Case Study: The Chesapeake Bay
Fifty years ago the Chesapeake Bay was one of the most beautiful and productive estuaries on our planet. Water quality was good and extensive grass beds were an integral part of the Bay's ecology. The aquatic vegetation provided habitat and sanctuary for many species of marine life, and was a primary source of food for wintering waterfowl. The vegetation helped stabilize the Bay's bottom, improved water clarity, and increased the estuaries' dissolved oxygen. Oysters were an important part of the Bay ecosystem; their reefs provided habitat for a wide variety of marine life, and they filtered a large amount of nutrients which helped improve water quality. Waterfowl, finfish, shellfish, and the blue crab were all relatively abundant throughout the Chesapeake Bay at the middle of the 20th century. Over the past half century most of the aquatic vegetation disappeared. The waterfowl that fed primarily on the Bay's underwater grasses and couldn't adapt to feeding on the land now fly over the Chesapeake Bay to winter further south. The Bay's common loon population has been reduced approximately 90% following almost a decade of poor recruitment of juvenile Atlantic menhaden, it's primary food source. Declining water quality has stressed the Bay's living resources and fish kills are becoming more frequent throughout most of the Bay. There are warning signs that indicate the bottom of the food chain has been affected by pollution. The number of ecologically less desirable species of phytoplankton (algae) such as bluegreen algae and potentially toxic dinoflagellates (e.g. Pfiesteria) is increasing. Bacteria levels in the Bay are among the highest known to exist in any estuarine environment. Zooplankton, the food base for many fish species, are declining throughout the main stem of the Bay during the summer growing season, similar declines have also been documented during early spring and fall in the lower Bay. In contrast, comb jellyfish, an important predator of zooplankton and fish larvae, has dramatically increased in the mid-Bay. The numbers of harmful algae blooms that are potentially harmful to humans, and have been proven lethal to aquatic life, are increasing in the Bay. These blooms also lower the Bay's dissolved oxygen and block sunlight preventing underwater grasses from growing. The Chesapeake's commercial fisheries are but a remnant of what they were fifty years ago, even the forage fish are at historically low densities. Data collected from 1985 to 1999 by the Chesapeake Bay Program (CBP) indicate that blue crab larvae entering the Chesapeake Bay from our coastal waters have declined approximately 70% at the mouth of the Bay. Shellfish populations are only a fraction of their historic levels because of over harvesting, loss of habitat, pollution, and disease, and now one of the Bay's top predators, the striped bass, has been diagnosed with a disease that may significantly reduce its population.
Among the major nutrients that enter the bay are 272 million kg (600 million pounds) of nitrogen and 14 million kg (30 million pounds) of phosphorus.The nitrogen and phosphorus come from three major sources. The first source is water discharged from sewage treatment facilities that carries high amounts of nutrients from human waste. The second source is animal waste produced by concentrated animal feeding operations generating large amounts of manure that can make its way into nearby streams and rivers.The third source is fertilizer that is spread on both agricultural fields and suburban lawns. Much of this fertilizer leaches out of the soil and into local streams, eventually making its way to the Chesapeake Bay. When these nutrients reach the bay, the algae in the bay experience an explosive population growth that is known as an algal bloom.
Increased sediments are also an issue in the Chesapeake Bay. Sediments are soils washed away from fields and forests as well as soils washed away from the banks of streams and the ocean shoreline. The current estimate is that 8.2 billion kg (18.7 billion pounds) of sediments come into the bay each year.The tiniest soil particles stay suspended in the water, make the water cloudy,and prevent sunlight from reaching the grasses that have been historically abundant in the bay. These grasses are important because they serve as a habitat for fish and blue crabs (Callinectes sapidus).
The Chesapeake Bay also receives inputs of anthropogenic chemicals. Many of these are pesticides that are sprayed throughout the water-shed for growing crops and controlling pests.They can arrive in the bay by direct application over water, by running off the surface of the land when it rains, or by being carried by the wind immediately after application. The bay also contains pharmaceutical drugs that pass through the human body and enter sewage treatment plants, eventually discharging into the streams and rivers that feed the bay. In 2009, the U.S.Fish and Wildlife Service announced that anthropogenic chemicals appeared to be responsible for the discovery that 23 percent of male largemouth bass and 82 percent of male smallmouth bass developed into hermaphrodites with male sex organs that grow female eggs. This impact is not only a concern for fish, but also a concern for humans who share many similarities in their endocrine systems.
The enormous size of the Chesapeake Bay watershed means that cleaning it up will require a monumental effort. In 2000 the surrounding states formed a partnership along with multiple federal departments to develop the Chesapeake Bay Action Plan. This plan outlines a series of goals to reduce the impacts of nutrients,sediments, and chemicals coming into the bay. In 2010 the governors of the surrounding states, along with many local leaders,announced that many of the Action Plan’s goals were being met, including a reduction in nitrogen, an increase in water clarity, and an increase in the number of blue crabs. In fact, the improved water quality combined with earlier reductions in the number of blue crabs that could be harvested allowed the blue crab population to increase 60 percent from 2009 to 2010. This represents the largest crab population in the bay in 13 years. The story of Chesapeake Bay serves as an excellent example of the wide variety of pollutants that can impact aquatic ecosystems and of effective and substantial efforts that can only be made when all parties work together toward a common goal. 
Sources: Chesapeake Bay Program: A watershed partnership,http://www.chesapeakebay.net/index.aspx?menuitem=13853; U.S. Fish and Wildlife Service, News Release, April 22, 2009,http://www.fws.gov/ChesapeakeBay/pdf/IntersexPR.pdf.