Location: Agroecosystems Management ResearchTitle: Stream bank erosion as a source of sediment and phosphorus in grazed pastures of the Rathbun Lake Watershed in southern Iowa, USA Author
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2012
Publication Date: 11/1/2012
Citation: Tufekcioglu, M., Isenhart, T.M., Schultz, R.C., Bear, D.A., Kovar, J.L., Russell, J.R. 2012. Stream bank erosion as a source of sediment and phosphorus in grazed pastures of the Rathbun Lake Watershed in southern Iowa, USA. Journal of Soil and Water Conservation. 67(6):545-555. Interpretive Summary: Livestock grazing in pastures has been identified as a possible factor contributing to non-point source pollution of Rathbun Lake and associated water bodies in southern Iowa. To demonstrate that practices that alter timing, frequency, duration, and/or intensity of cattle grazing near pasture streams in the watershed can reduce sediment and phosphorus (P) losses to surface water, we measured eroded stream bank lengths and areas, soil bulk density, and P in bank soil to calculate sediment and P lost via stream bank erosion in 13 pastures with varying numbers of cattle per unit land area during a three-year period. The number of severely eroded stream banks and soil compaction near the streams increased with an increase in the number of cattle grazing in the stream corridors. Stream bank erosion and P losses from two sites enrolled in the Conservation Reserve Program (CRP) were lower than those from all grazed pasture sites, suggesting that the impact of grazing could be reduced through management of cattle numbers within these stream corridors. The results of this work will contribute useful information to cattle producers, local environmental groups, and Cooperative Extension and NRCS personnel interested in reducing the negative effects of livestock grazing on water quality.
Technical Abstract: Livestock grazing of riparian areas can have a major impact on stream banks and stream integrity if improperly managed. The goals of this study were to determine the sediment and phosphorus (P) losses from stream bank soils under varying cattle stocking rates and to identify additional factors that impact stream bank erosion in the Southern Iowa Drift Plain. The research was conducted on thirteen cooperating beef cow-calf farms within the Rathbun Lake watershed in South Central Iowa. Stream bank erosion rates during three years were estimated by using an erosion pin method. Eroded stream bank lengths and area, soil bulk density and, total P (TP) concentrations in stream bank soil were measured to calculate soil and TP lost via stream bank erosion. The length of severely eroded stream banks and soil compaction of the riparian areas of the pastures were positively related to an increase in stocking rates of grazing livestock on the pasture stream reaches. While there was no direct relationship between bank erosion and stocking rate, the erosion rates from two sites enrolled in the Conservation Reserve Program (CRP) were significantly lower than those from all grazed pasture sites, especially when seasonal effects, specifically winter/spring, were considered. These results suggest that use of riparian areas as pasture may negatively impact water quality and channel integrity through increased sediment and P losses from bank erosion, and that the impact could be reduced through management of livestock stocking densities within these riparian areas.