Mechanisms of groundwater arsenic variations induced by extraction in the western Hetao Basin, Inner Mongolia, China

Abstract High arsenic (As) groundwater has posed a serious threat to human health. Due to the complex spatial-temporal distributions of dissolved As, the influence of groundwater extraction on As enrichment has attracted great attention. To ascertain spatial-temporal variations in dissolved As and driving mechanisms impacted by extraction, we monitored groundwater levels and chemicals in different aquifers in the western Hetao basin, China. Results revealed that groundwater levels decreased during irrigation season in both shallow ( 42 m bls) aquifers, and the decreases in deep aquifer were more evident. During irrigation, the estimated proportion of recharge from shallow groundwater to affected deep groundwater (around 45 m bls) increased from 21% to 53% in the distal of the alluvial fan and sharply from 53% to 86% in the flat plain. In the distal of the alluvial fan, the vertical recharge of shallow groundwater with low As concentrations (