COMMUNITY STRUCTURE AND SPECIES DIVERSITY OF PROTOZOA IN FIVE INTERCONNECTED LAKES IN HANYANG
To investigate the community structure,species diversity,and influencing factors on protozoa in five interconnected lakes(Houguan,Sanjiao,Nantaizi,Moshui,and Longyang Lakes)of Changjiang(Yangtze)River networks in Hanyang,Hubei,China,as well as their response to eutrophication,this study was conducted seasonally from 2021 to 2022.Results show that the eutrophication levels of the five lakes were different.Houguan Lake had mild eutrophication level,Sanjiao Lake and Nantaizi Lake had moderate eutrophication level,and Moshui Lake and Longyang Lake had severe eutrophication level.In the five lakes,59 protozoa species from 31 genera were identified,among which Houguan Lake had the least species(21 species),while Longyang Lake(41 species)and Moshui Lake(40 species)had most species.The mean annual density of protozoa ranged from 123.37 to 579.47 ind./L,while the mean annual Shannon-Wiener index and Margalef index were 0.75~1.73 and 0.47~1.32,respectively.The density and diversity of protozoa were the highest in autumn,and the lowest in Houguan Lake in space.Multiple stepped-regression analysis showed that chlorophyll a and rotifer density were the main factors affecting the species number,density and diversity index of protozoa.Canonical correspondence analysis and redundancy analysis showed that water temperature(WT),cladocera density,phytoplankton density,transparency(SD),chlorophyll a(chl a),and total nitrogen(TN)were important factors driving the changes of protozoa community structure.The piecewise linear regression model showed that the species number,density and Margalef index of protozoa could better reflect the development law of lake eutrophication.When 44≤TLI(Σ)≤77,the parameters increased first and then decreased with the increase of TLI(Σ),and the peak value occurred when the TLI(Σ)was about 70.The connectivity among lakes improved the overall eutrophic status of the water network,but the diversity of protozoa was still not high.Further governance of lakes and rivers is needed,while controlling pollution sources,gradually improving the ecological environment,and enhancing biodiversity.