Rare Earth Elements as Tracers for Quantifying Reach-scale Sediment Dynamics in a Second-order Stream in Southwestern Virginia

Sediment, particularly erosion from stream banks, can be the dominant water-quality pollutant in streams and rivers, as well as in lakes and reservoirs. However, the erosion, transport distances, and re-suspension frequency of these sediments are poorly understood, particularly for silt and clay particles at the event scale. We have examined the use of rare earth elements (REE) as a label for quantifying sediment fate and transport of an injected sediment load at the Virginia Tech StREAM Lab along Stroubles Creek in southwestern Virginia. This experiment was carried out over a series of storm events, using a unique REE tracer for each event, to evaluate single event sediment dynamics, as well as sediment re-suspension in subsequent events. We used a Langmuir isotherm to characterize the sorption of the REEs to the stream bank soil and inform the application of the REEs to the injected sediment. By understanding the characteristics of sediment transport at the event scale, it will then be possible to improve sediment transport models, and hence, better predict bank erosion and pollutant loading caused by sediment.