Hydrochemical insights on the signatures and genesis of water resources in a high-altitude city on the Qinghai-Xizang Plateau, South-west China

Water resources have crucial implications for the steady development of the urban social economy. This study investigated the hydrochemical signatures and genesis of water resources in the urban area of Lhasa City (UALC). To this end, several analyses, such as ion ratio analysis and correlation analysis, were performed by comprehensively applying mathematical statistics and integrated hydrochemical methods. The results show relatively low concentrations of major ions in the groundwater and surface water (GSW) of the UALC. The primary anions and cations are HCO₃⁻ and Ca²⁺, reflecting the HCO₃-Ca water type. Nevertheless, groundwater exhibits higher concentrations of key chemical components compared to surface water. GSW are weakly alkaline, with pH values of 7.78 and 7.61, respectively, and they have low salinity with average concentrations of total dissolved solids being 190.74 and 112.17 mg/L, respectively. Anthropogenic inputs have minimal influence on the hydrochemical features of GSW, whereas rock weathering is the dominant controlling factor. Furthermore, cation exchange is a significant hydrogeochemical process influencing their hydrochemical features. According to the isotope analysis (²H and ¹⁸O), the primary source of recharge for GSW is atmospheric precipitation, with some input from melted ice and snow. Moreover, GSW samples from the UALC show relatively similar ²H and ¹⁸O isotopic compositions, indicating the existence of a discernible hydraulic connection linking the two water sources. The research findings can serve as a valuable scientific reference and foundation for the sustainable development, effective utilization, and proper safeguarding of regional water resources in high-altitude areas.