Study On The Correlation Between Phytoplankton Community Structure And Water Environment In Dongting Lake And River Channel Entering The Lake

As the second largest freshwater lake in China,Dongting Lake is not only rich in lake products,but also plays an important role in regulating and storing the Yangtze River,regulating precipitation,purifying the environment and providing habitats for living things.However,in recent decades,Dongting Lake has presented a series of problems,such as lake shrinkage,ecosystem degradation,water quality deterioration,water eutrophication and so on.Phytoplankton can be used to quickly and intuitively indicate changes in the water environment in the body of water.By studying the correlation between phytoplankton and water environment in Dongting Lake and the river channels into the lake,we can understand the water quality,nutrient level and ecological situation of Dongting Lake,and find the key factors for its recovery.In this study,20 sampling sections were set up according to the characteristics of Dongting Lake and its inflow channels,the area distribution of Dongting Lake and the surrounding environment.The sampling sections are in the Lake district and the Lake District;Out of the Lake district,etc.Through monitoring and investigation of phytoplankton and water environmental factors in flood season and non-flood season at different sampling sections,the following conclusions were drawn:1.Phytoplankton community structureA total of 57 species of phytoplankton belonging to 53 genera and 6 phyla,8classes,19 orders,31 families were detected in Dongting Lake and its river channel in2021,with the abundance ranging from 8.73×10~5cells/L to 140.68×10~5cells/L.The dominant phytoplankton species were 9 species in 4 phyla,mainly cyanobacteria and green algae in flood season,and diatoms in non-flood season.The species and abundance in upper flood season were higher than those in non-flood season.In terms of spatial distribution,the species and abundance of the lake and the channel into the lake were higher,but the species and abundance of the inlet and outlet control sections were lower.In the lake area,the inner lake is mildly flooded.Biodiversity:Shannon-wiener diversity index,Margalef richness index and Pielou evenness index ranged from 0.73 to 3.72,0.11 to 0.89 and 0.21 to 0.98,respectively,with annual average values of 2.53,0.48 and 0.75,indicating that the water ecological status was moderate.The water ecological condition in flood season was better than that in non-flood season except for the mild bloom in neihu flood season.In terms of spatial distribution,the ecological condition of the control section at the outlet and inlet of the four rivers is better than that of the lake area and inlet of the lake,the ecological condition of the lake in the middle lake area is the worst,and the ecological condition of the water in the west Dongting area is the best.2.Water environmental qualityIn 2021,the water quality of Dongting Lake and its river channels ranged from classⅱto inferior classⅴ.In terms of time distribution,the water quality in flood season is better than that in non-flood season.In terms of spatial distribution,the water quality of Dongting Lake and its inlet is in the range ofⅳ～ⅴ,and the pollution factors are total nitrogen and total phosphorus,and the main pollution factor is total nitrogen.The water quality of the control section of the river entering the lake and the control section of the outlet is basically classⅱ～classⅲ.In 2021,except for the opposite side of Dongting Lake,the lake area and its entrance were between mild eutrophication and moderate eutrophication.The items with high scores in nutritional status index were transparency,total nitrogen and total phosphorus.In terms of time distribution,the average nutrient status index in flood season was slightly lower than that in non-flood season.In the inner part of the lake,the nutrient status index was the highest and reached moderate eutrophication.3.Correlation between phytoplankton community structure and water environmentPearson correlation analysis and RDA analysis were performed on the correlation between phytoplankton community structure and water environment from the aspects of phytoplankton abundance,species and biodiversity.The results showed that water temperature,p H,electrical conductivity,permanganate index,dissolved oxygen,total phosphorus,total nitrogen and lead had great influence on phytoplankton community structure.Diaphaneity and ammonia nitrogen also had certain effects on some dominant phyllophyta.