Abstract:

Lake Taihu is a large shallow lake of the Yangtze River,one of China's five largest freshwater lakes.Since 1980s,the trophic state of Lake Taihu changed from oligotrophic to meso/eutrophic conditions due to humaninduced pressures.Crustacean zooplankton has long been used as an indicator of lake trophic level,which plays an extremely important role in water ecosystems.Sensitivity and adaptability to different environments vary from species to species,which lead to different response patterns.It has important application value to detect the water environmental quality evaluation effectively.In this paper,redundancy analysis (RDA) was employed to study the relationships between crustacean zooplankton community structure and temporalspatial variations of water environmental factors in Meiliang and Gonghu Bay in Lake Taihu from November,2004 to October,2005.The results showed that temporalspatial differences existed in nutrient concentrations between Meiliang and Gonghu Bay.It had relatively higher nitrogen concentrations in lake water in winter and spring,while higher phosphorus concentrations in summer and autumn.The trophic levels were significantly higher in Meiliang Bay than in Gonghu Bay,due to different nutrient inputs from the surrounding rivers.Nineteen species (12 species of cladocerans,7 species of copepods) of crustacean zooplankton were identified.There were no significant differences in species composition,and Bosmina spp.was the first dominant species of crustaceans in Meiliang and Gonghu Bay.Temporalspatial differences of crustacean zooplankton also existed in Meiliang and Gonghu Bay.In spring,the dominant species were large body crustaceans such as Daphnia spp.,while small individuals such as Bosmina and copepod larvae dominated in summer.Temporalspatial variations and community structure of crustacean zooplankton were mainly affected by temperature,chlorophylla and nutrient concentrations in lake waters.Correlation analysis indicated positive relationships between total biomass and density of crustacean zooplankton and temperature,chlorophylla and nutrient concentrations.RDA analysis suggested that different species showed different response characteristics to aquatic environmental factors