Analysis of recharge sources to terminal lake during high-flow period in alpine inland river based on hydrochemistry and water isotopes: A case study of Hurleg Lake in the Bayin River Basin

Terminal lake is an important component of the oasis ecosystem in the lower reaches of inland rivers basins in arid regions, and its water supply sources is of great significance for maintaining the watershed ecological balance, rationally developing and utilizing resources, and preventing hydrological risks. Based on the analysis of the ion control factors within the water bodies of the Bayin River Basin in the Qaidam Basin, this study adopted the water chemical characteristics method and stable isotope techniques to explore the water supply sources of the terminal lake, Hurleg Lake. The results showed that: 1) The hydrochemical type of water in the Bayin River Basin was predominantly characterized as HCO3-Ca·Mg type, with its ionic composition primarily controlled by both rock weathering and evaporation-crystallization processes. 2) There were significant differences in δ18O values among different water bodies in the Bayin River Basin. Lake water exhibited the most enriched δ18O signature, followed by river water, while groundwater was the most depleted. In Hurleg Lake area, the spatial distribution of δ18O showed clear variability. The river water at the lake outlet was the most enriched in δ18O, whereas both the river water and lake water at the inlet were relatively depleted. 3) The water of Hurleg Lake was recharged by both surface rivers and groundwater, with contribution ratios of 86.84% and 13.16%, respectively, during the wet season. Rivers served as a stable and major recharge source for lakes. Under the combined influence of climate change and human activities, variations in riverine input volume and the flux of associated pollutants jointly regulated the lake’s recharge mechanisms, areal extent, and water quality dynamics. These findings provide theoretical support for the optimization and management of water resources in terminal lakes within cold and arid inland river basins.