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

Abstract

Concentrations of various S compounds (SO42-, H2S, SO, acid-volatile sulfide and total S) were determined in the profundal sediments and overlying water column of a shallow eutrophic lake. Low concentrations of SO42- relative to those of acid-volatile sulfide and total S, and a decrease in total S with sediment depth implied that the contribution of dissimilatory S reduction to H2S production was relatively minor. Addition of 1.0 mM Na235SO4 to upper sediments in laboratory experiments resulted in the production of H235S with no apparent lag. Kinetic experiments with 35S demonstrated an apparent Km of 0.068 mmol SO42- reduced/l sediment per day; tracer experiments with 35S indicated an average turnover time of the sediment SO42- pool of 1.5 h. Total SO42- reduced per m2 per day, which corresponds to a mineralization of 30% of the particulate organic matter entering the sediment. Reduction of 35SO occurred at a slower rate. High rates of SO42- reduction occur in these sediments despite low concentrations of oxidized inorganic compounds, and this reduction can be important in the anaerobic mineralization of organic C.