| At present,non-point source pollution of farmland seriously affects the water quality of our country and restricts the sustainable development of society and economy.In order to protect the rural ecological environment properly,the Qingpu District of Shanghai built a variety of ecological ditches in accordance with local conditions,but there are few studies on the removal of main runoff pollutants from farmland in the area of ecological ditches.This thesis,taking the ecological ditches in Qingpu District of Shanghai as the research object,explores the effect of ecological ditches on the removal of runoff pollutants under the conditions of natural rainfall.This thesis studies the characteristics of plant and microbial communities in ecological ditches,and explores the impact of microbial community characteristics on farmland water purification.This thesis reconstructs the ecological ditches,and carries out natural rainfall and artificial water distribution to simulate rainfall experiments,in order to explore its effect on the removal of runoff pollutants.The paper will provide scientific basis and technical support for the promotion and application of farmland ecological ditches.The main findings are as follows:(1)The concentrations of total nitrogen(TN)and ammonium,nitrogen(NH4+-N)in the ditch runoff decreased gradually with heavy,moderate and light rain events.The total phosphorus(TP),chemical oxygen demand(COD)and suspended solids(SS)concentrations of ditch runoff were higher in heavy and moderate rain,while the TP,COD and SS concentrations of ditch runoff were lower in light rain;the concentrations of TN,NH4+-N,TP,COD,and SS in the ditch runoff decreased along the trend of the water flow during the rainfall period.The average removal rates of TN,NH4+-NTP,COD,and SS in the well-operated Jingyang Village No.1,No.2 and Blueberry Orchard ecological ditches were 23.33%-35.74%,24.45%-40.91%,20.65%-38.17%,8.33%-32.43%,21.19%-52.91%,which were better than the control ditch.(2)The diversity index,coverage and biomass of the four plants in the ecological ditch were higher than those of the control ditch.Ditch water and bottom sludge separately contained 23 and 38 functional bacteria related to the removal of farmland runoff pollutants.The total relative abundance of functional bacteria in ecological ditch water and sediments ranged from 15.32%to 25.62%and 8.83%to 17.45%,respectively,which were higher than those in control ditch(13.01%,8.65%).Redundant analysis showed that the microbial community in the ditch system had an impact on the removal of farmland runoff pollutants,and the Proteobacteria and y-Proteobacteria had a greater impact on the removal of TN and TP,which can enhance the removal of TN and TP by the ditch system;the main factors of changes in related functional bacteria’s community structure in the water were SS,NH4+-N,and COD.(3)The plant screening experiments showed that both Thalia dealbata Fraser and Iris pseudacorus L.had good removal effects on farmland runoff pollutants.On the 22nd day after adding pollution sources,the total relative abundance of functional bacteria phylum,Proteobacteria and functional bacteria in the Iris pseudacorus L.system had the most obvious change,increased by 9.5%,14.87%and 2.04%,respectively.Therefore,Iris pseudacorus L.was selected as the main plant for the reconstruction of the ecological ditch.With reconstruction of the ecological ditch under natural rainfall conditions,the removal rates of TN,NH4+-N,TP,COD,and SS were 32.35%,38.3%,29.59%,31.03%,and 25.78%,respectively,and the removal effect was better than that of the cement open ditch before reconstruction.During the drainage period,artificially simulating rainfall experiments identified that the removal rates of TN,NN4+-N,TP,COD,and SS by the reconstruction of ecological ditches were 46.86%,37.32%,39.86%,26.96%,and 39.51%,respectively,indicating that the reconstruction of ecological ditches can remove pollutants effectively from farmland. |
PDF Full Text Request