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Harvard Forest Symposium Abstract 2013

  • Title: An improved understanding of the biosphere-atmosphere exchange of H2: tower-based H2 fluxes in a mid-latitude forest
  • Primary Author: Laura Meredith (University of Arizona)
  • Additional Authors: Roisin Commane (Harvard Research Group); Andrew Crotwell (NOAA); J. William Munger (Harvard University); Ronald Prinn (Massachusetts Institute of Technology); Peter Salameh (Scripps Institute of Oceanography, Univ. of California, San Diego); Steven Wofsy (Harvard University)
  • Abstract:

    Ecosystem-scale flux measurements of atmospheric hydrogen (H2) were made in a mid-latitude forest with the goal of increasing the process-based understanding of biosphere-atmosphere H2 exchange. Atmospheric H2, an indirect greenhouse gas, plays a notable role in the chemistry of the atmosphere and ozone layer. The H2 budget is dominated by the microbe-mediated soil sink, and although its significance has long been recognized, our understanding is limited by the low temporal and spatial resolution of traditional field measurements.



    The results of this study confirm that soil uptake of atmospheric H2 was the dominant process in a forest ecosystem (midday summertime fluxes of approximately -5 to -10 nmol m-2 s-1). We present correlations of the H2 flux with environmental variables (e.g., soil temperature and moisture) to investigate their influence on soil uptake. H2 soil uptake continues to dominate local ecosystem H2 exchange in the winter season, even across a 70cm snowpack. In this study, a custom, automated instrument was deployed at the Harvard Forest (42°32’N, 72°11’W) from September 2010 to present to measure the annual ecosystem-scale flux of H2 both above and below the forest canopy. A flux-gradient technique was used to estimate the H2 flux from the H2 concentration gradient and the turbulent eddy coefficient. A ten-fold improvement in precision was attained over traditional systems, which was critical for quantifying the whole ecosystem flux from small H2 concentration gradients above the turbulent forest canopy.



    This study is the most comprehensive attempt to elucidate the processes controlling biosphere-atmosphere exchange of H2. Our results will not only reduce uncertainty in the present-day H2 budget but also will improve projections of the response of the H2 soil sink to anticipated changes in anthropogenic H2 emissions and shifting soil conditions concomitant with climate change.

  • Research Category: Forest-Atmosphere Exchange