Effects of soil heavy metal contamination and remediation on the size, activity, and structure of soil microbial communities

Heavy metal contamination and remediation of sites impacted by heavy metals are significant environmental issues, due to the fact that heavy metal contamination can result in losses in soil quality. To prevent ecosystem degradation and to determine the effectiveness of remediation, sensitive methods are needed to assess the impacts of heavy metals. Due to their sensitivity to heavy metals, soil microbial communities could be useful as indicators of heavy metal impacts. In this dissertation, two techniques for analysis of microbial community structure, BIOLOG and the Phospholipid Fatty Acid (PLFA) assay, were applied in conjunction with measures of microbial community size (plate counts and biomass) and activity (dehydrogenase activity) to several metal impacted soils. The application of these assays to soils in the vicinity of a zinc smelter indicated that high level metal contamination had resulted in decreases in microbial population size and activity, and changes in BIOLOG and PLFA profiles, including decreases in indicator fatty acids for fungi, actinomycetes, gram positive bacteria, and arbuscular mycorrhizal fungi. The analysis of remediated soils from this smelter site indicated that remediation had resulted in increases in microbial population size and activity, as well as increases in indicator fatty acids for fungi, actinomycetes and gram positive bacteria, suggesting recovery of microbial populations with remediation. The addition of zinc to soils in the laboratory did not have a similar long term impact on microbial population size. However, zinc amendment in the laboratory did result in a long term decrease in microbial community activity and long term shifts in BIOLOG and PLFA profiles similar to the shifts seen for the zinc smelter soils. Analysis of microbial communities from a sludge application study site indicated that the elevated metal levels caused by sludge application had resulted in changes similar to those observed for the smelter soils: decreased microbial activity, shifts in PLFA profiles, and decreases in indicator fatty acids for fungi, actinomycetes, and arbuscular mycorrhizal fungi. However, sludge applied metals did not result in shifts in BIOLOG metabolic profiles. These results indicate the utility of microbial community analysis for assessing the impacts of soil heavy metal contamination.