Abstract: The migration and distribution of Microcystis colonies under waves are of great significance for understanding Microcystis blooms. This work experimentally investigates the trajectory, concentration distribution, and aggregation of Microcystis colonies under small amplitude waves. Results show that unlike the approximately vertical upward migration trajectory in still water, the Microcystis colonies show periodic motion in waves but still take an upward trend. The closer the Microcystis colonies are to the water surface, the greater the influence of water waves on them. The larger the wave height, the stronger the water carrying capacity caused by water waves. This leads to a more extensive range of periodic movement, and a more uniform profile of vertical concentration. When floating on the surface under large wave heights, the Microcystis colonies are prone to fragmentation and dispersion into the lower water layer by water waves. Large-scale Microcystis populations have a strong capability of vertical autonomous migration and tend to aggregate on the water surface, forming higher surface concentrations, while small-scale ones are weak in autonomous migration and are easily carried by water waves to the lower layer of water, with a relatively uniform vertical distribution.

Key words: wave action, Microcystis, migration distribution, concentration distribution