Phytoplankton Community Characteristics And Evaluation Of Water Quality And Trophic State Of Taihu Lake

Taihu Lake is the third largest fresh lake in China, and is an important water resource in the lower reaches of the Yangtze River. The impact of human activities leading to water quality deterioration and high level eutrophication, it has draw attention of the State Environmental Protection Administration, and a series of investigations and control measures have been carried out. We set9sample sites, five are in the north of Taihu Lake and the other four are in the south. The phytoplankton composition characteristics and water quality were investigated from January2011to December2011. We evaluate the actual condition of water quality then estimate its eutrophication degree. Nland N2, two sample sites were chosen to do all-day investigation on June8th and9th and August19th and20th. This investigation is important for assessing water quality, prevention and control of Taihu Lake eutrophication. It provides background data for the ecological restoration of the water. In this paper, the main results are as follows:Eight Phyla, including74genera, were identified from9monitoring stations based on a monthly sampling, Cyanophyta, Bacillariophyta, Chlorophyta, Euglenophyta, Chrysophyta, Xanthophyta, Pyrrophyta and Cryptophyta are with8,32,23,3,2,2,3and2genera, respectively. Cyanophyta,Chlorophyta and Bacillariophyta accounted for phytoplankton was about99%of the total individuals, especially the predominant spiece of Cyanophyta. The phytoplankton densities and Chlorophyll-a (Chla) concentrations of each sampling station ranged from6.80×106-256.00×106cells/L, and0.48-366.25mg/m3, respectively. There were much more phytoplankton individuals in summer and autumn than that in winter and spring. The phytoplankton densities and Chla concentration are higher in the northern sample sites than that in the southern. TN, TP and TN/TP ranged from1.34-4.24mg/L,0.090-0.241mg/L and6-33, respectively. Concentrations of TN and TP, exceeding the related standards grievous, so N and P are not the limiting factors for phytoplankton growth in Taihu Lake. The phytoplankton density and Chla were higher in August of all-day investigation than in June, The maximum phytoplankton density basically turn up at10:00. Chla concentration trend is inconsistent with the density of phytoplankton, the maximum concentration turned up at10:00or12:00.Using alga saprobic index to evaluate the water quality of Taihu Lake suggests that it has been polluted heavily. The assessment results are not totally consistent by ways of biological assessment, water pollution index and comprehensive analysis of eutrophication. But they all suggest that Taihu Lake is up to eutrophication. Phytoplankton densities and TP had positive correlations with Chla, TN and TN/TP had negative correlations with Chla. Pearson correlation coefficients were0.654,0.697,-0.603and-0.693(p<0.05). Based on Chla and other factors, we set a multiple linear regression model.