The Study Of Eutrophication Condition And Aquatic Community Structure Of Taihu Lake

Taihu Lake is the third largest fresh lake in China, located in the southern margin of the Yangtze River Delta, Taihu Lake basin is the main drinking water source, and both flood storage, irrigation, shipping, tourism, culture and so on. In the past 50 years, due to improper human activities and environmental pollution and other factors of production, leading to eutrophication, water alkalinity, ecological destruction and the deterioration of water quality and other environmental issues.Eutrophication of the lake is one of the most important water environmental problems. So the index of Taihu Lake water chemistry and aquatic community structure were investigated according to a quarterly from November 2007 to August 2008.We evaluate the actual condition of water quality and the main pollutions of Taihu Lake by ways of water pollution index and comprehensive analysis of eutrophication. Evaluation of water pollution index analysis revealed that the main pollutants in Taihu Lake were nitrogen (N), phosphorus (P) and organic oxygen consumption (CODMn). Total phosphorus (TP) shared the largest pollution load index (34.34% ~ 54.34%), the average pollution index for 48.36%. TN, TP and CODMn had significant positive correlations with Chlorophyll-a (Chl-a), Pearson correlation coefficients were 0.715 (p<0.01), 0.666 (p<0.01) and 0.740 (p<0.01) respectively. According to comprehensive analysis of nutritional status indicators, it also showed that TLI (Σ) values of Taihu Lake were between 60 and 70 in four seasons, with a mean value of 65.54. The seasonal changes of water quality were small. In a word,Taihu Lake was in a moderately eutrophication, and some of the region had shown a serious eutrophication.The main phytoplankton constitute 8 phylum, there were Cyanophyta, Cryptophyta, Pyrrophyta, Chrysophyta, Xanthophyta, Bacillariophyta, Euglenophyta and Chlorophyta. Cyanophyta, Chlorophyta and Bacillariophyta accounted for phytoplankton was about 90% of the total individuals, especially the predominant spiece of Cyanophyta. Cyanophyta can find throughout the year and of the whole lake. The dominant species were Microcystis aeruginosa and M. flosaquae. The average density of phytoplankton was 1.87×107 ind?L-1, the average biomass was 5.36 mg?L-1. The phytoplankton diversity index changes from 0.16 to 2.43 and the average of diversity index was 1.08. Evenness index changes from 0.08 to 0.82 with an average of 0.41.The results of diversity index and evenness index showed that the situation of Taihu Lake was moderately polluted.The common protozoa species were Difflugia gloculosa, Difflugia oblonga, Vorticella sp., Halceria grandinella, Tintinnidium fluviatile stein, Epistylis sp. and Cyphoderia ampulla Ehrenberg. Dominant species were Tintinnidium fluviatile stein, Vorticella sp., Difflugia gloculosa and Epistylis sp.. Brachionus calycif lorus and three kinds of rotifer in Keratella sp. occur throughout the year. The commom rotifer contain Brachionus angularis, Keratella quada, Keratella ualga, Filinia longiseta and Polyarthra trigla.The dominant species of Cladocera were Bosmina sp., Ceriodaphnia sp. and Diaphanosoma sp..The dominant specie of Copepoda was Cyclops sp. and the sub-dominant specie was Sinocalanus sp..The number of zooplankton Change between 410.93 ind?L-1 and 8672.05 ind?L-1, the mean 3277.19ind?L-1. Biomass changes between 1.04 mg?L-1and 11.73 mg?L-1, the mean is 5.35 mg?L-1. The zooplankton diversity index changes from 0.03 to 1.88 and the average was 0.90, zooplankton diversity increased as the temperature rises, and the diversity index higher in summer and autumn than winter and spring.The investigation of Taihu Lake benthic community showed the main benthic organisms were Corbicula ftuminea, Cipangopaludina cathayensis and Tubifiex sinicus. The frequencies of occurrence about dominant species were 73.2%, 21.4% and 44.6%. A total of 23 species of the benthos were collected: 15 species of Gastropod,1 species of Mussels,4 species of Arthmpoda,3 species of Annelida. The main dominant species is Corbicula ftuminea in middle area of Taihu Lake, Alocinma longicornis and Stenothyra glabra in East Taihu Lake, Gammarus and Tubifiex in Meiliang Bay and Lake Wuli. Compare to the historical data, the species of benthic organism reduced significantly. And the number of stain resistance species increased.