HR: 10:40h
AN: H52B-02 INVITED     [Abstracts]
TI: Mapping the Spatial and Temporal Distribution of N and O Isotopes in Precipitation Nitrate Across the Northeastern and Mid-Atlantic United States
AU: * Elliott, E M
EM: eelliott@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Kendall, C
EM: ckendall@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Harlin, K
EM: kharlin@uiuc.edu
AF: NADP Central Analytical Lab, Illinois State Water Survey, Champaign, IL 61820 United States
AU: Butler, T
EM: tjb2@cornell.edu
AF: IES, Cornell University, Rice Hall, Ithaca, NY 14853 United States
AU: Carlton, R
EM: rcarlton@epri.com
AF: EPRI, 3412 Hillview Ave., Palo Alto, CA 94304 United States
AU: Wankel, S
EM: sdwankel@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: Atmospheric deposition of N is a universally important pathway by which ecosystems receive fixed, bioavailable N. Since the 1880s, atmospheric deposition of N has become increasingly important, as NO$_{x}$ emissions from fossil fuel combustion have steadily increased. In particular, the Northeastern and Mid-Atlantic U.S. receive some of the highest rates of nitrate wet deposition in the country, causing a cascade of detrimental effects. In order to effectively mediate the impacts of nitrate deposition, it is critical to understand the dynamics among NO$_{x}$ sources, atmospheric chemical transformations and transport, and the characteristics of the nitrate that is ultimately deposited. To address this need, this research takes advantage of recent methodological improvements, coupled with national networks (NADP, AIRMoN) of archived precipitation, to characterize N and O isotopic composition of nitrate in precipitation across the Northeastern and Mid-Atlantic U.S. We investigate the critical question of whether variations in \delta$^{15}$N and \delta$^{18}$O of nitrate wet deposition are mainly a function of atmospheric processes (e.g., seasonal variations in reaction pathways) or variable NO$_{x}$ source contributions (e.g., power plant emissions, vehicle exhaust). Spatial and seasonal variability of \delta$^{15}$N and \delta$^{18}$O is investigated using bimonthly archived samples from 2000. Furthermore, a high resolution record of daily precipitation from a single site is used to highlight within-season isotopic variability. Potential correlations between isotopic values and major NO$_{x}$ sources are explored using EPA datasets for monthly county-level emissions from two major NO$_{x}$ sources, electric generating units and on-road vehicles. Analysis of samples for \Delta$^{17}$O is in progress. A key concern regarding analysis of archived samples is nitrate preservation. We tested the stability of nitrate concentrations, and hence potential isotopic fractionations, by reanalyzing filtered, refrigerated, archived NADP samples with a range of nitrate and ammonium concentrations. We found highly significant correlations (R$^{2}$=0.9995, p$<$0.001, n=28) between nitrate concentrations measured in 2000 and 2003, indicating that no major alterations had occurred. With regard to spatial patterns, preliminary isotopic analyses indicate that \delta$^{15}$N of precipitation nitrate varies considerably among states. Moreover, initial data corroborate previously reported seasonal trends in both \delta$^{15}$N and \delta$^{18}$O, with higher values in the colder months. Seasonal trends in \delta$^{15}$N are remarkably consistent, with up to an 8 \permil difference between winter and summer months. \delta$^{18}$O values of nitrate are generally higher and have a smaller range than previously reported for precipitation, with values ranging from +60 to +90 \permil. In addition, archived daily precipitation collected during 2000 from a single AIRMoN site give insight into the seasonal and within-season variability of \delta$^{15}$N and \delta$^{18}$O of precipitation nitrate. Back-trajectory analyses are used to examine the geographic source of air masses for individual events, and seasonal frontal patterns are discussed.
DE: 1854 Precipitation (3354)
DE: 1040 Isotopic composition/chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
DE: 0345 Pollution--urban and regional (0305)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting