HR: 1330h
AN: H32A-0508    [PDF]
TI: Gas Push-Pull Test for In-Situ Quantification of Vadose Zone Microbial Activities
AU: * Schroth, M H
EM: schroth@ito.umnw.ethz.ch
AF: Institute of Terrestrial Ecology - Soil Biology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, CH-8952 Switzerland
AU: Urmann, K
EM: urmann@ito.umnw.ethz.ch
AF: Institute of Terrestrial Ecology - Soil Biology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, CH-8952 Switzerland
AU: Gonzalez-Gil, G
EM: gonzalez-gil@ito.umnw.ethz.ch
AF: Institute of Terrestrial Ecology - Soil Biology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, CH-8952 Switzerland
AU: Zeyer, J
EM: zeyer@ito.umnw.ethz.ch
AF: Institute of Terrestrial Ecology - Soil Biology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, CH-8952 Switzerland
AB: Soils can act as a source or sink for greenhouse gases such as methane, carbon dioxide, and nitrous oxide. The dynamics of such gases in the subsurface is largely driven by microorganisms. To better understand greenhouse gas dynamics it is therefore necessary to quantify microbial activities and associated rates of gas transformation. Here we propose a novel field technique, the "Gas Push-Pull Test" (GPPT), for the in-situ quantification of vadose zone microbial activities. In a GPPT, a specified volume of a gas mixture containing one or more reactive gases (e.g., methane, carbon dioxide, oxygen) and non-reactive gas tracers (e.g., argon, neon, helium) is injected into the vadose zone at a desired location. Gas injection takes place through the perforated tip of a rod previously driven into the soil. Upon completion of the injection, flow is reversed and the gas mixture together with native soil gas is extracted from the same location. Rates of gas transformation are computed from the analysis of breakthrough curves obtained by measuring gas concentrations of tracers, reactants and/or metabolic products during extraction. In a first application, we present data on the quantification of vadose zone methanotrophic (i.e. methane-oxidizing) activity above the methanogenic zone of a petroleum-contaminated aquifer. In agreement with previously measured methane and oxygen profiles, first-order rate coefficients for methane oxidation during GPPTs ranged from 0.68 1/h at 110 cm below soil surface to 2.19 1/h near the groundwater table (290 cm below soil surface). Microbially-mediated methane oxidation was verified in an additional experiment in which acetylene was co-injected to inhibit methanotrophic activity, and by measuring shifts in stable carbon isotope ratios of methane (up to 40 per mill) during the GPPTs. Gas push-pull tests should provide useful quantitative information on a range of different vadose zone microbial processes.
DE: 1615 Biogeochemical processes (4805)
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting