HR: 1340h
AN: B43B-0150    [Abstracts]
TI: Assessment of Microbial Methane Oxidation Above a Petroleum-Contaminated Aquifer Using Gas Push-Pull Tests, Stable Carbon Isotope Fractionation and Profile Modeling
AU: Urmann, K
EM: karina.urmann@env.ethz.ch
AF: Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, CH-8952 Switzerland
AU: Gonzalez-Gil, G
EM: graciela.gonzalez-gil@env.ethz.ch
AF: Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, CH-8952 Switzerland
AU: * Schroth, M H
EM: martin.schroth@env.ethz.ch
AF: Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, CH-8952 Switzerland
AU: Zeyer, J
EM: josef.zeyer@env.ethz.ch
AF: Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, CH-8952 Switzerland
AB: Microbial methane oxidation is an important process reducing methane emissions from different environments such as landfills, peat bogs and contaminated aquifers. We applied the recently developed gas push-pull test (GPPT) to quantify methanotrophic activity and stable carbon isotope fractionation in-situ above a methanogenic petroleum-contaminated aquifer in Studen, Switzerland. The GPPT consists of the injection of a gas mixture of reactants methane and oxygen and non-reactive tracers neon and argon into the vadose zone followed by its extraction together with soil air from the same location. Rate constants of methane oxidation are then calculated from breakthrough curves of extracted methane and neon. We performed six GPPTs, four at 2.7m depth, directly above the groundwater table and two at 1.1m depth. Methane injection concentrations ranged from 17 ml/L to 195 ml/L. At 2.7m depth, rate constants decreased with increasing injection concentration. This indicated that methane oxidation followed Michaelis-Menten kinetics. Rate constants measured at low or medium methane concentrations in the GPPTs were in good agreement with a rate constant calculated from a previously measured gas profile. During the GPPTs we also quantified stable carbon isotope fractionation in methane. The computed fractionation factor $\epsilon$ ranged from 5.3 $\permil$ to 29.5 $\permil$ with stronger fractionation during the tests with higher methane concentrations. The strongest fractionation occurred during the tests at 1.1m depth. At this depth calculated rate constants were more than three times lower than in the zone directly above the aquifer while methane concentrations remained higher throughout the tests. Thus, while GPPTs and gas profile modeling allowed direct quantification of microbial methane oxidation, the use of stable carbon isotope analysis for this purpose may be more complicated due to the observed variability in isotopic fractionation.
DE: 1694 Instruments and techniques
DE: 1875 Unsaturated zone
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting