Hydrochemistry and its controlling factors of rivers in the source region of the Yangtze River on the Tibetan Plateau

•Comprehensive study of hydrochemistry of rivers was conducted.•Major rivers are compared and strong spatial heterogeneity is observed.•There are significant differences between southern rivers and northern rivers.•The chemistry of waters was mainly the type of Cl·HCO3–Na·Ca.•Due to complex geological setting, the controlling factors are complicated.

This study focuses on the chemical composition, and the factors controlling it, of the high mountain-rivers in the source region of the Yangtze River on the Tibetan Plateau. By comprehensive and systematic analysis, the chemical signatures, spatial variations of water quality, as well as the factors controlling them are studied. The value of the average total dissolved solids (TDS) is 778 mg/l, ranging from 117 to 5496 mg/l. In order of decreasing concentration, the main cations are Na+, Ca2 +, Mg2 +, and K+, while the main anions are Cl−, HCO3−, SO42 −, and NO3−. Na+ and Cl− are the dominant ions, accounting for 74.2% and 63.7% of the total cations and anions, respectively, followed by Ca2 + and HCO3−, which account for 14.3% and 25%, respectively. The Piper diagram shows the main water type to be a Cl−·HCO3−–Na+·Ca2 + type. From the Gibbs boomerang model, we conclude that the chemistry of the river water is controlled by lithogenic weathering processes. The Na-normalized ratio end-member diagram indicates that the weathering of silicates and carbonates is relatively significant, on the whole. There exists pronounced regional heterogeneity in the water chemistry and the factors affecting it. The northern rivers, including Chumaer He, Beilu He, and Ranchiqu, are mainly affected by evaporation and crystallization processes, while the southern rivers (Tuotuo He, Gaerqu, and Buqu) show effects from the weathering of carbonates and silicates.