Hydrodynamic and biochemical interactions of cyanobacterial blooms with the air-water interface in lakes

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Cyanobacterial surface blooms (surface scum layers) are a harmful phenomenon that negatively affect water quality, human and animal health. Colony-forming Microcystis is one of the most important and ubiquitous genera that can suddenly accumulate at water surfaces. Improved knowledge about the physical processes and environmental conditions that govern and promote Microcystis scum formation is critical for successful prediction and for the development of lake management and mitigation strategies. The objective of this project is improvement of the mechanistic understanding on the formation, persistence and decline of Microcystis surface blooms in inland waters. As a novel aspect, we study the interactions of surface blooms with interfacial hydrodynamics at the air-water interface. We expect that extracellular polymeric substances, which are released by Microcystis, promote colony formation and surface bloom development. In addition, also the physical properties of the water surface are affected by these surface-active substances, leading to more stable conditions and therewith to more favorable conditions for bloom persistence. While the microlayer at the water surface, surface scum and colony growth are promoted by weak levels of turbulence, they are susceptible to mechanical stress and vertical mixing at high turbulence intensities. The project aims at identifying the main environmental controls on these interactions in laboratory and field experiments. The multidisciplinary project combines the complementing expertises of the Chinese and German team in phytoplankton ecology and in physical limnology, respectively. Joint experiments will be conducted in Germany and in China and involve extensive exchange of researchers and students from both countries.