Abstract: Chemical characteristics and ion compositions are important indices of water environment,and have important indicative effect on climate and environment changes. The Qiangyong Glacier-Karuxung River-Dremtso Lake located in the southern Tibet(90°8'10″-90°38'38″ E,28°46'21″-29°0'28″N,elevation:4 390-7 185 m) was chosen as the study area. A total of 115 water samples were collected from 13 points during July and August 2015,including 1 point in the Qiangyong Glacier runoff,1 point in the Karuxung River,and 11 points in the Drem-tso Lake. TDS,pH,and EC of the glacier runoff and river water were tested using Multi-Parameter PCSTestrTM 35,while TDS,pH,EC,temperature,and turbidity of the lake water were tested by EXO-2 multi parameter water quality instrument. The cation concentrations of Ca²⁺,K⁺,Na⁺ and Mg²⁺ were tested with ICP-OES and the anion concentrations of Cl^-,NO₃^- and SO₄^2- were analyzed with ICS-900. The study preliminarily analyzed the chemical characteristics and controlling factors of the Drem-tso Lake and its supplying runoff. Although the lake water temperature showed stratification phenomenon,pH,EC,TDS,and dominant ionic concentrations of the lake water did not show significant spatial variation during the sampling period. The uniform distribution of lake water chemical characteristics indicated that sampling at individual point in the lake had the potential to study the chemical characteristics of the Drem-tso Lake,as long as keeping away from the locations close to the supplying runoff. From the upstream glacier melting water,down to the midstream river and the downstream lake water,the TDS,EC and major ion concentrations generally increased. The average EC was 154,440,1 529 μs·cm^-1 while the average TDS was 121,346,1 219 mg·L^-1 in the glacier runoff,the river and the lake water,respectively. The EC and TDS of the lake water were nearly 10 times of the glacier runoff,and about 3.5 times of the river water. The chemical type of the Qiangyong Glacier runoff and the Karuxung River water were both SO₄^2--Ca²⁺-Mg²⁺, controlled by the weathering of rocks. Major ions of the Drem-tso Lake water were mostly from the supplying runoff and mainly controlled by evaporation and crystallization,resulting in the chemical type of SO₄^2--Na⁺-Ca²⁺ due to the low solubility of calcium carbonate but high solubility of sodium salt.

Key words: plateau lake, water chemistry characteristics, major ion composition, Gibbs, controlling factor