Abstract:

The Yangtze River originates from Geladandong snow mountain located at the north of Tanggula mountains It is 1 217 km long in Qinghai province. In order to know more about community structure of phytoplankton from Qumalai to Yushu section in the upstream reach of the Yangtze River and to provide important basic data and scientific basis for water ecological environment evaluation and reasonable development and utilization of water resources from Qumalai to Yushu section in the upstream reach of the Yangtze River. The phytoplankton community from Qumalai to Yushu section in the upstream reach of the Yangtze River was investigated in spring(April) and autumn(October),2012 The community structure and environmental conditions were analyzed according to species composition,quantity,biomass and ShannonWiener diversity and the Pielou diversity and Marggalef diversity.The results showed that most of the phytoplankton was rivertype It was adapt to the piateau climate and watery environment.There were 3 phyla including 62 species of phytoplankton from Qumalai to Yushu section in the upstream reach of the Yangtze River in spring and autumn.Bacillariophyta were represented by the highest number of taxa(42，678%), follwed by Chlorophyta(11，177%)，Cyanophyta(9，145%) .14 dominant species were Diatoma vulgare，Diatoma elongatum，Synedra acus，Achnanthes sp.，Navicula sp.，Cymbella sp.，Fragilaria sp.，Melosira sp.，Gomphonem sp.，Hantzchia sp.，Cyclotella sp.，Oscillatoria tenuis，Phormidium sp.and Chlorella sp.,among which 12 species were Bacillariophyta. As the seasons changed,the variation of phytoplankton was not obvious. Bacillariophyta were dominant population in spring(April) and autumn(October).The phytoplankton density from Qumalai to Yushu section in the upstream reach of the Yangtze River in spring(April) and autumn(October) ranged from 1263×104cells/L to 4541×104cells/L, with the averge of 3487×104 cells/L，and the phytoplankton biomass ranged from 0050 8 mg/L to 0298 9 mg/L, with the averge of 0138 8 mg/L.The mean density and the mean biomass of Bacillariophyta was 87.86% and 96.68%，respectively. The phytoplankton standing crops showed higher in spring (April) than in autum (October)， and higher in tributaies streams than in main streams.The mean ShannonWiener diversity was 2.51，the mean Pielou diversity was 070，and the mean Marggalef diversity was 089. The ShannonWiener diversity, the Pielou diversity and Marggalef diversity was higher in autumn(October) than spring(April).Compared with the research of the middle and lower reaches of the Yangtze river, proportion of Bacillariophyta from Qumalai to Yushu section in the upstream reach of the Yangtze River was higher than the middle and lower reaches of the Yangtze River At the same time,that result showed that the quality of water at Qumalai to Yushu section in the upstream reach of the Yangtze River was better than the middle and lower reaches of the Yangtze River.Combined with the indicators of phytoplankton, these structure characteristics indicated that phytoplankton from Qumalai to Yushu section in the upstream reach of the Yangtze river was more stable,species distribution was more evenly，trophic state of this river was oligotraphentic,and the aquatic environment was good