Study On Effect And Mechanism Of Aquatic Plant On Water Purification

As the main component of aquatic system,aquatic plants are the important primary producers of the system,and are the basis for maintaining the healthy operation of the ecosystem.As a commonly used ecological restoration technology,aquatic vegetation restoration plays an important role in the control of eutrophication.Aquatic plants can directly absorb nutrients through growth,and can also influence water quality by pro-moting deposition,increasing water transparency,releasing allelochemicals,providing suitable habitats for microbes,promoting the growth of microorganisms in water and rhizosphere.However,the relative contribution of different mechanisms to the change of water quality indices is quite different in different studies.In different studies,the direct absorption of nutrients by aquatic plants accounted for 1.5%to 42%of total ni-trogen and phosphorus removal.To investigate the effect of plants in water purification,we studied the changes of water quality indices included NH₄⁺-N,NO₃^--N,PO₄^3--P,TN,TP of an Elodea nuttalli microcosm in response to high nutrient concentrations.We controlled for nutrients at 3 concentration level（C₀,C₁,C₂）in microcosms with non-plant（B₀）,intermediate（B₁）and high levels（B₂）,respectively;we then compared between the dynamics of main water quality indices and their relationships with the corresponding plant biomass.In addition,we also analyzed the correlation between water quality indicators and envi-ronmental factors DO and pH,and simulated the consumption of nitrogen indicators.Results showed that:（1）After added high concentration of nutrients in the microsystem of Elodea nut-talli,the water quality indices of the system decreased continuously after that reached the maximum,but all the indices（except NO₃^--N）did not reach the target concentration.The change process of each index was different.The NO₃^--N began to decline while the concentration of NH₄⁺-N droped to a lower level,and the concentration of TN re-mained high when both NH₄⁺-N and NO₃^--N decreased to a lower level.（2）Except for the high biomass group（C₀B₂）,the biomass of each treatment group increased.The relative growth of biomass in intermediate concentration intermediate biomass（C₁B₁）was 39.61%+ 9.82%,and the relative growth in others were decreased successfully in C₂B₁（27.37%±6.72%）,C₀B₁（22.89%±8.21%）,C₁B₂,（14.74%±4.21%）,C₂B₂（8.34%±2.04%）.（3）The average concentrations of NH₄⁺-N,NO₃^--N,PO₄^3--P and TP decreased with B0,B1 and B2.And The TN and PO₄^3--P in the B2 were significantly smaller than the Bi and the Bo at the two concentration levels of C₁ and C₂.At the C₁,the NH₄⁺-N and NO₃^--N in the plant group were significantly lower than the Bo,while the difference of NH₄⁺-N and NO₃^--N between the different biomass groups was not significant.At the C₂ level,the difference between the NH₄⁺-N and NO₃^--N in each biomass treatment groups did not reach the significant level;The difference of TP in different treatment groups was not reach the significant level.（4）The correlation of the changes of water quality indices of the microcosm showed that the correlation degree of NH₄⁺-N and P indices was the highest;The cor-relation degree between PO₄^3--P and TP in plant groups were the highest,and the cor-relation degree between TN and pH in the non-plant groups were the highest;The cor-relation degree of DO and pH was the highest,and decreased with the increase of bio-mass and nutrient concentration;There were strong correlation between DO,pH and water quality indices.The environmental factors of C₂ and B₂ have higher interpretation rate on the change of water quality indices.Compared with pH,the correlation of DO with the change of water quality indices was higher.The decrease rate of NH₄⁺-N can be explained by the Michaelis-Menten equation.When the biomass increased,the con-centration of indices decreased and the decrease rate of NH₄⁺-N may remain constant at first,but after the biomass increased to a certain extent,the consumption rate of NH₄⁺-N may decreased rapidly.On the whole,after added different concentrations of the nutrients to the different biomass of Elodea nuttalli microcosm,the experimental results showed that the exist-ence of aquatic plants significantly reduced the variation of nutrients,and the average concentration of the water quality indices decreased with the increase of biomass,alt-hough the increases of high biomass group in lower,the water quality indices in high biomass groups were significantly lower than that in intermediate groups.Compared with the increase of plant,the total biomass has a relatively large influence on the change of water quality indices,which suggest that the indirect effect of plant growth may be greater than the direct absorption of plants to the changes of water quality indi-ces.The response of different indices to biomass is also different,Nitrogen had closer relation with the existence of plants,while phosphorus had closer relation with the bi-omass.