Reduction of Sulfur Compounds in the Sediments of a Eutrophic Lake Basin

Concentrations of various sulfur compounds (SO4 2− , H2 S, S0 , acid-volatile sulfide, and total sulfur) were determined in the profundal sediments and overlying water column of a shallow eutrophic lake. Low concentrations of sulfate relative to those of acid-volatile sulfide and total sulfur and a decrease in total sulfur with sediment depth implied that the contribution of dissimilatory sulfur reduction to H2 S production was relatively minor. Addition of 1.0 mM Na2 35 SO4 to upper sediments in laboratory experiments resulted in the production of H2 35 S with no apparent lag. Kinetic experiments with35 S demonstrated an apparentKm of 0.068 mmol of SO4 2− reduced per liter of sediment per day, whereas tracer experiments with35 S indicated an average turnover time of the sediment sulfate pool of 1.5 h. Total sulfate reduction in a sediment depth profile to 15 cm was 15.3 mmol of sulfate reduced per m2 per day, which corresponds to a mineralization of 30% of the particulate organic matter entering the sediment. Reduction of35 S0 occurred at a slower rate. These results demonstrated that high rates of sulfate reduction occur in these sediments despite low concentrations of oxidized inorganic compounds and that this reduction can be important in the anaerobic mineralization of organic carbon.