MICROBIAL COMMUNITY COMPOSITION AND FUNCTION IN SHALLOW GROUNDWATER ON THE MICHIGAN STATE UNIVERSITY CAMPUS: PREDICTING BIOGEOCHEMICAL RESPONSES TO ENVIRONMENTAL CHANGE

There are a number of anthropogenically changes at the land surface that may have both direct and indirect effects on groundwater quality. These include the introduction of contaminants, changes in land use, climate variability, and water overextraction. Each of these things poses a potential concern for the availability and quality of fresh water. It is particularly important to understand how microbial communities in shallow groundwater respond to environmental change, as they play a key role in catalyzing biogeochemical transformations. In this study, we examined natural microbial populations in shallow groundwater and sediment cores on the Michigan State University campus using both cultivation-dependent and -independent techniques. Particle-associated populations within the aquifer (from the drill cores) included microbial taxa known to catalyze transformation of nitrogen and sulfur compounds, in addition to other populations such as Pseudomonadales and Actinobacteria that have broad metabolic capabilities. In contrast, shallow groundwater hosted lower microbial diversity, dominated by species of Burkholderiales. We complemented this work with experimental studies using groundwater amended with environmentally relevant concentrations of nitrate, a potential contaminant and proxy for other anthropogenic compounds. Differences in denitrification capabilities and microbial diversity were observed in both aerobic and anaerobic treatments. These results suggest that subtle changes in aquifer chemistry can influence biogeochemical processes, and that cultivation-based approaches, coupled with high throughput DNA sequencing can be used to parse out the functional responses of shallow groundwater microbial communities.