United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA 600-R-98-147
November 1998
www.epa.gov
v®xEPA Condition of the
Mid-Atlantic Estuaries
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Chesapeake Bay, Delaware Estuary, and Delmarva coastal estuaries are vital Mid-Atlantic resources. They provide
habitat for many kinds of animals and plants, including commercially valuable fish and shellfish, and are enjoyed each
year by millions of recreational boaters, fishermen, and other visitors. For many years, the U.S. Environmental Protec-
tion Agency (EPA) has led efforts to protect and restore these estuaries by implementing such laws as the Clean
Water Act and by participating in projects like the Chesapeake Bay Program.
Are these protective measures having an impact? What is the current condition of our natural resources? How
widespread are ecological problems and what are their probable causes? To answer these questions, and to identify
the most effective protection measures for the future, we need to regularly take stock of our natural resources. EPA
is now pursuing these goals by preparing a series of State-of-the-Region Reports for the Mid-Atlantic, of which this
report is the first. These peer-reviewed reports aim to gather and evaluate the best available scientific information and
knowledge about the ecological resources of the region. Future reports will address the condition of our streams,
forests, and other resources.
This report breaks new ground in employing the latest scientific tools and by drawing upon carefully designed sampling
plans that provide broad coverage of all of these estuaries. It also demonstrates the value of forging close scientific
collaboration among federal and state agencies and other organizations. We hope this report will help you understand
more about the estuaries and encourage further efforts to protect these natural treasures.
W. Michael McCabe
Regional Administrator
Region III
Henry L. Longest II
Acting Assistant Administrator
Office of Research and Development
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This report, Condition of the Mid-Atlantic Estuaries, was prepared by staff from the Atlantic Ecology Division
(AED), National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S.
Environmental Protection Agency, Narragansett, Rhode Island. The staff included John F. Paul, Technical Leader,
Brian Melzian, Technical Coordinator, Barbara S. Brown, Branch Chief, and team members Charles Strobel, John
Kiddon, James Latimer, Daniel Campbell, and Donald Cobb. The report was prepared with the collaboration of indi-
viduals from Delaware Department of Natural Resources and Environmental Control, Maryland Department of
Natural Resources, Virginia Department of Environmental Quality, National Oceanic and Atmospheric Administration,
U.S. Geological Survey, U.S. Fish and Wildlife Service, EPA Regions II and III, AED Community-Based Assessment
Team in Annapolis (special thanks to Tom DeMoss, Pat Gant and Ron Landy), Kevin Summers and others from EPA/
ORD Gulf Ecology Division, EPA/ORD Western Ecology Division, Chesapeake Research Consortium, and EPA
Office of Policy, Planning, and Evaluation. Geographic information systems support was provided by Jane Copeland,
Randy Comeleo, and George Morrison, OAO Corporation. We would like to thank William Nelson, Gerald Pesch,
Richard Pruell, Steven Schimmel, Darryl Keith, and Walter Galloway of EPA/AED; Robert Diaz; and Kenneth
Tenore; as well as a large number of other reviewers from government and academia for their valuable reviews of this
document. This report represents the synthesis of information published in a variety of scientific reports or contained
in established scientific databases. We collected no new data specifically for the production of this report. We thank
the many researchers involved in the original collection and reporting of these data.
Because of the vast number of different research projects producing the data used in this report, no attempt was made
to verify the quality of these data. It was assumed that if the data were published or were stored in established
databases that they had been verified. However, any data that appeared "unusual" or questionable were checked with
the originator of those data. The spatial displays presented in this report were not prepared to meet EPA spatial
locational guidelines; the displays were prepared from disparate datasets and represent a best attempt at approximating
locations.
This report has been reviewed and approved for publication by the U.S. Environmental Protection Agency. Approval
does not signify that the contents necessarily reflect the views and/or policies of the EPA. Mention of trade names,
products, or services does not convey, and should not be interpreted as conveying, official EPA approval, endorsement,
or recommendation.
This report is contribution USEPA-NHEERL-NAR-1822 of the Atlantic Ecology Division of the EPA National
Health and Environmental Effects Research Laboratory.
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Estuaries are transitional zones where salt water from
the sea mixes with fresh water flowing off the land.
Estuaries in the Mid-Atlantic Region provide habitats for
many birds, mammals, fish, and other aquatic life. They
also are important assets that humans use in a wide
variety of ways. This report focuses on the current
condition of the Mid-Atlantic estuaries (circa early to
mid 1990s) and, where information is available, how the
estuaries have changed over the years and why.
The pervasive issues across the Mid-Atlantic Region
include the oyster harvest and disease in shellfish.
Shellfish, particularly the American oyster, traditionally
have been one of the major living resources harvested
in the Mid-Atlantic states. Oyster harvests have
declined from a high of 133 million pounds in 1880 to
today's annual catch of about one million pounds.
Disease, specifically Dermo and MSX, appears to be
one of the major causes of the recent drastic decline in
oyster populations in Chesapeake Bay and the Dela-
ware Estuary, with over-harvesting and pollution also
playing a major role in Chesapeake Bay. Although no
immediate solution to the problem is known, researchers
currently are working on the concept of introducing
disease-resistant strains of oysters to the Mid-Atlantic.
With the decline of the oyster industry, the most impor-
tant shellfish industry in the Mid-Atlantic Region is now
the blue crab. However, the significantly increased
fishing pressure on the already heavily exploited popula-
tion is beginning to take its toll. To avoid a serious
impact, both Maryland and Virginia have placed restric-
tions on crabbing in Chesapeake Bay waters.
The Delaware Estuary is characterized by an historical
lack of submerged aquatic vegetation (SAV), due
predominantly to naturally-occurring low water clarity.
It is also one of the most nutrient enriched estuaries in
the world, although harmful phytoplankton blooms are
held in check by other factors, including low water
clarity. The estuary also is highly impacted by lingering
toxic contaminants associated with urbanization and
industrialization of the Delaware River. The Delaware
Estuary has some of the nation's highest levels of
chemical contaminants in fish and shellfish. Fishing
, Photo by: U.S. Fish and Wildlife Service
bans or advisories on the consumption of finfish are
posted for parts of the estuary because of elevated
PCB concentrations. Concentrations of Chlordane in
fish exceeding the FDA action level have been reported
in the upper estuary.
Chesapeake Bay continues to be affected by low
dissolved oxygen and is the most hypoxic estuary in the
region. Low dissolved oxygen levels are associated with
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L^xecutwe
Photo by: U.S. Fish and
Wildlife Service
nutrient overenrichment and eutrophication. In 1987, the
Chesapeake Bay Agreement stipulated a 40% reduction
in nutrient loading by the year 2000. Nutrient levels in
Chesapeake Bay are declining in response to improved
wastewater management practices, implementation of
best management practices on agricultural lands (nitro-
gen), and bans on certain types of detergents (phospho-
rus). However, there has been more success in control-
ling point sources than nonpoint sources of nutrients.
Historically, high nutrient concentrations have contributed
to prolonged phytoplankton blooms in the Bay. Blooms
during the 1970s and 1980s significantly reduced water
clarity and, as a result, contributed to the massive loss of
SAV that occurred during that time period. This critical
habitat has since partially recovered.
The Delmarva coastal bays are the least degraded
systems in the Mid-Atlantic Region but are threatened
by encroaching urbanization. These bays are moderately
enriched, particularly in Delaware, largely from agricul-
tural sources. Eutrophication is increasingly noticeable in
the dead-end canals along developed shorelines in the
Delmarva coastal bays. SAV historically has been absent
from the Delaware portion of the coastal bays because of
high natural turbidity in these systems. Species composi-
tion of shore zone fish in the Delaware coastal bays
indicates impacted environmental conditions. In contrast,
Maryland coastal bays' species composition suggests a
healthy habitat; however, researchers have observed
evidence of early stages of degradation in northern areas.
Coastal waters presently exhibit low levels of nutrients
and chlorophyll. However, evidence suggests that these
levels may be rising, indicating the potential for future
environmental problems.
Estuaries of the Mid-Atlantic Region are being ad-
versely affected by man's activities. Therefore they
need active management if environmental quality is to
be sustained. The states, in conjunction with EPA
through the Chesapeake Bay Program and the National
Estuary Programs, have instituted successful environ-
mental management programs to address these environ-
mental challenges.
IV
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f ontenis
..........................,
Greetings from the U.S. Environmental Protection Agency
Acknowledgements 11
Executive Summary 111
Most of the Mid-Atlantic Region's population is concentrated along the coast, and that places a great deal of
pressure on the protected areas where freshwater from rivers mix with seawater—our estuaries.
DESCRIPTION OF THE ESTUARINE RESOURCE
[[[<
The Mid-Atlantic Region contains a significant portion of the United States estuaries. The physical characteristics of
these estuaries are important factors in understanding their ecological condition.
WATER QUALITY
Many areas in the Mid-Atlantic Region are "overfed" by nutrients such as nitrogen and phosphorus.
Increased levels of nutrients from activities such as land clearing, fertilizer application and runoff, and sewage
discharges can lead to excessive vegetation, algal blooms, and low levels of dissolved oxygen.
Nutrients 9
Phytoplankton 11
Dissolved Oxygen 12
SEDIMENT CONTAMINATION 15
Chemical contaminants from a variety of point and nonpoint sources enter our estuaries and accumulate in
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HABITAT CHANGE 17
Developmental pressures have resulted in substantial habitat change in the Mid-Atlantic. Coastal Wetlands have
been destroyed for residential and commercial development. The submerged aquatic vegetation, which provides
food, shelter and nursery grounds for many species of shellfish, finfish, and other organisms, has decreased as
human population has increased.
Coastal Wetlands 17
Submerged Aquatic Vegetation 18
CONDITION OF LIVING RESOURCES 19
Fish and other aquatic life are often the first affected by the substances deposited in our waterways. Since they are
also consumed by people, the condition of our living resources is a significant public health concern.
Benthic Condition 19
Shellfish Harvest 21
Shellfish Closures 23
Fish Stock Assessment 25
Contaminants in Fish and Shellfish 28
Incidence of Disease 29
Waterfowl 31
Threatened and Endangered Species 33
SUMMARY 36
SOURCES OF INFORMATION 40
GLOSSARY 44
TECHNICAL APPENDIX: Criteria Used for Presenting Indicator Data 48
Vll
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troducti
ucuon,
A broad-scale view of the Mid-Atlantic Region1 of our
country reveals that local ecological resources such as
water supplies and wildlife do not exist as isolated groups
but are interconnected across long distances. The health of
blue crabs in Virginia or waterfowl in Delaware can be
affected by conditions dozens or even hundreds of miles
away. Therefore, studying and protecting ecological re-
sources must take a similarly broad view. EPA is working to
Photo by: Chesapeake Bay Program
implement just such an approach through its Office of
Research and Development and the Region III Office,
which is based in Philadelphia and encompasses the District
of Columbia and the states of Delaware, Maryland, Penn-
sylvania, Virginia, and West Virginia.
In this report, the first in a series of State of the Region
reports, we present information on estuaries in EPA Region
III, which includes Chesapeake Bay, the Delaware Estuary,
and the coastal bays on the Atlantic coast in the states of
Delaware, Maryland, and Virginia (Delmarva Peninsula).
To properly assess the ecological condition of Region
Ill's estuaries, one must look at more than just the water
bodies themselves. The entire watershed must be
studied, meaning all the land that drains into these
estuaries. For this reason, this report uses information
extending beyond the political bounds of EPA "regions,"
treating the estuaries as ecological units rather than
political entities.
Information in this report will be presented primarily as
percent of the estuarine area in some desired or undesired
condition, rather than the actual area (square miles). This
will allow easier comparison between subregions. For
example, questions like "Is more of Chesapeake Bay in an
undesired condition than the Delaware Estuary?" will be
addressed. If area estimates were compared, Chesapeake
Bay would dominate almost all comparisons because of its
size (81% of the estuarine surface area in the region). The
actual areas can be compared by multiplying percent area
by the areas given in the next chapter.
What are estuaries?
Estuaries are transitional zones where salt water from the
sea mixes with fresh water flowing off the land. For this
report we will use the term estuaries to include waters that
extend from the coast of the Atlantic Ocean (or bound-
aries that extend across the mouths of the Delaware
Estuary and Chesapeake Bay) upstream to the fresh
waters that drain to the ocean as far as the influence of
the tide is detectable. For rivers like the Susquehanna, this
tidal influence is limited to the first dam encountered as
one goes upstream. For others, such as the Delaware and
Potomac Rivers, the tidal influence can extend many miles
upstream to the fall line. The salinity of estuaries can
range from full strength sea water to brackish to fresh
water. When we discuss the condition of estuaries, we
mean the condition of the waters that span this full range
ofsalinities.
'Terms in the glossary are highlighted at first usage.
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Why are estuaries important?
Estuaries are valuable in many ways. They provide
important habitat for thousands of species of plants and
animals. As spawning, nursery, and feeding grounds,
they are invaluable to fish and shellfish. These waters
provide corridors for anadromous fish that migrate
upstream to spawn.
Estuaries support many kinds of natural habitats, including
wetlands. Wetland habitats are used by shorebirds,
migratory waterfowl, fish, invertebrates, reptiles, and
mammals. They are the home to many threatened or
endangered species. Wetlands also improve water
quality by filtering outpollutants and sediment, and serve
as buffers that protect upland areas from flooding. They
also stabilize shorelines and stream banks from erosion.
In addition to their biological and habitat value, estuaries
provide for many diverse human uses. They supply water
for municipalities, industry, and agriculture; support
commercial and sport fisheries; and support tourism and
recreation. They also are important locations for manu-
facturing and shipping. Finally, estuaries are valued for
their aesthetic qualities.
How are estuaries threatened?
Estuaries are threatened because of the numerous ways
that humans use them and the land area that drains into
them. As a result, they exhibit a multitude of environ-
mental problems. The most common problems—
degraded natural habitats, declining plant and animal
populations, diminishing fish and shellfish harvests, and
impaired water quality—are clearly observable in parts
of the estuaries in the Mid-Atlantic Region. Growth of
human populations in the estuarine watersheds, combined
with the spread of industrial and agricultural technologies
that are potentially harmful to ecological systems and
place greater demands on natural resources, has ad-
versely affected our valuable estuarine ecological
systems. Most of the problems observed in estuaries are
related to land use practices and are closely linked to
human population density. The northeast corridor
extending from Washington to Boston, of which the Mid-
Atlantic is part, is one of the most densely populated
areas of our country.
What dynamics occur
in estuaries?
This report is an accounting of our estuarine resources at
the present, which are, in part, the legacy of our past
actions. Our description of these resources is a snap-
shot of estuarine conditions in the Mid-Atlantic Region
based upon currently available information. However, we
know that ecological systems adapt and evolve with time
under the influence of external factors, that also change
Estuaries are home to a wide variety of wildlife.
Photo by: U.S. Fish and Wildlife Service
through time. This dynamic aspect of ecological systems
is not the subject of this report. Nevertheless, it is the
context within which this report is presented, and the
present ecological conditions are the basis upon which
management decisions about the future will be made.
Estuaries in the Mid-Atlantic Region are expansive and
dynamic systems, consisting of physical and chemical
environments, and living creatures. The fresher and
saltier waters in estuaries are constantly intermingling
with the rivers, ocean waters, the shoreline, and the air,
all of which are changing with the tides and seasons.
These natural mixing bowls of physical, chemical, and
biological interactions, combined with the myriad of
human uses, challenge our ability to understand and
manage these great natural resources. We have at-
tempted in this report, to summarize our current
understanding of how well estuaries as
a whole are doing in the Mid-Atlantic
Region.
\
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A discussion of the characteristics of estuaries in the Mid-
Atlantic Region provides a useful starting point. The
estuarine waters in the Mid-Atlantic Region encompass
approximately 5,467 mi2 of surface area. These estuarine
waters contain a significant amount of the estuarine area in
the United States; Chesapeake Bay is the single largest
estuary in North America. The estuarine areas for the
major natural subregions discussed in this report are 4,431
mi2 for Chesapeake Bay, 795 mi2 for the Dela-
ware Estuary, and 237 mi2 for the Delmarva
coastal bays.
What land areas do the
estuaries drain?
The estuaries of the Mid-Atlantic Region drain
78,859 mi2 of land area, with 65,712 mi2 of these
watersheds residing within the EPA Region III
state boundaries. Chesapeake Bay drains a
watershed of 64,325 mi2, the Delaware Estuary
drains 13,533 mi2, and the Delmarva coastal bays
drain 1,003 mi2. About 43,710 mi2 of western
Region III in the mid-Appalachian area do not
drain to the Atlantic Ocean. This land area
primarily drains to the Ohio and Tennessee
Rivers and Lake Erie. Runoff from these land
areas does not directly affect the Mid-Atlantic
Estuaries; however, transport by the atmo-
sphere from these land areas can influence the
estuarine drainage areas. Approximately 10,629
mi2 in southern Virginia drain to the Albemarle-
Pamlico estuarine system in North Carolina. This
land area also does not directly affect the Mid-
Atlantic estuarine waters.
How are the estuarine
watersheds used?
The use of land within watersheds is a basic factor in
understanding the ecological condition of the Mid-Atlantic
estuaries. A pictorial representation of the land cover is
shown in Figure 1. This figure displays the major land
Figure 1. Land cover for estuarine
watersheds in the Mid-Atlantic
region.
Source: Vogelmann, 1997
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Figure 2. Land cover categories in the Mid- Atlantic Region
estuarine watersheds.
Source: Vogelmann, 1997
cover categories (urban, forests, agriculture, wetlands, and
lakes and streams) as classified by the U.S. Geological
Survey. Figure 2 summarizes these land cover categories
for the region and subregions. Note that the Delaware
Estuary watershed is the most urbanized and that the land
cover distribution in the Delmarva coastal bays is distinctly
different from the rest of the region.
Nearly three out of every ten acres in the ^
Mid-Atlantic watershed is currently being used
for agriculture.
Photo by: Chesapeake Bay Program
For the region, forest is the dominant land cover category,
comprising 61% of the watershed area. Forests are
important because trees filter sediment and nutrients
from runoff, and their roots stabilize the shoreline and
reduce erosion. They also shade the water, reducing
summer water temperatures. Many of the Mid-Atlantic
forests are in areas distant from estuarine shores. In
some parts of the region, forests are
rapidly being replaced by agricultural
and urban lands.
Agricultural land comprises two
groupings—pasture and cropland.
Pasture land consists of grassy areas
for raising and feeding livestock.
Cropland is cultivated to provide
various food products. Approximately
one-third of the land in the region is
agricultural.
Urban land (5% of the watershed)
generally is close to the estuarine
shoreline (see Figure 1). Urban land
provides space for homes, roads, and
places of employment, and increases
the amount of impervious surface
area (for example, pavement) and
storm water runoff. As a watershed
becomes more developed, the amount
of pollutants carried in the storm water increases, as does
the amount of wastewater and solid waste requiring
disposal. The storm water flows in urban and developing
areas also cause habitat damage and destruction. It is
expected that the amount of urban land will continue to
increase across the region.
What does the population
distribution look like?
Population growth is the single most important factor
underlying various impacts on Mid-Atlantic estuaries.
The population has grown from 13 million residents in
1950 to 21 million in 1990 (Figure 3). By 2020 an
estimated 25 million people will be living in the estuarine
watershed of the Mid-Atlantic Region. Growing
Figure 3. Human population estimates for the
Mid-Atlantic estuarine watershed.
Source: Culliton et al, 1990
4
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(maximum lurb diiy zone)
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sewage treatment
plaats (N+Tj
.Nonpoinl sources Ji±Tjnjbod diain
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Figure 4. Schematic diagram of physical, chemical, and biological processes interacting in estuaries.
Source: Redrawn from USEPA, 1987
population requires land for homes, transportation,
shops, jobs, and recreation. Forests and other land of
environmental significance often are converted to meet
these needs. In addition to changes in land use, popula-
tion growth results in high flows from wastewater
treatment plants. The volume of discharge by waste-
water treatment plants has increased with the general
population trend. Nevertheless, efforts to protect
estuaries, such as improving wastewater treatment,
maintaining buffer zones around estuaries, and control-
ling pollutant runoff, can offset or even reverse some of
the impacts of growing populations.
What characterizes estuaries in
the Mid-Atlantic Region?
A schematic description of a typical estuary is shown in
Figure 4. The depth of the water is a basic parameter
that influences the type of plants and animals that can
inhabit the estuary. Shell fisheries usually are limited to
relatively shallow areas. Plants rooted in the bottom
sediments also require shallow depths. Large migratory
fish typically require deeper water for their excursions.
Large draft vessels are restricted to deeper portions of
estuaries or to dredged channels. Water depth also
influences circulation in the estuary, which in turn
determines the distribution of nutrients and pollutants.
Vertical stratification, or layering of waters of different
density, occurs in an estuary when colder, saltier water
underlies warmer and fresher water. This condition can
be sustained only in deeper waters because wind and
tidal motions usually are sufficient to keep shallow
water from stratifying. Stratification, which occurs in
the mainstem of Chesapeake Bay and lower portions of
the major tidal tributaries, isolates the deep layer of
water from the atmosphere. As dissolved oxygen in
this deep layer is depleted by decaying organic material
(dead algae that sink after peak production), stratifica-
tion does not permit replenishment of the dissolved
oxygen from the atmosphere. This leads to the ex-
tremely low oxygen levels observed in these deeper
waters. A description of dissolved oxygen conditions
across the region is presented in the next chapter.
Salinity, temperature, and depth are the primary factors
that affect the physical behavior of estuarine waters.
Warmer, lighter freshwater flows seaward over a layer
of saltier and denser water flowing in from the ocean.
This stratification varies within any season depending on
the rainfall and air temperature. Stratification usually
intensifies in the spring as the amount of freshwater
increases due to melting snow and frequent rain.
Stratification is maintained through the summer due to
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warming of surface waters and intense rainfall. Maxi-
mum reductions of dissolved oxygen in estuarine bottom
waters occur during the late summer (see section on
"Dissolved Oxygen"). In autumn, fresher surface
waters cool faster than deeper waters and sink. Vertical
mixing of the water layers occurs rapidly. This mixing
moves nutrients up from the bottom sediments, making
them available to phytoplankton and other organisms
inhabiting the upper water levels. This turn-over also
distributes much-needed dissolved oxygen to deeper
waters. During the winter, water temperature and salinity
are relatively constant from surface to bottom.
The degree of water column stratification is determined
by the difference in density between surface and bottom
water, and categorized by low, moderate, and high
stratification. Summer data on stratification are depicted
in Figure 5. Most estuarine waters in the Mid-Atlantic
Region exhibit little or no stratification. However, deeper
portions of Chesapeake Bay do become highly stratified.
The Delaware Estuary has areas of moderate stratifica-
tion, while Delmarva coastal bays typically are not
stratified due to their shallow depths.
The average depth of estuaries in the Mid-Atlantic
Region is 20 ft, with a maximum of 175 ft in the
mainstem of the Chesapeake Bay. The average depth
in Chesapeake Bay is 20 ft, 19 ft in the Delaware
Estuary, and 5 ft in Delmarva coastal bays. The
maximum depth in the Delaware Estuary is 148 ft in a
shipping lane, while in Delmarva coastal bays it is
approximately 115 ft at the Indian River Inlet.
Temperature dramatically changes the rate of chemical
and biological activity within estuarine waters. Because
Figure 5. Summer water column stratification
in Mid-Atlantic estuarine waters as observed in 1990-
93. Categories are low (green), moderate (yellow),
and high (red) stratification and are defined in the
technical appendix.
Sources: Strobel et al, 1995; Paul et al, 1997
the estuaries in the Mid-Atlantic Region are relatively
shallow, their capacity to store heat over the year is
relatively small. As a result, water temperature fluctu-
ates throughout the year, ranging from 32° to 84° F.
These water temperature changes influence when plants
and animals feed, reproduce, move locally, or migrate.
The density of water is dependent on temperature, as
well as salinity. In spring, as the air temperature rises,
the surface waters of the estuaries warm and become
stratified over the colder, heavier deeper waters. Air
motion, particularly during storms, can vertically mix
water. However, in deeper portions of Chesapeake Bay
and the Delaware Estuary, this mixing is restricted to the
upper portion of the water column.
Salinity is a measure of the total salt content in water.
The common measurement unit of salinity is concentra-
tion, usually expressed as parts per thousand (ppt)—the
Photo by: U.S. Fish and Wildlife Service
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SaliDity
Distribution
number of grams of dissolved salts in 1,000 grams of
water. Salinity measurements in estuarine waters range
from less than 0.5 ppt in fresh water to 5 ppt in brackish
water to 33 ppt in coastal ocean water. Because fresh
water contains fewer salts, it is lighter (less
dense) than sea water, and tends to remain
at the surface in a stratified estuary.
Salinity distribution in the Mid-Atlantic
estuarine waters during the summer is
summarized by three salinity categories:
salinity less than 5 ppt (oligohaline waters),
between 5 and 18 ppt (mesohaline waters),
and greater than 18 ppt (polyhaline/euhaline
waters). Bottom water salinity data for the
summer is depicted in Figure 6. Oligohaline
waters represent a small fraction of the
estuarine area of the region. Mesohaline
Figure 6. Summer salinity distribution in
Mid-Atlantic bottom estuarine waters as observed
in 1990-93. Categories are oligohaline (green),
mesohaline (yellow), and polyhaline/euhaline (red).
Sources: Strobel et al, 1995; Paul et al, 1997
waters are dominant in Chesapeake Bay, while the
Delaware Estuary and Delmarva coastal bays are
mostly polyhaline waters.
Sediments are the materials deposited on the bottom of
the estuary. They are comprised of sand, silt, and clay.
The silt-clay (mud) content of sediments (less than 63
microns or 0.0025 inches particle diameter) is an
important factor determining the composition of the
biological community that inhabits the bottom sediments
in estuaries. Although sediments are a natural part of
estuarine ecosystems, accumulation of excessive
amounts of sediments is undesirable. Accumulated
sediments can fill in ports and waterways. Sediments
suspended in the water column cause the water to
become cloudy, or turbid, decreasing light available for
plant growth and animal feeding. Further, as sus-
pended sediments settle to the bottom, the sediments
can smother bottom-dwelling plants and animals.
Sediments also can carry pollutants. Smaller or fine-
grained sediment particles (silts and clays) have a
relatively large surface area. Many pollutant molecules
easily adsorb, or attach, to small particles. As a result,
fine-grained sediments can adsorb metals, nutrients, oil,
pesticides, and other potentially toxic substances.
Thus, areas of fine-grained sediments can contain high
concentrations of sediment-bound pollutants.
An example of a plume of water, heavily
laden with suspended sediments,
entering an estuary.
Photo by: Chesapeake Bay Program
-------
Estuarine sediments are summarized by three catego-
ries: sediment with silt-clay content less than 20%
(sand), silt-clay content between 20% and 80% (mix),
and silt-clay content greater than 80% (muds). Sand is
the primary sediment category found across estuaries in
the region. The Delaware Estuary is dominated by
sandy sediments, while Chesapeake Bay and the
Delmarva coastal bays have a relatively uniform split
across the categories. However, the estuaries tend to
be sandier near their openings to the coastal ocean.
Clear waters are valued by society and contribute to the
maintenance of healthy, productive biological communi-
Water Clarity
Good
Fair
Poor
Figure 7. Summer water column clarity in
Mid-Atlantic estuarine waters as observed in 1990-93.
Water clarity categories are poor (red), fair (yellow),
and good (green) and are defined in text and technical
appendix.
Sources: Strobel et al, 1995; Paul et al, 1997
ties. Submerged aquatic vegetation, discussed in a later
section, is sensitive to water clarity. Water clarity in
estuaries is influenced by biological processes (for
example, phytoplankton blooms)', inputs of sediment and
detritus from streams, rivers, and nonpoint source runoff;
and resuspension of bottom sediments during intense
water movement, such as storms.
The clarity of estuarine water is determined by how far
light can penetrate into the water. We define poor water
clarity as water in which a diver would not be able to see
his hand when held at arm's length. Fair water clarity
corresponds to a wader not being able to see his feet in
waist deep water. Most estuarine waters in
the Mid-Atlantic Region have good water
clarity (Figure 7). The degree of water clarity
problems across the major subregions is
related to the depths of the systems. Chesa-
peake Bay, being the deepest, has the overall
highest water clarity. The shallow Delmarva
coastal bays have the lowest. It should be
recognized that not all water clarity problems
are due to man's intervention. Wind mixing in
shallow water resuspends sediments and
decreases water clarity.
This overview of estuarine resource character-
istics in the Mid-Atlantic Region sets the
context for describing the state of the estuaries.
For example, many factors underlie the changes
in fish abundance, sizes, and species composi-
tion in estuaries. Among these factors are
turbidity (water clarity) from resuspension of
sediments, surface runoff, and phytoplankton
growth; salinity; depth; and temperature.
Susceptibility of fish to poor water quality is, in
part, determined by estuarine characteristics.
The next chapters provide our snapshot of the
state of the estuarine environment in the Mid-
Atlantic Region. They summarize what we
know about a set of indicators, or measures, of
estuarine condition for water and sediment
quality, habitat change, condition of living
resources, and aesthetic quality. Each indicator
is briefly discussed relative to its importance for
understanding estuarine condition, then summa-
rized as to current condition using data from the
early to mid 1990s. The final chapter in this
report is our attempt to bring together the
current conditions into an overall evaluation of
estuarine condition.
-------
Nutrients
All plants and animals need small amounts of nutrients,
such as nitrogen and phosphorus, to grow and repro-
duce. However, an excess of nutrients can lead to
eutrophication, a condition in which prolonged blooms
of algae rob light and oxygen from other organisms
while turning waterways green and foul smelling. The
concentrations of dissolved nutrients measured during
the summertime are shown in Figure 8. The highly
urbanized Delaware Estuary exhibits some of the largest
concentrations of nutrients measured anywhere in the
Nitrogen
• Poor
Fair
• Good
Phosphorus
Pom-
Pa ir
Good
Figure 8. Concentrations of dissolved inorganic nitrogen and phosphorus measured during the summer
months in surface waters. Nutrient levels are higher than optimum in most of the rivers and upper bays.
The categories are defined and discussed further in the technical appendix.
Sources: Chesapeake Bay Program; Delaware Estuary Program; Bohlen and Boynton, 1996; Chaillou et al, 1996
-------
world. Nutrient levels are high in the upper bay and
most tributaries of Chesapeake Bay, more so for
nitrogen than phosphorus. The northern coastal bays
are more enriched than the southern bays, reflecting the
population and development trends in coastal Delaware
and Maryland. Nutrient levels in the coastal waters are
relatively low.
Nutrient overenrichment does not automatically lead to
eutrophication. Other factors such as water clarity and
salinity also play a role (refer to the technical appendix
for more information). In the following section on
phytoplankton, we examine a surprising illustration of this
complex phenomena.
Nutrients can originate at either point sources (highly
localized spots such as sewage treatment plants and
industries) or nonpoint sources (more diffuse regions
such as leaking septic systems, farmlands, lawns, and the
atmosphere). A loading rate is the quantity of nutrients
delivered by humans each year to each acre of estuary.
This is a measure of the intensity of a nutrient source.
Figure 9 compares the point and nonpoint loading rates of
nitrogen and phosphorus in the major estuaries.
Figure 9. Nutrient loading (quantity of
nutrients per acre per year) for the Mid-Atlantic
estuaries in the early 1990s. Loads to the Delaware
Estuary are high. Point sources are relatively well-
controlled, except in the Delaware Estuary.
Sources: Chesapeake Bay Program; Bohlen and Boynton, 1996;
Pennock et al, 1994; Cerco et al, 1994
Nitrogen
25
20
10
S
Q
.
Phosphorus
60
70
Date
80 85 90 95
Figure 10. Trends in the quantities of nutrien
delivered to Chesapeake Bay from point sources
since 1950. Recently, the nutrient loads have
been decreasing. Municipal sources are much
greater than industrial sources.
Sources: Chesapeake Bay Program
It is clear from Figure 9 that the Delaware Estuary
suffers the greatest loads. In part, this reflects the fact
that this region is highly urbanized, but the loads also are
high because of comparatively large contributions by point
sources. Fortunately, point sources are relatively easy to
identify and control; therefore reductions in the high loads
to the Delaware Estuary are possible. Elsewhere,
remediation programs must focus on controlling the more
diffuse nonpoint sources such as runoff from city streets
and farms and deposition from the atmosphere.
Figure 10 shows the quantities of point-source nutrients
delivered to Chesapeake Bay since 1950. Cities and
towns contribute far more nutrients to the bay than do
industries. Phosphorus releases declined steadily since
1970 when the Clean Water Act became law and a
phosphate detergent ban was implemented. Control of
nitrogen discharges is more difficult, but progress is
evident following the upgrading of sewage treatment
plants.
10
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Wale,
In summary, large portions of the region's estuaries are
nutrient over-enriched, especially in tributaries and near
urban centers. Efforts to reduce nutrient levels must
focus on controlling nonpoint sources in all watersheds
and point sources in the Delaware Estuary. Encourag-
ingly, long-term trends are showing signs of improve-
ment in response to environmental protection programs.
Phytoplankton
Phytoplankton blooms
Like plants everywhere, estuarine plants convert
sunlight and nutrients through photosynthesis into food.
Although bay grasses and macroalgae are common in
some shallow sites,phytoplankton (tiny floating algae)
are by far the most common plants in Mid-Atlantic
estuaries. Paradoxically, these phytoplankton commu-
nities are unnoticeable most of the year because they
are eaten as quickly as they grow. However, phy-
toplankton can bloom profusely for a few days or
weeks when growth conditions are optimal. These
blooms are part of the normal cycle in healthy estuar-
ies (see sidebar). However, if extra nutrients are
continuously available, as is often the case in estuaries
near urban areas and farms, the blooms can persist
longer, sometimes for the entire summer. Such unbal-
anced plant growth caused by excess nutrients is called
eutrophication.
Prolonged phytoplankton blooms ineutrophic estuaries
are detrimental for several reasons. Dense growths of
the algae cloud the water and rob light from sensitive
Phytoplankton Blooms
As with all plants, phytoplankton need light and
nutrients to grow and reproduce. However, neither
component is available year-round in Mid-Atlantic
estuaries. Sunlight is limited during the winter, and
nutrients normally are in short supply during the
summer and fall. A large 'spring bloom' occurs
when the increasing sun angle delivers enough light
for the dormant algae to begin using the abundant
nutrients available from the well-mixed wintertime
waters. Smaller blooms occur throughout the
summer when storms mix the water, bringing
nutrients from the bottom into the sunlit surface
waters where the phytoplankton reside. In a healthy
system, the blooms are short-lived because nutrients
quickly become depleted, and the population of
zooplankton (microscopic plant-eating animals)
explodes to graze the phytoplankton crop.
Crustaceans, insects, and small fish then eat the
zooplankton, and larger fish eat these organisms,
etc. The estuary is fed and the murky waters clear
until the next bloom. However, this balanced cycle
is disrupted if extra nutrients are available.
Phytoplankton (and in some places the macroalga,
Ulvd) then bloom continuously, clogging the
estuaries with uneaten and decaying plant material.
Phytoplankton bloom in an estuary. If the
bloom is persistent, the green algal mats can
block light to other plants and deprive animals of
oxygen. Area shown is about 5' x 6'.
Photo by: U.S. Chesapeake Bay Program
beds of submerged aquatic vegetation (SAV), which are
underwater grassy regions that are critical habitats for
many other estuarine organisms. The massive losses of
SAV in Chesapeake Bay during the 1960s were attrib-
uted to such persistent blooms. Blooms upset the
ecological balance of estuaries by altering normal food
webs and encouraging the spread of exotic or toxic plants
at the expense of native species. Moreover, the dying
blooms generate unpleasant odors and consume dissolved
oxygen that would otherwise support the respiration of
fish and bottom-dwelling organisms, forcing these
organisms to move away or die.
To estimate phytoplankton abundance in estuaries,
biologists measure the concentration of chlorophyll
suspended in water. Chlorophyll is the green pigment
present in all plants. Figure 11 compares summer
chlorophyll levels throughout the Mid-Atlantic Region
estuaries. A rating of 'good' designates healthy crops
of algae, while 'poor' indicates the likely occurrence of
blooms persistent enough to harm sensitive SAV beds.
Figure 11 shows that the largest levels of chlorophyll are
found in the tributaries and upper regions of Chesa-
peake Bay. The coastal bays are moderately eutrophic,
with particularly high levels of phytoplankton measured
in several tributaries and man-made canals. Generally,
11
-------
these chlorophyll patterns closely follow the patterns of
nutrient availability seen in Figure 8. In contrast how-
ever, the lower Delaware Estuary shows little indication
of eutrophication despite the very high levels of nutrients
found there (see sidebar). The coastal waters show
low levels of chlorophyll, as is normal for these coastal
regions.
Historically, eutrophication has decreased remarkably in
parts of Chesapeake Bay. For instance, chlorophyll concen-
trations in the upper and middle Potomac Rivers are now
about one fifth the levels evident in the 1970s and 1980s
when foul-smelling mats of algae bloomed in response to
high nutrient concentrations. Presently, blooms occur in the
Chesapeake and coastal bays after periods of intense
rainfall, probably in response to nutrients in runoff from
farms and city streets. In the coastal bays, eutrophication is
increasingly noticeable in the Indian and St. Martin's Rivers
and in canals along developed shorelines.
Where are all the phytoplankton?
Surprisingly, the Delaware Estuary shows relatively
low levels of chlorophyll despite the very abundant
quantities of nutrients available in the bay. Why are
summertime algal blooms infrequent? In part, the
answer involves the fact that the bay is muddy.
Because the Delaware basin is broad and shallow, the
sediments are easily stirred by the winds and tides.
Erosion from farms deposits additional sediment loads.
The resulting low light levels in the water keep
potentially harmful blooms in check. Ironically,
managers are now concerned that improved land
management practices might clear the water enough
to permit eutrophication in the bay.
Olorophyll
• Poor
D Fair
• Good
Despite recent improvements, most tributaries
still are threatened by eutrophication. Chloro-
phyll-rich regions (bloom areas) generally
mirror patterns of nutrient over-enrichment,
except in the Delaware Estuary where murky
water inhibits persistent algal blooms. In most
cases, decreasing the sources of nutrients is a
viable solution to eutrophication.
Dissolved Oxygen
Dissolved oxygen (DO) is a fundamental
requirement for the maintenance of balanced
populations offish, shellfish, and other aquatic
biota. The nature and extent of an organism's
response to hypoxia (low dissolved oxygen
concentrations) depend on several factors,
including the concentration of oxygen in the
water, the duration of the organism's exposure
to reduced oxygen, and the age and physiologi-
cal condition of the organism. Most estuarine
animals can tolerate short exposures to
reduced dissolved oxygen concentrations
without apparent adverse effects. Prolonged
exposures to moderate hypoxia, defined as DO
below 5 milligrams of oxygen per liter of water
(mg/L, or parts per million), may result in
altered behavior, reduced growth, adverse
Figure 11. Chlorophyll concentrations
(a measure of algal abundance) measured
during the summer season in surface waters.
The chlorophyll patterns mirror nutrient
distributions, except in the Delaware Estuary.
Categories are defined in the technical
appendix.
Sources: Chesapeake Bay Program; Delaware Bay Estuary
Program; Bohlen and Boynton, 1966; Chaillou et al, 1996
12
-------
Wale,
reproductive effects, and possible mortality to sensitive
species and juveniles. Some aquatic animals may
avoid low dissolved oxygen waters. This behavior may
result in increased predation and decreased access to
preferred feeding areas or spawning habitat. In
addition, aquatic populations exposed to low dissolved
oxygen concentrations may be more susceptible to
adverse effects from other stresses, such as disease
and toxic substances. Severe hypoxia (DO below 2
mg/L) results in death to most aquatic animals, espe-
cially during summer months when metabolic rates are
high.
As discussed in the prior section on "Nutrients",
nitrogen and phosphorus fuel the growth of phy-
toplankton (see Figure 12). The nutrients enter the
estuarine waters primarily through wastewater dis-
charges, agricultural and urban runoff, and atmo-
spheric deposition. Decomposition of dead algae
consumes oxygen, which reduces the dissolved oxygen
available to support aquatic life. Algal growth in-
effluent
1 1-
V
. • t Ptiytop-anKton 8locim
thitwtt an nutitsivts
Dissolved Oxytjnn
'•on <*site acton
&
Figure 12. Physical, chemical, and biological
processes affecting dissolved oxygen (DO) in estua
rine waters that can result in hypoxia (low DO).
Source: Redrawn from USEPA, 1992
Factors Affecting Dissolved
Oxygen Levels
The amount of oxygen available to estuarine organ-
isms is affected by salinity and temperature. Cold
water can hold more dissolved oxygen than warmer
water, and fresh water holds more than salt water.
The concentration of dissolved oxygen varies with
location and time of day. Oxygen is transferred from
the atmosphere into the surface waters by diffusion
and the aerating action of wind. It is also added as a
by-product of photosynthesis. Floating and rooted
aquatic plants and phytoplankton release oxygen as
part of photosynthesis. Because this process requires
light, production of oxygen is limited to shallow water
areas, usually less than 6 feet deep. Surface water is
nearly saturated with oxygen most of the year, while
deep bottom water ranges from saturation to anoxia
(no oxygen present).
creases with light and temperature, and decomposition
also speeds up with elevated temperatures. Vertical
stratification in estuarine waters (warmer, fresher water
over colder, saltier water) during the late spring to
summer period restricts reoxygenation of bottom
waters. The amount of oxygen that can remain dis-
solved in water is reduced as temperatures increase.
Therefore, natural processes that occur in estuarine
waters set the stage for maximum reductions of dis-
solved oxygen in bottom waters during the late summer.
The summer distribution of DO within one meter of the
bottom across the Mid-Atlantic estuarine area is shown
in Figure 13. Dissolved oxygen conditions are summa-
rized by three categories: good, with DO greater than 5
mg/L (green); moderate hypoxia, with DO between 2
and 5 mg/L (yellow); and severe hypoxia, with DO less
than 2 mg/L (red). During the summer, 17% of the
estuarine bottom waters are moderately hypoxic, and
8% are severely hypoxic. Chesapeake Bay exhibits the
most hypoxia, with 21% of its area between 2 and 5 mg/
L, and 10% below 2 mg/L. These areas in Chesapeake
Bay are located in the middle portion of the Bay, the
lower portion of the Potomac River, and the Patuxent,
Patapsco, Chester, Rappahannock, and York Rivers.
Many of these areas are stratified and are continuously
depleted of DO during the summer months rather than
experiencing a cyclic condition where low dissolved
oxygen occurs only late at night, when photosynthesis is
not replenishing the oxygen. Because the data depicted
in Figure 13 were derived from daylight hours observa-
13
-------
Delaware River
a i, iz
Dissolved Oxygen Conditions
Miriam H»pri»
F-., •
Graph Sources: Strobel et al, 1995; Paul et al, 1997
Map Sources: Chaillou et al, 1996; CBP, 1997; USEPA,
1995; Magnien et al, 1993; Strobel et al, 1995; Paul
et al, 1997
Figure 13. Distribution of summer-time dissolved oxygen within one meter of bottom sediments across estuarine
waters in the Mid-Atlantic Region. Categories are defined in the technical appendix. Data were derived from daylight
observations and do not necessarily reflect night time depressions that may occur in some areas. Map depicts spatial
distribution derived from multiple sources of information. Bar graph shows percent areas derived from EPA EMAP
1990-93 data.
tions, the extent of depleted DO conditions in the
Delmarva coastal bays may not be properly character-
ized. Strongly associated with decreasing levels of
dissolved oxygen is the poor condition of
bottom-dwelling organisms. While other environmental
stresses also appear to affect bottom organisms, low
levels of dissolved oxygen most often co-occur with
poor conditions of bottom-dwelling animals in estuarine
waters of the Mid-Atlantic Region.
14
-------
eaime
L
ovuamina
tion,
Potentially toxic substances reach estuaries from
industrial and municipal effluents, storm water runoff,
and atmospheric deposition. Many types of contami-
nants pose a potential threat to estuarine waters. These
contaminants include trace metals (chromium, copper,
lead, mercury, silver, arsenic, zinc) and organic com-
pounds such as PAHs (polycyclic aromatic hydrocar-
bons), PCBs (polychlorinated biphenyls), and pesti-
cides such as DDT, Chlordane, and atrazine. Most of
these contaminants bind to particles suspended in the
water and settle to the bottom; therefore, their concen-
trations in sediments typically are much higher than in
the overlying waters. Measuring toxic substances in
estuarine sediments is an efficient method of determin-
ing contamination levels in estuaries and identifying
areas that may require further evaluation.
Contaminated sediments and their potential toxicity to
aquatic life are considered by the public as a major
threat to estuaries. Contaminated sediments often are
Contaminated sediments present a danger to the ^^
organisms living in or near them and to the consumers
of these organisms.
Photo by. U.S. Fish and Wildlife Service
Potentially Toxic Contaminants
Trace metals naturally occur in the earth's crust.
Their presence in estuarine sediments does not
necessarily indicate contamination from human
activities. Many of these metals are essential to
organisms, in minute quantities, but if present in
sufficiently high quantities they canbecome toxic.
PAHs are organic compounds, like PCBs and many
pesticides. They are released to the environment
primarily through burning fossil fuels. Spills of
petroleum compounds, including leaking oil from cars,
also may cause environmental contamination.
Due to the widespread use of fossil fuels and the
large number of vehicles, PAHs are now ubiquitous
in the environment.
considered an indicator of poor estuarine condition even
if the sediments are not presently toxic to estuarine
plants and animals. The concentration in the sediment
at which a contaminant becomes toxic depends on the
species and life stages of the organisms present, as well
as the physical and chemical characteristics of the
sediments and overlying waters. Due to the difficulties in
determining toxic concentrations of trace metals, PAHs,
PCBs, and pesticides, no state or federal regulatory criteria
or standards exist to determine "acceptable" sediment
concentrations of all these substances.
Sediment contaminant distribution across estuaries of the
Mid-Atlantic Region is shown in Figure 14. Sediment
contamination is categorized as sediments which pose no
risk to aquatic life (green), minimal risk to aquatic life
(yellow), and potential risk to aquatic life (red). Approxi-
mately 53% of the Mid-Atlantic estuarine sediments have
sediment contaminant levels considered to pose no risk to
15
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Delaware River
0 6 Li
NoRsK
Minimal Rah
R -k
1OJ-
Graph Sources: Strobel et al, 1995; Paul et al, 1997
Map Sources: Chaillou et al, 1996; Costa and Sauer, 1994;
USEPA, 1995; Strobel et al, 1995; Paul et al, 1997
Figure 14. Distribution of sediment contamination across Mid-Atlantic estuaries expressed as risks to
aquatic life. Categories are defined in the technical appendix. Map resolution is not in sufficient detail to indicate
that the Anacostia River, a tributary to the Potomac River in Washington, D.C., has been identified as having
potential risk from sediment contamination. Map depicts spatial distribution derived from multiple sources of
information. Bar graph shows percent area derived from EPA EMAP 1990-93 data.
aquatic life. Only 6% of the sediments contain contaminant
levels considered to pose a potential risk to aquatic life.
These sediments are focused around the major industrial
areas in the region, such as Baltimore and Philadelphia.
The sources of toxic substances include point sources
(industrial and wastewater treatment plant discharges)
and nonpoint sources including urban stormwater runoff
(from streets, parking lots, and grassy areas), atmo-
spheric deposition (directly on the water surface and on
the land that eventually enters the estuary), and agricul-
tural runoff. Urban stormwater runoff and point sources
are the major sources for metals entering the estuarine
waters of the Mid-Atlantic Region. The major sources
for PAHs and PCBs are urban stormwater runoff and
atmospheric deposition. Pesticide loadings to estuarine
waters primarily are from agricultural runoff and
atmospheric deposition. Recent studies by the National
Oceanic and Atmospheric Administration's (NOAA)
National Status and Trends Program indicate that
sediment contaminant levels in the
Mid-Atlantic Region generally
have been decreasing over the
last decade.
-------
bit at CA
an,ae
Coastal Wetlands
Wetlands were once considered to be little more than the
bothersome breeding grounds of mosquitoes and foul
smelling gases. We now realize they are extraordinarily
productive habitats that offer protective shelter and
abundant food to juvenile fish, shellfish, migrating water-
fowl, and thousands of other species, many of which
are threatened or endangered. Coastal wetlands also
buffer the coastline from severe storms and intercept
Chesapeake Bay Sail Marshes
ifii ft
i
ira
lad
ISO
Causes at Loss
nutrients and sediments that would otherwise interfere
with the sensitive nutrient and light requirements of
estuarine organisms.
Ecologists estimate that more than half of the region's
original coastal wetlands have been lost because of
human activities dating from pre-colonial times. Pres-
ently, about two thirds of the coastal wetlands are salt
marshes colonized by salt-tolerant grasses and bushes.
Much of the balance are tidal mudflats, areas that are
exposed at low tide and are densely packed with shellfish,
invertebrates, crabs, and other organisms. The remainder
are freshwater marshes, forests, and shrublands.
Figure 15 presents information about recent changes in
Chesapeake Bay salt marshes. From 1956 to 1989, about
6% of the region's wetlands were drained or filled to
accommodate human needs. The practices responsible
for most of these losses include pond construction,
channelization for mosquito control, urban and rural
development, and dredging for marinas. Conversion to
agricultural lands, along with natural processes such as
rising sea level and coastal subsidence, have contributed
to wetland destruction as well. More recently, the loss
rate has slowed in response to strict state and federal
conservation plans and slowed development. Agricultural
practices account for an increased portion of current
losses. Similar trends are evident in Delaware Bay and
the Delmarva coastal bays.
The near-term goal for the Mid-Atlantic Region is "no net
wetland loss." This strategy implies that the remaining
wetlands will survive as robust habitats able to provide
shelter, food, and recreation for many organisms,
including humans.
Figure 15. Trends in the acreage of salt marsh in the
Chesapeake Bay region and the causes of loss over two
recent time periods. Recently, the losses have stabilized,
largely due to slowed development.
Source: Tiner et al., 1994
17
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12dp
: .'.i
••UL » W B9 94 9fi
Maryland Coastal Bays
3 CO::
1
3UOD
2DQD
if.-!.:
Figure 16. Recent changes in the coverage of
SAV in the Chesapeake and Maryland coastal bays.
An interim goal in the Chesapeake region is to
restore sea grasses to all areas where they were
observed prior to 1970 (about 114,000 acres) and to
enhance bed densities.
Sources: Chesapeake Bay Program; Bohlen and Boynton, 1996
Submerged Aquatic Vegetation
The swaying meadows of bay grasses found in the
shallow waters of the Chesapeake and coastal bays are
called submerged aquatic vegetation or SAV. Bay
grasses such as eelgrass and widgeon grass provide
critical food, shelter, and nursery grounds for many
species of waterfowl, shellfish, finfish, and other organ-
isms. In one study, biologists found that SAV beds
supported 30 times more young blue crabs than areas
without grasses. The grasses also stabilize the shifting
sediments and inject life-sustaining oxygen into the water.
Unfortunately, this important resource is very sensitive to
pollution. SAV is equivalent to the "miner's canary,"
warning of poor conditions in the bays.
More than many other plants, bay grasses need plenty
of sunlight to grow. High levels of nutrients are
detrimental because they can stimulate extended
blooms of phytoplankton that block light to the SAV.
Sunlight is further attenuated by runoff from farms and
construction sites and by sediments suspended by
storms and tides. SAV originally colonized over
600,000 acres of the Chesapeake and coastal bays.
Only a tenth of that domain remains today.
The reasons for these historical losses are quite
different in the three estuary systems. The losses in
Chesapeake Bay are blamed on phytoplankton blooms
and nutrient over-enrichment, while the decline in the
coastal bays is attributed to an excess of suspended
sediments, in part associated with boating and construc-
tion. Eelgrass blight also decimated eelgrass beds
Submerged aquatic vegetation
Photo by: Robert Orth
throughout the Mid-Atlantic region in the 1930s. In
contrast, Delaware Estuary probably never had
extensive SAV beds because the water in this shallow
bay is kept naturally murky by tides and storms. Clearly,
restoration strategies for the estuaries must be tailored
to the unique conditions of each bay. Figure 16 shows
encouraging signs of SAV recovery. The colonized
areas have doubled since the mid 1980s in the Chesa-
peake Bay and Maryland coastal bays. Presently, SAV
beds are nearly absent from the Delaware Estuary and
the Delaware coastal bays.
Wetland and SAV habitats are essential to the survival
of all estuarine life. However, both resources are very
sensitive to disruptions caused by humans. Loss of salt
marshes has mostly been stabilized
and the challenge now is to keep the
remaining marshes healthy. SAV
beds are slowly but steadily returning
to their former ranges, largely in
response to improved water quality.
18
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f onalilon of
Benthic Condition
Bottom dwelling animals or benthos are linked with other
estuarine animals and plants through a network of
interactions that preserves the health of the estuarine
ecosystem. For example, benthic filter feeders promote
a healthy ecosystem by filtering algae and sediment from
the water, which helps maintain water clarity. That in
turn promotes good plant growth required for a produc-
tive bottom community. Benthic organisms are a
critical component of the estuarine food web, supporting
many commercially important species offish and
shellfish.
Benthic organisms inhabit the bottom sediments where
contaminants tend to accumulate and where the bottom
waters are subject to low dissolved oxygen or fast
currents. Many remain in one spot on the bottom or
move relatively short distances over their life time.
Therefore, the condition of the benthic community often
is a good indicator of the condition of the local estuarine
environment. Benthic communities have been shown to
Illustration of a typical mud bottom benthic
community.
Benthic Condition Index
The change in salinity from fresh water to the sea
is the dominant factor determining the variety of
benthic animals. Therefore, an index of benthic
condition uses information on the variety of
animals we expect to find at different salinities.
This gives us an expectation for the condition of a
healthy benthic community. Large-scale patterns
of change in salinity are expected to cause large
changes in the expected variety of species.
However, if salinity remains the same and the
number of species found in the benthic community
is very different from that expected based on the
salinity, we can be fairly certain that some other
factor is causing this change. These departures
can be caused by natural or human factors. The
circumstances surrounding each case must be
examined to determine what factors or combina-
tions of factors are responsible.
respond to human impacts in specific ways. A knowl-
edge of these patterns helps us understand benthic
conditions in relation to the factors acting on the bottom
community.
Figure 17 displays the distribution of benthic community
condition across the Mid-Atlantic Region. Impacted
benthic condition refers to benthic communities deter-
mined to be in a degraded state. However, areas with
impacted benthic condition may not be related directly to
human effects because both anthropogenic and natural
disturbances can cause effects.
The Delmarva coastal bays have impacted benthic
communities in approximately one-fourth of their area.
The Indian River is the most impacted; three-fourths of
its area exhibit impacted benthic communities.
Chincoteague Bay is the least impacted, with approxi-
19
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(^.audition o.
mately 10% of the area exhibiting impacted benthic
communities. Many of these impacted areas are
associated with nutrient overenrichment.
About one-fourth of the Delaware Estuary has im-
pacted benthic communities. The highest density of
impact occurs in the Delaware River. Poor benthic
conditions in the Delaware River are associated with
levels of chemical contamination that commonly affect
estuarine organisms. Some areas exhibiting impact in
lower Delaware Bay occur where fast currents scour
the bottom, while other areas appear to be affected by
excess phytoplankton production due to nutrient
overenrichment, resulting in increased levels of organic
carbon in the sediments.
Approximately one-fourth of the area of Chesapeake
Bay contains bottom sediment habitats with poor benthic
communities. A large portion of this area (middle
mainstem and lower Potomac and Rappahannock
Rivers) is impacted by low dissolved oxygen conditions.
Toxic contaminants are responsible for impacts in
industrialized locations around the Bay. Small systems
near Baltimore, Norfolk, and Washington, D.C. are
areas where chemical contamination has affected the
benthic communities. Localized areas of eutrophication
also occur in some small embayments and estuaries and
along some river reaches (e.g., Pocomoke and upper
Potomac Rivers). Natural stressors, such as highly
variable salinity regimes, cause impacts in a few areas in
Chesapeake Bay (e.g., Elk River).
Delaware River ji
X-
X
0 6 12
ismlhic Community Condition
• Good
D Impacted
• Severely Impacted
iDO
E
< 60
Graph Source: Strobel et al, 1995; Paul et al, 1997
Map Source: Chaillou et al, 1996; USEPA, 1995; Strobel et
al, 1995; Paul et al, 1997
Figure 17. Distribution of benthic community condition across estuarine waters in the Mid-Atlantic Region.
Categories are defined in the technical appendix. Map depicts spatial distribution derived from multiple sources of
information. Bar graph shows percent area derived from EPA EMAP 1990-93 data.
20
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(^.audition o.
Overall, approximately one-fourth of the estuarine waters
of the Mid-Atlantic Region exhibit impacted benthic
communities. Many occur close to urban centers.
Benthic communities dominated by species that are
adapted to high sediment carbon concentrations occur in
the Delaware Estuary, the Delmarva coastal bays, and in
some small estuarine systems in Chesapeake Bay. The
most prominent cause of impacted benthic communities in
the Mid-Atlantic estuaries is low dissolved oxygen
concentrations in the bottom waters. This problem is
largely confined to Chesapeake Bay. Similar types of
stressors on the benthic communities (e.g., low dissolved
oxygen, chemical contamination, eutrophication, high
velocity currents, dredging, and trawling) occur in each of
the Mid-Atlantic estuaries; however, the relative impor-
tance and magnitude of the effects caused by each
stressor are different across the estuaries.
Shellfish Harvest
The annual oyster harvest for Mid-Atlantic estuaries has
been as high as 133 million pounds (in 1880, Figure 18).
Today's annual catch of about one million pounds is only a
small fraction of past harvests. Most of the bottom of the
Virginia portion of Chesapeake Bay is classified as
potential oyster ground. These areas did support popula-
tions of oysters in the past; however, today the only
productive ground left in lower Chesapeake Bay is the
middle portion of the James River, Virginia.
The American Oyster
Shellfish, specifically the American oyster,
Crassostrea virginica, have traditionally been one
of the major living resources harvested in the Mid-
Atlantic states. Today oysters are the most
seriously threatened. The oyster has played an
important role in both the economics of the area
and the ecology of the estuaries. Oysters prefer
shallow water with a hard substrate and are
tolerant of salinities ranging from approximately 5
ppt to over 30 ppt, meaning they are well suited to
much of Chesapeake Bay, the Delaware Estuary,
and the Delmarva coastal bays.
Delaware Bay
Coastal Bays
Figure 18. Annual oyster harvest for Mid-Atlantic estuaries. Gaps in
the late 1880s and early 1900s do not represent zeros, but rather
missing data.
Sources: NOAA/NMFS; Chesapeake Bay Program; Haskin Shellfish Lab; Lyles, 1967a,b
As will be discussed in a later section, disease, specifi-
cally Dermo andMSX, appears to be one of the major
causes of the recent drastic decline in oyster populations
in the Chesapeake and Delaware Bays. Over-harvest-
ing and pollution also play major roles in Chesapeake
Bay. The impact of these diseases extends beyond their
direct effects on native populations of oysters. The
oyster is a filter feeder, meaning it pumps water
through its gills for both respiration and feeding. As it
pumps this water, the gills filter out particulates, including
phytoplankton, from the water. It has been estimated that
the pre-1870 population of oysters in Chesapeake Bay
could filter the entire water column of the
Bay in a few days. This suggests they
played a major role in clarifying the water
of the Bay, allowing more light to reach
the bottom where SAV grows. Because
of the drastic decline in the number of
oysters in Chesapeake Bay, it now takes
about 11 months for this filtering to occur.
The loss of this filtering capacity can
profoundly effect the ecosystem and may
have contributed to the decline in SAV.
Although no immediate solution to the
problem is known, researchers are
working on the concept of introducing
disease-resistant strains of oysters to Mid-
Atlantic estuaries (see "Incidence of
Disease" section).
With the decline of the oyster industry,
the most important shellfish industry in
the Mid-Atlantic Region is now the blue
crab (Callinectes sapidus) fishery. As
oysters have disappeared from the
waters of major Mid-Atlantic estuaries,
many oyster fishermen have switched to
21
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(^.audition o.
fishing for blue crab. This has significantly increased
the fishing pressure on a population that already was
heavily exploited (approximately 75% of the adult crabs
of Chesapeake Bay are harvested yearly). Over the
past 40 years there has been a five-fold increase in the
Virginia Chesapeake Bay blue crab fishing effort. An
increase also has been seen in the Delaware Estuary.
New Jersey issued permits for 3,001 crab pots for the
Delaware Estuary in 1969. By 1993, that number had
risen to 40,688 pots.
Annual harvest of the blue crab has been variable over
the past decades (Figure 19). This variability likely is due
to natural environmental factors compounded by fishing
pressures. Environmental conditions play an important
role in the condition of crab stocks. The low catch
experienced in 1977 and again in 1981 in the Delaware
Estuary has been attributed to unusually severe winters in
which ice conditions resulted in high mortality among
over-wintering crabs. Another major factor is the speed
and direction of surface currents during spawning season.
Females typically travel "down bay" into the higher
salinity waters to release eggs. The larvae are photo-
positive, meaning they are attracted to light and, therefore,
reside in the surface waters. Wind-generated currents
may carry the larvae back into the bay, resulting in in-
creased populations. Different wind patterns may carry
the larvae out to sea, causing lower catches in subsequent
years. Another important factor contributing to the
decline in crab populations is the loss of habitat, specifi-
cally beds of submerged aquatic vegetation that provide
shelter for juvenile crabs. As discussed in an earlier
section, there has been considerable loss of SAV in Mid-
Atlantic estuaries.
40
f.
DcJ.fMii-c Day
i Bays
Blue crabs harvested from Mid-Atlantic estuaries
Photo by: Chesapeake Bay Program
Although the blue crab catch in Chesapeake Bay and the
Delaware Estuary remains about average, the catch per
unit effort (number of crabs caught per pot per day) has
decreased. Some scientists believe the harvest is being
kept up by increasing effort, not stable populations. Over
the past several years the blue crab
harvest in the coastal bays has been
minimal, predominantly due to disease,
which has significantly reduced blue
crab populations in these estuaries.
1
1962 1966 1970 1974 w« iga?
1990 1934
Figure 19. Annual blue crab harvest for Mid-Atlantic estuaries.
Sources: NOAA/NMFS; Chesapeake Bay Program; Lyles, 1967a,b
Scientists are concerned that consecu-
tive years of poor environmental
conditions combined with heavy fishing
pressures could result in such a serious
impact on blue crab populations that it
would be difficult to recover. To avoid
such a situation, both Virginia and
Maryland have placed restrictions on
crabbing in Chesapeake Bay waters.
New Jersey and Delaware also have
taken steps to protect the fishery in the
Delaware Estuary, limiting the number
of commercial licenses issued and
placing restrictions on the collection of
egg-bearing female crabs.
-------
Shellfish Closures
Each state monitors their estuarine waters for coliform
bacteria and closes those waters to shellfishing when
the concentration reaches a critical level. In addition,
some areas can be closed for administrative reasons
such as the absence of a monitoring program and/or the
potential for contamination. For example, the low salinity
areas of upper Chesapeake Bay are not very productive
shellfish grounds; therefore, it is not cost-effective to
monitor these waters for coliform bacteria and, hence,
they are closed to shellfishing. Also, several coastal bays
Oyster harvest in the Chesapeake Bay
Photo by: Chesapeake Bay Program
are closed to shellfishing because of the potential for
contamination from a variety of sources.
Shellfishing is prohibited in 3% of the
3,660,000 acres classified as poten-
tially productive shellfish ground.
Shellfishing is restricted (shellfish can
be harvested but must be brought to
another location to depurate prior to
consumption) in an additional 179,000
acres (5% of the area). Approximately
67,000 acres (2%) are conditionally
closed, such as after rainfall events that
may wash contaminants into the
estuary. The breakdown by major
Filter Feeding
Bivalve shellfish are filter feeders, meaning
they pump water through their gills for both
respiration and feeding. As they pump this
water, the gills filter out particulates, removing
suspended material from the water. Because
shellfish are such effective filters of the water,
they tend to accumulate whatever pollutants
are in the water. This can result in the closing
of an area to shellfishing due to their contami-
nation. Most frequently, this is due to bacterial
contamination from a multitude of possible
sources.
estuary is shown in Figure 20. Figure 21 shows the
locations of closures. Considering the degree of urban-
ization in the Mid-Atlantic Region, it is encouraging that
the relative acreage of closed waters is low, and it has
decreased from 18% in 1985 and 1990 to 10% in 1995.
Of the total acreage in Chesapeake Bay that is harvest-
limited (conditional, restricted, or prohibited), the most
common sources of contamination are marinas, urban
runoff, upstream sources carried down the tributaries, or
unidentified sources (Figure 21). This figure also illus-
trates the relative magnitude of the effects of the major
sources on harvest-limited acreage. Any given system
may be impacted by more than a single source, compli-
cating remediation efforts. The major contributors in the
Delaware Estuary are sewage treatment plants and
leaking septic systems. Because of the wide diversity of
land uses on the Delmarva Peninsula, there are no
dominant sources of contamination.
Figure 20. Shellfish closures in
Mid-Atlantic estuaries expressed
as a percent of acreage classified
as productive grounds. (See text
for definitions)
Source: NOAA, 1997
D Restricted
• Nnl limrtrvj
2%
23
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IP.. IO
of cfL.il/lna t\ie6ou,fce6
PA
NI
{Ddawpt Eaaafy)
:
I
llll Illll
» 3T Cr 30 M* BO SE JP m OT *L UP
DE
MD
VA
'.--:.,:• -.. Kl.
CS OD u* BO S€ DR K1 OT WL UP
II HIiLill
0 15 30
Bar Graph Key
IN - ftuusiv SE •• ScpUt-
ST • SffWBJt"I*«raTW* PlF) I-H - Jrtlin Ft/nrfl"
Ffl • FMdM Fkuvl
DT-Ot«
Figure 21. Shellfish closure areas (in red) and bar graphs showing relative importance of major sources
of contamination. Many closure areas are too small to show up on this map.
Sources: State closure records; NOAA, 1997
24
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? I... IP..
.ondiiion of tsi.tin.n
Fish Stock Assessment
Fish generally occupy higher trophic levels in the
marine environment, and their abundance, distribution,
and condition are considered indicators of ecosystem
health. Many factors cause changes in fish abundance
and species composition. Among them are nutrient
concentrations, turbidity from suspended sediment,
phytoplankton abundance, salinity, current velocity,
overfishing, wetland loss, weather and oceanic condi-
tions, and predator abundances. Fish are mobile and
able to detect and react to changing environmental
conditions. Tolerant fish remain in degraded coastal
systems, whereas more sensitive species move to more
habitable regions or simply succumb to the stress.
Abundant juvenile fish and diversity in species indicate
that a system provides sufficient habitat to support
reproduction and growth. Juvenile fish are sensitive to
anthropogenic stresses and, therefore, their abundance
may indicate how much contamination exists in a
system. Because higher trophic levels in estuarine
systems require a rich diversity of intact ecosystem
functions to survive, grow, and reproduce, fish abun-
dance and species richness can be a broad and useful
indicator of estuarine health.
Summary of Fish Trends Data
The striped bass fishery in Chesapeake Bay
and the Delaware Estuary is considered to be
recovering.
American shad populations are improving
region-wide.
The white perch population is stable but low in
Chesapeake Bay.
Summer flounder populations are stable or
perhaps declining in the Delaware Estuary.
Summer flounder populations are improving in
the Maryland coastal bays.
Drum species populations are variable in the
Delaware Estuary.
Shore-zone species composition suggest
degraded conditions in the Delaware coastal
bays.
Shore-zone species compositions suggest
generally healthy conditions with slight
indications of degradation in the northern
coastal bays of Maryland.
Striped Bass
Photo by: U.S. Fish and Wildlife Service
The Mid-Atlantic Region is a diverse area containing
many different types of habitat suitable for fish. This
variety of habitats, along with the complexity offish
community interactions and the migratory nature of
many species makes it extremely difficult to assess the
overall condition of the fish community in an estuary.
In addition, different types of indices are used to assess
trends in different fish populations. Because of these
problems, this section focuses on specific, commercially
important species rather than the fish community as a
whole. Generally, fish monitoring in the region is based
on a combination of trawl sampling and seine surveys.
In addition, commercial fish landings data are available
and were used for this report.
Striped Bass (Morone saxatilis)
The striped bass (or rock fish) is an important commer-
cial and game fish for the Mid-Atlantic Region. It is an
anadromous fish that uses freshwater environments
such as the upper Chesapeake Bay and the Hudson,
Roanoke, and Delaware Rivers for spawning. Adult
striped bass use feeding areas in the Delaware Estuary,
Chesapeake Bay, and along the Atlantic Coast north-
ward to Maine. Striped bass were plentiful before the
industrial revolution, and population reductions were
apparent by the early 1900s. This species has under-
gone significant scrutiny since the decline of stocks in
the 1930s. Factors involved in these declines include
both overfishing and pollution. Moreover, habitat
degradation and losses from stress such as low dis-
solved oxygen in bottom waters of coastal embayments
have been associated with the lowered populations.
Researchers have attributed recovery throughout the
25
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(^.audition o,
Delaware River
Chesapeake Bay - VA
Chesajpeake Bay - MO
Figure 22. Normalized indices for juvenile striped bass indicating
recent improvements to juvenile fish stocks. For the Delaware River
it represents the seine index; for Chesapeake Bay it represents the
juvenile index for VA and MD. Numerical comparisons between
systems cannot be made due to the differences in the indices.
Source: NOAA; Chesapeake Bay Office; Dove and Nyman, 1995.
1980s to improved water quality as well as reduced fishing
pressure. Water quality improvements were primarily due
to upgraded sewage treatment. Overfishing was halted
by protective management practices implemented by the
states, including a fishing moratorium from 1985-1990 in
Chesapeake Bay and the Delaware Estuary.
Since that time, population levels have improved
(Figure 22). Because of the improved conditions,
the Atlantic States Marine Fisheries Commission
declared the fish stock restored, and fishing
restrictions on the striped bass have been liberal-
ized (but still exist). The 1996 data in the Chesa-
peake Bay show a record juvenile population
index in both Virginia and Maryland, exceeding the
previous record set in 1993.
American Shad (Alosa sapidissima)
The situation for the American shad is quite
different from that of the striped bass. Another
anadromous fish, the American shad migrates
annually into freshwater areas of the Delaware
Estuary and Chesapeake Bay. Since its high
mark in the late 1800s, a precipitous drop in
commercial landings has been seen in both
systems due to excessive harvesting, pollution,
and construction of dams and other waterway
obstructions causing loss of spawning grounds
(Figure 23). Over the past few years,
region-wide abundances have improved dra-
matically as a result of federal, state, and
interstate efforts to reduce fishing pressure,
increase spawning ground accessibility, and
improve water quality by improving wastewater
treatment (Figure 23 insert). However, this
species remains under strict management.
White Perch (Morons americana)
The white perch, an important commercial and
sport fish in the Delaware Estuary and Chesa-
peake Bay, has shown a relatively stable
population over the past 100 years. In Chesa-
peake Bay, fluctuations in the Maryland juvenile
index were greatest in the late 1960s through
the 1970s and decreased throughout the 1980s.
The index jumped markedly in 1993 to its
highest level—more than four times the average
over the survey period. Thus, some consider
the white perch to be an under-used resource.
Several factors are considered important in its
ability to maintain a stable population, including
its fecundity, early maturation, expansive
spawning and nursery grounds, and tolerance of
poor water quality.
Summer Flounder (Paralichthys dentatus)
The summer flounder is a popular sport and commercial
fish in the Mid-Atlantic Region. It ranges from Canada
Shad
Figure 23. American shad landings in Chesapeake Bay
showing decreased commercial landings since the late 1800s.
Gaps in the late 1800s and early 1900s do not represent zeros,
but rather missing data. 1993-94 data are preliminary.
Recent data on the abudance of adult fish in the upper
Chesapeake Bay (insert) show improvement of stocks.
Source: NOAA; Chesapeake Bay Office; Chesapeake Bay Program 1997.
26
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to Florida and is a migratory resident of coastal estuaries
during the summer, moving offshore to the continental
shelf m the winter. The summer flounder is heavily
exploited and has been managed by federal and state
regulations during the 1990s. Despite high fishing pressure,
the summer flounder persists in the Delaware Estuary. In
the Maryland coastal bays, summer flounder showed a
peak in abundance in the early to mid-1980s followed by a
decrease in the late 1980s. A gradual improvement in the
population during the 1990s has been documented.
Drum species
Many species within the drum family are important
recreational and commercial fish and significant contribu-
tors to the food web due to their abundance and range.
In the Delaware Estuary and Maryland coastal bays, four
species of drum are significant—spot (Leiostomus
xanthurus), black drum (Pogonias cromis), Atlantic
croaker (Micropogonias undulatus), and weakfish
(Cynoscion regatis). Significant historical variations in
young-of-the-year abundances and annual commercial
landings of spot, black drum, and Atlantic croaker are
thought to be due to many factors. These include
summer wind regimes, winter temperature, environmental
variations in spawning grounds, and effects of juvenile
predators such as jellyfish. The most recent data for
Atlantic croaker and weakfish show improved recruit-
ment. For example, above average recruitment for
Atlantic croaker in the Maryland coastal bays was
observed from 1993 to 1995; however, it was still much
lower than the recruitment observed in 1974. The
Delaware Estuary showed nearly a 10-fold increase in
1992 compared with the 1980s. Finally, the 1995 trawl
catch for weakfish was the second largest catch between
1972 to 1995.
Shore-Zone Species
Historical data on shore-zone species (those that inhabit
shore-zone habitats and shallow water environments)
have been studied to evaluate changes in species compo-
sition in response to changes in environmental stress. In
the Delaware coastal bays, significant physical, chemical,
and habitat changes have occurred over the last 60 years,
including increased levels of chlorophyll, suspended solids,
nutrients, and salinity. These changes have resulted in
shifts in species composition. For example, in the White
Creek area of the Delaware Estuary, species have
shifted from juvenile menhaden, tidewater silversides, and
bay anchovy to killifish and mummichog. Overall,
pollution-tolerant species such as cyprinodontids (e.g.,
killifish) are becoming more dominant as sensitive species
decrease (Figure 24). These changes are consistent with
the hypothesis that more sensitive fish have left the areas
Sensitive Species
Menliaoefi
Silversidl
Tolerant
Delaware Coastal Bays
Sensitive Species Remain Stable
Maryland Coastal Bays
Figure 24. Schematic depiction of the changes
in the Delaware and Maryland coastal bays' shallow
water fish species over the past 20-30 years. Note
changes from sensitive species to more tolerant
species in the Delaware coastal bays compared
to the stability in the species composition in the
Maryland coastal bays.
Source: Chaillou et al., 1996
and more tolerant species have taken their place. In the
Maryland coastal bays, fish community diversity has
remained relatively stable; however, in some northern
areas, pollution tolerant species have increased in abun-
dance. Future environmental alterations could result in a
more significant shift, as has occurred in the Delaware
coastal bays.
Illustration of Summer Flounder
27
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/? /.,. IP.. IP
(Condition, of oL wing t\e6ou,rce5
Contaminants in Fish and
Shellfish
Chemical contaminants may enter a marine organism in
several ways—direct uptake from contaminated water,
consumption of contaminated sediment, or consumption
of previously contaminated organisms. Once an
organism is contaminated, it tends to retain
(bioaccumulate) these chemicals unless there is an
effective cleansing mechanism. Chemical concentra-
tions may increase with subsequent feedings. An
organism higher on the food chain may "inherit" the
levels of chemicals present in the organisms lower in the
chain. This process, known as biomagnification, leads
to an increase of chemical contaminants, perhaps to
toxic levels. All organisms that consume contaminated
organisms, including humans, may be at risk of suffering
some toxic effect. The accumulation of these contami-
nants also may result in increased susceptibility to disease
or effects on growth or reproduction. It should be noted
H FCB*
I Kspcos
• Chliwdant;
I CUwdane & PCB»
that some chemical contaminants are not bioaccumulated
orbiomagnified.
Contaminant levels in fish and shellfish from the Dela-
ware Estuary, Chesapeake Bay, and the Delmarva
coastal bays vary widely. Some of the lowest fish or
shellfish contaminant levels in the nation have been
found in the Mid-Atlantic Region. At the same time,
fish or shellfish from other sites in the region have
tissue residues that are among the highest in the nation.
Many contaminants generally are at or below the
national average, and the levels in both fish and shellfish
appear to be declining. Generally, tissue residues are
higher in samples from the Delaware Estuary than in
samples from Chesapeake Bay, while levels in the upper
Chesapeake are higher than in the lower Chesapeake
Bay. The ban on the use of certain chemicals (e.g.,
Chlordane, Kepone, PCBs, DDT) apparently has led to
gradual, though significant, declines in the concentrations
of these chemicals in fish and shellfish. In some cases
(e.g., Kepone in the lower James River) tissue residues
have dropped below action or advisory levels,
resulting in the lifting or downgrading of bans on
consumption. Concentrations of a few heavy
metals in fish and shellfish may, however, be
increasing in some localized areas. Samples taken
from urban watersheds (e.g., Patapsco River near
Baltimore Harbor, the Potomac River near Wash-
ington, D.C., the James and Elizabeth Rivers near
Norfolk) generally have elevated concentrations of
multiple contaminants, typical of anthropogenic input.
Contaminant Levels in Fish
Although concentrations of many contaminants
are low or not detected in fish in the Mid-Atlantic
Region, several hot spots exist. Fish consump-
tion bans or advisories exist in many of these
areas (Figure 25). In Delaware, bans or adviso-
ries on consumption of fish due to elevated PCB
concentrations are in effect for the tidal portions
of the Red Clay, Christina, Brandywine, and
Delaware Rivers, as well as Little Mill Creek,
White Clay Creek, and Delaware Bay. Chlordane
levels that exceed the FDA action level have been
reported in the upper Delaware Estuary. High
Chlordane concentrations have resulted in con-
sumption advisories for several fish species in the
Figure 25. Fish consumption bans or adviso-
ries in effect for Delaware Estuary, Chesa-
peake Bay, and Delmarva coastal bays.
Sources: DNREC, 1994, 1996; Chesapeake Bay Program,
1993; Delaware Estuary Program, 1996
28
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(^.audition o.
Back River and Baltimore Harbor, Maryland. Chlor-
dane and PCB levels in the Anacostia and Potomac
Rivers in the District of Columbia have prompted
advisories, while kepone levels, although decreasing,
have resulted in an advisory on the consumption offish
from the lower James River in Virginia.
Contaminant Levels in Shellfish
Tissue residue data from shellfish collected throughout
the region are difficult to characterize. Some of the
lowest tissue residues measured in shellfish in nation-
wide studies have been found in the Delaware Estuary,
Chesapeake Bay, and the Delmarva coastal bays.
Other contaminant levels are among the highest re-
corded. Figure 26 compares shellfish tissue residues
from the region to national averages. Silver concentra-
tions in oysters from the region range from the lowest
nationwide to within the highest 12 percent nationwide.
Copper, cadmium, and zinc levels in bivalves are among
the highest measured in the nation, including the highest
measurements for zinc and cadmium. Mercury tissue
residues from Chesapeake Bay are low, accounting for
many of the lowest levels in the nation. Some of the
lowest chromium tissue residues were found in the Mid-
Atlantic estuaries, but four locations had high levels.
Similarly, lead levels ranged from very low to one site
with a high concentration. DDT and related com-
pounds, Chlordane and related compounds, and PCB
concentrations tended to be higher than the national
average at most of the sampled sites in the Mid-Atlantic
Region, with multiple sites rated high. PAH concentra-
tions in the region also range from the lowest in the
nation to one site classified as high. In general, more of
the contaminants were classified as having high concen-
trations in the Delaware Estuary than in Chesapeake
Bay and the coastal bays. The extremes in the concen-
trations probably indicate the presence of hot spots
associated with urban activities surrounded by more
pristine conditions.
Relatively few areas in the region have bans or adviso-
ries on the consumption of shellfish. In Virginia, high
levels of PAHs and their metabolic breakdown products
have led to bans on the consumption and collection of
oysters and crabs in the Elizabeth River and Little
Creek. Similarly, shellfish collection and consumption is
prohibited in the Lafayette River. PCB levels in blue
crabs have resulted in consumption advisories for
portions of the Delaware Estuary. In general, however,
shellfish contaminant levels are relatively low throughout
the Region.
« more b|gb
i 1 or more
I 1 flf mart high unit
«• mm Icrw
* ] or murw vwry
and. L ar more isiw
Figure 26. Shellfish tissue residues compared to national
averages. "High" indicates concentrations that are
significantly above the national average; "low" means
significantly below the national average. This illustrates
the range of concentrations encountered in the Region.
Source: NOAA, 1994
Incidence of Disease
Probably the most disturbing sign of pollution to the angler
is catching a fish with some form of external abnormality.
However, to the untrained observer, this is a poor indica-
tor of degraded water quality. What the angler believes is
fin rot or an open ulcer might actually be an injury.
Athough the cause of an abnormality may not be chemi-
cal contamination, a high incidence of such conditions
would indicate an environmental problem.
EPA's Environmental Monitoring and Assessment
Program (EMAP) conducted an examination of fish for
external abnormalities in its 1990-1993 survey of the
Mid-Atlantic estuaries. A total of 13,467 fish from 177
29
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(^.audition o.
stations (138 in the Chesapeake system, 32 in the
Delaware Estuary, and seven in the Delmarva coastal
bays) were examined by trained personnel. Only 41
fish, or three per thousand (0.3%) examined, were
afflicted with fin erosion, ulcers, growths, or abnormal
lumps (Figure 27). The majority of these fish were of
bottom-dwelling species such as channel or white
catfish, or brown bullhead. No affected fish were
collected in the Delmarva coastal bays. At 13 of the 20
stations where fish with a pathological condition were
found, only a single fish with an abnormal condition was
collected per station. The station with the highest
incidence was located in Maryland's Back River. The
low incidence of pathologies found in the Mid-Atlantic is
comparable to the overall incidence determined for the
east coast from Cape Cod, Massachusetts, to the mouth
of the Chesapeake. The incidence rate is only slightly
higher than the 0.2% determined for the South-Atlantic
coast. It is considerably lower than the 1 % determined
by EMAP for the estuaries of the Gulf of Mexico.
I
Enliffl RogxHi CheaapejlM! Dolavjrc CaaslJl Says
flay
Figure 27. Incidence of pathological condition in
fish of Mid-Atlantic estuaries.
Source: U.S. EPA, EMAP Database (1990-1993)
Although over fishing and environmental factors may
have contributed to the depletion of oyster stocks,
disease generally is recognized as the major cause of
the decline over the past few decades. The two main
diseases affecting oysters are Dermo and MSX, caused
by the protozoan parasites Perkinsus marinus and
Haplosporidium nelsoni, respectively. Dermo was
discovered affecting oysters in Chesapeake Bay waters
in the 1950s and the Delaware Estuary in 1990. Al-
though Dermo was first introduced to the Delaware
Estuary in the 1950s with imports of seed oysters from
the Chesapeake, it failed to become established at that
time. MSX was first observed in Chesapeake Bay in
Disease Issues
There are three major disease issues of ecologi-
cal and economic importance in the Mid-Atlantic
estuaries: pathological conditions in fish, oyster
disease, and fish kills due to bacterial infection.
The incidence of pathological conditions in fish
and fish kills due to disease is low in Mid-Atlantic
estuaries. Unfortunately, the prevalence of
oyster disease is high and has nearly destroyed
the oyster fishery.
1959 and in the Delaware Estuary in 1957. These two
diseases have decimated the oyster populations of both
estuaries. Both parasites are most active in waters with
salinities between 15 ppt and 30 ppt, which is why the
most productive oyster beds today are in lower salinity
areas, such as the middle James River. Most of the
waters of the Mid-Atlantic estuaries fall within this mid-
salinity range (Figure 6), resulting in an extremely wide-
spread problem. The spatial extent of these diseases
has varied over the past decades with climatic conditions
(e.g., amount of rainfall and summer temperatures). The
mid-1980s were unusually dry and warm years in the
Mid-Atlantic states, which resulted in the intrusion of
more saline waters further up into the estuaries than
usual. This intrusion introduced the diseases to oyster
beds throughout the bays and resulted in mass mortalities.
More than 75% of all oysters in Chesapeake Bay were
killed, and the stock has not recovered. Both diseases
are present in the Delmarva coastal bays, but are not as
virulent in the higher salinity seawater. Although some
oysters in the Delmarva coastal bays have been affected,
large-scale kills like those in the Chesapeake Bay and the
Delaware Estuary have not occurred. However, signifi-
cant reductions in oyster populations have occurred in
other coastal systems.
One question frequently asked is why have the oysters
become infected. One popular theory is that stress from
pollution reduced the oyster's resistence to disease.
Researchers have shown that pollutant stress increases
the oyster's susceptibility to disease. Although there is no
known way to combat the disease directly, researchers
are currently studying the feasibility of introducing
disease-resistant strains of oyster or other species of
oysters to local waters to reclaim the fishery. It is
important to note that these diseases pose no known
human health threat, either through contact with seawa-
ter or the ingestion of contaminated shellfish.
Another highly visible indicator of environmental
degradation is the incidence offish kills. Fish kills can
result from a number of both natural and anthropogenic
30
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Of «/, < villa /X e$0i il'Ci?A
causes. The majority offish kills are probably a result
of low dissolved oxygen (hypoxia) in the water due to
high water temperatures, over-enrichment (eutrophica-
tion), or simply the movement of too many fish into an
embayment (the fish use up the oxygen as they breath).
Other potential causes offish kills include fishing by-
catch, chemical pollution, toxic algae, and disease. The
massive kills of millions of menhaden in upper Chesa-
peake Bay in the late 1980s was attributed to a Strepto-
coccus infection combined with high water tempera-
tures (resulting in hypoxia). We have not seen such
conditions in the 1990s. NOAA reported that the
highest number offish kills in the Mid-Atlantic Region in
the 1980s occurred in Maryland's Anne Arundel and
Baltimore Counties. Most of these fish kills were
attributed to disease and low dissolved oxygen due to a
combination of over-enrichment and large numbers of
fish entering relatively small embayments. This trend
has continued into the 1990s with the same portion of
Chesapeake Bay exhibiting the highest incidence offish
mortalities. However, disease has played a less impor-
tant role.
During the summer of 1997, a number of fish kills
occurred in several of the small tributaries of Chesa-
peake Bay and some of the coastal bays. The caus-
ative agent for these kills was determined to be the toxic
dinoflagellate Pfiesteria piscicida or Pfiesteria-]ike
organisms. This complex organism can reside as a cyst
in the sediments of estuaries or as a non-toxic di-
noflagellate. These cysts can turn into toxin-producing
cells when conditions are right (warm water, high
nutrient loads, moderate salinity, poor flushing) and they
Pfiesteria
Pfiesteria is not a "disease" but a dinoflagellate.
Dinoflagellates are unusual organisms, part
plant and part animal.
Dinoflagellates are a normal component of the
marine ecosystem.
Pfiesteria has 24 different life stages, including
bottom-dwelling cysts and toxic stages.
Most outbreaks occur in warm water and at a
salinity of about 15 ppt.
The organism occurs naturally from the Gulf of
Mexico to the Delaware Estuary.
A large number of research projects are
currently underway to better understand this
organism.
Fish exhibiting sores caused by Pfiesteria.
Photo by: Maryland Department of Natural Resources
detect large numbers of fish. These cells release a
powerful neurotoxin that stuns the fish. Fish then
develop sores and begin to die. These kills can last a
few hours or several days. Usually by the time the kill
has been noticed, the organism has reverted back to
cysts and has settled back into the sediment. Within a
day or so, the toxin in the water has degraded, leaving
no signs of the organism.
Waterfowl
Another important living resource of Mid-Atlantic
estuaries is waterfowl (e.g., ducks, geese, swans) and
other birds associated with the water (e.g., herons,
egrets, osprey, eagles). Birds not only play a major
ecological role in these systems, but also provide a
recreational opportunity for hunters, photographers, and
bird watchers. Many species are highly dependent upon
wetlands and submerged aquatic vegetation for their
survival, and alterations to these environments affect the
populations of resident and migratory birds. Today,
habitat alteration is probably the major factor controlling
local bird populations. We stress "local" because many
of the species found in the estuaries of the Mid-Atlantic
are migratory, meaning they spend only a part of the
year in this area. As such, their overall abundance may
be determined by environmental factors where these
birds summer and breed, such as the Prairie Pothole
wetlands of the north-central United States and plains of
Canada. This makes the "bird story" a particularly
complicated one. For example, green-winged teal
(Anas crecca) are at their highest levels since the
1950s, not because of conditions in the Mid-Atlantic, but
because conditions in the Prairie Pothole region have
31
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(^.audition o
been favorable over the past several years. Significant
rain has resulted in the emergence of many ponds that
had dried up during 30 years of drought.
One interesting ecological story playing out in
Chesapeake Bay is the competition between the
black duck (Anas rubripes) and the mallard (Anas
platyrhynchos). Whereas mallard populations are on
the rise, black ducks are decreasing (Figure 28). This is
largely due to habitat loss and the release of mallards to
the Bay. Valuable black duck habitat is lost as wetlands
are eroded and land is developed for human use. Black
ducks tend to stay away from people, and will abandon
wetlands in close proximity to human development.
Mallards, on the other hand, are more adaptable to the
presence of people and are more likely to be found in
developed areas. Also, over the past several decades
mallards have been released to the Bay to increase
populations for hunting. The effect of this on the black
duck population is unknown, but both species are in
competition for the same resources. Further complicat-
ing this story is the fact that these two species can inter-
breed, resulting in hybrids. The picture is different for
the coastal bays (Figure 28) and the Delaware Estuary,
where black ducks outnumber mallards and both
populations are stable.
Another species of migratory waterfowl that is now a
resident of Mid-Atlantic waters is the Canada goose
(Branta canadensis). Although geese have always
wintered in the Mid-Atlantic, they did not become
permanent residents until the early 1900s when some
Figure 28 . Trends for mallards and black ducks in
Chesapeake Bay (heavy lines) and the Delmarva
coastal bays (thin lines). The Delaware Estuary has
been excluded for the purpose of clarity. The graph
shows the mid-winter survey count, not an actual
population count.
Sources: U.S. Fish and Wildlife Service, Mid-Winter Migratory
Bird Survey
Mallard Ducks
Photo by: U.S. Fish and Wildlife Service
were brought to Chesapeake Bay from the Great Basin
population to be used as live decoys. This practice
ended in the 1920s, but the birds remained and bred,
with some taking up residence in the Delaware Estuary
as well. The largest populations of resident geese are
Black Duck
Photo by: Wayne Munns
32
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Figure 29. Trends for Canada geese in Chesapeake
Bay and the Delmarva Coastal Bays. The Delaware
Estuary has been excluded for the purpose of clarity,
but the trend is similar to that of the coastal bays. The
graph shows the mid-winter survey count, not an
actual population count.
Sources: U.S. Fish and Wildlife Service, Mid-Winter Migratory
Bird Survey
found on the western side of Chesapeake Bay. Be-
cause this area is more densely populated by man, most
of the hunting occurs on the more remote eastern shore.
Most of the geese along the eastern shore are migrants,
and because of overharvesting and weather patterns to
the north, the population of migrant geese has declined
sharply. However, these populations are beginning to
recover (Figure 29). Therefore, despite an overall
abundance of Canada geese in the Chesapeake Bay
basin, hunting has been restricted to early September to
ensure that only resident geese are taken and to allow
migrant populations to recover.
Other species of waterbirds with increasing populations
include the diving ducks (canvasbacks have reached the
Canada Geese
Photo by: U.S. Fish and Wildlife Service
DtHrrwi Coral Bvya
Figure 30. Overall trend for all waterfowl in
Chesapeake Bay and the Delmarva coastal bays.
The graph shows the mid-winter survey count, not an
actual population count.
Sources: U.S. Fish and Wildlife Service, Mid-Winter Migratory
Bird Survey
restoration goal for Chesapeake Bay) and the great blue
heron (a colonial nesting bird). Figure 30 shows the
trend in the mid-winter survey count for all waterfowl in
Chesapeake Bay and the Delmarva coastal bays. It
shows how variable counts can be from year to year.
This variability can be due to a number of conditions,
both natural and man-induced. Although there has been
no significant overall trend for waterfowl as a group,
some species have increased while others have de-
creased. Scientists are concerned that local populations
of some species have not increased over the past few
years. Wet conditions in the Prairie Pothole region of
the country has led to a significant increase in the
overall national population of many migratory species.
A similar increase has not followed in the Mid-Atlantic
because the birds are favoring other wintering sites,
such as along the Gulf Coast. One popular theory
among scientists is that the increase in human activity
along Mid-Atlantic coast, coupled with the loss of SAV
and wetlands, is making this region less "attractive" to
many species of migratory waterfowl. One question
being asked is what will happen to the Mid-Atlantic
migratory waterfowl populations if prolonged drought
conditions return to the Prairie Potholes.
Threatened and Endangered
Species
Species of plants or animals can become threatened or
endangered due to habitat loss, unregulated killing or
collection, pollution, disease, predation, or competition
with other species. Although a species may become
33
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(^.audition o.
extinct for "natural" reasons such as being out-com-
peted by another species, over the past century the rate
at which species are becoming endangered has signifi-
cantly increased due to man's activities. In many areas
of the United States, rapid growth in population, industry,
and agriculture has led to significant stresses on a range
of native species of plants and animals. Recognizing the
impacts of these stressors, Congress took action in 1973
by passing the Endangered Species Act, "making the
conservation of endangered and threatened species and
the ecosystems that sustain them a National priority and
instituting public policy to work for their recovery."
The Mid-Atlantic Region has experienced some of the
most rapid population growth, industrial development,
and intensive agriculture in the country. Not surpris-
ingly, many organisms relying on the estuaries of the
Mid-Atlantic have suffered. Over 50 species of plants
and animals are listed as threatened or endangered in
the Mid-Atlantic states. Although most are not associ-
ated directly with estuaries, several are. These include
the bald eagle, peregrine falcon, piping plover, several
species of sea turtles, and shortnose sturgeon. New
Jersey, Delaware, Maryland, and Virginia have made
formal declarations to protect threatened and endan-
gered species. For example, "it is in the best interest of
the state to preserve and enhance the diversity and
abundance of nongame fish and wildlife and to protect
the habitat and natural areas harboring rare and vanish-
ing species offish, wildlife, plants, and areas of unusual
scientific significance or unusual importance to the
survival of Delaware's native fish, wildlife and plants in
their natural environments." These efforts have
Bald eagle
Peregrine falcon
Pilling plover
Kemp's ridlef turtle
Shortnose sturgeon
t
t
t
t
• A
Figure 31. Trends in selected threatened ^
and endangered species in the Mid-Atlantic
estuaries. Up arrow indicates improving trend,
question mark indicates trend is uncertain. None
of the major estuarine threatened or endangered
species currently are declining.
Source: U.S. FWS Endangered Species Database
Bald Eagle
Photo by: U.S. Fish and Wildlife Service
reversed the process of extinction for most of the
species we associate with the estuaries (Figure 31).
Continued efforts to protect these sensitive organisms
hopefully will result in their populations reaching levels
sufficient to ensure their continued existence.
PROFILES OF SELECTED
ENDANGERED SPECIES
Bald eagle (Haliaeetus leucocephalus)
This species formerly nested throughout North
America. Population declines were attributed to habitat
loss, illegal shooting, and the effects of DDT on repro-
ductive success. The eagle has benefited from in-
creased regulation of pesticides, nest site protection,
aggressive habitat management, and reintroductions.
Many states have successfully reestablished nesting
populations by translocating young birds from areas with
healthy populations to suitable, unoccupied habitat.
Public awareness campaigns and vigorous law enforce-
ment have helped reduce illegal shooting of eagles.
Bald eagle numbers in the lower 48 states have in-
creased from approximately 417 nesting pairs in 1963 to
34
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/? /.,. $/? I... IP.. \O
(Condition, of (Condition, of oLwinfi Ke6ou,rce66
more than 4,000 pairs in 1993. In addition, there are an
estimated 5,000 to 6,000 juvenile bald eagles in the
lower 48 states. As a result of the significant progress
toward recovery, the species has been reclassified from
endangered to threatened in the lower 48 States. The
bald eagle is an example of
success in the recovery of an
endangered species and is the
result of more than twenty years
of national effort to change the
trend in population decline. A
wide range of actions were taken
to conserve and restore habitat
and control pesticide contamina-
tion problems.
Kemp's ridley turtle
(Lepidochelys kempii)
There are only seven living
species of sea turtles in the world
and the Kemp's ridley is under the
greatest threat of extinction.
Virtually the entire world popula-
tion nests annually in a single
locality on a beach near Rancho
Nuevo, Mexico. When this nesting site was first
discovered in 1947, the adult female population was
estimated to be greater than 40,000 but has decreased
to approximately 490 based on recent estimates.
Juvenile turtles are thought to be carried north via
passive transport in the Gulf Stream, where they feed
Photo by: U.S. Fish and Wildlife Service
Shortnose sturgeon
(Acipenser brevirostrum)
The shortnose sturgeon is the smallest of the three
sturgeon species in eastern North America. It is an
anadromous fish that spawns in coastal rivers of eastern
North America from Canada to Florida. The
sturgeon is a fairly large fish (maximum known
length of 56 inches), is long-lived (maximum
known age is 67 years), and was commercially
important until the 1950s. They prefer the
nearshore marine, estuarine, and brackish
habitats of large river systems. Shortnose
sturgeons, unlike other anadromous species in
the region such as shad or salmon, do not
appear to make long distance offshore migra-
tions. Principle stressors that have resulted in
the severe population decline of the shortnose
sturgeon are pollution, incidental overfishing in
shad gillnets, construction of dams, and habitat
alterations from discharges, dredging, or
disposal of material into rivers.
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ummaru
Estuaries are transitional zones where salt water from
the sea mixes with fresh water flowing off the land.
Estuaries in the Mid-Atlantic Region provide habitats for
many birds, mammals, fish, and other aquatic life. They
also are important assets that humans use in a wide
variety of ways.
From the information presented in the prior chapters, the
complexity and value of the estuarine resources of the
Mid-Atlantic Region (circa early to mid 1990s) is appar-
ent. Estuaries are natural mixing bowls for physical,
chemical, and biological interactions; and they are threat-
ened by a myriad of human uses. This complexity
challenges our ability to understand and manage these
great natural resources.
In this report, we have summarized our current understand-
ing of how well estuaries, as a whole, are doing in the Mid-
Atlantic Region by presenting information on individual
indicators. These individual measures tell us the condition
of the Mid-Atlantic estuaries within the context of that
particular indicator. A synopsis of our findings follows.
• Nutrient concentrations are relatively high in many of
the rivers and smaller bays in the Mid-Atlantic estuar-
ies. High nutrient levels are not harmful in themselves;
however, overenrichment can cause prolonged phy-
toplankton blooms that can disrupt estuarine processes.
Nonpoint sources such as leaking septic systems, runoff
from farms and construction sites, and deposition from
the atmosphere are the most common sources of
excess nutrients. However, municipal and industrial
point sources also contribute large nutrient loads,
especially to the Delaware Estuary. Although the
Delaware Estuary is one of the most enriched estuaries
in the world, harmful phytoplankton blooms are held in
check by other factors such as poor water clarity
attributed to both natural and human processes. Nutri-
ent loads in Chesapeake Bay are declining, largely in
response to improved control of point sources (for
example, the upgrading of sewage treatment plants)
and bans on certain types of phosphorus detergents.
The Delmarva coastal bays are moderately enriched,
particularly in Delaware. Coastal waters presently
exhibit low nutrient levels, but there is evidence that
these levels are increasing. Future progress must focus
on controlling nonpoint nutrient sources.
Prolonged phytoplankton blooms can disrupt the
growth of submerged aquatic vegetation and promote
hypoxia and anoxia in stagnant estuarine waters. High
concentrations of chlorophyll during the summer
indicate that eutrophication is a problem in the tributar-
ies and upper reaches of Chesapeake Bay and the
coastal bays of Delaware and northern Maryland. At
present, extended blooms in the Delaware Estuary are
uncommon despite high nutrient loadings because
phytoplankton growth is limited by the naturally high
turbidity in this estuary. The widespread eutrophication
that was common in the upper Chesapeake Bay during
the 1960s and 1970s has been successfully reduced, in
large part by improved nutrient management practices.
Eutrophication is increasingly noticeable in the dead end
canals along developed shorelines in the Delmarva
coastal bays. Chlorophyll levels presently are low in
off-shore waters, but there is evidence that levels may
be increasing.
Dissolved oxygen (DO) is a fundamental require-
ment for estuarine organisms. During the critical late
summer time period, 17% of the estuarine bottom
waters of the region exhibit moderate hypoxia (DO
between 2 and 5 mg/L) and 8% exhibit severe hypoxia
(DO less than 2 mg/L). Chesapeake Bay is the most
hypoxic estuary, largely due to natural processes (water
column stratification) made worse by nutrient enrich-
ment and eutrophication. The Delaware Estuary and
the Delmarva coastal bays have small areas of hy-
poxia. Low dissolved oxygen does not appear to be of
concern in coastal waters. Poor condition of bottom-
dwelling organisms is strongly associated with de-
creased DO levels.
Sediment contamination with trace metals, PAHs,
PCBs, and pesticides, and the associated potential
toxicity of these sediments, are considered by the public
to be a major threat to estuaries in the Mid-Atlantic
Region. More than half of the estuarine sediments in the
region have contaminant levels considered to be accept-
able. Less than 10% of the sediments contain contami-
nant levels considered to pose a potential risk of effects
to aquatic organisms. Most of the contaminated areas
are adjacent to historical urban, industrial, and agricultural
sources. In general, sediment contaminant levels in the
region have been decreasing over the last decade.
36
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(7
^_)u.fnfnap'i
The historical loss of coastal wetlands in the
Mid-Atlantic estuaries has largely been stabilized by
state and federal conservation plans, even though there
is a continuing loss of wetlands in upland areas. The
challenge now is to ensure that the wetlands are
healthy despite severe anthropogenic stresses. The
precipitous loss of submerged aquatic vegetation
(SAV) in Chesapeake Bay during the 1970s also has
been checked. SAV beds are returning to Chesapeake
and Chincoteague Bays in response to diminished
eutrophication associated with improved nutrient
management practices. SAV historically has been
absent from the Delaware Estuary and the Delaware
portion of the Delmarva coastal bays because of high
natural turbidity in these estuaries.
Impacted benthic communities can be found in all of
the major estuarine systems of the Mid-Atlantic, but
are most prevalent near urban centers such as Philadel-
phia, Baltimore, Washington, and Norfolk; and in areas
suffering from low dissolved oxygen. The most
prominent association of impacted benthic communities
in Mid-Atlantic estuaries is with low dissolved oxygen
concentrations in bottom waters. This condition is
located primarily in Chesapeake Bay.
Harvest of the American oyster (Crassotrea
virginica) traditionally has been one of the major
Mid-Atlantic industries but it is now one of the most
seriously threatened. The decline in the oyster industry
has been precipitous, declining from an annual catch of
133 million pounds in 1880 to about one million pounds
today. The primary causes for the recent demise of the
oyster fishery are the oyster diseases Dermo and MSX,
with overfishing and pollution contributing. Scientists
currently are investigating the feasibility and ecological
consequences of introducing disease-resistant strains of
oysters to Mid-Atlantic estuaries to reestablish the
fishery.
Another important component of the shellfish industry
in the Mid-Atlantic region is the blue crab
(Callinectes sapidus). Annual harvest of blue crabs
has been variable over the past decades, especially for
the Delaware Estuary. This variability likely is due
predominantly to natural environmental factors com-
pounded by fishing pressures. Although the annual
catch of crabs has not decreased significantly, the
catch per unit effort has. The current harvest is being
kept up by increased effort, not neccessarily stable
populations. Scientists are concerned because the
increased fishing pressure would make it difficult for
crab populations to recover if they were impacted by
severe environmental conditions such as occurred in
the Delaware Estuary in 1977 and 1981 (unusually
severe winters).
Each state monitors their estuarine waters for coliform
bacteria and closes those waters to shellfishing when
the concentration reaches a critical level. Shellfishing is
prohibited or restricted in approximately 10% of the
3,660,000 acres of potentially productive shellfish
ground in the Mid-Atlantic estuaries. These closings
can be attributed to contamination from a variety of
sources, including sewage treatment plants, leaking
septic systems, marinas, industry, wildlife, boating and
runoff. The closings also may be administrative in
nature (e.g., inadequate monitoring to ensure the
waters are safe). Considering the degree of urbaniza-
tion in the area, it is encouraging that only a relatively
small percentage of the area is closed to shellfishing.
In addition, improvements in wastewater treatment
have led to a decrease in closed acreage, from 18% in
1985 to 10% in 1995.
Fish abundance, distribution, and condition are consid-
ered indicators of ecosystem health because fish
integrate effects of environmental stress over space
and time. The Mid-Atlantic Region contains many
habitat types, making region-wide judgements about
fish populations difficult. In addition, market forces and
environmental fluctuations obscure causes offish
population declines. Nevertheless, scientists have
documented improvements for some species. For
example, striped bass and American shad populations
are improving after significant historical declines. This
is due to reductions in fishing pressure from restrictions
that have been, or still are, in effect. Scientists also
attribute the observed recovery to improved water
quality. Species composition of shore zone fish in the
Delaware coastal bays indicate impacted environmental
conditions. In contrast, Maryland coastal bays' species
composition suggests a healthy habitat; however,
researchers have observed evidence of initial degrada-
tion in northern areas.
Fish and shellfish contaminant levels throughout
the region appear to be decreasing over time due to
bans and restrictions on the use of such chemicals as
PCBs, DDT, and Kepone and stricter limits on point
source discharges. The contaminant concentrations in
fish and shellfish generally are at or below the national
averages; however, much higher levels may be present
in organisms collected near urbanized areas, such as
Baltimore Harbor. Generally, contaminant levels in
fish and shellfish are higher in the Delaware Estuary
than in Chesapeake Bay or the Delmarva coastal
bays, perhaps reflecting the degree of urbanization in
the estuarine watersheds.
EPA's Environmental Monitoring and Assessment
Program included a pathological examination of
13,467 fish from 177 stations in the Mid-Atlantic
37
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estuaries. Only three per thousand examined were
afflicted with external pathological abnormalities,
indicating a low incidence of such abnormalities. This is
considerably lower than the 10 per thousand determined
by EMAP for the estuaries of the Gulf of Mexico.
• In general, Mid-Atlantic waterfowl populations are in
relatively good condition. The major factors affecting
these birds are local habitat alteration associated with
human development and environmental conditions in
other areas along the birds' migratory path. Of some
concern is the fact that favorable environmental condi-
tions over the past few years in other parts of the
country where migratory birds nest during the summer
have resulted in increased populations of those birds, but
that increase is not being seen in the Mid-Atlantic.
Many of those birds are favoring other wintering sites,
such as along the Gulf of Mexico. One possible explana-
tion is habitat loss in the highly developed Mid-Atlantic.
• The Mid-Atlantic Region has experienced some of the
most rapid population growth, industrial development,
and intensive agriculture in the country. Many organ-
isms relying on the estuaries of the Mid-Atlantic have
suffered. In the states surrounding the estuaries of the
Mid-Atlantic, numerous species of plants and animals are
listed as threatened or endangered and virtually every
county has at least one listed species. It is encouraging
that the threatened and endangered species directly
associated with the estuaries are improving.
Table 1 is an "environmental report card" for the estuar-
ies of the Mid-Atlantic Region. For the entire region and
each of the major systems, we assigned a color repre-
senting the condition of individual indicators. These colors
represent our best judgment summarization of the
information presented in this report. Where multiple
colors are shown, our best estimate is that condition
ranges between the two categories. Problem areas are
determined by individual indicator values. The table does
not imply that problem areas are always man-induced.
The pervasive issues across the Mid-Atlantic Region
include shellfish harvest for oysters and disease in
shellfish. Shellfish, particularly the American oyster,
traditionally have been one of the major living resources
harvested in the Mid-Atlantic states. Oyster harvests
have declined from a high of 13 3 million pounds in 18 80 to
today's annual catch of about one million pounds. Dis-
ease, specifically Dermo and MSX, appears to be one of
the major causes of the recent drastic decline in oyster
populations in Chesapeake Bay and the Delaware
Estuary, with over-harvesting and pollution also playing a
major role in Chesapeake Bay. Although no immediate
solution to the problem is known, researchers currently
are working on the concept of introducing
disease-resistant strains of oysters to the Mid-Atlantic.
With the decline of the oyster industry, the most important
shellfish industry in the Mid-Atlantic Region is now the
blue crab. However, the significantly increased fishing
pressure on the already heavily exploited population is
beginning to take its toll. To avoid a serious impact, both
Maryland and Virginia have placed restrictions on
crabbing in Chesapeake Bay waters.
The Delaware Estuary is characterized by an historical
lack of submerged aquatic vegetation (SAV), due pre-
dominantly to naturally-occurring low water clarity. It is
also one of the most nutrient enriched estuaries in the
world, although harmful phytoplankton blooms are held in
check by other factors, including low water clarity. The
estuary also is highly impacted by lingering toxic contami-
nants associated with urbanization and industrialization of
the Delaware River. The Delaware Estuary has some of
the nation's highest levels of chemical contaminants in
fish and shellfish. Fishing bans or advisories on the
consumption of finfish are posted for portions of the
estuary because of elevated PCB concentrations.
Concentrations of Chlordane in fish exceeding the FDA
action level have been reported in the upper estuary.
Chesapeake Bay continues to be affected by low
dissolved oxygen and is the most hypoxic estuary in the
region. Low dissolved oxygen levels are associated with
nutrient overenrichment and eutrophication. In 1987, the
Chesapeake Bay Agreement stipulated a 40% reduction
in nutrient loading by the year 2000. Nutrient levels in
Chesapeake Bay are declining in response to improved
wastewater management practices, implementation of
best management practices on agricultural lands (nitro-
gen), and bans on certain types of detergents (phospho-
rus). However, there has been more success in control-
ling point sources than nonpoint sources of nutrients.
Historically, high nutrient concentrations have contributed
to prolonged phytoplankton blooms in the Bay. Blooms
occurring during the 1970s and 1980s significantly
reduced water clarity and, as a result, contributed to the
massive loss of SAV that occurred during that time
period. This critical habitat has since partially recovered.
The Delmarva coastal bays are the least degraded
systems in the Mid-Atlantic Region but are threatened by
encroaching urbanization. The coastal bays are moder-
ately enriched, particularly in Delaware, largely from
agricultural sources. Eutrophication is increasingly
noticeable in the dead end canals along developed
shorelines in the Delmarva coastal bays. SAV historically
has been absent from the Delaware portion of the coastal
bays because of high natural turbidity in these systems.
Species composition of shore zone fish in the Delaware
coastal bays indicates impacted environmental conditions.
In contrast, Maryland coastal bays' species composition
suggests a healthy habitat; however, researchers have
-------
(7
,-^jUftia'i'ia.i':
Table 1. Summary of ecological conditions across the Mid-Atlantic estuaries. Colors represent the best estimate of
condition based upon information presented in this report—green for good condition, yellow for a moderate problem,
and red for a problem. A lack of color indicates that inadequate information was available. Where multiple colors are
shown, our best estimate is that condition ranges between the two categories. Problem areas are determined by
individual indicator values. The table does not imply that problem areas are always man-induced.
Mid-Atlantic
Region
Bay
'.'.."•.inf-j
Delaware Estuary
LLKVC-
observed evidence of early stages of degradation in
northern areas.
Coastal waters presently exhibit low levels of nutrients
and chlorophyll. However, evidence suggests that these
levels may be rising, indicating the potential for future
environmental problems.
The mix of colors in Table 1 indicates that the estuaries
of the Mid-Atlantic Region are being impacted. There-
fore, they are at risk and in need of active management
to restore and maintain environmental quality and
sustainable resources. The states, in conjunction with
the Chesapeake Bay Program and the National Estuary
Programs, have instituted environmental
management programs to address
these concerns. We now are seeing
the positive results of these environ-
mental programs.
39
-------
ource6
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DATABASES AND
ORGANIZATIONS -
Chesapeake Bay Program
Delaware Department of Natural Resources &
Environmental Control
a) Division of Water Resources
(shellfish information)
b) Watershed Assessment Branch
(contaminants in fish and shellfish)
Haskin Shellfish Laboratory, Rutgers University,
Bivalve, NJ
Maryland Department of Natural Resources
Maryland Department of the Environment
NOAA, Chesapeake Bay Office, Fisheries Statistics
Database
NOAA, National Marine Fisheries Service, Fishery
Statistics Division
17.5. Fish and Wildlife Service
a) Mid-Winter Migratory Bird Survey, Annapolis, MD
office (waterfowl information)
b) Endangered Species Home Page
http://www.fws.gov/~r9endspp/endspp.html
U.S. EPA, EMAP Database, Environmental Monitor-
ing and Assessment Program-Estuaries database. U.S.
EPA, Atlantic Ecology Division, Narragansett, RI.
Virginia Department of Health, Division of Shellfish
Sanitation
Virginia Marine Resources Commission
43
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Advisory Level: Chemical concentration in fish or
shellfish above which consumption of the fish would
pose a human health risk. Levels may be determined by
various federal or state agencies and may lead to
advisories such as restricted consumption or consump-
tion bans. Typical chemicals for which advisories exist
include PCBs, chlordane, and dioxin.
Algae: Simple rootless plants that grow in bodies of
water (e.g., estuaries) at rates in relative proportion to
the amounts of nutrients (e.g., nitrogen and phosphorus)
available in the water.
Anadromous Fish: Fish that spend their adult lives in
the sea but swim upriver into fresh water to spawn
(e.g., striped bass, American shad).
Anoxic (anoxia): A condition where very little or no
oxygen is present in the water body.
Anthropogenic: Originating from man, not naturally
occurring.
Atmospheric Deposition: The flux (flow) of chemicals
and materials from the atmosphere to the earth's
surface. Depending on the chemical or material, "dry"
deposition (e.g., by particles) can be less than, equal to,
or greater than "wet" deposition (e.g., precipitation).
Benthos: Plants or animals that live in or on the bottom
of an aquatic environment such as an estuary.
Bioaccumulation (bioaccumulate): The uptake and
storage of chemicals (e.g., DDTs, PCBs) from the
environment by animals and plants. Uptake can occur
through feeding or direct absorption from water or
sediments.
Biomagnification: The progressive increase in the
concentration of chemical contaminants (e.g., DDTs,
PCBs, methyl mercury) from the bottom (e.g., phy-
toplankton, benthic animals) to the top of the food web
(e.g., striped bass).
Brackish: Having a salinity between that of fresh and
sea water.
Catch per unit effort (CPUE): A term used in fisheries
science to standardize catch information. For example,
the CPUE for blue crab harvest might be described as the
number of crabs caught per crab pot per day.
Chlorophyll: A group of green pigments found in most
plants, including phytoplankton, which they use for
photosynthesis. The individual pigment generally
measured is chlorophyll a. For the sake of clarity we
use "chlorophyll" throughout this document; however,
we are specifically referring to "chlorophyll a."
Coliform bacteria: A group of bacteria primarily found
in human and animal intestines and wastes. These
bacteria are widely used as indicator organisms to show
the presence of such wastes in water and the possible
presence of pathogenic (disease-producing) bacteria.
Escherichia coli (E. coif) is one of the fecal coliform
bacteria widely used for this purpose.
Community: The assemblage of populations of plants
and animals that interact with each other and their
environment. The community is shaped by populations
and their geographic range, the types of areas they
inhabit, species diversity, species interactions, and the
flow of energy and nutrients through the community.
Contamination: The impairment of water, sediments,
plants, or animals by chemicals or bacteria to such a
degree that it creates a hazard to public and environ-
mental health through poisoning, bioconcentration
(bioaccumulation), or the spread of disease.
Continental Shelf: A gently sloping submarine plane of
varying width between the shoreline of a continent and
the continental slope, a steep slope which extends into
the oceanic abyss.
Crustacean: Any of various predominantly aquatic
arthropods of the class Crustacea, including lobsters,
crabs, shrimps, and barnacles, having segmented bodies,
achitinous exoskeleton, and paired, jointed limbs
(appendages).
DDT: A group of colorless chemicals used as insecti-
cides. DDTs are toxic to man and animals when
swallowed or absorbed through the skin.
Delmarva Peninsula: The land separating Chesa-
peake Bay from the Atlantic Ocean. The Delmarva
Peninsula falls within the states of Delaware, Maryland,
and Virginia, from which it gets its name - Delmarva.
44
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Depurate: To cleanse. For example, shellfish contami-
nated with coliform bacteria can be placed in clean
seawater to depurate. Clean water flowing through the
organism will remove the bacteria over a period of time.
Note that this process does not apply to all contaminants
(e.g., chlorinated pesticides).
Dermo: Oyster disease caused by the protozoan
parasite, Perkinsus marinus.
Detritus: Non-living organic matter (e.g., dead organ-
isms or leaves) in water.
Dissolved Oxygen: Oxygen that is dissolved in water
and therefore available for plants (phytoplankton),
shellfish, fish, and other animals to use. If the amount
of oxygen is too low, aquatic plants and animals may
die. Wastewater and naturally occurring organic matter
contain oxygen-demanding substances that, when
decomposing, consume dissolved oxygen.
Ecosystem: A natural unit formed by the interaction of
a community of plants and animals with their environ-
ment (physical and biological).
Effluent: The discharge to a body of water from
a defined or point source, generally consisting of a
mixture of waste and water from industrial or municipal
facilities.
EMAP: Environmental Monitoring and Assessment
Program - an EPA Office of Research and Develop-
ment research program.
Endangered: A species that is in immediate danger of
becoming extinct and needs protection to survive.
Estuary (estuaries): Regions of interaction between
rivers and near-shore ocean waters, where tidal action
and river flow mix fresh and salt water. Such areas
include bays, mouths of rivers, salt marshes, and
lagoons. These brackish water ecosystems shelter and
feed marine life, birds, and wildlife.
Eutrophic: Highly productive condition, generally the
result of nutrient enrichment in the water column that
may cause algae (e.g., phytoplankton) to bloom.
Eutrophication: A condition in an aquatic ecosystem
where high nutrient concentrations stimulate blooms of
algae (e.g., phytoplankton). Algal decomposition may
lower dissolved oxygen concentrations. Although
eutrophication is a natural process in the aging of lakes
and some estuaries, it can be accelerated by both point
and nonpoint sources of nutrients.
Extinct: A species of plant or animal that is no longer
living.
Fall Line: A break in the flow of all rivers as they
flow from the Appalachian plateau to the Atlantic
coastal plain. This region is characterized by the
transition of steep, rapidly flowing streams to wider,
slower rivers. Large cities are frequently located at the
fall line since this represents the upward limit of naviga-
tion from the sea.
Fecundity: Fish reproduction potential. Fecundity is
usually measured by the number of eggs a female
produces.
Filter Feeder: Animals (e.g., clams and oysters) that
feed by filtering out of the water column small food
items such as detritus, phytoplankton, and zooplankton.
Filter feeders also are known as "suspension feeders."
Fish Consumption Advisory: An advisory issued by
state government agencies and used to reduce human
health risks associated with exposure to chemical
contaminants (e.g., PCBs, DDTs, mercury) found in
fish and shellfish. Advisories may recommend bans and
restricted consumption of specific species in specific
geographical areas of an estuary.
Food Web: An assemblage of organisms in an ecosys-
tem, including plants, herbivores, and carnivores, which
shows the relationship of "who eats whom."
Habitat: The place where a population or community
(e.g., micro-organisms, plants, animals) lives and its
surroundings, both living and non-living.
Hot Spot: A problem area or location where pollution,
especially a chemical concentration, is very high.
Generally located near urbanized areas or point-source
discharges.
Hybrid: The offspring of two animals or plants of
different races, breeds, varieties, species or genera.
Hypoxia: A condition where very low concentrations
of dissolved oxygen are in the water column.
Invertebrates: Animals that lack a spinal column or
backbone, including molluscs (e.g., clams and oysters),
crustaceans (e.g., crabs and shrimp), insects, starfish,
jellyfish, sponges, and many types of worms that live in
the benthos.
Land Cover: Anything that exists on, and is visible
from above, the earth's surface. Examples include
vegetation, exposed or barren land, water, snow, and
ice.
Land Use: The way land is developed and used in
terms of the kinds of anthropogenic activities that occur
(e.g., agriculture, residential areas, industrial areas).
45
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Larvae (larva): Early form of an animal that is unlike
its parent and must metamorphose before assuming
adult characteristics.
Macroalgae: Non-rooted aquatic plant. Commonly
referred to as "seaweed".
Marsh: A wetland where the dominant vegetation is
non-woody plants, such as salt grasses and sedges, as
opposed to a swamp, where the dominant vegetation
consists of woody plants such as trees and shrubs.
Mid-Atlantic Estuaries: In this document, they are
defined as Delaware Bay and its tributaries, Chesa-
peake Bay and its tributaries, and the coastal bays of
the Delmarva Peninsula.
Mid-Atlantic Region: For the purpose of this report
this is defined as the watershed of the Chesapeake Bay,
Delaware Estuary, and the Delmarva coastal bays. It
includes all or portions of Virginia, West Virginia,
Maryland, Delaware, Pennsylvania, New Jersey, and
New York.
MSX: An oyster disease caused by the protozoan
parasite, Haplosporidium nelsoni.
Nonpoint Source: Refers to pollution that enters water
from dispersed and uncontrolled sources, such as
surface runoff, rather than through pipes.
Nutrients: Essential chemicals (e.g., nitrogen and
phosphorus) needed by plants for growth. Excessive
amounts of nutrients can lead to degradation of water
quality by promoting excessive growth, accumulation,
and subsequent decay of plants, especially algae
(phytoplankton).
Pathological condition: Abnormal anatomic or
physiological condition.
Pesticides: A general term used to describe chemical
substances that are used to destroy or control insect or
plant pests. Many of these substances are manufac-
tured and do not occur naturally in the environment.
Others are natural toxins that are extracted from plants
and animals. Chlordane, DDT, and Kepone are ex-
amples of pesticides.
Polychlorinated Biphenyls (PCBs): A group of
closely related and manufactured chemicals made up of
carbon, hydrogen, and chlorine. PCBs can persist for a
long time in the environment and they can bioaccmulate
and biomagnify in aquatic food webs. PCBs are
suspected of causing cancer in humans. They are an
example of an organic contaminant.
Phytoplankton: Small, often single-celled plants that
live suspended in bodies of water (e.g., estuaries).
Phytoplankton Bloom: A sharp increase in the
population of phytoplankton, as often occurs in the
spring, summer, or fall in different areas of an estuary.
Point Source: Refers to a source of pollutants from a
single point of conveyance, such as a pipe. For ex-
ample, the discharge from a sewage treatment plant or
factory is a point source.
Polycyclic Aromatic Hydrocarbons (PAHs): A class
of chemical compounds composed of fused six-carbon
rings. PAHs are commonly found in petroleum oils
(e.g., gasoline and fuel oils) and are emitted from
various combustion processes (e.g., automobile ex-
hausts, electric companies).
ppm: Parts per million; equivalent to microgram per
gram (ug/g) or milligrams per liter (mg/L).
ppt: Parts per thousand (used as a measurement of
salinity).
Recruitment: Entry of fish into a fishery either through
the attainment of a size large enough to be taken by a
fishery or from an external source (e.g., fish entering an
estuary from the ocean). Recruitment also can refer to
fish reaching sexual maturity for non-exploitable spe-
cies.
Salinity: A measurement of the amount of salt in
water. Generally reported as "parts per thousand" (i.e.,
grams of salt per 1,000 grams of water) and abbreviated
as "ppt" or %o. Salinity also is reported as "practical
salinity units" and abbreviated as "psu."
Salt Marsh: Class of wetlands consisting of salt-
tolerant grasses and other plants that are periodically
exposed to salt water flooding.
Sediment: Mud, sand, silt, clay, shell debris, and other
particles that settle on the bottom of rivers, lakes,
estuaries, and oceans.
Seine Survey: A fish capturing procedure where fish
are enclosed and drawn to shore using a large net with
sinkers on one edge and floats on the other.
Shellfish: An aquatic animal, such as a mollusc (e.g.,
clams, oysters, and snails) or crustacean (e.g., crabs
and shrimp), having a shell or shell-like external skeleton
(exoskeleton).
Spatial Extent: As used in this document, the total area
(water and land) where a condition (e.g., shellfish
diseases) or populations of plants and animals are found.
Spawning: Sexual reproduction in fish.
Species: A group of individuals similar in certain
46
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morphological and physiological characteristics that are
capable of interbreeding and are reproductively isolated
from all other such groups.
Stratification: The formation, accumulation, or deposi-
tion of materials in layers, such as layers of fresh water
overlying higher salinity water (salt water) in estuaries.
Submerged Aquatic Vegetation (SAV): Rooted
vegetation that grows under water in shallow areas of
estuaries where light can penetrate to the bottom
sediments.
Substrate: A surface on which a plant or animal grows
or is attached.
Suspended Sediments: Particles of soil, sediment,
living material, or detritus suspended in the water
column.
Threatened: A species that is likely to become endan-
gered if not protected.
Tidal Mud Flat: The unvegetated shore exposed to air
during low tide.
Tissue Residues: Chemical contaminants present in
fish or shellfish and usually concentrated in the tissues
(e.g., muscle, liver) as opposed to the bones or shell.
Toxic Substances (or material): Chemical compounds
that are poisonous, carcinogenic, or otherwise directly
harmful to plants and animals.
Trace Metals: Metals such as silver, copper, lead,
cadmium, zinc, and mercury that normally occur in
water and sediments at concentrations less than one
part per million (ppm).
Tributary (Tributaries): A body of water flowing into
a larger body of water. For example, the Potomac
River is a tributary of Chesapeake Bay.
Trophic level: A grouping of organisms that uses the
next lower grouping of organisms as a food source.
Used to describe where on the food web (see definition
of Food Web in this glossary) organisms feed. For
example herbivores feed on plants, and carnivores feed
on herbivores.
Turbidity: The clouding of a naturally clear liquid due
to suspended solids. Because turbidity reduces the
amount of light penetrating the water column, high
turbidity levels may be harmful to aquatic life (e.g.,
SAV).
Virulent: Extremely poisonous or venomous. Regard-
ing a disease, virulent is defined as the ability to rapidly
overcome bodily defensive mechanisms.
Water Clarity: Measurement of how far you can see
through the water. The greater the water clarity, the
further you can see through the water.
Water Column: The water between the surface and
bottom of a river, lake, estuary, or ocean.
Watershed: The entire area of land whose runoff of
water, sediments, and dissolved materials (e.g., nutri-
ents, contaminants) drain into a river, lake, estuary, or
ocean.
Wetlands: An ecosystem type, generally occurring
between upland and deepwater areas, that provides
many important functions, including fish and wildlife
habitat, flood protection, erosion control, water quality
maintenance, and recreational opportunities.
Young-of-the-Year: Fish produced in the current
year's spawn. Fish less than 1 year old.
Zooplankton: Small, sometimes microscopic animals
that float in the water. They feed on detritus, phy-
toplankton, and other zooplankton. They are eaten by
fish, shellfish, whales, and other zooplankton.
47
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'ecnntca
Criteria used for presenting
indicator data
Stratification
Sigma-t is a measure used in physical oceanography to
describe water density. It is a measurement of the
density that a parcel of water with a given temperature
and salinity would have at the surface (i.e., at atmo-
spheric pressure), and is expressed as (density - 1) *
1000 (Strobel et al, 1995). The degree of water
column stratification is determined from the difference
in sigma-t between surface and bottom waters. The
three categories used to summarize stratification are
low (sigma-t difference less than 1), moderate (sigma-t
difference between 1 and 2), and high (sigma-t differ-
ence greater than 2) stratification.
Water Clarity
The clarity of estuarine water is determined by a
measure of the attenuation of sunlight through the water
column. It is measured by an attenuation coefficient,
which is the natural logarithm of the ratio of the inten-
sity of light of a specified wavelength on a horizontal
surface to the intensity of the same wavelength light on a
horizontal surface 1 m deeper in the water (Strobel et al.,
1995). We define poor water clarity as an attenuation
coefficient greater than 2.30, which is equivalent to the
transmission of 10% of the light incident on the water
surface to a depth of 1 m. Fair water clarity is defined
for an attenuation coefficient between 1.39 and 2.30,
which is equivalent to the transmission of 25% of the light
incident on the water surface to a depth of 1 m. Good
water clarity refers to an attenuation coefficient of less
than 1.39.
Nutrients
The nutrient levels of Figure 8 show the concentrations
of dissolved inorganic phosphate (DIP) and dissolved
inorganic nitrogen (DIN, calculated as the combined
values of dissolved inorganic nitrate and ammonium
ions). These values were measured in surface waters
during the summer months. The conditions for Chesa-
peake Bay reflect data collected annually from 1985
through 1995, while the Delaware Estuary data were
collected in 1986 and 1987, and the coastal bays data
were measured in 1993.
The classification scale for DIN is: good, < 0.15 mg N/L
(ppm); fair, 0.15 - 0.45 ppm; and poor, > 0.45 ppm. For
DIP, the scale is: good, < 0.02 mg P/L (ppm); fair, 0.02
- 0.06 ppm; and poor, > 0.06 ppm. For mesohaline
waters (medium saltiness, defined as salinities from 5-18
ppt), the criterion for 'good' DIP levels is <0.01 ppm.
To be conservative with respect to statistical confi-
dence, a region is classified using the upper limit of its
90% confidence interval. For example, the average
DIP and standard deviation in Assawoman Bay is 0.090
± 0.033 ppm. Thus 90% of all DIP values measured in
this bay are 0.156 ppm or less (calculated as the mean
plus two standard deviations). Therefore, Assawoman
Bay is designated as 'fair' based on this conservative
upper limit for DIP.
The boundary between good and fair nutrient categories
are the values set by the Chesapeake Bay Program as
the criteria necessary to promote continued survival of
submerged aquatic vegetation (SAV) in Chesapeake
Bay (Chesapeake Bay Program, 1992). The boundary
between fair and poor is three times the lower criteria,
comparable to the various criteria used in different
studies. Caution is advised in drawing conclusions
based on these classification limits for several reasons.
First, the SAV-related criteria were developed specifi-
cally for use in Chesapeake Bay and their applicability
in other estuaries is uncertain and currently is under
investigation. Also, the relationships between nutrient
enrichment and eutrophication are complex and involve
more details than were discussed in the text. For
example, excess phosphorus promotes eutrophication in
the less salty tributaries, while nitrogen encourages
blooms in saltier open waters. Therefore, while the
'poor' DIN conditions in the upper Chesapeake Bay
and the Delaware Estuary are indications of high
nutrient concentrations, they do not necessarily imply
high potential for eutrophication. Furthermore, in some
places such as the Delaware Estuary, blooms are
inhibited by muddy waters despite high levels of nutri-
ents. In summary, Figure 8 is an accurate comparison of
nutrient concentrations in the Mid-Atlantic Region
48
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^Je
estuaries. However, the interpretation of nutrient
enrichment with respect to eutrophication should be
performed carefully and is an area of active research.
Phytoplankton
Chlorophyll a is a measure of the green pigment in
phytoplankton. Concentrations of chlorophyll a in
surface waters measured during the summer months is
used to represent phytoplankton levels. The conditions
for Chesapeake Bay reflect data collected annually from
1985 through 1995, the Delaware Estuary data were
collected in 1986 and 1987, and the coastal bays data
were measured in 1993. The scale for the criteria is:
good, < 15 mg/L; fair, 15-30 mg/L; poor, > 30 mg/L. To
be conservative with respect to statistical confidence, a
region is classified according to the upper limit of its 90%
confidence interval (see note regarding nutrients for
further explanation). The boundary between good and
fair nutrient categories are the values set by the Chesa-
peake Bay Program as the criteria necessary to promote
continued survival of submerged aquatic vegetation
(SAV) in Chesapeake Bay. The boundary between fair
and poor is comparable to the various criteria used in
different studies.
Dissolved Oxygen
Dissolved oxygen (DO) is a fundamental requirement
for the maintenance of balanced indigenous populations
offish, shellfish, and other aquatic biota. Most estuarine
populations can tolerate short exposures to low dis-
solved oxygen concentrations. However, prolonged
exposures to less that 60% oxygen saturation may result
in altered behavior, reduced growth, adverse reproduc-
tive effects, and mortality. Exposure to less than 30%
saturation (~ 2 mg/L for seawater at summer tempera-
tures) for one to four days causes mortality to most biota,
especially during summer months, when metabolic rates
are high. Stresses that can occur in conjunction with low
dissolved oxygen (e.g., exposure to hydrogen sulfide or
ammonia) may cause as much, if not more, harm to
aquatic biota than exposure to low dissolved oxygen
concentration alone. In addition, aquatic populations
exposed to low dissolved oxygen concentration may be
more susceptible to adverse effects of other stressors
(e.g., disease, toxic substances).
The biologically important value is species-dependent,
and the regulatory values vary among states in the
Region. For comparison purposes in this report, thresh-
olds of 2 and 5 mg/L are used for DO measured in the
bottom waters. A concentration of approximately 2 mg/
L often is used as a threshold for oxygen concentrations
thought to be extremely stressful to most estuarine
biota. A threshold concentration of 5 mg/L is used by
many states to set water quality standards. The U.S.
EPA, as of this writing, has not established DO water
quality criteria for estuarine and marine waters, but is in
the process of developing the database from which
criteria will be developed. Data available for prepara-
tion of Figure 13 were from daylight observations.
Region-wide estimates of possible night time depression
of DO were not available.
Sediment Contamination
Informal guidelines for interpreting sediment contamina-
tion based on many field and laboratory studies have
been developed. These guidelines attempt to relate
observed chemical concentrations to concentrations
known to either cause biological effects in laboratory
spiked-sediments or spiked-water experiments, or be
associated with biological effects in field studies.
Examples of these approaches are the Puget Sound
(Malek, 1992) apparent effects thresholds (AETs); State
of Washington (Phillips, etal, 1988) screening level
concentrations (SLCs); Long and Morgan's (1990), as
updated in Long et al. (1995), effects range median
(ER-M) and effects range low (ER-L) concentrations;
and refinements to Long and Morgan by MacDonald
(1994) for potential effects level (PEL) and threshold
effects level (TEL). These approaches benefit from the
weight of evidence afforded by large data sets associat-
ing sediment contaminant concentrations with biological
effect, but suffer from a failure to incorporate the effects
of multiple chemicals in complex mixtures, as the chemi-
cals exist in the environment.
While these approaches have shortcomings, they are the
best overall benchmarks available for assessing sedi-
ment contamination for a wide variety of contaminants.
The Long and Morgan ER-Ls and ER-Ms and
MacDonald's TELs and PELs are used in this report to
summarize sediment contamination in estuaries of the
Mid-Atlantic Region. The "no risk" category represents
areas with no contaminants in excess of ER-L or TEL
values. The "minimal risk" category represents areas
with contaminants in excess of threshold ER-L/TEL
values but below higher probable-effect ER-M/PEL
values. The "potential risk" category represents areas
with contaminants in excess of probable-effect ER-M/
PEL values. It should be noted that this categorization
does not account for the potential role of sub-lethal
effects of contamination, such as susceptibility to
disease or impairment in growth and reproduction.
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.Uecknlca
Benthic Condition
The numbers of animals of each species observed at a
location has been a basic measure used by benthic
ecologists to describe the condition of the benthic
community. More recently, estuarine scientists have
been conducting research on ways to combine individual
pieces of information about benthic communities into a
single measure that tracks the condition of benthic
communities, similar to how the Dow Jones average is
used to track the "condition" of the stock market. Two
examples of this approach for the Mid-Atlantic Region
are the Chesapeake Bay benthic restoration goal index
(RGI) and the EPA Environmental Monitoring and
Assessment Program (EMAP) benthic index (BI). We
have used information from the Chesapeake Bay and
EMAP approaches to characterize the condition of
benthic communities in the Mid-Atlantic Region.
The RGI was developed by examining benthic commu-
nities from areas relatively free of pollution and compar-
ing them with those in areas more affected by pollution
(Weisberg et al, 1997). A score is assigned based
upon attributes of the benthic community, such as
number of species, total number and mass of organisms,
presence of organisms in deeper layers of the sediment,
and relative abundance of species that are tolerant of
pollution. The scores for each of the attributes are
averaged to give an overall rating of the community's
condition, then aggregated to the following three catego-
ries— meets goals, impacted, and severely impacted
(USEPA, 1995).
The EMAP BI is an attempt to reduce many individual
measures of the benthic community into a single number
that has a high level of discriminatory power between
good and poor environmental conditions (Strobel et al.,
1995; Paul et al., 1997). Independent measures of
environmental conditions, such as dissolved oxygen
concentrations and sediment contamination levels, are
used to select stations that are in good or poor condition
for development of the BI. Parameters in the BI include
a measure of species diversity and measures of pollution
intolerant organisms. A positive BI indicates good
conditions, while a negative value indicates impacted
benthic community. Severely impacted represents the
10% worst areas as observed by EMAP during 1990-93
(Delaware Estuary Program, 1996).
Fish/Shellfish Advisories
Fish or shellfish consumption advisories are issued by
state government agencies to protect human health by
reducing the health risks associated with eating fish or
shellfish contaminated with chemical pollutants. Advi-
sories are recommendations to limit consumption of
certain fish or shellfish taken from contaminated areas.
These advisories are issued when the levels of chemical
pollutants present in the fish or shellfish exceed an
action level. Although states use different methods for
calculating the action levels, the common threads are
that they are based on the presence of high concentra-
tions of pollutants in the fish or shellfish, and that they
are meant to protect human health. Two basic ap-
proaches to deriving action levels are: 1) using the U.S.
Food and Drug Administration (FDA) action levels; and
2) conducting a risk assessment that factors in such
things as typical meal size, frequency of consumption of
fish or shellfish, average body weight of consumer,
pollutant concentration in the fish or shellfish, and risk of
causing cancer. Due to these differences in the calcula-
tion of action levels by different states, the fish or
shellfish contaminant concentrations in one state's
advisory area may not be the same as another state's,
but in both areas the concentrations would be high
enough to cause concern about possible human health
risk. Therefore, fish or shellfish advisories are used in
this report to highlight areas of concern rather than to
compare contaminant levels in fish and shellfish.
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EPA903-R-98-012
Condition of the Mid-Atlantic Estuaries
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