<p>Anthropogenic contributions to global reactive N pools have more than doubled since the agricultural and industrial revolutions. Although N is an essential plant nutrient, enrichment of reactive N in air pollution can initiate a cascade of deleterious effects including increased smog and haze, ecosystem acidification, increased invasion of non-native grasses, and reduced biodiversity. However, the ecological impacts of N deposition in historically N-limited, semi-arid regions are not well understood. Here, I report the findings from field studies of automobile pollution in Grand Canyon National Park (GCNP; Study 1) and long-range N deposition from the nearest coal-fired power plant, the Navajo Generating Station (NGS; Study 2). To identify potential indicators of N enrichment, I measured four different metrics of N pollution: 1) atmospheric nitrogen oxides (NO<sub>x</sub>) with Ogawa passive air samplers, 2) natural abundance δ<sup>15</sup>N signatures of soil and foliage of pinyon pine (<i>Pinus edulis</i>), 3) spectral analysis of pinyon pine foliar nitrogen, and 4) leaf area on pinyon pine branches. </p><p> In both studies, the amount of NO<sub>x</sub> measured by the Ogawa samplers decreased significantly with increasing distance from N-source. In heavily trafficked sites in GCNP, atmospheric NO<sub>x</sub> was 52% higher at the roadside compared to 30 m away from the road. Atmospheric NO<sub>x</sub> on the Paria Plateau was 54% higher 25 km from NGS compared to 50 km away from the coal-fired power plant. Across both study areas, δ<sup>15</sup>N values in plant tissues reflected inputs from emission sources. According to our data, the biggest ground level N inputs in GCNP are from vehicular emissions, not NGS. Although I detected patterns in terrestrial responses to both small and larger-scale N deposition gradients, future field studies focused on plant community composition and sensitive biological indicators are needed to determine ramifications of elevated N inputs caused by pollution from motor vehicles and power plants. </p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:1537787 |
| Date | 22 June 2013 |
| Creators | Kenkel, Julie Ann |
| Publisher | Northern Arizona University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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