Simulation Of The Mechanism Of Blue-green Algal Bloom Formation And Disappearing

According to the item named"Mechnaism of Algal Bloom Formation and Disappearing in River-type Reservoir Firth"which supported by the national Natural Science Foundation of China (No. 50679038), the paper took M.aeruginos as an example, and studied the effect of environmental conditions, nutrient concentrations and hydraulic dynamics on the blue-green algal bloom formation and disappearing during April 2006 to April 2007.The results showed as following:1. The effect of environmental conditons on the algae growth and bloom formation:(1)The initial pH value at 8 would promote the growth of algae. Under different initial pH value conditions, the pH would be alkalescency along with the growth of algae. The pH would go to be 8.6 to 9.9, after 18 to 20 days when algal began to grow.(2) Along with the rising of water temperature from10℃to 32℃, the multiplied speed of alga will be augmented. The quadratic regression equation used to show the relationship between the multiplied speed of algaμ(y) and the water temperature(x) was y=-0.0022x²+0.1356x-1.0208,(R²=0.9833). From this equation, we could draw a conclusion that when water temperature was 30.82℃, the maximum of multiplied speed of alga would be 1.069.(3) Along with the irradiation ranged from 50lx to 5300lx, the multiplied speed of alga will be augmented. The quadratic regression equation used which shows the relationship between the multiplied speed of algaeμ(y) and the irradiation(x) was y=-3E-08x²+0.0003x+0.125,(R²=0.9839). Base on this equation, we found that when irradiation was 5000lx, the maximum of multiplied speed of alga was 0.875.(4) The multiplied speed of alga increased with the light period prolonging. More longer the light period, more quickly the growth of M.aeruginosa.2. The impact of nutrient concentration on the algae growth and bloom formation:(1) It was appropriate for the growth of M.aeruginosa when the P concentration ranged from 0.14 mg/l to 0.62 mg/l. The phorsphor half saturation constant KSP and the multiplied speed of alga were 0.019mg/l and 0.667 seperately based on the Monod equation and Droop equation.(2) It was appropriate for the growth of M.aeruginosa when the N concentration ranged from 1.8mg/l to 4.1 mg/l. The nitrogen half saturation constant K_SN and the multiplied speed of alga were 0.751mg/l and 0.900 seperately based on the Monod equation and Droop equation.Therefor, we found that K_SN was higher than K_SP, which indicated the effect of phosphorus on the growth of M.aeruginosa was further more significant than that of nitrogen,in other words, increase of phosphorus concentration would promote the growth of M.aeruginosa more easily than nitrogen.(3) The multiplied speed of M.aeruginosa risen up firstly, then fall down with the N/P ranged from 2 to 383. The regression equation between the multiplied speed of algaμ(y) and N/P ratios (x) was y =-0.0645x² + 0.3769x+0.3363,(R²=0.9398). Base on this equation, we drew a conclusion that when N/P=18, the maximum of multiplied speed of alga was 0.875.(4) The orthogonal experiment showed that it was appropriate for the growth of M.aeruginosa when P=0.8mg/l,N=3.6mg/l,WT=29-30℃,irradiation 3300-3400lx; the irradiation condition was the most sensitive to the growth of algae, moreover, the effect of P is stronger than that of N.3 The effects of hydraulic dynamics on the algae growth and bloom formation:(1)Low flow velocity: The multiplied speed of algae changed from 0.437 to 0.657 with the flow velocity from 0 to 11cm/s, which showed that there was unconspicuous difference on the growth of algal and formation of bloom in different flow velocity.(2) Hight flow velocity:When the flow velocity were 10,20,30 and 40cm/s seperately, the life cycle of algae was 24-28d. The time for the occurrence of maximal chlorophyll a concentration was 12-18d. The risen of flow velocity will restrict the growth of algae and stay the formation of bloom. When the flow velocity was 30cm/s, the multiplied speed of M.aeruginosa was the maxiaml value. There maybe has a critical velocity(V₀) between 30cm/s and 40cm/s.Based on the regression equation between the multiplied speed of algaμ(y) and flow velocity V(x): y = -0.0002x² + 0.0146x + 0.0656,(R² = 0.9485), we drew a conclusion that V0=36.50cm/s,which will be verified in furture.