Riparian Water Quality Buffers: Estimates of Effectiveness and Minimum Width in an Agricultural Landscape, Western Tennessee

The adverse effects of agricultural non-point source pollution (e.g., sediment, nitrogen, phosphorous) on water quality are widely recognized and documented. Riparian vegetation, however, can help to filter out these pollutants by detaining or processing the pollutants. In this study, we estimate the effectiveness and adequacy of riparian buffers in an agricultural landscape in Fayette County, Tennessee, through the use of a mathematical model—the Riparian Buffer Delineation Equation (RBDE)—and a geographic information system (GIS). Based on edaphic characteristics, slope, and surface roughness, the minimum buffer width needed to filter 90% of nitrates from surface flow was estimated using the RBDE for 18 soil types along five reaches of the Wolf River and in a tributary basin, Hurricane Creek. The minimum buffer widths suggested by the model ranged from 2.3 m to 64.3 m. We then digitized existing land cover, soil type, and hydrography into a GIS and compared the minimum estimated buffer widths with the widths of existing buffers in the study area. Results from the GIS buffer analysis indicated areas where actual buffer widths were less than the proposed minimum buffer widths. Lower-order streams were generally less adequately buffered than higher-order streams, yet previous studies have suggested that more pollutants may enter streams through low-order intermittent and perennial streams. This finding suggests that the Wolf River may be more susceptible to agriculturally derived inputs of sediment and nutrients from tributary streams than from runoff directly into the main stem.