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

蓝藻表面水华（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。集落形成微囊藻是一种重要的、普遍存在的能在水面突然聚集的微囊藻属。提高知识的物理过程和环境条件，管理和促进微囊藻浮渣的形成是成功的预测和湖泊管理和缓解战略的发展至关重要。本项目的目标是提高对内陆沃茨微囊藻表面水华形成、持续和衰退的机理认识。作为一个新的方面，我们研究了在空气-水界面的界面流体动力学的表面水华的相互作用。我们预计，微囊藻释放的胞外聚合物，促进菌落形成和表面水华的发展。此外，水表面的物理性质也受到这些表面活性物质的影响，导致更稳定的条件，从而导致对水华持续性更有利的条件。虽然在水面的微层，表面浮渣和菌落生长的促进弱水平的湍流，它们是容易受到机械应力和垂直混合在高湍流强度。该项目的目的是在实验室和实地实验中确定对这些相互作用的主要环境控制。该多学科项目结合了中国和德国团队分别在浮游植物生态学和物理湖沼学方面的互补专业知识。联合实验将在德国和中国进行，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.