Study On The Transfer And Transformation Of Nitrogen And Phosphorus Nutrients During Ecological Restoration Of Eutrophic Water

In today's society,the eutrophication of lakes is getting more and more serious,and the relative technologies and effects have attracted much attention,and ecological restoration technologies treating eutrophic lakes have been proved to be the mainstream today.The ecological restoration materials and methods used in the project are all different,but the final purpose is to reduce the concentration of nutrients such as nitrogen and phosphorus and the density and biomass of phytoplankton in the lake,restore large-scale submerged plants,increase water biodiversity,and enhance the vitality of water quality so that the self-recovery capacity of the water environment can be enhanced,which will finally provide a stable water ecosystem in the lake.In this study,under the conditions of a small water body,Vallisneria natans and Daphnia magna were used as submerged plant and zooplankton respectively to simulate the eutrophic lake treatment in ecologicalproject.The specific studies include: 1.The effects of V.natans on the total nitrogen,total phosphorus and various forms of nitrogen and phosphorus concentrations in eutrophic waters;2.The research on the treatment of eutrophic water bodies with the combination of Daphnia magna and V.natans;3.Study on simulating the construction of stable water ecosystem and the concentration balance of nitrogen and phosphorus.The research methods and results are as follows:(1)The establishment of biological communities of submerged plants plays an important role in the restoration of aquatic ecosystems.Modular planting plants are used to treat eutrophic water bodies,and eutrophic water bodies are used as blank groups to study the total nitrogen,total phosphorus and its various forms of nitrogen and phosphorus concentration changes in water.The results showed that the final removal rates of total nitrogen and total phosphorus were 87% and 86%,respectively;Ammonia nitrogen decreased from 83.50% to 24.59%,nitrate nitrogen increased from 6.16%to 53.37%,and the change of the ratio of nitrite nitrogen concentration was very small in this experiment;the proportion of particulate phosphorus decreased from 63.22% to 19.50% and soluble phosphorus increased from32.90% to 75.61%;the water was crystal clear at 35d;the V.natans reduced the total nitrogen and total phosphorus concentration,and first absorbed the concentration of ammonia nitrogen in the water,it also reduced the waterparticles,which improved the transparency of the water and the evident water purification effect.(2)In the practice of ecological restoration,the technology of jointly treating eutrophic water with more than two kinds of organisms has attracted extensive attention.In this study,Daphnia magna and V.natans were chosen as representatives of zooplankton and submerged plants,which established a combined treatment system.The group with V.natans was used as the control group and eutrophication water as the blank group.Water quality indicators,sediment indicators and changes in biomass of plants during the treatment process were studied.The results showed that the water and sediment quality of the combined system were better than that of the V.natans group.The final removal rates of total nitrogen,total phosphorus and ammonia nitrogen were 87%,88%,96% and the maximum removal rates were 70%,70 % and 86% respectively;What's more,the removal rate of total nitrogen in sediment was 16%,and the total phosphorus was 2.9%,and the water was crystal clear at 27 th days,and the growth rate of V.natans was 740%.However,in the control group,the final removal rates of total nitrogen,total phosphorus,and ammonia nitrogen were 35%,33%,and 57%,respectively,and the maximum removal rates were 35%,30%,and 57%,respectively.The removal rate of total nitrogen in sediment was 2.9%,and the total phosphorus was 9.3%,the water bodywas not clear enough to see the bottom at 48 th days,and the growth rate of V.natans was 470%.Therefore,Daphnia magna promote the settlement of suspended matter,facilitate the growth of V.natans,and help stabilize the system.The ability of combined system to treat eutrophic water bodies is greater than that of a single V.natans system.The Daphnia magna and V.natans combined system will improve water transparency more quickly.The growth rate of V.natans is greater and it is easier to maintain stability.(3)Simulate an aquatic ecosystem in which Daphnia magna,V.natans,grass-shrimp and blackfish were selected as zooplankton,large-scale sub merged plants,herbivorous animals and carnivorous animals,respectively.Then study the changes of nitrogen and phosphorus concentrations in water quality,sediment,and species of this ecosystem,which lead to the flow characteristics of nitrogen and phosphorus in this system.Finally,equilibrium equations about the nitrogen and phosphorus concentration were calculated.The results showed that only 1.4% and 0.26% of nitrogen and phosphorus in the water body were infused into the V.natans,and only0.71% and 1.11% flowed into the fish and shrimp.In the whole experimental system,the changes of nitrogen and phosphorus concentration in the water accounted for 45.76% and 19.88% of the system,54.24% and80.12% in the sediment,7.85% and 0.7% in submerged plants,0.05% in fish and shrimp with nitrogen changes only,and 59.91%,60.35% inplankton.Thus,it can be seen that plankton accumulates a large amount of nitrogen and phosphorus concentrations in this system,in the process of eutrophic water treatment,the concentration of nitrogen and phosphorus in plankton is also the most variable.The experimental results provide references for guiding the practice of ecological restoration engineering.