Wet Dust Deposition Across Texas During the 2012 Drought: An Overlooked Pathway for Elemental Flux to Ecosystems

Airborne dust can alter ecosystem productivity and biogeochemical cycling by enhancing atmospheric nutrient and pollutant deposition. Wet dust deposition (dust-in-rain) is less frequently quantified than dry deposition but represents a potentially significant flux to ecosystems. We quantified dust-in-rain event frequency, dust influence on rainwater ionic and elemental composition, and wet dissolved and particulate deposition during weeks affected by dust-in-rain and all other weeks (background samples) at two sites across Texas (one arid, Guadalupe Mountains, and one humid, Gulf coastal prairie) during the centennial-scale 2012 drought. Although dust-in-rain was sporadic, a clear dust signature was evident in rainwater. Compared to background samples, crustal species (Fe and Mn) were more prevalent than anthropogenic species (Cu and Zn) in dust-in-rain. Volume-weighted mean rainwater concentrations of K+, Na+, and Cl- and of all particulate elements were also significantly greater in dust-in-rain than in background samples. In the Guadalupe Mountains, West Texas, dust-in-rain contributed nearly 50% of annual wet dissolved Na+ and Cl- and 22-35% of dissolved Ca2+, Mg2+, K+, and PO43- deposition. In the Gulf coastal prairie, East Texas, dust-in-rain delivered 19%, 13%, and 9% of annual wet dissolved PO43-, Ca2+, and K+ deposition, respectively. A major proportion of annual wet particulate deposition (>56% in Guadalupe Mountains and 30% in Gulf coastal prairie) similarly occurred with dust-in-rain. Our findings show that infrequent dust-in-rain events constitute an important but overlooked pathway for elemental flux to ecosystems in arid source and humid receptor sites during severe drought. Quantifying these fluxes is crucial to determine dust impacts on ecosystem processes. Plain Language Summary Blowing soil dust is a frequent phenomenon in Texas caused by dry conditions, strong winds, and bare soil. Across the U.S. Southwest, severe drought and land use change are projected to increase in the future, contributing to more frequent and intense dust storms and eventually dry dust fallout or dust washout from the atmosphere with rain (dust-in-rain). Dust-in-rain contains dissolved substances that act as nutrients to plants and ecosystems, as well as others that can be toxic pollutants. Dust-in-rain also contains particles that contribute to soil formation and fertility. How will warmer, drier, Dust Bowl-like conditions affect raining dust events? To answer this question, we examined rainwater samples collected by the National Atmospheric Deposition Program at two Texas sites (one arid, Guadalupe Mountains, and one humid, Gulf coastal prairie) during 2012, a year of extreme drought (and dust) in Texas. We determined the number of dust-in-rain events at each site, analyzed concentrations of diverse substances (some nutrients and some pollutants) in rainwater, and quantified the annual proportion of nutrients and pollutants delivered to the sites in rain during weeks affected by dust. Although dust-in-rain occurred infrequently in 2012, concentrations of many substances in dust-in-rain samples were considerably higher compared to samples not affected by dust. As a result, dust-in-rain events delivered a major proportion (as much as 60% for some key elements) of the annual nutrient and pollutant input to ecosystems. Thus, our research indicates that dust-in-rain is an important source of nutrients and pollutants to ecosystems worthy of consideration by scientists and land managers. Key Points