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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 SO4•HCO3-Ca•Mg, SO4•Cl•HCO3-Na•Ca, SO4•HCO3•Cl-Ca•Na, Cl•SO4-Na•Ca, and HCO3•SO4-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. [ABSTRACT FROM AUTHOR]

Changes in the surface area of lakes can indicate climate change and human activity, and there are few reports on the characteristics of such changes in North Xinjiang, China. The normalized difference water index (NDWI) was modified by using the middle infrared band (MIR) instead of the near infrared band (NIR). The modified NDWI (MNDWI) can effectively extract the lake boundary. Changes in the number and area of lakes (surface area > 1 km2) were examined using topographic maps (1:100,000) and Land Remote-Sensing Satellite (System, Landsat) series images (multispectral scanner, thematic mapper, enhanced thematic mapper plus, and operational land imager) for the period from 1960 to 2018. The results showed that more than 85.00% of the lakes were identified in the Erqis River Basin (ErRB), Ulungur River Basin (URB), and Central North Tianshan (CNT) between 1960 and 1980, few lakes were observed in the Ebinur Lake Basin (ELB), Jimunai River Basin (JRB), Emin River Basin (EmRB), Guerbantonggute Desert Area (GDA), and Ili River Basin (IRB), and no lakes were observed in the Eastern North Tianshan (ENT). The surface area and numbers of lakes in North Xinjiang were increased by 795.99 km2 (35.54%) and 39 (195.00%), respectively, between 1960 and 2018. Multiple factors influenced the changes observed for different types of lakes. The number and surface area of mountain lakes fluctuated and increased mainly in response to precipitation and temperature. The number of oasis lakes remained unchanged until 1990, but then increased in response to precipitation and temperature. The fluctuations in the surface area of oasis lakes, which were affected by climate and groundwater development, were relatively small between 1960 and 1990, but then became larger. However, the number and surface area of plain lakes increased between 1960 and 2018 and were mainly influenced by climate change and human activity, such as water diversion for irrigation, ecological restoration projects, and the implementation of the river chief system. [ABSTRACT FROM AUTHOR]

Surface water (SW) and groundwater (GW) are crucial water supply sources in the southern margin of Junggar Basin in Xinjiang. The sources of toxic components in SW and GW and their negative effects on human health are of great concern. A total of 40 SW and 596 GW samples were collected at the oasis belt to analyze distribution, sources and potential health risks of inorganic pollutants in SW and GW. Results revealed that SW quality was severely affected by Hg, 30.0% of which had Hg concentration greater than the national drinking water standard. High Hg SW was mainly distributed near Manas County and Urumqi City. GW quality was mostly affected by SO 4 2−, 24.7% of which had SO 4 2− concentration greater than the national drinking water standard. High SO 4 2− GW primarily occurred in the northwest and middle of the study area. Source apportionment of inorganic pollutants identified geological background, municipal wastewater disposal, water-rock interaction, geological environment, geological structure and industrial emission were the prominent potential sources of inorganic pollution in SW, with contribution rates of 1.2%, 10.0%, 43.6%, 35.1%, 6.3% and 3.8%, respectively. Five potential pollution sources in GW (including geological background, municipal wastewater disposal, water-rock interaction, geological environment and aquifer burial depth) were identified, with contribution rates of 0.7%, 9.6%, 77.6%, 11.1% and 1.0%, respectively. Probabilistic health risk assessment showed that Cl− and As in SW and GW were the main inorganic pollutants threatening human health. Non-carcinogenic risks for adults and children were negligible, while carcinogenic risks cannot be negligible. Furthermore, the contribution of potential pollution sources to health risks was quantified using positive matrix factorization coupling with health risk assessment model. Based on which, we offered the suggestion that water quality improvement in contaminated areas should be implemented in combination with pollution monitoring systems. • The main inorganic pollutants were Hg in surface water and SO 4 2− in groundwater. • Sources of toxic components in surface water and groundwater were identified. • PMF and HRA models were used to quantify health risk contributions. [ABSTRACT FROM AUTHOR]