Study On Species Diversity Of Phytoplankton And Evaluation Of Water Quality During Spring And Summer In Lake Chaohu

Eutrophication prevention of water bodies has become a global hot problem and is one of the global environmental problem. For the past many years, Eutrophication problem by polluted water is serious in China, which is one of the main environmental problems. Chaohu Lake is the largest lake for Anhui Province, but its eutrophic levels increased significantly. It has already become one of problems need to solved about economic and social development in Chaohu city.We studied the seasonal variation of phytoplankton species composition, investigated the index of water quality including water temperature, SD, TN, TP and Chlorophyll a, analyzed the correlational dependence between phytoplankton biomass and index of water quality. Based on the data from spring-summer seasons in 2008 and 2009, we have selected three evaluation methods to assess the water body eutrophication degree, and these are Chlorophyll a, Shannon-Weaver Index, Evenness Index.One-hundred and fourty-five species of phytoplankton were found in 2008 Chaohu Lake, belonging to 7 phyla and 73 general. One-hundred and twelve species of phytoplankton were found in 2009 Chaohu Lake, belonging to 7 phyla and 59 general. One-hundred and ninteen species of phytoplankton were found in the enclosure, belonging to 7 phyla and 67 general. The difference of phytoplankton density is remarkable in the enclosure and Chaohu Lake. The range of phytoplankton density in the enclosures was from 2.95 to 102.43×10~5 cells/L. The range of phytoplankton density in the 2008 Chaohu lake was from 46.06 to 2439×10~5 cells/L, with the average 1163.83×10~5cells/L. The range of phytoplankton density in the 2009 Chaohu Lake was from 117.43 to 1241.16×10~5 cells/L, with the average 485.39×10~5cells/L. The range of phytoplankton biomass in the enclosure was from 0.06 to 7.39mg/L. The average of phytoplankton biomass in the eastern and western enclosures are 0.77mg/L and 1.32mg/L. The dominant species in the enclosures were Anabaena sp., Cyclotella meneghiniana and Dinobryon cylindricum.The average of phytoplankton biomass in 2008 is 15.50mg/L. The range of phytoplankton biomass in the 2008 Chaohu lake was from 5.29~29.55 mg/L. Its maximal biomass is 29.55mg/L appeared in June and the dominant species is Microcystis. Its minimal biomass is 29.55mg/L appeared in June and the dominant species is Cyclotella meneghiniana and Dinobryon cylindricum. The range of phytoplankton biomass in the 2009 Chaohu Lake was from 4.56~9.73mg/L. Its maximal biomass is 9.73mg/L appeared in July and the dominant species is Microcystis. Its minimal biomass is 29.55mg/L appeared in April and the dominant species is Cyclotella meneghiniana. The average of Chlorophyll a in EE,WE,2008 Chaohu Lake and 2009 Chaohu Lake are respectively 3.32μg/L,3.71μg/L,43.01μg/L,30.67μg/L. Many evaluation methods shows that the enclosure were polluted in middle levels and the 2008 Chaohu Lake were polluted in middle levels in spring (March-May) and in serious levels in summer(June-Augest). 2009 Chaohu Lake were polluted in middle levels in spring (March-May) and in serious levels in summer (June-July).The influence of phosphorus and cladoceran grazing on spring-summer variations of phytoplankton biomass and community structure in Lake Chaohu was important.