Effects of different fluid fields on the formation of cyanobacterial blooms

Cyanobacterial blooms have been attracting more and more attention, and the mechanism is widely studied. However, the effects of fluid fields on the bloom formation were rarely reported. In this study, the effects of fluid fields formed under different external conditions were investigated. The results indicated that low wind speed (3 m/s) was conducive to the formation of cyanobacterial blooms, while high wind speed (6 m/s) was adverse. For low wind speed, an upward fluid field was detected by particle image velocimetry. This fluid field accelerated the algal growth by 58.6%, and improved the buoyancy by up-regulating the genes involved in the synthesis of gas vesicles and extracellular polymeric substances. In addition, the boundary shear stress induced the colony formation of cyanobacteria and improved the aggregation proportion significantly (p < 0.05), which was beneficial to bloom formation. As a result, cyanobacterial blooms are more likely to form on the lake shore under moderate breeze. When wind speed increased to 6 m/s, a downward fluid field was formed, causing algal cells to gather at the bottom and hindering the bloom formation. These results provided a theoretical basis for field researches related to the formation of cyanobacterial blooms and the treatment of cyanobacteria.