Water quality of the southern Tibetan Plateau: hydrogeochemical assessment of the Yarlungzangbo River.

The Yarlungzangbo River is the largest river system draining the northern slopes of the Himalayan ranges on the southern Tibetan Plateau and has a crucial role in the supply of water downstream. We investigated the chemical composition of the Yarlungzangbo River and its major tributaries (the Nianchu and Lhasa rivers). Water samples (n = 165) were collected and analysed for major ions and trace elements. Multivariable analyses showed that the geology and climate are the major explanatory variables for the spatiotemporal variations of the water chemistry in this river system. The water chemistry is mainly controlled by carbonate weathering, with Ca²⁺ and HCO₃⁻ as the dominant ions. Another potential ion source affecting the river water chemistry is the discharge from hot springs, which is rich in Na⁺, Cl⁻, SO₄²⁻ and Li, resulting in higher solute concentrations in the source region and upstream, with the total dissolved solids reaching 176.9 mg L⁻¹. The concentrations of most trace elements are generally low, although elevated concentrations of As (16.6 μ g L⁻¹) and Sb (2.08 μ g L⁻¹) are found in the headwaters and additions from untreated wastewater are evident. These concentrations exceed the national drinking water standard for China and the World Health Organization drinking water guideline, posing a risk to people living in both the local and surrounding areas. Supplementary material: The basic field records, water chemical compositions and trace elements of the Yarlungzangbo River and its main tributaries, and concentrations of chemicals of health significance as described by the international guideline (WHO) and the China national guideline (GB) for drinking water quality are available at https://doi.org/10.6084/m9.figshare.c.6850720 [ABSTRACT FROM AUTHOR]