Evaluation For The Effectiveness Of Best Management Practices(BMPs) Based On SWAT Model

Non-point source(NPS)pollution plays an important role in water body eutrophication,especially in developed agricultural areas.In agricultural production activities,excessive fertilizer,pesticides abuse,excessive reclamation and breeding waste water discharge,lead to nutrient leaching and soil erosion.Therefore,to control NPS pollution is of great significance to water environment protection.Best management practices(BMPs),as an integrated system for pollution prevention and control,which combines both structural and non-structural measures,has been considered as one of the most effective solution for NPS pollution.There are many different kinds of NPS pollution control measures.How to select the best management practices is the key to establish a comprehensive watershed control scheme.Take West Tiaoxi basin as the study area,by using the tool of SWAT model,the spatial and temporal distribution of NPS pollution load was analyzed.And,the critical source areas(CSAs)was identified according to the intensity of NPS pollution.Several BMPs were selected to implement in the CSAs of West Tiaoxi basin,and the nutrient loss were evaluated at different scale,and the water quality affected by combined BMPs at watershed outlet were assessed.Furthermore,economic factor was also combined in the evaluation of BMPs.By means of cost-effectiveness analysis,the measures with both environmental benefits and economic benefits were expected.The main research results are as follows:(1)Through field investigation,face-to-face interviews and information consultation,the data including topography,river distribution,land use,soil type,agricultural production information,pollution source in West Tiaoxi basin were collected and prepared for constructing spatial database and attribute database.The watershed was divided into 26 sub-watersheds and 510 HRUs.Based on the data of 2011-2014,the model was calibrated and validated.The results show that value of R2 are above 0.7 and Ens are around 0.6,indicating that the model has good applicability in the area.(2)According to the results of model simulation,average monthly nutrient loads in West Tiaoxi basin show the characteristic of fluctuation among the whole year,the nutrient loads rise with fluctuations from January to June,achieve peak value from June to August,and then gradually decrease from August to December.From the point of spatial distribution,the loss intensity of TN and TP was 7.2-18.6 kg/ha,1.28-4.14 kg/ha respectively.Overall,the nutrients loading increase from upstream to downstream,and loss intensity of main channel was obviously higher than that of tributary stream.(3)The Load per Unit Area Index method and Jenks method was adopted to classify the order of nutrients loss intensity and identify critical source area.Results show that CSAs of TN were in keeping with that of TP,which mainly distribute in the region with developed agricultural production and high population intensity.(4)Scenario analysis method was adopted to select BMPs.Measures were set from two aspects,including source control and process control,and SWAT model was used to evaluate environmental effectiveness.Results show the performance of filter strip and grassed waterway is excellent,with average reduction rate of above 40%.Pollution reduction effect of fertilizer reduction and zero tillage measures is limited,the reduction rate were below 10%.Significant difference of reduction rate of intercept measures among HRUs indicates the location of BMPs in the watershed plays a significant role in removal efficiency.Meanwhile,the location,area and loss intensity of CSAs have changed after implementing measures.For the water quality of watershed outlet,combined BMPs assessment results show that the NT+FR20+FS scenario has the best performance of pollution reduction,the TN and TP concentration of watershed outlet was reduced by 11.19%and 13.38%respectively.(5)In the cost-effectiveness analysis,the cost-effectiveness value of intercepting measure(filter strip and grassed waterway)were higher than the source control measures(fertilizer reduction10%,fertilizer reduction 20%and no tillage).Grassed waterway was the most cost effective,fertilizer reduction 10%was the worst.