The Research Of Phytoplankton Community Structure Of Yangcheng Lake In Suzhou

Yangcheng Lake is the third freshwater lake of Taihu plain; the total area of thelake is119.04km2. It has a variety of functions such as fishing, farming, industrialwater using, irrigation, tourism, shipping, and flood control. It also plays a unique rolein conserving biological diversity and maintaining ecological balance. Aquatic plantsare dense providing a food source for crabs and Yangcheng Lake yields high numbersof the Chinese mitten crab (Eriocheir sinensis). Currently, although the ecologicaleffects of the pen culture on the environment has received extensive attention, theymainly focus on aquatic plants, physical and chemical factors, environmental effectsand benthic animals, but rarely reported on the phytoplankton community structures.Phytoplankton community structure in17sites were investigated from January2008to December2009, and investigated the phytoplankton community structure in3controlled sites in net-pen closing and lake areas of Yangcheng Lake during January2008to December2009. Through statistical analysis of a large number of originaldata to analyze the micro-zooplankton community, temporal variation and speciesdiversity indices, at the same time to analyze the relationship of phytoplanktoncommunity in different areas, in order to provide the basic data for the researching ofthe ecology of phytoplankton in freshwater ecosystem in Yangcheng Lake, and alsoprovide the biodiversity conservation and sustainable development ofecological-pen-culture.The main results are as below:1. The phytoplankton community structure and the annual variation of speciesmultiplicity inYangcheng Lake were primarily studied from January2008toDecember2009. A total of368species of phytoplankton belonging to8phyla,132genera were observed in the Lake. The SJof the phytoplankton between2008and2009was0.70. The dominant species of2008were Microcystis aeruginisa, Phorimidium tenus,M. incerta, M. densa, and the dominant species of2009were M. incerta,Merismopedia tenuissima, P. tenus, Dictyosphaerium enrenbergianum, Ulothrix sp..2. The average annual density of phytoplankton of2008and2009were3570.45±7573.35×104cell/L and3339.24±4036.28×104cell/L in Yangcheng Lake, thedensity in2009was6.5%lower than2008, the difference of density was notsignificant between the two years. The average annual biomass of phytoplankton of 2008and2009were8.09±6.86mg/L and3.14±2.28mg/L in Yangcheng Lake, thebiomass in2009was61.19%lower than2008, the difference of biomass was verysignificant between the two years. The anniversary change trend of Phytoplanktonbiomass and density was similar, both were very significant positive correlation.3、 The average value of Shannon-Wiener diversity of phytoplankton inYangcheng Lake from2008to2009was2.46±0.58,2009was9.83%higher than2008; the average value of Margalef species richness index was3.20±0.95,2009was32.36%higher than2008; the average value of Pielou evenness index was0.63±0.14,2009was a litter higher than2008.4、The temperature and pH were the primary factor on the phytoplankton in Yangcheng Lake. TPand TN provide adequate nutrition elements for phytoplankton, and the influence of TN and TPwere reduced gradually from the creeks to the east-lake. As the important source of food to rotifer,the phytoplankton and the main rotifer had good correlation.5、The annual average of phytoplankton density and biomass in net-pen closings werelower than in lake areas from2008-2009in Yangchenglake, and the phytoplanktondensity and biomass in2009wer lower than2009. The result showed that the theeutrophication of net-pen closings was lighter than in lake areas, and the rich nutritionlevel of2009was eased. Water quality analysis shows that the water quality ofnet-pen closings was superior to in lake areas, and the water quality of2009wassuperior to2008.Utilizing all kinds of methods of evaculations, the water quality ofYangchenglake in2008-2009could be regarded as eutrophic. Through the comparisonof the phytoplankton community structure in net-pen closings and the lake areas, thenet-pen closings of the Chinese mitten crab could purifying water quality effectivelyand mak the development of eutrophication in Yacheng Lake slow down.