STRUCTURE AND DYNAMICS OF PHYTOPLANKTON COMMUNITY IN A TRIBUTARY OF GANJIANG RIVER——A CASE STUDY IN YUANHE RIVER

In the present study,phytoplankton abundance and community structure were investigated and analyzed in June and November 2009 and April 2010(e.g.high-water period,low-water period and normal-water period,respectively) in Yuanhe River,a tributary of the lower reaches of Ganjiang River.The results showed that 109 species of phytoplankton were identified,belonging to 61 genera of 6 phyla,among which there were 54 species of 27 genera in Chlorophyta,30 species of 15 genera in Bacillariophyta,12 species of 11 genera in Cyanophyta,6 species of 6 genera in Euglenophyta,4 species of 3 genera in Pyrrophyta and 3 species of 2 genera in Cryptophyta.The phytoplankton abundance ranged from 1.12×105 to 129.20×105 ind./ L.Cyanophyta was the dominant phylum in high-water period and low-water period,while Bacillariophyta dominated in normal-water period.The constructive species of phytoplankton were the saprobic indicators and they were Fragilaria capucina and Phormidium tenue in high-water period,Chroomonas caudate and Synedra amphicephala in low-water period and Cyclotella meneghiniana in normal-water period,respectively.Through the analysis of biodiversity index,the Shannon-Wiener diversity index,Simpson diversity index,Pielou evenness index and Margalef abundance index of phytoplankton were 1.14~2.92,0.45~0.93,0.36~0.92 and 0.42~2.78,respectively.Furthermore,using the methods of modified bioindicator community and biodiversity index to biologically assess the water pollution,we found that both methods came to the general same results,It indicated that Yuanhe River was in α-β-moderate pollution,and that there was a big difference in pollution levels among different sampling sites.