Study On Interception Effects Of The Main Agricultural Non-point Source Pollution By Grass Vegetative Filter Strips

Wider use of mineral fertilizer did not only significantly increase crop yields but also result in serious water pollutions. Agricultural non-point source pollution problem more and more gets the attention of the whole society. Grass vegetation filter belt, as a kind of ecological engineering measure, has a significant effect on prevention and control of agricultural non-point source pollution. This experiment includes two parts, soil bin simulation experiment and runoff plot experiment.In the soil bin simulation experiment, the corroded wire segments instead of grass plant stems, simulated its distribution in the vegetation filter belt, considering the physical block and mechanical filtration effect. Vegetative filter strips (VFS), which planted along streams or lakes to remove sediments and nutrients carried in runoff, were regarded as one of the best management practices in the controlling of agricultural non-point source pollution in many countries. Interception rates of pollutants by VFS were largely depended on VFS width, type of VFS (grasses, shrubs, trees, or their mixtures), and type of pollutants (particle or soluble), but these effects have not been adequately tested. A simulated experiment was conducted in this study to determine the interception rates of runoff, sediment, nitrogen, and phosphorus by the artificial grass-like VFS with different widths (1m,2m, and3m). The results showed that the interception rates of runoff and pollutants were greatly influenced by the width of VFS under the same conditions (water flow rate and speed were0.173L/s and0.7m/s, respectively). The outflow of runoff was decreased by32%,51%, and69%by the1m,2m, and3m wide VFS, respectively, while the outflow of sediment was decreased by78%,88%, and92%by the1m,2m, and3m wide VFS, respectively. Correspondingly, the outflow of total nitrogen was decreased by65%,75%, and84%, respectively, while the outflow of total phosphorus was decreased by80%,93%, and95%, respectively.In the runoff plot experiment, vegetative filter strips (VFS), which planted along streams or lakes to remove sediments and nutrients carried in runoff under different slopes and different widths. A runoff plot experiment was conducted in this study to determine the interception rates of runoff, sediment, nitrogen, and phosphorus by the grass VFS with different slopes (5%and10%). The results showed that, the interception rates of runoff and pollutants were greatly influenced by the slope of VFS under the same conditions. The outflow of runoff was decreased by69%and52%by the5%and10%slope VFS, respectively, while the outflow of sediment was decreased by96%and91%by the5%and10%slope VFS, respectively. Correspondingly, the outflow of total nitrogen was decreased by86%and78%, respectively, while the outflow of total phosphorus was decreased by96%and93%, respectively.The runoff plot experiment was also conducted in this study to determine the interception rates of runoff, sediment, nitrogen, and phosphorus by the grass VFS with different widths (3m,5.5m,7.5m and10.5m). The results showed that the interception rates of runoff and pollutants were greatly influenced by the width of VFS under the same slope with5%. The outflow of runoff was decreased by35%,47%,58%and72%, respectively, while the outflow of sediment was decreased by85%,89%,92%and95%, respectively. Correspondingly, the outflow of total nitrogen was decreased by68%,76%,81%and86%, respectively, while the outflow of total phosphorus was decreased by89%,92%,93%and96%, respectively. The conclusion showed, under the same water flow rate and speed, the ability of grass VFS to intercept pollutants will be weakened with the increasing slope, instead corresponding enhanced with the increasing width. That is to say, the interception effect of VFS were significantly negatively correlated with the slope, instead positively correlated with the width. Compared with the slope, VFS is more sensitive to the width. From the conclusion, with the width of5.5m, the highest interception rates of runoff, sediment, nitrogen, and phosphorus by the grass VFS were67%,95%,82%and67%, respectively.We conclude that grass VFS are very effective in reducing runoff, sediment, nitrogen, and phosphorus in the control of agricultural non-point source pollution, and also have important scientific and practical significance. Moreover, the results can provide theoretical basis for the application and popularization of VFS technology in our country, and also can improve the surface water environment, improve the surface quality, and give a help to ensure the safety of drinking water in China.