of
pollution except when humans transport its
polluted sediments into the main Bay during
dredging activities.
Patuxent River (TF-1, RET-1, LE-1)
The Patuxent River contains high levels of
nutrients; it is class 6 for both TN and TP in the
tidal-fresh reaches, improving to class 4 in the
lower estuary. Its chlorophyll a maximum levels
range from 200 ug L"1 in the tidal-fresh segment
to 70 ug L"1 in the lower estuary. These values
are among the highest observed in the Bay in
similar segments. It is, therefore, not unusual in
the summer to see minimum DO values ap-
proaching 2 mg L"1 in the tidal-fresh segment and
anoxic conditions (0 mg L"1) in the deep water of
the lower estuary. An analysis of the long-term
trend data indicates continuing water quality
degradation, although a decline in TP in summer
should be noted. In terms of toxic chemicals, there
have been a few recorded dissolved metal criteria
violations in the river, most often in the tidal-fresh
areas. Unfortunately, there are insufficient data
to assess the degree of organic chemical or metal
contamination in the sediments.
-------
Summary by Geographic Areas 75
Potomac River (TF-2, RET-2, LE-2)
The Potomac estuary supports major develop-
ment arid urbanization, particularly in its tidal-
fresh reaches. Significant degradation of water
quality had occurred by the mid-1900's. Because
of public pressure in the late 1960's, an effort was
made to significantly reduce the sewage treatment
plant nutrient loadings to the river and to improve
water quality. This policy appears to have had
some positive effect on the Potomac River. We see
a decrease in TP in the upper segment and a
decrease in TN in the lower segment (Figures 3
and 4): seasonal TN declines are observed in TF-2
in summer. This general trend is further cor-
roborated by Secchi depth measurements that
have increased in the 1970's, indicating better light
penetration due to lower levels of organic and in-
organic material in the water.
In addition to the nutrient enrichment prob-
lems in the upper Potomac estuary, there are some
problems with toxic chemicals. There have been
a number of recorded violations of total residual
chlorine and dissolved metal criteria in the up-
per Potomac (Figures 19a and b). Also, the degree
of metal contamination is high (> 14) in the up-
per reaches (Figure 17). This toxic chemical prob-
lem is not so evident in the lower portion of the
river. The urbanized Washington, DC area is an
important source of toxic substances to the river,
although the major source of some metals is from
above the fall line
Rappahannock and York Rivers
(TF 3-4, RET 3-4, LE 3-4)
These rivers are considered to be the least im-
pacted areas of the western shore. Nonetheless,
they contain moderate levels of nutrients (class 4
or 5), particularly in tidal-fresh reaches. Trend
analysis indicates that phosphorus is increasing in
the lower and mid-Rappahanock River; nitrogen
is increasing in the upper York River. No trends
in chlorophyll were identified.
Toxic chemical problems are evident in several
sections of the Rappahannock and York Rivers.
Violations of EPA water quality criteria occur
along both rivers (Figures 19a and b). The degree
of metal contamination in the sediment is high
(> 14) in the lower Rappahannock and at the
juncture of the Mattaponi and York Rivers.
The principal factor responsible for the high
degree of contamination is Cd. It is possible that
the high concentrations of Cd are natural: the
result of weathering of the Fairhaven diatona-
ceous member of the Calvert Formation, known
to be high in Cd and known to be exposed in the
lower Rappahannock and along the Calvert Cliffs.
Unusually high metal concentrations in the
water column are also found on the York at the
juncture of the Mattaponi and Pamunkey Rivers
(Figure 17). These findings justify continued
monitoring of the Rappahannock and York Rivers
for possible toxicant contamination.
James River (TF-5, RET-5, LE-5)
The James River contains high levels of
nutrients (class 5 in TF and RET segments). Point
sources are most important in this river, as the
James River supports several major urban centers.
In the upper James, TN and TP concentrations
have reached a maximum of 2 mg L'1! and 0.5
mg L"1! and DO levels have dipped to 3 mg L"1!
during the period of record. However, both
nitrogen and phosphorus are declining through
most of the estuary. No trends in chlorophyll were
identified.
Toxic metals and organic compounds occur in
high concentrations in several areas of the James
River. Recorded toxic violations occur all along
the river but appear to be more concentrated in
the uppermost reaches of the James River and in
the Elizabeth River (Figures 19a and b). The
degree of metal contamination in the sediment is
very high in the Elizabeth River and the upper
James and relatively low in the lower sections of
the James River (Figure 17).
Although there are insufficient data to
characterize the general level of organic com-
pounds in the James River, it is valuable to look
at the one compound that has been extensively
studied — Kepone (Section 4). Discharged in tidal-
fresh waters, relatively high levels were detected
as far as 120 km from the source. Because organic
compounds tend to adsorb to sediment, it is not
surprising that high concentrations of Kepone are
found in turbid waters of the James River and in
the bed sediments of the turbidity maximum area.
The Kepone incident has resulted in intensified
efforts to improve water quality in the river.
-------
76 Chapter 1: Water and Sediment Quality
CONCLUSIONS
From information presented in this chapter,
several conclusions can be drawn:
• Upper and mid-Bay main stem, tidal-fresh,
and transition reaches of major tributaries,
and many smaller tributaries contain high
levels of nutrients. Nutrient concentrations
tend to decline down estuary.
• The pattern of toxic substances in water or
sediments —metals and organic com-
pounds — is generally similar. However, tox-
ic contamination is also found near urban
areas in the lower Bay.
• Chlorophyll a, an indicator of increased
phytoplankton biomass and, thus, of nutri-
ent enrichment, is showing an upward
trend throughout the Bay main stem and
in several tributaries.
• Nitrogen concentrations (including TN,
NO2, NOs, TKN, and ammonia) are in-
creasing in the upper half of Chesapeake
Bay, and in several tributaries, including
the Chester, Patuxent, Potomac, York,
Nanticoke, and Wicomico Rivers. Declin-
ing trends occur in the Patapsco and James
Rivers.
• Phosphorus concentrations (including TP
and IPF) are increasing in the upper and
mid-Bay, except for CB-4 where declining
trends were observed. Increased phosphorus
trends also occur in the Chester, Choptank,
mid-Patuxent, lower Potomac, and Rappa-
hannock Rivers, and in Tangier and
Pocomoke Sound. Declines occurred in the
upper Potomac and throughout the James.
• There is an increase in the duration and ex-
tent of low DO in deep water of Chesa-
peake Bay in summer. This trend is most
pronounced in the upper and mid-Bay;
there is no apparent anoxia in lower Bay
deep waters, probably due to rapid mixing
and exchange in this region. The DO trend
is best explained by increased production
of organic material due to elevated levels
of nutrients in the upper half of the
Chesapeake.
• Levels of trace metals and organic chemi-
cals in the tissues of shellfish seem to parallel
(in a general way) the observed patterns of
toxic contamination in the Bay.
Although the ability to quantify this "pollu-
tion" is imperfect, we believe these conditions and
trends warrant attention. Although the Eastern
Shore contains moderate to high levels of nutri-
ents, waters of this area show very little toxic
chemical contamination. The lower Bay is rela-
tively unimpacted except locally. With additional
effort in reducing input, significant improvements
in several areas of the Bay could be achieved. For
example, increased pollution control in the Poto-
mac and James Rivers has resulted in improved
water quality at least with regard to nutrients.
-------
SECTION 9
RANKING GBP SEGMENTS ACCORDING TO
CURRENT WATER QUALITY CONDITIONS
INTRODUCTION
Ranking segments can help identify areas of
the Bay experiencing degraded environmental
quality clue to high levels of nutrients and tox-
icants. A ranking system has been established to
characterize the water and sediment quality of the
45 Bay segments (Table 17). Water nutrient con-
centrations, scaled linearly 1 to 6, and sediment
toxic metal concentrations, scaled 1 to 5, are add-
ed for each segment to give an overall water qual-
ity value. A high value reflects high enrichment.
Nutrient Ranking
The overall nutrient ranking used here was
developed from data compiled by the GBP of an-
nual mean nutrient concentrations. Two vari-
ables, total phosphorus and total nitrogen, were
each grouped into six gradations based upon their
concentrations in the estuary. Ranges of TN and
TP used to develop these ranks are given in Table
4 of this chapter. The overall rank was based on
the nutrient in greatest abundance. Data were
available for 43 segments (Figure 21).
Toxic Metal Ranking
The toxicant enrichment ranking shows the
relative distribution of metals in bottom sediments
of the Bay segments. It is based on the Contamina-
tion Index that sums the anthropogenic enrich-
ment above natural levels for the six most fre-
quently sampled metals in the surface sediments.
After being mapped and contoured according to
three divisions (Q<4, 4 to 14, >14, indicating
less than 400 percent; 400 to 1400, and over 1400
percent enrichment) (Figure 17), the metal con-
tamination map was over-laid by the GBP
segmentation map of the Bay. Values ranking
from 1 to 5 to represent the three categories and
two gradations between them values were given
for the 26 segments for which sufficient data
existed.
As discussed earlier in this chapter, concen-
trations of organic substances in the sediments are
too poorly characterized spatially to be of use in
this assessment.
77
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78 Chapter 1: Water and Sediment Quality
TABLE 17.
RANK OF CBP SEGMENTS ACCORDING TO SELECTED PRESENT WATER QUALITY
Segment
CB-1
CB-2
CB-3
CB-4
CB-5
CB-6
CB-7
CB-8
WT-1
WT-2
WT-3
WT-4
WT-5
WT-6
WT-7
WT-8
EE-1
EE-2
EE-3
WE-4
TF-1
RET-1
LE-1
TF-2
RET-2
LE-2
TF-3
RET-3
LE-3
TF-4
RET-4
LE-4
TF-5
RET-5
LE-5
TN
5
5
5
4
4
ND
r
ND
5*
5
3
6'
6
2
2
3
2
2*
3
2
6
5
4
5
5
2
4
2
2
3
2'
2*
5
5*
3
TP
3
3
3
2
2
ND
ND
ND
2*
2
2
6*
3
2*
2
3
3
2'
2
2
6
5
4
4
4
2
5
3
2
4
3
3
5
3*
3
Nutrient
Overall
5
5
5
4
4
—
1
—
5
5
3
6
6
2
2
3
3
2
3
2
6
5
4
5
5
2
5
3
2
4
3
3
5
5
3
Ci
3
4
4
3
2
1
1
1
ND
3
3
5
5
ND
ND
ND
ND
ND
1
1
ND
ND
3
4
2
2
ND
ND
4
ND
ND
ND
3
1
3
CONDITIONS
Water
Quality*
Overall
8
9
9
7
6
1 +
1
1 +
5 +
8
6
11
11
2 +
2 +
3 +
3 +
2 +
4
3
6 +
5 +
7
9
7
4
5 +
3 +
6
4 +
3 +
3 +
8
6
6
(continued)
-------
Ranking CBP Segments 79
Segment
ET-1
ET-2
ET-3
ET-4
ET-5
ET-6
ET-7
ET-8
ET-9
ET-10
TN
4*
5
3*
4
5
5
5
3*
3*
4
Table 17
TP
2*
3
2*
5
3
2
4
2*
2*
3
(continued).
Nutrient
Overall
4
5
3
5
5
5
5
3
3
4
Ci
5
3
ND
1
1
ND
1
ND
ND
ND
Water
Quality*
Overall
9
8
3 +
6
6 +
5 +
6
3 +
3 +
4 +
*= Based on limited data (Table 4)
ND = Limited data
+ = Ranking based on nutrients or C\ only
-------
80 Chapter 1: Water and Sediment Quality
Limited
data
FIGURE 21.
Rank of Chesapeake Bay segments according
to nutrient status.
-------
CHAPTER 2
LIVING RESOURCES:
A HISTORY OF BIOLOGICAL CHANGE
-------
CHAPTER 2
LIVING RESOURCES:
A HISTORY OF BIOLOGICAL CHANGE
-------
SECTION 1
INTRODUCTION
HOW DO WE ASSESS IMPORTANT
BIOLOGICAL CHANGES?
Chesapeake Bay supports a diversity of life,
from microscopic plants to fish, birds, and mam-
mals. The well-being of the Bay's biota depends
on the physical and chemical processes that take
place within it (Chapter 3). The objective of this
chapter is to describe the health of Chesapeake
Bay and to identify biological changes that may
have resulted from water quality changes.
A temperate, natural system is normally fairly
diverse, containing several trophic levels with
many species at each level. Major change may be
reflected when species decline dramatically or
become overly abundant. A biological continuum
may exist, ranging from a system in which many
species are present in moderate abundance, to a
degraded system ' - which a few pollution-tolerant
species piersist. Biological changes also occur in
response to factors other than water quality
(Chapter 3).
In this analysis, biological change is assessed
through historical analysis of trends in species
distribution, abundance, and harvest. The pres-
ent condition in the Bay system was spatially com-
pared, assuming that physically and chemically
similar areas can be expected to be biologically
similar. Where major differences exist, it is in-
ferred that biological change has occurred
This chapter discusses phytoplankton, sub-
merged aquatic vegetation (SAV), benthic
organisms, shellfish, and commercial finfish
because the historical and/or spatial data were suf-
ficient to attempt an assessment. In addition, these
resources are of ecological and/or economic im-
portance;. In an effort to define regional and local
differences, results are discussed in terms of two
geographical divisions: basins (Figure 22) and
segments.
INDICATORS OF CHANGE
Phytoplankton form the major base of the
estuarine food web. Changes in abundance, diver-
sity, and species composition of phytoplankton
may cause turbidity, toxicity, odor, and unaes-
thetic floating mats. Other direct effects include
shading of submerged grasses and loss of food
(through shifts to unpalatable phytoplankton
species) for zooplankton through fish. Excessive
phytoplankton biomass can lead to loss of dis-
solved oxygen from bottom waters. Historical
changes in phytoplankton species composition,
diversity, and biomass, as documented for upper
Chesapeake Bay (above the Bay Bridge) and up-
per Potomac River (tidal-fresh reach), are
discussed.
Submerged aquatic vegetation is a major com-
ponent of the detrital food web. These Bay grasses
provide habitat for many crabs, fish, and their
food. This chapter focuses on historical changes
in the distribution and abundance of SAV and
compares the present condition of beds across
geographical areas.
Benthic invertebrates may indicate environ-
mental change because they may be exposed to
low dissolved oxygen and toxic materials. A spatial
comparison of the present species composition and
diversity in Baltimore Harbor is presented here.
The shellfishery is a major economic and
cultural element of the Chesapeake Bay region.
Historical changes in commercial landings of
83
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84 Chapter 2: Living Resources
esopeake Bay North
Chesapeake Bay Upper-Central
icoke
Chesafceak^Bay
Lower Central
Pamunkey
Chesapeake Bay General
FIGURE 22.
NOAA National Marine Fisheries Service
(NMFS) basins used in living resources
analysis.
-------
Introduction 85
oysters and crabs, as well as oyster spat set (the
abundance of juvenile oysters), are described. As
immobile bottom-dwellers, oysters are good in-
dicators of some forms of environmental stress.
Commercial finfish are of tremendous econo-
mic importance; landings are the most spatially
and temporally complete biological data avail-
able. Landings are not an unequivocal indicator
of stocks; however, the conclusions drawn from
the analysis of landings data are supported with
basic biological data, the finfish juvenile index.
Attempts to adjust landings data for fishing ef-
fort would be of little value because of the
unavailability of acceptable effort data (Roths-
child et al. 1981).
MAJOR BIOLOGICAL COMPONENTS
AND THEIR INTERACTIONS
To interpret biological changes, the species in-
volved should be understood as well as possible.
Important information includes environmental
tolerances, life cycles, and interactions among
species.
In the analysis of finfisheries, data existed for
13 species taken from 18 major basins. Thus the
data were aggregated. Because its life cycle helps
determine the likelihood that a species will be ex-
posed to environmental stress, the CBP considered
grouping species on the basis of their spawning
habits. This suggestion was supported by similar
trends in harvest and juvenile index data within
such aggregations (discussed in Section 6). Thus,
finfish are considered in two groups: marine
spawners and freshwater spawners.
During the spring, freshwater spawners
(alewife, catfish, shad, striped bass, white perch,
and yellow perch) release their eggs in the fluvial
or tidal-fresh reaches of the Bay system. Such
reaches tend to be the first exposed to toxic
chemicals and suspended sediments from the rivers
feeding into the Bay. Some of these areas have also
been subjected to extensive physical changes such
as construction of dams and deposition of
sediment.
Larvae and juveniles of some marine spawners
enter the Bay during the late spring and summer
to reach their upstream nursery areas; others enter
in late fall through the winter (e.g., spot and
croaker). Anoxia of bottom waters during this
period can restrict their habitat and food avail-
ability, particularly for spot and croaker, which
tend to feed on the bottom. Oysters and crabs are
also potentially subject to hypoxic waters. The
oyster habitat is detailed in Appendix C, Section 2.
One of the aspects that determines a species'
ability to survive and reproduce in its environment
is its environmental tolerances, or "survival
envelope." When these tolerances are exceeded by
natural or man-induced stress, the species will be
reduced or eliminated.
When organisms are exposed to non-optimal
conditions for some factors, they may be more
vulnerable to other stress. For example, the com-
mon sand shrimp (Crangon sp.) has a broader
tolerance for salinity and temperature at saturated
dissolved oxygen levels than at low (2 to 3 ppm)
dissolved oxygen levels (Haefner 1970). Thus,
variations in water quality can affect an or-
ganism's sensitivity to other forms of stress.
One life stage may be more sensitive to stress
than another. For most species, the period of
reproduction (spawning, hatching, and early lar-
val development) is most critical. For example,
the salinity tolerance of striped bass eggs ranges
from 0 ppt to about 10 ppt, but adults can tolerate
salinity gradients from freshwater to ocean water
(0 to 35 ppt) (Setzler et al. 1980). In general, lar-
vae are considered to be more sensitive than other
life stages of fishes (Sindermann et al. 1982).
Once its environmental tolerances are under-
stood, a species' life history must be known so that
the likelihood that sensitive stages will be exposed
to stressful conditions can be assessed. Life cycles
of major species are considered in detail in Ap-
pendix C, Section 1.
Water quality may affect organisms directly
through physiological effects, or indirectly
through species interactions. The well-being of
one species can affect that of another through
feeding relationships, competition for food or
habitat, and in other ways. The feeding relation-
ships that support fish in Chesapeake Bay are
shown in Figure 23; they are described in greater
detail in Appendix C, Section 1. Figure 23 graph-
ically shows that the larger phytoplankton (net
phytoplankton) directly provide food for several
adult fish species and for zooplankton. The direc-
tion of the arrows shows the pathways of food in
-------
86 Chapter 2: Living Resources
Net
Zoopiankton
Menhaden
Larval Fishes
Anchovies
Shad
S- Alewife
Killifishes
Silversides
Mummichog
Gobies
Hogchoker
t
1
White Perch
Eels
Winter Flounder
Catfishes
S- Atlantic Croaker
t
S- March to November in System —— —*~
I
S- Bluefish
Striped Bass
S- Weakfishes
S- Spot
S- Drum
"""""
\ '
\ x 4
terrfhie
Crtistooedre
Poiyehaelss :
Bivalves
i J
,—_ „.„... ; ^ ' f
1
lue
:rabs
Larvalforrm
FIGURE 23, Feeding relationships of fish in Chesapeake Bay (after Green 1978). [Seasons(s) as specified in
this chart are incorrect for spot which occur year-round. March to November also applies to
shad.]
the food web for the other components.
Of basic importance to the estuarine food web
are the primary producers. These are the plant
forms, able to use light as an energy source. All
other organisms in the Bay depend directly or in-
directly on plants for food. In Chesapeake Bay,
the most important primary producers are phy-
toplankton, followed by Bay grasses. Marshes and
other wetlands also contribute to estuarine food
webs, mostly through detrital inputs.
Many benthic species (oyster, clam, etc.) feed
on living and detrital phytoplankton. The species
of phytoplankton is important, as this determines
whether it can be used for food. Ryther (1954)
describes the classic example of Moriches Bay,
New York, in which changes in phytoplankton
species composition led to the demise of a once-
prosperous oyster industry. The change in phy-
toplankton species resulted from increased
nutrient inputs by duck farms.
Submerged aquatic vegetation provides a
direct and indirect food source as well as habitat
for many estuarine animals. It may supply much
of the diet of sheepshead (Archosargus pro-
batocephalus) as well as turtles; as a major source
of detritus, SAV provides food for a variety of
filter-feeders (Stevenson and Confer 1978). Sub-
merged aquatic vegetation affords substrate for
organisms like mussels, barnacles, and molluscs
(Green 1978). Fish, including Atlantic silversides
-------
Introduction 87
(Menidia menidia), feed on these epifauna. The
blue crab depends on SAV beds to furnish shelter
from predators (Darnell 1959).
With the exception of the Atlantic menhaden
that feeds on phytoplankton as an adult, most of
the fishes treated in this study, as well as crabs,
tend to be carnivorous and are opportunistic
feeders. Changes in one food source may not af-
fect them significantly because they can switch
to another source. However, some species may be
more limited; sciaenids, such as spot and croaker,
depending heavily on benthic organisms for much
of their food.
Understanding predator-prey relationships
suggests a second major species interaction: com-
petition for food. It could be hypothesized that
species with similar food habits are potential com-
petitors; if food becomes limiting, one species may
decline relative to the other. Also, one species may
depress populations of the other species (May et
al. 1979).
-------
SECTION 2
CHANGES IN BIOMASS AND SPECIES COMPOSITION
OF PHYTOPLANKTON IN TWO
WELL-DOCUMENTED AREAS
INDICATIONS OF ENRICHMENT
Because most phytoplankton use inorganic
nutrient elements directly, changes in abundance
and species composition of these primary pro-
ducers may be the first indications of excessive
nutrient enrichment in a system. In this section,
two areas, the upper Bay (above the Bay Bridge)
and upper Potomac River (tidal-fresh reach), in
which increased dominance by single species and
increased biomass have paralleled increased
nutrient enrichment, will be discussed. These are
the areas for which the most comprehensive data
are available; similar changes may be occurring
elsewhere, or could occur if nutrient enrichment
increases.
Excessive nutrient enrichment, a corollary of
eutrophication, frequently produces increased
biomass of algae as its first observable effect
(Heinle et al. 1979). Excess nutrients may lead to
blue-green algal blooms in the tidal-fresh portions
of estuaries (Darnell and Soniat 1981). In the early
stages, this may be beneficial to harvestable
resources. The increased algal biomass (indicated
by high cell numbers and high chlorophyll a con-
centrations), however, may not be used by
grazers, either because the phytoplankton growth
rate is too rapid or because the forms produced
are inedible (Darnell and Soniat 1981). As a result,
excess organic matter accumulates in the water
column. Subsequent decay of this accumulated
organic matter depletes dissolved oxygen from the
water column.
Excellent relationships have been demon-
strated between phosphorus loads and chlorophyll
a concentrations in lakes (Schindler 1981).
Estuaries are more complex and less well-studied,
but Lee and Jones (1981) have shown a relation-
ship between nutrient loads and chlorophyll a con-
centrations in the Potomac River.
In addition to increased algal biomass, shifts
in species may occur in response to nutrient
enrichment. Blue-green algae are particularly suc-
cessful under enriched conditions because some
species can fix atmospheric nitrogen, or may pro-
duce toxins detrimental to other algae (Lane and
Levins 1977). The tidal-fresh portion of the
Potomac estuary is the best known example of
blue-green algal blooms causing water quality
problems in the Chesapeake Bay system (Clark et
al. 1980). Enrichment of higher salinity reaches
may result in blooms of dinoflagellates (Darnell
and Soniat 1981).
ENRICHMENT IN CHESAPEAKE BAY
The Potomac River has demonstrated changes
in rooted vegetation and phytoplankton that
parallel increases in nutrient enrichment. Prior to
1920 the river was subject to no major plant
nuisances (Pheiffer et al. 1972, Champ et al. 1981,
Haramis and Carter 1983). In the 1920's, the river
experienced an invasion of water chestnut (a
rooted aquatic plant), which has been linked to
overenrichment from wastewater discharges
(Champ et al. 1981, Haramis and Carter 1983).
Another rooted plant, Eurasian water milfoil,
began to replace water chestnut in the late 1940's
and became a major plant problem. In the 1960's,
milfoil was in turn supplanted by massive blue-
green algae blooms, causing widespread nuisance
conditions (Haramis and Carter 1983). These algal
blooms persisted into the 1970's though the
89
-------
90 Chapter 2: Living Resources
amount of organic carbon from wastewater dis-
charges had been reduced by almost 50 percent
(Pheiffer et al. 1972). In September 1978, under
maximum bloom conditions, the blue-greens
amounted to 80 percent of the phytoplankton
population with total cell counts ranging from 60
to 80 million cells per liter (Clark et al. 1980)
(chlorophyll a values during this period ap-
proached 140 ug L"1).
Some researchers believe that water quality
in the upper Potomac River has improved because
of recent phosphorus reductions by extensive
removal from wastewater discharges starting in
1970 (Champ et al. 1981). The 1979 algal popula-
tions were mixed. Phytoplankton composition
under maximum bloom conditions shifted from
dominance by large numbers of filamentous blue-
green algae to smaller numbers of single-celled
blue greens, which made up only about 25 per-
cent of the summer population. Phytoplankton
counts for 1979 and 1980 were lower than in
previous years,4 perhaps caused partly by high-
flow conditions that have characterized the river
in the past few years. Such conditions tend to flush
out phytoplankton.
The Potomac River is surpassed only by the
Susquehanna River in its contribution of nutrient
load to the Bay (Smullen et al. 1982). Trends in
nutrient enrichment of the upper Bay tributaries
have closely paralleled those of the Potomac, and
a similar process is probably underway in the up-
per main Bay. Visual observations of massive algal
blooms are frequently noted. The elevated chlor-
ophyll levels recorded in this area in the early
1970's were due in part to increasing occurrences
of blue-green algae (Clark et al. 1973). Earlier
observations of water from this area by Flemer
(unpublished) revealed only occassional occur-
rences of blue-green algae.
In 1979, a study by the Maryland Power Plant
Siting Program showed cell counts at stations
located in segment CB-2, ranging from 10 million
to 27 million cells per liter during the month of
June (Grant et al. 1979). In 1980, phytoplankton
sampling was conducted by the State of Maryland,
Water Resources Administration (Allison 1980).
Total cell counts in the upper Bay ranged from
18.5 to 21.2 million cells per liter in June.
Chlorophyll a values in 1980 approached 114 ug
L-1 in CB-2 (Chapter 1).
From October 1955 to October 1956, a phy-
toplankton study (Whaley and Taylor 1968) was
conducted on the Bay by continual underway
sampling. The June cell counts in CB-2 ranged
from 2200 to 12,900 cells per liter. However,
Whaley and Taylor, who used net samples, prob-
ably missed smaller species caught in Allison's
whole water samples. Assuming that nannoplank-
ton compose between 75 and 93 percent of the
phytoplankton population (McCarthy et al. 1974,
VanValkenburg and Flemer 1974), Whaley and
Taylor's numbers could be elevated to as much
as 86,000 cells per liter. Allison's 21.2 million cells
per liter represents an increase of 247 fold over
the 86,000 cells per liter. This increase is probably
attributable to an increase in nutrient supply in
the upper Bay. With increasing nutrient enrich-
ment in the segments of the upper Bay, we can
expect to see the total cell counts elevated with
a movement toward blooms of nuisance algal
forms like those documented in the Potomac
River.
Much of the information on the upper Bay
cited above is limited and should be supported by
a more concerted effort. It is recommended that
intense monitoring of the upper Bay for nutrient
inputs and actual phytoplankton species iden-
tification and enumeration be done. This would
provide concrete evidence of the species shifts
believed to be taking place.
-------
SECTION 3
THE DECLINE OF SUBMERGED AQUATIC
VEGETATION
The Chesapeake Bay's other major primary
producer, submerged aquatic vegetation, is an im-.
portant ecological resource. About 10 species of
submerged vascular plants are collectively called
submerged aquatic vegetation (Table 18). Sub-
merged aquatic vegetation harbors food, provides
habitat to major fish species, and is a source of
food for waterfowl and aquatic mammals. The
grasses have undergone a precipitous decline in
the past 10 to 15 years. In this section, the time
course of that decline and its geographic nature
is discussed. Finally, a geographic assessment of
the present use of its habitat by SAV with respect
to its potential is shown. Data contributing to this
section are given in Appendix C, Section 5.
Submerged aquatic vegetation was the subject
of a major Chesapeake Bay Program research ef-
fort (Orth and Moore 1982). Since the late 1960's
a dramatic, Bay-wide decline has occurred in the
abundance of submerged aquatic vegetation, and
its distribution has changed. Although the rates
and patterns of decline have not been uniform
throughout the estuary, some patterns do appear.
Loss has moved progressively down-estuary, par-
alleling nutrient enrichment trends. Submerged
aquatic vegetation now occupies a significantly
more restricted area than previously. As a conse-
quence, the scope of its role in Bay ecosystem pro-
cesses has also been reduced, and its ability to
recover from its current status without an im-
provement in ambient water quality is
questionable.
Submerged aquatic vegetation is restricted to
shallow areas of Chesapeake Bay because of its
requirements for light. Reduction in light avail-
ability has been implicated as a significant source
of stress to SAV. For example, increased nutrients
leading to increased phytoplankton growth and
greater production of leaf-surface epiphytes have
been shown in pond studies to decrease SAV bio-
TABLE 18.
MAJOR SPECIES OF SUBMERGED VASCULAR PLANTS (SAV) IN CHESAPEAKE BAY
Ceratophyllum demersum
Elodea canadensis
Myriophyllum spicatum
Najas guadalupensis
Potamogeton pectinatus
Potamogeton perfoliatus
Ruppia maritime
Vallisneria americana
Zannichellia palusfris
Zostera marina
Coontail
Elodea
Eurasian Watermilfoil
Water Nymph
Sago Pondweed
Redheadgrass
Widgeongrass
Wildcelery
Horned Pondweed
Eelgrass
91
-------
92 Chapter 2: Living Resources
mass (Kemp et al. 1982b). Kemp et al. (1982b)
have reviewed other microcosm, pond, and field
data that implicate nutrients as a major cause of
SAV decline. Microcosm studies have shown that
turbidity (total suspended solids) causes decreased
photosynthesis (Kemp et al. 1982c). Herbicides
can inhibit SAV photosynthesis but, in most parts
of Chesapeake Bay, plants are not likely to be ex-
posed to concentrations from which they could not
recover (Kemp et al. 1982b).
Work on submerged aquatic vegetation in the
Potomac River, by the U.S. Geological Survey
(USGS), also concluded that excessive nutrients
are the primary cause of SAV declines in the tidal
river (storms and other extreme events are also
important factors) (Haramis and Carter 1983).
However, evidence from transplant and caging
experiments, in which grazers are kept in with the
plants (results still in preparation), indicates that
grazing may have significant effects on the abil-
ity of plants to recolonize former habitat. The sur-
vival of SAV populations in the estuarine-riverine
transition zone may be linked to adverse effects
of this unstable environment on potential biolog-
ical competitors or predators (e.g., periphyton,
phytoplankton, and grazers) (Haramis and Carter
1983).
HISTORICAL CHANGES
Historically, SAV has been abundant
throughout the estuary. Biostratigraphic analysis
of selected sites shows continuous presence of the
grasses over several centuries. However, changes
in species composition were apparent from 1930
to L965 (Orth and Moore 1982). From 1958 to
1962, there was a dramatic proliferation of the
exotic species watermilfoil (Myriophyllum
spicatum) in the upper Bay (Bayley et al. 1978).
A similar pattern occurred in Lake Mendota,
Wisconsin, where Myriophyllum invasion oc-
curred in response to eutrophication (Lind and
Cottam 1969). In Chesapeake Bay, the milfoil
populations declined after 1962, probably because
of pathogens, and the native vegetation returned
(Bayley et al. 1978). However, plants were pre-
sent in less abundance than before the milfoil in-
vasion, and species composition was different.
This pattern may have resulted from increased
turbidity and nutrients in the upper Bay (Bayley
et al. 1978).
Progressive and general decline in SAV abun-
dance has characterized the period from 1965 to
the present (Orth and Moore 1982, Figure 24).
This decline was first observed in the upper Bay
and in fresher reaches of tributaries. The lower
Bay first showed effects in the early 1970's.
Statistically significant declines in SAV
coverage have been demonstrated in a survey of
SAV at approximately 650 stations conducted an-
nually by the Maryland Department of Natural
Resources and the United States Fish and Wildlife
Service (USFWS) Migratory Bird and Habitat
Research Laboratory. At least 50 stations occurred
in each Chesapeake Bay Program segment ana-
lyzed (Appendix C, Section 5). In 1971, 28.5 per-
cent of the stations were vegetated; coverage
declined to about 10.5 percent by 1973 and
dropped to 5 percent in 1981 (Figure 25). In 1971,
10 Bay segments reported no vegetated stations,
but in 1981, 14 segments had none. Statistically
significant' declines in SAV coverage occurred
since 1971 within seven of the vegetated Maryland
segments (CB-5, EE-1, EE-3, ET-5, ET-8, ET-9,
WT-7), as well as in the total surveyed area (Ap-
pendix C, Section 5). Other segments showed no
clear trends, or had so little remaining vegetation
in 1971 that significant declines after that date
could not be demonstrated.
Preliminary results from the 1982 summer
survey indicate a continued downward trend
(James 1982, Macknovitz 1982). In 1982, only 4.5
percent of the 646 stations visited had rooted
vegetation. On the Eastern Shore, Smith Island
had the highest percentage of SAV (41.2 percent
vegetated stations). Vegetation in the Chester
River (ET-4) had dropped to 0.0 percent and to
4.3 percent in Eastern Bay. Vegetation increased
slightly to 6.7 percent in the Choptank River. On
the western shore, the Susquehanna Flats showed
a strong increase (to 13.5 percent; however,
milfoil was the only species recorded). Submerged
aquatic vegetation in the Magothy and Severn
Rivers declined to 0.0 percent in 1982. In general,
SAV trends continue downward, although gains
occurred in the Susquehanna Flats and Smith
Island areas.
Species diversity also declined significantly in
eight segments (CB-5, EE-1, EE-2, EE-3, ET-5,
-------
The Decline of Submerged Aquatic Vegetation 93
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94 Chapter 2: Living Resources
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The Decline of Submerged Aquatic Vegetation 95
ET-9, WT-6, WT-7) and in the total surveyed
area (Appendix C, Section 5). Remaining SAV
populations are primarily characteristic of the
higher salinity forms. Relatively little SAV
characteristic of tidal-fresh and oligohaline waters
remain; these populations are chiefly confined to
small tributary creeks and the headwaters of some
major rivers.
ASSESSMENT OF PRESENT CONDITION
IN CHESAPEAKE BAY SEGMENTS
To estimate the present ability of Chesapeake
Bay segments to support submerged aquatic
vegetation, the 1978 distribution (the most recent
year for which Bay-wide data are available) was
compared with the maximum distribution to be
expected. The expected distribution is based on
the potential habitat (Shea et al. 1980), the area
for which substrate, salinity and depth meet the
requirements for various species of SAV. Because
of the requirement for light, submerged aquatic
vegetation is limited in its distribution to a depth
of 2 to 3 meters in Chesapeake Bay (Stevenson and
Confer 1978). To be conservative, two meters was
selected as the boundary of the SAV potential
habitat for this Bay-wide analysis. The area of
potential habitat was determined by planimeter-
ing the two-meter contour area for each sampling
area. The resulting potential habitats are listed
in Appendix C, Section 5.
Because factors other than depth affect the
distribution of SAV, the potential habitat will
rarely be entirely occupied. To estimate the pro-
portion of potential habitat that could be expected
to be occupied by SAV, two approaches were
taken: case studies and ground truth surveys.
Aerial photographs of the Poplar Island and
Tilghman Island areas in 1971 were obtained from
the United States Fish and Wildlife Service. SAV
had not begun to decline in these areas in 1971.
The two-meter contour and SAV distribution were
planimetered based on the aerial photographs;
SAV was found to occupy 25 to 30 percent of the
potential habitat.
The USFWS-Migratory Bird and Habitat
Research Laboratory (MBHRL) has also surveyed
areas in Maryland that fall within the potential
habitat range since 1971. The percent of sites
vegetated ranged from 7 to 83 (Appendix C, Sec-
tion 5).
As a result of these approaches, 50 percent was
chosen as the proportion of potential habitat that
could be expected to be vegetated to reflect the
theoretical range of 25 to 83 percent. The pur-
pose of establishing this expected habitat is not to
quantify SAV decline, but to formulate a theo-
retical baseline for geographically comparing
Chesapeake Bay segments. The area of expected
habitat is shown for each sampling area in Ap-
pendix C, Section 5.
The percentage of expected habitat filled in
1978 was determined for each sampling area; the
areas were then ranked from 6 to 1 (Appendix C,
Section 5). The ranking scheme (6 = 0 to 2.5 per-
cent; 5 = 2.6 to 6.3 percent; 4 = 6.4 to 15.8
percent; 3 = 15.9 to 39.8 percent; 2 = 39.9 to 75
percent; 1 = 76 to 100 percent) was chosen to pro-
vide greater resolution at the lower end of the
range and reflects the logarithmic frequency
distribution of values. The range of 6 to 1 was
chosen to be consistent with the nutrients scheme
(Chapter 1), in which a 1 rank indicates a better
condition than presently exists.
The ranks of Chesapeake Bay segments are
shown in Appendix C, Section 5, and Figure 26.
To corroborate the ranking of segments using the
expected habitat approach, the USFWS/MBHRL
data for Maryland were assessed (Appendix C,
Section 5). The maximum of sites vegetated be-
tween 1971 and 1981 was used as a baseline; the
1978 percent of vegetated sites was divided by the
maximum and ranked according to the scheme
discussed previously. There is good agreement for
the Maryland segments.
According to this analysis, SAV now occupies
about 24 percent of its expected habitat for the
Bay as a whole; 19 percent in Maryland and 37
percent in Virginia.
WETLANDS
Submerged aquatic vegetation is one of many
types of wetland found in the Chesapeake Bay
area (McCormick and Somes 1982). Other types,
also of ecological importance, include fresh and
brackish marshes, saline high and low marsh,
wooded and shrub swamps, and transition zones
-------
96 Chapter 2: Living Resources
FIGURE 26.
Percent of expected submerged aquatic
vegetation habitat occupied in 1978 for
aggregated sampling areas,
-------
The Decline of Submerged Aquatic Vegetation 97
between these. Wetlands, both headwater and
tidal, are important to the Chesapeake Bay
ecosystem for a variety of reasons. They are
shelter, feeding, and breeding areas for mammals,
waterfowl, finfish, and shellfish. In fact, Daiber
et al. (1976) estimate that 80 to 90 percent of the
total Chesapeake Bay seafood harvest depends at
some stage on wetlands. One major function is the
contribution of detrital material into food webs
that support major finfish larval feeding patterns:
an example is the relationship between inputs of
ice-scoured detritus from freshwater marshes in-
to zooplankton food webs and the spawning suc-
cess of striped bass (Heinle et al. 1976). Marshes
and other wetlands thus serve as transformers or
processors of nutrients and as seasonal sinks,
releasing in winter nutrients incorporated during
the growing season.
Vegetated wetlands are also important as buf-
fers to the aquatic environment. Nutrients from
runoff or other sources may be removed by the
wetland through denitrification, precipitation,
sorption on organic matter, and vegetative assim-
ilation (Van der Volk et al. 1979). Differences
among the nutrient removal efficiencies of wet-
lands appear primarily related to differences in
hydrology ((Van der Volk et al. 1979, Nichols
1983). \Vetlands may often intercept considerable
quantities of sediment from runoff, as well as pro-
tect vulnerable shoreline areas from erosion (Allen
1979, Novitzki 1979). Wetlands can absorb and
hold considerable quantities of water; it is estim-
ated by Kusler (1977) that one acre of flooded
marsh may absorb over 300,000 gallons of water.
In this manner, wetlands contribute to flood con-
trol through water storage and slowing, as well
as to groundwater recharge (Davis 1978). Pollu-
tants such as heavy metals, pesticides, and fecal
contaminants may also be absorped and trapped
in wetlands. Local conditions within the wetland
largely determine the level of removal of these
pollutants (Gallagher and Kibby 1980).
Despite the ecological importance of marshes
and other wetlands, losses of these areas have oc-
curred throughout the Chesapeake Bay water-
shed. It was estimated by Metzgar (1973) that
some 23,700 acres of wetlands were lost in the
state of Maryland between 1942 and 1969, about
7 percent of the total wetlands in the state at the
beginning of the period. In 1976, all coastal (tidal)
wetlands in Maryland were mapped; at that time
261,000 acres were identified (McCormick and
Somes 1982). In Virginia, approximately 4000
acres were lost between 1955 and 1969, out of a
total area of 220,000 acres of tidal marsh (of which
90,000 acres are salt marsh) (Settle 1969). In
Maryland, most losses (52 percent) were due to
agricultural drainage, 13 percent to housing
development, six percent to industrial develop-
ment, four percent to marinas, and five percent
to dredging and spoil activities (Metzgar 1973).
Erosion, natural succession, and drainage for mos-
quito control accounted for much of the remain-
der. Overall losses are probably much greater. The
Report of the Maryland Conservation Commis-
sion for 1908 to 1909 states that (at that time)
wetlands within Maryland totaled some 500,000
acres, of which 204,400 acres were salt marsh and
the remainder fresh marsh and swamp. This rep-
resented one-twelfth of the total area of the state.
Losses in Virginia were estimated by Settle (1969)
to be due to channelization (purposes not speci-
fied) (47 percent), residential development (27
percent), and 17 percent to industrial projects.
The magnitude of loss of non-tidal wetlands has
not been quantified for either state; an ongoing
National Wetlands Inventory may allow estimates
of this acreage.5
A growing appreciation of the role and value
of wetlands led to passage of wetlands protective
legislation in Maryland (1970) and Virginia
(1972). These acts were designed to protect tidal
wetlands; non-tidal wetlands are still vulnerable.
In recent years, the rate of wetlands loss has slow-
ed to approximately 20 to 25 acres per year per
state of vegetated tidal wetlands.6
-------
SECTION 4
SPATIAL TRENDS IN BENTHIC ORGANISMS
Benthic animals are useful indicators of pollu-
tion because most are relatively immobile and
cannot readily escape unfavorable conditions
(Boesch 1973, Pfitzenmeyer 1975). Changes in
benthic biomass, community structure, and diver-
sity can indicate a variety of stressful conditions
(Boesch 1977a). Stresses may be natural (e.g.,
salinity, temperature, and predation) or an-
thropogenic (e.g., nutrient enrichment, toxicant
contamination). For example, increases in
nutrient loading may alter sediment organic con-
tent to favor dominance by detritivores (Bascom
1982). Toxic pollutants may eliminate sensitive
species, producing benthic communities domi-
nated by resistant, opportunistic forms (Grassle
and Grassle 1974, Dauer et al. 1979). Reduced
dissolved oxygen in overlying waters can severe-
ly limit benthic fauna; where anoxic episodes are
frequent, benthic communities may become
ephemeral or be eliminated completely (Holland
et al. 1979, Mountford et al. 1977). Toxic
materials may be concentrated in tissues of ben-
thic organisms, potentially affecting the
organism's physiological processes (Frazier 1976)
or even the suitability of shellfish for human
consumption.
Historical data on benthic organisms, that is,
data showing trends over some period of time, are
not available for many areas of Chesapeake Bay.
Although most major regions of the Bay have had
benthic surveys performed within the last two
decades, time history information exists only for
such regions as Calvert Cliffs, and the Patuxent,
Potomac, lower York and lower James Rivers.
Current conditions are better documented. Under
auspices of the EPA's Chesapeake Bay Program,
present conditions were investigated for the
Maryland portion of the Bay mainstem (Reinharz
and O'Connell 1981), Virginia mainstem (Nilsen
et al. 1981), Patapsco River (Reinharz 1981), and
Elizabeth River (Schaffner and Diaz 1982). These
data were examined for trends in species diver-
sity and community structure. The ratio of an-
nelids to Crustacea and annelids to molluscs was
calculated for each station; previous studies have
shown dominance by polychaetes and oligochaetes
in stressed environments (e.g., Pfitzenmeyer 1975,
Dauer et al. 1979) (Figure 27). Species diversity
(the Shannon diversity index) was also compared
for evidence of spatial trends.
MAIN BAY
Diversity, annelid:crustacean, and an-
nelid: moll use ratios were compared over the Bay
mainstem. Stations having less than 25 percent
sand were used to minimize the effect of substrate.
(Sand substrates support benthic communities
very different from those on fine grained
sediments. Also, sand does not accumulate tox-
icants to any great extent.) The range in values
was large, reflecting the natural variability in ben-
thic distribution (Reinharz and O'Connell 1981).
Species diversity was higher in more saline sta-
tions, reflecting the general distribution of ben-
thic organisms along a salinity gradient (Boesch
1977a). Annelid:mollusc ratios were more variable
in the upper Bay (mean = 40.0, range 1 to 242)
than in the Virginia stations (mean = 6.3, range
0.8 to 58) (Table 19). The pattern for the an-
nelid: crustacean ratio is similar: upper Bay
mean = 73.7, range 0.01 to 598; lower Bay
mean = 35.5, range 0.3 to 242. These trends are
99
-------
100 Chapter 2: Living Resources
c
O
fc
to
0
"O
0)
Q.
CO
6
O)
<
Reference
Stations
Semi-Healthy
Environment
Semi-Polluted
Environment
Polluted
Environment
FIGURE 27. Number of specimens of benthos in Chester River reference stations and in
three environmental zones of Baltimore Harbor (station represents 0.2m2 area)
(Pfitzenmeyer 1975).
TABLE 19.
RANGE OF ANNELID:MOLLUSC VALUES FOR CHESAPEAKE BAY SEGMENTS
Segment Range of Values Number of Stations
CB-1. 2
CB-3
CB-4
CB-5
CB-6
CB-7
EE-3
LE-3
WE-4
34
4.5- 66.0
1.6- 58
1.0-242.0
0.8- 8.9
1.4- 16.0
1.6- 58
3.8
6.1- 57.0
1
2
6
7
3
4
5
1
2
-------
Spatial Trends in Benthic Organisms 101
not significant, although they do reflect a greater
tendency for dominance of upper Bay commu-
nities by polychaetes.
TRIBUTARIES
The Patapsco and Elizabeth Rivers are heavily
affected by human activities (Reinharz 1981,
Schaffrier and Diaz 1982). The Rhode and Ware
Rivers, relatively "unpolluted" reference estuaries,
were selected for comparison. In addition,
Patapsco River benthos was surveyed by Pfitzen-
meyer (1975) and compared to that of the Chester
River. Water and sediment quality and resources
in the Elizabeth River were characterized by the
Virginia State Water Control Board in 1982.
In Ihe Patapsco and Elizabeth Rivers, the ef-
fects of pollution are reflected in benthic com-
munity changes, including loss of species richness
and diversity, and enhancement of resistant, op-
portunistic forms such as annelids, relative to
Crustacea and molluscs. Highly impacted stations
in the Elizabeth River were characterized by
young individuals of a few resistant species, in-
dicating low survival of recruits (Schaffner and
Diaz 1982). These stations also had the lowest
species richness (number of species) and diversity.
In the Patapsco River (which showed the most
distinct trends), diversity declines up estuary,
generally along the gradient of increasing con-
tamination of metals and organic chemicals (Bieri
et al. 1982a) (Table 20, Figure 28). Similarly,
dominance by annelids increased greatly at im-
pacted stations, when compared to reference areas
(Table 20). This situation will be discussed fur-
ther in Chapter 3.
TABLE 20.
SPECIES DIVERSITY (H), REDUNDANCY (r), ANNELID:MOLLUSC, AND ANNELID:CRUSTACEAN RATIOS
(AS NUMBERS OF INDIVIDUALS) ALONG A GRADIENT OF POLLUTION IN THE PATAPSCO RIVER
(REINHARZ 1981)
Station*
Po
PI
P3
P4
P5
P2
P9
PS
PIO
P11
P6
P7
P13
P12
P14
H
0.330
0.561
0.343
0.590
0.246
0.838
0.678
1173
1.296
1,193
1.615
1.416
1.400
2.879
2.715
r
0.864
0.831
0.906
0.783
0.893
0.491
0.731
0.630
0.634
0.676
0.523
0.603
0.549
0.307
0.312
Annelid:
Mollusc
23
15
51
11
37
—
29
5
33
30
2
3
14
3
4
Annelid:
Crustacean
—
—
253
1276
—
—
350
62
115
115
203
47
138
11
0.9
'See Figure 28 for station locations.
-------
102 Chapter 2: Living Resources
Baltimore City
Patapsco
River
Low diversity
Moderate diversity
High diversity
FIGURE 28. Diversity index of benthic communities in the Patapsco and Rhode Rivers (Reinharz 1981),
-------
SECTION 5
THE SHELLFISHERY:
CHANGES IN OYSTERS AND CRABS
The Chesapeake Bay shellfishery is an integral
part of the economic and social qualities of the
region. The American oyster, Crassostrea
virginica, and blue crab, Callinectessapidus, sus-
tained harvests of 21,958,100 and 58,956,500
pounds, respectively, in 1980. (Other shellfish
species, like the soft clam and hard clam, com-
prise much smaller harvests and will not be
discussed here.) This section focuses first on
oysters, describing their environmental re-
quirements, harvest, spat set, and condition in-
dex. Then, the harvest of blue crabs will be
summarized.
ENVIRONMENTAL REQUIREMENTS
OF OYSTERS
Because they are sedentary organisms, oysters
cannot avoid long-term environmental stresses in
their surroundings (Appendix C, Section 1). Salini-
ty and temperature affect their feeding rate and
reproductive success. Oysters are physiologically
restricted to areas ranging in salinity from 5 to
35 ppt. However, the diseases caused by Min-
chinia (Haplosporidium) nelsoni (MSX) and
Perkinsus marinus (Dermo), as well as predators,
reduce their abundance in areas of over 15 ppt
salinity. Adult oysters can tolerate temperatures
from 1 \o 35C;7 peak spawning occurs between
24 and 28C,
Another factor affecting oyster survival is
suspended sediment which, upon settling, can
smother adult oysters and prevent setting of spat
(Galtsoff 1964). Excessive sedimentation in upper
reaches of rivers has shifted the upstream limit of
oysters downstream several miles (Alford 1968).
Low oxygen concentrations may also affect
oyster populations; oyster larval growth ceases
when oxygen levels drop below 2.4mgL"1(1.7
ml L"1). Adults can survive up to five days in water
with oxygen levels less than 1.0 mg L-l (0.7 ml
L-l)(Galtsoff 1964). Haven et al. (1978) believe
that there may be some connection between the
decline in spat fall and the oxygen deficiency
observed in the deeper regions in the lower por-
tions of the Rappahannock River.
Oysters are particularly sensitive to heavy
metals. Calabrese et al. (1973) found that embryos
are most sensitive to Hg, silver (Ag), Cu, and Zn,
with LCso concentrations of 0.0056, 0.0058,
0.103, and 0.31 ppm, respectively (Kennedy and
Breisch 1981). Shuster and Pringle (1969) reported
a strong sensitivity to Cd among adult oysters with
100 percent mortality occurring after a 20 week
exposure to 0.2 ppm.
OYSTER HARVEST
The oyster industry in Chesapeake Bay is
heavily managed, and harvest practices vary in
Maryland and Virginia. Observed declines or ap-
parant stability in oyster harvests may be partly
related to economic factors and management
practices. Oyster landings include those from
public and privately leased areas.
Oyster harvest in Maryland comes largely
from public oyster grounds; very few private leases
exist. Maryland carries out extensive shell plant-
ing which may enhance spat set and, ultimately,
harvests (Ulanowicz et al. 1980). In Virginia,
oyster harvests come from public grounds and
large areas of leased grounds. The leased grounds,
-------
104 Chapter 2: Living Resources
which must be planted if they are to be produc-
tive, yield about 50 percent of the total
production.8
Harvest data were obtained and analyzed as
described in Appendix C, Section 2. Oyster land-
ings data were obtained in a much different man-
ner in the 1800's and early 1900's than at present.9
As discussed in Appendix C, Section 3, methods
changed in about 1930; as a result, data taken
before 1930 are more suspect than recent data.
Harvest of oysters in Chesapeake Bay is shown
in Figure 29. Annual yields of about 30,000,000
pounds of shucked oyster meat were sustained be-
tween 1930 and 1960; since 1960, annual yields
have been about 20,000,000 pounds. Landings ap-
pear to have decreased dramatically between 1880
and 1930, but data from this period may be
unreliable.
Harvest data for individual basins are
available from 1962 to the present. To assess
historical changes in harvest in Chesapeake Bay
basins, we divided the data into two periods of
approximately equal length, 1962 to 1970 and
1971 to 1980. Oyster harvest was recorded as
pounds per acre of natural and privately leased
bars (Appendix C, Section 2).
Annual mean oyster harvests for the two
periods considered are shown in Table 21. Signifi-
TABLE21.
OYSTER HARVEST FOR 1962 TO 1970 AND 1971 TO 1980, ANNUAL MEAN
(POUNDS PER ACRE OF NATURAL OYSTER HABIT AT) t
Western Shore
Patuxent River
Potomac River
Rappahannock River
York River
James River
Main Bay
Chesapeake Bay
North
Upper Central
Lower Central
South
General
Eastern Shore
Chester River
Eastern Bay
Choptank River
Honga River
Fishing Bay
Nanticoke River
Wicomico River
Tangier Sound
Pocomoke Sound
1962-1970
67.6
98.0
40.3
23.9
46.3
35.9
87.0
8.9
22.2
116.6
37.3
963.2
12.6
19.4
489.8
67.0
11.1
4.5
1971-1980
84.5
44.5*
30.8*
7.6*
23.4*
13.4
125.7
13.7
6.8'
104.6
155.0*
1553.1*
43.8
50.2*
384.9
59.4
48.0*
14.6
tTable does not separate natural recruitment from seed planting efforts.
'Significantly different from 1962 to 1970 at 0.05 level.
-------
The Shellfishery: Changes in Oysters and Crabs 105
o
'tf
o
D
0
x
CM
O
X
X
o
X
o
X
OO
o
X
o
X
X
CO
X
CM
OO
O
O
oo
op
_
D
0
a
D
0
u
spunod
o"
TJ
0)
T3
I
O
O
a
CM
O
-------
106 Chapter 2: Living Resources
cant decreases occurred in four of the five western
shore basins; significant increases occurred in four
eastern shore basins. This shift from the western
to eastern shore suggests a change that should be
examined by more extensive analysis of biological,
social, and economic factors.
OYSTER SPAT SET
The density (spat per bushel of cultch or
suitable substrate) of oyster spat set indicates the
success of natural oyster reproduction and recruit-
ment. Oyster spat set is a reasonable predictor of
oyster harvest (Davis et al. 1981). The Maryland
Department of Natural Resources has collected
oyster spat set data in the Maryland portion of
Chesapeake Bay since 1939 (Meritt 1977; Davis
et al. 1981); the Virginia Institute of Marine
Sciences has collected similar information since
1946 (Haven et al. 1978). The methodology of
oyster spat set data collection is described in more
detail by Davis et al. (1981).
Comparison of the average oyster spat set for
the past ten years with the previous ten to thirty
years indicates significant declines in a number
of locations in the Bay (Davis et al. 1981 and Table
23). Recent declines are most evident in upper,
central Chesapeake Bay, certain rivers —Chester,
James, Nanticoke, Patuxent, Pocomoke, Potomac,
Rappahannock, and Wicomico —and Eastern
Bay, Fishing Bay, and Pocomoke Sound (Table
22). The year 1980 was a good one for spat fall
in the Choptank River. Eastern Bay, and Tangier
Sound, areas that have shown increased oyster
harvest. Spat set from 1980 was also high in the
Honga River and at the mouth of the Potomac
River, while spat set in the upper Chesapeake and
its western tributaries was generally light (Figure
30). The high spat set of 1980 is most readily ex-
plained by high salinities in the Bay during the
1980 to 1981 spawning season that favored high
survival and set of larval oysters. However, the
York and James Rivers did not experience this high
spat set, indicating that factors other than salin-
ity were involved. Predators and disease have
more effect on spat in Virginia than does salinity.
Trends in spat set have been documented in
detail for the Potomac River (Krantz and Carpen-
ter 1981, Figure 31). Although spat set in the
lower Potomac varies in response to salinity, set
in the middle and upper Potomac has been sup-
pressed since the late 1960's and has shown no in-
crease in 1980. This result suggests that some river-
borne factor may be responsible for decreasing
spat sets.
TABLE 22.
TRENDS IN MEANS OF OYSTER SPAT SET FOR THE PERIOD 1938-1980,
COMPARING POST-1970 TO PRE-1970
Basin
CB South
CB Low Central
CB Upper Central
Chester River
Choptank River
Eastern Bay
Fishing Bay
Honga River
James River
Trend
N
N
N
N
Basin
Trend
+ = Positive Trend at >0.05
- = Negative Trend at >0.05
N = Not significantly different
Nanticoke River
Patuxent River
Pocomoke River
Pocomoke Sound
Potomac River
Rappahannock
Tangier Sound
Wicomico River
York River
N
N
-------
The Shellfishery: Changes in Oysters and Crabs 107
1980
Spat per bushel
Chester R.
FIGURE 30,
Geographic distribution of spat set on
natural oyster bars in the Maryland por-
tion of Chesapeake Bay, fall I960 [Davis et
al. I98I).
-------
108 Chapter 2: Living Resources
TABLE 23.
CRAB HARVEST* FOR 1962 TO 1970 AND 1971 TO 1980,
ANNUAL MEAN (POUNDS PER ACRE OF BASIN)
Western Shore
James River
Patuxent River
Potomac River
Rappahannock River
York River
Main Bay
North
Upper Central
Lower Central
South
General
Eastern Shore
Chester River
Choptank River
Eastern Bay
Fishing Bay
Honga River
Nanticoke River
Pocomoke Sound
Tangier Sound
Wicomico River
1962-1970
15.08
1.81
12.83
52.57
69.73
0.18
4.41
44.58
3,86
41.23
4.78
0.22
7.79
ND
ND
ND
ND
97.69
ND
1971-1980
4.66b
3.79b
9.30
27.89b
50.26
0.52b
6.21
38.52
19.69b
33.91
5.32
0.71b
4.58
ND
ND
ND
ND
40.70b
ND
'Harvest figures do not take catch per unit effort (CPUE) into account. CPUE data
are not available.
Significantly different from 1962 to 1970 at 0.05 level
OYSTER CONDITION INDEX
Data used for determination of the oyster con-
dition in Maryland were obtained from the
Maryland Department of Natural Resources,
Tidewater Administration, Oxford, Maryland.
Evaluation of these data showed no clear spatial
or temporal patterns. Analysis relating these data
with stress index and spat set data did, however,
show some interesting correlations in the Chester
and Patuxent Rivers (Chapter 3).
Oyster condition data for Virginia were taken
from Haven et al. (1978) and from Dexter Haven's
files at the Virginia Institute of Marine Sciences.
Evaluation of these data revealed no clear tem-
poral trend; however, the Rappahannock River
showed consistently higher values. Haven (1965)
suggests that this may be related to the nutritional
content of waters. Natural sources of organic
detritus or algal species composition may be fac-
tors. The condition index in Virginia does not ap-
pear to be related to spat set (Haven et al. 1978).
HARVEST OF CRABS
Many biological and ecological differences ex-
-------
The Shellfishery: Changes in Oysters and Crabs 109
ist between blue crabs and oysters. For example,
blue crabs are mobile and able to leave un-
favorable conditions, while oysters are sessile. Blue
crabs spawn in the mouth of the Bay; oysters re-
main in the estuary.
Landings data for blue crabs were obtained
in the same way as that for oysters and are sub-
ject to the same caveats. Landings for Chesapeake
Bay, 1880 to 1981, are shown in Figure 32.
Harvests of crabs have generally increased since
the 1930s, in contrast to the decrease exhibited
by oysters. On the average, crabs have been
declining Bay-wide since 1970. There have, how-
ever, been some shifts in areas where crabs are
captured (Chapter 3).
Landings for individual basins are shown in
Table 23. Significant increases occurred in the
Patuxent and Choptank Rivers, and Chesapeake
Bay, north and south. Significant decreases oc-
curred in the Rappahannock and James Rivers,
and Tangier Sound.
O
(D
a
D
a.
co
400
200
100
20
10
5
400
200
100
20
10
5
400
200
100
20
10
5
_ Upper
Middle
Lower
40
45
50
55 60
Year
65 70 A 75
Agnes
80
FIGURE 31. Oyster spat settlement on natural cultch in the Potomac River, I939 to I960
(Krantz and Carpenter I98I),
-------
110 Chapter 2: Living Resources
10x107
9x107
8x107
7x107
i/>
-Q
C 6x107
O
_ 5x107
D
O
•— 4x107
3x107
2x107
1x107
I
I
1880 1895 1910 1925 1940
Year
1955
1970
1982
FIGURE 32. Historical landings of blue crabs for Chesapeake Bay, I860 to I98I.
-------
SECTION 6
CHANGES IN THE FINFISHERY
Another economically important biological
resource in Chesapeake Bay is its finfishery. The
species listed in Table 24 were assessed because
of their economic importance. In this section, the
environmental tolerances of these organisms are
discussed first to understand some of the factors
that affect them. This information is used in
Chapter 3 to compare species sensitivities with
ambient water quality conditions. More detailed
information on environmental tolerances is in-
cluded in Appendix C, Section 1, and in
Kaumeyer and Setzler-Hamilton (1982).
Next, commercial landings of the species listed
in Table 24 are examined. A discussion of the
historical procedures for collecting landing stat-
istics and caveats concerning their use is found in
Appendix C, Sections 3 and 4. Landings are a re-
flection of stock sizes, but are affected as well by
fishing effort. Because of the unavailability of ac-
ceptable historical effort data for most species
TABLE 24.
PRINCIPAL COMMERCIAL FINFISH SPECIES IN CHESAPEAKE BAY
Common Name
Alewife
Blueback herring
Bluefish
Catfish
Croaker
Menhaden
Shad
Spot
Spotted sea trout
Striped bass
Weakfish
White perch
Yellow perch
Scientific Name
Alosa pseudoharengus
Alosa aestivalis
Pomatomus saltatrix
Ictalurus sp.
Micropogonias undulatus
Brevoortia tyrannus
Alosa sapidissima
Leiostomus xanthurus
Cynoscion regalis
Morone saxatilus
Cynoscion nebulosus
Morone americana
Perca flavescens
Total 1980 Landings
(Ibs X 1000)
(1369.1°)
(1369,1a]
27912
2265.7b
622.1
443,977,6
903,3
1755,3
(5113,6C)
2563.3
(5113,6C)
1101.9
28.0
462491,1
aCombined in landing statistics as Alewife; 1369,100 Ibs for both species combined.
bRepresents three species (/. catus, I. nebulosus, and /. punctatus)
cCombined in landing statistics as sea trout; 5113,600 Ibs for both species combined.
111
-------
112 Chapter 2: Living Resources
(Rothschild et al. 1981), an attempt to adjust land-
ings statistics for fishing effort was not done. In-
sufficient data were available to fully evaluate
recreational catch, but Williams et al. (1982) have
shown that recreational catch in the Maryland
portion of the Chesapeake Bay may represent
from about 40 percent of the combined recrea-
tional and commercial landings of striped bass to
90 percent of the total landings of spot. Therefore,
recreational fishing may have a substantial im-
pact on game fish species.
Commercial landings are the most spatially
and temporally complete fishery data available.
However, these data are affected by economic fac-
tors like fishing effort, as well as stock abundance.
Thus, trends in commercial landings will be sub-
stantiated with data from surveys of young fish,
expressed as the juvenile index, for four basins in
Maryland and two basins in Virginia.
Juvenile finfish seining survey data have been
collected by the Maryland Department of Natural
Resources annually since 1954. Replicate hauls
were first collected from a total of 22 permanent
sampling locations in four major spawning areas
using a 30.5 m beach seine in 1961.
Methodology was standardized in 1966 when
samples were first taken at each station once in
July or the first week of August, once during the
last three weeks of August, and once in September
or the first week in October. The Maryland De-
partment of Natural Resources annual striped bass
juvenile index for each river system is the average
catch/haul in river over the sampling year. The
expanded index for Chesapeake Bay in Maryland
for a given year is a weighted average catch/haul
for all stations sampled in that year.
The Virginia Institute of Marine Science has
been collecting data on abundance and distribu-
tion of juvenile fishes in Virginia waters with bot-
tom trawls since February 1955. Efforts have been
focused primarily on the sciaenids (croaker, spot,
and weakfish), hence the choice of bottom trawls.
Analysis of these data through March 1982 are
presented by species and river and include annual
estimates of relative abundance, five point mov-
ing averages, and Virginia commercial landings
(Wojcik and Austin 1982). These surveys are a
reasonable indicator of stock sizes for young fish,
particularly bluefish, striped bass, and white
perch in Maryland, and croaker, spot, and weak-
fish in Virginia.
The thirteen species in Table 24 will be con-
sidered in two groups, based on the similarity of
trends among species in each group. The groups,
freshwater spawners (alewife, catfish, shad,
striped bass, white perch, and yellow perch) and
marine spawners (bluefish, croaker, menhaden,
spot, spotted sea trout, and weakfish), are also
significantly different in the proximity of their
spawning grounds to riverine sources of anthro-
pogenic materials.
ENVIRONMENTAL REQUIREMENTS AND
TOLERANCES OF ESTUARINE FISH
The principal water quality parameters
available to gauge possible impacts on finfishes
include concentrations of dissolved oxygen, heavy
metals, and halogenated hydrocarbons. Unfor-
tunately, data are completely lacking for at least
one half of the species examined. Interpretation
and comparison of marine and estuarine toxicity
data are difficult tasks because of the large
number of variables affecting an organism's
response to a particular pollutant. However, to
give the reader some indication of the level of sen-
sitivity to the key water quality parameters cur-
rently known, the following summary is provided.
More detail is available in Appendix C, Section
1 and Kaumeyer and Setzler-Hamilton (1982).
Dissolved Oxygen
Thornton (1975) compared the DO tolerances
of some 24 estuarine and marine fishes experimen-
tally and from the literature, concluding "that a
conservative estimate for maintaining diversity for
marsh [estuarine] fish would require minimum
permissible dissolved oxygen levels of 2 to 3 ml
L-1 [2.8 to 4.2 mg L'1] at 20 to 25C." He also rank-
ed these 24 species in order of their sensitivity to
low oxygen levels. Listed in order from most to
least sensitive are those of special concern in this
analysis (Thornton 1975):
Blueback herring Alosa aestivalis
Alewife Alosa pseudoharengus
Atlantic menhaden Brevoortia tyrannus
-------
Changes in the Finfishery 113
Atlantic silversides Menidia menidia
Bluefish Pomatomus saltatrix
Weakfish Cynoscion sp.
Spot Leiostomus xanthurus
Striped Bass and Morone sp.
White perch
Mummichog Fundulus sp.
Adults of Alosa aestivalis will die at oxygen
levels of 2.0 to 3.0 mg I/1 if held up to 16 hours.
For striped bass, Morone saxatilis, oxygen concen-
trations of 3.3 mg Lr1 at 18C are lethal for yolk
sac larvae (Rogers and Westin 1981); concentra-
tions of 5 to 6 mg L"1 seem acceptable for larval
development (Bogdanov et al. 1967).
Toxicity Studies for Selected Species
Spot
Middaugh et al. (1975) examined the effect of
cadmium on larvae and the effect of DO reduc-
tion on Cd toxicity. With exposure concentrations
ranging from 0.09 to 0.80 ppm Cd, they noted
17 to 42 percent less survival at 1.6 ppm than at
6.5 ppm DO. This result is most likely related to
increased stress on the larvae at lower oxygen
concentrations.
Six pesticides (dieldrin, DDE, DDT, en-
dosulfan, endrin, and toxaphene) were tested for
their effect on juvenile spot by Lowe (1964, 1966,
undated). All were very toxic: for most of these
compounds, exposure to 0.001 ppm resulted in at
least 50 percent mortality.
Hansen et al. (1971) examined the chronic tox-
icity of PCBs (Arochlor® 1254) to juvenile spot.
They determined an LCso value of 0.005 ppm
under several temperature and salinity combina-
tions with exposure for 18 and 26 days.
White Perch
The major toxicity data for white perch are
in a study by Rechwoldt et al. (1977), who
reported a 96 hr LCso value of 0.42 ppm for lar-
val white perch using aldrin (pesticide), and 40.0
ppm using 2,4-D (herbicide).
Striped Bass
Of all species examined, striped bass had the
largest toxicity data base. O'Rear (1972) compared
the toxicity of Cu and Zn to the embryos. Cop-
per was the most toxic with a 48 hr LCso value
of 0.74 ppm. Hughes (1973) has tested the toler-
ance of larval striped bass to Cd, Cu, and Zn. She
determined that Cd was by far the most toxic.
With a 96 hr exposure, 0.001 ppm cadmium chlor-
ide was required for 50 percent mortality. Juvenile
striped bass also exhibited strong sensitivity to Cd
with a 96 hr LCso of 0.002 ppm. Of all the metals
tested, Zn and Cr were the least toxic to juvenile
striped bass, with LCso values ranging from 10
to 18 ppm in 96 hr tests.
Hughes (1973) also examined the toxicity of
aldrin and dieldrin to striped bass larvae. She
determined that the larvae were more sensitive
to dieldrin. Several investigations have tested the
toxicity of nine pesticides to juveniles. Endrin was
the most toxic, with a 96 hr LCso value of 0.1 ppb
(Korn and Ernest 1974).
The herbicide data were somewhat conflict-
ing. Hughes (1973) reported a 96 hr 2,4-D LCso
of 3.0 ppm, while Rechwoldt et al. (1977) listed
an LCso of 70.1 ppm with similar test conditions.
It was not possible to determine a possible ex-
planation for the reported differences in toxicity
to 2,4-D.
Benville and Korn (1977) tested ethyl benzene,
benzene, and toluene (monocyclic aromatic hy-
drocarbons) . The juveniles tested were relatively
tolerant to all three compounds; 96 hr LCso values
ranged from 4.3 to 7.3 ppm. Ethyl benzene was
the most toxic.
The current toxicity data are useful in that the
relative intolerance of several species to particular
pollutants is apparent. For example, striped bass
are extremely sensitive to Cd. The striped bass
tolerance will be compared with current monitor-
ing data for Cd in Chapter 3 to see if survival is
possibly being limited by this metal.
COMMERCIAL FINFISH LANDINGS
Landings data were obtained and analyzed as
described in Appendix C, Section 3 for the species
listed in Table 24. These species were selected
because of their economic importance. NOAA
and/or Maryland fishery codes were initially
grouped into basins (Figure 22). These 32 basins
were then grouped into thirteen major tributary
-------
114 Chapter 2: Living Resources
basins, which were finally combined to produce
total landings for the entire Chesapeake Bay (Ap-
pendix C, Section 3). This approach provided in-
formation for local, regional, and Bay-wide
comparisons.
Because of a lack of local and regional infor-
mation for the entire period of record (1880 to
1980), the long-term analysis of fisheries trends
is restricted to the entire Chesapeake Bay. Analysis
by decade (Table 25) indicates that landings of
marine spawners have increased from 38.08
pounds per acre (1881 to 1890) to 143.88 pounds
per acre (1971 to 1980). This increase has occurred
in two waves: an early peak occurred from 1911
to 1920 (129.30 pounds per acre), followed by an
abrupt decline, and an increase to present levels.
Most of this increase is accounted for by men-
haden; bluefish have shown a dramatic increase
during the 1970's; croaker and sea trout, on the
other hand, show sporadic recent increases that
do not approach historical levels.
As a group, freshwater spawners have declined
from a maximum of 20.44 pounds per acre (1901
to 1910) to 5.64 pounds per acre (1971 to 1980).
The largest yields throughout the period have been
of alewife (herring); landings of these species, as
well as of shad and yellow perch, are now at un-
precedented low levels. Striped bass landings were
maximal from 1961 to 1973, but have declined
abruptly in the present decade. White perch also
show a recent decline; catfish show no clear
pattern.
The increased yield of marine spawners and
decreased yield of freshwater spawners have
resulted in a major shift in the proportion of the
finfishery accounted for by each group: from 1881
to 1890, the proportion of freshwater to marine
spawners was 25:75; from 1971 to 1980, this pro-
portion was 4:96.
RELATIONSHIP BETWEEN LANDINGS
AND JUVENILE INDEX
For some species, fisheries landings tend to
track the occurrence of successful year classes if
fishing pressure is stable or landings are adjusted
for catch per unit effort. Examples of such con-
currence may be seen in Atlantic menhaden
(Cronan 1981), as well as in striped bass (Boone
1980) and white perch (Richkus and Summers
1981). Without doubt, in the absence of several
consecutive successful year classes, fishery landings
do decline, often dramatically.
To show relationships between juvenile fin-
fish surveys (Boone 1980) and landings, and to at-
tempt to validate landings trends for the principal
species in the Chesapeake, the Maryland juvenile
index for each species was aggregated for the four
collection areas of the Bay (Nanticoke River,
Choptank River, Potomac River, and head of the
Bay). Moving averages of these data were plot-
ted against total Chesapeake Bay landings for each
species. For example, a moving average of three
years aggregates three annual means of juvenile
index to form a single mean (i.e., mean for 1960,
1961, and 1962) for part of a longer period of
record and repeats the process for all possible se-
quential combinations of three years (1961, 1962,
and 1963, etc.) for the entire period of record.
Moving averages that bracketed the typical time
for a year class to enter the fishery were selected.
For example, striped bass are thought to enter the
fishery at two to three years of age, but the
slowest-growing fish of the species treated here,
white perch, is thought to enter the fishery be-
tween six to eight years of age. Therefore, two to
eight year moving averages were calculated for
species where data were available. The moving
averages have the effect of lagging the data by the
number of years covered by the moving mean;
that is, a 3-year moving mean of the juvenile in-
dex should provide the best fit with the landings
curve, if the landings are mainly comprised of 3
year-old fish.
Table 26 indicates the expected age to enter
the fishery and the "best fit" moving average for
each species treated. Regression analysis was also
conducted in which the juvenile index was lagged
against landings, with less success.
Through the use of this method, bluefish pro-
vide the best apparent correspondence among
marine spawners; menhaden provide a fair to poor
fit. This result indicates that although Maryland's
juvenile index is not designed explicitly to sam-
ple marine spawners, it does provide some indica-
tion of future harvest for bluefish and menhaden.
It also appears that increased harvests of bluefish
-------
Changes in the Finfishery 115
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-------
116 Chapter 2: Living Resources
TABLE 26.
CORRESPONDENCE OF MARYLAND FINFISH JUVENILE INDEX AND FINFISH LANDINGS
FOR CHESAPEAKE BAY (1958 TO 1980)
Species
Alewife
Bluefish
Catfish
Croaker
Menhaden
Shad
Spot
Striped bass
Weaktish
White perch
Yellow perch
Approx. Age Enters
Fishery (yrs.)
2 +
1-3
3 +
2 +
1 +
4-6
3-5
2-3
2-4
6 +
4 +
Visual
Correspondence
Poor
Good
Poor
Fair— Poor
Poor
Good
Fair
Poor
R Value
(>0.05)
—
0.97
0.53
(Insufficient Data)
0.38
(Insufficient Data)
—
0.71
(Insufficient Data)
0.54 + 0.50
—
Best Fit Moving
Mean (yrs.)
None
4
8
3
None
4
3 + 6
None
and menhaden are not strictly a function of in-
creased effort, but are supported by increased
availability of fish.
Juvenile indices of other marine spawners have
behaved similarly during the historical record.
Pearson correlation analysis indicates that
menhaden correlated (0.05 level) with bluefish
(r = 0.70) and with spot (r = 0.87). Spot correlated
with croaker (r = 0.55) and bluefish (r = 0.50).
Thus, to some extent, the annual variation in the
juvenile index of these species seems to be con-
trolled by similar factors.
A good relationship has been shown between
landings and juvenile index for striped bass (Boone
1980) and white perch (Richkus and Summers
1981). Chesapeake Bay Program data, unadjusted
for fishing effort, also showed a good relationship
with striped bass and a fair relationship with
white perch (Table 26). Thus, the juvenile index
does provide some support for using landings as
an indicator of trends for these two species. The
decline in striped bass and white perch availability
suggested by decreased landings is supported by
the juvenile index data.
Juvenile success of some freshwater spawners
may be affected by similar factors. For example,
Pearson correlation analysis indicates that juvenile
indices of white perch correlated with those of
alewife (r = 0.69) and striped bass (r = 0.47) at the
0.05 level. Thus, these species may be respond-
ing to similar environmental factors.
LANDINGS AND JUVENILE INDICES
OF MARINE SPAWNERS
As previously discussed, landings of menhaden
have increased during the historical period from
1880 to 1980. This increase is shown graphically
in Figure 33, which illustrates the early upward
trend, culminating in approximately 1920, fol-
lowed by a second upward trend (data were ac-
quired less frequently before 1930, accounting for
the lower apparent variability during the early
period).
Historical landings of bluefish are shown in
Figure 34, indicating the recent major peak in
1978 with a very slight decline since then. Land-
ings of croaker and weakfish, showing declines
since the 1940's but with sporadic recent increases,
are shown in Figures 35 and 36.
Commercial landings data for individual
basins are available since 1962. Mean annual com-
mercial landings for marine spawners for two
periods, 1960 to 1970 and 1971 to 1980, are shown
in Table 27. These two periods were selected
-------
Changes in the Finfishery 117
O
O
6x108
5x108
4x108
3x108
2x108
108
I
1
1880
1895 1910
1925 1940
Year
1955
1970 1982
FIGURE 33. Historical landings of menhaden for Chesapeake Bay, I880 to I98I.
"D
c
O
a.
o
o
4x106
3x106
2x106
1x10*
1880
1895
1910
1925 1940
Year
1955
1970 1982
FIGURE 34. Historical landings of bluefish for Chesapeake Bay, I860 to I98I,
-------
118 Chapter 2: Living Resources
to
"D
6x10?
5x107
4x107
3x107
2x10'
1x107
1880 1895 1910 1925 1940 1955 1970 1982
Year
FIGURE 35. Historical landings of croaker for Chesapeake Bay, I880 to I98I.
24x10*
21x10*
18x10*
15x106
c
D
O
a 12x10*
9x10*
6x10*
3x10*
1880 1895 1910 1925 1940 1955
Year
1970 1982
FIGURE 36. Historical landings of weakfish for Chesapeake Bay, I860 to I98I.
-------
Changes in the Finfishery 119
TABLE 27.
LANDINGS FOR MARINE-SPAWNING FINFISH, ANNUAL AVERAGE FOR 1962 to 1970
AND 1971 to 1980 (POUNDS/ACRE)**
Western Shore
James River
Patuxent River
Potomac River
Rappahannock River
York River
Main Bay
North
Upper Central
Lower Central
South
General
Eastern Shore
Chester River
Choptank River
Eastern Bay
Fishing Bay
Honga River
Nanticoke River
Pocomoke Sound
Tangier Sound
Wicomico River
1962-1970
13.21
0.12
20.73
38.34
47,44
1.37
0.12
4.28
1.99
314.23
0,08
0.24
0.02
4.68
0.93
1.78
0.09
0.54
0.66
1971-1980
0.47'
0.31*
45.14
67,43
38,68
0.51
1.88*
4.84
5.21*
454,19*
0.88*
0.69
0.27
14.15*
16.64*
3,18
0.14
0.35
0.25
'Significantly different from 1962 to 1970 at 0.05 level
'*One pound/acre = 0.112 g/m2
because trend analysis showed shifts in the trends
of both freshwater and marine spawning fishes oc-
curring around 1969 to 1970. Basins in which
significant change occurred showed increased
landings of marine spawners, with the exception
of the James River (whose finfishery was closed
for part of the 1971 to 1980 period).
Trends in finfish juvenile survey data were
determined by inspection of moving means (three-
year in Maryland; five-year in Virginia) for each
basin (head of Bay, Potomac, Choptank, Nan-
ticoke, Rappahannock, and York). The Maryland
survey is designed to assess the abundance of
young-of-the-year (age 0) alewife, bluefish,
striped bass, shad, white perch, and yellow perch
(Boone 1980). It also provides evidence of the
abundance of multiple year classes of Atlantic
menhaden, Atlantic silversides, Bay anchovy, cat-
fish, spot, and mummichog. The Virginia survey,
on the other hand, is designed to assess the abun-
dance of young croaker, spot, and weakfish and
is not exclusively selective for age 0 fish (Wojcik
and Austin 1982).
Trends in Maryland tributaries were verified
by comparing pre- and post-1970 means for the
period of record, 1958 to 1980 (Table 28). The
marine spawners menhaden, bluefish, and spot
show statistically significant increases in all four
-------
120 Chapter 2: Living Resources
TABLE 28.
COMPARISON OF 1971 TO 1981 ANNUAL MEAN JUVENILE INDICES WITH 1958 TO 1970
ANNUAL MEANS
Species
CB North Choptank Nanticoke Potomac
Alewife1
American shad1
Atlantic menhaden2
Atlantic silversides2
Bay anchovy2
Bluefish1
Catfish2
Mummichog2
Spot2
Striped bass1
Weakfish2
White perch1
Yellow perch1
N
+
N
N
N
N
N
N
N
+
N
N
N
N
N
N
N(-)
N
-t-
N
+ = Statistically significant increase (0.05 level)
- = Statistically significant decrease (0.05 level)
N= Not significantly different
()= Increase or decrease at 0.10 level
1Based on 0 age class fish
2Based on mixture of age classes
areas. These statistical increases in annual means
are manifestations of several strong year classes
during the recent period; Figure 37 shows a
typical example.
The Virginia small fish trawl (Wojcik and
Austin 1982) showed the trends in the York and
Rappahannock Rivers to be similar to those deter-
mined by the GBP analysis of the Maryland De-
partment of Natural Resources juvenile finfish
survey (Boone 1980) for marine spawners.
LANDINGS AND JUVENILE INDICES
OF FRESHWATER SPAWNERS
Landings of alewife, shad, striped bass, white
perch, and yellow perch show substantial declines
over previous levels in Chesapeake Bay. Landings
of shad and yellow perch have declined steadily
over the period (Figures 38 and 39); declines in
alewife, white perch, and striped bass landings
have been more recent (Figures 40, 41, 42).
Mean annual commercial landings for fresh-
water spawners are shown in Table 29. Signifi-
cant decreases occurred in several basins; these
decreases were fairly evenly distributed among the
three regions.
Comparison of the Maryland juvenile indices
of freshwater spawners for the period 1971 to 1981
with the previous period (1958 to 1970) (Table 28)
indicates that alewife declined in the Choptank
River; American shad declined in all basins ex-
cept the Potomac River; striped bass showed a
statistically significant decline only in the Potomac
River; and white perch and yellow perch showed
increases in the Potomac River. That striped bass
appeared to decline in only one basin may seem
surprising because of the public perception of a
dramatic Bay-wide decline. By inspection, one
sees declining trends in all four basins studied. The
-------
Changes in the Finfishery 121
x
0
T5
c
1.5
1.4
1 3
1 2
1 1
1 0
09
08
07
0.6
05
04
03
0.2
0 1
0.0
1951
1956
1961
1966
Year
1971
1976
1981
FIGURE 37. Historical changes in the juvenile index (weighted average catch per
seine sample for all stations sampled that year) for bluefish in
Chesapeake Bay.
-------
122 Chapter 2: Living Resources
175x105
150x105
125x105
100x105
O
a
75x105
SOxlO5
25x105
0
1880
1895
1910
1955
1925 1940
Year
FIGURE 38. Historical landings of American shad for Chesapeake Bay, I860 to I98I.
1970 1982
175x104
150x104
125x10"
100x10"
0.
O
75x10"
50x10"
25x10"
1880 1895 1910 1925 1940 1955 1970 1982
Year
FIGURE 39. Historical landings of yellow perch for Chesapeake Bay, I880 to I98I.
-------
Changes in the Finfishery 123
7x107
6x107
5x107
C 4x107
O
a
3x107
2x107
1x107
\ /v
V
A.'
1880 1895 1910 1925 1940 1955
Year
1970 1982
FIGURE 40. Historical landings of alewife for Chesapeake Bay, I880 to I98I.
27x105
24x10'
21X105
w 18x105
"D
D
Q_ 15x106
12x105
9x10s
6x105
3x106
1880 1895 1910 1925 1940 1955 1970 1982
Year
FIGURE 41 Historical landings of white perch for Chesapeake Bay, I880 to I98I.
-------
124 Chapter 2: Living Resources
8xio6r
7x10*
05
"D
c
O
Q.
O
O
6x10*
5x10*
4x106
3x106
2x106
1x106
1880
1895
1910
1925
1940
1955
1970 1982
Year
FIGURE 42. Historical landings of striped bass for Chesapeake Bay, I860 to I98I.
statistical result occurred because there was a very
strong year class early in the recent period, fol-
lowed by a decline. For example, in the Nanticoke
River (Figure 43) there was a very strong year class
in 1972, followed by a decade of no strong year
class. Declining trends may be contributed to by
climate (as it affects the success of year classes),
overfishing of spawning stock, and anthropogenic
effects that destroy spawning areas (such as the
installation of Conowingo Dam on the Susque-
hanna River which has restricted shad spawning),
and, finally, by the effects of toxic materials on
the various life stages of fishes.
The Maryland Department of Natural Re-
sources juvenile finfish survey for 1982 has been
completed. Indications are that striped bass
recruitment is average in the Nanticoke River, bet-
ter than average in the Choptank River, average
in the Potomac River, and relatively poor in the
head of the Bay. Reproduction of marine
spawners continues to be successful.10 These trends
support the conclusions drawn by the GBP based
on the period of record for the juvenile finfish
survey of 1958 to 1981.
Because the Virginia survey (Wojcik and
Austin 1982) is not designed to capture most of
the freshwater spawners that are taken in the
Maryland Department of Natural Resources
survey, results in this group of species cannot be
compared. Recent modifications in collecting pro-
cedures should improve fisheries comparisons in
the future.
ESTUARINE FORAGE FISH
Juvenile indices for three estuarine species,
mummichog (Fundulus heteroclitus), Atlantic
-------
Changes in the Finfishery 125
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-------
126 Chapter 2: Living Resources
TABLE 29.
LANDINGS FOR FRESHWATER-SPAWNING FINFISH, ANNUAL AVERAGE FOR 1962 TO 1970
AND 1971 TO 1980 (POUNDS/ACRE)"
1962-1970 1971-1980
Western Shore
James River 26.85 9.39*
Patuxent River 4.74 4.13
Potomac River 34.56 13.90*
Rappahannock River 52.61 20.13*
York River 51.76 8.31
Main Bay
North 20.86 12,49*
Upper Central 10.93 7.13*
Lower Central 3.51 1.66*
South 1.61 1.07
General 14.63 3.73*
Eastern Shore
Chester River 9.27 4.73*
Choptank River 12.53 4.53*
Eastern Bay 1.73 1.04*
Fishing Bay 14.50 4.74*
Honga River 1.02 0.80
Nanticoke River 26.89 12.57*
Pocomoke Sound 0.50 0.32
Tangier Sound 1.15 0.50*
Wicomico River 8.23 6.77
"Significantly different from 1962 to 1970 at 0.05 level
"One pound/acre = 0.112 g/m2
silverside (Menidia menidia), and Bay anchovy 1982) differs in that while the Bay anchovy has
(Anchoa mitchilli) were analyzed to determine been declining during the past decade in the
trends in these noncommercial species. Results for Maryland tributaries surveyed (Table 29), the Bay
Maryland are shown in Table 28. Mummichog in- anchovy has been shown to be increasing in the
creased in all basins. Bay anchovy and Atlantic Virginia tributaries surveyed during the same
silversides, which use SAV as habitat, declined in period.
all basins. The Virginia survey (Wojcik and Austin
-------
SECTION 7
SYNTHESIS: A GEOGRAPHIC ASSESSMENT
Changes in several biological resources have
been discussed, from the ecologically important
phytoplankton to the economically important
commercial fisheries.
Historical changes have been seen in phyto-
plankton abundance and species composition in
the two areas (upper Bay, upper Potomac) for
which data are available. These changes are usu-
ally associated with nutrient enrichment.
The decline of SAV begun in the late 1960's
has continued to the present, following a down-
estuary direction. Thus, at present, the most abun-
dant SAV is found in the lower Bay and eastern
shore.
Berithic animal species composition in the Pa-
tapsco River, Elizabeth River, and main Bay was
assessed. The Patapsco and Elizabeth Rivers
demonstrated a decrease in diversity and an in-
crease in pollution-tolerant species in more im-
pacted areas. The upper Bay (segments CB 1-5)
had very high annelid:mollusc ratios when com-
- pared to those of the lower Bay segments (CB 6,
7).
During the past decade, oyster spat levels have
decreased from pre-1970 averages in most regions
of the Bay. The years 1980 and 1981 were good
ones for many of the eastern shore tributaries; this
was probably due to high salinities.
Oyster landings have decreased since 1880, but
have remained relatively stable since 1962. How-
ever, there has been a basic change in the spatial
distribution of the oyster fishery. Harvest in the
western shore has decreased substantially; in the
Eastern Shore, it has increased. This may reflect
a shift in fishing effort from the western to the
eastern side of the Bay.
RANKING OF CHESAPEAKE BAY SEGMENTS
ACCORDING TO CURRENT CONDITONS
To summarize the present condition of some
important resource variables, and to identify areas
of lower resource productivity, a numerical rank-
ing system was developed. Ranking of individual
segments with respect to their potential according
to their biological resources is useful because it
allows one to compare patterns of resource vari-
ables with patterns of water quality to identify
possible relationships.
In this characterization, segments will be
ranked according to their 1978 distribution of
SAV, their 1971 to 1980 anadromous and estuar-
ine fishery landings, and according to their 1980
to 1981 oyster spat set. These variables were
selected as representing the condition of resources
because basic biological components (SAV and
spat set) provided two of the variables, while a
biological-economic component provided the
third (fishery landings). These variables provided
appropriate spatial distribution.
Submerged Aquatic Vegetation
Segments are ranked on the SAV scale accord-
ing to the extent to which their SAV expected
habitat is filled. The expected habitat is defined
as 50 percent of the potential habitat, the area
delineated by the 2 m bathymetric contour. Two
meters is the maximum depth at which SAV are
likely to be found; test studies showed that, on
the average, half of this area could be expected
to contain SAV under the best conditions.
127
-------
128 Chapter 2: Living Resources
Spat Set from 1980 and 1981
Spat set from 1980 and 1981 is used to rank
segments because those were recent years of
especially successful spat set partly because
salinities were optimal for spat. Thus, basins
should have been allowed to express their max-
imum potential unless other factors, such as water
quality, prevented their doing so.
Because spat fall is in part a function of salini-
ty, before segments could be compared with each
other, it was desirable to normalize against salini-
ty. This was attempted by ascertaining the max-
imum spat fall observed in each segment and di-
viding the present spat fall by this maximum.
Anadromous and Estuarine Fishery Landings
On a Bay-wide basis, the decade 1971 to 1980
represents a major shift: while landings of marine
spawners continued to increase, landings of ana-
dromous species decreased. The anadromous and
estuarine landings provide an indication of the ex-
tent to which any tributary contributes to this re-
cent trend.
Because fishery data are not available by seg-
ment, basin data are applied to all segments in
the basin.
Table 30 summarizes the segment rankings
and the total, where at least two variables were
available. Where one variable was missing, the
mean of the other two was added to provide
equivalent values (shown in parentheses).
Trends, as determined by three- and five-year
running means, indicated that juvenile indices of
marine spawners increased, and those of fresh-
water spawners decreased. The Potomac River is
a notable exception, in which indices of some
freshwater spawners increased.
The past ten years indicate a basic change in
the pattern of Chesapeake Bay fisheries harvest
over the previous period. While freshwater
spawners have entered an unprecedented decline,
marine spawners, coincidentally, have continued
to increase.
REGIONAL ASSESSMENT OF
CURRENT CONDITIONS AND TRENDS
Western Shore
The western shore shows a general pattern of
decline in certain biological resources. Detrimen-
tal changes in species composition and increased
biomass of phytoplankton have been shown in the
upper Potomac River and may occur in other
western shore tributaries if conditions deteriorate.
The Potomac River itself has improved in recent
years because of advanced waste treatment there
(Champ et al. 1981). A result of this improvement
has been a more diverse algal population with a
decrease in the numbers of filamentous blue-green
algae.11
Submerged grasses were lost from the
maximum-turbidity reaches of all western shore
tributaries except the Potomac River before 1970,
as well as from the tidal-fresh reaches of the Patux-
ent, Potomac, and James Rivers. At present, no
tidal-fresh reaches sustain substantial SAV. The
maximum-turbidity reach of the Potomac River
still contains SAV; most lower-estuarine SAV is
confined to the York and Potomac Rivers. Sub-
merged aquatic vegetation still does occur in some
small western shore tributaries that are less en-
riched, such as the Magothy and Severn Rivers
and Seneca Creek.
Oyster harvest has declined significantly in the
Potomac, York, and James Rivers. (The latter is
apparently not related to the closure of the river
because of Kepone contamination in 1975; the ban
on shellfish was very brief.)12 The fishery appears
to have remained constant in the Patuxent River.
Spat set has declined significantly (over pre-1970
values) in all but the York River where no signifi-
cant trend appeared.
Juvenile indices of freshwater spawners have
not declined in the Potomac River as extensively
as in the other areas surveyed, possibly also a
reflection of improved water quality there. Land-
ings of freshwater spawners decreased in all areas
of the western shore.
-------
Synthesis: A Geographical Assessment 129
TABLE 30.
SUMMARY OF SEGMENT RANKS
Western Shore
TF-1
RET-1
LE-1
TF-2
RET-2
LE-2
TF-3
RET-3
LE-3
TF-4
RET-4
LE-4
TF-5
RET-5
LE-5
WT-1
WT-2
WT-3
WT-4
WT-5
WT-6
WT-7
WT-8
WE-4
Main Bay
CB-1
CB-2
CB-3
CB-4
CB-5
CB-6
CB-7
CB-8
Eastern Shore
EE-1
EE-2
EE-3
ET-1
ET-2
ET-3
ET-4
ET-5
ET-6
ET-7
ET-8
ET-9
1978 SAV
6
6
6
6
4
6
6
6
6
6
6
5
6
6
6
6
6
6
4
6
3
3
5
4
6
6
4
5
5
5
3
—
3
3
4
6
6
6
3
5
6
6
6
3
1971-1980
Landings
5
5
5
5
5
5
2
2
2
2
2
2
3
3
3
6
6
6
6
6
6
3
3
4
6
6
6
3
5
4
4
4
2
4
4
6
6
6
4
4
4
4
3
3
1980-1981
Oyster Spat Set
-(5)
-(5)
5
5
-(4)
3
-(4)
6
4
-(4)
6
6
-(5)
-(5)
4
-(6)
-(6)
-(6)
-(5)
-(6)
-(4)
-(3)
6
-(4)
-(6)
-(6)
-(6)
3
2
-(4)
-(3)
—
3
2
2
-(6)
-(6)
-(6)
6
-(4)
-(5)
4
5
-(3)
Total
16
16
16
16
13
14
12
14
12
12
14
13
14
14
13
18
18
18
15
18
13
9
14
12
18
18
16
11
12
13
10
—
8
9
10
18
18
18
13
13
15
14
14
9
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130 Chapter 2: Living Resources
Main Bay
The upper-main Bay (above the Bay Bridge)
shows changes in phytoplankton species composi-
tion and biomass that are a reflection of increases
in nutrient enrichment. This region no longer sup-
ports SAV, has a depressed juvenile finfish index,
and is not a source of high fish yields. It shows
high annelid:mollusc ratios when compared to
those ratios from the lower Bay (segments CB 5-7).
These differences, however, are not statistically
significant.
Eastern Shore
The Eastern Shore sustains relatively healthy
SAV growth in Eastern Bay, the mouths of the
Chester and Choptank Rivers, and Tangier
Sound. Greater loss has occurred in Pocomoke
Sound, Wicomico River, Nanticoke River, Fishing
Bay, and Honga River.
Harvests of oysters have increased in the
Eastern Shore region, an indication of its relatively
good environmental quality. The high 1980 to
1981 spat set was largely confined to the Eastern
Shore, particularly Eastern Bay, Tangier Sound,
and the Choptank River. With respect to finfish,
landings of marine spawners have increased, while
those of freshwater spawners declined in all basins
except Tangier Sound.
CONCLUSIONS
The two major primary producers of the Bay
system, Bay grasses and phytoplankton, have
undergone substantial changes. Phytoplankton
biomass and species composition, difficult to docu-
ment because of their ephemeral nature, have
shown eutrophication-related changes in the up-
per Potomac and main Bay (above the Bay
Bridge). The abundance of Bay grasses has de-
clined dramatically, particularly in fresher reaches
of the estuary.
Species diversity and composition of benthic
fauna show pollution-related changes in the
Patapsco and Elizabeth Rivers. The upper main
Bay has a higher proportion of pollution-tolerant
annelids than the lower Bay, but the effect is not
strong enough to be clearly distinguishable from
response to natural gradients. It appears that the
benthos of the main Bay is not stressed enough to
show clear pollution-related effects, while the
Patapsco and Elizabeth Rivers are sufficiently
stressed.
Harvests of oysters have increased on the
Eastern Shore, but decreased on the western
shore. Spat set shows a similar pattern: while den-
sities have declined everywhere, the recent high
spat set (1980 to 1981) was sustained primarily by
Eastern Shore areas.
Juvenile indices of freshwater-spawning fin-
fish show recent absence of strong year classes,
which is also reflected by declines in harvests. The
fishery for marine-spawning finfish continues to
be strong. We do not know what the role of nat-
ural climatic factors is in determining the health
of the fishery. However, the unprecedented nat-
ure of the recent decline in freshwater spawners
suggests that other factors in addition to climate
may be affecting these organisms. Their spawn-
ing areas are in close proximity to riverine sources
of anthropogenic materials, implying that they are
much more likely than other fish to be exposed
to such materials at a sensitive stage. It would not
be surprising that effects of anthropogenic
materials should be expressed first by fresh-
water-spawning fish, though, in reality, there is
little information to compare the relative sensitivi-
ty of juvenile marine spawners to anthropogenic
materials in nursery areas.
The Eastern Shore generally appears to be the
most productive region of the Bay system. This
conclusion is supported by the regional com-
parison; Eastern Bay, and the Choptank and
Chester Rivers ranked most favorably. The up-
per Patuxent, lower James, and Patapsco and
Middle Rivers showed poor ranks.
-------
CHAPTER 3
RELATIONSHIP BETWEEN WATER
AND SEDIMENT QUALITY, AND
LIVING RESOURCE VARIABLES
-------
CHAPTER 3
RELATIONSHIP BETWEEN WATER
AND SEDIMENT QUALITY, AND
LIVING RESOURCE VARIABLES
-------
SECTION 1
INTRODUCTION
Chapters 1 and 2 summarized information on
trends in water and sediment quality, and living
resources. This chapter examines the relationships
between these observed trends by determining if
there is a reasonable potential linkage and if such
a relationship can be demonstrated analytically.
After a discussion of how various environmental
parameters can affect the Bay's ecosystem, and
ultimately, its living resources, more detailed in-
formation will be presented on finfish, oysters,
other benthic organisms, and submerged aquatic
vegetation.
ANALYTICAL PROCEDURE
It is important to mention that relatively few
data sets were collected at the same time and
place. Major climatic variables and physical fac-
tors, (e.g., temperature, salinity, and freshwater
flow) typically provided the most complete data
for time-series analyses. Unfortunately, most his-
torical water quality data and biological data
(e.g., finfish juvenile index, spat set, and fishery
landings) were not obtained in the same spatial
and temporal scales. This created difficulties with
many statistical approaches. In some cases, there-
fore, analyses were made by visual inspection of
tabular or graphical material. Such conditions
have forced a more conservative interpretation of
trends than in cases where statistical requirements
are met.
Briefly, for the analytical strategy for this
chapter, reasonable potential effects of observed
water and sediment quality trends on Bay organ-
isms were postulated, and these possible responses
were documented by the use of published mater-
ial. With these hypotheses as a framework,
available data were analyzed to identify where
these effects appear to be demonstrated. In-
completeness of much data necessitated more des-
criptive analyses in some cases. The GBP tried to
work with the data in spite of many shortcom-
ings, and we hope that we have worked within
acceptable grounds of credibility.
THE ECOSYSTEM PERSPECTIVE
The Trophic Web
A better understanding of how environmen-
tal perturbations affect living resources can be
achieved if Chesapeake Bay is examined from an
ecosystem perspective. The system as a whole acts
to sustain the productivity of the estuary, but can
also transfer effects of environmental changes to
many levels.
As discussed in Chapter 1, Chesapeake Bay,
organisms inhabiting it, and the processes that link
them constitute the Bay ecosystem. Material and
energy are transferred from one portion of the
system to another through a trophic web (an im-
portant concept to understand in evaluating the
effect of environmental influences on resources).
These relationships can be detailed conceptually
by the use of a trophic diagram, showing major
components and flows. Figure 44 is one such
diagram, representing a simplified plankton-based
food web leading to finfish. Theoretically, similar
diagrams could be constructed for all components
of the Bay ecosystem (Green 1978, Mackiernan
et al. 1982). The actual species represented by the
boxes, the direction and relative importance of the
pathways, and the magnitude of flows vary with
133
-------
134 Chapter 2: Living Resources
O
-0)
"o
D
DO
1
•D y
-------
Introduction 135
season, location, and physical aspects of the en-
vironment. The system, in a sense, represents a
series of switches that can shunt material or energy
flows in various directions. A change (in species
makeup, for example) at one level can impact
other portions of the ecosystem by altering direc-
tion or size of these flows.
Because of such interrelationships, organisms
may be affected by factors acting on other trophic
levels. This is a key point — many hypothetical im-
pacts of water quality discussed in this chapter do
not act on the resource species directly, but on
some ecosystem component upon which it de-
pends. For example, even though an environmen-
tal perturbation does not directly impact a
resource, that resource could decline if survival
tolerances of a key food organism were exceeded.
Similarly, changes in population of a predator,
parasite, or competitor could affect the abundance
of a resource species.
RELATIONSHIPS BETWEEN WATER
QUALITY AND LIVING RESOURCES
Anthropogenic Impacts on Resources
In general, organisms can be considered as
responding to a number of interacting en-
vironmental variables. Some of these are natural,
usually related to climate, hydrography, or
biological interactions; others may be primarily
anthropogenic, coming from many human ac-
tivities. Estuaries, particularly those of the
temperate zone, are inherently variable en-
vironments; organisms inhabiting them are sub-
ject to a wide annual range of air and water
temperatures, freshwater inflow, wind, light, and
circulation. It has been demonstrated that much
of the annual variability in spawning success of
fish and shellfish, for example, is influenced by
natural variation of flow, temperature, and salin-
ity (Setzler et al. 1980, Ulanowicz et al. 1980).
Although these may be altered by man's actions
(e.g., changes in timing and extent of freshwater
inflow due to dams), most are within the range
of tolerance of estuarine organisms.
Anthropogenic impacts may increase natural
environmental variability, or may introduce non-
natural stresses outside the adaptive repertoire of
estuarine organisms (e.g., toxic chemicals). Trends
in water quality identified in Chapter 1 with a
major anthropogenic component, are:
1. Nutrient enrichment, particularly of the
upper Bay and western shore tributaries.
Increased eutrophication is reflected in in-
creased particulate carbon and turbidity.
In conjunction with summer stratification
of the water column, this can lead to three
more trends in water quality with an an-
thropogenic component;
2. Extended periods of low dissolved oxygen
or even complete anoxia in deeper water
of the upper and mid-Chesapeake;
3. Bay sediments that are anthropogenically-
enriched with large amounts of heavy
metals, organic chemicals, and similar tox-
ic materials; and
4. Levels of toxic materials in the water col-
umn that sometimes exceed the published
EPA ambient water quality criteria, par-
ticularly in the upper Bay and western
tributaries.
DETECTING EFFECTS OF
ANTHROPOGENIC STRESS ON
LIVING RESOURCES
Separating effects from natural, as opposed to
anthropogenic, causes, or even showing any ac-
tual cause and effect relationship, is no trivial task.
A major problem is that the complexities of eco-
system function, coupled with the natural varia-
bility of organism distribution and abundance,
make it difficult to identify changes and to ascribe
particular causes to the observed effects (Wolfe
et al. 1982). Sindermann (1980) describes in some
detail the difficulty of isolating and quantifying
pollution effects on resource species (as distinct
from effects of natural environmental variations).
Paraphrasing Sindermann (1980), chemical pol-
lutants cause stress and death in individual marine
animals; this can be easily demonstrated, and has
been done repeatedly. Descriptions of lethal and
sublethal effects of heavy metals, petroleum com-
pounds, and halogenated hydrocarbons abound
in the experimental literature. Whether or not
stress from chemical pollutants can have signifi-
cant quantifiable effects on resource species abun-
-------
136 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
dance (apart from localized effects in severely con-
taminated coastal and estuarine zones) is much
more difficult to demonstrate and has not been
documented satisfactorily.
A recent review of ecological stress in the New
York Bight (Mayer 1982) supports this view, for
even in an area as heavily impacted as the New
York Bight, it is difficult to demonstrate pollution-
induced changes in the growth and distribution
of populations of plankton (Lee et al. 1982), inver-
tebrate communities (Wolfe et al. 1982), fishes
(Sindermann et al. 1982), and species or groups
(Boesch 1977a, 1982; Franz 1982), except in the
most heavily-impacted areas.
Changes to some populations have been
demonstrated in certain areas including: elimina-
tion of sensitive species or groups (Boesch 1977a);
changes in species diversity of the community
(Jacobs 1975); increase in pathologies (tumors, le-
sions), or incidence of disease (Sindermann et al.
1982). Laboratory studies, or use of microcosm
systems, where one variable at a time can be
manipulated, can help link observed cause and
perceived effect. Examples of the latter are the
Controlled Ecosystems Pollution Study (CEPEX)
conducted on the west coast, and the Marine
Ecosystems Research Laboratory (MERL) studies
currently underway in Rhode Island. Coupled
with improved monitoring and field experimen-
tal procedures, designed to answer specific ques-
tions, such studies can strengthen the understand-
ing of cause and effect relationships. Nevertheless,
complete understanding is probably not possible
(or feasible). In that light, Sindermann (1980)
argues that "to insist on demonstration of easily
discernible effects on overall species abundance
is to establish too harsh a criterion of pollution
damage. A much more acceptable concept is that
the effects of pollution, clearly demonstrated on
even a single individual or a local population,
must be considered a cause for management ac-
tion to protect the total population —just as is the
case with humans."
-------
SECTION 2
POTENTIAL IMPACTS OF WATER AND SEDIMENT QUALITY
ON LIVING RESOURCES
In this section reasonable potential impacts
(called hypothetical impacts here) of documented
trends in water and sediment quality upon the
Bay's living resources will be formulated. The im-
pacts of natural variables, such as freshwater in-
flow and temperature, insofar as they appear to
relate to observed trends in living resources, will
also be discussed. Other factors will be addressed
where appropriate (e.g., fishing pressure, habitat
loss due to dams), although these were not part
of the; data analysis. These hypothetical impacts
will be tested by various analytical procedures,
depending on strength and availability of the
data. Finally, those relationships which seem sup-
ported by available data and analyses, as well as
those where relationships could not be demon-
strated, will be summarized.
It is anticipated that in many cases strong rela-
tionships cannot be supported by the data; the
signal is lost in the noise of natural variability.
Howesver, even the framing of reasonable hypo-
theses is a useful exercise, because this allows
researchers and managers to focus on areas where
effects could be expected, and where monitoring
or research efforts may yield the most useful
information.
NUTRIENT ENRICHMENT
Increases in levels of, primarily, forms of
phosphorus and nitrogen may increase standing
crops of phytoplankton (Heinle et al. 1980)
(Chapter 1). Provided the phytoplankton species
composition matches nutritional requirements of
larvae^ of commercial species (or zooplankton
which feed these species), this early stage of
eutrophication may actually benefit productivi-
ty in portions of the system (Ukeles 1971; Sharp
et al. 1982).
a. As nutrient enrichment progresses,
however, chlorophyll concentrations in-
crease, as do particulate carbon and tur-
bidity. Nutrient enrichment during
warmer temperatures results in greater
fluctuation in DO concentrations in surface
water, and to extended periods of near
anoxia in bottom water (also discussed
below) (Heinle et al. 1980; Taft et al.
1980).
Hypothetical Impact
Effects of these changes could include:
shading of SAV by increased
phytoplankton or epiphyte growth,
leading to decline in SAV abundance
(Twilley et al. 1981); and/or organic
enrichment of sediments leading to
changes in benthic communities such
as increased dominance by detrivores
(Bascom 1982).
b. Shifts in phytoplankton species composition
may occur, possibly resulting in blooms of
undesirable species (Ryther 1954).
Hypothetical Impact
Effects of these changes could include:
increased dominance of blue-green
algae in tidal-fresh areas, or
flagellates in saline regions (Thomas
1972); and/or alteration of biomass
137
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138 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
and composition of zooplankton or
filter-feeding communities, with
ultimate impacts on larval fish (Greve
and Parsons 1977) or shellfish (Ryther
1954).
c. The extent and duration of low DO in
deeper water has apparently increased in
recent decades (Tart et al. 1980) (Appen-
dix B).
Hypothetical Impact
Impacts of this change could include:
elimination of natural benthic com-
munity assemblages in deeper water
(or replacement with ephemeral op-
portunistic assemblages) (Mountford
et al. 1977); and/or decreased habitat
for oysters and other commercially
important shellfish (Haven et al.
1978). Increased incidence of shellfish
mortality at the boundaries of the im-
pacted area might be expected.13
Finally, habitat for fish, particularly
demersal species such as sciaenids, is
reduced; this could be reflected in
declines in abundance or condition.14
CONTAMINATION WITH TOXICANTS
a. The sediments are enriched with metals
and contain hundreds of organic com-
pounds. High levels of heavy metals have
been measured in Chesapeake Bay sedi-
ments; this anthropogenic enrichment may
reach ten times or more background
(natural) values. Similarly, over 300 an-
thropogenic organic chemicals have been
isolated from Bay sediments; most are toxic
(Bieri et al. 1982a).
Hypothetical Impact
Impact of these toxicants could in-
clude: changes in benthic communi-
ty structure or abundance; elimina-
tion of sensitive species and replace-
ment by a resistant fauna (Boesch
1973); bioaccumulation of toxic
materials in tissues of shellfish, other
benthic species, or submerged aquatic
vegetation (O'Connor and Rachlin
1982); and/or change in physiology,
reproductive success, or behavior of
benthic dwelling species (Schaffner
and Diaz 1982; Phelps et al., in
prep.). There is also the possibility of
further accumulation of these
materials in the tissues of benthic-
feeding fish and waterfowl.
The water column may be contaminated
with toxic materials. Levels of heavy
metals, certain organic materials (chiefly
pesticides), and total residual chlorine have
been measured at levels which exceed the
EPA ambient water quality criteria. As
these criteria have been developed to pro-
tect the integrity of aquatic ecosystems,
measured concentrations above these levels
may represent reason for concern if ex-
posures are of sufficient duration.
Hypothetical Impact
Impacts of these toxicants could in-
clude: mortality or stress to exposed
organisms, particularly sensitive lar-
val stages (e.g., oysters, larval fish).
This might be reflected in reduced
recruitment to impacted populations,
lowered resistance to disease or other
stresses, or even gross tissue abnor-
malities (lesions, etc.) (Calabrese et al.
1982). Bioaccumulation of material in
tissues of fish, filter-feeding benthic
species, or even plankton or SAV may
result (O'Connor and Rachlin 1982).
This could have implications for
higher trophic levels as well.
IMPACTS OF NATURAL VARIABLES
It is useful to discuss the effects of major
natural variables to gain a perspective on the
possible impacts of anthropogenic factors. It is not
unreasonable that variability due to one, or a com-
bination of man-induced stresses, may represent
only a small fraction of that caused by natural per-
turbations. However, even an incremental in-
crease in the mortality of a larval fish, for
example, or a small percentage decline in photo-
-------
Potential Impacts of Water and Sediment Quality on Living Resources 139
synthetically available light to SAV may result in
an eventual severe impact to the resource.
Although estuarine organisms are to a great
extent tolerant of an estuary's naturally-variable
environment, much of the year to year differences
in distribution and abundance can be accounted
for by variations in freshwater inflow, salinity,
air and water temperature, wind, and other pa-
rameters. The influences of stochastic processes,
particularly of extreme events such as storms or
droughts, can be considerable (Boesch et al. 1976).
Finally, biological interactions such as predation,
competition, or disease influence the distribution
of many species (Virnstein 1977).
An example of the effects of natural variables
on a resource is the striped bass. Success of striped
bass year classes has been positively correlated
with colder than normal winters and high spring
runoff (Setzler et al. 1980). Cold winters are
thought to contribute increased detrital loads in
spawning areas because of ice scouring marshes
and shorelines (Heinle et al. 1976). The detritus
provides additional food for zooplankton, which
in turn are fed upon by the larval fish. Increased
runoff carries dissolved nutrients that support the
phytoplankton and larval fish food chain; it also
physically extends the area of the spawning and
hatching grounds.
In contrast, blue crabs spawn near the mouth
of Chesapeake Bay, while menhaden spawn 16
to 25 km15 from shore over the continental shelf.
Larvae of both species drift with shelf currents
and are highly dependent on these currents to
return them at the appropriate time to the mouths
of suitable estuaries. When shelf circulation —
driven by climate and wind patterns —is toward
the west or northwest during this critical period,
there is a high probability that these and other
marine-spawned species will be returned to the
estuary, resulting in a successful year class (Nelson
1979).16 Within the Bay, freshwater outflow
drives upstream flow of saline water at depth,
assisting these species in reaching low salinity
nursery areas.
-------
SECTION 3
SUBMERGED AQUATIC VEGETATION
AND WATER QUALITY
INTRODUCTION
Submerged aquatic vegetation (SAV) was one
of three major problem areas addressed by GBP
research. For this reason, an integrated picture
of factors impacting SAV exists; these factors can
be reasonably implicated in recent vegetation
declines. The two major anthropogenic factors
that were hypothesized in Section 2 as affecting
SAV were:
1. Impacts of toxic materials, particularly
herbicides, the use of which has increased
greatly during the period of maximum SAV
decline;
2. Reduction in available light to the plants,
either by an increase in turbidity of the
water column or an increased growth of
epiphytes on the plant leaves (or a com-
bination of these). Turbidity changes were
hypothesized to be due to increased sus-
pended material and/or phytoplankton
growth, enhanced by nutrient enrichment.
In this section, results of GBP-supported
research in these areas are discussed, and an at-
tempt to relate field observations to research
results is made.
EVIDENCE FROM RESEARCH
Herbicides
The major toxic materials considered in assess-
ing anthropogenic factors on SAV decline were
agricultural herbicides. The use of these chemicals
has increased significantly in the recent decade,
and it was hypothesized that runoff from agricul-
tural fields might deliver enough of these toxicants
to impact SAV in Bay waters (Stevenson and Con-
fer 1978).
Details of the research projects and results sup-
ported by the GBP are contained in the 1982 EPA
report, Chesapeake Bay Program Technical
Studies: A Synthesis. In general, projects focused
on the following areas: fate and transport of herbi-
cides within the estuary, action of the herbicide
on SAV, and potential community effects of herbi-
cide exposure. The herbicides atrazine and linu-
ron — most widely used — were the primary types
examined.
In general, maximum herbicide concentra-
tions observed did not exceed 1 ppb in the
estuarine portions of the lower Bay and 5 ppb in
the upper Bay (Hershner et al. 1982, Boynton et
al. 1983). Ephemeral concentrations of up to 20
ppb were observed in some estuarine areas; these
persisted for two to eight hours at most. Much
higher levels (up to 100 ppb) were observed after
rainstorm events in small tidal tributaries adja-
cent to fields.
Plants exposed to atrazine and linuron show
a rapid reduction in photosynthesis, followed (in
the case of low herbicide concentrations) by
gradual recovery. The higher the initial exposure,
the longer the recovery time. Plants exposed to 10
to 15 ppb atrazine took two to five weeks to regain
a photosynthetic rate comparable to controls
(Cunningham et al. 1982). Plants treated with 50
ppb atrazine and above showed severe and persis-
tent loss of productivity.
There are four conclusions from the herbicide
research:
• Because herbicide concentrations did not
exceed 20 ppb in estuarine waters and rare-
ly exceeded 5 ppb, it is likely that herbicides
141
-------
142 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
are not the primary cause of SAV decline
in most areas of the Bay.
• Herbicides may be a major impact in small
tributaries directly adjacent to herbicide-
treated fields.
• Herbicides degrade relatively rapidly and
do not appear to build up in sediments.
However, relatively little is known about
phytotoxicity of major herbicide degrada-
tion products (Jones et al. 1982).
• Very low (ambient) concentrations of her-
bicide (less than 10 ppb) are predicted to
cause a reduction of 10 to 20 percent of SAV
photosynthesis. If exposure intervals are less
than SAV recovery time, this could lead to
increases in the stressed condition of the
plants. In particular, light limitation could
act in concert to adversely impact plant
populations (Kemp et al. 1982c).
Light Limitation
Research on light limitation of SAV focussed
on several major areas: characteristics of light in
Chesapeake Bay; factors contributing to light at-
tenuation; and response of SAV communities to
changes in light regime. Many details are con-
tained within the above-cited Synthesis Report.
In general, light falling on the SAV bed can
be attenuated and scattered by suspended parti-
culate material (both living and dead), as well as
by dissolved and colloidal materials of organic
origin collectively termed Gelbstoff (Wetzel et al.
1982). In addition, epibiota and sediment on the
SAV leaves can further reduce the amount of pho-
tosynthetically active radiation (PAR) reaching the
plants. Sources of suspended material may include
sediments carried in river runoff, material from
local shore erosion resuspended from the bottom,
or of organic origin (phytoplankton and detritus,
in particular) (Biggs 1970).
There is evidence that the quantity of light has
been reduced in recent years, and that quality
(that is, the amount in the critical blue and red
spectral regions) has also declined at a lower Bay
study site (Wetzel et al. 1982). Spectral measure-
ments for the upper Bay are available only for
channel areas; however, the general pattern is for
selective light attenuation in the blue region of the
spectrum, with a shift to orange as the most
penetrating wavelength (Champ et al. 1980). In-
creases in chlorophyll pigments, due to greater
phytoplankton biomass, have also occurred in the
upper and mid-Bay, as well as in most major trib-
utaries. This is linked to increases in nutrient
enrichment in the corresponding areas of the
Chesapeake (Heinle et al. 1980). As discussed in
Chapter 1, there has been an increase in summer
turbidity in recent years for many areas of the
Bay.
In addition, nutrient enrichment has been
hypothesized as leading to increased fouling of
SAV leaves with epibiota (epiphytes and certain
particle-filtering animals such as bryozoans).
Epiphytes can significantly reduce the amount of
PAR reaching the leaf surface: less than 10 per-
cent of incoming radiation was transmitted
through dense epiphytic cover on older Zostera
blades (Borum and Wuim-Andersen 1980).
These conclusions from the light-limitation
research support the hypotheses proposed in Sec-
tion 2 on nutrient enrichment:
• Studies indicate a reduction in the quanti-
ty for the upper and lower Bay and in the
quality of available light. For the growing
season, there appears to be a progressive in-
crease in light attenuation in the PAR part
of the spectrum. There is a seasonal com-
ponent to attenuation, although it is highly
variable. Vertical PAR attenuation in-
creases in the spring, affecting the initia-
tion of growth for most SAV species.
• In situ studies indicate that Bay plant com-
munities are generally operating under con-
ditions of light limitation. No apparent light
saturation is reached in the upper Bay, nor
did Zostera communities in the lower Bay
exhibit light saturation.
• Decline of SAV over the past several de-
cades has in general followed a "down-
estuary" pattern, corresponding to a pat-
tern of nutrient enrichment.
• Microcosm and mesocosm (pond) ex-
periments indicate that nutrient loading
leads to a progressive enhancement of phy-
toplankton biomass, seston, and epiphytes
(Twilley et al. 1981).
• The combination of water column attenua-
tion and epiphytic shading was sufficient
to markedly reduce SAV photosynthesis.
-------
Submerged Aquatic Vegetation and Water Quality 143
Loss of SAV occurred in ponds exposed to
highest nutrient loads.
• Preliminary evidence suggests that the in-
ability of light-stressed plants to compen-
sate for respiration may lead to reduced
energy storage for over-wintering and
spring regrowth (Twilley et al. 1982).
• Reduction of grazers by various natural or
anthropogenic perturbations may allow ex-
cessive fouling of SAV leaves by periphyton
(Orth et al. 1983).
Ability to Recolonize
Transplantation experiments have indicated
that survival of SAV is possible in some areas now
denuded of plants17 (Orth et al. 1982). These
observations emphasize the importance of
availability of seeds or propagules in determin-
ing whether SAV can recolonize former habitat.
If no nearby source of vegetation exists, and if
sediments no longer contain viable seeds, tubers,
or rhizomes, then physical transplanting may be
necessary to restore some beds. Impacts of grazers
or "users" of SAV and present suitability of former
habitat must be considered in these cases (Orth
et al. 1982)
EVIDENCE FROM FIELD OBSERVATIONS
Research indicates that light limitation,
possibly related to nutrient enrichment, is the ma-
jor cause of SAV declines in most areas of the Bay.
One might expect to see correlations between SAV
abundance and such water quality parameters as
nutrient concentrations, chlorophyll a, turbidity,
and DO (through their relationship to phyto-
plankton biomass). Observations made in the field
suggest that some of these correlations exist.
Biostratigraphic evidence from sediment cores
shows tha.t the decline of SAV, the reduced abun-
dance of epiphytic diatoms, and the decrease in
diatom diversity, along with the simultaneous in-
crease of sedimentation rate and the number of
planktonic diatoms, are related to anthropogenic
impacts (Brush and Davis 1982). Clearing of land
for agriculture in the 1800's and increased sewer
loadings were apparently major contributing fac-
tors. For example, since the 1600's, Furnace Bay
(off the Susquehanna Flats) has changed from a
clear, SAV-dominated embayment to a turbid
phytoplankton-dominated water body.
Comparison of maps of current SAV distribu-
tion, and of areas of greatest historic decline
(Figures 45a and 45b) with a map of Chesapeake
Bay nutrient status (Figure 46) reveals striking cor-
respondence. Submerged aquatic vegetation now
occurs primarily in those areas characterized with
low or moderate amounts of nutrients: Eastern
Bay, lower Choptank, Tangier Sound, and the
lower Bay main stem, as well as a few small
western shore tributaries (Magothy and Severn
Rivers). Greatest loss has occurred in areas with
the highest levels of nutrients: Susquehanna Flats,
upper and mid-Bay, major western shore tribu-
taries, and upper reaches of Eastern Shore
tributaries (Orth and Moore 1981).
Trend Comparison
Comparison of graphs of SAV decline with
similar water quality trend information reveals
a number of apparent correlations. Such com-
parisons suggest, but do not confirm, relationships
between SAV and changes in water quality
variables. For example, in CB-1 a negative cor-
relation is apparent with SAV against both nitrate
(Figure 47a) and annual chlorophyll a concentra-
tions. In EE-1, Eastern Bay, SAV decline appears
to be related to increases in total chlorophyll a
levels (Figure 47b).
Regression Analysis
Because SAV declines are hypothesized to be
related to some water quality factors, certain
variables were tested (by correlation analysis)
against vegetation abundance in those Chesapeake
Bay segments where sufficient data existed. A par-
ametric test (Pearson's correlation coefficient) and
a non-parametric test (Spearman's rank correla-
tion coefficient) were used. The 11-year data set
from the Maryland DNR and the USFWS on SAV
abundance was used as an estimator of vegetation
abundance. Among the water quality variables
screened were: TN, nitrate, TP, dissolved in-
organic phosphorus, chlorophyll a, turbidity,
Secchi depth, DO, salinity, temperature, and pH.
-------
144 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
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Submerged Aquatic Vegetation and Water Quality 145
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FIGURE 46.
Rank of Chesapeake Bay segments
according to nutrient status.
-------
146 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
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Submerged Aquatic Vegetation and Water Quality 147
TABLE 31.
SUMMARY OF CORRELATION ANALYSIS OF WATER QUALITY VARIABLES AGAINST SAV.
TABLE OF STATISTICS IS LOCATED IN APPENDIX D, SECTION 2
+ = POSITIVE CORRELATIONS; - = NEGATIVE CORRELATIONS;
DIGIT INDICATES NUMBER OF CORRELATIONS WITH EACH VARIABLE IN EACH SEGMENT
VARIABLE
SEGMENT
CB-1
CB-2
CB-3
CB-4
CB-5
EE-1
EE-2
EE-3
ET-4
ET-5
LE-1
WT-2
WT-3
WT-5
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1- 4- 1- 1+ 1+
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4- 2- 2-
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4- 10- 1+ 2+ 3- 1+ 1+ 2+ 1+
2- 1- 1- 2-
1- 1-
3- 6- 1- 3+ 4+ 2 +
1- 3- 4- 1+ 4+ 2- 3- 6- 3-
2+ 2- 1+ 1+ 2+ 1- 2+ 2+ 3- 1+ 1- 2-
1- 1- 2-
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Subtotals by geographic areas.
Main Bay
Eastern Shore
Western Shore
2- 1-
1+ 2+ 2-
4-
1 +
1_ 2- 9- 4- 1- 5+ 2- 1- 7- 1- 2-
1+2+ 2+ 2 +
1- 2+ 2+ 2+ 4- 2- 2+ 4-
1 +
3- 3+ 5- 7- 3- 6- 2- 4+ 10 +
1+ 5+ 2+ 5 +
1- 2 +
1- 3- 1- 2+ 2+ 1+ 2- 3- 3-
1+ 5+ 6+
2-
1 +
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Grand Total 9- 17- 15- 5- 1- 7+ 5- 4- 12- 1- 2- 1+ 5- 3- 9- 7- 5- 6- 7- 2- 13+ 6-
3+ 5+ 3+ 2+ 4+ 3+ 6+ 3+ 12+ 2+ 5+ 2+ 5+ 4 +
These were compared to total percent vegetation
using annual, spring, summer means, and 95th
percentile values for each variable in each seg-
ment. Data were tested using direct comparison
of a particular year's SAV data against water
quality variables of that year (e.g., 1971 to 1971,
1972 to 1972). In addition, under the hypothesis
that the growing conditions of a previous year
might have a significant effect on SAV success the
next growing season, vegetation data were tested
against water quality variables for the preceding
year (e.g., 1971 SAV against 1970 variables).
Summary results of the correlations are
presented in Table 31. Complete results of the
analyses are given in Appendix D, Section 2. There
are differences as to which variables correlate with
SAV in the various segments; also, a number of
areas show few significant relationships. How-
ever, some generalities can be made. The greatest
number of significant correlations occur between
SAV and nutrients, particularly nitrogen and IFF.
Correlations are, with few exceptions, negative
between SAV and TN, NOs and IFF, and posi-
tive between SAV and TP. Correlations with tur-
-------
148 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
bidity are usually negative; those with Secchi
depth are generally positive. There is little con-
sistency in correlations with DO. There are neg-
ative correlations with chlorophyll a levels of the
preceding year in most segments; however,
positive correlations exist when chlorophyll levels
of the current year are assessed. This may be due
to the peak of chlorophyll a coming after initial
growth of SAV within a particular year. Salinity
showed positive correlations with SAV in main
Bay segments, but generally negative in Eastern
Shore areas. Temperature, however, demonstrates
negative correlations with SAV in main Bay seg-
ments and positive values in Eastern Shore areas.
The water quality variable, pH, always correlates
positively with SAV, but the 95th percentile of pH
values (i.e., very high pH values) shows negative
correlations.
It should be emphasized that this analysis only
identifies correlations (i.e., correspondence of
trends) in SAV and water quality variables. It does
not show cause and effect. However, the major-
ity of correlations identified are consistent with
hypotheses presented in the preceding sections.
Multiple Regression Analysis
To achieve better insight into the contribution
of water quality variables to SAV abundance, step
wise least squares multiple regression analysis was
used to identify factors that best explained ob-
served vegetation trends.
For the first trials, all of the previously listed
water quality variables were included. However,
a low number of observations of certain variables
(i.e., n<10) in some segments necessitated their
elimination before regression equations could be
successfully derived.
Complete results of the preliminary analyses
are given in Appendix D. There is relatively lit-
tle consistency from segment to segment or from
season to season among the major independent
variables in the equations. It is not unexpected
that SAV responses should differ from area to area
because different SAV species are involved; also
areal trends in water quality vary. In addition,
the selection of variables affects the outcome of
the analysis.
As these analyses were, by necessity, limited
by the 11-year SAV data base from the MD DNR
and the USFWS, they are, at best, suggestive
rather than predictive. With small data sets, it is
unlikely that an independent variable beyond the
first or second have predictive capability.18 There-
fore, these results should be viewed with some
caution and should be considered preliminary. In
addition to the above caveats, it is admittedly dif-
ficult to identify or eliminate spurious correla-
tions, or those where a variable represents a sur-
rogate or analog of the actual (but not tested)
predictor. Also, in some segments, paucity of
water quality leads to low degrees of freedom,
weakening the statistical validity of the resulting
equation.
In CB 1-3, most SAV variability can be ex-
plained by a negative correlation with annual or
spring NOs concentrations. In CB-4, a negative
correlation exists with summer NOs, but a positive
one exists with spring TP. Annual TN was the ma-
jor (negative) predictor in CB-5.
Results in eastern embayments and tributaries
were less consistent, possibly due to smaller data
sets. Major predictors are TP (negative, EE-1;
positive, ET-4), summer TN and turbidity
(negative, EE-3), and DO (positive, ET-5).
In western tributaries, major predictors are
turbidity (negative, WT-2), Secchi depth
(positive, WT-5 and\VT-6), TN (negative, WT-5;
positive, WT-2 and WT-6), and NOs (negative,
WT-2, WT-3, and WT-5).
In general, SAV seems to respond negatively
to nutrients, particularly to TN and NOs concen-
trations. This is, however, not exclusively true.
The multivariable equations are only suggestive,
not conclusive. It should be emphasized that none
of these relationships are causative; SAV could be
responding to a non-tested variable that co-occurs
with the tested predictors.
Bay-wide Comparison of Segments
The preceding linear and multiple regression
analyses serve to identify water quality factors that
may be affecting SAV abundance within each seg-
ment. To determine if anyf&ctor or factors could
be acting consistently on all segments, a non-
parametric test, Spearman's rank correlation coef-
ficient, was used. Total percent vegetation within
each segment was compared to a number of water
quality variables, including TN, NOs, NHs, TP,
-------
Submerged Aquatic Vegetation and Water Quality 149
TABLE 32.
SPEARMAN RANK CORRELATION COEFFICIENT RESULTS FOR SUBMERGED AQUATIC VEGETATION
AGAINST WATER QUALITY VARIABLES. rs=CORRELATION COEFFICIENT, ALPHA = LEVEL OF
PROBABILITY THAT rs IS NOT EQUAL TO ZERO.
% SAV
% SAV
5 yr x % SAV
% SAV
% SAV
% SAV
% SAV
5 yr x % SAV
% SAV
% SAV
% SAV
% SAV
% SAV
% SAV
% SAV
% SAV
% SAV
% SAV
% SAV
% SAV
% SAV
y rs Alpha
- x annual TN 0.70 0.001
- x annual TN of 0.70 0.001
preceding year
- 5 yr x TN 0,41 0.05
- x annual NO3 0.08 N.S,
- x annual NO3 of 0.43 0,025
preceding year
- x summer TN 0.11 N.S.
- x maximum summer TN -0.09 N.S.
- 5 yr x summer TN -0.11 N.S,
+ x annual TP 0,10 N.S.
- x annual TP 0.08 N.S.
+ x annual TP of 0.03 N.S
preceding year
+ maximum annual TP 0.08 N.S.
+ maximum annual TP of 0.06 N,S.
preceding year
- x annual chl a 0.30 0.10
+ x annual chl a 0.16 N.S.
- x annual chl a of 0.19 N.S.
preceding year
+ x annual chl a of 0.13 N.S.
preceding year
- annual maximum chl a 0,37 0.05
- annual max. chl a of 0.25 N.S.
preceding year
+ annual maximum chl a 0.20 N.S.
+ annual dissolved oxygen 0.37 N.S.
DO, and chlorophyll a. Annual means, five-year
means, and maximums of various parameters
were tested. The Maryland DNR and USFWS
SAV data from 22 Maryland Bay segments were
used. Results are given in Table 32.
Percent SAV was compared for possible
positive or negative relationships with nutrients,
chlorophyll a, and DO. Significant negative rela-
tionships were identified between percent SAV
and mean annual TN of both the current and pre-
ceeding year (p<0.001). In addition, if five-year
means of SAV are compared to five-year means
of TN, they are significant at the 95 percent level.
There was no apparent relationship between SAV
and annual NO3, but a significant negative cor-
relation was observed between SAV and NO3 of
the proceeding year (alpha = 0.025). No significant
correlations were found between SAV and total
phosphate. When chlorophyll a levels (an indica-
tion of possible nutrient enrichment) are com-
pared to SAV levels, a significant correlation oc-
curs with maximum chlorophyll a of the preceding
year. In addition, the relationship of SAV to mean
annual chlorophyll a (of current year) is signifi-
-------
150 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
cant at the 90 percent level.
In general, on a comparative segment basis,
SAV appears to be responding negatively to in-
creased TN of both the current and the preceding
year. This, as well as the negative relationship
with NOs of the preceding year, seems to support
results of previous correlation analysis. Negative
response to maximum chlorophyll a, an analog of
both nutrient loading and turbidity, is also con-
sistent with the SAV/nutrient enrichment
hypothesis.
SUMMARY
When using a variety of statistical approaches
with field observations, SAV abundance generally
shows a negative relationship with nutrient nitro-
genous concentrations, as well as with turbidity
and chlorophyll a levels. Total nitrogen, NOs, and
IFF levels seem to most consistently correlate with
SAV trends. These results are consistent with ex-
perimental conclusions that link the recent loss of
Bay vegetation to an increase in nutrient enrich-
ment and, ultimately, to light stress due to increas-
ed phytoplankton and epiphyte growth. The large
number of correlations with nitrogen are in-
teresting, and perhaps significant. A plot of per-
cent vegetation in each segment against annual
mean TN of the previous year (using the most re-
cent year for which both SAV and TN data are
available) is revealing (Figure 47c). Physical
variables, such as salinity, temperature, and pH
also appear to exert influence on SAV.
These observed correlations between SAV
abundance and several parameters associated with
nutrient enrichment are supported by strong ex-
perimental evidence. Such an integrated approach
is the most satisfactory means of identifying
causative relationships. In particular, microcosm
and mesocosm experiments allow testing of vari-
ous hypotheses under controlled but reasonably
"natural" conditions. Similar methodologies may
be indicated to strengthen understanding of other
potential relationships between water quality and
living organisms.
50 r
A ET-4
ET= Eastern Tributary
WT=Western Tributary
CB=Chesapeake Bay
EE = Eastern Embayment
IH Spring
A Summer
25
50
75 1 00 1 25 1 50
Seasonal total nitrogen of previous year (1977)
(mg/L)
FIGURE 47C. Correlation between percent vegetated stations and annual total nitrogen of previous year.
-------
SECTION 4
BENTHIC ORGANISMS
AND WATER AND SEDIMENT QUALITY
INTRODUCTION
Increased stress on benthic communities can
result in changes in the abundance and structure
of these assemblages (Boesch 1977a). Sensitive
species may be eliminated, for example, and resis-
tant forms enhanced. In particular, populations
of opportunistic polychaete or oligochaete worms
may come to dominate in stressed areas, while
relatively sensitive molluscs and crustaceans are
reduced in abundance (e.g., Pfitzenmeyer 1975).
In addition to effects on sensitive species or groups,
overall species diversity may be reduced (Jacobs
1975). For example, heavily impacted areas of the
New York Bight and Lower Bay Complex area
showed low faunal abundance and low diversity
as well as an absence of sensitive species (Mearns
and Word 1982, Wolfe et al. 1982).
Such changes may be caused by natural or an-
thropiogenic perturbations. Toxic contamination
of bed sediments and overlying water with heavy
metals or organic chemicals may be reflected in
the accumulation of these materials in animal
body tissues (O'Connor and Rachlin 1982), altera-
tion of physiological processes such as respiration,
shell deposition (Calabrese et al. 1982), or disrup-
tion of reproduction or development (Epifanio
1979, Calabrese et al. 1982). Nutrient enrichment
may result in increased organic loads to the
sediments, changing their structure and thus alter-
ing the type of benthic organisms found within
them. In particular, increased numbers of in-
faunal detritivores have been associated with
organic loading from sewage treatment outfalls
(Bascom 1982). Oxygen depletion, due both to
bacterial decomposition of organic matter and
night-time respiration of algal blooms, is a ma-
jor factor influencing benthic communities (Pearce
et al. 1976, Mearns and Word 1982). In mid-
Chesapeake Bay, summer hypoxia in water below
10 meters depth severely limits distribution and
survival of benthic fauna (Holland et al. 1977,
Mountford et al. 1977).
There is a certain difficulty in assessing the ef-
fects of anthropogenic stress on benthic com-
munities. Natural variability in organism distribu-
tion and the dominant controlling mechanisms of
sediment type, salinity, and predation, complicate
identification of distinct cause and effect relation-
ships (O'Connor 1972; Boesch 1973,1977a; Virn-
stein 1977, 1979; Wolfe et al. 1982). Experiments
with simplified systems (i.e., microcosms or
mesocosms), where single factors may be manip-
ulated, can give insight into community effects.
An examination of the responses of benthic
organisms (on communities) along a gradient of
stress may also be useful.
EVIDENCE FROM RESEARCH
A series of experiments conducted at the
University of Rhode Island's Marine Ecosystems
Research Laboratory (MERL) used microcosms
to investigate impacts of nutrient and toxicant
stress on coupled benthic and pelagic com-
munities. For example, nutrient additions de-
signed to simulate sewage loading produced a
marked response in microcosm benthic com-
munities (Nixon et al. 1983). At intermediate
nutrient concentrations (comparable to the
Potomac River or Delaware estuaries), benthic
abundance and biomass were greatly elevated,
with a particular increase in bivalves. Secondary
151
-------
152 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
production was effectively shunted from zoo-
plankton to the benthos. At high nutrient levels,
comparable to the Hudson estuary, the alteration
of the ecosystem structure was large; normally
dominant bivalves were replaced by an almost ex-
clusively polychaete community.
Similarly, additions of low concentrations of
petroleum (No. 2 fuel oil) to the microcosms led
to a dramatic reduction in benthic biomass and
diversity (Olsen et al. 1982). As concentrations of
oil rose in the surface sediments, sensitive species
(such as the amphipod Ampelisca) were
eliminated. Recovery did not occur within one
year after oil additions ceased. Several interesting
side effects were observed: phytoplankton biomass
and productivity increased in oiled tanks, ap-
parently because of reduction in herbivorous ben-
thic species. Biomass of fish and wall-attached
molluscs also increased. Water column nutrients
declined, probably because of reduced rates of
recycling by benthic organisms.
Application of microcosm results to field con-
ditions is not always easy. However, comparison
of the behavior of MERL microcosms to Nar-
ragansett Bay conditions shows remarkable
similarity in annual cycles, in diversity, and in the
abundance of organisms (Olsen et al. 1982).
EVIDENCE FROM FIELD OBSERVATIONS
Field experiments can sometimes help cor-
roborate results observed in the laboratory. Blue
mussels transplanted to sites in Narragansett Bay
along a pollution gradient of (primarily) hydrocar-
bons and heavy metals showed significant declines
in condition and physiological performance as
stress increased (Widdows et al. 1981). A before-
and-after study of benthic assemblages close to an
area of oil pollution showed a reduction in species
richness and total biomass as the concentration
of petroleum in the sediments increased over time
(Addy et al. 1978). Similarly, benthic species
richness and biomass increased significantly as
controls over oil pollution were implemented
(Reish 1971, Leppakowski and Lindstrom 1978).
The distribution and abundance of benthic
macrofauna were studied by several GBP projects
as part of an investigation on toxic substances in
Chesapeake Bay. Benthic forms, particularly in-
fauna, can influence the movement of toxic
materials within the sediments, or the movement
of dissolved materials out of the sediments to
overlying waters. The Bay main stem and several
tributaries were studied (Nilson et al. 1981,
Reinharz 1981, Reinharz and O'Connell 1981,
Schaffner and Diaz 1982). These data give an ex-
cellent idea of spatial distribution of benthic
macrofauna within the Bay; however, except for
a limited number of sites, temporal information
is incomplete.
Major anthropogenic factors identifiable in
Chesapeake Bay and hypothesized previously as
affecting benthic organisms are:
1. Impacts of toxic materials in bed sediments
or in the overlying water column; effects
might be acute (elimination of susceptible
species) or sublethal (accumulation in body
tissues, etc.).
2. Impacts of nutrient enrichment, primarily
through the link to increased duration and
extent of low DO, and resulting loss of
habitat.
Toxic Materials
Direct comparison of several benthic com-
munity parameters to contamination of bed
sediments was made. Unfortunately, data on
organic chemicals were too few to allow mean-
ingful comparisons. However, it should be em-
phasized that organic chemicals can still be con-
sidered a major potential threat to benthic species.
One conclusion from a CBP-sponsored workshop
on toxicant and organism relationships was the
consensus that more information is needed on the
distribution and biological effects of synthetic
organic compounds in Bay sediments. Ongoing
microcosm studies on potential effects of con-
taminated dredge spoil from the Elizabeth River
show toxicity to be related to the suspended solid
phase and associated with the organic fraction.19
In addition, motile species were observed to ac-
tively leave contaminated sediment when clean
substrate was available (Alden et al. 1981). When
observing community structure, highly significant
differences were apparent in control, "dump," and
"adjacent" sites (Alden et al. 1981). Much of this
was due to loss of motile species. MERL micro-
cosm experiments with petroleum (No. 2 fuel oil)
-------
Benthic Organisms and Water and Sediment Quality 153
showed low concentrations to have a much more
drastic effect than metals on benthic infauna20
(Olsen et al. 1982).
Data on heavy metals in sediments were
available from many areas of the Bay (Chapter
1); these were used in several analyses that allowed
the CBP to look at the effects of heavy metals on
diversity, dominance, and abundance. These an-
alyses and results are detailed in Section 2 of Ap-
pendix D. Contamination of sediments with
metals (Cj, the Contamination Index) and the
potential toxicity of the sediments (Tj, the Tox-
icity Index21) were compared to benthic diversity
and community structure. The Shannon diversity
index (H) and the annelid: crustacean and
annelid-.mollusc ratio were the community para-
meters tested (discussed in Chapter 2).
In the Bay mainstem, temporal and spatial
variability in diversity appeared more related to
the estuarine salinity gradient and sediment type
than to Q. Although there was a slight difference
in annelid-.mollusc and annelid: crustacean ratios
between upper and lower Chesapeake Bay, no sig-
nificant relationships could be identified using the
Spearman rank correlation test. One difficulty is
that benthic organisms and toxic materials were
not sampled at exactly the same places. Innate
variability of organisms' distribution would tend
to obscure any relationships in such cases.
The Patapsco River has been subject to signifi-
cant contamination with toxicants and could be
expected to show more effect than does the main
Bay. Within the Patapsco, diversity of benthic
organisms generally declines along a gradient of
increasing contamination with metals and organic
chemicals (Reinharz 1981) (Figures 48 and 49,
Table 33). Only stations near the mouth retained
diversity comparable to the Rhode River reference
area. Species found in the most contaminated
areas are ephemeral opportunists, generally an-
nelids, inhabiting only the upper layers of sedi-
ment. Anthropods and molluscs become more im-
portant in less polluted regions. For example, the
tube-dwelling amphipod Leptochierius
plumulosus is an important species in the Rhode
River. However, in the Patapsco, it is found only
at the two least contaminated stations (Figure 50).
This is similar to the observation of Wolfe et al.
(1982) that the tube-dwelling amphipod
Ampelisca was absent from impacted areas of the
New York Bight.
Statistically significant relationships were
identified between contamination of sediments,
diversity, and community composition. In
general, the weighted Toxicity Index (described
in Appendix D) appeared a better measure of
potential impacts than did the Contamination In-
dex alone. In the Elizabeth River, another severely
contaminated tributary, trends were less distinct.
This is probably because there are smaller dif-
ferences in contamination from site to site within
the river (Virginia State Water Control Board
1982). However, Schaffner and Diaz (1982) iden-
tified a group of stations characterized by shallow
dwelling, young populations of relatively low
diversity; these stations were considered impacted
by high levels of toxicants in the bed sediments.
The effect of sediment contamination on ben-
thic organisms was further explored using bioassay
techniques. Using Elizabeth and Patapsco River
sediments, bioassays were performed to determine
the effect of sediments on the survival rate of a
burrowing amphipod (Rhepoxynius abronius)
(Swartz and DeBen, in prep.). Statistical analysis
indicated that survivorship strongly correlates
with the degree of contamination (Q), as well as
with the Cf for Ni and Zn, and approximates an
exponential response to dose (Figure 51). An
estimated LCso would be Q = 15. However, it
should be emphasized that this association does
not necessarily imply causation. Unmeasured
metals or organic materials co-associated with the
measured parameters may be contributing to, or
actually causing, the observed mortality.
This view is supported by the observation that
Spearman rank correlation of the annelid:mollusc
and annelid:crustacean ratios with the contamina-
tion factor (Cf) for both Zn and Ni in the
Patapsco showed no significant relationship. Thus,
the relation between Q and percent survival can-
not be used to identify specific anthropogenic
substances whose control can result in improved
survival. However, it does indicate the probable
presence of one or more toxic materials in the
tested sediments.
In general, these correlations support the find-
ing that a relationship exists between benthic com-
munity diversity, species composition, and con-
-------
154 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
Baltimore City
Patapsco
River
[ | Moderate diversity
High diversity
FIGURE 48. Diversity index (d) of benthic communmities in the Patapsco and Rhode Rivers (Reinharz 1981).
-------
Benthic Organisms and Water and Sediment Quality 155
Baltimore
Harbor
Baltimore County
Anne Arundel County
Metal Contamination (Cp of the Patapsco River (Data from Biggs, 1982)
Baltimore
Harbor
Distribution of PNA, Benzo (a) Pyrene in channel sediments from Baltimore Harbor and the Patapsco
River. (Data from Huggett, 1982)
FIGURE 49. Contamination of Patapsco River and Baltimore Harbor sediments with heavy metals and
organic chemicals (Bieri et al. 1982b).
-------
156 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
Baltimore City
P2
Not present
< 10 individuals nv2
10-50 individuals m
>50 individuals rrr2
Rhode River
FIGURE 50. Density of Leptochierus p/umulosus in the Patapsco and Rhode Rivers (Reinharz I98I).
-------
Benthic Organisms and Water and Sediment Quality 157
Bioassay of Amphipod against
Patapsco River Sediment
(As a Function of Nickel Enrichment]
100 r
75
50
CO
25
0
• 1 •
o
.500 100
Ni (Cf)
1.50 2.00
FIGURE 51. Percent survivorship of the amphipod Rhepoxynium abronius compared with the
contamination factor for nickel,
-------
158 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
TABLE 33.
DIVERSITY, REDUNDANCY, AND SPECIES NUMBER FOR PATAPSCO AND RHODE RIVER STATIONS.
GROUPS ARE ALL SIGNIFICANTLY DIFFERENT FROM ONE ANOTHER
Station
H
Po
PI
PS
PS
P2
P9
P8
PIO
PH
P6
P7
P13
P12
P14
Reference
R2
0.330
0.561
0.343
0.590
0.246
0.838
0.678
1.173
1.296
1.193
1,615
1.416
1.400
2.879
2.715
2.286
2.348
2.501
0.864
0,831
0.906
0.783
0.893
0,491
0,731
0.630
0,634
0,676
0.523
0.603
0.549
0.307
0.312
0.420
0,369
0.366
P= Patapsco River stations
R= Rhode River stations
H= diversity
r= redundancy
N= number ot species present
N
1
8
8
6
4
3
5
8
10
11
9
10
8
16
14
15
13
15
tamination of the sediments, at least in the more
impacted areas. Only the most general relation-
ships could be demonstrated for the main Bay, in-
dicating that other aspects of the environment
tend to mediate benthic abundance and distribu-
tion. Only when levels of toxic materials become
high — perhaps exceed some threshold — does the
sediment contamination begin to play a major role
in benthic community ecology.
Foraminifera in Baltimore Harbor and the
Elizabeth River
Historical perspective on changes in sediment
metal loads or changes in associate microflora or
fauna can be obtained by examination of sediment
cores. Foraminifera, which are microscopic
animals, have proven to be useful indicators of
environmental conditions. For example, several
studies have shown changes in foraminifera abun-
dance and shifts in species composition near
sewage outfalls (Bandy et al. 1965, Bates and
Spencer 1979). To better assess man's impact on
the Bay's ecology, the CBP funded studies of
foraminifera from Baltimore Harbor and from the
Elizabeth River (Ellison and Broome 1982, Ogilvie
and Ellison 1983).
In the preliminary study, three cores were
taken from the harbor and one from the river. Ten
representative core sections were sampled. Each
sample was weighed, disaggregated in water,
screened, and washed. Foraminifera were sepa-
-------
Benthic Organisms and Water and Sediment Quality 159
rated from the sediment, mounted, and identified
using standard procedures. The diversity and
abundance in the foraminifera were compared to
metal concentrations in the sediment.
On the basis of both investigations, the re-
searchers concluded that the change in benthic
communities paralleled salinity and increased
enrichment of the bed sediments with metals. Six
species were identified in the studies: one ag-
glutinated or arenacious species, Ammobaculites
crassis, and five calcareous species: Ammonion
beccarii, Buliminella sp., Cibicides lobatulus,
Elphidium davatum and Elphidium subarcticum.
In general, large populations and non-diverse
communities were found at the higher salinity
sites: the mouth of Baltimore Harbor and the
Elizabeth River. The somewhat fresher upstream
sites in Baltimore Harbor, which are highly
enriched with trace metals and synthetic organic
compounds, had only one species, A. crassus, in
limited numbers. In all four cases, there was an
increase in A. crassus in the surface samples
relative to the samples taken at depth. This
paralleled an increase in concentrations of Mn.
In the higher salinity cores, the populations of
Elphidium davatum decreased up-core, parallel-
ing the general increase in metal concentrations
(Ellison and Broome 1982).
Subsequently, six additional cores were
taken — two in the Elizabeth River and four in
Baltimore Harbor.
The diversity of foraminiferal communities de-
clines up the estuary of Baltimore Harbor.
Although this is typical of other estuaries and can
be related to lowered salinity, it is unclear why
the number of forams (especially A. crassus) also
declines upstream. Possibly, salinity is not the
primary, or only factor (Ogilvie and Ellison 1983).
For example, an unknown factor potentially influ-
encing these relationships is the low level of DO.
In the Elizabeth River, two cores with similar
trace metal distributions had different densities
and diversities of foraminifera. Salinities are
similar at these sites so these differences may also
be caused by another factor (Ogilvie and Ellison
1983).
In some deeper and less contaminated Balti-
more Harbor sediments, A. crassus is found in the
greatest number — comparable to other less con-
taminated estuaries. This suggests that, in the
more contaminated areas of the harbor, metals
have played a role in preventing this hardy species
from forming larger populations (Ogilvie and
Ellison 1983).
Toxic Materials in Tissues of Shellfish
Contamination of sediments or overlying
water with toxic materials may result in an ac-
cumulation of these materials in the tissues of ben-
thic organisms (O'Connor and Rachlin 1982).
Tissue levels are not simply related to the bulk con-
centration of toxicants in sediments, particularly
in the case of trace metals, but rather to their
bioavailability. Toxic materials may be bound in
forms that are normally unavailable biologically
or chemically, but which may be liberated by
rigorous laboratory analyses (Bricker 1975). Levels
of toxicants in animal tissues can, however, be
considered an indicator of the presence of pro-
cesses which render these contaminants available
to organisms.
Marine organisms employ a variety of
mechanisms for sequestering and detoxifying
metals, including the production of metallopro-
teins (O'Connor and Rachlin 1982). For that
reason, apparent body burdens of some con-
taminants may not result in measurable physio-
logical impacts, at least to some threshold (e.g.,
Frazier 1976). However, mussels transplanted
along a gradient of pollution show an accumula-
tion of Ni in body tissues, corresponding to the
concentration in the overlying water column;
physiological stress and other indicators showed
a similar gradient (Widdows et al. 1981).
Accumulation from contaminated sediments
varies with the species of organism, as well as with
the nature of the sediment; bioavailability was
generally related to EDTA extraction values for
the metals rather than to bulk concentration (Ray
et al. 1981). Ayling (1974) found correspondence
between oyster (Crassostrea gigas) tissue levels and
sediment metal concentrations for Zn and Cd; Cu
and Cr appeared more related to the size of the
animal. Similarly, Frazier (1976) found a relation-
ship between sediment metal levels and oyster
tissue concentrations; the relationship, however,
was not linear. Oysters in areas with high en-
vironmental metal concentration had significantly
thinner shells (^16 percent).
-------
160 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
The processes governing availability of sedi-
ment and water column toxicants to benthic
organisms are not well understood. Evidence ex-
ists suggesting that tissue concentrations reflect
these processes (environmental concentrations also
reflect them to a varying extent). However, con-
siderable work is needed before these processes are
identified, and before ecological effects of tissue
contamination are understood (O'Connor and
Rachlin 1982). Biomagnification of toxic materials
through the food chain has been documented in
numerous instances and is one potential serious
impact of the accumulation of toxicants in tissues
of major forage organisms (Wolfe et al. 1982).
Trends of metals and pesticides in Chesapeake
Bay shellfish were discussed in Chapter 1. Because
the majority of these data concern oysters, the
relationship of tissue contamination to sediment
concentration will be discussed later in the sub-
section on oysters and water and sediment quality.
Nutrient Enrichment, Low Dissolved Oxygen
Bascom (1982) and Mearns and Word (1982)
relate changes in species composition of benthic
communities subject to high organic loads from
municipal wastewater discharges. An Infaunal In-
dex was developed that used feeding characteris-
tics and the number of individuals in each trophic
group to identify degraded areas. In general, such
areas were characterized by increased biomass,
reduced species richness, and shifts from domi-
nance by suspension feeders to surface and sub-
surface deposit feeders, primarily polychaetes.
This index was calculated for a number of mud
(<25 percent sand) stations from the Bay
mainstem (Reinharz and O'Connell 1981, Nilson
et al. 1981) and examined for possible spatial dif-
ferences relating to nutrient enrichment patterns
in Chesapeake Bay. Although there was no signifi-
cant spatial trend, in general, polychaetes
dominated to a greater extent up-estuary. Suspen-
sion feeders such as Ampelisca were more abun-
dant in the lower Bay. However, it is probable
that salinity and physical variability of the en-
vironment are most important in mediating this
organism distribution. The Infaunal Index would
be useful, however, in examining data sets from
a before-and-after situation, to identify effects of
nutrient or wastewater controls, etc. Similarily,
it could be employed in localized areas where
spatial variability of the environment is minimal.
A major factor affecting benthic populations
is occurrence of low DO concentrations in the
overlying water column. Instances of low DO
values in the New York Bight area have been
associated with faunal changes, including exten-
sive loss of oyster beds (Carriker et al. 1982, Franz
1982). These hypoxic events have been caused by
increased carbon loading from sewage and runoff,
and from decay of phytoplankton blooms stimu-
lated by excess nutrient enrichment (Mearns and
Word 1982). It was suggested by Mearns and
Word that a large-scale reduction in nitrogen in-
put, especially in the summer, might alleviate
some of these problems.
Episodes of low DO have been described for
the Chesapeake Bay area since 1917; in September
1912, bottom water in the lower estuarine por-
tion of the Potomac River was less than 35 per-
cent saturated with oxygen (<2.0 ml L"1) (Sale
and Skinner 1917). At the same period of time,
bottom water between Annapolis to off Hamp-
ton Roads was over 60 percent saturated. Strong
evidence exists indicating that the areal extent and
duration of such episodes of low DO has increased
over time in Chesapeake Bay, particularly in the
past 20 years (Chapter 1). At the present time,
for example, almost 19 percent of the bottom area
of Bay segments CB-2 through 5, are impacted
by DO values of less than 0.5 ml L'1 (Table 34).
Furthermore, these changes appear related to in-
creases in nutrient loadings into the upper Bay
(Chapter 1).
Numerous Chesapeake Bay investigators have
linked changes in benthic fauna to episodes of low
DO. Near-total faunal depletion occurred at mid-
Bay sites > 9 m deep caused by episodes of hypoxia
(Holland et al. 1977); this single factor was the
major influence limiting benthic biomass below
8 m depth (Holland et al. 1979). Low DO general-
ly restricts oyster beds to depths less than 10 m
(Haven et al. 1981); however, where circulation
is good, oysters can exist at much greater depths
(Merrill and Boss 1966).
In areas subject to low DO, benthic commu-
nities may be completely eliminated, or replaced
by ephemeral, opportunistic assemblages recruited
after cessation of hypoxic conditions (Holland et
al. 1977). Most benthic species are stressed when
-------
Benthic Organisms and Water and Sediment Quality 161
oxygen concentrations fall below 1.5 to 2.0 ml L"1
for extended periods and are killed by exposures
to 0.5 ml L"1 or less (Table 34). As the area im-
pacted by these DO levels has increased, summer
benthic communities become restricted to the
shallower Bay margins. Reduction in available
forage could have impacts on bottom-feeding
predators, particularly sciaenid fishes or crabs.
Predation pressure on benthic communities is very
intense during the summer months (Homer and
Boynton 1978, Holland et al. 1979, Virnstein
1979); food limitation could affect abundance,
growth, and condition of predators.
Increasing instances of oyster mortality
(measured as percent empty shells or "boxes") have
been reported for upper Bay sites in recent years.22
One hypothesis is that intrusions of low oxygen
water onto shelf areas occur with greater frequen-
cy now because the area impacted by hypoxia has
increased. Because of the low gradient of this
shelf, slight decreases in depth of the oxycline can
greatly increase the area under stress. For exam-
ple, if the 0.5 ml L"1 DO isopleth occurs at 12 m,
26 percent of CB-4 bottom is impacted. If depth
of the isopleth decreases to 10 m, the area im-
pacted more than doubles, to 58 percent (Table
34). Internal waves at the oxycline may cause
variations of 1 m or so in depth within minutes
(Flemer and Biggs 1971). Additionally, wind
events can shift Bay surface waters, allowing deep
low oxygen water to intrude onto the shelf. "Crab
wars" or "jubilees" may occur when northwest
winds persist for hours or days; crabs and other
mobile species congregate in the shallows or even
move onto the beach, to avoid anoxic conditions
(Carpenter and Cargo 1957).
Recent interviews with watermen support this
hypothesis and give further insight into possible
impacts of DO and other water quality para-
meters on crab and oyster harvests. Some of the
major changes in crab and oyster harvest with
depth were summarized by Mr. Pete Sweitzer of
Tilghman Island, Maryland. Prior to the 1960's,
blue crabs were potted in deep water, often at
depths greater than 15.3 m, from about April 15
to mid-May, and from September 15 into early
fall. This fishery captured the male crabs as they
emerged from winter hibernation in the deep
channel. Now, there is little potting either in the
early spring or late fall, because too few crabs are
taken to warrant the effort. No crabs are presently
taken in oyster dredges in deep water of the mid-
Bay; winter males are now observed in relatively
shallow, sandy areas at the channel shelf "break".
Crabs potted in the summer are taken at a max-
imum of 3.7 m. The condition of crabs caught in
August seems to be weaker than in previous years,
with many crabs dving before they are landed.
j .- o J
Watermen report that changes in oyster catches
with depth have not been as dramatic as with
crabs, but that there is a tendency now to take
fewer oysters in deeper water (>9.2 m) than in
the mid-1960's.
The watermen also cite changes in the foul-
ing communities on crab pots and in water clar-
ity. In the late 1940's, little fouling occurred over
TABLE 34.
AREA OF CHESAPEAKE BAY BOTTOM AFFECTED BY LOW DO WATERS IN SUMMER;
% = PERCENT OF BAY SEGMENTS CB 3, 4, AND 5 IMPACTED
DO Level
ml L-1
0,5
1.0
2,0
3.0
4.0
m2x1
62
228
824
1191
1545
July
06
.3
,0
.0
.0
,0
1950
%
2,
7,
27,
39,
50,
i
1
,5
2
,3
,9
m2x1
344
535
629
889
1455
July
06
.0
.0
.0
.0
.0
1969
%
11
17
20
29
48
>
.3
,6
,7
,3
,0
July
m2x106
603
789
1196
1417
2022
1980
%
19
26
39
46
66
1
,9
.0
,4
,7
,7
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162 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
a three to five day period. Beginning in the late
1950's, a green growth covered the pots, replaced
by a grey mud in the late 1960's. By the late 1970's,
this material became dominated by a brown
"grass-like growth." Visibility seems to be less now
than in earlier years. The water, they say, grows
more cloudy earlier in the spring; this condition
lasts longer into the fall.
SUMMARY
Nutrient enrichment affects benthos through
the impact of increasing low summer DO in
deeper water. Complete loss of benthic habitat
in some areas or replacement with ephemeral
assemblages, as well as possible mortalities of com-
mercially important species such as clams, crabs,
and oysters are effects that have been observed
in the field. Though the relationship between
hypoxic events and increased mortalities of
oysters, etc. is at this point speculative, it is worth
further investigation.
Effects of toxic substances are difficult to
separate from natural variability in the field, at
least in those areas where contamination is
minimal or moderate. In heavily impacted areas,
however, benthic community structure is
changed: sensitive species are eliminated and op-
portunistic, resistant forms are relatively en-
hanced; generally, a loss of species diversity oc-
curs. The accumulation of toxicants in body tissues
of benthic species occurs. These may have direct
physiological impacts on the organisms or may be
transmitted and biomagnified in the food chain.
-------
SECTION 5
OYSTERS AND WATER AND SEDIMENT QUALITY
INTRODUCTION
Oysters are essentially immobile and, for that
reason, are considered excellent indicators of en-
vironmental conditions. Because of their commer-
cial importance, fairly good data exist (both
spatially and historically) on distribution, general
abundance, harvest, spat set, and condition. Their
ecology and physiology are also well-known.
However, fundamental questions still perplex
scientists and managers. For example, what is the
'role of the natural cycles of environmental varia-
bles versus the anthropogenic factors in the
distribution and abundance of oysters in Chesa-
peake Bay? Are the spatial and temporal scales
of these controlling factors reasonably constant
over time? What are the effects of harvest and
management (i.e., seed or clutch plantings)? For
example, Ulanu ' z et al. (1980) showed that var-
iations in spat density and seed plantings explain
56 percent of the variability in the annual harvest.
Though such studies increase the understand-
ing of the environmental regulation of oysters,
they fail to explain the long-term decline in oyster
harvest since the late 1800's (Figure 52). Conven-
tional wisdom indicates that sedimentation, poor
water and sediment quality, and over-harvesting
(economically related) are probably key factors;
however, their importance over the past century
is still a matter of conjecture. The constancy in
oyster harvest since about 1960 is probably related
to shell planting, especially in Maryland.
The purpose of this section is to assess the
nature of available environmental information
concerning the oyster in the Bay and provide a
synthesis of this information to gain a better
understanding of the factors operating as poten-
tial environmental controls.
FACTORS POTENTIALLY
IMPACTING OYSTERS
Numerous natural and anthropogenic factors
can impact oyster distribution, harvest, and
recruitment. Among these are:
• Impacts of nutrient enrichment and resulting
oxygen depletion. Excessive nutrients could
result in shifts of phytoplankton species to
forms less usable by oysters (e.g., Ryther
1954), or in the fouling of shells with epibi-
ota; the latter would interfere with the set-
tling of young oysters. Episodes of low DO
could kill oysters outright, as well as restrict
productive beds to shallow areas.
• Impacts of sedimentation and increased
suspended solids loads. Sediment deposited
on shells prevents the setting of spat and, if
excessive, can "smother" beds or interfere
with feeding.
• Impacts of toxic materials in bed sediment
or water column. This could result in the re-
duction of spat set or oyster survival, or in
the accumulation of toxicants in oyster
tissues.
• Impacts of disease, parasites, or predators.
The effects of disease may be exacerbated by
other stresses (Farley et al. 1972).
• Impacts of natural variables, particularly
freshwater discharge and salinity, or man-
agement practices (shell or seed planting) on
distribution and abundance. Oyster larvae
require salinities above 10 to 12 ppt to suc-
cessfully develop and set (Shea et al. 1980);
for that reason, recruitment at lower salin-
ity bars is often sporadic.
It is probable that all these factors act at one
time or another to affect oysters. In the follow-
163
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164 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
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Oysters and Water and Sediment Quality 165
ing section, each will be discussed in greater
detail.
Nutrient Enrichment and Oxygen Depletion
Nutrient enrichment may cause shifts in
phytoplankton species to forms less suitable for
oyster food. Ryther (1954) reported a case where
runoff from duck farms produced excessive nu-
trients in Moriches Bay, Long Island, New York;
a predominantly diatom flora was replaced by a
small non-motile green algae. These were not
usable by oysters for food, so the local oyster
fishery declined precipitously. It is well-
documented that all algae are not equally suitable
for oyster food (Walne 1963, 1970). Eutrophica-
tion often results in blooms of types considered less
desirable: bluegreens, non-motile greens, and
dinoflagellates (Ryther and Officer 1981). Blue-
greens are not generally a problem in saline areas
where oysters are found. However, in some coastal
regions, blooms of certain dinoflagellate species
are the cause of episodes of paralytic shellfish
poisoning (PSP); the dinoflagellate blooms them-
selves have been related to the nutrient enrich-
ment of coastal waters, at least in some areas
(Prakash 1975).
In Chesapeake Bay, there is little evidence that
significant changes in the phytoplankton com-
munity structure have taken place in oyster-
growing areas (Chapter 2). Although blooms of
dinoflagellates occur frequently, these are not
species generally known to be toxic (Mackiernan
1968). However, continued monitoring of phyto-
plankton communities and comparison to histor-
ical data are recommended.
As with benthic organisms in general, the
strongest link to nutrient enrichment is probably
through DO. Oyster larval growth ceases at 1.7
ml L'1 DO, and adult oysters close up when levels
reach 0.7 ml L"1 or less. During this time, they
undergo anaerobic metabolism, which is energet-
ically costly. In warm summer months, oysters can
survive about five days in this manner; if
anaerobic conditions persist much longer, they
will die (Kaumeyer and Setzler-Hamilton 1982).
In many areas of the Bay, oysters are restricted
to depths less than 10 m by low oxygen (Haven
et al. 1980). Increased mortalities of oysters
observed in recent years may be due to intrusion
of hypoxic water into shelf areas, or the combined
stress of low DO and disease such as MSX.23
Landings of all commercial finfish and shell-
fish from 1980 were compared to nutrient con-
centrations for the most recent year of record. A
significant inverse relationship (p<0.01) was
found between shellfish from 1980 and mean an-
nual TN (i.e., high nitrogen values were cor-
related with low harvest). This relationship was
apparently due primarily to oysters: a significant
inverse relationship (p<0.05) existed between
1980 oyster harvest and TN. The Chester River
was omitted in this comparison because of its re-
cent unexplained oyster mortality. Also, this rela-
tionship was not statistically significant in other
years.) Such a relationship could be due to low
DO impacts, food web shifts, or both.
Sedimentation
The removal of substrate (by harvest) has
lowered the profile of many oyster bars in
Chesapeake Bay; that is, they are closer to the
sediment surface (Marshall 1954). This makes
them more vulnerable to sedimentation. As
discussed in Chapter 1, sediment transport and
deposition into Chesapeake Bay has increased
dramatically in the last 150 years. The existence
of extensive buried oyster beds where substrates
are now unsuitable is an indication of sedimen-
tation effects (Alford 1968). Sediment also affects
recruitment; a few millimeters of sediment on a
shell may prevent the setting of spat (Galtstoff
1964). For that reason, spat set is usually better
on freshly planted shell (Davis et al 1981). In ad-
dition, Ulanowicz et al. (1980) have shown that
spat set success negatively correlates with the
previous year's harvest; this may result from
removal of substrate (or possibly brood stock).
Toxic Materials
The comparison of the EPA water quality
criteria to measured and estimated concentrations
of toxicants in the water column reveals a number
of instances where these criteria are exceeded
(Chapter 1, and Appendices B and D). Oyster lar-
vae are sensitive to Cu and Hg, while adults are
sensitive to Cd (Kaumeyer and Setzler Hamilton
1982). Thus, although direct cause-and-effect can-
-------
166 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
not be demonstrated, the occurrence of compar-
atively high levels of toxicants in the water col-
umn near oyster beds would be cause for concern.
The accumulation of trace metals by oysters
was described by Ayling (1974). He found Cr and
Cu to be adsorbed to a weight proportional to,
and limited by, the size of the oyster and ap-
parently independent of sediment concentration.
Cadmium and Zn were accumulated in propor-
tion to their concentration in the sediment. Lead
was concentrated randomly at sites containing
high sediment Pb concentrations.
Mean levels of Cd, Cu, and Zn in oyster tissues
from Chesapeake Bay were compared to the sedi-
ment contamination factors for each metal, using
Spearman rank correlation coefficient. Levels of
Zn in shellfish tissue correlated at p<0.01 with
Zn in bed sediment, in agreement with Ayling's
findings. Copper levels in oyster tissue also
positively correlated with sediment concentrations
(p<0.01). Tissue concentrations could not be
related to the size of the organisms because tissue
analysis had been performed on composite samples
of various sized oysters. No statistical relationship
could be demonstrated between Cd in oysters and
that in sediments, although levels of both tend to
be low in Mobjack Bay, the Potomac River, and
the upper main Bay.
Disease
The impacts of disease and predators can be
significant. In the early 1960's, an epidemic of
MSX, the protozoan parasite Minchinia (Haplo-
sporidium) nelsoni, decimated the Virginia oyster
population. From 50 to 90 percent of susceptible
individuals succumbed, and harvest fell by two
thirds (Fincham 1983). The disease MSX is
restricted to waters generally greater than 15 ppt
salinity, and the mid-1960's drought years has-
tened its spread. Lower salinities since 1968 and
during the 1970's, as well as some acquisition of
genetic resistance by the oysters, had reduced im-
pacts in the last decade. However, there is strong
evidence that drought conditions in the 1980's has
again allowed MSX to spread. This time, areas
of Maryland as far north as the Choptank River
and Eastern Bay have been affected, and the
parasite has moved into regions with previously
unexposed populations (Fincham 1983). Present
increases in oyster mortality in these areas are
probably related to the disease, although losses in
deeper regions may also be caused by DO stress.
If salinities decline in the upper Bay, oysters may
recover from the parasitic infection.
Other diseases and predators are more
prevalent at higher salinities; these include "Der-
mo" disease (Perkinsus marinus), the oyster drills
Urosalpinx and Eupletira, the mud blister worm
Polydora, the boring sponge Clionia, and the spat
predator Stylochm, a flatworm. Many of these
weaken the oyster and may render it more
vulnerable to other stresses.
Natural Variables
The success of biological resources is also af-
fected by natural variables. Ulanowicz et al.
(1980) have shown that success in spat set cor-
relates positively with high salinity and negatively
with the previous year's harvest. Krantz and
Carpenter (1981) report that the impact of
Tropical Storm Agnes (1972) on the Potomac
River oyster populations was largely responsible
for a decrease in production and a shift in harvest
from upstream of Cobb Island to the lower
Potomac below Ragged Point-Piney Point. In ad-
dition, there has been no significant oyster recruit-
ment in the upstream estuarine portion of the
Potomac River since 1965; this may be due in part
to increased freshwater flows during the last
decade. However, failure of spat set in the upper
Potomac in response to increased salinities dur-
ing 1980 to 1981 (low-flow years) points to a
decline in water quality as an additional stress
(Figure 31). Biggs (1981) notes that buried oyster
reefs occur in Chesapeake's upper main stem
above the current distribution of oysters. These
(and similar buried reefs in the Potomac) indicate
that oysters once inhabited the reaches of Ches-
apeake tributaries no longer suitable for them.
Deforestation of the watershed has created a more
"flashy" pattern of runoff where peak flows may
be 30 percent greater today, shifting the riverine-
estuarine transition zone downstream, and com-
pressing oyster habitat. Finally, Davis et al. (1981)
have reported very high oyster spat sets for the
years 1980 to 1981 in the Maryland portion of
-------
Chesapeake Bay. These years were characterized
by above average salinities during the oyster
spawning season (May through July). Spat set was
larger, on the average, during 1980 in areas of the
middle and upper Bay than had been observed
in many years.
However, this greater-than-aver age spat set
did not occur in all reaches of the Bay, suggesting
that other factors are operating there that affect
oyster recruitment. For example, the Chester
River exhibited spat set between about 10 to 25
spat per bushel during the 1940's and 1950's, and
since 1971, has averaged zero spat set. This may
result, in part, from a loss of natural spawning
stock because the present production depends on
seed planting. If spat set conditions are assumed
to be adequate now, then some recruitment from
the nearby Bay would be expected. Thus, a water
and sediment quality factor could be limiting spat
set in the Chester River and similar areas.
Oysters and Water and Sediment Quality 167
SUMMARY
It is apparent that a number of factors — both
natural and anthropogenic — affect oyster distri-
bution and abundance. Physical variables, such
as salinity, disease, predators, and the socio-
economic aspects of harvest and management tend
to obscure most relationships. However, sufficient
evidence exists to give cause for concern. Available
habitat and harvest are related negatively to in-
creased nutrients and areas of low oxygen water,
and tissue contamination can be linked to
materials in the bed sediments. The loss of
harvestable areas and the failure of natural
recruitment in upstream areas potentially most
impacted by man are strong arguments that an-
thropogenic trends in water or sediment quality
affect oysters in Chesapeake Bay. The close mon-
itoring of future trends, particularly in possible
high impact areas, is recommended.
-------
SECTION 6
FINFISH AND WATER QUALITY
INTRODUCTION
Finfish may respond to a number of natural
or anthropogenic variables. Although mobile and
thus able to avoid certain stressful conditions, fish
may nevertheless be impacted by factors operating
at the individual, population, or community level.
A number of natural environmental factors have
been shown to affect spawning and juvenile sur-
vival (Ulanowicz et al. 1981); changes in recruit-
ment may then be reflected in catch statistics
(Richkus and Summers 1981). Similarly, toxic
pollution may result in outright mortality of sen-
sitive individuals or species, in an increase in
incidence of disease or pathologies, in an ac-
cumulation of toxicants in fish tissues, or in more
subtle effects on spawning success (Sindermann
et al. 1982). It is, however, often difficult to
separate out the more moderate impacts from res-
ponses to natural climatic cycles. This section ad-
dresses these considerations to make the most
reasonable assessment of effects of water quality
on finfish.
Five major hypotheses have been advanced to
explain observed trends in finfish (Chapter 2):
1. Increased toxic material contamination in
areas where anadromous fishes spawn and
larval development occur is exceeding the
tolerances of these vulnerable early life
stages. In addition, accumulation of toxic
chemicals in fish body tissues may be af-
fecting spawning success (e.g., viability of
eggs) or resistance to disease.
2. Nutrient enrichment of areas of
Chesapeake Bay is impacting spawning
success of anadromous fish, either by shift-
ing phytoplankton communities (altering
the type and the amount of zooplankton
upon which these fish larvae feed) or by
increasing areas impacted by low DO
(reducing available habitat for many
species). Marine and estuarine spawning
species that utilize low-salinity nursery
areas, or that inhabit bottom waters (e.g.,
sciaenids) could also be adversely impacted
by nutrient enrichment. Finally, the loss
of SAV, an important habitat and forage
area for juvenile fish and their prey, has
been linked to increases in nutrient loads
to the Bay.
Freshwater spawning fish are being re-
duced in number by sub-optimal climatic
conditions that affect the entire Bay water-
shed, and that are expressed as variations
in temperature, precipitation, and river
flow. This hypothesis also embodies the
concept that moderately increased fresh-
water flows may improve hatching and lar-
val success in some species by carrying
more nutrients into the nursery area (sup-
porting the phytoplankton and zoo-
plankton larval fish food chain), as well as
by physically extending the area of the
spawning and hatching grounds
(Herrgesell et al. 1981, Mihursky et al.
1981). Additionally, climatic conditions
(e.g., wind and flow) may enhance marine
spawners principally by increasing recruit-
ment into the estuary.
Some species (particularly anadromous
fish) are being reduced in number by over-
fishing. This hypothesis embodies the con-
cept that sport and commercial fishing are
harvesting so many fish of these species that
169
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170 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
remaining breeding stock is not sufficient
to sustain recruitment.
Modification of habitat, particularly in
areas of the watershed used by spawning
anadromous fish and in those used as
nursery areas, may be having significant
impacts on the ability of some tributaries
to support recruitment. Among these mod-
ifications are the construction of dams, the
draining and loss of wetlands, stream chan-
nelization, and the urbanization of
watersheds.
IMPACTS OF TOXIC MATERIALS
Studies of the impact of toxic pollutants, in-
cluding heavy metals, organic chemicals, and
petroleum on fishes of the New York Bight iden-
tified a number of responses: heavy metals resulted
in the increased mortalities of (particularly) early
life stages; the sublethal exposure of adults to toxic
pollutants drains energy reserves and may affect
their response to other environmental stresses
(Calabrese et al. 1982); and the abnormalities in
mackerel eggs were associated with elevated tox-
icant levels (Longwell and Hughes 1982). How-
ever, it was difficult to show many changes in
abundance directly attributable to pollution,
because of the simultaneous effects of natural en-
vironmental variation and over-fishing (Sinder-
mann et al. 1982).
Research sponsored by the Emergency Striped
Bass Research Study (USFWS, NMFS) is reveal-
ing some effects due, in part, to toxic pollutants.
Whipple et al. (1982) studied striped bass in the
San Francisco Bay area, correlating pollutants
(metals, and chlorinated and petroleum hydrocar-
bons) with parasite burdens, body and liver con-
dition, and with egg and gonad condition. It was
estimated that there was a 45 percent reduction
in the number of viable eggs for 1978 females
before spawning; pollutants most implicated were
Zn and monocyclic aromatic hydrocarbons
(MAH). Closer to home, work in progress by
Ludke et al. (1982) reveals that combinations of
contaminants (Table 35) at concentrations similar
to those found in spawning habitats of Chesapeake
Bay significantly decreased the survival of striped
bass larvae, particularly in freshwater. These con-
taminants include pesticides, other organic chem-
icals, and heavy metals. Preliminary results
indicate that larvae exposed to the highest con-
centrations in freshwater experienced 90 percent
mortality within 15 days, as compared to 10 per-
cent in controls. Sublethal effects included
changes in swimming, feeding, and predator
avoidance.
TABLE 35.
MIXTURE OF CONTAMINANTS CAUSING LETHAL AND SUBLETHAL EFFECTS
IN LARVAL STRIPED BASS (LUDKE ET AL. 1982)
Compound
Arochlor 1248
Arochlor 1254
Arochlor 1260
DDE
Toxaphene
Chlordane
Kepone
Perylene
Fluorene
Phenanthrene
Anthrene
Concentration L-t Compound
10 ng
10 ng
10 ng
3 ng
3 ng
5 ng
15 ng
40 ng
40 ng
40 ng
40 ng
Fluoranthrene
Pyrene
Benzoanthrene
Chrysene
Atrazine
Simazine
Arsenic
Selenium
Lead
Cadmium
Copper
Concentration L-1
40 ng
40 ng
40 ng
40 ng
1 ug
1 ug
1 ug
2 ug
1 ug
3ug
1 ug
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Finfish and Water Quality 171
Analyses performed by the GBP (discussed in
Chapters 1 and 3, and Appendices B and C) show
that measured and estimated levels of heavy
metals and chlorine often exceed the EPA water
quality criteria in areas where anadromous fish
spawn and develop. In particular, Cd, Cu, and
Ni criteria are exceeded. As the larvae of many
fish are extremely sensitive to these metals
(Kaumeyer and Setzler-Hamilton 1982), high am-
bient concentrations would be potentially serious.
Although the data do not allow an estimate of ac-
tual extent and duration of exposure, a prudent
approach would regard these findings with con-
cern. It appears as though the potential for signifi-
cant acute or sublethal impacts due to toxicants
may exist in many areas.
NUTRIENT ENRICHMENT AND
DISSOLVED OXYGEN
Impacts of nutrient enrichment might be
reflected in food web shifts of finfish, particularly
those of larval forms, or in direct effects due to
low DO.
The correlation of abundance and survival of
fresh water spawning species such as striped bass
with the density of zooplankton food organisms
(Setzler et al. 1980, Martin et al. 1982) indicates
the importance of plankton food webs to finfish.
Hypothetically, the shifts in the phytoplankton
community to less desirable forms might result in
lower zooplankton abundance (Officer and Ryther
1980). Eutrophication with associated algal and
water quality problems may be one reason for
striped bass failing to use previous spawning areas
near Washington, DC (Lippson et al. 1979). How-
ever, as (discussed in the section on oysters, there
is little evidence that major changes have occur-
red in phytoplankton communities in most other
Bay areas. This could be, admittedly, due to the
paucity of data.
However, in the Chowan estuary in North
Carolina, current work is building a case for a
nutrient enrichment-food web shift effect on
fish.24 Increased nutrient loading from nonpoint
sources has caused proliferation in blue-green
algae and in other small forms. A decline in the
size and abundance of herbivorous zooplankton
accompanied this trend. A reduction in the growth
rate of larval and juvenile blueback herring,
which are spawned in the area, has been observed.
Gut analysis has shown a shift toward benthic
feeding in these normally planktivorous fish.
These results are preliminary, but observed effects
are consistent with the food chain impact hypo-
thesis.25
One major direct impact on finfish, both
adults and juveniles, could be observed increases
in the extent and duration of hypoxic events.
Tolerances of fishes vary with the species, the stage
of life cycle, the level of stress from other factors,
the previous history of exposure (acclimation
time), the temperature of the water, and other
intrinsic and extrinsic factors (Anon. 1976).
However, a sufficient body of information has
been developed to set criteria levels objectively
and to suggest the general effects expected at
various concentrations of DO.
To quote from the Environmental Protection
Agency's Quality Criteria for Water (Anon. 1976):
Dissolved oxygen historically has been a ma-
jor constituent of interest in water quality in-
vestigations. It generally has been considered
as significant in the protection of aesthetic
qualities of water as well as for the mainte-
nance of fish and other aquatic life. Tradi-
tionally, the design of waste treatment
requirements was based on the removal of ox-
ygen demanding materials so as to maintain
the DO concentration in receiving waters at
prescribed levels. Dissolved oxygen concentra-
tions are an important gauge of existing water
quality and the ability of a water body to sup-
port a well-balanced aquatic fauna. A mini-
mum concentration of DO to maintain good
fish populations is 5.0 mg L"1 (3.6 ml L'1).
The reader is referred to a documented discus-
sion of the rationale for the selection of 5.0 mg
L-1 (3.6 ml L'1) in the EPA Quality Criteria for
Water (Anon. 1976, pp. 123 to 127). It is of in-
terest to note that the EPA DO criterion is based
principally on freshwater fish.
Davis (1975) established minimal DO re-
quirements for fish and other aquatic life in
Canada using an extensive review of available
literature. The oxygen criteria for fish are based
on oxygen response thresholds for freshwater,
marine, and salmonid fishes. The data were
treated in a fashion to normalize the different ex-
perimental conditions, fish tested, and factors such
as temperature.
-------
172 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
Three levels of protection were devised by
Davis (1975) to provide flexibility in
interpretation:
"Level A is one standard deviation above the
mean response level for the group
and represents an oxygen level that
assures a high degree of safety for
very important fish stocks in prime
areas.
Level B represents the oxygen level where
the average member of a species in
a fish community begins to exhibit
symptoms of oxygen stress. Some
degree of risk to a portion of fish
populations exist[s] at this level if
the oxygen minimum period is pro-
longed beyond a few hours.
Level C At this level a large portion of a
given fish population or fish com-
munity may be affected by low ox-
ygen. The values are one standard
deviation below the B level or class
average for the group. The deleter-
ious effect may be severe, especial-
ly if the oxygen minimum is pro-
longed beyond a few hours."
The pertinent criteria for water temperatures
of 0 to 25C adapted from Davis (1975) are given
in Table 36.
Thornton (1975) compared the DO tolerances
of some 24 mid-Atlantic estuarine and marine
fishes experimentally and from the literature and
concluded "that a conservative estimate for main-
taining diversity for marsh (estuarine) fish would
require minimum permissible DO levels of 2 to
3 ml L'1 (2.8 to 4.2 rag L'1) at 20 to 25C." He
also ranked 24 species in order of their sensitivity
to low oxygen levels. Kaumeyer and Setzler-
Hamilton (1982) summarized oxygen tolerances
where available for the species of interest in this
study, and Carpenter and Cargo (1957) reported
on blue crab oxygen tolerances.
Table 37 is a composite listing of oxygen
tolerances from the above-mentioned sources.
Doudoroff (1957) and Mackenthun (1969)
describe the following probable effects of DO defi-
ciency on fishes based on a review of the literature:
3.6 ml L"1 Probably the limiting or critical
level below which normally
varied fish populations do not
persist if subjected to such con-
ditions for long periods of time.
2.1 ml L'1 Rapidly fatal at fairly high
temperatures to susceptible fishes
and to resistant species under
otherwise unfavorable conditions
of water quality. Known to af-
fect physiology' and reproductive
processes in a variety of fishes.
1.4 ml L"1 Often critical to sensitive forms.
0.7 ml L"1 Typically, tolerated only by the
most resistant species, although
susceptible species may be able to
tolerate these levels if they have
sufficient time to acclimate to
low DO concentrations.
In July 1976, substantial mortalities of surf
TABLE 36.
SUGGESTED LEVELS OF PROTECTION FOR SELECTED GROUPS OF FINFISH
Group
Freshwater mixed
fish population
(no salmonids)
Marine, non-anadromous
Anadromous marine
species including
salmonids
Protection
Level
A
B
C
A
B
C
A
B
C
ml 02L-1 Range of % Saturation
3.85
2,80
1.75
6,13
4.73
3.15
6.30
4,55
2,80
(0-250Q
60-66
47-48
35-36
88-100
69-98
50-65
100
79-94
57-58
-------
Finfish and Water Quality 173
clams, ocean quahogs, and other benthic animals,
including fishes, were recorded in an 8,600 square
kilometer26 area of the New Jersey continental
shelf. At the height of the event, DO values were
measured at 0 to 2 ml L/1 within the area (Swan-
son and Sindermann 1979). An intensive investiga-
tion by government and academic scientists
revealed that, although there were a few recorded
finfish mortalities, adult finfish, in most cases,
were able to avoid the low DO area barring some
form of entrapment. Although adult fishes either
avoided the large area of anoxic water or perish-
ed, the area is a spawning ground for a host of
fishes. One may conclude that spawning was dis-
rupted off New Jersey during the summer of 1976
(Azarovitz et al. 1979). It should also be obvious
that commercially or recreationally important
species are typically no longer available to
fishermen in areas experiencing such stresses.
It is apparent from Table 37 and from the cri-
teria established by Davis (1975) that most of the
species listed demonstrate behavioral stress, and
probably some form of metabolic stress, when ox-
ygen concentrations fall below 3 ml L"1; the ma-
jority of the species will die if subjected to oxygen
concentrations of less than 0.5 ml L"1 for a day
or more.
In another portion of this report (Chapter 1),
the history of anoxic water intrusion in Chesa-
peake Bay is described, and evidence of the in-
crease in the anoxic condition during the summer
(July) since 1950 in the area between Gibson
Island above the Bay Bridge to a line approximate-
ly between Tangier Island and the mouth of the
Great Wicomico River is provided (Figure 53).
These data are summarized below for July 1950
and July 1980 in Table 38.
By comparing the tolerances of representative
species (Table 37 and Doudoroff 1957, Macken-
thun 1969) with the amount of potential habitat
excluded to them by DO levels below their toler-
ances (Table 38) one may offer the following con-
clusions about current (1980) conditions in
Chesapeake Bay:
1. Nearly 100 percent of the 23,000 x 10s
cubic meters of mid-Bay water during Ju-
TABLE 37.
SUMMARY OF OXYGEN TOLERANCE DATA INVOLVING PRINCIPAL CHESAPEAKE BAY SPECIES
Species
Alosa sapidissma
Alosa aestivalis
Pomatomus saltatrix
Crassostrea virginica
Menidia menidia
Icfalurus punctalus
Icfalurus nebulosus
Morone saxatilus
American shad
Blueback herring
Bluefish
American oyster
Atlantic silverside
Channel catfish
Brown bullhead
Striped bass
LD50 (ml L-i)
Death occurs
2.0-3.6
1.4-2.1
0.9
0.7
0.6
0.5-0.6
EC50(ml L-1)
Stress behavior
1, 7-2,1
—
2.3
1.7
11
—
4.8-4,9
Morone americana
Callinectes sapidus
Brevoortia tyrannus
Leiostomus xanthurus
Fundulus heteroclitus
Larvae, Juveniles
Adults
White perch
Blue crab
American menhaden
Spot
Mummichog
0.5
0.4-0,7
0.5
0.4
0.4
0.04
2.9
3.0*
2,0
1,8
1.0
0.9-2.7
0.9-3.2*'
Note '—adults avoid areas with less than 44 % oxygen saturation.
"—reduced hatching of eggs below this level.
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174 Chapter 3; Relationship between Water and Sediment Quality, and Living Resource Variables
JQ
DDD
o
OO
o
o
o
LO
o
2
o
-------
Finfish and Water Quality 175
TABLE 38.
VOLUME OF WATER AFFECTED BY REDUCED OXYGEN CONCENTRATIONS
EXPRESSED AS MILLIONS OF CUBIC METERS AND AS THE PERCENT OF THE ESTIMATED TOTAL VOLUME
OF AQUATIC HABITAT AVAILABLE
(23000 x 106 CUBIC METERS). ERROR OF ESTIMATE IS APPROXIMATELY ± 5 PERCENT
July 1950
July 1980
Oxygen
Concen.
mIL-i
0.5
1.0
2.0
3.0
4.0
m3x106
294
1366
6445
10702
15396
Percent
Affected
1
6
28
45
67
m3x,0*
4294
6444
10680
13488
23000
Percent
Affected
19
28
46
59
100
Oxygen Isopleth
depth, below surface
meters
13
12
10
7
4
ly is estimated to be below or barely above
the EPA criterion (3.6 ml L"1) for main-
taining healthy fish populations. This pro-
portion of habitat loss has increased from
67 to 100 percent since 1950 (Table 38).
2. Nearly 60 percent of the total available
habitat is estimated to have DO concen-
trations below the level (3.0 ml L"1)
thought to produce respiratory, metabolic,
and behavioral stresses on most fish species.
This proportion of habitat loss has increas-
ed from 45 to 59 percent since 1950.
3. Approximately 20 percent of the total
available habitat is estimated to have DO
concentrations below the level (0.5 ml L"1)
necessary to sustain life in all but a few
hardy fish species. This proportion of lethal
anoxic habitat has increased from 1 to 19
percent since 1950.
In summary, during those years in the sum-
mer to early fall, when natural hydrographic con-
ditions and anthropogenic inputs facilitate anox-
ic conditions, the majority of fish species would
be excluded by potential lethal conditions from
about 20 percent of the deeper waters of the mid-
Bay area; very likely, they would be excluded by
behavioral avoidance from about 60 percent of
the mid-Bay waters, leaving only shallow (2 to 3
meters) surface waters available for feeding and
spawning.
The fishes and shellfish most likely to be af-
fected by the mid-Bay anoxic conditions are those
that are primarily benthic feeders (e.g., spot,
croaker, and channel catfish), Bay spawners that
spawn in mid-late summer (e.g., Bay anchovy,
Atlantic silversides, and weakfish), and benthic
dwellers (e.g., Blue crab, soft clam, and the
oyster) in waters below approximately 7.0 meters
in depth. Of the species mentioned as examples,
all have shown declines in the last decade except
for blue crabs and weakfish. Benthic species were
discussed more fully in Section 5.
Table 39 [adapted from Lippson et al. (1979)
and Shea et al. (1980)] shows that a variety of
species are thought to frequent the deep trough
area of Chesapeake Bay. Those species that would
typically enter the area to feed or spawn during
the period from May through October would most
likely be excluded from the area by hypoxic con-
ditions. Those species potentially affected would
include striped bass (Flemer et al., draft manu-
script), summer flounder, spot, croaker, silver
perch, black and red drum, Bay anchovy, blue
crabs, oyster, and menhaden, as well as many
other organisms not listed.
The exclusion of a variety of species from the
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176 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
TABLE 39.
PERIOD OF UTILIZATION OF DEEP WATER BY ECOLOGICALLY AND
COMMERCIALLY IMPORTANT SPECIES OF FINFISH AND BLUE CRABS
Adult winter flounder
Adult summer flounder
Adult and juvenile striped bass
Adult and juvenile white perch
Gizzard shad
Spot
juvenile
Atlantic croaker
juvenile
Silver perch
Black and red drum
Bay anchovy, adult and juvenile
Atlantic silversides
Male blue crabs (upper, mid-Bay)
Female blue crabs (lower Bay)
Menhaden, post larvae
pre-juvenile and juveniles
November—May
April—November
October—March
November—March
November—April
April—October
March—May
March—November
September—April
June—October
June—October
November—April
only during coldest weather
October—April
October—April
January—March
March—October
deep trough from May through October has been
substantiated by a trawl survey conducted by the
Maryland Department of Natural Resources (Gu-
cinski and Shaughnessy 1983). They collected 19
species from the area in November 1982 when ox-
ygen values for most of the area were above 7 ppm
(5.0 ml L"1). In contrast, from May through Oc-
tober in 1982, only five or fewer species were col-
lected from the area; these typically were from
shallow, more highly oxygenated stations. Dur-
ing this period, there was a substantial volume of
completely anoxic water in deeper channels;
values in the majority of the area were less than
5 ppm (3.6 ml L"1) (Gucinski and Shaughnessy
1983). During the August and October 1982
sampling efforts, no fish or crabs were collected
at the six deepest stations when DO levels were
determined to be less than 1 ppm at these depths.
Although it is not possible to quantify precisely
the effects of habitat exclusion on individual
fisheries, it is fair to say that for the majority of
species treated in this analysis, the reduction of
available habitat for spawning and feeding must
have a depressing effect on local fisheries.
IMPACT OF NATURAL VARIABLES
There is no doubt that natural variables — in
particular those related to climate —have major
impacts on finfish. Precipitation, runoff, wind
speed and direction, and temperature can directly
and indirectly affect the success of various species
in different ways and at different times of their
life cycles. For example. Ulanowicz et al. (1981)
and Heinle et al. (1980) report that the success
of alewife and shad is related to high winter tem-
peratures; the success of blue crab, menhaden, soft
clam, striped bass, and white perch is related to
colder winter temperatures. Croaker and spot
have been shown by Norcross and Austin (1981)
and Wojcik and Austin (1982) to suffer severe
winter kills when winter temperatures are un-
usually low. Menhaden may be a special case;
although its success is related to colder inland
winter temperatures, Sutcliffe et al. (1977) have
shown that its success is also related to high winter
sea-surface temperatures.
The effects of increased precipitation on
fisheries manifest themselves principally in the
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Finfish and Water Quality 177
reduction of salinity in the estuary, in the increases
in dissolved nutrients and suspended solids, and
in the increases in the physical effects of flow
through the estuary. The latter effects, when ex-
treme, can reduce the spawning habitat of fresh-
water spawning species by the disruption of
spawning sites. At the same time, flow can en-
hance transport of marine-spawned species into
the estuary by stratifying the vertical water
column and facilitating the upstream flow of the
bottom "salt layer" (Tyler and Seliger 1978). Herr-
gesell et al. (1981) and Anon. (1981b) report that
the improved success of alewife, blue crab, oyster,
shad, soft clam, striped bass, and weakfish is
related to increased freshwater flow, particular-
ly at the time of spawning and early larval life.
The positive effects of increased runoff are thought
to include: (1) increased transport of plant nutri-
ents and detritus to the nursery area that increases
phytoplankton and zooplankton populations on
which shellfish and fish larvae feed; (2) a physical
expansion of the optimal nursery area, particu-
larly for fresh to slightly brackish spawners; and
(3) increased upstream transport of estuarine and
marine-spawned larvae.
Colder winter temperatures can affect the tim-
ing and volume of spring runoff through ice and
snow formation. During colder winters, spring
runoff (with its associated detritus and dissolved
nutrient load) and increases in water temperatures
are delayed. Theoretically, in such cases, the
positive effects of runoff may be more in phase
with the spawning times of species like the striped
bass (Mihursky et al. 1981).
The striped bass requirement for a flowing
water nursery (Setzler et al. 1980) undoubtedly
makes this species unique. The bass not only re-
quires higher freshwater flows for survival and
hatching of its eggs, but probably tolerates higher
flows than other freshwater spawning species.
These special requirements also appear to have
caused the striped bass to shift its principal
ancestral spawning area from the Susquehanna
Flats to the Chesapeake and Delaware Canal
because of the optimal current velocities for
suspension and survival of the eggs in the latter
location (Dovel and Edmunds 1971).
Most of the work to date relating climate and
other factors to finfish utilizes the statistical regres-
sion approach. It should be emphasized that these
correlations are suggestive, but not a definitive ex-
planation of cause and effect. Information on the
role of climatic variables in explaining natural
variability is a necessary condition to the assess-
ment of anthropogenic effects.
JUVENILE INDEX
Young-of-the-year juvenile finfish collected in
four representative tributary areas of the Bay
(Head of Bay, Potomac River, Choptank River,
and Nanticoke River) were used to assess the im-
pact of various natural environmental variables
on finfish. This juvenile index is believed to be a
better index of stock abundance than the direct
use of landings because it is influenced less by
fishing pressure and other factors. Though not im-
mune to uncertainty as an index of stock abun-
dance (Polgar 1982), the juvenile index was cor-
related with environmental variables to elucidate
possible factors that affect the recruitment of
young fish into the harvestable population. Details
of these analyses can be found in Section 4 of Ap-
pendix D.
FINFISH JUVENILE INDEX
REGRESSION ANALYSIS
The relationship of the finfish juvenile index
to natural and water quality variables was ad-
dressed through regression analysis (details of the
analysis are in Appendix D, Section 4). Linear
regression and multiple regression analysis were
performed.
Linear Regression Analysis
By linear regression analysis, the juvenile in-
dex was compared with freshwater inflow and air
temperature in the four tributaries. Results are
summarized in Table 40. In general, species
responded positively to increases in flow and air
temperature. In the Northern Bay, alewife
responded negatively to February and March
flows, which may be related to water temper-
ature. The same may be true for anchovy and
silverside. In both the Potomac and the Nanticoke,
striped bass responded negatively to increased
April air temperatures.
Although Table 41 indicates some subtle dif-
-------
178 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
TABLE 40.
RESULT OF LINEAR REGRESSION ANALYSIS OF JUVENILE INDEX AGAINST AIR TEMPERATURE
Species
Alewife
Spot
Spot
Atlantic
Menhaden
Bluefish
Catfish
Spot
Atlantic
Menhaden
Bluefish
Catfish
Spot
Atlantic
Menhaden
Bluefish
Spot
Striped Bass
Age 0
Atlantic
Menhaden
Yellow Perch
Age 0
Weakfish
Munnichog
Yellow Perch
Age 0
Spot
Striped Bass
Age 0
Spot
Basin
Choptank
Choptank
Choptank
Potomac
Potomac
Potomac
Potomac
Potomac
Potomac
Potomac
Potomac
Potomac
Potomac
Potomac
Potomac
Upper Bay
Upper Bay
Upper Bay
Choptank
Nanticoke
Nanticoke
Nanticoke
Choptank
Time
Feb. & March
Feb. & March
Feb., March & April
Feb. & March
Feb. & March
Feb. &. March
Feb. & March
Feb., March & April
Feb., March & April
Feb., March & April
Feb., March & April
March
March
March
April
March
March
April
February
February
March
April
Spring
Correlation
Coefficient
-.46
.43
.44
.49
.66
.45
.48
.58
.73
.52
.49
.54
.56
.48
-.49
.51
-.46
-.42
-.48
-.52
.42
-.44
.52
P<.05
.0281
.0381
.0351
,0165
.0007
,0312
.0209
.0037
.0001
.0109
.0170
.0078
.0051
.0210
.0178
.0136
.0286
.0447
.0216
.0101
.0475
.0360
.0103
ferences among species and among river basins as
they relate to flow, the most believable results are
those represented by the combined basins (ag-
gregated flows and aggregated juvenile indexes).
This approach shows that striped bass responds
positively to strong spring flows, results that agree
with Mihursky et al. (1981). The marine spawn-
ers, bluefish, menhaden, and spot are responding
positively to strong fall, winter (which are com-
bined as "late"), late and annual flows. This
argues for the estuarine transport of the larval and
juvenile forms of these species by the upstream
migration of the bottom waters (Tyler and Seliger
1978).
Multiple Regression Analysis —
Analytical Methodology
A multivariate regression analysis was used to
-------
Finfish and Water Quality 179
TABLE 41.
RELATIONSHIP AS REPRESENTED BY R VALUES AND DETERMINED BY CORRELATION ANALYSIS
(P < 0.05) FOR FINFISH JUVENILE INDEX VERSUS FLOW (N = 24)
Species
Choptank River
Alewife
White perch
Menhaden
Mummichog
Nanticoke River
Anchovy
Potomac River
Striped Pass
Bluefish
Silversides
Upper Bay
Spot
Annual Winter Spring Summer Fall
Flow Flow Flow Flow Flow
0.48
Early
Flow
Late
Flow
-0.42
0.50
0.51
0.40
-0.49 -0.44 -0.43
0.38
0.43
-0.46 -0.53
0.56
0.46
-0.49
-0.46
0.59
0.60
Striped Pass
Bluefish
Silversides
Combined Basins
Striped bass
Bluefish
Menhaden
Spot
Silversides
-0.54
0.42
0.45
-0.60
0.47
0.51
-0.49 -0.41
0.45
0.52
0.60
0.42
-0.49
-0.53
0.43
0.46
0.67
-0.43 -0.54
-0.42
0.52
0.41
0.65
-0.51
identify the freshwater variables that best explain
observed trends in the juvenile index. Maximum
and minimum freshwater inflows, as "windows"
of flow in periods from 7 to 28 days, and air
temperature were used. Emphasis in the analysis
was placed on freshwater spawners and selected
forage fish because these species spawn within the
Bay system, including fluvial streams; they were
hypothesized to have sensitive young life stages
exposed to higher concentrations of natural and
anthropogenic factors than marine spawners.
In lieu of the non-continuous record of the
water quality data, the initial analyses included
only the juvenile indices, air temperature (sur-
rogate of water temperature), and stream flow.
For all months, the juvenile indices were regressed
in a step-wise fashion using a maximum r2 im-
provement against streamflow and air tempera-
ture. Predictive models for each juvenile index
species in each basin were obtained, and equa-
tions using air temperature and streamflow were
derived (examples shown in Figure 54). Through
the use of the residuals from each statistically
significant equation, other water quality variables
were tested. Because of infrequent data in the
Choptank and Nanticoke Rivers, the water quality
-------
180 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
Predicted (color) and observed (black) Juvenile indices
30
3
D
CD
.Q
E
CO
CO
o
CD
20
CD
Q.
CO
10
(a)
1955
1965
1975
1985
Years
Predicted (color) and observed (black) Juvenile indices
60
45
CO
CD
E
c
O
Q.
CO
30
15
\
(b)
1955
1965
1975
1985
Years
FIGURE 54. Observed and predicted juvenile indices for (a) striped bass in the Potomac River and (b)
spot in the Choptank River based on models derived from multiple regression analysis.
-------
Finfish and Water Quality 181
tests in these Rivers were excluded. Monthly MAX
R2 stepwise regression of water quality variables
including salinity, TN, TP, DO, and chlorophyll
was performed against the residuals from the
physical models to see if improvement can be
made on the models. Because of the infrequent
number of years available, these results may be
considered suggestive only.
Summary of Results from Juvenile Index versus
Water Quality — Multiple Regression Models
Although up to four significant variables were
allowed to enter multiple regression models
describing relationships between the success of
juvenile finfish indexes and various water quali-
ty parameters, the first variable to enter was ac-
cepted as having the best biological credence.
Based on moving 7, 14, 21, and 28 day windows,
almost all relationships with minimum and max-
imum flows were established in April and May,
reflecting possible influences on spawning times
for freshwater spawners and larval recruitment
times for marine spawners. However, there was
almost no consistency within a species, among
spawning groups (fresh or marine) or basin loca-
tions. Biased on monthly means for temperature
significant positive and inverse relationships were
established in March, April, and May possibly
relating to spawning and recruiting; the relation-
ships again lacked consistency within species or
among spawning groups and basins.
The two relationships, showing consistency
with the literature, include the positive relation-
ships among winter temperatures (November to
December) and the juvenile index for bluefish,
catfish, menhaden, and spot (this is consistent
with the findings of Dow 1975) and an inverse
relationship in the Potomac basin among colder
than no rmal winters and the success of striped bass
year classes or the juvenile index (this agrees with
Mihursky et al. 1981).
IMPACTS OF OVERFISHING
Fishing stocks may be reduced by growth over-
fishing and recruitment over-fishing (Gushing
1975). In the former, recruitment is not affected
by over-fishing, but fishing mortality is so high
that young fish are not given the chance to grow,
perhaps not even to reach reproductive maturi-
ty. A local example was seen in the Atlantic
menhaden fishery during the 20th century where
the fishery was initially established for approx-
imately ten-year-old fish and has progressively
reduced the availability of older fish until now.
At present, one- to two-year old fish constitute the
great majority of the catch (Henry 1965, Price
1973, and Cronan 1981).
The other form of over-fishing is recruitment
over-fishing where death by fishing is great
enough to reduce recruitment. Herring (Gushing
and Bridger 1966) and whales are examples of
fisheries that have suffered from recruitment over-
fishing (Gushing 1975).
Another way of stating the issue is that recruit-
ment is dependent upon stock density in recruit-
ment over-fishing and independent of stock den-
sity in growth over-fishing. Typical of both forms
is that the catch per unit of effort is reduced as
over-fishing progresses (Gushing 1975).
Typically, however, with the exception of a
few carefully studied fisheries in Chesapeake Bay
(e.g., the Atlantic menhaden), it is virtually im-
possible to predict levels of over-fishing. Catch
statistics (landings) cannot be related to species
abundance because the effects of fishing effort,
reporting error, and market demand are virtual-
ly unknown and cannot be adjusted for using cur-
rently collected statistics (Rothschild et al. 1981).
Bortone (1982) attempted to develop predictive
models for Chesapeake Bay fisheries relating land-
ings (catch) to quasi-effort statistics such as
numbers of boats, numbers of fishermen, numbers
of nets, etc. and was unsuccessful in establishing
meaningful relationships among these parameters.
Therefore, although there has been a long-
standing concern that over-fishing by both com-
mercial and sports interests has caused declines
in local fisheries (McHugh 1981 and Williams et
al. 1982), there is little statistical evidence to sup-
port the claim or to interpret the level of effect
for the majority of Chesapeake Bay fisheries. It
is interesting to note that one important conclu-
sion of the Emergency Striped Bass Research
Study (Anon. 1981a) is that "the level of fishing
mortality affects the magnitude of the contami-
-------
182 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
nant mortality that the stock can withstand and
vice versa." That is to say, over-fishing can reduce
the resiliency of the stock to rebound from toxic
material stresses and vice versa.
These two forces may well be reducing the
stocks of anadromous (fresh water spawners)
species as evidenced by their measurable decline
during the past ten years (Chapter 2).
HABITAT MODIFICATION
Habitat modification — construction of dams
or similar structures, draining of wetlands, or
modification of stream channel through dredging
or channelization — can have significant impacts
on the spawning success of anadromous and semi-
anadromous fish, or on the suitability of the area
for a finfish nursery.
Dams
Large dams and impoundments can alter the
volume and timing of freshwater inflow to the
estuary, which in turn may affect downstream
salinity, circulation, transport, and flushing. This
in turn can affect habitat for numerous estuarine
species, including finfish (Shea et al. 1980,
Mackiernan et al. 1982). Water quality down-
stream is often affected: impounded water warms
more slowly in spring and remains warmer longer
in autumn; water released from depth may be de-
ficient in DO or significantly colder than ambient
river water; released surface waters typically con-
tain more algae and less silt than river water
(Ridley and Steel 1975).
One major effect of dams and other in-stream
structures is the blockage of spawning migrations
of anadromous or semi-anadromous species. The
impact of the barrier depends on its location and
physical structure, as well as on the species of fish
involved. For example, alewife and salmonids
may pass barriers that halt shad, sturgeon, or
striped bass (Fefer and Shettig 1980). Barriers may
be man-made or natural (waterfalls, beaver dams,
logjams). Some relatively small barriers, such as
poorly-designed road culverts, may block passage
of white or yellow perch (O'Dell et al. 1980). The
extent of the potential impact is documented by
a survey of anadromous fish spawning areas done
from 1975 to 1979 by the Maryland Department
of Natural Resources (O'Dell et al. 1980). For ex-
ample, within the Chester River study area, 153
constructed barriers were documented on 120
streams; eight streams had natural barriers. Of
the 120, thirteen streams had completly blocked
migration of such species as white and yellow
perch, alewife, and blueback herring. The reduc-
tion of shad due to dam construction on the Sus-
quehanna has been well documented (Weinrich
et al. 1980).
Wetlands Loss
Loss of wetlands adjoining Chesapeake Bay
and its tributaries can occur through natural or
anthropogenic processes: the latter include filling,
draining, dredging, ditching, spoils disposal, and
other development. It is estimated that approx-
imately 23,700 acres (approximately 7 percent) of
tidal wetlands were lost in Maryland between
1942 and 1967; in Virginia, 4000 acres were lost
between 1955 and 1969 (Metzgar 1973, Settle
1969). The amount of non-tidal wetlands lost is
unknown, but probably significant. Daiber et al.
(1976) estimate that 80 to 90 percent of
Chesapeake Bay's total seafood harvest is depen-
dent on wetlands at some point in its life cycle.
This dependence may be direct, through habitat
or grazing, or through the detrital food-web
pathway. Commercially or recreationally impor-
tant animals such as furbearers or waterfowl also
heavily use wetlands heavily for food or habitat.
Wetlands also act as buffers for habitat, through
sediment trapping, erosion control, floodwater ab-
sorption, and nutrient trapping and transforma-
tion (Metzgar 1973, Davis 1978, Nichols 1983).
Marshes may also absorb and trap other pollutants
such as metals and pesticides (Gallagher and
Kibby 1980).
Because of their value as sources of detritus
and as habitat buffers, the loss of wetlands in areas
impacting anadromous fish spawning and nursery
grounds could represent a significant problem.
Other Modifications
Stream channelization, bulkheading, and
watershed modification can all have significant
impacts on water quality or physical suitability
-------
Finfish and Water Quality 183
of a habitat for finfish. The clearing of stream-
side vegetation often results in warming of the
stream:; the removal of marginal wetlands
eliminates the previously discussed "buffering"
capacity and allow a more rapid transport of
water from the surrounding areas downstream
(Spier et al. 1976). In an investigation of the ef-
fects of channelization on small coastal plain
streams; in Maryland, Spier et al. (1976) found
substantial amounts of sediment generated dur-
ing the active construction phase, the period of
initial stabilization (which is greater than 3 years
in these streams), and through induced erosion
downstream. Biological impacts noted were the
reduction in the diversity and type of benthic com-
munities, compared with unmodified and older
modified streams, although biomass levels were
not significantly different (Spier et al. 1976). Fish
populations in these small, relatively unstable
streams, were not so significantly impacted as
were the larger coastal plain streams studied by
Tarplee et al. (1971). However, impacts on
anadromous species in these and impacted
downstream areas were not evaluated in Spier et
al. (1976). Streams appeared to shift from
allochothonous detrital-based food webs to auto-
chothonous production because of (in stabilized
streams) aquatic and streamside vegetation. In
North Carolina, ditching and drainage practices
in coastal plain streams were shown to create
unstable salinity and food supply conditions in
downstream nursery areas, making them less
suitable for shrimp, spot, croaker, flounder, and
blue crab (Pate and Jones 1981). As a result of this
study, it was recommended by the authors that
(among other things) consideration be given to the
cumulative impacts of extensive alteration of small
estuaries, and that wooded swamps and marshes
be utilized as natural filters for upland drainage.
The modification of watersheds due to urban-
ization and other development, particularly the
increase in area of impervious surfaces, has been
related to declines in water quality in small
streams (Klein 1979). Nutrients and toxic sub-
stances (particularly heavy metals, oil, and salt)
are elevated and fish diversity reduced in direct
relation to the amount of imperviousness in the
watershed.
SUMMARY
A variety of factors impact finfish, and natural
variables represent major influences on fish
distribution, abundance, and recruitment. How-
ever, evidence suggests that anthropogenic stresses
also have the capacity to affect fish populations;
such effects may be occurring in Chesapeake Bay.
In particular, nutrient and toxicant enrichment
of low-salinity spawning and nursery areas may
be related to recent declines in anadromous spe-
cies. The loss of potential habitat in large areas
of the upper and mid-Bay due to summer low DO
is well-documented. Demonstrating clear effects
on finfish populations will not be a simple a task,
however. Though the effects of harvest, particu-
larly on already declining populations, may hypo-
thetically be significant, sufficient data do not ex-
ist to demonstrate such impacts. Finally, habitat
modification, especially construction of dams, has
the potential to seriously impact important
freshwater-spawning finfish.
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SECTION 7
SUMMARY
In general, a number of the hypotheses for-
mulated in the preceeding chapter appear sup-
ported by available information. Other relation-
ships may exist in Chesapeake Bay, but our data
are insufficient to demonstrate clear linkages.
However, comparison with information from
other regions, as well as from microcosm ex-
periments, lend credence to the hypotheses. Fi-
nally, certain hypotheses cannot be supported by
the data now available; further monitoring or
research is suggested.
SUBMERGED AQUATIC VEGETATION
Both the field data and the laboratory analyses
support the hypothesis that increases in nutrients
represent the major impact on SAV in Chesapeake
Bay. Submerged aquatic vegetation appear to be
responding primarily to forms of nitrogen and to
IFF on a Bay-wide basis. Whether the mechanism
is operating through increases in phytoplankton
biomass or epibiota on SAV leaves, or both, is not
certain. However, negative correlations of SAV
abundance with chlorophyll a concentrations lend
support to the phytoplankton hypothesis. There
appears to be little field or laboratory evidence
to support the hypothesis that herbicides are a
primary cause of SAV declines. Localized effects,
particularly in small tributaries or on populations
already light-limited, may occur.
BENTHIC ORGANISMS
(INCLUDING OYSTERS)
Benthic organisms, including commercial
shellfish such as oysters, are possibly affected by
a number of factors, Where sediment contamina-
tion by toxicants is relatively severe, significant
changes are observed in benthic community abun-
dance and structure. However, when sediment
toxicant burdens are slight, then other factors in-
cluding natural variables and biological interac-
tions such as predation appear to control benthic
organisms. The proposed loss of benthic habitat
due to low DO — linked to nutrient enrichme fit —
is supported by field observations. This
phenomenon may also be related to observed mor-
talities of shellfish in affected areas. Finally, the
accumulation of toxicants in tissues of benthic
organisms may have physiological impacts, or
may be magnified in the Bay food web.
FINFISH
As with benthic organisms, finfish appear to
respond to a number of factors, both natural and
anthropogenic. There is evidence that the levels
of toxicants observed in some areas of the Bay are
within the range to affect survival or health of lar-
val fishes. However, no clear cause and effect can
be demonstrated at this point; the relationship re-
mains hypothetical. There is little support from
Chesapeake Bay for the hypothesis that food-web
shifts have been impacting anadromous species,
except in a few areas. Again, this is primarily due
to lack of extensive data on spatial and temporal
trends in phytoplankton and zooplankton popula-
tions. However, the loss of habitat for fishes in
the Bay main-stem due to summer low DO is sup-
ported by field observations. Whether this loss of
habitat is producing major impacts on finfish
populations is as yet unknown. The hypothesis
that finfish populations are responding strongly
to natural, climatic variables is supported by a
185
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186 Chapter 3: Relationship between Water and Sediment Quality, and Living Resource Variables
number of correlative techniques. In fact, the dif-
ficulty in assessing anthropogenic impacts is
primarily due to the strong influence of natural
factors. However, it should be kept in mind that
even a relatively small additional impact on some
populations could eventually result in significant
effects. Finally, there are insufficient data to ad-
dress the subject of possible over-fishing of some
species, although ongoing studies by other pro-
grams (particularly the Striped Bass Study group)
may shed light on this subject.
CONCLUSION
As anticipated in the introduction to this
chapter, there is considerable difficulty in
demonstrating unequivocal "cause and effect" bet-
ween changes in environmental quality and trends
in living resources. At best, we can show signifi-
cant correlations, which support reasonable
hypotheses as to potential effects. When these cor-
relations are further strengthened by the results
of research or monitoring performed under
relatively controlled conditions, the cases become
stronger and more compelling.
We stated earlier that "the correspondence of
the patterns infers that the nutrient and toxicant
enrichment reflect. . . human intervention in the
Chesapeake Bay ecosystem, and that at least some
trends in SAV, shellfish, and anadromous fish
reflect the integrated response to that interven-
tion." Based, in part, on this assessment, Bay
managers will decide what actions are
appropriate.
The Bay ecosystem is not amenable to exact
solutions because uncertainty always will sur-
round the causes of problems. The CBP antici-
pates that future research and monitoring will
continue to reduce uncertainty. However, prudent
management will not wait for science to provide
a precise level of assurance or run the risk of the
"ultimate experiment." It is contemplated that a
coherent approach to problem identification and
probable cause will yield dividends in spite of our
acknowledged uncertainties.
-------
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NOTES
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NOTES
1. 1 m = 3.28 ft
2. Personal communication: "Total Residual
Chlorine Criteria," Bill Brungs, U.S. EPA
Naragansett, 1983.
3. 1 km = 0.62 mi.
4. Personal Communication: "Phytoplankton Cell
Numbers in the Potomac River," Ron Cohen,
USGS, 1982.
5. Personal Communications: "Wetlands Inven-
tory," Anonymous, Maryland Department of
Natural Resources, 1983.
6. Personal Communication: "Wetland Loss," G.
Silberhorn, Virginia Institute of Marine Science,
1983.
7.
= 5/9(°F-32)]
8. Personal communication: "Oyster Harvest in the
James River," Dexter Haven, VIMS, 1982.
9. Personal communication: "Oyster Harvest in
Maryland," Harold Davis, Maryland Depart-
ment of Natural Resources, 1982.
9. Personal communication: "Juvenile Finfish
Survey," Joe Boone, Maryland Department of
Natural Resources, 1982.
10. Personal communication: "Phytoplankton Cell
Numbers in the Potomac," Ron Cohen,
U.S.G.S., 1982.
11. Personal communication: "Phytoplankton Cell
Numbers in the Potomac," Ron Cohen,
U.S.G.S., 1982
12. Personal communication: "Oyster Biology,"
Dexter Haven, VIMS, 1982.
13. Personal Communication: "Oyster Mortality,"
G. Krantz, Horn Point Environmental
Laboratory, 1982.
14. Personal Communication: "Finfish Habitat," H.
Austin, VIMS, 1982.
15. 1 km = 5/8 mile
16. Personal Communication: "Blue Crab Recruit-
ment," C. Epifanio, University of Delaware,
1982.
17. Personal Communication: "SAV Transplant Ex-
periments," V. Carter, USGS, 1982.
18. Personal Communication: "Multiple Regression
Interpretation," R. Ulanowicz, Chesapeake
Biological Laboratory, 1982.
19. Personal Communication: "Results of
Microcosm Experiments with Benthos," R.
Alden, Old Dominion University, 1983.
20. Personal Communication: "Effects of Organic
Materials on Benthos in MERL Tanks," C.
Oviatt, U.R.I. 1982.
21. The Toxicity Index was developed in an attempt
to modify the Contamination Index to better
predict potential biological impact of con-
taminated sediments. It is based on weighting the
contamination factors for the six metals by their
relative toxicities from bioassay information.
The analysis is described in detail in Appendix
D, Section 1.
22. Personal Communication: "Oyster Mortality,"
G. Krantz, H.P.E.L., 1982.
23. Personal Communication: "Oyster Mortality,"
G. Krantz, H.P.E.L., 1982.
24. Personal Communication: "Preliminary Results
of Food Web and Finfish Study," S. Mozley,
N.C. State University, 1983.
25. Personal Communication: "Preliminary Results
of Food Web and Finfish Study," S. Mozley,
N.C. State University, 1983.
26. 1 km2 = 0.386 mi2
200
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