Chesapeake Bay Wetlands

Suzanne Dome, Mike Lewis, Rick Moran, Doug Nyman

May 2009

ES 767, Wetland Environments

Emporia State University



The Chesapeake Bay located on the northeast coast of the United States is the largest estuary in the USA. The bay is home to 3,600 species of plants and animals. In the winter 1 million waterfowl reside in the bay.  The watershed is also the permanent home to 16.6 million people. In the last few decades mitigation efforts have taken place to minimize the impact human occupation has on the wetlands and wildlife.


The bay is surrounded by the states of New York, Pennsylvanian, Delaware, Maryland, Virginia, West Virginia, and the District of Columbia. It is 320 km long with 19,000 km of shoreline and a surface area of 11,600 square kilometers.  It opens up to 55 km wide where the Potomac enters the bay.  The bay's average depth is 7 meters with some deep troughs exceeding 30 meters. Half the water comes from salt waters of the Atlantic Ocean.   The remaining 50% is from fresh river water and rainfall. The Susquehanna River contributes half of that fresh water.

Several protected wetlands are around the Bay including: Blackwater National Wildlife Refuge in Cambridge, MD; Wicomico Wetlands in Somerset County, MD; Great Dismal Swamp National Wildlife Refuge in Virginia; Rappahannock River Valley National Wildlife Refuge in Virginia; Presquile National Wildlife Refuge in Virginia; James River National Wildlife Refuge in Virginia; and the Plum Tree Island National Wildlife Refuge also in Virginia.

From 1998 to 2008, 13,000 acres of wetlands were established or restored around the Bay. Ongoing land acquisition is occurring by the surrounding states for preservation and restoration. Most recently the 996 acre Dover Farm was purchased for restoration.


The Chesapeake Bay’s Atlantic margin contains a buried crater. It formed in the Late Eocene 35 million years ago from an asteroid or comet impact.  The initial impact created a deep central crater 38 km across and an 85 km wide broad outer zone.  Fracturing is estimated to occurred down to a depth of 11 km.  At the time of impact the area was part of the Atlantic Ocean under several 100’s of meters of water.  In 2006 the Chesapeake Bay Impact Structure Deep Drilling Project drilled a continuous core near the center of the impact site north of Cape Charles to a depth of 1766 meters.  The core found the crater filled with 433 meters of fine grained marine sediments consistent with stratigraphic sequences indicative of sea level changes.  Below the sediments to a depth of 1393 meters large displaced granitic blocks were encountered that fell back in after the initial impact. Below that the host rock to total drilled depth is brecciated from the impact shock. Studies of the impact fracturing are striving to determine their possible influence on current local fresh water reservoirs.


The Chesapeake bay area is a vast shallow estuarine complex including beaches, dunes, mudflats, open water and submerged water plants, tidal and freshwater marshes and lakes. A wide variety of vegetation provides habitats for various endangered species.

A dominant plant species in the area is wild rice. Submerged aquatic vegetation includes rope eel grass and widgeon grass, Zostera marina and Ruppia maritima respectively. Canadian and American water weed is also common, as well as tubers and water milfoil. Marshy sectors support Spartina grasses, freshwater sweet flag and phragmites. The forested ares include loblolly pine, red maple, black gum, green ash and bald cypress. This large layered estuarine habitat supports as many as 25,000 water fowl during winter months.

Submerged aquatic vegetation is used as a key indicator of bay health. They are not only an engine oxygenating the bay floor keeping anoxic environments down. They are also a habitat and food source for many of the bay’s animals. Many crustaceans feed and live on the bay
grasses as the base of the bay’s food chain. The bay grasses also improve water clarity by trapping sediment that would otherwise
cloud the water; this permits increased photosynthesis and therefore more vigorous grass growth, creating a positive feedback loop.

In 2008 the bay saw a large increase in bay grasses over the prior year. Estimates of grass bays have increased from 64,917 acres in 2007 to 76,861 acres in 2008, the fourth largest increase since record keeping began in 1984. The expansion of the Susquehanna Flats in the north and the return of eel grass fields in the lower bay account for much of this increase. This increase is welcome news to many concerned by the current state of the bay.

Invasive species have presented a problem to native flora and fauna of the Chesapeake which are already struggling against the pressures of increased pollution and habitat loss. Nutria, Mute Swans, Zebra Mussels, Phragmites, Purple Loostrife, and Water Chestnut all are species from outside the Chesapeake. These are supplanting other native species in competition for survival in the Chesapeake.  


The Chesapeake Bay Estuary is home to thousands of different plants and animals.  From the fish and aquatic animals to birds and mammals that live in the area around the bay itself. 

About 350 species of fish are found in Chesapeake Bay.  Some species are year-round residents of the bay.  Others migrate from the ocean or freshwater tributaries arriving at different times of the year to feed and spawn.  The resident fish of the Chesapeake Bay fall into two categories, freshwater and estuarine.  The freshwater fish live in non tidal areas of the tributaries that feed Chesapeake Bay.

The migratory fish are put into three categories, marine, anadromous, and catadromous.  Marine fish live and spawn in coastal waters with salinities over 30 ppt.  They move into the lower bay during different times of the year.  Few of these fish species travel into the Maryland portion of the Bay.  Anadromous fish migrate from the ocean to fresh water to spawn.  An example of the Anadromous fish is the American shad.  Catadromous fish migrate from fresh water to the costal waters to spawn.  The American eel is the only catadromous fish that live in the Bay area.  Depending on the temperature where they live, estuarine fish live throughout the Bay and its tidal tributaries. 

Every different species of fish that is found in the Bay has its own place in the food chain of the Chesapeake Bay.  Small filter feeders like Atlantic menhaden and Bay anchovies are critical in the lower food chain.  They feed on plankton and are a major part of the diet of the striped bass and bluefish which are both economically valuable species to the Bay area.

The birds that inhabit the Chesapeake Bay in the bay’s woodland and shoreline habitats constitute some of the most beautiful and vulnerable species.  These birds include ospreys, bald eagles, many other species.  Waterfowl, like ducks, geese, and swans.  Most are migratory, however, some Canada geese and mute swans have taken up residence in the bay.  Several shorebirds live in the Chesapeake Bay including ibis, willets, plovers, sandpipers, oystercatchers, and ruddy turnstones.  Most of these birds are only found in the Bay during certain seasons.  Egrets and herons are wading birds that can be found in the Bay.  The only two residence wading birds living in the Bay are the great blue heron and the black crowned night heron.  Egrets and other types of herons migrate south for the winter.  There are several types of birds referred to as “aerial gleaners” that feed on fish or insects.  These birds are gulls, terns, cormorants, and barn swallows.  Most of the terns are only in the Bay during late spring, summer and early fall.  They leave the Bay during the cold winter months.  Gulls can be found there year around. 

Many types of mammals can be found in the Chesapeake Bay region.  Some live on land and some live in the water and some spend there time in both environment.  Deer, squirrels and raccoons, rabbits and foxes are some of the most common mammals that live on the land.  The semi aquatic species that live in the Bay include beavers, muskrats, and river otters.  The aquatic mammals that live in the Bay dolphins and an occasional lost manatee. 

Reptiles and amphibians are also found in the Chesapeake Bay.  The most common for the region are turtles, snakes and lizards.  The most common amphibians found in the Chesapeake Bay are frogs, toads, newts, and salamanders.

Dozens of species of crabs and shellfish are found in the Chesapeake Bay wetlands and shorelines.  Oysters, blue crabs are well known are common where amphipods and isopods are not as familiar but are abundant in the Bay region.  The crabs and shellfish fall under two categories in the Bay: mollusks and arthropods.  Mollusks include bivalves, which have two valves or shells and a foot.  Clams, oysters, mussels and scallops are this type of mollusks.  Snails, which are gastropods have only one shell. Cephalopods, which have an internal shell, an example of this is a brief squid.  The arthropods have an exoskeleton or their skeleton is on the outside of their body such as crustaceans, like crabs, shrimps, barnacles, amphipods and isopods.  Horseshoe crabs, which are not true crabs and are more closely related to spiders and scorpions are also found in the Chesapeake Bay Estuary.  Examples of the invertebrates in the Bay:

Population and industrial

The Chesapeake Bay watershed is one of the historical population centers of the United States. Today the watershed is home to over 16.6 million people, an 18% increase over 20 years ago, and is expected to rise to 20 million by 2030. The primary component of pollution in the bay watershed is from storm water runoff from impervious surfaces in urbanized areas such as roads and parking lots. 

Unlike run-off or airborne pollution, agriculture based pollutants have no control mechanisms. Nitrogen used across the watershed by agricultural industry runs into the bay and presents a serious problem to water quality. Nitrogen fuels algae blooms that can consume all oxygen in the water creating an anoxic event.

The effects of land use can be seen in this map from in the poor water quality associated with the high population centers around the bay as well as in agricultural areas of the watershed.

Health of Freshwater Streams in Watershed

Image courtesy of the Chesapeake Bay Program, used with permission


Heavy fishing during the past 200 years has decimated many of the fish populations that once thrived in the Chesapeake. Sturgeon, once abundant, are now nearly unknown in the bay. The primary industrial fisheries include Blue Crab, Oysters, and Rockfish or Striped Bass. Crab populations are currently at an all time low and Oyster populations are equally depressed. Current debate has centered on the question of introducing new pollution tolerant species from Asia to replace the position of native oysters in the Chesapeake ecosystem.

The Blue Crab is perhaps the most iconic of the Chesapeake’s production crops. Poor water quality has continued to expand a growing dead zone in the bay however, killing off the clams and worms on which the crabs feed. In 1990 the estimated blue crab population was 791 million, as of 2007 the population was 260 million. 

Even while these populations have plummeted both Virginia and Maryland have permitted catch counts higher then what is thought to be sustainable according to the Chesapeake Bay Program. This combined with the already record low crab stocks mean a larger proportion of the population is being harvested making long term viability more uncertain.

Restoring Water Quality

The Chesapeake watershed is huge, and it encompasses a myriad of land-uses and natural land types. Any effort to improve the bay’s water must tackle the problem from many sources. Currently, watershed management area wastewater facilities are being upgraded to reduce nitrogen output into the bay. However, such gains have been undone by even faster suburban development in the region. Agricultural run-off may be curbed by a small measure by volunteer management plans that are site specific in order to reduce nitrogen and nutrient run-off. While pollution originates from many sources, land-use tends to exacerbate pollution issues. Currently no mandatory long-term plan is in place for Chesapeake Bay area land-use management.

Pollution measures in the individual tributary watersheds have had some mixed success in reducing some pollutants. Phosphorous levels have been dropping since the mid-80s in the Susquehanna, Potomac, and Patuxent Rivers. However, simultaneously the Susquehanna and Potomac has seen an increase in nitrogen levels although the rate of increase is slowing. 

The bay continues to be in danger. The Chesapeake Bay Foundation (CBF) states the reasons are many but among the most important is the EPA’s lack of action on behalf of the bay. Since the Chesapeake crosses multiple administrative units it’s virtually impossible for any agency at the state level to attempt to guide the bay’s restoration as an integral ecosystem. According to the Chesapeake Bay Foundation the EPA has failed to enforce the federal Clean Water Act or to actively attempt to clean up the bay environment by 2010 as agreed in 2000.

Economic value of the bay was estimated at over $1 trillion four years ago according to the CBF this includes activities like fishing, tourism, and boating.

Who's killing the bay

Image courtesy of Tom Chalkey, used with permission


The area is home to a diverse and complex ecosystem heavily impacted by human inhabitation in the last 300 years. In the last 3 decades prior and ongoing studies have influence policies towards protecting and restoring habits along and in Chesapeake Bay. The significance of storm runoff has come to the forefront, and mitigation efforts are occurring to reduce nitrate influx into the bay. Many areas considered uninhabitable were added to wildlife refuges in the mid 20th century. And currently an active program of land acquisition is occurring by surrounding states to add to nature conservatories.


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U.S. Geological Survey. Chesapeake Bay: Measuring Pollution Reduction.

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