Stream channel erosion as a source of sediment and phosphorous in a central Iowa stream

A growing body of evidence suggests that a substantial portion of the sediment and phosphorus delivered to surface waters from agricultural landscapes originates from stream bed and bank erosion. Improved quality of information on the processes controlling the erosion and transport of sediment and phosphorus will aid in planning targeted conservation practices to reduce sediment and phosphorus export from agricultural landscapes. A major objective of this research was to quantify the importance of stream bank erosion as a source of downstream sediment and phosphorus flux in a small agricultural watershed in Boone and Story counties, Iowa. Stream bank recession rates were estimated using erosion pins installed into a randomly selected subset of severely eroding banks. Between March 2012 and May 2015, bank sediment loss exceeded sediment export from the watershed by 29%. Phosphorus losses originating from stream bank erosion were found to account for 35% of the cumulative particulate phosphorus export from the watershed. Bank recession rates, along with sediment and phosphorus export, were closely related to maximum discharge rates. Three major storm flow events contributed 79% of the cumulative recession, 49% of the total sediment export, and 38% of the particulate phosphorus export. These results increase our understanding of the relative contribution and processes controlling erosion and transport of sediment and phosphorus from stream bank erosion.