Temporal And Spatial Variation Research On Yilong Lake Water Quality

Yilong Lake(located in Shiping County,Honghe Prefecture,Yunnan Province)has suffered serious eutrophication in recent years due to the increase in the discharge of industrial,agricultural and domestic sewage in the basin caused by the rapid economic and social development.As one of the four heavily polluted lakes in the nine high-altitude lakes in Yunnan Province and one of the 18 sub-standard water quality sections for assessing the surface water environment quality of Yunnan Province,the target of water quality of the Yilong Lake is required to be “COD?60mg/L by 2019”,issued by the country in the Target Responsibility Letter of Water Pollution Prevention and Control in Yunnan Province.Based on the above background,the research on eutrophication of Yilong Lake and water quality protection are particularly important.In this project,Yilong Lake is divided into three areas in the direction of east,west and middle sections.Each area is equipped with 4 monitoring points,which are monitored monthly from March 2017 to February 2018.In the rainy season,an additional monitoring was added every month from April to October.Based on these data,the water quality characteristics of the annual water quality of the Yilong Lake were analyzed.The historical and dynamic analysis of the water environment of the Yilong Lake has also carried out based on data from the past 30 years.The following research results were obtained:(1)The current status of water quality in Yilong Lake is inferior V,and the main pollutants exceeding the standard are chemical oxygen demand.Compared with 2015,the index of important pollutants dropped significantly.There are obvious seasonal differences in the variation of water quality during the year,which is mainly caused by the seasonal differences in the nutrient input of the lakes under the influence of the characteristics of the dry and wet seasons.(2)The water quality of Yilong Lake in the West area is significantly better than that in the middle and east areas,which is influenced by the fact that the water purification project of the Yilong Lake promotes a large number of clean water sources to enter the Yilong Lake in the West area.(3)In the past 35 years,Yilong Lake has been under the eutrophication for a long time,and the water quality and nutrition status can be divided into three main stages.From 1980 to 1994,the nutritional status of lake water quality showed a rising trend,mainly caused by agricultural sources in the basin.From 1994 to 2010,the trend of eutrophication slowed down,which may be related to the dilution of lake nutrients during the inter-basin water diversion.From 2010 to 2015,the trend of eutrophication began to aggravate significantly,which was associated with the industrial pollution,the agricultural non-point source pollution and the release of sediments in the lake due to the drought as well as the sustained social and economic development.