Effects of water level fluctuation on phytoplankton succession in Poyang Lake, China – A five year study

Poyang Lake is the largest freshwater lake in the Yangtze floodplain in China, with dramatic seasonal water level changes each year. The quarterly monitoring data from 2009 to 2013 was used to study the impact of the water level fluctuation on the phytoplankton biomass and taxonomic composition variation in different hydrological phases in Poyang Lake. Bacillariophyta species are generally dominant in Poyang Lake, constituting more than 50% of the total phytoplankton biomass, except from July 2009 and January 2012. The results that phytoplankton biomass increased gradually from 2009 to 2013, especially after 2012, indicated there is some time lag in the response of phytoplankton biomass to nutrient loading in Poyang Lake. Our results support the hypothesis that water level fluctuation exert great influence on phytoplankton succession and hydrology fluctuations have an indirect impact on a decrease of Cyanophyta biomass with regard to dilution of nutrients (P, N) in Poyang Lake. This study indicates that we should keep the water level changes more or less as they are because ecologically relevant in Poyang Lake.