Hydrological Processes and Surface Water Quality in the Ili‐Balkhash Headwater Region, China: Insights From Stable Isotopes and Hydrochemistry

ABSTRACT

The increasing scarcity of water and deteriorating water quality are intensifying social, economic, and environmental challenges in arid Central Asia. In this context, the characterisation and assessment of water quality in the headwater region of the Ili‐Balkhash Basin is crucial, given its significance in sustaining human livelihoods and ecological balance. A total of 171 water samples were collected from the headwater region of the Ili‐Balkhash Basin, China. Major ionic concentrations and stable isotopes were analysed in the laboratory. Results revealed remarkable spatiotemporal heterogeneity in stable isotopic values, ranging from −21.8‰ to −9.4‰ for δ ¹⁸ O and −166.2‰ to −64.4‰ for δ ² H. These values were markedly depleted in the upstream and became increasingly enriched downstream during both summer and spring, which resulted from meltwater recharge in the upstream regions and evaporative enrichment along the flow path. The MixSIAR models indicated that meltwater contributed significantly to river water composition, which was estimated at 41.7% ± 10% in summer and 52% ± 14% in spring. Further analysis using the Gibbs diagrams and ionic ratio plots demonstrated that mineral dissolution predominantly affected the chemical concentrations, alongside carbonate, silicate weathering processes, and irrigation activities. The assessment of water suitability for drinking and irrigation from Na ⁺ % and sodium adsorption ratio (SAR) analysis suggested that while most of the river water retained its natural water quality, there are safety concerns at certain locations. These findings offer a comprehensive understanding of the hydrochemical processes in the headwater regions of the Ili‐Balkhash Basin, contributing to the sustainable management of water quality in this critical region.