Study On The Main Algae Aggregation And Vertical Migration Behavior Of The Algal Bloom

Planktonic Cyanobacteria are remarkable for their ability to regulate their buoyancy, which is supposed to facilitate their development in stratified waters. It grows better in layered waters than other cells, and becomes advanced colony.This is common phenomena when nutrients become scarce in the surface layer of stratified waters. The competitive advantage of moving up and down in a stratified water column plays the following significant roles on the photosynthesis of Cyanobacteria. Generally, the cell nitrogen quota is utilized to represent the internal nutritional status.We proposed a nitrogen quota model, and investigated the behavior of vertical migration, and compared the similar and differences of the population migration in different colony diameter, temperatures and population diameter. The model is run in the simplified and typical cases of the summer stratified water column in the temperate regions.The main results go as follows:1. The algal bloom breakout in a short time and rapidly aggregate and migrates to the surface layer water. We investigate the behavior of vertical migration in the different colony diameter. The calculate results show that the colony periodic migration is caused by the rhythmic illumination. In the daytime, the colony displays photosynthesize function, thus carbohydrate (ballast) in cells shows accumulating, and the cells migrate to underwater as soon as the ballast of cells rising. At night, the Carbohydrate in cells were depleted because of the respiration, and thus colonies turns to migrate to surface layer water column as the density of cells decreasing. Furthermore, the depth of migrate and the speed of colony migrate increase with the increasing of the diameter of colony, it also indicate that the small colony can stay longer in depths.2. The vertical migration behavior of algal bloom is controlled by multi-factors. The migration patterns show that the Cyanobacteria can adjust with the light, temperature of the character of stratified waters.The reduction on the depth of population migration and migration cycle occurs as the temperature change from 19℃to 29℃, while the speed of migration increases and diameter keeps constant simultaneously.3. The intensities and time of the illumination determine algal photosynthetic efficiency in certain circumstances of pH,temperature and nutrient. Meanwhile, it play an important role in the Cyanobacteria growth rate. The simulation results show that the cells migrate to the deep water as the intensity of illumination, but the increase amplitude not significant. When the illumination intensity is above 900μmol·m-2·s-1, the migrtation velocity and displace of the colony are markedly increase.