Hydrogeochemical Signatures, Genetic Mechanisms, and Sustainable Utilization Potential of Groundwater Resources in a Typical Arid Alluvial–Proluvial Plain of the Closed Qaidam Basin on Tibetan Plateau

Clarifying the hydrochemical attributes and genesis of groundwater within arid endorheic basins is crucial for ensuring its sustainable utilization locally. This research examines the hydrochemical properties, evolutionary processes, and water quality suitability of groundwater in a representative arid closed basin located on the Tibetan Plateau. Findings indicate that groundwater exhibits neutral to weakly alkaline conditions, with TDS and major ions showing marked spatial heterogeneity, increasing from the river valley alluvial plain to the alluvial-lacustrine plain. Hydrochemical types transition from mixed ClMg·Ca to ClNa type along the groundwater flow path. Groundwater chemistry is co-influenced by natural factors and human activities. Evaporative concentration is the dominant natural factor (composition contribution of 38.1%), followed by evaporite dissolution (composition contribution of 27.7%) and silicate weathering, while agricultural activities and domestic pollution contribute significantly to nitrate and ammonium contamination. EWQI assessment indicates most groundwater is unsuitable for direct drinking, with only 23.33% of samples rated as good or excellent. Nitrate is identified as the primary health risk factor, particularly threatening children and infants. This study recommends targeted nitrate control measures in high-risk areas to ensure drinking water safety.