LINKING MICROBIAL COMMUNITY COMPOSITION TO IN SITU NATURAL ATTENUATION OF EMERGING CONTAMINANTS
The presence of low concentrations of hydrophilic, organic emerging contaminants pose a threat to the quality of groundwater resources utilized for drinking water purposes. While extensive monitoring of the chemical composition of groundwater has revealed the presence of a variety of organic contaminants, relatively little is known about the natural attenuation of these compounds in situ. Biodegradation has been shown to be an effective transformation processes for a wide variety of emerging contaminants. However, it remains difficult to translate these results to in situ degradation in (usually) oxygen-depleted, oligotrophic groundwater with heterogeneous distribution and low emerging contaminant concentrations. Research was performed to gain insight on biodegradation of emerging contaminants in groundwater by examining microbial community composition and geochemistry. Groundwater samples collected at discreet depths ranging from 12 to 55 m in two monitoring wells were chemically analyzed to determine groundwater chemistry and contaminant distribution. Additionally, samples were analysyed for microbial community composition by sequencing of a PCR-amplified fragment of the 16SrRNA gene. Results indicate a distinct difference in both groundwater composition and microbial community diversity between wells and in depth. The groundwater profiles demonstrate the heterogeneity of subsurface geochemistry, highlighting the fact that contaminated water travels through a variety of environments between its source and extraction for drinking water. Differences in the abundance of electron acceptors, concentration of nutrients, and presence of electron donors, such as DOC, in addition to emerging contaminants play an important role in microbial community composition and in situ biodegradation. Redundancy analysis of groundwater geochemical characteristics, emerging contaminant concentrations, and microbial community diversity indicates a negative correlation between the availability of electron acceptors (nitrate and sulfate) and the presence of contaminants. In contrast, dissolved organic carbon correlated with the presence of organic contaminants. Overall, the results presented here are a first step towards better understanding the geochemical and microbiological factors affecting in situ emerging contaminant biodegradation.