Comparative Study On Nitrogen-phosphorus Removal And Allelochemical Inhibition Of Algae By Three Submerged Plants

The restoration of eutrophic water,the reduction of nutrient content and the restoration of water ecological function have become the research focus of global environmental problems.In recent years,the use of submerged plants for ecological restoration has been widely used in eutrophication water purification due to its advantages of less investment,good treatment effect and simple operation.In view of the problems such as water depth and lack of light in turbid water,this paper puts forward two solutions.The growth mode of submerged plant planting bed can break the limitation of water transparency on submerged plant growth by adjusting the floating bed depth;the harmful algae in eutrophic water can be controlled by submerged plant allelopathy,so as to improve the water transparency and increase the light intensity.The main research contents and conclusions are as follows:(1)In this study,three kinds of common submerged plants,Ceratophyllum,Myriophyllum and Vallisneria were taken as the test objects.The purification effect of three submerged plants on eutrophication water body was compared by measuring TN,TP and algae content in the natural pond raw water and simulated eutrophication water body.The results show that under the planting bed model,the TN removal rates of Vallisneria.Myriophyllum and Ceratophyllum were 49.4%,55.9%and 53.8%respectively,the removal rates of TP were 15%,39.6%and 47.8%respectively.Through the comparison and selection of three kinds of submerged plants purification effect,Vallisneria was selected as the research object,setting original planting density gradient of 750g/m~3,1500g/m~3,2000g/m~3,and natural and simulated eutrophic water were adopt to determine the content changes of TN,TP and algae in the water body,to compare the purification effect of submerged plants with different planting density on nitrogen and phosphorus in eutrophic water.The results show that the higher the planting density,the faster the nitrogen and phosphorus removal rate.Among them,the water purification rate of the experimental group with planting density of1500g/m~3 and 2000g/m~3are much faster than that of the experimental group with planting density of 750g/m~3.From the plant growth potential index,the growth trend of the experimental group with planting density of 1500 g/m~3 is better than that of the experimental group with planting density of 2000g/m~3.(2)The algal suppressor prepared by Phytoallelopathy has been proved to be an environmentally friendly method for controlling harmful algal blooms in eutrophic water.Ultrasonic enzymatic extraction of allelochemicals is an efficient and time-saving method.In this paper,the effects of ultrasonic enzyme extracts of different concentrations of Ceratophyllum,Myriophyllum and Vallisneria on Microcystis aeruginosa were studied,set the concentration gradient as 0.5g/L,1g/L,5g/L,10g/L and 20g/L.Through the study on the growth index,photosynthetic system and oxidative stress system of Microcystis aeruginosa,the results show that the growth of Microcystis aeruginosa cells could be inhibited in the concentration range of 5g/L by three kinds of submerged plants.After one day of experiment,ROS activity,SOD activity,SOD content and MDA level of cells were significantly increased,which indicated that three plant extracts could induce oxidative stress of Microcystis aeruginosa cells.After 3 days of experiment,the metabolism activity of algal cells decreased,almost no algal growth.The results show that the growth of Microcystis aeruginosa could be inhibited by the three extracts.