B23E-0639
Impacts of Seasonal Flooding on Arsenic Release in Tropical River Deltas
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Katherine A Roberts, Stanford Earth Sciences, Stanford, CA, United States, Scott E Fendorf, Stanford University, Earth System Science, Stanford, CA, United States, Michael Schaefer, Stanford University, Stanford, CA, United States, Shawn G Benner, Boise State University, Boise, ID, United States and Amy kirsten Salvador, University of California Riverside, Riverside, CA, United States
Abstract:
More than 140 million people in South and Southeast Asia drink groundwater contaminated with toxic levels of arsenic. Arsenic release from sediment is controlled by oxidation of reduced organic carbon coupled to iron and arsenic reduction; this process occurs principally under anaerobic conditions and is constrained to surficial (<1 m depth) sediments in the Mekong Delta. However, there is limited knowledge of water level changes in seasonal wetlands that control carbon oxidation pathways and subsequently arsenic release from sediments to groundwater. During drained periods, soils undergo aerobic carbon oxidation, diverting electron flow away from iron and arsenic reduction, decreasing arsenic release from sediments to groundwater. Additionally, draining may lead to fresh Fe-oxide precipitation that sequesters As. We monitored soil moisture and porewater chemistry of a seasonal wetland in the Mekong Delta through a wetting and drying cycle. We examined temporal trends in arsenic release from the solid phase over the flooding and drying cycles. Based on frequent field measurements we determine the timing and magnitude of arsenic release in surficial sediments of seasonal wetlands typical of the Mekong Delta. These results show the importance of surface processes on arsenic release and aid in developing mechanistic and predictive models of arsenic concentrations in the subsurface throughout Asia.
