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Volume 15, issue 22
Atmos. Chem. Phys., 15, 13003–13021, 2015
https://doi.org/10.5194/acp-15-13003-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 15, 13003–13021, 2015
https://doi.org/10.5194/acp-15-13003-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 24 Nov 2015

Research article | 24 Nov 2015

Isotopic signatures of production and uptake of H2 by soil

Q. Chen1,2, M. E. Popa1, A. M. Batenburg1,3, and T. Röckmann1 Q. Chen et al.
  • 1Institute for Marine and Atmospheric research Utrecht, Utrecht University, Utrecht, the Netherlands
  • 2Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
  • 3Department of Applied Physics, University of Eastern Finland, Kuopio, Finland

Abstract. Molecular hydrogen (H2) is the second most abundant reduced trace gas (after methane) in the atmosphere, but its biogeochemical cycle is not well understood. Our study focuses on the soil production and uptake of H2 and the associated isotope effects. Air samples from a grass field and a forest site in the Netherlands were collected using soil chambers. The results show that uptake and emission of H2 occurred simultaneously at all sampling sites, with strongest emission at the grassland sites where clover (N2 fixing legume) was present. The H2 mole fraction and deuterium content were measured in the laboratory to determine the isotopic fractionation factor during H2 soil uptake (αsoil) and the isotopic signature of H2 that is simultaneously emitted from the soil (δDsoil). By considering all net-uptake experiments, an overall fractionation factor for deposition of αsoil = kHD / kHH = 0.945 ± 0.004 (95 % CI) was obtained. The difference in mean αsoil between the forest soil 0.937 ± 0.008 and the grassland 0.951 ± 0.026 is not statistically significant. For two experiments, the removal of soil cover increased the deposition velocity (vd) and αsoil simultaneously, but a general positive correlation between vd and αsoil was not found in this study. When the data are evaluated with a model of simultaneous production and uptake, the isotopic composition of H2 that is emitted at the grassland site is calculated as δDsoil = (−530 ± 40) ‰. This is less deuterium depleted than what is expected from isotope equilibrium between H2O and H2.

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We investigated soil production and uptake of H2 and associated isotope effects. Uptake and emission of H2 occurred simultaneously at all sampling sites, with strongest emission where N2 fixing legume was present. The fractionation constant during soil uptake was about 0.945 and it did not show positive correlation with deposition velocity. The isotopic composition of H2 emitted from soil with legume was about -530‰, which is less deuterium-depleted than isotope equilibrium between H2O and H2.
We investigated soil production and uptake of H2 and associated isotope effects. Uptake and...
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