Delineating Sources of Groundwater Recharge in an Arsenic-Affected Aquifer in Jianghan Plain Using Stable Isotopes

Consumption of arsenic (As)-contaminated groundwater adversely impacts the health of almost 20 million people in China. Determining the sources of As-affected groundwaters may help to improve our understanding of the controlling processes on As mobilization in groundwater systems. In this study, stable hydrogen and oxygen isotopes of water (δ¹⁸O and δD) were employed to delineate the groundwater recharge sources and the interactions between river/pond and groundwater in Shahu village, a typical high-As groundwater area in Jianghan Plain, central China. Utilizing a two-component mixing model based on δ¹⁸O and δD, we successfully calculated the river water contribution to groundwater including its uncertainty analysis and roughly distinguished the different water bodies within the aquifer system. Cl/Br was used to further identify the recharge contributions for shallow (10 m below the ground surface, low As concentrations), intermediate (25 m below the ground surface, high-As concentrations) and deep (50 m below the ground surface, high-As concentrations) groundwaters. The hydrogen and oxygen stable isotope signatures of high As and high total organic carbon (TOC) groundwaters (intermediate and deep aquifer) generally plotted near the local meteoric water line (LMWL). However, the δ¹⁸O and δD signatures of low As and low TOC groundwaters (shallow aquifer) tended to shift away from the LMWL along evaporation lines. These relationships revealed that the low As groundwater principally derived from surface water (river and pond), while the high-As groundwater mainly recharged from local precipitation through preferential channel as well as the bedrock and/or adjacent aquifer. Our results will enhance the comprehension of the genesis of high-As groundwater in Jianghan Plain.