Microbial respiration and diffusive transport of O2, 16O2, and 18O16O in unsaturated soils and geologic sediments

Lee, E. S., Birkham, T. K., Wassenaar, L. I. and Hendry, M. J. (2003) Microbial respiration and diffusive transport of O2, 16O2, and 18O16O in unsaturated soils and geologic sediments. Environmental Science and Technology, 37(13), pp. 2913-2919. (doi: 10.1021/es026146a)

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Molecular oxygen (O2) in unsaturated geologic sediments plays an important role in soil respiration, biodegradation of organic contaminants, metal oxidation, and global oxygen and carbon cycling, yet little is known about oxygen isotope fractionation during the consumption and transport of O2 in unsaturated zones. We used a laboratory kinetic cell technique to quantify isotope fractionation due to respiration and a numerical model to quantify both consumptive and diffusive fractionation of O2 isotopes at a field site comprised of unsaturated lacustrine sandy materials. The combined use of laboratory-based kinetic cell experiments and field-based isotope transport modeling provided an effective tool to characterize microbial respiration in unsaturated media. Based on results from the closed-system kinetic cells, O2 consumption and isotope fractionation were attributed to the alternative cyanide-resistant respiration pathway. At the field site, the modeled depth profiles for O2 and δ18O matched the measured in situ data and confirmed that the consumption of O2 was via the alternative respiration pathway. If the cyanide-resistant respiration pathway is indeed widespread in soils, its high oxygen isotope enrichment factor could help to explain the discrepancy between the predicted present-day Dole effect (+20.8‰) and the observed Dole effect (+23.5‰). Thus, further soil O2 isotope studies are needed to better characterize and model the fractionation of oxygen isotopes during subsurface respiration and the potential impact on the isotopic content of atmospheric O2.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Hendry, Professor Martin
Authors: Lee, E. S., Birkham, T. K., Wassenaar, L. I., and Hendry, M. J.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Environmental Science and Technology
Journal Abbr.:EST
Publisher:American Chemical Society
ISSN (Online):1520-5851
Published Online:23 May 2003

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