| Soil CO2 concentrations reflect subsurface CO2 production and transport and provide valuable information on soil CO 2 dynamics. We measured CO2 concentrations in a rangeland soil near Laramie, WY from July 2009 to November 2010. Depth-wise CO 2 production and flux were calculated using a "soil-CO2 profile method" based on continuous measurements of soil CO2 concentration, temperature, and water content. Carbon dioxide transport due to diffusion in air, diffusion in water, and convection in air were considered. Tortuosity in the air diffusion calculation was estimated using the Moldrup et al. (1997) expression for undisturbed soil and the classic Millington and Quirk (1961) expression. Maximum soil CO2 concentrations of 0.006 m3 m-3 were observed at 15 cm depth during the peak of the growing season in mid-June. Calculated soil efflux was compared to ecosystem respiration (Reco) as measured by an opaque surface flux chamber. The calculated soil effluxes were higher than the measured Reco for both tortuosity models, showing that the calculations and measurements were not in agreement. The Moldrup et al. (1997) tortuosity model showed values closest to R eco and hence was used in the "soil-CO2 profile method" to estimate soil CO2 production and flux. Calculated CO 2 production was highest in the wettest, most fine textured, soil layer at 7.5-15 cm depth for most of the study period. As expected, diffusion in air was the main contributor to total CO2 flux at each depth. Calculated soil CO2 efflux showed good correlation with soil temperature (coefficient of determination R2 = 0.57-0.74, depending on the depth of the temperature measurement) with temperature sensitivity (Q10) being 4.58 and 6.97 at the 7.5 and 15 cm depths, respectively. |
