Assessment of the Soil CO2 Gradient Method for Soil CO2 Efflux Measurements.

This paper uses a refined soil gradient method to estimate CO₂ efflux. To do so, six different models are used to determine the relative gas diffusion coefficient (ξ). A weighted harmonic averaging is used to estimate soil CO₂ diffusion coefficient, yielding a better estimate of CO₂ efflux. The resulting soil CO₂ efflux results are then compared to the soil CO₂ efflux measured with a soil chamber method. Depending on the choice of ξ model used, the estimated soil CO₂ efflux using the gradient method reasonably approximate the efflux obtained using the soil chamber method. In addition, the estimated soil CO₂ efflux obtained by this improved method is well described by an exponential function of soil temperature at a depth of 0.05 m with the temperature sensitivity (Q₁₀) of 1.81 and a linear function of soil moisture at a depth of 0.12 m, in general agreement with previous findings. These results suggest that the gradient method emerges as a practical cost-effective mean to measure soil CO₂ emissions. Results from the present study suggest that the gradient method can be used successfully to measure soil CO₂ efflux provided that proper attention is paid to the judicious use of the proper diffusion coefficient.