Hydrogeochemical characteristics and groundwater quality assessment in the plain area of Yarkant River Basin in Xinjiang, P.R. China.

The deteriorating groundwater quality due to natural genesis and anthropogenic activities has prevented the sustainable use of groundwater. The characteristics and factors affecting groundwater quality for drinking in shallow aquifers (depth ≤ 100 m) in the plain area of Yarkant River Basin in Xinjiang were analyzed using water quality index (WQI), geostatistics, and geochemical methods. Results showed that the groundwater was weak-alkaline with neutral pH, with dominant water types being SO•HCO-Ca•Mg, SO•Cl•HCO-Na•Ca, SO•HCO•Cl-Ca•Na, Cl•SO-Na•Ca, and HCO•SO-Mg•Ca. WQI ranged between 31.79 and 549.37, and about 14.43%, 31.96%, 18.56%, 22.68%, and 12.37% of the all samples were excellent, good, medium, poor, and extremely poor quality, respectively. The proportion of excellent quality was the highest in single structure phreatic aquifer (SSPA, 50.00%) and good quality were the highest in multilayered structure phreatic aquifer (MSPA, 34.21%) and multilayered structure confined aquifer (MSCA, 28.89%). With the extension of the river, the groundwater quality gradually degenerated from south to north in phreatic aquifer (PA, including SSPA and MSPA). The further away from the Yarkant river, the worse the groundwater quality of PA. Furthermore, the WQI showed excellent, good, and an alternation of medium and poor quality (including extremely poor quality) from south to north in the MSCA. The groundwater quality deterioration might have been affected by the dissolution of evaporite minerals, such as halite, gypsum, and anhydrite and ion exchange process. In addition, local effects of anthropogenic activities and land usage patterns on the groundwater quality should be reckoned as well.