The following article was featured in the 2023 NLRS Biennial Report.
Streambank erosion is a significant but unquantified non-point source of phosphorus to total Illinois riverine export to the Mississippi River and thus the Gulf of Mexico. Recent work in Iowa suggests that at least one-third of state riverine phosphorus exports are due to streambank erosion (18-year average). However, the Illinois Nutrient Loss Reduction Strategy does not distinguish between agricultural and non-agricultural sources of non-point phosphorus. This leads to overestimated agricultural contributions, potential misdirection of mitigation resources, and likely inaccurate expectations on the magnitude and timescales of phosphorus loss reductions from Illinois. Quantifying streambank erosion and subsequent phosphorus loads — location and amount — is necessary for the accurate apportioning of sources of non-point phosphorus losses and to establish cost-effective mitigation strategies for successful loss reductions.
New research for 2019-24 is being supported by the Illinois Nutrient Research & Education Council. It is motivated by a fundamental question: How much of Illinois’ total phosphorus export attributed to agricultural losses are in fact due to streambank erosion? The central hypothesis is that streambank erosion is likely a major non-point source of Illinois riverine total phosphorus export to the Mississippi River Basin. Given Illinois’ lower cropland-to-stream ratio of 256 acres per mile versus Iowa’s 366 acres per mile, as well as having more meandering streams, the phosphorus export load from streambank erosion in Illinois is expected to align with or even exceed what is reported for Iowa.
The overarching goal of this work is therefore to quantify streambank erosion and phosphorus losses across Illinois to develop a much needed, but currently absent, accounting of a non-point source of phosphorus that is not directly due to agriculture (i.e., not field erosion or fertilizer loss). Specifically, this work will:
- Quantify the extent and magnitude of long-term (decadal) streambank erosion across Illinois, including the 1980–96 period used as baseline by the Illinois NLRS;
- Assess short-term, fine-scale streambank erosion and its drivers at representative watersheds that capture the diversity of streams, soil, and landscape characteristics of Illinois;
- Develop estimates of statewide streambank phosphorus loads using assessments at representative HUC-8 watersheds.
This project will integrate soil science, hydrology, geomorphology, and remote sensing knowledge and approaches. It will also specifically quantify historical and contemporary streambank erosion within eight HUC-8 watersheds. These watersheds will be selected to cover Major Land Resource Areas, major river systems of Illinois, and available U.S. Geological Survey gaging stations which gather streamflow characteristics. This project will leverage artificial intelligence and big data analytics to quantify statewide historical streambank erosion by capitalizing on historical aerial imagery and LiDAR Digital Elevation Models, and by compiling information and data collected by numerous state, federal, and private sectors. Over the course of two years, this project will measure high-resolution assessments of streambank erosion and phosphorus loads by using erosion pins, streambank surveys, drone mapping, terrestrial laser scanners, smartphones, and streambank soil characterizations.
The results of this project will determine how much of the non-point source phosphorus export from Illinois is from streambank erosion. This is essential to establish scientifically sound, fair, and cost-effective phosphorus mitigation targets for the non-point source sector. Determining the quantity of phosphorus entering the state’s riverways due to streambank erosion, which is a non-point source not directly due to agricultural contributions (e.g., not fertilizer or in-field erosion), is essential to achieving the Illinois NLRS targets of a 25% reduction in total phosphorus by 2025 and a final sustained reduction of 45%. This work is the first to measure statewide streambank erosion contributions to phosphorus losses in Illinois. It will establish a comprehensive and firm basis for informing management and policy of non-point source contributions to statewide phosphorus export. The results of this work are therefore directly relevant to the Illinois NLRS assessment by:
- Allowing attribution of phosphorus losses to agricultural and non-agricultural sources of non-point phosphorus
- Identifying which stream characteristics contribute to streambank erosion
- Providing stakeholders with calibrated methods (e.g., erosion pins and smartphone-based tools) to monitor streambank erosion.
References
Schilling, K. E., Isenhart, T. M., Wolter, C. F., Streeter, M. T., & Kovar, J. L. (2022). Contribution of streambanks to phosphorus export from Iowa. Journal of Soil and Water Conservation, 77(2), 103-112.
