Research On Agricultural Non-point Source Pollution Control Based On Cascade Ditch System

Farmland ditches have the dual characteristics of "source" and "sink",and play an important role in the interception and purification of agricultural non-point source pollutants.Therefore,how to effectively use the interception function of ditches is important for preventing and controlling agricultural non-point source pollution in river basins.The theoretical and practical significance of Based on the on-site monitoring of the distribution and interception of non-point source pollutants in different characteristic ditches in the Anhui section of the Huaihe River Basin,this paper uses indoor simulation to study the effects of cascade ditches on pollutants under the influence of different functional sections and different factors.Removal effect,combined with field small-scale experiments to compare the pollutant retention effect of cascade ditches under practical application,and compare the change characteristics of nitrogen and phosphorus in four different wet and dry intensities under different sediment substrates through indoor simulation.The results of the study are as follows:1)The nitrogen and phosphorus content of different characteristic channels in the study area is farmland ditches>tributary ditches>river ditches;sediment nitrogen content is river ditches>farmland ditches>tributary ditches;sediment phosphorus content is farmland ditches>river ditches>Tributary ditches.2)The indoor simulation experiment results of the cascade trench show that the total nitrogen content of artificial water distribution fluctuates down along the way,the reduction efficiency is 10.2%,the total nitrogen interception efficiency of the natural water body is 11.54%,and the single column TG1 intercepts nitrogen.It reaches 44.86%,which proves that TG1 simulates anoxic environment to promote the denitrification of nitrogen;the interception rate of phosphorus by the system under natural water bodies by intercepting sediment is 56.87%.Under different environmental conditions,the interception effect of nitrogen and phosphorus is more obvious when the temperature is 8-20℃.The content of total nitrogen changes most obviously at pH=8,but the effect on phosphorus is small;the hydraulic retention time has a smaller effect on nitrogen and phosphorus.The removal effect is more obvious,and the long-term water covering can achieve the maximum removal of nitrogen and phosphorus by 40%and 50%,respectively.3)The small-scale experimental data of the field cascade ditches show that the overall nitrogen retention effect in the hypoxic zone is outstanding,and the local retention rate can reach 47.96%,but due to the lack of subsequent denitrification and the sediment nitrogen under the disturbance of water flow The release of nitrogen makes the final effluent nitrogen interception in the canal section only 5.4%,and the stepwise nitrogen interception size is TJ2>TJ3>TJ4>TJ1.The interception rate of phosphorus is 88.8%.The upstream sediment contains a large amount of particulate phosphorus.Through the step baffle,the lateral flow velocity is slowed down,so that the output of phosphorus is greatly reduced.4)In the dry-wet alternation experiment,the reduction rate of nitrogen and phosphorus content in the sediment of the straw-free group was better than that of the straw group.The total nitrogen reduction rate was low intensity(37.9%)>medium intensity(35.12%)>control group(28.98)%)>high intensity(27.92%);the total phosphorus decreased by the control group(20.62%)>low intensity(16.06)>high intensity(14.49%)>medium intensity(13.57%);TN under different conditions of alternating dry and wet experiments The content changes were all decreased.The change rate of the undisturbed sediment group was greater than that of the mixed straw sediment group,while the TP content showed a significant increase trend in the straw group,which was significantly different from the straw-free group.Figure[70]Table[13]Reference[87]...