Research on the community structure of zooplankton after comprehensive treatment in Lake Dadianhu,Shanghai

A comprehensive treatment was made in Lake Dadianhu(Shanghai) to desilt and restore ecological system during 2005 and 2006.A series of investigations on the dynamics of zooplankton community structure were made to evaluate the treatment from Sep.2006 to Aug.2007,monthly sampled.The investigations explored species diversity,density,biomass of zooplankton and the correlation between zooplankton and environmental facts.149 species of zooplankton were recorded including 80 species of Protozoa,61 species of Rotifer,2 species of Cladoceran and 2 species of Copepods.Amoeba sp.and DiffLugia globulosa were the dominant species of Protozoan while Polyarthra trigla and Trichocerca stylata were the dominant species of Rotifer.However,the dominant species changed in different seasons.The annual average density and biomass of zooplankton in Lake Dadianhu were 13.10×104 ind/L and 10.51 mg/L,respectively.The highest density and biomass emerged in spring(13.10×104 ind/L,10.51 mg/L).The highest proportion of density and highest proportion of biomass in the zooplankton community were both the proportion of Protozoan(98.02%,83.55%) and the second was the rotifer(1.99%,12.79%),Cladocera and Copeoda were low.The annual average density and biomass of Cladocera were 9.5 ind/L and 0.11 mg/L while the Copeoda were 0.32 ind/L and 0.01 mg/L.The average annual Shannon-Weiner index of Rotifer was 2.30 and Protozoan was 1.91 while Cladocera and Copeoda were both below 0.5.The characteristic of zooplankton community structure of Lake Dadianhu after treatment was that the proportion of density and biomass of Cladocera and Copeoda in the zooplankton community was very small and diversity index of them was small,too.The water quality was Ⅲ-Ⅵ grade classified by GB3838-2002 while it was eutrophic assessed by the biomass of zooplankton and α-β mesosaprobity by the index of Shannon-Weiner.GAM analysis showed that the correlation between zooplankton biomass and chlorophyll-a or nitrate nitrogen was significant.