Studies On Structure Of Planktonic Community Of Yuanshui River

Yuanshui River, originated from southeast of Guizhou Province, is one of four sourceof Dongting Lake. According to the survey of species composition, density, biomass,dominant species, diversity of plankton of nine investigation stations (fromⅠtoⅨ) inYuanshui River, which were Gedong,Guazhi,Tuokou,Qiancheng,Hongjiang,Chenxi,Yuanling,Lingjintan and Niubitan in turn, in March, June, September, December, 2005.the main research results are as follows:1. Structure of the phytoplanktonic communities(1)The. phytoplankton in Yuanshui River were divided into 6 phylums and 147species, among which there were 64 Bacillariophyta species,54 Chlorophyta species22 Cyanophyta species,3 Euglenophyta species,3 Xanthophyta species,1 Pyrrophytaspecie. The specie of phytoplankton in the upper stream of Yuanshui River was moreabundant than in the down. The number of species of phytoplankton was largest inautumn, in the second places in winter and summer, lowest in spring. The dominant algaewere Bacillariophyta and Chlorophytwith in the whole year.(2)The average phytoplankton density was 2.21×10~5ind/L. Among all the categoriesof phytoplankton, the amount of Cyanophyta was the largest one, which was1.33×10~5ind./L on average and represented 60.18% of total density. Bacillariophyta wasin the second place, which represented 29.41%. Chlorophyta, Pyrrophyta, Xanthophytaand Euglenophyta represented a ratio of 4.98%, 2.71%, 1.81% and 0.91%, respectively.The average phytoplankton biomass was 3.97mg/L. Among all the categories ofphytoplankton, Cyanophyta was the largest one, which was 3.42mg/L on average andrepresented 86.11% of total biomass. Bacillariophyta was in the second place, whichrepresented 13.54%. Chlorophyta, Pyrrophyta, Euglenophyta, Xanthophyta represented aratio of 0.13%, 0.09%, 0.07% and 0.04%, respectively. The order of all stations'densityfrom large to little was:Ⅸ＞Ⅱ＞Ⅳ＞Ⅶ＞Ⅷ＞Ⅲ＞Ⅰ＞Ⅴ＞Ⅵ. And it almost increasedgradually from the upper to down of the river. The order of all stations'biomass from largeto little was:Ⅸ＞Ⅳ＞Ⅷ＞Ⅲ＞Ⅴ＞Ⅱ＞Ⅰ＞Ⅶ＞Ⅵ.In four seasons, the average phytoplanktondensity in autumn was the largest of all, second in winter, third in spring and the least insummer, and the average phytoplankton biomass in winter was the largest of all, secondin spring, third in autumn and the least in summer.(3)The dominant species of phytoplankton were as the following: Fragilariacrotonensis, Melosira granulate, Fragilaria capucina, Asteronella Formosa andAsteronella gracillima in Bacillariophyta. Oscillatoria limosa, Microcystis aeruginosa in Cyanophyta and Pediastrum simplex var. clathratum in Chlorophyta.(4) Shannon-Wiener diversity index and Margalef diversity index of phytoplanktonwere 2.13 and 4.47, respectively. And Bacillariophyta biological index was 109.82. Infour seasons, the three indeices were all the largest of all in winter, second in autumn,third in spring and the least in summer.2. Structure of the zooplanktonic communities(1)Seventy species of zooplankton were identified, among which there were 19Protozoa species, 31 Rotifer species, 12 Cladocera species and 8 Copepoda species with aratio of 27.1%, 44.3%, 17.1% and 11.4%, respectively. Generally, the species ofzooplankton in the upper stream was more abundant than in the down stream. Speciescomposition of zooplankton was different in different seasons. But Rotifer was dominantspecies in four seasons.(2)The average zooplankton density was 122ind./L. Among all the categories ofzooplankton, the amount of Rotifer was the largest, which was 99ind./L on average andrepresented 81.15% of total density. Copepoda was in the second place, whichrepresented 10.66%. The average density of Protozoa and Cladocera were both vere low,with a ratio of 8.2% together. The average zooplankton biomass was 0.79mg/L. Amongall, Copepoda was the largest one, which was 0.37mg/L on average and represented46.84% of total biomass. Cladocera and Rotifer was in the second place, whichrepresented 27.85% and 25.32%, respectively. The biomass of Protozoa was very low,which represented less 1% of total biomass. The order of all stations'density ofzooplankton from large to little was:Ⅶ＞Ⅳ＞Ⅸ＞Ⅱ＞Ⅷ＞Ⅴ＞Ⅲ＞Ⅵ＞Ⅰ. The order of allstations'biomass was:Ⅶ＞Ⅳ＞Ⅸ阿Ⅴ＞Ⅷ＞Ⅱ＞Ⅲ＞Ⅵ＞Ⅰ. In four seasons, the averagezooplankton density and biomass were both the largest in autumn, second in summer,third in spring and the least in winter.(3)The dominant species of the zooplankton were Centropyxis aculeate,Brachionusforficula,Brachionus falcatus,Filinia maior,Polyarthra trigla,Keratella vaIga,KeratelIa cochlearis,Bosmin longirostis,and Mesocyclops leuckarti。(4) Annual average Margalef diversity index of zooplankton was 4.61. Average indexrange of horizontal dynamics was from 2.86 to 6.42. It was greatest in Deceber of thewhole year. In four seasons, the index in winter was the largest of all, the second inautumn, the third in spring and the least in summer.