Effect of herbicide residues on microbial processes in pond sediment

An assay system is described for examination of potential effects of herbicides on non-target sediment microorganisms. A key feature was to standardize a procedure for collecting and incubating intact miniature soil samples for assaying a variety of microbial activities. Potted pond sediment compared to undisturbed sediment cores showed no difference in initial carbon mineralization, acetylene reduction, phosphatase, and dehydrogenase activities, but did show a significant difference in methanogenesis. CuSO₄, after one week in pond sediment, inhibited phosphatase activity (1,000 ppm CuSO₄) and methanogenesis (20-1,000 ppm CuSO₄); no effect was noted for acetylene reduction, dehydrogenase activity and glucose mineralization. Simazine stimulated pond sediment acetylene reduction (1,000 ppm simazine); inhibited phosphatase activity (1,000 ppm simazine) and methanogenesis (50-1,000 ppm simazine); and had no effect on dehydrogenase activity and glucose mineralization. Chronic effects and effects at lower concentrations by these herbicides were less apparent. The results support the concept that a battery of tests are required to profile and evaluate the effects of herbicides on sediment microbial communities.