Phytoplankton dynamics and their relationship with environmental variables of Lake Poyang

Field investigations were conducted to identify environmental variables influencing phytoplankton dynamics in Lake Poyang. The results showed that diatoms predominated in the phytoplankton community. Concentrations of nutrients were high, and levels of phytoplankton biomass and chlorophyll a were low. During the low water level period (WLP), from January to May 2013, phytoplankton biomass was low. It increased from July 2013 and peaked in September 2013 during the high WLP. From October 2013 to January 2014, phytoplankton biomass decreased again. Highest values were generally measured in the middle district and lowest in the northern district. It decreased from October 2013 to January 2014. Redundancy analysis showed that water temperature and suspended solids (SS) concentrations were the principal factors regulating the growth of phytoplankton. The variations in SS were contrary to the biomass variations at the spatial level. During the high WLP, the blocking effect of the Yangtze River led to decreased water velocity and prolonged water retention time in Lake Poyang. Due to both the SS sedimentation and increase in water temperature, phytoplankton grew rapidly. Based on these findings, the variety of phytoplankton dynamics was caused by the combined effects of the Yangtze River effect, water temperature, and SS.