| Eutrophication of lakes is one of the most severe environmental problems because lakes provide many ecological services including freshwater supply for drinking water and irrigation, and fisheries. Eutrophication usually results in degradation of aquatic ecosystems including shifts in primary producer, bacterial and zooplankton communities. Severe eutrophication in freshwater ecosystems often results in systems with extensive and recurrent cyanobacteria blooms. Global warming is expected to intensify cyanobacteria bloom occurrences. In Lake Taihu, the third largest freshwater lake of China, the cyanobacteria Microcystis now dominates the phytoplankton community. Microcystis can be toxic for humans when drinking the water and textbook knowledge dictates that Microcystis is poor food for zooplankton. However, Microcystis blooms in Lake Taihu are accompanied with high numbers of small zooplankton suggesting that energy is transferred from the cyanobacteria to zooplankton consumers. We suggest that most carbon flows via detrital and bacterial pathways rather than via herbivory and that the importance of these pathways will increase with an increase in Microcystis dominance. In this project we will (1) study phytoplankton dynamics using a combination of biomarker (pigments, polar lipid derived fatty acids) and rate measurements (group specific primary production), (2) quantify rate of nitrogen and carbon cycling using state-of-the-art tracer techniques, (3) use a combined stable isotope and biomarker approach to quantify the contribution of Microcystis carbon to the diet of zooplankton and (4) use stable isotopes as deliberate tracers to elucidate the flows among phytoplankton, detritus, heterotrophic bacteria and zooplankton consumers. Such quantitative understanding of food web interactions is a prerequisite for understanding and predicting the response of aquatic ecosystems to eutrophication, de-eutrophication and eventual remediation measures including biomanipulation techniques. |
