Spatial And Temporal Variation Of TN And TP In Erhai Lake And Analysis Of Driving Factors During 2017～2019

Lakes were related to the production and life of the population in the basin.The safety of lake water quality was the key to the sustainable utilization of water resources,which would be affected by several impacts such as the discharge of pollution loads in the basin,the hydrological rhythm,and the landscape features such as topography,soil,and land use.Therefore,the main driving factors affecting lake eutrophication could be obtained by analyzing the temporal and spatial variation of lake water quality,which could provide scientific support for the prevention and control of lake eutrophication and the guarantee of water environment quality and sustainable development.In this paper,11 sampling points were set up in Erhai Lake,and 24 sampling points were set up at the mixing uniformity of water quality of the main inflow rivers into the estuary of the lake.After monthly sampling,TN and TP water quality indexes were monitored.The temporal and spatial variation of water quality in Erhai Lake from 2017 to 2019 was studied by using partial least squares regression and other methods,and the main driving factors of water quality change were analyzed.The conclusions are as follows :(1)From 2017 to 2019,apparent temporal and spatial heterogeneity was shown by the TN and TP water quality indexes of 11 sampling points in Erhai Lake.Temporally,the TN and TP concentrations were high in wet season(May– October).According to the actual precipitation,a month difference exists between years.Spatially,TN and TP showed a spatial pattern of high in the west – low in the east,high in the north,followed in the south,and low in the middle.From 2017 to 2019,an insignificant upward trend of TN and a downward trend of TP were shown in Erhai Lake showed over time.(2)The PLSR model was used to analyze the water quality indicators such as TN and TP at 11 sampling points in the Erhai Lake.The result showed the ranking of the importance index,which explains 15.5% of the time variation of TN concentration and 56.3% of the time variation of TP concentration.Therefore,the main driving factors that caused the concentration of TN and TP over time in the Erhai Lake were: the monthly water level changed,the monthly water level changed,and the TP load in the monthly.(3)The PLSR model was used to analyze the water quality indicators such as TP and TN at the entrance of the 24 major rivers in the Erhai Lake.The result showed the ranking of the importance index,which explains 61.9% of the spatial variation of TN concentration and 58.8% of the spatial variation of TP concentration.Therefore,in Erhai Lake,the main driving factors affecting the spatial variation of TN were the proportion of grassland area,the proportion of forest land area,the largest patch index,the edge density,the fragrance diversity index,and the spread index.The main driving factors of the spatial variation of TP were soil erodibility factor,area elevation integral,average slope,sprawl index,construction land area ratio,Shannon diversity index,edge density,and patch density.