EFFECTS OF PHOSPHORUS CONCENTRATION ON INTERACTIONS AMONG CYCLOTELLA SP., DAPHNIA MAGNA AND CERATOPHYLLUM DEMERSUM

In the present study, the effects of phosphorus concentration on bio-manipulation and restoration of aquatic vegetation were determined. Cyclotella sp., Daphnia magna and Ceratophyllum demersum were selected to be respectively as the representative of phytoplankton, zooplankton and submerged macrophyte to construct an aquatic microcosm system. The growth rate of Cyclotella sp., D. magna, and C. demersum and removal rate of nitrogen and phosphorus were tested in the certain conditions 25, 2600 lx illumination, 11 mg/L nitrogen concentration, four phosphorus concentration (0.05, 0.1, 0.5, 2 mg/L) and three types of co-culture operations. Our results showed that D. magna and C. demersum grew well but Cyclotella sp. was suppressed and its consistency kept slowly positive growth at 0.05-2 mg/L phosphorus concentration in the two co-culture systems (Cyclotella sp. and D. magna co-culture system, Cyclotella sp. and C. demersum co-culture system). In the co-culture system of Cyclotella sp., D. magna and C. demersum, the growth of D. magna and C. demersum was improved, but Cyclotella sp. was suppressed greater at 0.05-2 mg/L phosphorus concentration. Cyclotella sp. showed negative growth at 0.05-0.1 mg/L phosphorus concentration. Our results illustrated that the inhibition effect of zooplankton and large aquatic plants co-culture on the algae was better than that the single zooplankton or large aquatic plants. This inhibition effect decreased with the phosphorus concentration increasing. And the best inhibition effect presented at the phosphorus concentration0.1 mg/L. The highest phosphorus removal presented in the lowest phosphorus treatment (0.05 mg/L), while the highest nitrogen removal presented in the highest concentration of nitrogen (2 mg/L) at the end of the experiment.