AEOLIAN RESPONSE TO FIRE: TRENDS IN DEPOSIT MASS, PARTICLE SIZE AND GEOCHEMISTRY

The Soda Fire burned over 280,000 acres in southwest Idaho and southeastern Oregon in August 2015. The fire burned >25% of the Reynolds Creek Critical Zone Observatory, creating an opportunity to investigate post-fire aeolian deposition in a sagebrush-steppe dominated watershed with complex topography. While many post-fire wind related studies focus on entrainment and erosion, our study characterizes the trends in aeolian deposition to the watershed over a two-year post-fire period. We measure the spatial and temporal variability, magnitude, and character of aeolian deposition through the use of 1) passive dust traps and soil sampling 2) geochemical fingerprinting and 3) analysis of meteorological and hydrological data. Dust fluxes in the burned sites are four to eight times greater than unburned sites until the first growing season following the Soda Fire. Spatial and temporal trends within the D₅₀ and D₉₀ grain sizes indicate a decrease in grain size with time and distance from fire. The lack of shrub coverage over the burned landscape allows wind to maintain speeds above the surface threshold shear velocity. Interactions between complex topography and near-surface atmospheric turbulence allows for the entrainment and deposition of more material with a larger grain size in spatially controlled regions at multiple scales. The greater flux of material in, and proximal to, a post-fire environment has implications for soil properties, hydrologic function, and post-fire erosion within the sagebrush-steppe ecosystem.