Assemblage structure investigation of macrozoobenthos and water quality bioassessment of the main river systems in Taihu Basin

Aimed at characterizing the assemblage structure of macrozoobenthos,identifying the key influencing environmental factors and evaluating the water quality in terms of biological indexes,we investigated macrozoobenthos at 73 sites of the five river systems(Rivers Tiaoxi,Nanhe,Taoge,Huangpu and Yanjiang)within Taihu Basin during April and June of 2010.Total 88 species from 48 families,8 classes and 3 phyla have been found in the investigations.The mean density of macrozoobenthos was 5888.91ind./m2,in which the proportion of oligochaetes was 94.19%.The mean biomass of macrozoobenthos was 105.18g/m2,of gastropods with 72.50% in total biomass.Limnodrilus hoffmeisteri was the dominant species in all river systems.One-way analysis of similarity(ANOSIM)showed that macrozoobenthos assemblages in the Yanjinag River system differed significantly from other four river systems,and those of Tiaoxi and the Taoge River systems differed significantly.L.hoffmeisteri was primarily responsible for dissimilarities of macrozoobenthos assemblages among the five river systems,followed by Bellamya aeruginosa,Branchiura sowerbyi,Chironomus plumosus,Gammarus sp.,Propsilocerus akamusi,Corbicula fluminea,Microchironomus sp.,Chironominae sp.,Glyptotendipes lobiferus,Tanypus chinensis and Alocinma longicornis.Canonical Correspondence Analysis showed that CODMn,PO4-P,TN and NO3-N were strongly correlated with the macrozoobenthos assemblages.The results of bioassessment using the BPI and the Wright Indexes indicated that the five river systems were mostly at status of intermediate polluted.