Coupling Hydrochemistry and Stable Isotopes (delta H-2, delta O-18 and Sr-87/Sr-86) to Identify the Major Factors Affecting the Hydrochemical Process of Groundwater and Surface Water in the Lower Reaches of the Yarlung-Zangbo River, Southern Tibet, Southwestern China

In Tibet, water resource has been less studied due to remote and harsh conditions. In this study, hydrochemistry and stable isotopes (delta H-2, delta O-18 and Sr-87/Sr-86) were employed to investigate the major factors affecting the hydrochemical process of groundwater and surface water in the lower reaches of the Yarlung-Zangbo River, southern Tibet. Groundwater and surface water were weakly alkaline and very soft to moderately hard water. The hydrochemical type of surface water is mainly Ca-HCO3 (mainstream) and Ca-SO4-HCO3 (tributary), while the hydrochemical type of groundwater was mainly Ca-SO4-HCO3. Multivariate statistical analysis and Gibbs analysis proposed hydrochemical components were dominated by water-rock interaction. Ion ratio, saturation index, and Sr isotope revealed calcite dissolution and silicate weathering with local sulfide oxidation were involved in water-rock interaction. D-O isotopes indicated the recharge source was mainly derived from atmosphere precipitation. The entropy-weighted water quality index indicated surface water and groundwater reach the standard of drinking purpose in the lower reaches of the Yarlung-Zangbo River. The hydrochemical type varied regularly along the Yarlung-Zangbo River. The dissolution of carbonate rocks and local silicate weather and evaporate dissolution are the primary hydrochemical process along the Yarlung-Zangbo River. This study would provide a preliminary insight for hydrochemical process in the Yarlung-Zangbo River.