Isotopic Investigation Of Anthropogenic Sources Of Atmospheric Nitrogen And Carbon Along Spatial Gradients

Fossil fuel combustion from point and mobile sources is a key contributor to atmospheric CO2, a major greenhouse gas, and NOx, a precursor to acid rain and smog. Increased concentrations of these pollutants are found near the sources, i.e., in urban areas and close to roadways. Vegetation in urban and near-road environments represents an important sink for anthropogenic inputs of NOx and CO2, and understanding the nutrient dynamics of vegetation in urban and near-road ecosystems is critical to understanding budgets of NOx and CO2. However, little is known about how these ecosystems compensate for higher local atmospheric CO2 and NOx concentrations. This study uses stable isotope geochemistry to trace atmospheric nutrients to urban and roadway vegetation. Chapter 1 presents an introduction to the environmental problems associated with atmospheric reactive nitrogen and CO2, the use of stable isotopes to determine the sources of these pollutants, and a review of recent studies which use stable isotopes to determine the sources of plant nutrient uptake. The study described in Chapter 2 examines the fate and transport of gaseous reactive nitrogen from mobile sources along a highway road gradient. This study uses stable isotopes of nitrogen in dry nitrogen deposition to examine the extent of nitrogen loading along a gradient perpendicular to a major highway. In addition, this study examines the effects of increased roadway N deposition on local vegetation by using the isotopic composition of plant tissue as a biomonitor of atmospheric N exposure. Chapter 3 details a similar study; however it is scaled up to an urban to rural gradient. This study used similar methods to the road gradient research, but examines N deposition at urban, suburban and rural sites in two metropolitan areas