Vegetated Filter Strip Removal of Cattle Manure Constituents

Pasture runoff can contribute to elevated concentrations of nutrients, solids, and bacteria in downstream waters. The objective of this study was to determine the effects of vegetative filter strip (VFS) length on concentrations and transport of nitrogen, phosphorus, solids and fecal coliform in runoff from plots treated with cattle manure. Three plots with dimensions of 2.4 × 30.5 m were used. The upper 12.2 m of each plot was treated with cattle manure, while the lower 18.3 m acted as a VFS. Runoff produced by rainfall simulators was sampled at VFS lengths of 0, 6.1, 12.2, and 18.3 m and analyzed for total Kjeldahl nitrogen (N), ammonia N, nitrate N, total phosphorus (P), ortho-P, fecal coliforms, total suspended solids and other parameters. The VFS significantly reduced concentrations and mass transport of incoming solids, fecal coliform, and most nutrient forms, particularly P. The relationships among VFS length, concentration and mass transport were well-represented by first-order exponential decay functions. Approximately 75% of incoming total Kjeldahl N, total P, ortho-P, and total suspended solids was removed within the first 6.1 m of the filter strips. Runoff concentrations of fecal coliform concentrations entering the filter strips were as high as 2 × 107 FC/100 mL; after a filter length of 6.1 m, however, the runoff exhibited no measurable concentration of fecal coliforms. This experiment suggests that even relatively short filter strips can markedly improve quality of runoff from grassed areas receiving cattle manure.