A Numerical Examination of 14 CO 2 Chamber Methodologies for Sampling at the Soil Surface

Radiocarbon is an exceptionally useful tool for studying soil-respired CO 2 , providing information about soil carbon turnover rates, depths of production, and the biological sources of production through partitioning. Unfortunately, little work has been done to thoroughly investigate the possibility of inherent biases present in current measurement techniques, like those present in δ 13 CO 2 methodologies, caused by disturbances to the soil's natural diffusive regime. This study investigates the degree of bias present in four 14 C sampling chamber methods using a three-dimensional numerical soil-atmosphere CO 2 diffusion model. The four chambers were tested in an idealized, surrogate reality by assessing measurement bias with varying Δ 14 C and δ 13 C signatures of production, collar lengths, soil biological productivity rates, and soil diffusivities. The static and Iso-FD chambers showed almost no isotopic measurement bias, significantly outperforming dynamic chambers, which demonstrated biases up to 200‰ in some modeled scenarios. The study also showed that 13 C and 14 C diffusive fractionation are not a constant multiple of one another, but that the δ 13 C correction still works in diffusive scenarios because the change in fractionation is not large enough to impact measured Δ 14 C values during chamber equilibration.