Groundwater Quality Assessment and Pollution Source Apportionment in an Arid Basin of Central Asia Under Intensive Agricultural Expansion

The Weigan–Kuqa River Basin is a typical oasis agricultural area in arid regions, where shallow groundwater is vital for ecological sustainability and regional development, yet its water quality status and pollution risks remain insufficiently understood. This study integrates K-means clustering, the Nitrate Pollution Index (NPI), Entropy-Weighted Water Quality Index (EWQI), Irrigation Water Quality Index (IWQI) and Positive Matrix Factorization (PMF) to systematically evaluate groundwater quality and quantitatively identify pollution sources in a representative arid irrigation basin. Results indicated that from 2000 to 2020, cropland area continuously expanded while barren and grassland decreased, reflecting substantial anthropogenic alteration of land-use patterns. Groundwater-I is dominated by rock weathering and exhibits the HCO3-Ca·Mg type; Groundwater-II is influenced by evaporative concentration, cation exchange, and anthropogenic activities, resulting in water quality deterioration and evolution toward the Cl·SO4-Na (Ca·Mg) type. Human activities exert a significant impact on groundwater quality. The suitability rates of groundwater for drinking and irrigation are 67% and 30%, respectively, with approximately 30% of samples exhibiting nitrate contamination. PMF results reveal that groundwater degradation is predominantly driven by the combined effects of evaporite dissolution and external pollutant inputs (domestic wastewater, fertilizers, and irrigation return flow). Accordingly, zoned management strategies are proposed: high-quality aquifer zones should be prioritized as drinking water source protection areas; degraded zones require stringent control of domestic sewage discharge and salinity buildup caused by irrigation return flow; and intensively cultivated areas demand enhanced regulation of agricultural non-point source pollution. These findings provide a scientific foundation for sustainable groundwater management in arid regions.