Dynamics of bacterial sulfate reduction in a eutrophic lake

Bacterial sulfate reduction in the surface sediment and the water column of Lake Mendota, Madison, Wis., was studied by using radioactive sulfate (SO(4)). High rates of sulfate reduction were observed at the sediment surface, where the sulfate pool (0.2 mM SO(4)) had a turnover time of 10 to 24 h. Daily sulfate reduction rates in Lake Mendota sediment varied from 50 to 600 nmol of SO(4) cm, depending on temperature and sampling date. Rates of sulfate reduction in the water column were 10 times lower than that for the surface sediment and, on an areal basis, accounted for less than 18% of the total sulfate reduction in the hypolimnion during summer stratification. Rates of bacterial sulfate reduction in the sediment were not sulfate limited at sulfate concentrations greater than 0.1 mM in short-term experiments. Although sulfate reduction seemed to be sulfate limited below 0.1 mM, Michaelis-Menten kinetics were not observed. The optimum temperature (36 to 37 degrees C) for sulfate reduction in the sediment was considerably higher than in situ temperatures (1 to 13 degrees C). The response of sulfate reduction to the addition of various electron donors metabolized by sulfate-reducing bacteria in pure culture was investigated. The degree of stimulation was in this order: H(2) > n-butanol > n-propanol > ethanol > glucose. Acetate and lactate caused no stimulation.