Hydrochemical characteristics of surface water in Hengduan mountain region of Eastern Tibet and its response to human activities: A case study of Duoqu Basin, Jinsha River

The analysis of hydrochemical characteristics and influencing factors of surface river on plateau is helpful to study water hydrological cycle and environmental evolution, which can scientifically guide rational development and utilization of water resources and planning of ecological environment protection. With the expansion and diversification of human activities, the quality of surface rivers will be more directly affected. Therefore, it is of great significance to pay attention to the hydrochemical characteristics of plateau surface rivers and the influence of human activities on their circulation and evolution. In this study, surface water in the Duoqu basin of Jinsha River located in Hengduan mountain region of Eastern Tibet was selected as the representative case. Twenty-three groups of surface water samples were collected to analyze the hydrochemical characteristics and ion sources based on correlation analysis, piper trigram, gibbs model, hydrogen and oxygen isotopic techniques. The results suggest the following: (1) The pH showed slight alkalinity with the value ranged from 7.25 to 8.62. Ca²⁺, Mg²⁺ and HCO₃^– were the main cations and anions. HCO₃-Ca and HCO₃-Ca·Mg were the primary hydrochemical types for the surface water of Duoqu River. The correlation analysis showed that TDS had the most significant correlation with Ca²⁺, Mg²⁺ and HCO₃^–. Analysis on hydrogen and oxygen isotopes indicated that the surface rivers were mainly recharged by atmospheric precipitation and glacial melt water in this study area. (2) The surface water had a certain reverse cation alternating adsorption, and surface water ions were mainly derived from rock weathering, mainly controlled by weathering and dissolution of carbonates, and secondly by silicates and sodium rocks. (3) The influence of human activities was weak, while the development of cinnabar minerals had a certain impact on the hydrochemistry characteristics, which was the main factor for causing the increase of SO₄^2–. The densely populated county towns and temples with frequent incense burning activities may cause some anomalies of surface water quality. At present, the Duoqu River watershed had gone through a certain influence of mineral exploitation, so the hydrological cycle and river ecoenvironment at watershed scale will still bound to be change. The results could provide basic support for better understanding water balance evolution as well as the ecological protection of Duoqu River watershed.