The Study Of Reducing Agricultural Non-point Source Water Pollution With Irrigation And Drainage System Of Water Saving And Pollution Prevention In Rice-based Irrigation Districts

Focuses on the problem of agricultural non-point source pollution in the rice-based irrigation area in South China, Two experimental sites of irrigation and drainage system with "four lines of defense" for pollution mitigation were established in the rice-based irrigation area located in the zhanghe, Hubei Province and Qingshitan, Guangxi Autonomous Region. The field experiment for each link of the "four lines of defense" system (paddy field-field grass ditch-pond wetland-ecological trunk ditch) is engaged. The analysis and simulation are conduct on the basis of the results of the experiment. The effect of the pollution reduction and its mechanism of each link and the comprehensive system are studied. The main research contents and conclusions are as follows:(1)The pattern of loss of nitrogen and phosphorus in the water paddy fields under different treatment of water and fertilizer. The pattern of migration and transformation for nitrogen and phosphorus under different water and fertilizer are established.19.2%of the loss of total nitrogen and11.1%of the loss of total phosphorus are reduced under "shallow, wet, drying" irrigation than flooding irrigation.3.6%of the loss of total nitrogen and15.6%of the loss of total phosphorus are reduced under alter wet and dry irrigation than flooding irrigation. Not only the loss of nitrogen and phosphorus is reduced, but also yield is increased under water saving irrigation. Under the same condition of irrigation mode, the more the fertilization, the more the loss of fertilization.(2) The effect is studied to the pollution for nitrogen and phosphorus in rice growing period by field grass ditch and ecological trunk ditch. The reduction rate of TN、NH4+-N、NO3--N、TP is36.63%、18.44%、34.43%、15.38%by field grass ditch, The reduction rate of TN、NH4+-N、NO3--N、TP is54.5%、43.7%、-23.3%、7.3%by ecological trunk ditch. The effect is good.The effect to the pollution for nitrogen and phosphorus is very well by typical field grass ditch and ecological trunk ditch show that it is feasible to reduce non-point source pollutants by field grass ditch and ecological trunk ditch.(3) The effect of pollution for nitrogen and phosphorus is reduced by wetland through analyzing experimental data. The analysis of effect to reduce nitrogen and phosphorus by ponds wetland in different growth stages.49.62%of total nitrogen and 47.79%of total phosphorus are reduced by ponds wetland in2009,47.86%of total nitrogen and61.18%of total phosphorus are reduced by ponds wetland in2010.The effect is good.(4) The pattern of loss of nitrogen and phosphorus under the combined effects from "four lines of defense". In the "Four Defense Lines" system, nitrogen and phosphorus concentrations and load decrease with drainage process.91.17%of nitrogen loss and86.97%of phosphorus loss were reduced. The reduction of rice nitrogen and phosphorus pollution is achieved.(5) The relation of the rate of nitrogen and phosphorus by "four lines of defense" in the conditions of the water is totally enclosed or under natural conditions. In the conditions of natural, the reduce rate of TN should be decreased zero to ten percent and TP should be decreased ten to thirty percent according to the results of reduce rate in each link.(6) The study of the applicability for resolving the problem of "four lines of defense" system by using EPIC model and K-C model.The load of nitrogen and phosphorus in the outlet of paddy field is simulated by EPIC model, but the accuracy of the simulated results is low. So that the EPIC model is improved, the accuracy of simulation is better as the errors of the simulated results are less than30%by using the improved EPIC model. The water quality in the outlet of wetland is simulated by K-C model, but the accuracy is low also, So that the K-C model is improved, the accuracy of simulation is better as the errors of the simulated results are also less than30%. The improved model can be used to forecasting the water quality of outlet in pond wetland.