Surface Runoff Water Quality Comparisons Between Unimproved Pasture and Woodland

Abstract

AbstractThe influence of pasturing on surface runoff water quality was studied on a 26‐ha, unimproved pasture watershed in eastcentral Ohio. Data were collected for 2 y with no cattle in the pasture and for 3 y with summer grazing by a 17‐cow beef cattle herd. Because of springs and seep areas in the pasture, a small stream (accessible to the cattle) in the watershed flowed permanently. Samples of storm runoff were collected with a rotating vane sampler. The concentrations of most of the measured chemical parameters (NO3‐N, mineral N, organic N, total P, K, Ca, Mg, Na, S, Cl, HCO3, total organic C, salts) in the storm discharge water were low and changed very little as a result of grazing. The weighted annual NO3‐N concentrations for the ungrazed period and grazed period were 0.5 and 0.7 mg/L, respectively, and the highest event concentrations were 1.2 and 3.8 mg/L, respectively.A 17.7‐ha, wooded watershed that contained no pastured areas and received no agricultural chemical inputs, had concentrations of chemical parameters in surface discharge that were greater than or equal to those from the unimproved pasture during the grazing period.Nutrient transport during storm runoff from the unimproved pasture was greater during the 3‐y period with summer grazing than during the 2‐y, ungrazed period. This largely resulted from increased precipitation and subsequent increased surface runoff during the 3‐y period. The transport levels from the pasture during the 3‐y period were similar to or less than the transport levels from the wooded watershed during the same period. The increase in sediment transport from the pastured area was more than could be attributed solely to the increased surface runoff.