Community Structure Of Plankton And Plankton-based Fish Productivity In Tian-e-zhou Oxbow Of The Yangtze River

In this study, we investigated the community structure of the phytoplankton and zooplankton in Tian-e-zhou Oxbow of the Yangtze River to analysis the water quality and assess fish productivity, with the aim of providing a theoretical foundation for the water quality protection and fish stocking. Five times water samples were collected in the duration of April2011and July2012seasonally. And this study is divided into two experiments, the qualitative analysis and quantitative analysis of plankton in Tian-e-zhou Oxbow of the Yangtze River.1.In the first experiment, there were143phytoplankton species detected in Tian-e-zhou Oxbow of the Yangtze River, all phytoplankton species have been detected belong to7genera and77species,19.6%of which were Cyanophyta and14genera and28spices showed,15.4%were Bacillariophyta and14genera and22spices showed,44.8%were Chlorophytaand32genera and64spices showed,2.8%were Pyrrophyta and3genera and4spices showed,8.4%were Euglenophyta and3genera and12spices showed,2.8%were Cryptophyta and3genera and4spices showed,6.3%were Chrysophyta and5genera and9spices showed. It shows that Cyanophyta and Chlorophyta which are fond of rich nutritional water occupied the main part of phytoplankton community. The annual average density of Tian-e-zhou Oxbow of the Yangtze River was5.6X107cell/L, and Cyanophyta was the priority,accounted for88.8%of the total density, followed by green algae, accounted for7.7%. The annual average biomass of phytoplankton was7.2mg/L, in which the algae, cyanobacteria and algae are the main part, accounted for61.5%,17.9%and12.8%of the total biomass respectively. In drouthy spring and summer of2011the total density of Phytoplankton is3.2times than that in the summer of2012because of algae blooms. Phormidium mucicola, Microcystis aeruginosa, Merismopedia minima and Crucigenia quadrata, eutrophic indicator indicator species of12dominant species exist in the form of group. The phytoplankton-based fish productivity was40.5kg/hm2in2011. In the summer of2011, Tian-e-zhou Oxbow coincides with dry season, and the fish productivity phytoplankton can provide was29.3kg/hm2. 2.Through the zooplankton analysis in the river, we found87zooplankton species,43.7%of which were Protozoa and22genus and38spices showed,41.4%of which were Rotifer and25genera and36spices showed,10.3%of which were Cladocera and8genus and9spices showed,4.6%of which were Copepods and4spices showed. Protozoa and Rotifer took99.3%of total density of zooplankton while that of Cladocera and Copepods were less than0.7%. Zooplankton annual average density of25711.9ind./L, is given priority to with Protozoa and rotifers, took93.7%and5.6%of total density respectively; Annual average biomass was3.6mg/L, is given priority to with Protozoa and Cladocera, accounted for31.9%and28.1%of the total biomass. There are9kinds in15dominant species are the eutrophic indicator species. In terms of Seasonal succession of dominant species, the main dominant species of Strombidium viride, Strombidium gyrans, Urotricha furcated and Cyclidium oblongum form advantage throughout the year, while the main dominant species of Polyarthra trigla and Trichocerca pusilla form advantage in different seasons. The main dominant species of Strombidium viride, Urotricha furcated and Cyclidium oblongum, which are eutrophic indicator species were found more in6and10sampling sites which were much more seriously contaminated. The density of zooplankton were46182.0ind./L,30254.1ind./L, and biomass of zooplankton were8.7mg/L,2.4mg/L, respectively In July2011and July2012. The differences between two years were obvious, as a result of water levels fall caused by persistent droughts in spring and summer in2011. The zooplankton-based fish productivity was324kg/hm2in2011. In the summer of2011, Tian-e-zhou coincides with dry season, and the fish productivity zooplankton can provide was433kg/hm2.3.According to the standing crop and the dominant species, the trophic state of Tian-e-zhou Oxbow belonged to eutrophic level which were in agreement with the assessment results based on Shannon’s index and Pielou’s index.