Thursday, March 07, 2013, 4:30PM - 5:30PM
Geogenic arsenic (As) contamination affects more than 100 million people throughout Southeast Asia who rely on shallow groundwater for drinking water. Although the accurate prediction of groundwater As concentrations has eluded the scientific community, there is a consensus in the literature that microorganisms mediate the reductive dissolution of As- bearing iron (Fe) minerals in aquifer sediments, thereby playing a critical role in groundwater As mobilization. To date, laboratory experiments have characterized the potential for a small group of Fe- and As- reducing bacteria to increase rates of As release into groundwater. Recent research has proposed that some of these taxa may also influence groundwater As mobilization through humic substance (HS)- reduction. The high As aquifer sediments in Southeast Asia harbor diverse bacterial communities, and thus it is important to consider the capacity of the community, as opposed to select taxa, to influence the biogeochemical cycling of As in groundwater. This research employed an ecological approach to elucidating the biogeochemical controls on groundwater As mobilization at field sites located in Araihazar, Bangladesh. This approach was useful in finding that sedimentary properties, such as Fe, manganese (Mn) and organic matter concentrations, may be more important in structuring bacterial communities than As concentrations. In addition, dissolved organic matter (DOM) in groundwater significantly influences the assembly of bacterial communities, and thus the potential role of bacteria in cycling groundwater As. It is clear that a range of bacterial taxa are influenced by the chemical quality and source of groundwater DOM. Also, the analysis of environmental samples and laboratory experiments indicates that native bacteria within the aquifer sediment at multiple sites within the GBD are able to pair the oxidation of labile carbon to the reduction of redox-active, HS-like carbon sources to accelerate Fe- and As- mobilization.