2024 Abstracts

Impacts of Streambed Dynamics on Nutrient and Fine Sediment Transport in Mountain Rivers


Elowyn Yager1* (eyager@uidaho.edu), Nicole Hucke1, Rachel Watts2, Andrew Tranmer1, Janice Brahney2, Joel Rowland3, George Perkins3, Rose Harris3


1University of Idaho, Boise, ID; 2Utah State University, Logan, UT; 3Los Alamos National Laboratory, Los Alamos, NM


In mountainous watersheds, rivers typically have armor layers of coarse sediment that protects the finer subsurface from erosion. In theory, armor layer motion during high flows could release subsurface fine sediments that are often enriched in phosphorus (P) and particulate organic carbon (POC). Hysteresis and seasonal variations in POC, soluble reactive phosphorus (SRP), particulate phosphorus (PP), and suspended sediment (SS) may therefore be partly controlled by armor layer motion. In addition, streambed concentrations of these constituents may depend on whether a location is losing or gaining.

Researchers tested whether armor layer motion and streambed concentrations influence hysteresis patterns during summer monsoon and snowmelt flows in La Jara Creek in Valles Caldera National Preserve, NM. Before flow events, the team sampled streambed concentrations of POC, PP, SRP, and fine sediment and installed streambed baskets to capture SS deposition. During high flow events, researchers measured (1) surface and groundwater exchange at local (basket) and reach scales; (2) timing of armor layer motion; and (3) river concentrations of POC, PP, SRP, and SS. The team also conducted experimental floods to isolate the role of armor layer motion on these constituent concentrations in the water column.

Preliminary results suggest that the quantity of fine sediment captured in streambed baskets was related to the local hyporheic flux and near-bed flow velocity. SS, turbidity, PP, and POC often followed the same hysteresis pattern in each natural flow event, suggesting that they may have a similar source. During experimental floods, in which armor layer motion was the only source of particulate matter, hysteresis of SS and PP occurred. The timing of armor layer motion may have also controlled different observed constituent hysteresis patterns between natural flow events.

Researchers are currently investigating potential hysteresis sources during these events and constraining the exact timing of armor layer motion in each event.