Seasonal depletion of oxygen from bottom waters of Chesapeake Bay: roles of benthic and planktonic respiration and physical exchange processes

Abstract

In general, planktonic processes dominated O2 consumption, comprising almost 2/3 of the total. Oxygen consumption associated with benthic processes, however, exceeded planktonic rates in early spring prior to vernal warming and in late August when large S2- fluxes resulted from release of accumulated pore water pools. For stratified estuaries with bottom layers thicker than 5 m, seasonal O2 depletion is driven primarily by planktonic respiration rather than benthic consumption of accumulated organic pools. Comparison of mean monthly rates for bottom respiration (plankton plus benthos) and net physical O2 replenishment revealed that the two processes were highly correlated between March and October; both rates increased through July and declined thereafter. Relatively large reductions in respiratory O2 consumption (eg with decreased organic inputs) would lead to substantially smaller decreases in the extent of bottom water O2 depletion because of an inherent adjustment between the coupled biological and physical processes. -from Authors