Geochemistry and solute sources of surface waters of the Tarim River Basin in the extreme arid region, NW Tibetan Plateau

Major ion concentrations of river, lake and snow waters were measured to better understand the water quality, hydrochemical processes and solute sources of surface waters within the Tarim River Basin in the extreme arid region. Surface waters are slightly alkaline and are characterized by high total dissolved solids (TDS). TDS values varies over two orders of magnitude from fresh (76%) to brackish (24%) with a mean value of 1000mg/L, higher than the global river average and river waters draining the Himalayas and the southeastern Tibetan Plateau. Most of the samples were Ca ²⁺(Mg ²⁺)HCO3- type and suited for drinking and irrigation. Water quality of Aksu River (AK), Hotan River (HT) and Northern Rivers (NR) is better than the others. Rock weathering, ion exchange and precipitation are the major hydrogeochemical processes responsible for the solutes in rivers waters. Anthropogenic input to the water chemistry is minor and human activities accelerate increase of river TDS. The quantitative solute sources are first calculated using a forward model in this area. The results show that evaporite dissolution, carbonate weathering, atmospheric input, and silicate weathering contributed 58.3%, 25.7%, 8.7%, and 8.2% of the total dissolved cations for the whole basin. Evaporite dissolution dominated in Lake Waters (LW), HT, Yarkant River (YK), Tarim River (TR), and Southern Rivers (SR), contributing 73.5%, 53.4%, 56.7%, 77%, and 74.2% of the total dissolved cations, respectively. Carbonate weathering dominated in AK and NR, contributing 48% and 44.4% of the total dissolved cations, respectively. The TDS flux of HT, TR, AK, YK was 66.0, 118.6, 134.9, and 170.4t/km ²/yr, respectively, higher than most of the rivers in the world. Knowledge of our research can promote effective management of water resources in this desert environment and add new data to global river database.