HR: 0800h
AN: B31A-0968    [Abstracts]
TI: Methanotrophic Activity Along Diffusive Methane/Oxygen Counter-Gradients in Unsaturated Porous Media
AU: Urmann, K
B31A-0968 AF: Swiss Federal Institute of Technology (ETH) Zurich, ETH Zentrum, CHN G50.2 Universitaetsstr. 16, Zurich, CH-8092 Switzerland
AU: Norina, E
B31A-0968 AF: Swiss Federal Institute of Technology (ETH) Zurich, ETH Zentrum, CHN G50.2 Universitaetsstr. 16, Zurich, CH-8092 Switzerland
AU: * Schroth, M H
EM: martin.schroth@env.ethz.ch
AF: Swiss Federal Institute of Technology (ETH) Zurich, ETH Zentrum, CHN G50.2 Universitaetsstr. 16, Zurich, CH-8092 Switzerland
AU: Zeyer, J
B31A-0968 AF: Swiss Federal Institute of Technology (ETH) Zurich, ETH Zentrum, CHN G50.2 Universitaetsstr. 16, Zurich, CH-8092 Switzerland
AB: Methane (CH4) and O2 gradients can determine the location and extent of microbial CH4 oxidation, which is an important process reducing emissions of the greenhouse gas CH4 from various environments to the atmosphere. We designed a laboratory column with a diffusive CH4 / O2 counter-gradient to evaluate different quantification methods for CH4 oxidation activity along gradients and to study responses of activity to changing gradients. On average 0.046 mmol CH4 /h were consumed inside the column, which contained unsaturated sand inoculated with a methanotrophic enrichment culture. The methanotrophic community thus oxidized over 99% of the CH4 entering the column. In the active zone of the profile, stable carbon isotope ratios increased by 6.6-7.6 per mil. Activity calculated from this enrichment agreed with the activity determined from concentration profiles only when an enrichment factor of 7.4 per mil was used. The latter value agreed well with the enrichment factor previously determined in the inoculum under restricted CH4 availability. To examine the response of methanotrophic activity to changing gradients, the O2 concentration at the top of the column was changed from 0.41% to 0.25%. Subsequently, the zone of highest activity shifted from 55cm to 40cm depth within 1 day while total activity in the column remained similar. Despite the rapid response, the change in O2 lead to slightly increased CH4 emissions for 6 days. After 35 days O2 concentration was changed back to 0.41%, and the zone of highest activity returned to 55cm depth equally rapid. Thus, adaptation of methanotrophs to changes in O2 concentration was fast under the given conditions. Methodologically, concentration gradients allowed calculation of oxidation rates and identification of active zones. Conversely, to quantify CH4 oxidation based on stable carbon stable isotope fractionation required exact knowledge of the isotope enrichment factor, which may be difficult to obtain under field conditions.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1094 Instruments and techniques
SC: Biogeosciences [B]
MN: Fall Meeting 2005