DUST EMISSION POTENTIAL ALONG THE INTERSTATE 8 CORRIDOR, SOUTHERN CALIFORNIA AND ARIZONA

The Interstate 8 corridor in Imperial County, CA, Yuma County, AZ and surrounding areas frequently exceeds PM-10 air quality standards, causing visibility and health concerns. The area around the Salton Sea, as well as the Coachella Valley to the north, are well-known dust sources, however, dust sources have not been directly identified in the Imperial Valley and interstate corridor to the south. Dust is assumed to be generated from bare desert areas and disturbed landscapes including ORV areas and agricultural fields. We used the Portable in situ Wind Erosion Lab (PI-SWERL) to measure the dust emission potential of landforms in natural and disturbed settings, including sand dunes, lake sediments, distal alluvial fans, and alluvial plains. Our results indicate that dust emissions are largely driven by saltation bombardment on a fine-grained substrate and by releasing fines from reactivated sand dune deposits. Alluvial fans are major sources of sand, likely due to their proximity to weathering granitic bedrock. Coppice dunes grading into sandsheets commonly form on distal alluvial fan surfaces. Some distal alluvial fans have clearly been deflated as indicated by sand dunes adjacent to gravel lags formed atop old, buried soils. Lake sediments, associated with ancient Lake Cahuilla in the Salton Trough, as well as alluvial plains, such as those adjacent to the Gila River, are utilized for farming and are relatively stable unless eolian sand saltates on these surfaces, or if these surfaces are disturbed by farming practices. Alluvial surfaces such as ephemeral washes and floodplain deposits have variable emission potential depending on sand content, crust strength, and level of disturbance. Dunes, especially degrading coppice dunes and sandsheets, are the most robust natural sources of dust in the region, followed by distal fans, alluvium, and lake sediments. Disturbed surfaces emit one to two orders of magnitude more dust compared to undisturbed surfaces, suggesting that minimizing landscape disturbance in arid environments would help to limit, but not eliminate, dust hazards.