A method for measuring the response of sediment microbial communities to environmental perturbations

A method has been developed for studying direct and indirect responses of microbial processes in lake sediments to environmental perturbations. Responses of the entire microbial community as well as specific members of the community were studied using in vitro sediment systems for periods of weeks or months under control and experimentally perturbed conditions. Effects of perturbations at the community level were determined by comparing rates of organic matter decomposition (CO2 + CH4 production) in the control and test (acidified) systems. At the same time and under the same conditions, rates of specific processes such as mercury methylation and sulfate and nitrate reduction were assayed to see if these processes responded in the same manner as did the activity of the entire community. Acidification (lowering from pH 6.3 to 4.2) did not affect either community activity or nitrate reduction. However, decreases were observed in sulfate reduction and mercury methylation which were independent of community a...