The Succession Of Phytoplankton Community Structure And Water Quality Assessment Of Mingzhu Lake Of Chongming Island, Shanghai

Mingzhu Lake is located in the western Lvhua town of Chongming Islaand. It has an area of 3km2, and is the largest natural freshwater lake in Chongming Island. It was a tributary of the Yangtze River of south branch and an artificial embankment in seventies of last century. Now the Mingzhu Lake has two sluice gates for inletting and draining water. As the auxiliary project of Shanghai Word Expo and master region of westen water entertainment and ecological agriculture tourist area of the Chongming Island, monitoring water quality of this lake is much more necessary. The study on the community structure and species diversity of Phytoplankton based on the monitor of physical and chemical index and biology index,analyze and discuss the relativity between water quality of Mingzhu Lake and environmental factor lasted 3 years from January 2007 to December 2009.It offered the ecological assessment of Mingzhu Lake and the evolution of community structure of phytoplankton, and also prouvde the basic ecology date for monitoring the water quality and protecting the ecology environment of Mingzhu Lake.1,The phytoplankton community structure and the annual variation of species multiplicity in Mingzhu Lake, Chongming Island were primarily studied from January 2007 to December 2009. A total of 168 species of phytoplankton belonging to 8 phyla, 88 genera were observed in the Lake. The dominant species ascribing to Chlorphyta accounted for 47 percent and the quality is 78 species belonging to 25 Genera; Secondly the percentage of Cyanophyta is 23 percent and the quality was 38 species which belonging 20 Genera; The third was Bacillariophyta accounted for 23 percent and the quality was 25 species belonging to 17 Genera; The others were Euglenophyta,Xanthophyta,Pyrrophyta,Chrysophyta. 2,The annual average densities and biomass of phytoplankton were 4650.24×104cell·L-1 and 6.06 mg·L-1, respectively. On the issue of phytoplankton densities, it appears that Cyanophyta was the dominant kind. Chlorphyta,Bacillariophyta were also important to the construction of densities. The Cyanophyta also was the dominant kind of phytoplankton biomass. The Bacillariophyta was the secondly dominant kind and the Chlorphyta was the Third one. The rest of the phytoplankton densities and biomass were rare. The density and biomass in Mingzhu Lake have the seasonal variation, and it was lower in winter and spring, and higher in summer and autumn. However, there was no obviously differences between sites.3,There were 5 kinds of dominant species from 2007 to 2009, including Phormidium tenue,Meismopedia tenuissima,Spirulina laxissima,M. convolute,Synedra ulna. The law of succession of phytoplankton was consistent with PEG (Plankton Ecology Group) model, except the Chlorophyta : The Bacillariophyta is the dominant species in winter and spring, in summer the dominant species changed from Bacillariophyta to Chlorphyta, and till to autumn the dominant species would be the Cyanophyta.4,The result showed that the water temperature was the main factors affecting the phytoplankton distribution. We can see from the result of CCA, it had a great relationship between environmental factor and the standing crop of phytoplankton. The result by SPSS showed that the relationship between the density and biomass of phytoplankton and the physical and chemical factors were the density and biomass has a significant positive correlation between water temperature and pH, but a significant correlation between transparency and total nitrogen, and a negative correlation between total phosphorus and dissolved oxygen.5,The average value of Shannon-Wiener diversity of phytoplankton in Mingzhu Lake from 2007 to 2009 was 2.14±0.45, the average value of Margalef species richness index was 2.52±0.69, the average value of Pielou evenness index was 0.58±0.16. the average value of trophic state index(TSI) was 53.03±7.96. The Shannon-Wiener diversity and Pielou evenness index has the same law: The numerical value in spring and winter were higher than those in the other two seasons. On the contrary, the Margalef species richness index and TSI were higer in summer and autumn.6,Utilizing all kinds of methods of evaculations, the water quality of Mingzhu Lake in 2007,2008 lies in the status of semi-eutrophication. And in 2009, the Mingzhu Lake was moderately pollution. The water quality has trend of gradually changing.