The nutrients,chlorophyll a and phytoplankton in the Henggang Reservoir were monitored in May and November,2005.In May,the mean concentration of TN,TP and Chlorophyll a were 3.810 mg·L-1,0.172 mg·L-1 and 17.888 mg·m-3,respectively.Comprehensive Trophic State Index(TSIM),was 73.3,indicating that the Reservoir was hypertrophic.In November,the mean concentration of TN and TP were 1.302 mg·L-1 and 0.096 mg·L-1,respectively.The TSIM decreased to 55.6,indicating that the Reservoir was lightly eutrophic.However,the mean Chlorophyll a increased to 26.935 mg·m-3.The increase of chlorophyll a concentration was positively related to NH3-N and PO4-P,and changes in phytoplankton community composition.The phytoplankton community was dominated by Cyanophyta in May,but by Chlorophyta in November.In May,the mean cell abundance of phytoplankton was 2.75×108 cells·L-1.The dominant species were Merismopedia elegans and M.glauca,which composed about 90% of the total phytoplankton.In November,the mean cell abundance of phytoplankton was 1.27×107 cells·L-1.The dominance of Merismopedia reduced to 14.89% of total phytoplankton cells.Scenedesmus became one of dominant species,which composed 11.52% of total phytoplankton cells.
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