SULFATE REDUCTION AND DIFFUSION IN SEDIMENTS OF LITTLE-ROCK LAKE, WISCONSIN

Rates of sulfate diffusion and reduction were measured in sediments of Little Rock Lake, an oligotrophic, soft-water lake in northern Wiscon sin. Laboratory measurements of kinetics of sulfate reduction found ha lf-saturation constants (20-30 mumol liter-1) and Q10 values (2.6) sim ilar to values reported in the literature. Sulfate reduction under in situ conditions in sediment cores was limited by sulfate and followed similar uptake kinetics as in laboratory experiments. Some variation i n kinetic parameters was evident as a function of location in the lake . No seasonal variation was observed in sulfate reduction rates in the lake sediments, and littoral and pelagic sites exhibited similar rate s. Rates of sulfate reduction were much higher than fluxes of sulfate calculated from pore-water profiles. Pore-water profiles also indicate d little difference in diffusive fluxes among pelagic and littoral sit es and among seasons. The discrepancy between diffusive fluxes and sul fate reduction rates is ascribed to high rates of oxidation of reduced sulfur. Nonlinear rates of sulfate reduction and calculated turnover times of sediment sulfide pools support the hypothesis that sulfide ox idation occurs nearly as rapidly as sulfate reduction.