VERTICAL DISTRIBUTIONS OF CARBON DIOXIDE DIFFUSION COEFFICIENTS AND PRODUCTION RATES IN FOREST SOILS

In this study, we developed a new method for evaluating vertical profiles of CO 2 gas diffusivity and CO 2 gas production in soil samples. The CO 2 flux at the boundary and the steady‐state CO 2 gas profile are measured under two boundary gas conditions. The differential form of Fick's second law can then be used to calculate the gas diffusion coefficients and CO 2 production rate. This method was applied to an undisturbed forest soil sample in the laboratory. Both gas diffusion coefficients and CO 2 production rates decreased with increasing depth. The relative gas diffusion coefficients ranged between 0.03 and 0.15, and the CO 2 production rates ranged between 2.1 × 10 −8 and 4.7 × 10 −8 kg CO 2 m 3 s −1 at 20°C. Unsteady changes in the CO 2 concentration profile in the soil column, and flux from the soil surface were successfully simulated with these values.