SIGN - Sino-German water supply network – Clean water from the source to the tap

Mass development of phytoplankton, especially of blue-green algae, impairs the water quality of Lake Taihu. In this nutrient-rich, wind-exposed lake, phytoplankton growth and distribution is often controlled by physical factors like global radiation and intensity of turbulent mixing. Until now, light-dependency of phytoplankton growth is modeled using parameters which were measured under constant light intensities. These parameters are not valid for turbid mixed water bodies like Taihu, where algae experience rapid light fluctuations. 

This sub-project is aimed to quantify the effects of hydrophysics on phytoplankton develop­ment in Lake Taihu. The influence of meteorological conditions on vertical and horizontal distribution of phytoplankton will be analyzed using data from monitoring stations, own sur­veys and satellite images. Light-dependency of phytoplankton growth will be analyzed in field and in laboratory experiments. Phytoplankton cultures isolated from Taihu will grow under well-controlled lab conditions at fluctuating and at constant light intensities. In the lake, phyto­plankton communities will be incubated at constant depths or vertically moved by a com­puter-controlled lift. The growth rates of main species will be measured at relevant ranges of intensity and dynamics of light. The obtained parameters of the growth-light relation (light intensity at zero growth and at beginning light saturation, growth efficiency at low light, maximum growth rates) at different ranges and frequencies of light fluctuations will be implemented in ecosystem models. These improvements in our knowledge on effects of hydrophysical factors are crucial for better predictions of phytoplankton development under forecasted weather conditions or projected climatic changes.