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Molecular hydrogen uptake by soils in forest, desert, and marsh ecosystems in California

Smith-Downey, Nicole V. and Randerson, James T. and Eiler, John M. (2008) Molecular hydrogen uptake by soils in forest, desert, and marsh ecosystems in California. Journal of Geophysical Research G, 113 . G03037. ISSN 0148-0227. doi:10.1029/2008JG000701.

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The mechanism and environmental controls on soil hydrogen (H_2) uptake are not well understood but are essential for understanding the atmospheric H_2 budget. Field observations of soil H_2 uptake are limited, and here we present the results from a series of measurements in forest, desert, and marsh ecosystems in southern California. We measured soil H_2 fluxes using flux chambers from September 2004 to July 2005. Mean H2 flux rates and standard deviations were −7.9 + −4.2, −7.6 + −5.3 and −7.5 + −3.4 nmol m^(−2) s^(−1) for the forest, desert, and marsh, respectively (corresponding to deposition velocities of 0.063 + −0.029, 0.051 + −0.036, 0.035 + −0.013 cm s^(−1)). Soil profile measurements showed that H_2 mixing ratios were between 3% and 51% of atmospheric levels at 10 cm and that the penetration of H_2 into deeper soil layers increased with soil drying. Soil removal experiments in the forest demonstrated that the litter layer did not actively consume H_2, the removal of this layer increased uptake by deeper soil layers, and the exposure of subsurface soil layers to ambient atmospheric H_2 levels substantially increased their rate of uptake. Similar soil removal experiments at the desert site showed that extremely dry surface soils did not consume H2 and that fluxes at the surface increased when these inactive layers were removed. We present a model of soil H_2 fluxes and show that the diffusivity of soils, along with the vertical distribution of layers that actively consume H_2 regulate surface fluxes. We found that soil organic matter, CO_2 fluxes, and ecosystem type were not strong controllers of H_2 uptake. Our experiments highlight H_2 diffusion into soils as an important limit on fluxes and that minimum moisture level is needed to initiate microbial uptake.

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Randerson, James T.0000-0001-6559-7387
Additional Information:Copyright 2008 by the American Geophysical Union. Received 29 January 2008; accepted 30 June 2008; published 23 September 2008. N.S.D. thanks J. Leadbetter for lab and instrument use, X. Xu and G. Cane for assistance with the elemental analyzer at UC Irvine, L. Welp for assistance with field equipment design, and N. Downey for assistance in the field. We also thank colleagues working within the University of California Natural Reserve System, including B. Bretz, B. Berger, and M. Hamilton for their assistance in establishing and monitoring field sites. N.S.D. was supported by the NCER STAR program funded by the U.S. EPA. J.T.R. acknowledges support from University of California Irvine's School of Physical Sciences Dean's Innovation Fund. This work was also supported by a generous gift from General Motors and William Davidow and family.
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Environmental Protection Agency (EPA)UNSPECIFIED
University of California IrvineUNSPECIFIED
William Davidow and familyUNSPECIFIED
Subject Keywords:atmospheric H2 sink; soil oxidation of molecular hydrogen; temperature; moisture and diffusive controls on soil H2 uptake; hydrogen economy
Record Number:CaltechAUTHORS:SMIjgrg08
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Official Citation:Smith-Downey, N. V., J. T. Randerson, and J. M. Eiler (2008), Molecular hydrogen uptake by soils in forest, desert, and marsh ecosystems in California, J. Geophys. Res., 113, G03037, doi:10.1029/2008JG000701.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12132
Deposited By: Archive Administrator
Deposited On:24 Oct 2008 21:42
Last Modified:08 Nov 2021 22:25

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