Plants and animals currently living and reproducing in a habitat outside their historic native range are considered "exotic." Exotic species become "invasive" when they negatively impact an ecosystem or species by encroaching on habitat and food sources. Overfishing, along with pollution, diseases, and other stressors, has affected the populations of many fish and shellfish in the Bay and, in cases like the American shad, contributed to closures of commercial fisheries in the Bay. The Bay provides rich grounds for both commercial and recreational fisheries of the Chesapeake's signature species, including blue crabs, oysters, American shad, Atlantic menhaden, and striped bass. The fishing industry is essential to the Chesapeake Bay character and economy. Too much sediment makes the water cloudy, which keeps sunlight from reaching underwater grasses smothers oysters and other bottom-dwelling species degrades streams clogs ports and channels and binds with pollutants, which then spread throughout the Bay. Sediments come from the erosion of land and stream banks (watershed sources) and shoreline and nearshore areas (tidal sources). More than 18.7 billion pounds (8.5 billion kg) of sediment enter the Bay each year. SedimentationĮxcess sediments also contribute to the Bay's poor health. These excess nutrients also deplete dissolved oxygen, necessary for the survival of oysters, crabs, and other bottom-dwelling species in the Bay. Excess nutrients such as nitrogen and phosphorus-most of which come from agricultural sources such as fertilizer and manure-create algae blooms that prevent sunlight from reaching submerged aquatic vegetation, limiting growth of vital underwater Bay grasses. Nitrogen and chemical contaminants pose threats to the Chesapeake Bay when they enter the Bay either by falling directly into the water or by falling onto the land and being carried into the water by stormwater runoff. This affects the growth and reproduction of both terrestrial and aquatic species. Chemical contaminants persist in the environment, moving through the food web in a process called bioaccumulation. Airborne nitrogen increases the acidity of surface waters and soils, forms ground-level ozone, and contaminates drinking water. These airborne pollutants come from large point sources like power plants and industrial facilities, vehicles, and agricultural sources. Of particular concern to the Chesapeake region are airborne nitrogen and chemical contaminants such as mercury. Air and water pollution are intricately linked. PollutionĪir pollution threatens the air we breathe and the land and water. More people also means more cars on the road, increasing traffic congestion as well as air pollution. Lands that once absorbed rainfall have been transformed into impervious surfaces such as parking lots and roads that increase stormwater runoff-often full of sediment, excess nutrients, and chemical contaminants-flowing into the Bay and its tributaries. New homes, businesses, and roads replace forests and fields. Land use changesĪs people move to the area and development increases, land use in the watershed changes. A growing population creates issues that threaten the Bay ecosystem. At this rate, the population will reach 20 million by 2030. Nearly 17 million people live in the Chesapeake Bay watershed, and demographers estimate that the watershed's population is growing by about 157,000 residents per year.
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