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A Numerical Examination of 14CO2 Chamber Methodologies for Sampling at the Soil Surface

Published online by Cambridge University Press:  26 July 2016

Jocelyn Egan*
Affiliation:
Dept. of Earth Sciences, St. Francis Xavier University, 1 West Street, Antigonish, Nova Scotia B2G 2W5, Canada
Nick Nickerson
Affiliation:
Dept. of Earth Sciences, Dalhousie University, 1459 Oxford Street, Halifax, Nova Scotia B3H 4R2, Canada
Claire Phillips
Affiliation:
Dept. of Crop and Soil Science, Oregon State University, Corvallis, Oregon 97331, USA
Dave Risk
Affiliation:
Dept. of Earth Sciences, St. Francis Xavier University, 1 West Street, Antigonish, Nova Scotia B2G 2W5, Canada
*
Corresponding author. Email: jegan@stfx.ca.
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Abstract

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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 δ13CO2 methodologies, caused by disturbances to the soil's natural diffusive regime. This study investigates the degree of bias present in four 14C 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 Δ14C and δ13C 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 13C and 14C diffusive fractionation are not a constant multiple of one another, but that the δ13C correction still works in diffusive scenarios because the change in fractionation is not large enough to impact measured Δ14C values during chamber equilibration.

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