Spatio-Temporal Variation Of Water Quality And Chl-α Response To High Water Levels At Lake Xingyun

Lake eutrophication is the main environmental problem due to economic development and dense population in Yunnan-Guizhou Plateau(YGP).Mitigation of lake eutrophication has highest priority to improve water quality and solve water shortage problem in Yunnan Province.In this paper,Lake Xingyun,a shallow lake with severe environmental pollution in Yunnan province,is taken as a case study based on three-year monitoring of water quality parameters including water temperature(WT),total nitrogen(TN),total phosphorus(TP),ratio of nitrogen to phosphorus(TN/TP),phycocyanin(PC),chlorophyll a(Chl-a),turbidity(Turb),pH value,Optical dissolved oxygen(ODO),total dissolved substances(TDS)and conductivity(Cond).The purpose was to analyze the spatio-temporal characteristics of water quality during the monitoring period,the variation characteristics and influencing factors of Chl-a during high water level time,and to explore the main pollutants and their sources,so as to provide theoretical basis for pollution control at Lake Xingyun.The main conclusions are as follows:(1)The spatio-temporal variation of TDS and Cond are subtle;pH varies significantly with time but not in space;WT,TN,TP,TN/TP and Turb vary greatly with space and time;ODO,Chl-a and PC have significant temporal and spatial variations.It was found that most of the parameters with significantly spatio-temporal variation were correlated with algal growth.From the correlation between PC and other water quality parameters in the past three years,WT and pH affect nutrient release from sediments,so that Turb and ODO change with the proliferation of algae.TN has a strong correlation with algae growth for a long time due to air deposition.(2)During the period of rising water level,the overall Chl-a concentration increases with the rise of water level,and nutrient is the main factor driving the change of water quality at Lake Xingyun.Compared with the correlation between water quality parameters in recent three years,the influence of nutrients on algae growth was significantly enhanced in this period,and the correlation between physical and chemical parameters and nutrients was also enhanced,indicating that the physical and chemical properties of the lake changed with the change of water level in this period,and the influence on endogenous nutrient salts was enhanced.During this period,the algae indicators and nutrient salts had a certain lag with respect to the change law of precipitation,indicating that the endogenous pollutants deposited in the lake were correlated with the exogenous pollutants brought by precipitation,and the precipitation drive increased the endogenous nutrient salts in the lake.(3)During the period of water level rising,the nutrition degree of Lake Xingyun was severe eutrophication-abnormal eutrophication.The long-term water quality grade is between IV~ V,and the water quality function is poor.In summer,the water quality exceeds the standard most seriously.The main pollutants exceeding the standard are TN,pH and TP,so appropriate measures can be taken according to the nature of corresponding pollutants.(4)The spatio-temporal variation trends of TDS and Cond,Turb,TN,TP and PC of Xingyun Lake are similar,and the parameters in the two groups are significantly correlated,so the target parameters can be predicted by establishing a model.