Influence of Daphnia magna and Ceratophyllum demersum on the control of algae under different phosphorus concentrations

In order to evaluate the influence of Daphnia magna and Ceratophyllum demersum on the control of algae under different phosphorus concentrations, Cyclotella sp., Microcystis aeruginosa, and Chlorella vulgaris were selected to establish an aquatic microcosmic model. When the phosphorus concentration ranged from 0.05 to 2 mg L−1, D. magna significantly inhibited the three species of algae from different phylum, particularly M. aeruginosa, and the total growth rates of the three species of algae decreased with the increase of phosphorus concentration. When the phosphorus concentration ranged from 0.05 to 2 mg L−1, C. demersum imparted a significant inhibition of the three species of algae, particularly M. aeruginosa. The total growth rates of the three species of algae were reduced with higher phosphorus concentrations; however, the effect was lower than that of D. magna, with C. vulgaris as the dominant species. When the phosphorus concentration ranged from 0.05 to 2 mg L−1, D. magna combined with C. demersum inhibited the growth of the three species of algae to a considerable degree, which was an improvement over that of other experimental groups using only D. magna or C. demersum by themselves. The total growth rates of algae were reduced with higher phosphorus concentrations. When the phosphorus concentration ranged from 0.05 to 0.1 mg L−1, the removal rates of phosphorus exceeded 90%, and the phosphorus concentration became the limiting factor in the culture system. We observed that under higher initial phosphorus concentrations, the nitrogen removal rate increased, whereas the phosphorus removal rate decreased.