Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Diana Nemergut

Second Advisor

Diane McKnight

Third Advisor

Steve Schmidt

Fourth Advisor

William Lewis

Fifth Advisor

Richard Smith

Abstract

Bacterial communities can exert significant influence on the biogeochemical cycling of groundwater arsenic (As). This has globally important implications since As in drinking water affects the health of over 100 million people worldwide, including in the Ganges-Brahmaputra Delta region of Bangladesh where geogenic arsenic in groundwater can reach concentrations of more than 10 times the World Health Organization's limit. The overall goal of this dissertation research was to examine the relative effects of sediment geochemistry versus DOM chemistry on the structure of bacterial communities across groundwater gradients in an aquifer affected by geogenic arsenic contamination in Araihazar, Bangladesh. To this end, I employed interdisciplinary methods including analytical chemistry, 16S rRNA gene sequencing to characterize the composition and diversity of bacterial communities, and fluorescence spectroscopy and PARAFAC modeling in order to describe the chemistry and source of DOM in high As aquifers. My results indicate that differences in sediment grain size and geochemistry between sites significantly influenced the structure of bacterial communities, and the relative abundances of Deltaproteobacteria and Chloroflexi. However, my research also revealed that the supply and chemistry of groundwater DOM might have a greater effect on the composition of bacterial communities in aquifer sediments than site-specific differences in sediment geochemistry. While higher DOM concentrations in incubation experiments corresponded to a greater proportion of Deltaproteobacteria, Chloroflexi comprised a greater proportion of bacterial communities in environmental samples. Also, this research provided evidence suggesting that Chloroflexi, Epsilonproteobacteria and Deltaproteobacteria may influence groundwater As cycling through the respiratory reduction of quinone moieties in the high As aquifer environment. The combination of fluorescence spectroscopy and PARAFAC modeling, and 16S rRNA gene pyrosequencing was useful in deciphering novel relationships between bacterial taxa and DOM chemistry in the environment. Future research on geogenic As contamination should investigate the metabolic activities of Deltaproteobacteria, Chloroflexi, Epsilonproteobacteria under environmental conditions in high As aquifer environments.

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