Bacteria, dissolved organics and oxygen consumption in salinity stratified chesapeake bay, an anoxia paradigm

Abstract

SYNOPSIS. 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 liter1 d1 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.