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

Abstract

Chesapeake Bay is a bacterially dominated ecosystem driven, at least under summer conditions, by high levels of labile dissolved organics. Bacterioplankton are exceptionally abundant (20 × 109 cells liter−1) and productive (7 × 109 cells liter−1 d−1), and their biomass can equal or exceed 60% of phytoplankton biomass. In the salinity stratified Chesapeake Bay bacterioplankton account 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, chemically consumes oxygen at rates up to 9 mg O2 liter−1 d−1 maintaining the oxygen deficit. The organic matter driving this oxygen demand in the summer season is functionally dissolved. Dissolved organics, measured as biochemical oxygen demand, account for about 60% of microbially labile organics throughout the water column and 80% (sometimes 100%) in the subpycnoclinal water. Field studies suggest that reduced oyster stocks in Chesapeake Bay may be a major factor in the shift to this bacterially dominated trophic structure