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

蓝藻表面开花（表面浮渣层）是一种有害现象，对水质、人类和动物健康产生负面影响。集落形成微囊藻是最重要的和普遍存在的属之一，可以突然积聚在水面。提高对控制和促进微囊藻浮渣形成的物理过程和环境条件的认识，对于成功预测和制定湖泊管理和缓解战略至关重要。该项目的目的是提高对内陆水域微囊藻表面华的形成、持续和减少的机理认识。作为一个新的研究方向，我们研究了空气-水界面表面水华与界面水动力学的相互作用。我们认为微囊藻释放的胞外聚合物质促进了菌落的形成和表面水华的发展。此外，这些表面活性物质也会影响水体表面的物理性质，从而导致更稳定的条件，从而为水华持续提供更有利的条件。虽然水面微层、表面浮渣和菌落生长受到弱湍流水平的促进，但它们在高湍流强度下容易受到机械应力和垂直混合的影响。该项目的目的是查明在实验室和实地试验中对这些相互作用的主要环境控制。这个多学科项目结合了中国和德国团队在浮游植物生态学和湖泊物理学方面的互补专业知识。联合实验将在德国和中国进行，并涉及两国研究人员和学生的广泛交流。

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.