Zooplankton Community Structure And Its Relation To Environmental Factors In Taihu Lake

Taihu Lake,located on the southern edge of the Yangtze River Delta,spans Jiangsu and Zhejiang provinces.The lake area is 2338.1 square kilometers and the average water depth is 1.9 meters.It is one of the five largest freshwater lakes in China.Taihu Lake is rich in water resources which brings enormous social and economic benefits in water storage,irrigation,shipping,tourism,and drinking water etc..At the same time,it has also had a certain impact on the aquatic ecosystem in Taihu Lake,specially in large-scale cyanobacteria blooms.Our study was conducted by sampling zooplankton seasonally from Taihu Lake in 2017 and 2018,to analyze spatial and temporal distribution of zooplankton community,then explore the correlationship between zooplankton and environment,and finally evaluate water quality of Taihu Lake based on both zooplanktonic bioindex and physichemical variables,which would provide biological basis for the prevention and control of eutrophication and water ecological restoration of Taihu Lake.The main results were as follows:A total of 67 zooplankton species belonging to 34 genera were recorded in Taihu Lake,including 52 species 21 genus in rotifers,10 species 5 genera in cladocerans,and 5 species 5 genera in copepods.Zooplankton species richness was higher in summer and lower in winter;and,spatially,was lower in the center of the lake and higher in the northern coastal areas of Taihu Lake.In 2017 and 2018,the average annual density of zooplankton in Taihu Lake was respectively 518 ind./L and 526 ind./L,of which rotifers were predominant and account for 84%.Seasonally,the density of zooplankton was highest in August 2018,reaching 995 ind./L,and lowest in May 2017(269 ind./L).In terms of biomass,the average annual biomass of zooplankton for two years were seperately 1.638mg/L and 1.824mg/L,which was dominated by copepods,accounting for 50%.Zooplankton biomass was highest in August 2018(3.30 mg/L),and lowest in February 2018(0.63 mg/L).The seasonal variation of zooplankton biomass in Taihu Lake in the past two years was consistent with zooplankton density,which was higher in summer and autumn than that in winter and spring.In terms of dominant species,Polyarthra sp.was the most dominant species in Taihu Lake(Y=0.099 in 2017,Y=0.082 in 2018),followed by nauplii.In addition,Cyclopidae,Keratella tropica,Bosmina longirostris,and Keratella quartrata,were also predominant in Taihu Lake.The seasonal succession of dominant species was as follows: Synchaeta sp.and Polyarthra sp.in winter,Conochilus unicornis in spring,Keratella sp.in summer and in autumn.The Shannon-Wiener diversity index of the zooplankton community in Taihu Lake was 2.716,and the index in 2018 was slightly higher than that in 2017,which were 2.233 and 2.120 respectively.Pearson correlation analysis showed that the species number and density of zooplankton were significantly positively correlated with temperature and significantly negatively correlated with dissolved oxygen.Redundancy analysis(RDA)showed that nauplii,Cyclopidae and Keratella tropica were positively correlated with p H and water temperature,and negatively correlated with dissolved oxygen and TN.Synchaeta sp.were positively correlated with dissolved oxygen and TN,and negatively correlated with p H and WT.The results of water quality assessmnet based on physicochemical factors and biological indices in 2017 and 2018 showed that Taihu Lake was a middle eutrophiceutrophic lake,and the water quality in 2018 was better than that in 2017.Compared with Dianshan lake,zooplankton species richness and density in Taihu Lake were much lower.Compared with previous studies in Taihu Lake,the number of species slightly increased during the study period,and average density was higher than that in 2009 and 2010.Zooplankton was mainly distributed in Meiliang Lake,with less in the centre of the lake.