Inhibition Effects Of Submerged Macrophytes And Phytoplankton In The Nansi Lake On Microcystis Aeruginosa

Allelopathy is an important trait in competition between macrophytes and phytoplankton in freshwater ecosystem. It is of the extremely vital significance to composition of communities in freshwater ecosystems and ecological restoration in eutrophic lakes. Nansi Lake has been employed in the east route of the South-to-North Water Diversion Project for accommodating water storage and the water diversion channel. The effects of macrophytes and the dominant species of phytoplankton community in the Nansi Lake on Microcystis aeruginosa are an important aspect in studying preventing and controlling the occurrence of water bloom in the Nansi Lake, and ensuring diversion water quality. Allelopathy effects of three submerged macrophytes such as Potamogeton crispus, Potamogeton lucens, and Ceratophyllum demersum on M. aeruginosa were studied in this study, and the influence of the culture filtrates of three species of submerged macrophytes to M. aeruginosa were also observed. In addition, the growth of M. aeruginosa and the dominant species of phytoplankton community in the Nansi Lake were observed through the multi-culture experiment. The main researches included as follows:Allelopathic effects of submerged macrophytes such as P. crispus, P. lucens, and C. demersum on Microcystis aeruginosa were assessed using co-culture experiment and under controlled laboratory conditions. Excluded the influence of nutrient and light intensity condition, the results showed that all the three species of macrophytes had significant allelopathic effects on the growth of M. aeruginosa, and the effects depended on initial algae cell density, the species and biomass of macrophyte. The growth of M. aeruginosa was significantly inhibited by 10 g/L and 5 g/L of P. crispus at low initial cell density and; At high initial cell density 10 g/L P. crispus showed more inhibitation effect on M. aeruginosa than 5 g/L P. crispus. The allelopathic effects of 7 g/L and 4 g/L P. lucens on M. aeruginosa at two initial cell density were very significantly. Both 7 g/L and 4 g/L C. demersum performed significant growth inhibiting on M. aeruginosa at low initial cell density, while less effects were observed at high initial cell density. The allelopathic effects of the three submerged macrophytes are ranged as P. hicens> P. crispus> C. demersum. In the experiment of the three submerged macrophytes culture filtrates, culture water showed stimulatory growth effects on M. aeruginosa.Competition effects of several dominant species of phytoplankton in the Nansi Lake and Microcystis aeruginosa were assessed using multi-culture experiment and under controlled laboratory conditions. The results showed that there is competition between the phytoplankton in the Nansi Lake and M. aeruginosa in present experiment conditions, and the phytoplankton in the Nansi Lake is dominant in the competition. The effects depended on initial algae cell density of M. aeruginosa and the phytoplankton in the Nansi Lake. The growth of M. aeruiginosa was significantly inhibited and all cells of M. aeruginosa became death when the initial algae cell density ratio keeped to 10:1 or 1:1 between phytoplankton in the Nansi Lake and M. aeruginosa. It performed significant growth inhibiting on M. aeruginosa, the cell density decreased and maintain a low level when the initial algae cell density ratio keeped 1:10. Less effects were observed when the initial algae cell density keeped 1:100, cell density of M. aeruginosa showed a slow increasing while the growth of phytoplankton in the Nansi Lake is inhibited.