Studies On Structure Of Phytoplankton And Rotifer Community In The Three Gorges Reservior

The water level of the Three Gorges Reservoir moved up to 156m at the end of October 2006,which represents the Three Gorges Project have begun its primary operation period.In order to realize the actuality of water environment and the variation of phytoplankton and rotifer community of the Three Gorges Reservoir,the surveys in the Three Gorges Reservoir were carried out from January 2007 to October 2008.Thirty-five sampling sites were selected,eleven of which were in the mainstream from Zigui to Jiangjin and the others in eight tributaries(Xiangxi river, Tongzhuang river,Daning river,Meixi river,Daxi river,Modao river,Pengxi river, Wujiang river).The main research results are as follows:1.Structure of the phytoplankton community(1)The phytoplankton in the Three Gorges Reservior were divided into 7 phylums and 183 species,among which there were 93 Bacillariophyta species,52 Chlorophyta species,25 Cyanophyta species,4 Euglenophyta species,4 Cryptophyta species,3Chrysophyta species,2 Pyrrophyta specie.(2)The dominant species of the phytoplankton were as the following. Asterionella formsa,Synedra acus and Melosira granulata in Bacillariophyta, Pandorina morum in Chlorophyta,Microcystis sp.in Cyanophyta,Ceratium hirundinella and Peridiniopsis sp.in Dinophyta,and Cryptomonas ovata in Cryptophyta.(3) The standing crop of phytoplankton in the mainstream was low.The density ranged from 1.09×10~4 to 143.57×10~4 ind./L,and the annual average density was 16.04×10~4 ind./L.The biomass ranged from 0.02 to 2.71 mg/L,and the annual average biomass was 0.53mg/L.As the seasons changed,the order of the standing crop in 2007 from large to little was spring>autumn >winter> summer,and in 2008,it was spring>autumn>summer>winter.Zigui had the highest annual average standing crop while Changshou had the lowest.In the tributaries,the standing crop of phytoplankton was obviously higher than that in the mainstream.The density ranged from 15.76×10~4 to 792.85×10~4ind./L,and the annual average density was 164.47×10~4ind./L.The biomass ranged from 0.02 to 2.71mg/L,and the annual average biomass was 3.77 mg/L.The change law of standing crop was the same in 2007 and 2008,which from large to little was spring>summer >autumn >winter.Xiangxi river had the highest annual average standing crop while Wujiang river had the lowest.The order of the standing crop from large to little in the tributaries was as follow:Xiangxi river,Daning river,Meixi river,Tongzhuang river,Pengxi river,Daxi river,Modaoxi river,Wujiang river.(4) In the mainstream,the Shannon-Wiener diversity index of phytoplankton was between 1.35 and 2.42,and the annual average was 1.93.The evenness index was between 0.38 and 0.67,and the annual average was 0.57.The species richness index was between 2.02 and 5.01,and the annual average was 3.65.In the tributaries,the Shannon-Wiener diversity index of phytoplankton was between 0.64 and 2.65,and the annual average was 1.91.The evenness index was between 0.18 and 0.75,and the annual average was 0.53.The species richness index was between 1.85 and 5.57,and the annual average was 3.36.2.Structure of the rotifer community(1) The rotifer in the Three Gorges Reservior were divided into 24 genera and 11 families,among which 36 species were pollution indicator species.(2) The dominant species were Keratella valga,Keratella cochearis,Brachionus calyciflorus,Polyarthra trigla,Asplanchna priodonta,Synchaeta and Brachionus angularis.(3) In the mainstream,the density range of rotifer was 0～665ind./L,and the annual average density was 82.54 ind./L.The biomass range was 0～0.982mg/L,and the annual average biomass was 2.56 mg/L.During two years,the changes of density and biomass were not similar.The order of the density from high to low was spring, autumn,summer,winter.Zigui had the highest annual average standing crop while Jiangjin had the lowest.The standing crop of rotifer almost increased gradually from the upper to down of the river.In the tributaries,the density ranged from 0 to 1895ind./L,and the annual average density was 707.47 ind./L.The biomass ranged from 0 to 8.979mg/L,and the annual average biomass was 3.77 mg/L.The change law of standing crop was different from 2007 to 2008.The order of the density from large to little was spring,autumn, summer,winter.The order of the biomass from large to little was autumn,spring, summer,winter.Xiangxi river had the highest annual average standing crop while Wujiang river had the lowest.The order of the density from large to little in the tributaries was as follow:Daning river,Meixi river,Pengxi river,Daxi river, Tongzhuang river,Xiangxi river.The order of the biomass from large to little in the tributaries was as follow:Xiangxi river,Daning river,Meixi river,Tongzhuang river, Pengxi river,Daxi river,Modaoxi river,Wujiang river.(4) In the mainstream,the Shannon-Wiener diversity index of rotifer was between 1.62 and 2.31,and the annual average was 1.93.The evenness index was between 0.39 and 0.67,and the annual average was 0.56.The species richness index was between 0.71 and 1.79,and the annual average was 1.27.In the tributaries,the Shannon-Wiener diversity index of rotifer was between 1.05 and 2.44,and the annual average was 1.77. The evenness index was between 0.40 and 0.94,and the annual average was 0.71.The species richness index was between 0.53 and 1.94,and the annual average was 1.15.