PHYTOPLANKTON COMMUNITY STRUCTURE AND ITS RELATIONSHIP WITH ENVIRONMENTAL FACTORS IN A HEAVY EUTROPHIC LAKE

Field investigations were carried out in June 2011 and 2012 in Lake Qixinghu, a heavy eutrophic lake. Main environmental factors, phytoplankton community composition, the densities and biomasses of different phytoplankton species were measured. The influence of environmental factors on phytoplankton was analyzed through canonical correspondence analysis (CCA). Results have revealed that the mean concentrations of total nitrogen (TN) and total phosphorus (TP) reached 6.78 mg/L and 0.68 mg/L, respectively. Phytoplankton species was dominated by Chlorophyta (41 species), Bacillariophyta (25 species) and Cyanophyta (23 species), species belonging to other phyla were rare. Phytoplankton density ranged from 5.97x10(5) cells/L to 5.87x10(8) cells/L in different sample sites. The mean densities of Cyanophyta, Chlorophyta and Bacillariophyta accounted for 85.3%, 8.2% and 5.4% of the total phytoplankton density. The biomass of phytoplankton varied between 1.16 mg/L and 38.4 mg/L in different sites. Mean biomasses of Cyanophyta, Chlorophyta and Bacillariophyta accounted for 20.9%, 30.2% and 30.1% of the total phytoplankton biomass. Results of CCA showed that water temperature, TN, TP and dissolved oxygen were the significant environmental factors that influenced phytoplankton community. This research will be helpful in understanding the features of phytoplankton community and their influencing factors in heavy eutrophic lakes.