| Huayanghe Lakes,located in the middle and lower reaches of the Yangtze River,is an important place for migratory birds to overwinter and fish breeding grounds.However,from2000 to the end of 2017,because most of the waters of the Huayang Lakes were fished,and in order to develop fishery production,multi-scale seine aquaculture was carried out to increase the production of economic fish;resulting in deterioration of water quality and reduction of aquatic plants.Habitats have been destroyed and biodiversity has declined.Since 2018,with the strong support of the national Yangtze River protection policy,aquaculture seine nets have been removed in the Huayanghe Lakes,the aquatic plants has been quickly restored,and the water quality has been improved;further realize the sustainable use of water resources and the development of the ecosystem virtuous circle.In the August 2018-June 2020,this study took the Huayang Lakes after the removal of the seine as the research area,taking zooplankton as the research object,and analyzed the zooplankton species composition,dominant species,existing stock and diversity index,and further explore the relationship between the change characteristics of the zooplankton community structure and the improvement of the water environment after the removal of the seine.The main findings are as follows:1.96 species,48 genera and 26 families of zooplankton were collected and identified in the Huayanghe Lakes.There were 61 species of rotifers,23 cladocera and 10 copepods.In terms of seasonal distribution,the largest number of species were found in June 2020 and August 2018,both with 71 species,January 2019 had the fewest species,with 26.In terms of spatial variation,Lake Bo(64 species)> Lake Huangda(54 species)> Lake Longgan(50species).The number of rotifers species(61 species)is the largest in the total number of species,and the cladocera(23 species)and copepods(12 species)are less.2.The dominant species of zooplankton in the Huayanghe Lakes have significant seasonal and spatial changes.K.cochlearis,K.valga,B.budapestiensis were the dominant species in a year.M.lunaris and B.budapestiensis were the dominant species in spring;M.lunaris and K.cochlearis were the dominant species in summer;P.trigla and B.angularis were the dominant species in autumn;K.valga and A.saltanswere the dominant species in winter.Among the three sub-lakes,B.angularis was the dominant species in Lake Longgan,T.pusilla was the dominant species in Lake Huangda,K.cochlearis was the dominant species in Lake Bo.3.The density and biomass of zooplankton in the Huayanghe Lakes showed obvious seasonal and spatial changes,and their changing trends were roughly the same.The average annual density and biomass of zooplankton were 1317.90 ind./L and 6.36 mg/L,respectively.The average density of rotifers was significantly higher than that of crustaceans,but the average biomass of crustaceans was higher than that of rotifers.The highest zooplankton density in August 2018 was 2786.70 ind./L,the lowest zooplankton density was 202.39 ind./L in November 2018.The biomass of zooplankton reached the highest in April 2019,which was13.40 mg/L;the lowest was 3.13 mg /L in November 2018.In the three sub-lakes,the density of zooplankton varied in Lake Longgan(2651.53 ind./L)> Lake Huangda(840.66 ind./L)>Lake Bo(498.27 ind./L);at the same time,the density of crustacean zooplankton in the Lake Huangda and Lake Bo accounted for a higher proportion.And biomass changed to Lake Longgan(5.07 mg/L)> Lake Huangda(3.67 mg/L)> Lake Bo(2.64 mg/L).4.The annual average Shannon-Wiener index and Marglef index of zooplankton in the Huayanghe Lakes were 2.84±0.20 and 2.25±0.48 respectively.The water quality of the Huayanghe Lakes was moderately polluted by zooplankton index and comprehensive nutrient state index TLI,and some water areas were slightly polluted.The results of Preason correlation analysis and redundancy analysis(RDA)showed that transparency,water depth,Chl.a concentration,water temperature and p H were the main environmental factors affecting zooplankton community structure.In general,the removal of fisher purse seine in aquaculture mitigates the impact of habitat barrier and destruction on the ecosystem,and enables rapid restoration of aquatic vegetation,providing a sanctuary and breeding ground for zooplankton.The species of zooplankton increased,and the density and biomass of zooplankton increased slightly.Through this investigation and study,the important environmental factors affecting the community structure of zooplankton were found,which provided a basic theoretical basis for the restoration of lakes,reservoirs and other water ecosystems in the Yangtze River basin after the removal of the purse seine. |
