Diel migration of Microcystis during an algal bloom event in the Three Gorges Reservoir, China

The vertical migration patterns and buoyancy regulation of Microcystis in water bodies have important effects on algal bloom formation. To understand the migration mechanism of Microcystis in deep bodies of water, two sets of experiments were carried out to illuminate the complex vertical movements in the Three Gorges Reservoir. Samples were taken during a 46-h period, with detailed monitoring of key parameters such as the solar irradiance, chlorophyll-a concentration, and water temperature. The index of dispersion and mean residence depth were computed to better understand the vertical distribution over time. The Microcystis colonies moved upward from the early morning until noon and sank from the surface in the afternoon and night. The vertical migration of Microcystis was the dominant factor affecting the dynamic changes of Microcystis in the enclosure. The water motion was also important in the diel dynamic changes of the Microcystis distribution. These results enable us to better understand the process of the initiation, development and appearance of blooms and allow us to devise new control strategies of algal bloom.