Community structure of zoobenthos in spring and their application to bioassessment of water quality in Taihu Lake Watershed

The macrozoobenthic assemblages in 7 reservoirs,8 rivers,and 14 lakes of Taihu Lake Watershed were investigated in May,2010.Totally,57 species,belonging to 8 classes,representatives of 4 phyla,were collected.Of those,Insecta(17 species)and Oligochaeta(15 species)were the most abundant in species number.As a whole,the zoobenthic assemblage in this watershed was predominated by Limnodrilus hoffmeisteri.According to cluster analysis(CA),there existed 10 community types in the selected 29 water bodies,15 of which were prevailed by L.hoffmeisteri and 5 of which by Bellamya aeruginosa.The mean density and biomass in the whole basin were 2741.2 ind/m² and 47.2 g/m²,respectively.Oligochaeta was predominant in density(about 91%),and Bivalvia together with Gastropod contributed about 93% of the total biomass.Among the different water body types,there were marginally significant or conspicuous differences in density with the maximum for river and the minimum for reservoir,and in biomass with the maximum for lake and the minimum for reservoir.Meanwhile,the numerical composition of macrozoobenthic groups(i.e.at the taxonomic level of class)differed obviously between the water body types.Although Shannon-Weaver diversity index(H′)was conspicuously correlated with richness(species number,S),H′ was more strongly governed by evenness(J).H′,J,and Margalef species richness(R)in lake and reservoir were all significantly higher than those in river,respectively,and S did marginally conspicuously.The density in lakes with practice of aquaculture was significantly higher than in ones without.The reverse were found for biomass,H′,and J.According to BPI index and H′,the most stations of lake and river were moderately or seriously polluted,and the most reservoirs were clear or slightly polluted based on Wright index.