HR: 16:30h
AN: C34A-03    [Abstracts]
TI: Nitrous oxide fluxes from seasonally snow covered subalpine soils
AU: * Liptzin, D
EM: liptzin@nature.berkeley.edu
AF: UC-Berkeley, Department of ESPM 137 Mulford Hall #3114, Berkeley, CA 94720, United States
AU: Seok, B
EM: seok@colorado.edu
AF: University of Colorado, INSTAAR 1560 30th Street, Boulder, CO 80309, United States
AU: Philippa, G
EM: gianluca.filippa@unito.it
AF: Universita  degli Studi di Torino, DI.VA.P.R.A. - Chimica Agraria e Pedologia Via Leonardo da Vinci, 44, Grugliasco (TO), 10095, Italy
AU: Helmig, D
EM: detlev.helmig@colorado.edu
AF: University of Colorado, INSTAAR 1560 30th Street, Boulder, CO 80309, United States
AU: Hueber, J
EM: jacques.hueber@colorado.edu
AF: University of Colorado, INSTAAR 1560 30th Street, Boulder, CO 80309, United States
AU: Williams, M W
EM: markw@culter.colorado.edu
AF: University of Colorado, INSTAAR 1560 30th Street, Boulder, CO 80309, United States
AB: The release to the atmosphere of nitrogen oxides (N₂O and NO) produced by soil microorganisms is an important source of greenhouse gases and affects air quality. Recent evidence suggests that considerable microbial activity occurs beneath the snow in seasonally snow-covered soils, but relatively few studies have addressed nitrogen oxide emissions. The soils in the Colorado subalpine may be particularly prone to N₂O emissions during the winter. The snow-covered season typically lasts at least six months, and during this time the soils are prevented from freezing by insulation of the snow. Competition between denitrifiers and plants for nitrate is likely lower in the winter. Plant senescence in the fall has recently provided considerable labile carbon. Finally, the amount of N deposition is growing, likely increasing soil nitrate concentrations. In the winter of 2005- 2006 we measured N₂O concentration gradients through the snowpack hourly at a subalpine meadow site in the Front Range of the Colorado Rocky Mountains. We believe these measurements represent the first continuous record of winter N₂O fluxes from snow covered soils. The snowpack concentrations of N₂O were related to snow depth with concentrations peaking at 1000 ppbv at the time of maximum snow depth. On a daily basis the calculated N₂O fluxes averaged 1 ng N cm^-2 h^-1·. The flux also peaked at the time of maximum snow depth. The simultaneous measurements of NO and CO₂ in the winter indicated similar seasonal patterns in their concentration profiles. NO fluxes were measurable, but were typically an order of magnitude less than N₂O fluxes. Based on weekly chamber flux measurements, the summer fluxes of N2O were, on average, 4-fold greater than the winter fluxes but exhibited a rapid decline as the soils dried out from June to September. Although the fluxes were lower in winter, the cumulative winter flux contributed approximately 20% of the annual flux in 2005-6. A second year of flux measurements is underway which will allow comparisons of interannual variability. The pattern of the winter fluxes may be quite different because the snowpack development was significantly impacted by an unusual snow melt event in March 2006. This event caused the maximum snow depth to occur two months earlier than average. Overall, it appears that the rates of N₂O emissions from these seasonally snow-covered subalpine soils are significant, and a sizeable proportion of the annual flux occurred in the winter.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0469 Nitrogen cycling
DE: 0486 Soils/pedology (1865)
DE: 0793 Biogeochemistry (0412, 0414, 1615, 4805, 4912)
SC: Cryosphere [C]
MN: 2007 Fall Meeting