Influences of phosphorus concentration on interactions among microcystis aeruginosa, Daphnia Magna and ceratophyllum demersum

Abstract

In this study, Microcystis aeruginosa, Daphnia magna and Ceratophyllum demersum were selected to be respectively as the representative of phytoplankton, zooplankton and submerged macrophyte to evaluate the influence of phosphorus concentration on biomanipulation and aquatic vegetation restoration. When two or three of them were cultured together, with 4 kinds of phosphorus concentration(0.2,0.5,1.0,1.5 mg/ L), 25 °, 2000-3000lx illumination and 11mg/ L nitrogen concentration, the changes of growth rate and rate of removing nitrogen and phosphorus were studied. The results indicated that it was advantageous to D. magna multiplication and C. demersum growth when two of the three organisms were cultured together and the phosphorus concentration was no more than 0.2 mg/ L in pairwise culture. M. aeruginosa was keeping multiplication fast, but C. demersum biomass decreased obviously when phosphorus concentration range was 0.5 to 1.5mg/ L. When all organisms were cultured together, both D. magna density and C. demersum quantity increased, but M. density declined markedly, and the effect was best when phosphorus concentration range was 0.2 to 0.5mg/ L. The ratio of N/ P could obviously influence their interactions of M. aeruginosa, D. magna and C. demersum. In the co-culture system of M. aeruginosa and D. magna, addition of submerged macrophyte could enhance the effect of algal control, and lowered the negative effect that was triggered by the wave of N/ P ratio. When phosphorus concentration was 0.5mg/ L, there was better elimination effect on the nitrogen and phosphorus than other phosphorus concentration gradient.