Hydrochemical regime and its mechanism in Yamzhog Yumco Basin,South Tibet

The hydrochemistry of alpine lakes reflects water characteristic and its response to climatic change. Over 300 water samples had been collected from 52 sites of 5 lakes and 7 inflowing rivers in the Yamzhog Yumco Basin, South Tibet, during 2009–2014, basing which the hydrochemical regime and its mechanism were analyzed along with the adoption of hydrological investigations in 1979 and 1984 as well. Results revealed that the waters were hard with weak alkalinity for the Yamzhog Yumco Basin. Most of them were fresh, and the rest were slightly saline. The hydrochemical types of 5 lakes (i.e., Lake Yamzhog Yum Co, Puma Yum Co, Bajiu Co, Kongmu Co, and Chen Co) were SO₄ ^2––HCO₃ ^––Mg²⁺–Na⁺, HCO₃ ^––SO₄ ^2––Mg²⁺–Ca²⁺, SO₄ ^2––Mg²⁺–Na⁺, SO₄ ^2––HCO₃ ^––Ca²⁺, and SO₄ ^2––Na⁺–Mg²⁺–Ca²⁺, respectively. As for rivers, HCO₃ ^– and SO₄ ^2– were the major anions, and Ca²⁺ was the dominant cation. Lake Yamzhog Yum Co, the largest lake in the basin, exhibited remarkable spatial variations in hydrochemistry at its surface but irregular changes with depth. The weathering of evaporates and carbonates, together with evaporation and crystallization, were the major mechanisms controlling the hydrochemistry of waters in the Yamzhog Yumco Basin. Global warming also had significant impacts on hydrochemical variations.