Arsenic fate in upper Indus river basin (UIRB) aquifers: Controls of hydrochemical processes, provenances and water-aquifer matrix interaction

Major river basins of the Himalayas contain a significant amount of arsenic (As) in the geological matrix, which tends to contaminate the groundwater at a local and regional scale. Although As enrichment in Quaternary deposits has been linked to primary provenances (Himalayan orogeny), limited studies have reported As enrichment in bedrock aquifers. In the present study, the hard rock and groundwater samples were collected across the upper Indus river basin (UIRB), Ladakh to assess the hydrogeochemical processes and environments responsible for As mobilization and release. The higher As concentrations were found in Khardung volcanics followed by Ophiolitic melange, Dras volcanics, Nindam sandstone, and Nindam Shale. The variability in As concentration among different rock samples is largely governed by the presence of felsic minerals and the type of magmatic setting. The groundwater is less mineralized, with moderate electrical conductivity (EC), and weakly acidic to alkaline in nature. The results indicated that mineral weathering, dissolution, and active cation exchange reactions have a strong influence on the major ion chemistry of the groundwater. Redox-sensitive processes are influenc-ing the As mobilization and release under reducing environmental conditions. As in groundwater poses a serious threat to human health hence awareness is urgent towards achieving sustainable As mitigation globally. The study provided a significant dataset to better understand the processes and environmental conditions responsible for hydrogeochemical evolution, sources of solutes, and As mobilization and release in groundwater which will help in sustainable water resource management policies and ecosystem restoration across the Himalayas. (c) 2021 Elsevier B.V. All rights reserved.