Hydrogeochemical characteristics and recharge sources identification based on isotopic tracing of alpine rivers in the Tibetan Plateau.

Alpine rivers originating from the Tibetan Plateau (TP) contain large amounts of water resources with high environmental sensitivity and eco-fragility. To clarify the variability and controlling factors of hydrochemistry on the headwater of the Yarlung Tsangpo River (YTR), the large river basin with the highest altitude in the world, water samples from the Chaiqu watershed were collected in 2018, and major ions, δ2H and δ18O of river water were analyzed. The values of δ2H (mean: -141.4‰) and δ18O (mean: -18.6‰) were lower than those in most Tibetan rivers, which followed the relationship: δ2H = 4.79*δ18O-52.2. Most river deuterium excess (d-excess) values were lower than 10‰ and positively correlated with altitude controlled by regional evaporation. The SO42- in the upstream, the HCO3- in the downstream, and the Ca2+ and Mg2+ were the controlling ions (accounting for >50% of the total anions/cations) in the Chaiqu watershed. Stoichiometry and principal component analysis (PCA) results revealed that sulfuric acid stimulated the weathering of carbonates and silicates to produce riverine solutes. This study promotes understanding water source dynamics to inform water quality and environmental management in alpine regions.