Spatio-Temporal Variation Of Zooplankton Community Structure And Water Quality Assessment The River In Chongming Island

Located at the mouth of the Yangtze River,the rivers in Chongming Island is the world’s largest estuarine impact island.It is located in a tropical monsoon climate area with abundant rainfall,sub-dry river layout for the“One horizontal and sixteen vertical”inland river complex.The species composition of metazoan zooplankton(Rotifer,cladocerans,copepods)is characterized by a transition zone between freshwater and seawater.In recent years,with the city proposing to build Chongming Island into a world-class eco-island by 2035,therefore,the Chongming Island municipal government is paying more and more attention to the ecological monitoring of river water environment.The community structure of metazoan zooplankton can reflect the water quality of this area by its rapid response to the changes of water environment.In this study,a total of 192 vials of zooplankton were collected during the period of April 2019 to May 2019(due to covid-192021,no samples were collected in spring 2020)to investigate the community structure of zooplankton the rivers in Chongming Island,the relationship between community structure of metazoan zooplankton and environmental factors the rivers in Chongming Island was analyzed and discussed.The water quality the rivers in Chongming Island was evaluated by physical,chemical and biological monitoring methods,to provide basic data for the scheduled construction of Chongming as a world-class ecological island with world influence,and to evaluate the current situation of the island’s waterways,it is of great significance for scientific assessment of the construction process and effectiveness of Chongming Island,protection of the environmental quality of surface water in Chongming Island,and reference for the implementation of ecological restoration projects in Chongming Island.The main findings are as follows:A total of 93 metazooplankton species belonging to 22 families and 44 genera were collected and identified the rivers in Chongming Island during the study period.There were 34 species of rotifers,most of which came from brachiococcygiaceae and rhamnococcygiaceae,and most of the rotifers were widespread species.There were 27 species of daphnidae and 10 species of open water,most of which came from Daphnidae.There are 32 species of copepods.The copepods in Chongming river channel and surrounding waters reflect the characteristics of copepods in the transition area from fresh water to seawater at the genus level,and have certain regional characteristics at the species level.The total density of zooplankton after two years and eight quarters was 456.2ind./L and the biomass was 1.7316mg/L.The spatial variation of the present stock of epigenetic zooplankton was as follows: the maximum biodensity of the east Chongming Island was 520.1ind./L,the maximum biodensity of the river-sea junction was 2.2528mg/L,and the minimum biodensity biomass of the central Chongming Island was 424.5ind./L and 1.1275mg/L,respectively.The time variation of the present stock of metazoan zooplankton is as follows: In the summer of 2019,the highest biodensity and biomass were 2372.2ind./L and 4.5202mg/L,respectively,while the lowest biodensity was 67.9ind./L in the spring of 2019,and the lowest biomass was1.1853mg/L in the winter of 2021.The Shannon-Wiener index(H′),Margalef richness index(D)and Pielou evenness index(J)of river rotifers in Chongming Island were 0.94,0.49 and 0.83 respectively.The mean Shannon-Wiener index(H′),Margalef richness index(D)and Pielou evenness index(J)of river Cladocera in Chongming were 1.16,1.28 and 0.85 respectively.The mean Shannon-Wiener index(H′),Margalef richness index(D)and Pielou evenness index(J)of river copepods in Chongming were 1.60,1.72 and 0.83 respectively.RDA analysis showed that environmental factors such as salinity,electrical conductivity,total phosphorus,transparency,ph,chlorophyll a and dissolved oxygen were the main factors affecting the community structure of metazoan zooplankton the rivers in Chongming Island.Based on the comparison of the community composition of metazoan zooplankton in the four regions of the rivers in Chongming Island by PCOA,the community composition of metazoan zooplankton in the four regions has no significant difference,however,the composition of zooplankton community and the density of zooplankton in the four sites at the confluence of rivers and seas are quite different,there were no significant differences in zooplankton community composition and biological density among other sites in the west,middle and east of China.But the number of metazoan zooplankton species ithe rivers in Chongming Island is significantly higher than in most inland rivers.In this study,integrated environmental physical and chemical factors were used to evaluate the water quality of the rivers in Chongming Island channel using the Integrated Water Assessment index method,the indicator biological method,and the zooplankton stock method combined with the metazoan zooplankton data,the rivers in Chongming Island was judged to be in good condition,with the overall water quality reaching a level of moderate pollution and eutrophication,and the 2021 improved gradually from 2019 to 2010.