The scale required for attainment of the least cost solution determines the boundary of this larger area. The Chesapeake Bay airshed is estimated to be 910,000 km2, an area more than five times that of the watershed. The Chesapeake Bay, like other east coast estuaries, is eutrophic. Excess nutrient loads have reduced water quality and stocks of living resources far below their historic levels. Atmospheric deposition is unique in its ubiquitous nature.
Atmospheric deposition is a direct nutrient load when deposited on tidal waters.
Atmospheric deposition is also an indirect source, either through deposition on the watershed and subsequent transport to the Chesapeake, or through deposition to adjacent coastal waters and subsequent transport to the Bay. Twenty seven percent of the watershed nonpoint source load delivered to the Bay arises from atmospheric deposition. Work is underway to determine the atmospheric deposition portion of the coastal water nutrient load transported to the Chesapeake. The Chesapeake Bay Agreement To reduce nutrient loads to the Bay, the Chesapeake Bay Agreement was forged among the states of Maryland, Pennsylvania, and Virginia, the District of Columbia, and the EPA, which represents the federal government. In order to track the nutrient sources, the portions of the load that are controllable, and the load reductions possible, an integrated series of linked eutrophication models were developed.