HR: 0800h
AN: B51C-0606    [Abstracts]
TI: Hydrologic regulation of methyl chloride and methyl bromide fluxes from Alaskan Arctic tundra
AU: * Teh, Y
EM: yit@nature.berkeley.edu
AF: University of California, Berkeley, Department of Environmental Science, Policy and Management, 137 Mulford Hall, Berkeley, CA 94720, United States
AU: Mazeas, O
EM: omazeas@berkeley.edu
AF: University of California, Berkeley, Department of Geography, 507 McCone Hall, Berkeley, CA 94720, United States
AU: Atwood, A R
EM: atwood@uclink.berkeley.edu
AF: University of California, Berkeley, Department of Geography, 507 McCone Hall, Berkeley, CA 94720, United States
AU: Rhew, R C
EM: rrhew@atmos.berkeley.edu
AF: University of California, Berkeley, Department of Geography, 507 McCone Hall, Berkeley, CA 94720, United States
AB: Arctic tundra may be a significant regional sink for CH₃Cl and CH₃Br, although the magnitude of this sink is poorly constrained because of the limited extent of field measurements. We sought to close this gap in knowledge by comparing gross and net fluxes of CH₃Cl and CH₃Br in the northern coastal plain and the continental interior. Net and gross fluxes were deconvoluted using stable isotope tracers. Net flux measurements indicated that both regions were net atmospheric sinks for CH₃Cl and CH₃Br, averaging -590 ± 107 nmol CH₃Cl m^-2 d^-1 and -11.3 ± 2.6 nmol CH₃Br m^-2 d^{- 1}. Gross uptake rates averaged -793 ± 128 nmol CH₃Cl m^-2 d^-1 and -20.3 ± 2.9 nmol CH₃Br m^-2 d^-1. Hydrology strongly influenced CH₃Cl and CH₃Br uptake, which varied as a function of hydrologic regime, soil volumetric water content and water table depth. The overall trend showed increasing CH₃Cl and CH₃Br uptake with decreasing soil moisture. Laboratory incubations suggested that this inverse relationship was the result of mass transfer limitation in wetter soils, rather than because of reduced microbial consumption under anaerobic conditions. Water table depth was one of the best predictors of net and gross uptake, with uptake rates increasing proportionately with water table depth. This finding has potential regional significance as changes in water table depth may alter the Arctic tundra sink for CH₃Cl and CH₃Br. We also observed CH₃Cl and CH₃Br uptake under anaerobic conditions suggesting that freshwater anaerobes may be a previously unidentified sink for methyl halides.
DE: 0400 BIOGEOSCIENCES
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0456 Life in extreme environments
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting