Depth-Wise CO2 Production and Transport In a Wyoming Rangeland Soil.

Soil CO2 concentrations reflect subsurface CO2 production and transport and provide valuable information on soil CO2 dynamics. In this study, CO2 concentrations were measured in a rangeland soil near Laramie, WY. Depth-wise production and flux were calculated using a soil-CO2 profile method. 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 Quirck (1961) expression. 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 Reco and hence was used in the soil-CO2 profile method to estimate soil CO2 production and flux. Calculated CO2 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 (R2=0.48-0.60, depending on the depth of the temperature measurement) with temperature sensitivity (Q10) increasing from 2.44 to 4.19 with depth.