Water quality of the southern Tibetan Plateau: hydrogeochemistry assessment of the Yarlungzangbo River

The Yarlungzngbo River (YR) is the largest river system draining the northern slopes of the Himalayan ranges on the southern Tibetan Plateau and is critical to the water supply of the people downstream. In this paper the chemical composition of the YR and its major tributaries (Nianchu River and Lhasa River) are studied. Water samples (n=165) were collected and analyzed for major ions and trace elements. Multivariable analysis shows that geology and climate are the major explanatory variables for the spatio-temporal variation in water chemistry in this river system. Water chemistry is mainly controlled by carbonate weathering, with Ca 2+ and HCO 3 - being the dominant ions. Furthermore, hot spring discharge rich in Na + , Cl - , SO 4 2- and Li is another potential ion source affecting river water chemistry, resulting in higher solute concentrations in the source region and upstream, TDS reached 176.9 mg/L. Levels of most trace elements were generally found to be low. However, elevated As (16.6 μg/L) and Sb concentration (2.08 μg/L) in the headwaters and additions from untreated wastewater were evident, which exceeded the national standard of China (GB) and the World Health Organization (WHO) drinking water guide, posing a risk to human livelihood in the local and surrounding areas. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850720