Quantitative study of the damping effect of buffer strips with different slopes on runoff and pollutant removal efficiency

Using the constructed buffer strip experimental site and the hydrometric devices in the Dongfeng Port of Shanghai,a quantitative study is conducted to investigate the damping effect of buffer strips with different slopes on runoff and the pollutant removal efficiency of nitrogen (N)and phosphorous (P)from agricultural lands.The result shows that for a similar configuration of vegetation structure,the gentler the slope gradient is in relation to the damping effect of buffer strips,the slower the runoff moves,and the greater the hydraulic permeability is.For example,on a 19-m long buffer strip with a 2% slope,there will be a delay of 7.3 minutes for runoff starting to flow out of the strip compared to that with a 5% slope.The two slope configurations can lead to a ratio of 1:1.74 with respect to the seep-age water.The improvement in the pollutant removal efficiency of N and P would be more significant in comparison with the damping effect on runoff when the slope gradient increases.For instances,on the buffer strips with 2%, 3%,4% and 5% slopes,the improvement ratio of the two elements are 2.32,2.15,1.82 and 1.64,respectively. The gentler the slope gradient is in relation to the pollutant removal efficiency of N and P,the greater the total efficiency and unit area improvements will be.For example,on the buffer strips with 2% and 5% slopes,the two im-provement ratios are found to be 1.56 and 1.66,respectively.The buffer strip with a 2% slope would have the high-est pollutant removal efficiency of total nitrogen (TN),ammonia nitrogen (NH₃^-N)and total phosphorous (TP), which are 0.661、0.672 and 0.044 g/m²,respectively.