The Relationship Between Microbial Community Structure and the Mobilization of Groundwater Arsenic: Evidence from Araihazar, Bangladesh

Shallow (<100m) groundwater aquifers in the Ganges-Brahmaputra Delta (GBD), a drinking water source for approximately 40 million people in Bangladesh and West Bengal, often contain arsenic (As) levels that exceed World Health Organization (WHO) drinking water standards of 10 micrograms per liter. The mechanism(s) causing arsenic mobilization in GBD aquifers are not fully understood, although several geochemical models have been proposed. Recent studies suggest that As is released during the reductive dissolution of iron(III) oxyhydroxides. Laboratory studies have shown that a known iron-reducing bacterium can facilitate arsenic mobilization, and that native microbial communities may facilitate arsenic release in anaerobic, carbon-rich conditions. To build upon this previous research, and to better understand the native community structure in these systems, we created 16S rRNA gene bacterial clone libraries from aquifer sediments collected from various depths at sites along the groundwater flowpath. Results show that bacterial communities are very diverse, and that community structure shifts with depth and position along the flowpath. In addition, there is evidence that bacterial community structure may correlate with geochemical conditions in the aquifer environment.