PARENT SESSION
Poster Session # 6: Urban Ecology.

Monday, August 4 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

The use of stable isotopes to study urban nitrogen dynamics.

Kammerdiener, Susan^*,1, Ehleringer, James^*,1, ¹ University of Utah, Salt Lake City, UT, USA

ABSTRACT- The urban-rural gradient provides an opportunity to compare plant nutrient dynamics between systems with different sources and levels of available nutrients. The similar location, vegetation, and topography of the Salt Lake and Skull Valleys of northern Utah provide an excellent opportunity for a study on the effects of urban pollution on the vegetation and soils of Salt Lake City. NO_x, is one of the main components of air pollution in the Salt Lake Valley; therefore, it is important to monitor its deposition on plants and soil . Measuring the stable isotope ratio of ¹⁵N /¹⁴N in plant and soil materials is one way to do this. Results from the first season support the hypothesis that the ¹⁵N in Bromus tectorum leaves is more enriched in ¹⁵N in areas with high levels of atmospheric NO_x deposition than in areas with low levels of atmospheric NO_x. The ¹⁵N in the vegetation decreased significantly with distance from areas of high urban nitrogen deposition to rural areas with lower concentrations of predicted deposition. Research from the second season more thoroughly assesses the use of ¹⁵N as an indicator of anthropogenic nitrogen deposition on soils and plants. In addition to leaf and soil samples from every square mile of the urban and rural valleys, a set of genetically identical potted cheatgrass plants are grown in the same soil at one urban and one rural site. The plant and soil samples from the valleys and the potted samples are expected to follow the pattern found during the first season. In addition, it is hypothesized that the ¹⁵N in the soils supporting the Bromus tectorum will follow the same pattern as the leaf samples, but will be more enriched.

Key words: nitrogen isotopes, nitrogen pollution, Bromus tectorum, urban ecosystem