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 (NOx) with Ogawa passive air samplers, 2) natural abundance δ15N signatures of soil and foliage of pinyon pine (Pinus edulis), 3) spectral analysis of pinyon pine foliar nitrogen, and 4) leaf area on pinyon pine branches.
In both studies, the amount of NOx measured by the Ogawa samplers decreased significantly with increasing distance from N-source. In heavily trafficked sites in GCNP, atmospheric NOx was 52% higher at the roadside compared to 30 m away from the road. Atmospheric NOx 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, δ15N 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.
|Advisor:||Johnson, Nancy Collins|
|Commitee:||Hultine, Kevin R., Johnson, Nancy C., Sesnie, Steven E., Sisk, Thomas D.|
|School:||Northern Arizona University|
|Department:||School of Earth Sciences and Environmental Sustainability|
|School Location:||United States -- Arizona|
|Source:||MAI 51/06M(E), Masters Abstracts International|
|Subjects:||Ecology, Environmental science|
|Keywords:||Arizona, Automobiles, Grand Canyon National Park, NOx, Nitrogen, Pollution|
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