The Spatio-Temporal Variation of Hydrochemical Characteristics in Yamzhog Yumco Basin, South Tibet

Abstract:

From 2009 to 2014, more than 300 water samples of 52 sites from the five lakes and seven inflow rivers of Yumzhog Yumco Basin, South Tibet have been collected, and the hydrochemical types, sources of ions, and the spatial-temporal variation in waters analyzed annually. The basin waters are slightly saline or fresh because of the different sources of water replenishment, and are hardest water with weak alkalinity. The hydrochemical types of Yamzhog Yum Co, Puma Yum Co, Bajiu Co, Kongmu Co, and Chen Co are SO₄^2--HCO₃^--Mg²⁺-Na⁺, HCO₃^--SO₄^2--Mg²⁺, SO₄^2--Mg²⁺-Na⁺, SO₄^2--HCO₃^--Ca²⁺, and SO₄^2--Na⁺-Mg²⁺-Ca²⁺, respectively. As for rivers, HCO₃^- together with SO₄^2- is the major anion, and Ca²⁺ is the dominant cation. The weathering of evaporites and carbonatites, along with the evaporation-crystallization plays a significant role in the difference of hydrochemical compositions. In addition, anthropogenic impacts, such as the rapid tourism development and the utilization of Yamzhog Yumco hydropower should not be ignored. Compared with the salinity in 1984, Puma Yum Co has been desalinated obviously during 2009-2014 as a result of the accelerated glacier melt caused by the global warming. Furthermore, the Cl^- concentration has decreased consequently with the increased evaporation from 2009 to 2014. Yamzhog Yum Co, the largest lake in this basin with a complex zigzag bank and a different inflow river system, exhibits remarkable spatial variation for its surface waters. The mineralization degree, and the concentration of Mg²⁺ and (Na⁺+K⁺) are low with high concentration of Ca²⁺ in the river mouth entering into Yamzhog Yum Co. Moreover, the irregular changes in vertical direction can be attributed to the strong wind and comparatively abundant rainfall during the sampling period. To sum up, the combined impacts of environmental changes and human activities can account for the spatial distribution and temporal evolution of hydrochemical characteristics in Yamzhog Yumco Basin.