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Volume 8, issue 3
Biogeosciences, 8, 763–769, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 8, 763–769, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 23 Mar 2011

Research article | 23 Mar 2011

Isotopic fractionation during soil uptake of atmospheric hydrogen

A. Rice1, A. Dayalu2,*, P. Quay3, and R. Gammon3 A. Rice et al.
  • 1Department of Physics, Portland State University, Portland, Oregon 97207-0751, USA
  • 2Harvard University Earth and Planetary Sciences, 20 Oxford Street, Cambridge Massachusetts, 02138, USA
  • 3School of Oceanography, P.O. Box 357940, University of Washington, Seattle, Washington 98195, USA
  • *formerly at: Department of Chemistry, University of Washington, USA

Abstract. Soil uptake of atmospheric hydrogen (H2) and the associated hydrogen isotope effect were studied using soil chambers in a Western Washington second-growth coniferous forest. Chamber studies were conducted during both winter and summer seasons to account for large natural variability in soil moisture content (4–50%) and temperature (6–22 °C). H2 deposition velocities were found to range from 0.01–0.06 cm s−1 with an average of 0.033 ± 0.008 cm s−1 (95% confidence interval). Consistent with prior studies, deposition velocities were correlated with soil moisture below 20% soil moisture content during the summer season. During winter, there was considerable variability observed in deposition velocity that was not closely related to soil moisture. The hydrogen kinetic isotope effect with H2 uptake was found to range from −24‰ to −109‰. Aggregate analysis of experimental data results in an average KIE of −57 ± 5‰ (95% CI). Some of the variability in KIE can be explained by larger isotope effects at lower (<10%) and higher (>30%) soil moisture contents. The measured KIE was also found to be correlated with deposition velocity, with smaller isotope effects occurring at higher deposition velocities. If correct, these findings will have an impact on the interpretation of atmospheric measurements and modeling of δD of H2.

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