Inorganic nitrogen wet deposition gradients in the Denver-Boulder metropolitan area and Colorado Front Range – Preliminary implications for Rocky Mountain National Park and interpolated deposition maps

Wetherbee, Gregory A.; Benedict, Katherine B.; Murphy, Sheila F.; Elliott, Emily M.

doi:10.1016/j.scitotenv.2019.06.528

Cited by 15 publications

(17 citation statements)

References 47 publications

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“…While the elevated fluxes we measured at the Skywatch do not represent dust fluxes for the entire plains ecosystem, they do highlight the importance of dust emissions from construction, a constant activity in the rapidly growing Denver‐Boulder metro area. Urban emission and deposition rates can be hard to characterize due to high spatial variability (Wetherbee et al, 2019), but neglecting urban areas ignores a growing source of dust in the western United States.…”

Section: Discussionmentioning

confidence: 99%

“…The Front Range elevation gradient is also an urban‐wilderness gradient, with 3.3 million people estimated to live in the Denver‐Boulder metro area in 2020 (MDEDC, 2019). Agriculture is also an important land use east of the Front Range; farmland and numerous livestock feed lots are located northeast of the Denver‐Boulder metro area, contributing to the high levels of reactive nitrogen emissions from the region (Wetherbee et al, 2019). In contrast, the montane, subalpine, and alpine ecosystems of the Boulder Creek Watershed are largely national forests and wilderness areas.…”

Section: Methodsmentioning

confidence: 99%

“…Journal of Geophysical Research: Earth Surface and deposition rates can be hard to characterize due to high spatial variability (Wetherbee et al, 2019), but neglecting urban areas ignores a growing source of dust in the western United States.…”

Section: 1029/2019jf005436mentioning

confidence: 99%

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

et al. 2020

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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

et al. 2020

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“…We expected such a relationship given previous studies in arid cities, which show positive relationships between N deposition and urbanization proxies. For example, at sites in the Denver-Boulder metropolitan area and at oak savanna sites in central California, either bulk N concentrations or deposition exhibited positive relationships with population density [ 56 ] and proximity to urban core [ 55 ]. In contrast, Lohse et al [ 54 ] found that neither distance to urban core nor land use were related to rainwater N concentrations, while Cook et al [ 9 ] found little variation in bulk N deposition along an urban-rural gradient in the Phoenix metropolitan area.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, N deposition in DFW varies seasonally with lower rates in fall and pulsed deposition in spring. Several factors contribute to temporal variability in urban atmospheric wet deposition, including changes in the source and strength of emissions, meteorological conditions, and the rate of chemical reactions in the atmosphere (e.g., [9,[53][54][55][56]). At our study sites, 43% of NH 4 + -N, 34% of NO 3 --N, and 40% of the bulk inorganic N measured between April 2014 and March 2015 occurred in spring compared to 30% of rainfall, suggesting that both increased rainfall and N concentrations contributed to elevated deposition during this season.…”

Section: Nitrogen Deposition In Dallas-fort Worth: Magnitude Seasonality and Formmentioning

confidence: 99%

Ambient urban N deposition drives increased biomass and total plant N in two native prairie grass species in the U.S. Southern Great Plains

et al. 2021

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Remnants of native tallgrass prairie experience elevated atmospheric nitrogen (N) deposition in urban areas, with potential effects on species traits that are important for N cycling and species composition. We quantified bulk (primarily wet) inorganic N (NH4+-N + NO3--N) deposition at six sites along an urban development gradient (6–64% urban) in the Dallas-Fort Worth metropolitan area from April 2014 to October 2015. In addition, we conducted a phytometer experiment with two common native prairie bunchgrass species––one well studied (Schizachyrium scoparium) and one little studied (Nasella leucotricha)––to investigate ambient N deposition effects on plant biomass and tissue quality. Bulk inorganic N deposition ranged from 6.1–9.9 kg ha-1 yr-1, peaked in spring, and did not vary consistently with proportion of urban land within 10 km of the sites. Total (wet + dry) inorganic N deposition estimated using bulk deposition measured in this study and modeled dry deposition was 12.9–18.2 kg ha-1 yr-1. Although the two plant species studied differ in photosynthetic pathway, biomass, and tissue N, they exhibited a maximum 2-3-fold and 2-4-fold increase in total biomass and total plant N, respectively, with 1.6-fold higher bulk N deposition. In addition, our findings indicate that while native prairie grasses may exhibit a positive biomass response to increased N deposition up to ~18 kg ha-1 yr-1, total inorganic N deposition is well above the estimated critical load for herbaceous plant species richness in the tallgrass prairie of the Great Plains ecoregion and thus may negatively affect these plant communities.

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Interactions between tall oatgrass invasion and soil nitrogen cycling

Hinckley

Miller

Lezberg³

et al. 2022

Oecologia

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Increases in nitrogen (N) inputs to the biosphere can exacerbate the introduction and spread of invasive non-native plant species. Often, with elevated soil N levels, invasive plants establish and further enrich soil N pools, changing overall ecosystem function. This study examined the relationship between soil N cycling and an increasingly prevalent, invasive plant species, tall oatgrass (Arrhenatherum elatius subsp. elatius), in foothills ecosystems between the Colorado Rocky Mountains and the Denver-Boulder Metropolitan area—similar to many Western US grasslands and woodlands. It focused on investigating differences in soil N transformations, inorganic N pools, and vegetation characteristics across invaded and uninvaded plots at three sites in two seasons (summer and autumn). There was a statistically significant effect of invasion on rates of net N mineralization, but it was dependent on site and season (p = 0.046). Site had a statistically significant effect on soil moisture and aboveground biomass C:N (p < 0.04). The interactions of invasion x site were statistically significant for ammonium pools (p < 0.03). These findings suggest that A. elatius invasion can be associated with accelerated N cycling, but that the nature of the relationship differs by location and season in the foothills. More broadly, this study contributes to determining how the N cycle is shifting in grassland ecosystems subject to increasing pressures from anthropogenic change.

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Inorganic nitrogen wet deposition gradients in the Denver-Boulder metropolitan area and Colorado Front Range – Preliminary implications for Rocky Mountain National Park and interpolated deposition maps

Cited by 15 publications

References 47 publications

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

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

Ambient urban N deposition drives increased biomass and total plant N in two native prairie grass species in the U.S. Southern Great Plains

Interactions between tall oatgrass invasion and soil nitrogen cycling

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