STUDIES ON QUANTITATIVE DISTRIBUTION AND SPECIES COMPOSITION OF PHYTOPLANKTON IN STAR LAKE AND THE EVALUATION OF ITS TROPHIC STATUS

Studies were carried out in five small lakes of Star Lake,Zhaoqing,Guangdong Province,from April 1996 to June 1997. Eighty two species including 37 species of Chlorophyta,18 species of Cyanophyta,18 species of diatoms and 9 species of other algae were identified in samples of fifteen stations by six times sampling.The dominant species were Cosmarium,Scenedesmus,Chlamydomonas,Phormidium,Melosira,Peridinium and Euglena.Annual mean cell densities were between 10⁴ and 10⁵ cells per liter in most samples,the highest densities were observed in Xiannühu and Bohaihu.4.28×10⁵ cells per liter of annual mean cell density was obtained in whole lake.Total Nand Pconcentrations were below 1.0 and 0.1 mg/Lin all sampling stations respectively.The Trophic Level Index (TLI) of Chla,TN,TP,NH₃ N,COD and BOD were lower than 50 except Bohaihu.Based on results obtained,the trophic status of Star Lake was between meso eutrophication and eutrophication.The trophic levels of its five small lakes,from the highest to the lowest,were Bohaihu,Xiannühu,Lihu,Qinglianhu and Zhongxinhu successively.