Seasonal and Interannual Variability in Dust Flux to High-Elevation Ecosystems in the Southwestern United States

The transport of mineral dust from arid lowlands to higher elevations has profound consequences for the geoecology of mountain ecosystems.  With expanding human populations and widespread disturbance due to land use, dust deposition rates and compositions are changing, presenting unique challenges for human and ecosystem health.  The American Southwest, a region that has experienced a massive increase in dust deposition rates in the past century, is no exception to this trend.  Understanding the flux and composition of dust can help identify where dust is coming from, and can inform management strategies for dust emitting landscapes.  As part of the DUST^2 Critical Zone Thematic Cluster, this project utilized a network of 18 passive dust traps in the southwestern US, 15 of which were deployed on high mountains summits and ridgelines.  The dust traps were emptied biannually between 2020 and 2022 to reveal spatial and temporal differences in dust compositions and depositional fluxes.  Results demonstrate that dust flux is higher in the summer compared to winter; at the 13 collectors with the most complete data, summer fluxes averaged 47.9 mg/m²/day whereas winter fluxes averaged 24.2 mg/m²/day.  Interannual variability is notable: for instance, some collectors received 2x as much dust in summer 2022 vs. 2021, whereas for others the pattern was reversed.  In contrast, all collectors received more dust during winter 2021-22 than in 2020-21.  Superimposed on these temporal differences is a spatial disparity in accumulation rates, with the highest values at the urban sampler in Salt Lake City and at sites immediately downwind.  In contrast, lower fluxes are common at high elevation sites in Nevada, particularly during the winter.  Overall, measured dust fluxes span a wide range from 5.3 to 255 mg/m²/day.   The grain size distribution, color, mineralogy, and geochemistry of dust also vary notably between sites, supporting the interpretation that much of the dust is sourced from the immediately surrounding lowlands.