Bacteria, Dissolved Organics and Oxygen Consumption in Salinity Stratified Chesapeake Bay, an Anoxia Paradigm

Chesapeake Bay is a bacterially dominated ecosystem driven,at least under summer conditions, by high levels of labile dissolvedorganics. Bacterioplankton are exceptionally abundant (20 x10⁹ cells liter^–1) and productive (7 x 10⁹ cells liter^–1d^–1), and their biomass can equal or exceed 60% of phytoplanktonbiomass. In the salinity stratified Chesapeake Bay bacterioplanktonaccount for 60–100% of planktonic oxygen consumption,potentially driving the Bay to anoxia in days to weeks. Sulfide,released from sediments by sulfate reducing bacteria, chemicallyconsumes oxygen at rates up to 9 mg O₂ liter^–1 d^–1maintaining the oxygen deficit. The organic matter driving thisoxygen demand in the summer season is functionally dissolved.Dissolved organics, measured as biochemical oxygen demand, accountfor about 60% of microbially labile organics throughout thewater column and 80% (sometimes 100%) in the subpycnoclinalwater. Field studies suggest that reduced oyster stocks in ChesapeakeBay may be a major factor in the shift to this bacterially dominatedtrophic structure