Chesapeake Bay Anoxia: Origin, Development, and Significance

Abstract

Anoxia occurs annually in deeper waters of the central portion of the Chesapeake Bay and presently extends from Baltimore to the mouth of the Potomac estuary. This condition, which encompasses some 5 billion cubic meters of water and lasts from May to September, is the result of increased stratification of the water column in early spring, with consequent curtailment of reoxygenation of the bottom waters across the halocline, and benthic decay of organic detritus accumulated from plankton blooms of the previous summer and fall. The Chesapeake Bay anoxia appears to have had significant ecological effects on many marine species, including several of economic importance.

Net anthropogenic phosphorus inputs: spatial and temporal variability in the Chesapeake Bay region

“…Human activities, such as agriculture and urban development, have been linked to increases in nutrient and sediment loading (Correll 1987;Turner and Rabalais 1991;Carpenter et al 1998) and can adversely affect water quality, productivity, and trophic structure (Ryding and Rast 1989;Rekolainen et al 1995;Rast and Thornton 1996) in receiving lakes, wetlands, estuaries, and coastal waters (Orth and Moore 1983;Officer et al 1984;Jordan et al 1991a, b;Frink 1991;Golterman 1995;Howarth et al 1996;Vukadin et al 1996;Carpenter et al 1998;Boesch et al 2001). Coastal watershed eutrophication has become a regional and global issue as larger proportions of the earth's human population settle in coastal areas (Valiela et al 1992;de Jonge et al 2002).…”

“…Elevated inputs of both nitrogen and phosphorus to the Chesapeake watershed have resulted in excessive phytoplankton production within the Bay (Malone et al 1986(Malone et al , 1988Boynton et al 1982;Correll 1987;Jordan et al 1991a, b;Gallegos et al 1992;Harding 1994;Harding and Perry 1997). Consequently, submerged aquatic vegetation has declined (Kemp et al 1983;Orth and Moore 1983) and hypoxic conditions have increased in both magnitude and extent (Taft et al 1980;Officer et al 1984). The detrimental ecological effects of increased nutrient loading to the Chesapeake Bay have led to the multi-state Chesapeake Bay Agreement, which seeks to reduce nutrient discharges to Chesapeake Bay watershed streams and rivers (Boesch et al 2001).…”

Effects of land-use change on nutrient discharges from the Patuxent River watershed

“…Elevated inputs of materials-such as sediment, nitrogen, phosphorus, and organic carbon-foster a host of problems in freshwater and estuarine systems throughout the world (Nixon 1995; Rabalais et al 2001). In the Chesapeake Bay estuary, eutrophication has contributed to excessive phytoplankton production, hypoxia, the decline of submerged aquatic vegetation, and other environmental problems (Orth and Moore 1983;Officer et al 1984;Jordan et al 1991a,b;Boesch et al 2001).…”

Heat Shock Protein 70 Expression in Juvenile Eastern Oysters,Crassostrea virginica(Gmelin, 1791), Exposed to Anoxic Conditions

“…Anoxic water events in estuaries have been reported from all over the world, including the coasts of the United States (May 1973, Officer et al 1984, Balls et al 1996, Garnier et al 2001, Rabalais et al 2002, Yasuhara & Yamazaki 2005. Benthic organisms in those estuaries have shown negative impacts, including decreased population sizes, mass mortality, failure of larval recruitment, decreased growth rates, and lowered propagation of fish, crustaceans, molluscs, and phytoplankton (May 1973, Officer et al 1984, Osman et al 1991, Osman & Abbe 1995, Lenihan & Peterson 1998.…”

“…Benthic organisms in those estuaries have shown negative impacts, including decreased population sizes, mass mortality, failure of larval recruitment, decreased growth rates, and lowered propagation of fish, crustaceans, molluscs, and phytoplankton (May 1973, Officer et al 1984, Osman et al 1991, Osman & Abbe 1995, Lenihan & Peterson 1998. As studies suggest that fish and crustaceans are able to avoid anoxic water because they are motile (Pavela et al 1983), anoxic water events may have greater impacts on sessile organisms, leading to deterioration of benthic ecosystems and challenging restoration attempts.…”