A 2,500-YEAR HISTORY OF ANOXIA AND EUTROPHICATION IN CHESAPEAKE BAY

Ongoing monitoring programs and historical data are not sufficient to establish anthropogenic effects on the ecology of Chesapeake Bay. Howe ver, stratigraphic records preserved in the sediments can be used to r econstruct both prehistoric and historic sedimentation and water condi tions of the bay, including anoxia and eutrophication. Pollen, diatoms , total organic carbon (TOC), nitrogen, total sulfur, and an estimate of the degree of pyritization of iron (DOP) are being used as paleoeco logical indicators in dated sediment cores for the purpose of reconstr ucting a long-term environmental history of the bay. Analysis of the d ata indicates that sedimentation rates, anoxic conditions, and eutroph ication have increased in the Chesapeake Bay since the time of Europea n settlement. For example, since initial land clearance around 1760, s edimentation rates have increased from as low as 0.02 cm yr-1 to an av erage 0.22 cm yr-1, and TOC from 0.14 mg cm-2 yr-1 to a high 4.96 Mg C M-2 yr-1. Diatom community structure shows a steady decrease in overal l diversity since 1760 and the centric:pennate ratio has increased sig nificantly since 1940.