Rapid horizontal accumulation and bloom formation of the cyanobacterium Microcystis under wind stress

Wind plays a vital role in the distribution of algal biomass, but it remains unclear what wind conditions maximize the horizontal transport of Microcystis leading to formation of blooms in downwind areas of a lake. To determine relevant wind speeds, the current velocity and chlorophyll- a (Chl- a ) concentration in different water layers were measured for 6 days in Zhushan Bay of Lake Taihu. Results showed that a wind factor, the ratio of the current velocity in the water surface layer (0– 0.13 m) to the wind speed, decreased from 5 to 1.5% with an increase of wind speed and remained stable at around 1.5% at wind speed above 4 m/s. The current velocity in the surface layer was considerably greater than that in the lower layers, e.g., ~ 3–10 times higher than in a 0.52–0.65 m water layer. When the wind speed was 2.1 m/s in Zhushan Bay, about 50% of the Microcystis biomass of the whole water column accumulated in a 1 cm surface water layer. At this wind speed, the total horizontal transport rates of Microcystis were greatest, and the horizontal transport of Microcystis in the 1 cm surface water layer accounted for the 60–77% of that in the upper water layer with downwind current. Thus, intercepting or reducing surface Microcystis biomass can effectively prevent the horizontal accumulation and bloom formation of the cyanobacterium Microcystis in important functional areas and provide a direction for future research on water bloom control.