Riparian land-use, stream morphology and streambank erosion within grazed pastures in southern Iowa, USA: A catchment-wide perspective

Authors: TUFEKCIOGLU, MUSTAFA - Artvin Coruh University; SCHULTZ, RICHARD - Iowa State University; ISENHART, THOMAS - Iowa State University; Kovar, John; RUSSELL, JAMES - Iowa State University

Submitted to: Sustainability
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2020
Publication Date: 8/11/2020
Citation: Tufekcioglu, M., Schultz, R.C., Isenhart, T.M., Kovar, J.L., Russell, J.R. 2020. Riparian land-use, stream morphology and streambank erosion within grazed pastures in southern Iowa, USA: A catchment-wide perspective. Sustainability. 12(16). https://doi.org/10.3390/su12166461.
DOI: https://doi.org/10.3390/su12166461

Interpretive Summary: Streambank erosion contributes to non-point source pollution of Rathbun Lake and associated water bodies in southern Iowa. Stream channel morphology, for example, bank height, stream flow, and land use adjacent to the stream are factors that can influence bank erosion. To investigate the relationship of these factors to streambank erosion, we measured eroded stream bank lengths and areas and soil bulk density to calculate sediment lost via bank erosion at 13 cooperating beef cow-calf farm sites with varying numbers of cattle per unit land area in the Rathbun Lake watershed in south central Iowa (USA) during a three-year period. We found that streams draining more land area, i.e., larger catchment size, or catchments with more streams had more bank erosion (ranging from 8.6 to 38.3 cm/year). As the percent sand plus silt in the bank soil increased, bank erosion rates also increased, suggesting that bank soils with less cohesiveness are more erodible. Within the 50-meter corridor on both sides of the 13 stream reaches, 46 to 61 % of the land area was devoted to agricultural use, and only 6 to 11 % was in ungrazed perennial vegetation, much of it enrolled in the USDA Conservation Reserve Program. Overall, long-term, intensive agricultural use of land adjacent to the streams may be the most important factor related to excessive amounts of streambank erosion, and leading to impairment and reduction of ecological services of receiving streams and lakes. The results of this work will contribute useful information to watershed scientists, local environmental groups, and NRCS personnel interested in improving water quality in this and similar watersheds.

Technical Abstract: Factors influencing streambank erosion at the field/reach scale include both watershed and riparian land-uses, stream hydrology and channel morphology at the catchment scale. This study assesses the relationship of riparian land-uses, stream morphologic characteristics and catchment scale variables to streambank erosion within grazed riparian pastures in the Southern Iowa Drift Plain. Thirteen cooperating beef cow-calf farms and their catchments in the Rathbun Lake watershed in South Central Iowa (USA) were chosen to conduct this study. Results suggest that the integration of stream morphologic characteristics and riparian land-uses at both the reach and catchment scale are necessary to explain the current level of streambank erosion measured at reach scale. Larger catchment size or catchments with more total channel length were found to experience more bank erosion at the reach scale. A significant positive relationship between percent sand-and-silt in the bank soil and bank erosion rates infers that bank soils with less cohesiveness are more erodible. Catchment-scale assessments of the thirteen watersheds showed that within the 50 m corridor on both sides of the stream, 46 to 61 % of riparian area was devoted to agricultural use and only 6 to 11 % was in ungrazed perennial vegetation, much of it enrolled in the USDA Conservation Reserve Program. Overall, intensive agricultural use of riparian areas over such extent of time and scale could be directly (in field scale) and/or indirectly (watershed scale) related to excessive amounts of streambank erosion (ranging from 8.6 to 38.3 cm/yr) to receiving streams and lakes leading to their impairment and reduction of ecological services.