The Change Of Plankton Community During River Ecosystem Restoration In Suzhou Creek

The reconstruction and restoration of the damaged aquatic ecosystem has gradually become an essential topic that scientists often discuss about.Through the survey of the biotic community in the water area,it enable us to evaluate the growth and forecast the trends of the restoration process.It also can provide as a guide in ecology for the engineering project afterwards to make it more scientigically sound.The structure,function and dynamic of phytoplankton are closely related to the environment of the rivers.Suzhou Creek's synthetical water-control engineering was created in Shanghai in 1996,till now it has come to its third period.Momentous reconstruction engineering included pollution sweep,pollution cutting,water transfusion,artificial oxygen and dredge-up etc.Hypothetically speaking these violent man-made water interferential actions would make a strange token on phytoplankton's structure,function and dynamics in Suzhou Creek.Therefore,this thesis surrounds the ecological reconstruction of Suzhou Creek as a research object.I began the research by setting four sampling points such as Zhaotun,Huangdu,Beixinjing,Zhejiangluqiao.We had sampled fourteen times once a month from April of 2005 to May of 2006.We researched on the composition of species,density,dominant species,ind.icator species,diversity ind.exes of plankton community in Suzhou Creek,analysed its space-time change,we also analysed the dynamic change between plankton community restoration and water quality restoration.The main find.ings are as follows:1 173 species of phytoplankton were found in Suzhou Creek,including 25 kind.s of Cyanophyta,87 kind.s of Chlorophyta,38 kind.s of Bacillariophyta,11 kind.s of Phaeophyta,5 kind.s of Xanthophyta,6 kind.s of Chrysophyta,1 kind.of Cryptophyta. Chlorophyta take the obvious predominance.Based on the space change,the phytoplankton community structure of the upriver sampling sites were better than the downriver's.Based on the time change,the density in summer was obviously higher than the other three seasons,and Oscillatoria became the dominant species in summer.Main ind.icator species were Oscillatoria tenuis,Chlorella vulgaris, Cyclotella meneghiniana,Scenedesmus quadricauda,Ankistrodesmus.Faleatus, Rhizololenia longiseta.2 56 species of zooplankton were found in Suzhou Creek,including 4 kind.s of Protozoa,21 kind.s of Rotifer,17 kind.s of Cladocera,14 kind.s of Copepoda.The Rotifer was the dominant kind..Baesd on the space change,the zooplankton community structure of the upriver sampling sites were better than the downriver's.Based on the time change,the zooplankton community structure in spring and summer was better than in autumn and winter.3 Analyze the correlation between several environmental factors and phytoplankton community structure,the result showed that the water temperature had a marked positive correlation on the species and density of phytoplankton; TP,TN,COD_crhad a marked negative correlation on density,there was a lag on the change of density of phytoplankton compared with the change of the environmental factors;COD_crhad a marked positive correlation on the Shannon-Weaver ind.ex and the Margalef ind.ex of phytoplankton;NH₃-N,BOD₅ had marked correlation on water temperature,TN,TP,COD_cr,SO they had an ind.irect effect on phytoplankton community structure;SS had no effect on phytoplankton community structure.4 Compared the change of biological factor-zooplankton community structure with the change of phytoplankton community structure,the results showed that the change of species numbers had a positive correlation between zooplankton and phytoplankton,which means the species numbers of phytoplankton grow when the species numbers of zooplankton grow;there was a negative correlation between the density of phytoplankton and zooplankton,the relationship between two of them shows a lag phenomena which means the raise of phytoplankton density can't lead to the raise of zooplankton density simultaneously but can lead to the raise of zooplankton density anaphase.The diversity ind.ex of Shannon-Weaver and Margalef had a positive correlation between phytoplankton and zooplankton.5 Compared the change of physic-chemical factors with the change of phytoplankton community structure we found that the appear frequency of Cyanophyta become less,Cyanophyta and Bacillariophyta become more while the concentration of contamination grows.By analyzing it we found the physic-chemical factors had critical values for the influence on the phytoplankton community structure,the water temperature is 15℃,the TP is 0.6mg/L,the TN is 11 mg/L(considering the dominant type),10mg/L(considering the dominant species), the NH₃-N is 6mg/L,the COD_cris 30mg/L(considering the dominant type),20mg/L(considering the dominant species).This research also shows that the recovery of water quality of Suzhou Creek can be deduced by analyzing the density percentage of Chlorella vulgaris and Cyclotella meneghiniana.