HR: 0800h
AN: A31B-0058    [Abstracts]
TI: Observations of Molecular Hydrogen Uptake by Soils From a Mixed Conifer and Hardwood Forest in California
AU: * Smith, N V
EM: nicolev@gps.caltech.edu
AF: Environmental Science and Engineering California Institute of Technology, MS 100-23 Caltech 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Randerson, J T
EM: jranders@uci.edu
AF: Department of Earth Systems Science University of California, Irvine, 3212 Croul Hall, Irvine, CA 92697 United States
AB: Soil uptake of molecular hydrogen accounts for 62-92% of H$_{2}$ loss from the atmosphere, but ecologically relevant observations of H$_{2}$ uptake rates and distribution are sparse. New observations are needed to identify the sensitivity of H$_{2}$ fluxes to ecological and environmental drivers such as soil moisture, temperature and organic matter content. Here we present observations of H$_{2}$, CO and CO$_{2}$ uptake and vertical distribution in soils in both relatively dry and wet sites from a mixed conifer and hardwood forest in the San Jacinto Mountains of Southern California. Our sites were located within the University of California James San Jacinto Mountains Reserve located at $33\deg$ N and $116\deg$ W. The soils in these sites are uniform, well drained fine grain sands to at least 30 cm depth. Observed rates of H$_{2}$ uptake by these soils range from -4.6 nmol/m$^{2}$/s to -12.41 nmol/m$^{2}$/s. An apparent correlation between H$_{2}$ uptake and CO$_{2}$ soil respiration fluxes exists across the sites. Vertical distribution of H$_{2}$ shows that at 5 cm depth (just below the surface litter layer) the concentration of H$_{2}$ is less than 50% of ambient atmospheric levels, and decreases with depth to less than 50 ppb (by 25 cm) at all sites. These observations suggest that the steady-state compensation level of H$_{2}$ within soils is low. Vertical gradients in H$_{2}$ profiles are at a maximum in the late-afternoon and minimum at night. Within the soil, diurnal variability is greatest in the upper 5 cm of soil, and inter-site variability is greatest above 10 cm.
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting