Studies on population dynamics and the underlying impact factors of phytoplankton during the cyanobacteria bloom in Lake Erhai

Field studies were conducted in Lake Erhai from May to November in 2009. We investigated the phytoplankton composition and found that the cyanobacterial blooms occurred between June and October during which the phytoplankton abundance reached 107 cells/L or higher. The dominant species in the blooms were Microcystis sp., and their highest relative abundance could be above 90%. The analysis of the water quality showed that at currently Lake Erhai maintained a mesotrophic status. The trophic level of the water body was the highest in July, and the biomass of phytoplankton (Chl. a) reached the peak value in October. Furthermore, the results of the SPSS analysis suggested that compared to other phytoplankton species Microcystis sp. could be much more influenced by the total phosphorus (TP).