Hydrochemical Evolution and Pollution Source Apportionment of Groundwater in Arid Regions: A Case Study of the Datong River Basin, Northwest China

Understanding hydrochemical evolution and apportioning pollution sources are prerequisites for effective groundwater protection at the regional scale; nevertheless, the governing processes and anthropogenic drivers in arid regions remain poorly constrained. Here, we present a comprehensive geochemical survey of the Datong River Basin, a representative arid catchment in north-western China. Thirty-seven groundwater samples were analyzed with hydrochemical methods and Positive-Matrix Factorization (PMF) to delineate natural controls and contaminant sources. Results showed that the aquifer is dominated by HCO3–Ca(Mg) water controlled predominantly by silicate and carbonate weathering, modified locally by evapo-concentration and human activities. Water-quality indices classify 70.3% of the samples as excellent, but spatially restricted degradation is evident. PMF resolved three independent sources: a natural end-member enriched in Mn, Na+ and Cl−; a mixed source reflecting domestic wastewater, agricultural fertilizers and rock weathering; and an industrial source dominated by Fe. The mixed source contributes most major ions and chemical oxygen demand (COD), whereas the industrial source accounts for 75.7% of total Fe. These findings provide a robust scientific basis for groundwater management and pollution mitigation in arid regions under similar hydrogeological settings.