Reducing Nonpoint Source Pollution

76 Vegetated buff ers are a well-studied and widely used agricultural management practice for reducing nonpointsource pollution. A wealth of literature provides experimental data on their mitigation effi cacy. Th is paper aggregated many of these results and performed a meta-analysis to quantify the relationships between pollutant removal effi cacy and buff er width, buff er slope, soil type, and vegetation type. Th eoretical models for removal effi cacy (Y) vs. buff er width (w) were derived and tested against data from the surveyed literature using statistical analyses. A model of the form × = ×(1e ) b w Y K , (0 100 K < ≤ ) successfully captured the relationship between buff er width and pollutant removal, where K refl ects the maximum removal effi cacy of the buff er and b refl ects its probability to remove any single particle of pollutant in a unit distance. Buff er width alone explains 37, 60, 44, and 35% of the total variance in removal effi cacy for sediment, pesticides, N, and P, respectively. Buff er slope was linearly associated with sediment removal effi cacy either positively (when slope ≤ 10%) or negatively (when slope > 10%). Buff ers composed of trees have higher N and P removal effi cacy than buff ers composed of grasses or mixtures of grasses and trees. Soil drainage type did not show a signifi cant eff ect on pollutant removal effi cacy. Based on our analysis, a 30-m buff er under favorable slope conditions (≈ 10%) removes more than 85% of all the studied pollutants. Th ese models predicting optimal buff er width/slope can be instrumental in the design, implementation, and modeling of vegetated buff ers for treating agricultural runoff . A Review of Vegetated Buff ers and a Meta-analysis of Their Mitigation Effi cacy in Reducing Nonpoint Source Pollution