Removal Efficiencies Of Grass Filter Strips On Non-point Source Pollution:Experiments And VFSMOD-W Modeling

Vegetative filter strips(VFS)is one of the best management measures to control agricultural non-point source pollution.In this research,a soil trough device was set to simulate VFS.Then simulated runoff experiment was selected to study the effect of the VFS for the pollution with different treatment conditions.Then VFSMOD-W model was introduced to study the reduction ratio of non-point source pollution by constructing vegetative filter strips in Qixianghe River basin,and the best management measures of VFS were proposed.The main results are listed as follows:(1)The runoff reduction efficiency of VFS is between 30% and 61.1%.Compared with bare land,the reduction efficiency of surface runoff by VFS was increased by 90%.And it is better for Perennial ryegrass to retain surface runoff.Low initial soil water content and Low inflow flow can improve the retention efficiency of surface runoff by VFS.The concentration reduction efficiencies of suspended solid(SS),total nitrogen(TN)and total phosphorus(TP)by VFSs were 57.69%-82.45%,13.31%-30.17% and 32.73%-59.07%,respectively.The load reduction efficiencies of the above three pollutants is 71.32%-91%,46.81%-72.05% and54.41%-83.34%.Lower initial soil moisture content,smaller inflow flow and inflow concentration were more conducive to the reduction of SS,TN and TP by VFSs.(2)It is better for Perennial ryegrass to treat the particulate pollution,such as suspend solids,particulate nitrogen and phosphorus,the reduction efficiencies reached 91%,87.43%and 91.12%,respectively;Meanwhile,Ophiopogogon japonicus is more proper to treat the dissolved pollution,such as dissolved nitrogen and phosphorus,the reduction efficiencies reached 91%,87.43% and 91.12%.The retention efficiencies of runoff and suspended solids by the VFSs determines the retention efficiencies of nitrogen and phosphorus to a certain extent.Multiple linear regression model can be used to predict the nitrogen and phosphorus reduction efficiency of VFS based on the surface runoff reduction efficiency and suspended solids reduction efficiency.The formula is Rm TN=0.58·Rw+0.39· Rm SS-0.74,R2=0.93;Rm TP = 0.50·Rw + 0.62·Rm SS-5.5,R2 = 0.98.3)The simulation results of VFSMOD-W model showed that VFSMOD-W model could better simulate the reduction efficiencies of surface runoff and sediment by the VFSs.The simulated deviations between measured and predicted values of surface runoff and sediment reduction efficiency ranged from-4.09% to 11.89% and-3.29% to 10.85%,respectively.The simulation results also showed that there was a positive correlation between the width of VFS and the reduction efficiency of sediment,TN and TP.With the increase of width,the reduction efficiency of herbaceous vegetation decreased gradually.Slope was not a significant factor affecting sediment,TN and TP reduction efficiency of VFS.When the gradient was between3% and 21%,the reduction efficiency of VFS zone on sediment,TN and TP decreased by about 1%.Rainfall intensity significantly affected the effect of VFS on sediment,TN and TP reduction.The sediment reduction efficiency of the VFSs with six widths decreased significantly when the rainfall was between 25 mm and 40 mm.