Indicators of vehicular emission inputs into semi-arid roadside ecosystems

Julie A. Kenkel, Thomas D Sisk, Kevin R. Hultine, Steven E. Sesnie, Matthew A Bowker, Nancy Johnson

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The relative importance of pollution from non-point sources, such as vehicular emissions, is not well understood in sensitive semi-arid protected areas, such as Grand Canyon National Park (GCNP). Roadside N deposition could be substantial in areas with high visitation and traffic volume such as GCNP, although inputs of roadside pollution have not been quantified in GCNP. We used three potential indicators of N enrichment to evaluate impacts of vehicle emissions on roadside ecosystems in GCNP: 1) concentration of nitrogen oxides (NOx) captured by passive air samplers, 2) natural δ15N abundance in the foliage of mature Piñon pine trees and soil N, and 3) concentrations of available inorganic N (NO3 and NH4 +) in soil. Over an eight-month period, N enrichment was assessed at ten sites located across hypothesized gradients of vehicular N deposition based on distance from primary roadways and traffic levels in GCNP. Ogawa passive air samplers indicated that NOx levels were on average 52% higher at roadside locations compared to 30 m away, and were highest at the most heavily trafficked sites in the park. Natural abundance δ15N of foliage was significantly higher (F = 16.04, p = 0.007, n = 237) at roadside locations than at 15, and 30 m distances: a pattern that is consistent with local N inputs from vehicle emissions. Available inorganic soil N was significantly higher (F = 3.46, p = 0.013, n = 8) at the South Entrance roadside compared to areas with lower traffic densities. The direct measurement of atmospheric NOx using Ogawa samplers and δ15N of Piñon pine needle tissues were the best indicators of roadside N deposition. Our results also suggest that vehicular emissions on the South Rim of GCNP were incorporated in the plant nutrient pools near roadside environments. Although N emissions in GCNP comply with current annual air quality standards as specified by the Clean Air Act, it remains unclear whether the standards are low enough to sustain ecological integrity of native ecological communities along roadsides. Coupled with information on N-pollution tipping points and other ecological indicators, the metrics used here may prove to be a cost effective approach for monitoring roadside N-deposition and informing management decisions.

Original languageEnglish (US)
Pages (from-to)150-159
Number of pages10
JournalJournal of Arid Environments
Volume134
DOIs
StatePublished - Nov 1 2016

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canyons
canyon
national parks
national park
ecosystems
ecosystem
nitrogen oxides
samplers
traffic
sampler
traffic emission
pollution
air
foliage
roadside environment
point source pollution
soil
conifer needles
air quality
indicator

Keywords

  • Grand Canyon National Park
  • Nitrogen deposition
  • Roadside
  • Semi-arid vegetation
  • δN

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Earth-Surface Processes

Cite this

Indicators of vehicular emission inputs into semi-arid roadside ecosystems. / Kenkel, Julie A.; Sisk, Thomas D; Hultine, Kevin R.; Sesnie, Steven E.; Bowker, Matthew A; Johnson, Nancy.

In: Journal of Arid Environments, Vol. 134, 01.11.2016, p. 150-159.

Research output: Contribution to journalArticle

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