Seasonal Variation Of Phytoplankton Community In Xiaojiang Backwater Area Of The Three Gorges Reservoir

The worldwide famous project, Three Gorges Reservoir, which has the ability of navigation, flood control and power. The project changed the entironment of Three Gorges Area greately while the large benefit to the country, and will greatly affect the entironment of Yangtse River Basin persistently. Our group has been observing the area of Xiaojiang Backwater Area of the Three Gorges Reservoir regularly for one year. The study analysed the structure of alga community and its seasonal variation; imported the concept of algal functional groups which gradually arised in the ecological research presently, in order to receal the seasonal variation of the dominant algae and alga functional groups; and studied the correlationes between dominant algae and environmental factors, and alga functional groups and environmental factors. The purpose of the sdudy is to offer basis for establishing the succession model of alga community and the forecast system of alga bloom in the Three Gorges Reservoir.In the studing period from May 2008 to May 2009, the seasonal variation of algal cell density (CellD), algal biomass(BioM) and Chla in Xiaojiang Backwater Area are Consistent. And correlativity between CellD and Chla,BioM and Chla are distinct positive. In general, 7 phyla, 98 genera and 259 species (including varieties) of phytoplankton community on the backwaters of Xiaojiang River were identified. The proportion of the community composition was: Chlorophyta, 47.5%, includes 52 genera 123 species; Bacillariophyta, 29.7%, includes 20 genera 77 species; Cyanophyta, 12.7%, includes 15 genera 33 species. The 10 generas: Cryptomonas, Cyclotella, Chlamydomonas, Ankistrodesmus, Chlorella, Scenedesmus, Fragilaria, Synedra,Planktolyngbya , are the most common algae. And the seasonal succession of the phyla is: Dinophyta, Cyanophyta→Chlorophta→Bacillariophyta→Cyanophyta, Dinophyta.In the studing period, the seasonal succession of the dominant algae in Xiaojiang Backwater Area is quite obvious. And the 13 generas: Asterionnella, Aulacoseira, Cyclotella, Synedra, Eudorina, Anabaena, Microcystis, Planktolyngbya, Chroococcus, Merismopedia, Ceratium, Peridinium, Cryptomonas, are the most dominant algae. There are 4 blooms breaked out in the studing period in Xiaojiang Backwater Area: May 2008 Ceratium bloom, July to September 2008 Synedra bloom, March 2009 Asterionnella bloom,and April to May 2009 Anabaena bloom. The analysis of the correlation between alga and the environment factors showed that the correlation coefficient between tatle alga and environment factors was much higher than the correlation coefficient between each dominant alga and environment factors.According to the function classification of Reynolds, the study defined the alga function groups in Xiaojiang Backwater Area. The seasonal succession of function groups is: LO,LM→LO,LM,B,G,Y,J,X1,H1→LO,LM,D→P,D,B,Y,F,J→B,C,P,Y→H1→B,G,Y,LM. The result of the CCA of function groups and environment factors showed that Temp is the most influential factor for the distribution of the alga function group in Xiaojiang Backwater Area, and than are the factors of pH, SiO2, SD and SRP. However, the factors of NH4+-N, TN, TP and TN/TP affected little.