| In order to clarify the source of dissolved oxygen in the subsurface flow constructed wetland and the stress characteristics of wetland plant roots releasing oxygen,four deep subsurface flow constructed wetlands(0.1m,0.3m,0.6m,1.2m)are the main research objects,and the canna is the cultivated plant.At the same time,a 0.1m hydroponic tank system was set up as control.Use nitrogen to blow off the dissolved oxygen in the water and wax seal to isolate the atmospheric reoxygenation simulated plant oxygen release as the sole source of oxygen stress,and to isolate the simulated water inflow dissolved oxygen and the plant release oxygen as the sole source of oxygen stress by the influent aeration and wax seal.The additional treatment simulates three sources of dissolved oxygen in water,oxygen release from plants,and atmospheric reoxygenation.By comparing the differences in physiological metabolism and stress stress of plants in wetland and hydroponic tanks,the dissolved oxygen concentration of effluent at different depths,and the removal characteristics of pollutants,the growth characteristics of plant roots in wetland at different depths with or without atmospheric reoxygenation were clarified.The spatial and temporal distribution characteristics of dissolved oxygen in constructed wetlands,plant stress characteristics under oxygen source stress and their correlation with pollutant removal are discussed.Research indicates:(1)Although the depth of the ceramic bead filler in the 0.3,0.6m and 1.2m deep wetlands is relatively deep,the plant root zone is still mainly concentrated in the area0.1m down from the surface.In a 0.1m hydroponic tank,the presence of dissolved oxygen in water,atmospheric reoxygenation,and root system oxygen release will promote the development of total plant roots.When atmospheric reoxygenation does not exist,plants tend to develop fibrous roots compared to tubers.The root system tends to be evenly distributed in the hydroponic tank,and the area for plants to release oxygen is expanded.(2)When atmospheric reoxygenation is isolated,the biomass of plant roots is better than that of atmospheric reoxygenation,indicating that this isolation stress stimulates the growth of plant roots in the wetland,especially for the growth of fibrous roots in the 0.1m and 0.6m constructed wetlands.The amount is better than 0.3m constructed wetland plants,which are 1.43 times and 1.55 times respectively.It is also consistent with the difference in dissolved oxygen in the 0.1m effluent from the surface of the three deep underflow wetlands,indicating that the growth and development of fibrous roots can help improve root zone dissolved oxygen environment.(3)In the 0.1m hydroponic tank,0.1m and 0.3m wetland,when root secretion is used as the only oxygen source,there is no significant difference in the spatial distribution of dissolved oxygen in the 0.1m hydroponic tank(p=0.482>0.05),0.1m wetland There was no significant difference in the spatial distribution of dissolved oxygen(p=0.235>0.05),which remained at 4.15～2.19mg/L and 2.19～0.71mg/L,respectively.When atmospheric reoxygenation exists,there is no significant difference in the spatial distribution of dissolved oxygen in the 0.3m wetland(p=0.322>0.05).When root secretion is the only oxygen source,the vertical distribution of COD,ammonia nitrogen,TN,and TP removal rates corresponding to the distribution of dissolved oxygen in the 0.1m hydroponic tank is not significant(p=0.235,0.422,0.685,0.312>0.05),in the presence of atmospheric reoxygenation,the removal rates of COD,ammonia nitrogen,TN and TP in the 0.3m wetland were not significantly different in the vertical distribution of the wetland(p=0.238,0.547,0.163,0.162>0.05).It shows that atmospheric reoxygenation or root oxygen secretion can effectively diffuse the dissolved oxygen in the wetland and make the pollutant removal rate evenly distributed in the treatment system.(4)In the 0.6m constructed wetland,the dissolved oxygen concentration in the root zone of the surface layer 0.1m is extremely significantly different from the dissolved oxygen concentration in the bottom of the wetland(p=0.001<0.05),which is 10.01 times higher.There was no significant difference in the removal of COD in the 0.6m and 1.2m wetlands along the vertical direction of the wetland(p=0.238,0.537>0.05),and there was no significant difference in TN(p=0.769,0.759>0.05),but in the 0.6m wetland There is a significant difference between the TP removal rate of the effluent from the rooted area and the effluent removal rate of each depth in the rootless area(p=0.021<0.05).The NH4+-N and TP removal rate of the effluent from the rooted area in the 1.2m wetland is different from that of the rootless area.The effluent removal rate is also significantly different(p=0.039,0.043<0.05).The NH4+-N removal rate in the root zone of the 0.6m and 1.2m wetland is 2.04 times and 1.75 times that of the bottom layer removal rate,respectively;the TP removal rate is the bottom layer removal rate.2.5 times and 1.52 times indicate that the root zone is not only an important supply area for dissolved oxygen,but also an effective area for removing pollutants in the wetland.(5)Under the stress of the sole source of oxygen releasing oxygen from the roots,the chlorophyll content of plant leaves in the 0.1m hydroponic tank increases,and the biomass of the above-ground and underground parts of the plant is less than that of the two oxygen sources under the stress of dissolved oxygen in the water and the oxygen released by the roots.Plant biomass,and the MDA in the plant continued to increase in the first 3 days of stress,and the degree of membrane lipid peroxidation increased,which was more damaged than the plants in the constructed wetland under the same oxygen source stress,indicating that the hydroponic tank is more susceptible to environmental damage As a result,plants in wetlands are more tolerant of oxygen source stress.In addition,the amount of oxygen released by plant roots in the hydroponic tank was affected,and the dissolved oxygen concentration in the root zone was 21.3% lower than that under the stress of influent dissolved oxygen and root released oxygen.(6)In a 0.1m constructed wetland,when the root system is the sole source of oxygen,the content of root exudates is 45.54% lower than that of plants in the hydroponic tank under stress of the same oxygen source,but the ability to oxidize α-naphthylamine after stress The plant root-to-shoot ratio in the wetland increased by 19.95%,indicating that the plants in the 0.1m wetland increased their root activity after being affected by changes in the oxygen environment.Compared with plants in hydroponic tanks,the ability to provide a suitable micro-ecosystem for rhizosphere microorganisms is weaker. |
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