Surface Water Hydrochemistry in the Keriya River System, Southern Tarim Basin, China: Controlling Factors and Irrigation Suitability

Inland rivers in arid regions are important water resources that support ecosystem stability and human activities. This study comparatively investigated the hydrochemical characteristics, controlling factors, and irrigation suitability of six glacier-fed inland rivers along the southern margin of the Tarim Basin using hydrochemical analysis, Gibbs and Piper diagrams, ion-ratio analysis, principal component analysis (PCA), and PHREEQC inverse mass-balance modeling. The six rivers exhibited distinct hydrochemical characteristics despite their common origin in the Kunlun Mountains. Carbonate weathering dominated the Bostan and Nur rivers, while the Kaxi River exhibited relatively stable hydrochemical characteristics mainly associated with rock weathering. In contrast, evaporite dissolution and evaporative concentration exerted stronger influences on the Uruksayi and Buzang rivers, which also showed more pronounced longitudinal variations in major ion concentrations. The Keriya River showed an overall transition from silicate-weathering-dominated conditions in the upper reaches toward stronger evaporite dissolution and evaporative concentration downstream. PHREEQC inverse mass-balance modeling suggested that halite dissolution, gypsum dissolution, dolomite dissolution, calcite precipitation, and cation exchange contributed to the hydrochemical evolution of the Keriya River. Several abrupt variations in ion concentrations were observed along the river courses, suggesting that localized processes, including tributary mixing, groundwater inputs, or potential anthropogenic influences, may contribute to these hydrochemical changes. PCA extracted two principal components explaining 86.0% of the total variance. PC1 (70.5%) represented overall ion enrichment and mineralization, whereas PC2 (15.5%) reflected carbonate-related hydrochemical variations. Irrigation suitability assessment showed that all rivers exhibited low sodium hazards, while salinity was the main factor limiting irrigation suitability in the middle and lower reaches of the Keriya River and in the Uruksayi and Buzang rivers. This study improves the understanding of hydrochemical evolution and water quality assessment of arid inland rivers and provides scientific support for sustainable water resource management and oasis ecosystem protection in the southern Tarim Basin.