Stream bank erosion within agricultural landscapes is a major pathway for non-point source sediment and phosphorus loading to receiving waters. The objectives of this study were to: 1) compare the effect of livestock stocking rate on sediment and phosphorus loss from stream bank erosion in the Rathbun Watershed in southern Iowa; 2) assess the relationship between stream stage and stream bank soil erosion rates, and 3) evaluate the impacts of current riparian land-uses and stream morphologic characteristics at the field and catchment scale on stream bank erosion. Stream bank erosion rates over three years were estimated using the erosion pin method, with erosion rates correlated to pasture stocking rates and the number of high stream stage events, which were monitored using pressure transducers. The effects of stream morphology and land-use on stream bank erosion were assessed using parameters such as percent of land-use, bank soil texture, stream bed slope, and sinuosity at both the field and catchment scale.

While there was no significant correlation between stream bank erosion rates and stocking rates, erosion rates within sites under Conservation Reserve Program management were significantly lower than those within grazed pastures, particularly during the winter/spring season. The length of severely eroded stream banks and compaction of the riparian area were positively related to livestock stocking rates within pasture stream reaches. Approximately 75% of the variability in stream bank erosion was found to be correlated to the frequency of high stream stage events. Overall, these data and previous studies allow the speculation that, in the long term and at the catchment scale, a high percentage of agricultural land-use in riparian areas can be either directly and/or indirectly related to alteration of stream hydrologic regimes. In order to reach equilibrium state condition, where energy input to the stream channel is balanced with the minimal channel boundary resistance, such land-use changes will result in changes in stream bank erosion and channel morphology.