Atmospheric Dust Deposition Varies by Season and Elevation in the Colorado Front Range, USA

Abstract

As atmospheric dust deposition continues to increase across the southwestern United States, it has the potential to alter ecosystem productivity and structure by delivering nutrients, base cations, and pollutants to remote mountain sites. Due to the sparse distribution of dust monitoring sites, open questions remain about the spatial and temporal variability of dust fluxes and composition across mountainous terrain. We present a 1 year (November 2017 to November 2018) record of seasonal dust fluxes and composition from an elevation transect across the Colorado Front Range extending from the urban plains to the remote alpine. At all nine sites, dust was enriched in the essential nutrient phosphorus and the metals copper, zinc, lead, and cadmium, elements that are enriched in dust deposited at sites across the Rocky Mountain West. We observed a seasonal pattern in dust composition, with the highest concentrations of zinc and cadmium during the summer, when back trajectory modeling suggested a greater contribution of dust from local urban and agricultural regions to the east of the collection sites. During the summer, there was also a trend of higher dust fluxes at lower elevations; dust fluxes ranged from 18.9 ± 0.1 g m −2 yr −1 on the plains to 5.9 ± 0.2 g m −2 yr −1 in the alpine. Our results suggest that urban and agricultural land east of the Colorado Front Range is an important source of nutrients and pollutants to all elevations of the mountain range.Plain Language Summary Atmospheric dust deposition can be an important source of nutrients and pollutants to ecosystems and has been responsible for changes in ecosystem productivity and biodiversity. Currently, dust activity is increasing across the southwestern United States due to land use change and drought. Many questions remain about how the amount and chemical composition of dust varies throughout the year and across mountainous terrain. Over 1 year and at nine sites, we measured the amount and chemical composition of dust deposited to the Colorado Front Range. We found that during the summer, there was more dust deposited at lower elevations, which are close to urban and agricultural dust sources. In addition, the dust contained high levels of the nutrient phosphorus and many metals that are associated with anthropogenic emissions. Our results suggest that anthropogenic dust is transported up into the mountains, where it could influence ecosystem biodiversity and water quality. Given the growing evidence that the Southwest is becoming dustier, we call for more comprehensive dust monitoring and land management practices that work to limit dust emissions.

Long‐Term Trends in Acid Precipitation and Watershed Elemental Export From an Alpine Catchment of the Colorado Rocky Mountains, USA

“…However, it is unlikely that precipitation chemistry on Niwot Ridge is derived exclusively from Colorado sources. For example, Heindel et al (2020) found seasonal patterns in dust deposition that were driven by wind patterns that incorporated local and regional source areas similar to those described by Baron and Denning (1993). From a study in Rocky Mountain National Park, Gebhardt et al (2011) estimated that only 30% to 45% of sulfur dioxide and N‐containing species on the eastern side of the Continental Divide were from sources within Colorado, with the rest coming from other states and international sources.…”

Elevated Nitrogen Deposition to Fire‐Prone Forests Adjacent to Urban and Agricultural Areas, Colorado Front Range, USA

“…Although prevailing winds are westerly, thermally‐driven easterlies transport air masses from the Boulder‐Denver metro area and the eastern agricultural plains up into the mountains on regular diurnal cycles during the spring and summer months (Blanken et al., 2009; Heindel et al., 2020; Losleben et al., 2000). These seasonal easterlies have previously been connected to increased spring and summer Nr loads, ammonia concentrations, dust deposition, and ozone concentrations (Gebhart et al., 2011; Heindel et al., 2020; Sullivan et al., 2016). Synoptic‐scale upslope events also occur during the fall months and have the potential to transport N pollution to higher elevations (Benedict, Day, et al., 2013), but we found much lower concentrations and loads across the elevation transect during the fall.…”

Is There a Relationship between Lake Urmia Saline Lakebed Emissions and Wet Deposition Composition in the Caucasus Region?

“…The vast sedimentary carbonate formations around the Lake Urmia basin and marl formations to the east (Figure S5) support the reason why Ca 2+ EF and NSSF values are elevated. Although outside the scope of this work, there can be influence from elevation gradients and land use on crustal emissions . Our results confirm that crustal aerosol particles are significant in the region as agents in rainwater, which has implications for cloud microphysical processes and for neutralization of acidic components.…”

“…Although outside the scope of this work, there can be influence from elevation gradients and land use on crustal emissions. 103 Our results confirm that crustal aerosol particles are significant in the region as agents in rainwater, which has implications for cloud microphysical processes and for neutralization of acidic components. This is important for other study regions too to indicate that wind-blown salt and crustal matter not only impact aerosol properties but also clouds and rain.…”