title: Biomonitoring of traffic-related nitrogen pollution using Letharia vulpina (L.) Hue in the Sierra Nevada, California.
abstract: To assess the impact of vehicular emissions on a mixed conifer forest, we measured the contents of the trace elements, N, C, and their respective natural isotopes (δ(15)N and δ(13)C), in the epiphytic lichen, L. vulpina. The samples were collected along transects perpendicular to Interstate 80 (I-80) and along a more remote, secondary forest road (R07). Distance to the road verge, trunk cover, and stand basal area were also recorded. Percent N ranged from 1.10% to 2.00% near I-80 and from 0.78% to 1.13% along R07. Concentrations of N, (15)N, Na, As, Pb, and Zn were enhanced in lichen samples near I-80 and were negatively correlated with distance from the road. Trunk cover values differed between roads (p<0.001) and were negatively correlated with %N (r(2)=0.74; p<0.001). The results indicate that vehicular N emissions are significant enough to alter the surrounding ecosystem, modifying the presence of a sensitive component such as L. vulpina, and suggest that a clean-site threshold of 1.0%N may be too high as an indicator of critical N load exceedance. The study also underscored the potential role of wolf lichen in a large-scale assessment of N deposition and source identification.
authors.affiliation: LICA, Department of Chemistry and Soil Science, University of Navarre, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Bermejo-Orduna
authors.affiliation: Department of Environmental Science, Policy and Management, University of California, Berkeley, United States.
authors.forename: J R
authors.initials: JR
authors.lastname: McBride
authors.affiliation: LICA, Department of Chemistry and Soil Science, University of Navarre, Spain.
authors.forename: K
authors.initials: K
authors.lastname: Shiraishi
authors.affiliation: LICA, Department of Chemistry and Soil Science, University of Navarre, Spain. Electronic address: delusto@unav.es.
authors.forename: D
authors.initials: D
authors.lastname: Elustondo
authors.affiliation: LICA, Department of Chemistry and Soil Science, University of Navarre, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Lasheras
authors.affiliation: LICA, Department of Chemistry and Soil Science, University of Navarre, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Santamaría
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002140:California; D004784:Environmental Monitoring / Q000379:methods*; D004787:Environmental Pollution / Q000706:statistics & numerical data; D008011:Lichens / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis*; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D001335:Vehicle Emissions; D009584:Nitrogen
keywords: Critical load; Heavy metals; Isotopic signature; Letharia vulpina; Nitrogen; Traffic pollution