Macroinvertebrate Communitie Structure And Their Responses To Environmental Factors In Taihu Lake, China

Taihu Lake, located in Yangtze River delta plain, is the second largest freshwater lake in China. With the rapid economic development in the Taihu Lake basin, its eutrophication process has been increasingly deteriorating characterized by declining ecological health and more frequent cyanobacterial blooms. Macroinvertebrates are the important aquatic organism in aquatic ecosystem and widely used in the biological assessment of water quality. This thesis aimed to explore the temporal and spatial dynamics of composition and structure of macroinvertebrate community, from winter 2010 to autumn 2012, based on the survey data of water quality and macroinvertebrate at 18 sites, in the three main regions of Taihu Lake. The response of macroinvertebrate community to environmental factors was analyzed by use of 12 community structure metrics representing different characteristics of macroinvertebrates community.A total of 42 taxa,3 phylum 7 classes and 15 orders (hereinafter referred to as "species") were found from our surveys. Of which,15 species were mollusca, accounting for 35.71%; 17 species were arthopoda, accounting for 40.47%, including 11 species of insecta, accounting for 26.19%, and 6 species were crustacea, accounting for 14.28%; and 10 species were annelid, accounting for 23.80%. Indicator species analysis (ISA) showed that the top three indicator species of North Bay were Limnodrilus hoffmeisteri, Corbicula fluminea, and Polychaeta sp. The ISAs of East Bay were Nephthys sp., Branchiura sowerbyi, and Bellamya aeruginosa, and ISAs of Open Lake were Corbicula fluminea, Nephthys sp., and Cythura sp. The mean density of macroinvertebrate site was 679 individuals (ind.) per square meter, with a maximum of 1107 ind. and a minimum of 366 ind. The mean Shannon-Wiener diversity index was 2.04, ranging from 1.68 to 2.49. The mean Pielou evenness was 0.63, ranging from 0.51 to 0.71. The mean Simpson diversity index was 0.79, ranging from 0.69-0.88.The species richness dynamic showed a gradually decreased pattern from winter to summer, but rose in the autumn during the period of winter 2010 to autumn 2012. The highest species richness occurred in the spring (33 species) and summer (32 species),2012. The lowest species richness (21 species) occurred in the spring 2010 and 2011. Variation of species richness of mollusks and aquatic insects and the occurrence of rare species mainly contributed to the seasonal species richness dynamics. The average seasonal species turnover rate was 40%, with the highest in 2011 (average of 43%) and the lowest in 2012 (average of 35%). For the seasonal changes of density, the macroinvertebrate community density among years showed an upward trend after decline, with the largest in 2010 (943 ind. per square meter), followed by 2012 (684 ind. per square meter) and the lowest of three years in 2011 (463 ind. per square meter).The results of generalized linear mixed model (GLM) between 12 biological metrics and environmental variables across lake regions and seasons showed that some of the metrics were of significant difference in spatial and temporal scales. The seasonal changes in structure index of macroinvertebrate community are common. The abundance index of macroinvertebrate density showed no significant differences between regions and seasons, but metrics reflecting other aspects of community (such as chironomid density, percentage of advantage unit, BI, percentage of stain resistance taxa, shannon-wiener diversity, and simposon diversity) showed significant differences between regions or seasons, with a clear temporal trend. The insignificant difference in the abundance of space and time of community structure does not mean the structure of community had not changed, which may underwent a complex spatial and temporal variation of other aspects inside.The relationship between the biological index of the macroinvertebrate and the environmental gradients by use of distance based linear model and the results showed that the major environmental variables of different lake regions were closely related to the habitant conditions of the lake regions. Key environmental factors affecting macroinvertebrate community of each lake region were total nitrogen, total phosphorus, and ammonia for North Bay; pH, total nitrogen, and water temperature for East Bay, dissolved oxygen and water temperature for Open Lake. The macroinvertebrate community index of North Bay and East Bay had a better response to environmental factors compared to Open Lake, among which, the index of community composition presents an optimal responsed to environmental factors.