Study on the characteristics of water chemistry evolution in typical alpine karst basins

High-altitude karst basins, as vital components of the "Asian Water Tower," are critical for water resource conservation on the Qinghai-Tibet Plateau. To investigate the hydrochemical evolution characteristics of the Yepuqu River Basin, we analyzed 23 water samples (snowmelt, groundwater, and surface water) using hydrochemistry, hydrogen-oxygen isotopes, mass balance principles, and principal component analysis (PCA). Results showed that the hydrochemical types are predominantly HCO ₃ —Ca and HCO ₃ ·SO ₄ —Ca. Ion balance diagrams indicated that water mineralization was primarily controlled by rock weathering and dissolution, with additional contributions from cation exchange. PCA further reveals that hydrochemical evolution is influenced by carbonate mineral dissolution, evaporite dissolution, and anthropogenic activities. Isotopic analysis demonstrated that surface water was originated from atmospheric precipitation (8%), snowmelt (74%), and groundwater (18%), with dynamic mutual transformation between groundwater and surface water, accompanied by intense water-rock interactions and evaporation. Through comparison of the results of water chemical evolution of similar alpine karst basins, it was found that the strength of human activities directly affects the differences in water chemical evolution. The study provides the first comprehensive analysis of hydrochemical evolution in the high-altitude karst basin of the Yepuqu River, enhancing the theoretical foundation for water resource protection in the Lhasa River Basin and offering crucial data to advance research on surface water-groundwater cycling in alpine karst systems.