HR: 1340h
AN: B13C-0249    [Abstracts]
TI: Nitrogen Transformation And Transport In An Arctic Watershed
AU: * Yano, Y
EM: yyano@mbl.edu
AF: The Ecosystems Center, Marine Biological Laboratory, 7 MBL St., Woods Hole, MA 02543 United States
AU: Shaver, G R
EM: gshaver@mbl.edu
AF: The Ecosystems Center, Marine Biological Laboratory, 7 MBL St., Woods Hole, MA 02543 United States
AU: Giblin, A E
EM: agiblin@mbl.edu
AF: The Ecosystems Center, Marine Biological Laboratory, 7 MBL St., Woods Hole, MA 02543 United States
AU: Rastetter, E B
EM: erastetter@mbl.edu
AF: The Ecosystems Center, Marine Biological Laboratory, 7 MBL St., Woods Hole, MA 02543 United States
AU: Nadelhoffer, K J
EM: Knute@umich.edu
AF: University of Michigan Biological Station, 2014 Natural Science Bldg. 830 N. University, Ann Arbor, MI 48109 United States
AB: Arctic ecosystems are strongly N limited, while a large amount of N exists in soil and a significant amount of N is lost as dissolved organic N (DON) in hydrological flow, bypassing plant uptake. Thus, the long-term N limitation of arctic ecosystems may be determined largely by storage and losses of N in forms that are unavailable for plant uptake. Understanding fundamental processes that determine the forms of N and the relationship between the forms of N and their availability, retention, and losses in soil is critical for modeling the N budget of arctic watersheds. For a better understanding of N dynamics, we studied the turnover and downslope transport of N and the forms of N lost to hydrological flow in a small arctic watershed in northern Alaska. In the early growing season, $^{15}$NH$_{4}$ (58.8mg $^{15}$N/m$^{2}$) was added at 4 different locations along a hill slope (crest, mid slope, foot slope, and riparian). Soils, plants, and soil water were collected from the treatment plots as well as downslope locations, and resin bags were deployed to determine the chemical forms and turnover of the added $^{15}$N. At the end of the first growing season most of the $^{15}$N ($\sim$80%) was found in soil, most of this in the top 3 cm of the moss layer. DON was the predominant fraction of total dissolved N in soil solution collected by lysimeters (60-80% of total), followed by NH$_{4}$ (20-35%) and NO$_{3}$ (4-7%) of near detection limit. The resin bag study showed that NH$_{4}$ was transformed to NO$_{3}$ or DON within all the plots during the growing season. The del-$^{15}$N values from the resin bag study suggest that $^{15}$N added as $^{15}$NH$_{4}$ moved down the slope up to 2 m within the first growing season and was detected as NH$_{4}$, NO$_{3}$ or DON. A previous fertilization study in the same watershed, in which both NH$_{4}$ and NO$_{3}$ were added in much higher doses, detected significantly higher N concentrations in plants at 6 m down the slope after 1 year of N application. The shorter downslope movement observed in current study may be due to the N addition in a trace amount. Alternatively, significant transport of N down the slope may occur during snowmelt rather than in a growing season. Potential transformation processes and the retention and losses of N from the system will be discussed.
DE: 1866 Soil moisture
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting