HR: 0830h
AN: B31D-0329    [PDF]
TI: Tracking Urban Air Deterioration in San Francisco: Carbon and Nitrogen Isotope Study of Weedy Plants.
AU: * Colman, A S
EM: a.colman@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Inst. Washington, 5251 Broad Branch Rd, NW, Washington, DC 20015-1305 United States
AU: Wessells, A
EM: compost@futurefarmers.com
AF: The Exploratorium, Public Outreach 3601 Lyon St., San Francisco, CA 94123-1099 United States
AU: Swaine, M E
EM: compost@futurefarmers.com
AF: The Exploratorium, Public Outreach 3601 Lyon St., San Francisco, CA 94123-1099 United States
AU: Fogel, M L
EM: m.fogel@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Inst. Washington, 5251 Broad Branch Rd, NW, Washington, DC 20015-1305 United States
AB: Stable isotopes of carbon and nitrogen have long been used as indicators of ecosystem structure and nutrient cycling in natural and anthropogenically disturbed terrestrial ecosytems. However, relatively few of these studies have targeted urban environments, where nitrogen and CO$_{2}$ emissions dramatically impact atmospheric composition. Here we present the results of carbon and nitrogen isotope analyses of herbaceous plants growing in and around San Francisco. These plants were collected mainly as part of a public outreach walking tour of San Francisco ("The Weed Walk - Concrete Jungle") sponsored by the San Francisco Exploratorium. In all cases, the plants were sampled in areas with negligible forest canopy. A consortium of species was collected at each of several distinct sites to examine the localized and regional impact of automobile traffic and proximity to the ocean on isotopic compositions of carbon and nitrogen. $\delta$$^{13}$C measurements trend towards relatively light values in the range of --26 to --36 permil. In comparison, the leaves from similar types of herbaceous species in relatively unpolluted and unforested environments typically have $\delta$$^{13}$C values in the range of --22 to --28 permil. The observed light carbon isotopic compositions potentially reflect input of isotopically light CO$_{2}$ emissions from fossil fuel burning, boosting atmospheric CO$_{2}$ concentrations to $>$10 % above background. $\delta$$^{15}$N values range from +4 to +9 permil. This is substantially offset from the --4 to +1 permil values that typify vegetation in regions where nitrogen oxides from fossil fuel combustion dominate the nitrogen inputs. The nitrogen isotope compositions might suggest nitrogen contributions from a marine source (typically +6 permil).
DE: 0315 Biosphere/atmosphere interactions
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
SC: Biogeosciences [B]
MN: 2003 Fall Meeting