BUFFER WIDTHS AND NUTRIENT AND SEDIMENT REMOVAL EFFICIENCIES (2008)
Baris, RD, Q Ma, SZ Cohen. 2008.
Buffer Widths and Nutrient and Sediment Removal Efficiencies. Presentation at the American Water Resources Association, 2008 Summer Specialty Conference: Riparian Ecosystems and Buffers: Working at the Water's Edge, Virginia Beach, VA.
ABSTRACT: Vegetative buffers, as one type of Best Management Practices (BMPs), can serve many roles – preventing drift of turf chemicals, providing riparian habitats, and reducing contaminant loading from stormwater runoff via natural filtration. Most jurisdictions have either explicit or de facto regulations or guidelines for stream and wetland buffers. This paper provides an analysis of contaminant removal efficiency of vegetative buffers and critical buffer widths. Key parameters of concern are total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS). All three parameters can have significant impacts on wetland and freshwater systems. The literature was reviewed to determine the relationship between buffer width and pollutant removal efficiency. In addition, the relationship between buffer width and the onset of concentrated flow was examined. Plots of contaminant removal efficiency (RE) vs. buffer width (B) followed logarithmic relationships, i.e., RE(%)=a(lnRE)+b, R2 = 0.63, 0.57, and 0.42 for the TP, TN, and TSS relationships, respectively. (All relationships were significant at p = 0.01, except for TSS (p=0.058).) This indicates buffer width is a key factor but not the only factor. The second derivative of these plots can be used to estimate the 'point of diminishing returns', i.e., the approximate B at which a large increase in B results in only a relatively small increase in RE. These numbers were 18 m, 20 m, and 15 m, for TP, TN, and TSS, respectively. We suggest that these distances are governed by the transition from overland/sheet flow to concentrated/channelized flow. Calculations are done to demonstrate that the distances to reach concentrated flow in very short grass are 10.7 m, 15 m, and 21.6 m for slopes of 0.005, 0.01, and 0.02, respectively. Another key consideration for this type of analysis would be the extent to which stormwater runoff is treated with other BMPs prior to entering the vegetative filter strips. KEY TERMS: vegetative buffers; critical buffer width; pollutant removal efficiency; stormwater runoff