Phytoplankton Community Structure In Chaohu Lake

Chaohu Lake is one of the five largest fresh lakes in China. Its main function is flood control, irrigation, water supply, transportation, tourism and fishery. However, with economic development and increased population, Chaohu Lake has suffered increasingly from serious eutrophication. So the environmental issue of Chaohu Lake is now a very common one, as most lakes from eastern China are confronted with it.Phytoplankton live in fluctuating environments where many factors such as grazing pressure, nutrient uptake, light availability and turnover influence the distribution of phytoplankton in time and space. Phytoplankton composition is considered as a natural bioindicator because of its rapid responses to fluctuations of environmental conditions. So the studies on phytoplankton community structure and environmental factors in the lake should be done persistently, which might provide significant information about the development of the lake and some foundational data for further studies on the whole lake ecosystem.According to the phytoplankton data from the four investigations during 2008 in Chaohu Lake, the phytoplankton composition, dominant species, density, abundance, Shannon-Weaver index, Pielou's index and the relationship between phytoplankton community structure and environmental factors were analyzed and discussed.The results showed that a total of 114 phytoplankton species belonging to 8 phylum were found in Chaohu Lake, of which 16 species were Cyanophyta (14.04%),62 species were Chlorophyta (54.39%),15 species were Bacillariophyta (13.16%),9 species were Euglenophyta (7.89%),3 species were Chrysophyta (2.63%),3 species were Xanthophyta (2.63%),2 species were Dinophyta (1.75%), 4 species were Cryptophyta (3.51%). The dominant phytoplankton communities were Chlorophyta, Cyanophyta and Bacillariophyta. The dominant species were mainly Anabacna circinalis, Microcystis flos-aqnae, Aphanizomcnon flos-aquae, Cyclotella comta, Tribonema minas.The average density of phytoplankton was 12.02×105ind/L, the highest value was 19.28×105ind/L which appeared in summer; the lowest value was 6.24×105ind/L which appeared in winter. The average abundance of phytoplankton was 0.85, the highest value was 1.41 which appeared in winter; the lowest value was 0.36 which appeared in summer. The average Shannon-Weaver diversity index of phytoplankton was 1.79, the highest value was 3.19 which appeared in winter; the lowest value was 0.36 which appeared in summer. The average uniformity of phytoplankton was 0.69, the highest value was 0.94 which appeared in spring; the lowest value was 0.24 which appeared in summer.Relationship between phytoplankton density and water quality was tested by Pearson correlation analysis in SPSS 17.0. The results revealed that phytoplankton density was significantly related to conductivity, SD, COD, TN, TP, NH3-N. Moreover, dominant species density was strongly related to water quality, each environmental factor have different effect on dominant species density. Some dominant species were affected by many environmental factors at the same time.We choose winter phytoplankton community which have the highest species diversity as the research object. Discuss the impact of species composition on phytoplankton community by comparing diversity index and the CPV. The two curves of CPV and diversity index showed significantly opposite fluctuating patterns based on the Pearson correlation analysis (R=-0.468, P≤0.05). Our study suggests that phytoplankton community structure would not collapse in existence of a certain proportion of dominant species in the higher PB water body of the lake.