Characteristics and seasonal variations in the hydrochemistry of the Tangra Yumco basin, central Tibetan Plateau, and responses to the Indian summer monsoon

This study focuses on the characteristics, seasonal variations, and controlling mechanisms of the ionic composition of the Tangra Yumco basin for lake water, river water, and rainfall, which is located in the central Tibetan Plateau. The results showed that Na⁺ is the major cation in the lake water, Ca²⁺ is the major cation in the river water and rainfall, and \({\text{HCO}}_{3}^{ - }\) is the major anion in all the water samples. A comparison of the concentrations of calcium in the river water, lake water, and lake sediments reveal significant carbonate precipitation within the lake. The chemical composition of the lake water is mainly controlled by evaporation and crystallization, whereas the compositions of river water and rainfall are mainly controlled by carbonate weathering. Because the TDS content of the river water is lower than the lake water, the TDS content of the lake water is diluted, forming a decreasing trend during the beginning of the Indian summer monsoon. The lake water TDS content then increases rapidly from August to early September due to enhanced evaporation of the lake surface water and the introduction of a large amount of material carried by surface runoff. It then decreases slightly until December due to precipitation in the lake water and less input from the surroundings of the lake.