Study On The Effect Of Aquatic Macrophytes-microorganism System On Water Purification

At present, the environment of lakes in the country is worryied. A great deal of lakes are already at eutrophication or higher eutrophication level, such as Taihu Lake, West Lake, et al. How to control eutrophic waterbody, reduce nutriment and resume the function of waterbody have become the focus of global environmental problem.The previous study indicated that some hydrophytes and microorganisms could well purify waterbody. Thus, our experiment studied on the effect of different ecosystems of macrophytes and microorganisms on water purification. This experiment included three parts the indoor experiment, the experiment in BoGong Island and the experiment on the floating island of Tangpu Reservoir in Shaoxing.(1) In the indoor experiment, Nymphoides peltatum was taken as experimental material. We set up two grads of both total phosphorus (TP) and nitrogen (TN) and five concentrations for every grad to study the change of nutriment concentration of phosphorus and nitrogen associated with the total number of bacteria. We analyzed the change of the total number of bacterioplankton and rhizosphere bacteria. The pertinency between the number and the removal rate of TN and TP indicated that the increase of the bacterioplankton and rhizosphere bacteria was positive related with the removal rate of TN, but was not obviously with the removal rate of TP. And the total number reached the top on the 7th day. In the ecosystem of macrophytes and microorganisms, nitrogen was mainly removed by nitrogen bacteria including bacterioplankton and rhizosphere bacteria, while phosphorus was mainly removed by plant aborbing and rhizosphere phosphours bacteria acted some. For ecological restoration, Nymphoides peltatum could be collocated in some eutrophic rivers or shallow lakes, especially in those with high nitrogen concentration.(2) In this experiment, aquatic macrophytes Iris pseudacorus,Thalia dealbata and Canna generalis growing in ecotypic floating island were taken as experimental material. They promoted the growth of microorganisms. The water quality inside was better than that outside of the floating island. Thus, the system of emergent plants and microorganisms were effective on purifying waterbody. The total numbers of the rootzone microorganisms of these plants were fluctuated. But that of Iris pseudacorus was fluctuated less than the others. And that of Iris pseudacorus was maximum amoung them. Iris pseudacorus was a good plant on purifying waterbody.The total number of bacterioplankton and nutriment were both influenced by temperature inside and outside of the floating island obviously, showing that the temperature was the limited factor of them.(3) In this experiment, TP was the limited factor of bacteria. Nymphoides peltatum absorbed phosphorus and nitrogen perfectly, and it promoted the growth of bacteria. Moreover, the adaptability of Nymphoides peltatum is good and could be managed easily. It could be applied in some eutrophic rivers and shallow lakes. Potamogeton crispus absorbed phosphorus and nitrogen was perfect too when it was planted in large-scale. Algae could still absorb a great deal of nutrient when it grew.