Simulation of Nutrient Competition between Blue-green Algae in Chemostat under Gradient of N:P Ratio.

Competition of blue-green algae Microcystis aeruginosa and Phormidium tenue in chemostat was simulated to determine what was the cause of species shift among them. The model consists of 8 equations including Droop's equation, growth of algae depends on internal nutrient content. Simulation of growth of M. aeruginosa and P. tenue at N:P supply ratio 5 to 40 almost agreed with experimental data. It was suggested that outcome of competition in chemostat could be predicted by the simulation model. Differences in kinetic constants such as Qmin (minimum cell quota) and ρmax(maximal nutrient uptake rate) were assumed to be causes of change in weight ratio of each algae with increase in N:P supply ratio in chemostat, suggesting species shift among blue-green algae in lakes occurs due to differences in kinetic constants for growth and nutrient uptake. At N:P supply ratio <60 (P was fixed), total dry weight of M. aeruginosa and P. tenue in competition calculated with the model increased with increase in N:P supply ratio.