STREAM BANK EROSION UNDER DIFFERENT RIPARIAN LAND-USE PRACTICES IN NORTHEAST IOWA

Authors: ZAIMES, GEORGE - UNIVERSITY OF ARIZONA; SCHULTZ, RICHARD - IOWA STATE UNIVERSITY; ISENHART, THOMAS - IOWA STATE UNIVERSITY; MICKELSON, STEVE - IOWA STATE UNIVERSITY; Kovar, John; RUSSELL, JAMES - IOWA STATE UNIVERSITY; POWERS, WENDY - IOWA STATE UNIVERSITY

Submitted to: North American Agroforestry Conference
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2005
Publication Date: 6/15/2005
Citation: Zaimes, G.N., Schultz, R.C., Isenhart, T.M., Mickelson, S.K., Kovar, J.L., Russell, J.R., Powers, W.J. 2005. Stream bank erosion under different riparian land-use practices in northeast Iowa. In: Proceedings of the North American Agroforestry Conference. 9th North American Agroforestry Conference, June 12-15, 2005, Rochester, MN. 2005 CD-ROM.

Interpretive Summary: Row crop production and livestock grazing may increase erosion of stream banks. In this northeast Iowa study, we compared soil and phosphorus (P) losses from stream banks with trees and stream banks with pastures in which cattle were not allowed to grazed, were allowed to graze occasionally (rotational grazing), or were allowed free access. At the conclusion of the study, pastures with the cattle excluded from the stream and bank areas in which trees were growing had the least soil and phosphorus losses from stream bank. Rotationally grazed pastures had less soil and P loss than pastures in which cattle had free access. Differences in soil and P losses among the various practices were a function of the percentages of the stream bank lengths that were severely and very severely eroding within each practice. Total severely and very severely eroding lengths varied from about 10-11% for the areas with trees and pastures with the cattle excluded from the stream to 27% for the rotationally grazed pastures and 38% for pastures in which the cattle had free access. This suggests that if areas along stream banks are to be grazed, a rotational grazing system would be more environmentally friendly. The results of this study will be useful to cattle producers, land managers, and Cooperative Extension and NRCS personnel.

Technical Abstract: Row-cropping and grazing in riparian areas have altered the natural hydrologic cycle and accelerated stream incision and bank erosion. In incised streams, bank erosion can typically contribute 50 to 90% of the stream's sediment and phosphorus load. In this northeast Iowa project, stream bank erosion along riparian forest buffers was compared to bank erosion along continuous and intensive rotational pastures and pastures with the cattle excluded from the stream. Our hypothesis was that stream bank erosion would increase in the following order: riparian forest buffers, pastures with cattle excluded from the stream, intensive rotational pastures and continuous pastures. At the conclusion of the study, riparian forest buffers and pastures with the cattle excluded from the stream had the least soil and phosphorus losses from stream bank erosion followed by intensive rotational pastures which had lower losses than continuous pastures. Erosion rates of individual banks did not differ between grazing practices with full access to the stream or between buffers and pastures with cattle excluded from the stream. The differences in soil and phosphorus losses between practices were primarily the result of percentages of the total bank lengths that were severely and very severely eroding within each practice. Total severely and very severely eroding lengths varied from about 10-11% for the buffers and pastures with the cattle excluded from the stream to 27% for the intensive rotational and 38% for the continuously grazed pastures. This translated to 5-7 tons km-1 yr-1 soil losses and 3 and 2 kg km-1 yr-1 phosphorus losses for the two practices where the cattle had no access to the stream, to 156-235 tons km-1 yr-1 soil losses and 67-122 kg km-1 yr-1 phosphorus losses for the two practices with full access to the stream.