Sediment Fingerprinting in the Little Fork Watershed
In fall of 2019, a sediment fingerprinting study began in the Little Fork River watershed. This project is being led by the United States Geological Survey (USGS) and the Minnesota Pollution and Control Agency (MPCA) with support from the Koochiching SWCD and North St. Louis SWCD to address a 105-mile stretch that is impaired for turbidity (suspended soil particles in water). While it has been established that there is an excess of sediment present in the Little Fork River, it’s been unknown how to proceed in reducing it to acceptable levels. Identifying sediment sources is the first step in targeting sediment-laden stream reaches for projects.
What is Sediment Fingerprinting?
The sediment fingerprinting process is an analysis of sediment that can attribute the particles’ source to different locations in the watershed. The procedure establishes a set of physical and/or chemical properties (tracers) based on samples collected in upland or channel locations identified as potential sources of sediment. These properties are unique for each location within the watershed. Fluvial sediment samples (sediment transferred by a river system) collected exhibit a composite, or “fingerprint” of source properties. Through statistical procedures, the target sediment properties can be matched to their respective upland or channel source “fingerprints”.
Determining the sources (erosion sites) and sinks (deposit locations) of sediment is important in developing strategies to reduce sediment loads to water bodies impaired by turbidity.
What Has Been Done and What’s Next?
2021 sampling yielded 163 samples consisting of Upland, in stream, and event based samples throughout the watershed. This sampling was done on county, state, federal, and private lands and will be analyzed winter and spring of 2022. The event based samples will be collected in the spring and summer of 2022 due to drought conditions throughout the watershed the previous summer. These samples require a 1 inch rainfall event that influences the flow of the rivers substantially.