Open AccessQuantification of Microbial Methane Oxidation in an Alpine Peat Bog
Author(s) -
Urmann Karina,
GonzalezGil Graciela,
Schroth Martin H.,
Zeyer Josef
Publication year - 2007
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2006.0185
Subject(s) - anaerobic oxidation of methane , chemistry , methane , peat , tracer , fractionation , environmental chemistry , vadose zone , isotope fractionation , methanogenesis , diffusion , sorption , bog , isotopes of carbon , soil water , soil science , environmental science , total organic carbon , chromatography , ecology , physics , organic chemistry , adsorption , nuclear physics , biology , thermodynamics
Methane (CH 4 ) is an important greenhouse gas that is produced in different subsurface environments. Its main biological sink, microbial CH 4 oxidation, can be quantified in situ in the vadose zone using gas push‐pull tests (GPPTs). This field method is based on the comparison of breakthrough curves of the reactant CH 4 and a nonreactive tracer. Under diffusion‐dominated transport conditions, previously employed noble gases are unsuitable as tracers to calculate rate constants for CH 4 oxidation due to differing diffusion coefficients. Here, we show that by performing two consecutive GPPTs and coinjecting acetylene (C 2 H 2 ) as an inhibitor of CH 4 oxidation in the second test, the reactant CH 4 can be used as a substitute tracer. Applying this procedure, apparent first‐order rate constants for CH 4 oxidation ranging from 0.38 to 0.82 h −1 were obtained in the vadose zone of three hummocks in an alpine peat bog near Lucerne, Switzerland. Corresponding estimates of in situ rates ranged from 4 to 299 ng CH 4 g dry weight −1 h −1 In all but one GPPT, strong stable carbon isotope fractionation due to diffusion masked isotope fractionation due to microbial oxidation. Therefore, stable carbon isotope fractionation is suitable only to a limited extent as an indicator of microbial CH 4 oxidation during a GPPT with diffusion‐dominated gas transport. In contrast, the presented procedure for the quantification of microbial CH 4 oxidation using GPPTs can be applied without restrictions even in systems with high porosity. Furthermore, the presented method may be useful for quantifying other processes for which suitable inhibitors but no suitable tracers are available.