Characteristic Of Phytoplankton Distribution And Eutrophication Evaluation In The East-half Of Chaohu Lake

Eutrophication of water bodies has become a global and difficult problem in controlling water pollution and is one of the most important environmental problems. At present, eutrophication of inland water bodies is very serious in China, which is the main environmental problem of limiting economic development. Chaohu Lake is an important water source for Anhui Province, but its eutrophic levels increased significantly. It has already come to the attention of Nation, Provincial and City Enviroment Protection Agency. Protection and prevention from water pollution in three lakes, namely Taihu Lake, Dianchi Lake and Chaohu Lake, has been listed among the most important items in the ninth-five year plan of national environmental protection. The eutrophication degree in the west-half of Chaohu Lake is higher than the east-half,but the tendency of eutrophication in the east-half has aggravated gradually in recent years. So we studied the seasonal variation of phytoplankton species composition, the spatial and temporal distribution of primary production (Chlorophyll a), analyzed the index of water quality including water temperature, COD, SD, TN, TP. Based on the data from 2004 to 2005, we have selected three evaluation methods to assess the water body eutrophication degree, and these are biological assessment, grading point, and comprehensive nutrition state index. Then estimate its eutrophication degree based on these methods. The phytoplankton style is various, and we have 119 species of algae, which belong to 8 phyla and 73 general, the Cyanophyta, Bacillariophyta, Chlorophyta, Euglenophyta, Chrysophyta, Xanthophyta, Pyrrophyta and Cryptophyta are with 19, 41, 40, 2, 5, 6, 2 and 4 species respectively. The dominant phytoplankton species is Microcystis aeruginisa, Nostoc commune, Melosira islandica and Closterium lanceolatum belong to Cyanophyta, Chlorophyta and Bacillariophyta. The average density of phytoplankton is 68.06×105 cells per litre. Its density peaks in summer, and reached the peak 379.65×105 cells per litre in August 2004. While least in winter, and down to the lowest 8.23×105 cells per litre in February 2005. The density of Cyanophyta is 54.22×105 cells per litre and percentage is 79.67%, the Bacillariophyta, Chlorophyta, Cryptophyta, Pyrrophyta, Chrysophyta, Xanthophyta and Euglenophyta are with 9.58%, 8.77%, 0.82%, 0.09%, 0.04%, 0.65% and 0.40%, but Cryptophyta frequency attained 100%. The Chl-a, TN, TP, COD, and SD are with 6.14-18.26mg/m3,0.534-2.011,0.059-0.249,3.19-6.77mg/L 和 0.29-0.44m respectively in the east-half of Chaohu Lake from 2004 to 2005. The data shows that the pollution of organic compounds is not so serious, but the diaphaneity is very low, the total nitrogen and the total phosphorus exceeded the related temporary standards grievous. Three evaluation methods all indicate that the east-half of Lake Chaohu is up to eutrophication. But because different methods have different classification standard, and their classification are not sameness, so the result of eutrophication level are not completely consistent. The result of biological assessment indicate the east-half of Chaohu Lake had become eutrophicated, the result of grading point is eutropher-hyper eutropher, and the comprehensive nutrition state index is light-middle eutropher. We think the comprehensive nutrition state index is more objective through consult some literatures and analyzed these conclusions. According to these studies, we delimited the nutrition state in the east-half of Chaohu Lake is up to eutrophication, and it will be aggravated.