Hydrochemical characteristics and possible controls in the groundwater of the Yarlung Zangbo River Valley, China

The Yarlung Zangbo River Valley is situated in the Qinghai Tibet Plateau with high elevation, abundant water resources and less influence from human activities. In this study, 47 groundwater samples were collected to investigate the hydrochemical characteristics and possible control of these characteristics in the groundwater of the Yarlung Zangbo River Valley; the samples were statistically analyzed using a Durov diagram, Gibbs plot, ratio graphs of ions, and factor analysis. The study results showed that the mean concentrations of the major ions in groundwater were relatively low, and the predominance of cations and anions in the groundwater was Ca2+>Mg2+>Na+>K+ and HCO3->SO42->Cl-, respectively. Most groundwater samples fall in the category of HCO3-Ca and mixed HCO3SO4-Ca<bold>Mg</bold>. Upstream to downstream, the total dissolved solids and major cations and anions in the groundwater show a gradual decreasing trend due to the dilution effect of precipitation and lateral runoff recharge, except for the K+. The water-rock interaction was the primary mechanism controlling the groundwater chemistry in the study area. The dissolution of carbonates was the major contributor to the formation of the groundwater chemistry, and the dissolution of silicate and sulfate also contributed to the chemical composition of the groundwater in the study area, whereas the cation exchange was weak. In addition, H2SO4 participation in the dissolution and weathering of carbonate was an important source of SO42-.