Eutrophication and Dynamics of Phytoplankton Community in Nanshui Reservoir in Guangdong Province,China

Nanshui Reservoir is the third largest reservoir in Guangdong Province,which has been classified as a protection zone for first-grade drinking water supply.A hydrological,water quality and phytoplankton survey was conducted from January to December in 2011,with the objective to evaluate the trophic state based on trophic state index(TSI),and dynamics of phytoplankton community and associated influencing factors based on redundancy analysis(RDA).The results showed that Nanshui Reservoir was oligo-mesotrophic,with no obvious difference in phytoplankton types during the study period.A total of 50 phytoplankton genera or species were identified,which belonged to 6 phylum,and the dominant species were adapted to oligotrophic water.The abundance and biomass of phytoplanktons were in the ranges of 8.72×104~2.51×105 cells/L and 0.031~ 0.421 mg/L,whereas the concentration of chlorophyll a ranged from 0.83 to 2.80 mg/L.As far as the dynamics of phytoplankton community concerned,the phytoplankton composition was mainly dominated by Bacillariophyta,Pyrrophyta and Chlorophyta in each season,but Bacillariophyta dominated throughout the year.The specific composition of phytoplankton community displayeda seasonal pattern,from Bacillariophyta type,to Bacillariophyta-Pyrrophyta type,to Bacillariophyta-Chlorophyta type,and then to Bacillariophyta-Pyrrophyta type.Overall,the seasonal variation in temperature,concentration ratio of nitrogen and phosphorus,and water stability were the main driving factors for the dynamics of phytoplankton community in the reservoir.