Modeling Of Non-point Sources Pollution And Total Amount Control Of Pollutants In Hetao Irrigaton District Of The Inner Mongolia

There are two types of water pollution,namely,point source pollution and non-point source pollution.However,with the effective control of point source pollution,the water quality of the water body has not been improved obviously.And people have realized the existence and harm of non-point source pollution.According to statistics about 30%to 50%of the surface water in global have been afected by non-point source pollution,which the largest contribution comes from agricultural non-point source pollution.Due to the influence of soil,topography,climate,hydrology,land use and management,there are obvious different characters of agricultural non-point source pollution in regions,and the spatial difference of pollution load is very significant.Although the method of field monitoring are more accurate,it needs a lot of manpower and material resources,and it is difficult to describe the the process and mechanism of non-point source pollution with watershed scale.Therefore,the mathematical simulation as a more accurate technical method is used to analyze the spatial distribution of non-point source pollution.The combination of GIS,RS,GPS and hydrological model is a new way to assess the impact of non-point source pollution on the environment.The distribution hydrological model SWAT is the widestly used.The accurate construction of the hydrological model is the basis of runoff simulation,and the accurate delineation watershed is the prerequisite for the study of water balance in the whole watershed.In this paper,a typical representative of the Hetao irrigation district in Inner Mongolia is taken as an example.The mountainous ridge line,the natural river and the watershed boundary are divided into the watershed,and the correction coefficient is used to deal with the small terrain of the plain irrigation area.At the same time,the"Burn-in"and"Stacking algorithm"are used to process the DEM in turns,and then according to the irrigation and drainage system,the sub-basin boundaries are delineated,while the boundary of the watershed is determined with the land use map.In this paper,the SWAT model is used to simulate the runoff of the Hetao Irrigation District.The model evaluation index R~2=0.82,NSE=0.78 in calibration period and R~2=0.80,NSE=0.77 in evaluation period,which are all greater than that of the feasibility requirement of R~2=0.60 and NSE=0.50.And the evaluation indicators for TN,TP are also too.These results indicated that the model simulation results were credible and feasible.The runoff and non-point source pollution in the irrigation area are closely related to the management schedule such as irrigation water amount,irrigation time,fertilizer rate,etc.The change of TN load is basically the same as that of runoff,and there are two peaks in a year.One is caused by irrigation during the plant growing period and the other one is due to the irrigation in autumn.The change of TP load in monthly time scale is closely related to the time of precipitation during the year,and the peak value appears in the rainy seasons of June,July and August in each year.In the analysis of the spatial variation of pollutants,the contribution of TN is mainly from the wheat field in the plains of the irrigation area.The contribution of TP is mainly from the sunflower and the northeast mountain area.Comparing the two scenarios one is the seed fertilizing method,and the other is the seed manuring with topdressing.Taking spring wheat and maize as an example,the TN load in two scenarios was compared.The results showed that the fertilization method could effectively reduce the amount of nitrogen loss,and the reduction rate was 13%.The main part of the reduction was in shallow groundwater,and there is almost no effect on surface runoff.According to the simulation results,the water environment capacity was calculated by using Dillon model.Based on the third quality level of surface water standard,the environmental capacity is 980 ton for nitrate and 140 ton for phosphorus,respectively.The rationality of the total distribution scheme is evaluated by the Gini coefficient method.According to the reasonable distribution plan,the respective water environmental capacity of the four administrative regions of Linhe,Wuyuan,Dengkou and Hangjinhouqi are calculated.To further verify the rationality of the results of the distribution by SWAT model,and the emission load concentration from 2007 to 2013 is within the standard range.The establishment of the distributed model in irrigation area provides technical support for the research on the hydrological cycle process and non-point source pollution in the area.At the same time,by calculating the water environmental capacity and distribution in the irrigation area provides a reference.