SUCCESSION OF THE PHYTOPLANKTON COMMUNITY IN RESPONSE TO ENVIRONMENTAL FACTORS IN NORTH LAKE ERHAI DURING 2009-2010

Phytoplankton samples were taken weekly from September 2009 to November 2010 in Lake Erhai. The purpose was to obtain detailed information about the composition variations in the phytoplankton community during the serious drought in 2009 - 2010 and to determine the driving force for the succession of the dominant genera. A total of 147 phytoplankton species were identified during our investigation. Among the 7 main divisions, the maximum contribution (69%) belongs to the Chlorophyta division. The alternation of the dominant group was Cyanophyta, Chlorophyta, and Bacillariophyta. The weekly variations in cell abundance and biomass of the dominant phytoplankton genera were examined. A succession characterized by Psephonema and Asterionella (spring) -> Melosira (summer) -> Microcystis (autumn) -> Microcystis and Psephonema (winter) emerged from the monthly average biomass. Weekly variations in the Shannon Weaver index ranged between 0.269 and 2.183. Redundancy analysis results showed varied effects of environmental factors on the different phytoplankton dominant genera, with water temperature as the driving force for the seasonal succession of the dominant genera. The shift in succession pattern is induced by light intensity variation. In addition, the dominance of Psephonema in winter is the first report in Lake Erhai in recent years