Spatiotemporal Variation Characteristics Of Water Chemistry And Its Controlling Factors Of Basong Lake In Tibet

Basong Lake is the largest glacial barrier lake in southeastern Tibet.It is the largest source of replenishment in the upper reaches of the Niyang River,a tributary of the middle and lower reaches of the Yarlung Tsangpo River.It is also a deep-water outflow freshwater lake.This study took the Basong Lake area as the research object,and conducted four times in the warm season(July)and cold season(December)in 2019 and 2020,respectively.The water of Basong Lake,the rivers entering the lake and the water outlets were conducted four times.System sampling.Combining the laboratory instrumental analysis data of the water samples and the determination of on-site physical and chemical parameters,analyze the physical and chemical parameters of the water body in the Basong Lake area and the temporal and spatial distribution characteristics of the main ions,and analyze the characteristics of the water temperature stratification and the water temperature stratification of the vertical profile in different seasons in Basong.The response relationship with the physical and chemical properties of the water body,and the control factors of the main ion sources and the nutrient components in the dissolved phase of the water body are analyzed.The results show that:(1)In different seasons,the main physical and chemical parameters of the river entering the lake,the surface of the lake,the vertical profile,the lakeside and the water outlet in the Basong Lake area have changed significantly.Affected by regional climate change and precipitation,the water temperature and turbidity tend to be higher in the warm season than in the cold season.EC,TDS and Sal.have the same change characteristics,and the cold season is higher than the warm season.There is no obvious seasonal difference in pH and ROD.The water in the lake area is generally alkaline and has a high buffering capacity.(2)In terms of spatial changes,the values of physical and chemical parameters and the content of main ions of the rivers entering the lake vary greatly,and the overall trend tends to be stable after entering the lake.In the vertical section,the water temperature changes greatly on the vertical section,and there is a good response relationship between the water temperature and various physical and chemical parameters.The main ions all have a certain trend of change in the vertical profile,and all show a trend of increasing concentration with the increase of water depth.(3)Ca²⁺and HCO₃^-are the dominant anions and cations in lake water bodies,and SO₄^2-also meets the naming requirements.The water chemistry type of the Basong Lake area is HCO₃·SO₄-Ca.(4)The main ions in the water body of the Basong Lake area are significantly affected by the control of rock weathering in the lake area.The results of the ratio relationship between the equivalent concentrations of the ions show that the weathering of carbonate in the basin is the main source of ions in the lake area,and the weathering of silicate rock salt also exists in the lake area,but its effect is very small.In the natural process of carbonate weathering as the main body,sulfuric acid also participates in the weathering process of carbonate rocks,but its participation intensity is relatively low.(5)Orthophosphate was not detected in the cold season water in Basong Lake area,and ammonia nitrogen was only detected in a few samples.By calculating the ratio of nitrogen to phosphorus in the Basong water body,it is shown that nitrogen is the limiting factor for lake eutrophication.