ZHANG Xue-qin, SUN Rui, ZHU Li-ping
Alpine lakes on the Tibetan Plateau are regarded as an important and sensitive indicator of global and regional climate change. As the basic prerequisite for researching lake variation and its response to climate change, the basic chemical parameters, hydrochemical type, mineralization change and its causes, and water quality evaluation are explored for the five major lakes (i.e., Yamzhog Yumco, Kongmu Co, Chen Co, Bajiu Co and Puma Yumco) in Yamzhog Yumco basin in South Tibetan Region. The results are summarized as follows. Firstly, the concentrations of certain chemical parameters (e.g., mineralization, major ions) are different remarkably among the five lakes. The water chemical properties of the five lakes, however, still have some similarities. With high alkalinity, the lake water in the basin contains low concentration of dissolved oxygen (DO), fluoride, total phosphorus and total nitrogen, and trace amounts of selenium and other heavy metal ions. Secondly, the significant differences of hydrochemical types are also disclosed for the five lakes. The preponderant anion and cation of lake water in both of Yamzhog Yumco and Bajiu Co are SO42--Mg2+, and in Chen Co, Kongmu Co and Puma Yumco are SO42--Na+, HCO--3-Ca2+, HCO--3-Mg2+, respectively. Thirdly, there are disparate supply sources that cause obvious difference of mineral concentrations for the five lakes. The mineral concentration of Yamzhog Yumco, Bajiu Co and Chen Co supplied mainly by rainfall is much greater than that of Kongmu Co and Puma Yumco supplied by glacier and snow melt water. With global warming, the mineral concentration change of the lake water is influenced mainly by climate change in the sparsely populated alpine regions. Besides, the operation of Yamzhog Yumco Power Station has a negative impact on the lake water chemical property to some extent. At last, the water qualities of all the five lakes in the basin are evaluated to be unsatisfactory owing to high pH and low DO. In addition, it is the high mineralization that makes the lake water of Yamzhog Yumco, Chen Co and Bajiu Co neither drunk by local herdsmen and farmers residing nearby the alpine lakes, nor supplied for industrial and agricultural production. Lake water chemical parameter monitoring and water quality evaluation should be carried out continuously in the future, which will be beneficial to the investigation on water quality response to climate change in the alpine regions.