CONTRASTING DUST EMISSION PROCESSES IN THE NORTHERN AND SOUTHERN GREAT PLAINS, USA

The agriculturally important soils of the Great Plains are susceptible to wind erosion when subjected to prolonged drought. Specifically, wind erosion and dust storms during the 1930s Dust Bowl Drought were ubiquitous from Texas to North Dakota. Southern Great Plains (SGP) soils are typically sandy, associated with sand sheets and dunes, whereas Northern Great Plains (NGP) soils (Dakotas) are dominated by silt- and clay-rich shales and glacial till. We hypothesize that the processes of dust emission in the SGP and NGP vary based on soil types reflecting local geology. We used the Portable in situ Wind Erosion Lab (PI-SWERL) on soil textures and conditions in Dust Bowl-impacted areas to assess processes responsible for generating the “black blizzards” typical of the 1930s. Grain size distributions were compared of dispersed and non-dispersed soil samples to quantify proportions of sand-sized aggregates. PI-SWERL results reveal that the soils of the SGP and NGP have high but similar dust emission potential, despite having different soil textures. SGP soils have an average dispersed texture of sandy loam, whereas average NGP soils are loams. Non-dispersed soil textures more accurately measure the distribution of particles that can potentially be transported by the wind and are coarser than dispersed soil textures. The NGP soils have a large proportion of sand-sized aggregates composed of silt and clay, resulting in a non-dispersed texture of loamy sand, whereas SGP soils have a non-dispersed texture of sand. These similar non-dispersed sand-dominated textures may explain the comparable dust fluxes across the Plains and suggest local geology is deterministic of dust emission processes. We infer that saltation bombardment, with saltating mineral grains impacting the soil to liberate dust, is a primal process for dust emissions in the SGP. Disintegration of silt-clay aggregates during saltation also generates dust and heightens dust emissions in the NGP. Aggregate disintegration destroys the saltators responsible for dust generation and as a result, the NGP landscape has a lower proportion of eolian sand compared to the SGP. These results are important in identifying dust sources and processes that cause dust storms, especially during past droughts and forecasted aridification for the Great Plains in the 21^st century.