Hydrochemical characteristics and D-O-Sr isotopes of groundwater and surface water in the northern Longzi county of southern Tibet (southwestern China)

The protection of water resource has been the significant mission globally. Hydrochemical compositions and recharge source are the critical tools to analyze the water quality. In this study, 18 surface water and 5 groundwater samples were collected along the Xiongqu and Sequ rivers in the northern Longzi county of southern Tibet. The combination of factor analysis, correlation of major ions, geochemical modeling, and D-O-Sr isotopes were employed to clarify the hydrochemical compositions and recharge source. The concentration of major ions followed the abundance order of SO24 - > HCO3- > Cl- for anions and Ca2+ > Mg2+ > Na+ > K+ for cations. Ca-HCO3 and Ca-SO4 types were identified for groundwater and surface water. Based on ratios of major ions and geochemical modeling, it is proposed that the dissolutions of gypsum, calcite, and dolomite controlled the hydrochemical compositions. D-O isotopes indicated a meteoric origin for surface water and groundwater, with the recharge elevation of 2,519-3,731 m. The Sr-87/Sr-86 ratios of groundwater and surface water were compatible with those of sulfate and carbonate minerals, revealing the main type of minerals interacting with water. The achievements of this study can provide a vital reference for groundwater utilization and protection in the Longzi county and adjacent areas in the Tibet.