Stream Bank Erosion in Low Order Streams in Midwestern Agricultural Landscapes.
Richard Schultz1, George Zaimes2, Thomas Isenhart1, Keith Schilling3, Leigh Ann Long1, Mustafa Tufekcioglu1, Jason Palmer1, Kris Knight1, and David Heer1. (1) Iowa State Univ., Dept. of Natl Res. Ecology & Mngmnt, 339 Science II, Ames, IA 50011-3221, (2) Univ. of Arizona, School of Natural Resources, 310 Bio Sciences East, P.O. Box 210043, Tucson, AZ 85721, (3) Iowa Department of Natural Resources, Iowa Geologic Services, 109 Trowbridge Road, Iowa City, IA 52242
Stream bank erosion can contribute significant amounts of phosphorus and sediment to surface waters. Phosphorus and sediment are major non-point source pollutants that degrade surface water quality. The magnitude of bank erosion is a function of many variables including the kind and density of riparian vegetation and land use, precipitation amounts and rates as they influence discharge events, antecedent bank soil moisture, freeze-thaw action, season of the year, stage of channel development and composition of alluvial bank sediments. Stream bank erosion has been
monitored on first to third order streams over the past 5 years along reaches with riparian land-uses consisting of row crop agriculture, continuous, rotational or intensive rotational grazing or riparian forest buffers or grass filters. Between 40-50% of row-crop and continuous pastured stream reaches were found to have severe bank erosion compared to about 15% for banks with riparian forest buffers. Total soil loss from banks ranged from 75 tons/km for forested banks to about 560 tons/km for continuous pastured banks. In addition, livestock access points on pastured banks added as much as 280 tons/km of additional sediment to the channel in continuously grazed pastures. Losses from rotationally grazed pastures was not as large as from continuous pastures. Replacing grazed pastures and row cropped riparian land-uses with riparian forest buffers could reduce bank erosion by about 90%. Phosphorus losses closely follow those of sediment. Present studies are combining radioisotope tracers with stream sediment sampling and bank erosion pin plots. This combination will allow both the partitioning of sediment originating from the uplands and from stream banks and also from specific land-treated stream banks. In addition, wells with transducers are monitoring water table levels near stream banks under different plant communities to assess the role of plants in dewatering stream banks to increase stability.