A NUMERICAL EXAMINATION OF 14CO2 CHAMBER METHODOLOGIES FOR SAMPLING AT THE SOIL SURFACE

Radiocarbon is an exceptionally useful tool for studying soil-respired CO2, 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 delta(CO2)-C-13 methodologies, caused by disturbances to the soil's natural diffusive regime. This study investigates the degree of bias present in four C-14 sampling chamber methods using a three-dimensional numerical soil-atmosphere CO2 diffusion model. The four chambers were tested in an idealized, surrogate reality by assessing measurement bias with varying Delta C-14 and delta C-13 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 C-13 and C-14 diffusive fractionation are not a constant multiple of one another, but that the delta C-13 correction still works in diffusive scenarios because the change in fractionation is not large enough to impact measured Delta C-14 values during chamber equilibration.