The question of streambank erosion contributions to non-point sediment and P export is essential to answer if we are to establish scientifically sound and fair P mitigation targets for non-point sources, including the agricultural sector. Knowing how much sediment and P entering the surface waters of the Mississippi River Basin is due to non-agricultural non-point sources (i.e., streambank erosion) is therefore essential. By providing a gold-standard systematic literature review and meta-analysis of the state-of-the-art understanding, this work quantified the contribution of non-point, non-agricultural drivers of sediment and nutrient losses. The gaps identified provide a basis for informing priorities for research, management and policy, to ensure accurate and fair attributions of nutrient losses among non-point sources. The results of this project will be published as proposed two forthcoming peer-review publications, plus a third additional publication not originally proposed. Results were communicated at the annual ASA-CSSA-SSSA annual meeting in St. Louis in November 2024 to communicate to diverse stakeholders, including agriculturalists, environmentalists, and policy makers. Within the conference, a total of 2 presentations and 2 posters were presented by the research team. Additionally, PI Margenot gave a total of 23 additional talks on project findings (not originally proposed) to maximize communication of results, to organizations and groups across the Mississippi River Basin. Finally, a three-part webinar series is scheduled for mid-2024 to formalize an integrated overview of streambank erosion contributions to sediment and nutrient loading, targeting researchers and policy makers.

This work benefits U.S. soybean farmers by providing evidence that nutrient and sediment losses from soybean cropping systems are being overestimated because the contribution of streambank erosion loading of sediments and nutrients in these agricultural watersheds is largely unquantified. Focusing on the Mississippi River Basin, we show that most watersheds do not account for streambank erosion contributions to non-point source loads, but can account for up to 44% of phosphorus losses. There is a clear need to quantify how much streambank erosion contributes to water quality impacts in order to correctly distinguish the true contributions of agricultural, including soybean, to sediment and nutrient loads. Current state NLRS are thus overestimating soybean cropping system contributions to nutrient and sediment losses. This work also identifies a path forward to quantify such contributions.