Aquifer Arsenic Cycling Induced by Seasonal Hydrologic Changes within the Yangtze River Basin

• DOI: 10.1021/acs.est.5b04986
• Publication Date: 2016-01-20T18:38:46Z
• Authors: Michael V. Schaefer; Samantha C. Ying; Shawn G. Benner; Yanhua Duan; Yanxin Wang; Scott Fendorf
• Keywords: Cycling; Yangtze river

Consumption of groundwater containing >10 μg L–1 arsenic (As) adversely impacts more than 100 million people worldwide. Multiyear trends in aquifer As concentrations have been documented, but strong seasonal variations are not commonly observed. Here we report dramatic changes and chemistry within the Jianghan Plain Yangtze River, China. At some wells, fluctuate by an order magnitude a single year (100–1200 L–1). Groundwater extraction sustained water levels surface channels during dry season induces downward hydraulic gradient, seasonally supplying oxidizing (oxygen, nitrate) to otherwise anoxic aquifer. Oxygen and/or nitrate addition promotes transient drop for 1–3 months. When recharge ceases, reducing, low-arsenic conditions reestablished reactive, endogenous organic carbon. Temporal variability is especially problematic because it increases probability false-negative well testing seasons. However, periods low may also provide source less toxic irrigation or other uses. Our results highlight vulnerability resources inland basins Asia changing geochemical conditions, both natural anthropogenic, reinforce that continued monitoring wells high-risk regions essential.