Research On The Effect Of Ditch With Different Sediment And Plants On Nitrogen Elimination In Runoff

The use of farmland ecological ditches to intercept and absorb farmland drainage nitrogen and phosphorus is one of the important measures to prevent and control agricultural non-point source pollution.In order to study the absorption and interception effect and process of ecological ditch on nitrogen pollution load under different sediment conditions,this study used the farmland drainage ditch constructed in the same plot,taking reddish clayey soil and sand mud as Ditch Sediment respectively,set four treatment methods: reddish clayey soil + plant(CK1),reddish clayey soil + plant + pollutant(HW),sandy soil + plant(CK2),sandy soil + plant + pollutants(SW),quantitative study the difference of nitrogen uptake effect of natural ecological ditches under four conditions,and explore the influence of sediment and plant on nitrogen uptake and runoff reduction,so as to provide experimental theoretical basis for the construction of farmland drainage ditch and prevention and control of agricultural nitrogen pollution.The main results were as follows:(1)The plants in the drainage ditch play an irreplaceable role in the process of nitrogen absorption and transformation.When the plant increment in the ditch was low at the beginning of the experiment,the nitrogen absorption of the ditch mainly depends on the adsorption of the sediment soil,and the absorption efficiency is relatively low,only about 20%.With the growth of ditches plants,the removal rate of nitrogen from ditches is increasing continuously,reaching a maximum of 62.5%.(2)Under the condition of rainstorm,due to the excessive hydraulic load of the ditch and the increase of the flow velocity of the runoff water,the bottom mud of the drainage ditch releases nitrogen,which makes it a "nitrogen source",thus affecting the process of nitrogen absorption of the ditch,which may cause the nitrogen concentration in the water at the end of the ditch to be higher than that at the beginning.(3)The removal rate of NO3--N in drainage ditches is between 49.77%~66.82%,and the removal rates of TN and NH4+-N are 41.01%~45.31% and 36.21%~41.15%,respectively.The removal effect is obviously worse than NO3--N.However,the differences between different ditches are not significant.The removal rate of TN and NO3--N in the rear part of the ditch is higher than that in the front part,with the highest increase of 75.42% and 43.65% respectively.The difference in removal rate of NH4+-N before and after is not obvious,weed species and biomass in the back part of ditch are significantly increased.(4)The nitrogen absorption and removal of drainage ditch is closely related to the biomass of main plants,the types and biomass of ditch weeds.In addition,the above-ground plant parts of pollutant-added ditches absorbed and accumulated nitrogen in the ditch water significantly higher than those without pollutants.The nitrogen accumulations of the four treatments(CK1,HW,CK2,SW)were 247.07 g,379.217 g,338.66 g,374.68 g.The results show that the types of farmland weeds are related to the types of ditch bottom mud.(5)Soil particles and colloids in the ditch sediment can remove nitrogen pollutants by absorbing cations such as ammonium ions in the water,and at the same time lead to the increase of TN content.Therefore,after the experiment,the soil TN content in the sediment increased significantly,the increment was 17.96%~54.76%,and the red-yellow mud was significantly higher than the river sand mud.The content of alkali-decomposed nitrogen and organic matter decreased by 1.19%~31.8% and 9.30%~28.75%,respectively,and the red-yellow mud decreased more than river sand mud.