Direct Suspension as an Important Process of Wind Erosion within the Columbia Plateau.
Brenton Sharratt, USDA-ARS, 213 LJ Smith Hall, Pullman, WA 99164-6120 and Guanglong Feng, Washington State Univ, Biol. Sys. Engineering Dept, Pullman, WA 99164-6120.
Wind erosion is a common occurrence within the Columbia Plateau region of the Pacific Northwest United States due to the extensiveness of fine-textured soils, arid climate, and preponderance of high winds. In fact, wind erosion contributes to poor air quality in the region where the PM10 (particulates ≤10 µm in diameter) National Ambient Air Quality Standard is exceeded each year. Wind erosion occurs by three processes: creep, saltation, and suspension. Although process-oriented models of wind erosion (e.g. Wind Erosion Prediction System) include direct suspension as a process whereby soil particles erode from the surface, direct suspension has been found to be minor in comparison to creep and saltation in other regions of the world. The purpose of this study was to examine the size distribution of soil eroded by wind from an agricultural field within the Columbia Plateau and to determine the contribution of suspension to soil loss. We examined the size distribution of soil particulates captured by BSNE (Big Spring Number Eight) airborne collectors during various high wind events. Size distribution of particulates was measured using a sonic sieve. The BSNE collectors were mounted at heights of 0.1 to 1.5 m above the surface of a 9 ha field during the fallow cycle of a conventional winter wheat – summer fallow crop rotation. The field was located near Washtucna, WA (47°N, 118°W) and dominated by Ritzville silt loam. Of the total mass of eroded soil captured by the BSNE collectors, less than 10% was saltation-sized particles (100-500 µm in diameter) while more than 90% was suspension-sized particles (<100 µm in diameter). The largest fraction of soil eroded was in the size range of 30-45 µm. In addition, the proportion of suspension-sized particles in the eroded mass increased with height above the surface. These results indicate that direct suspension of fine soil particles is a dominant process whereby soil is eroded from agricultural fields on the Columbia Plateau. Thus, conservation tillage practices should be designed to minimize direct suspension of soil during high wind events.