Benthic Macroinvertebratre Community Structure And Health Assessement Of Taihu Lake, China

Taihu Lake is the second largest freshwater lake of China located in the Yangtze River delta plain. With the rapid development of economy in Taihu Lake watershed, the eutrophication level of Taihu Lake went high and the cyanobacterial blooms happened frequently, the ecological condition of Taihu Lake get worse. In this study, we seasonally sampled and measured macroinvertebrate assemblages and environmental variables at32sites in Taihu Lake from spring,2010to autumn,2012. The aim of our study is to explore the structure characteristics and temporal dynamics of benthic macroinvertebrate community of Taihu Lake, and to develop a benthic index of biotic integrity, and then to assess the health condition of Taihu Lake.A total of31647benthos individuals belonging to68taxa (thereafter species),15orders,7classes,3phylums were collected and identified based on the present literatures. The dominant phylum is arthropoda including34species, accounting for50%, of which there were6species of crustacean, accounting for8.82%and28species of insecta, accounting for41.18%. The followed were21species of mollusca, accounting for30.88%, and13species of annelida, accounting for19.12%. The common species were Corbicula fluminea, Nephthys sp and Limnodrilus sp. The mean density of32sites was605ind/m2ranging from54ind/m2to2608ind/m2. The mean value of Shannon-Wiener was1.65, ranging from1.27to2.06, for Pielou was0.66, ranging from0.59to0.71, and for Simpson was0.56, ranging from0.45to0.66.Spring and winter seemed to have more species than summer and autumn in the3years. Winter of2011and spring of2012were the seasons of most species(40and39species for each). Summer of2010, summer of2011and autumn of2012(33,24and32species, respecitively) were the seasons of least species for each year. Seasonal changes of mollusca and insecta mainly contributed to the seansonal changes of the macroinvertebrate community. Summer and autumn of2010had the highest desity of all the seasons (1295ind/m2and857ind/m2for each), while Spring of2010(741ind/m2), summer of2011(373ind/m) and autumn of2012(208ind/m) had the lowest desity of the year. There was no obvious seasonal dynamic of community density. Overall, the diversity of Taihu Lake macroinvertebrate showed a potential recovery trend.In order to develop a benthic index of biotic integrity for Taihu Lake (TLB-IBI) with the macroinvertebrate data of the11seasonal surveys, we used the method of least disturbed condition (LDC) to define reference condition, and a four-criteria to determine reference sites. TLB-IBI was developed separately for non-central region and central region of Taihu Lake. Metrics were stepwise examined for distribution analysis, discriminating power analysis, relationship with environmental variables and redundancy analysis. The core metrics of TLB-IBI for non-central region were total taxa number, Simpson diversity index,3dominant taxon%and BMWP score, One more metric, i.e.(Crustacea+Mollusca) taxa for central region. TLB-IBI value for non-central region and central region were respectively obtained by summing up core metrics, which were transformed into a uniform score by ratio score method, i.e. health when TLB-IBI>2.72for non-central region and TLB-IBI>3.46for central region. The result of assessment using TLB-IBI showed health condition of Taihu Lake was found to improve gradually from2010to2012. Total nitrogen was suggested as the major factor affected TLB-IBI. Our results suggest that long-term data would benefit the development of a robust TLB-IBI and its use in practice of Taihu Lake health assessment.