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Improving the accuracy of the gradient method for determining soil carbon dioxide efflux
Author(s) -
SánchezCañete Enrique P.,
Scott Russell L.,
Haren Joost,
BarronGafford Greg A.
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003530
Subject(s) - tracer , soil respiration , soil carbon , environmental science , soil gas , calibration , soil science , flux (metallurgy) , ecosystem , carbon dioxide , diffusion , ecosystem respiration , atmospheric sciences , chemistry , hydrology (agriculture) , soil water , mathematics , ecology , physics , primary production , statistics , geology , thermodynamics , organic chemistry , geotechnical engineering , biology , nuclear physics
Soil CO 2 efflux ( F soil ) represents a significant source of ecosystem CO 2 emissions that is rarely quantified with high‐temporal‐resolution data in carbon flux studies. F soil estimates can be obtained by the low‐cost gradient method (GM), but the utility of the method is hindered by uncertainties in the application of published models for the diffusion coefficient. Therefore, to address and resolve these uncertainties, we compared F soil measured by 2 soil CO 2 efflux chambers and F soil estimated by 16 gas transport models using the GM across 1 year. We used 14 published empirical gas diffusion models and 2 in situ models: (1) a gas transfer model called “Chamber model” obtained using a calibration between the chamber and the gradient method and (2) a diffusion model called “SF 6 model” obtained through an interwell conservative tracer experiment. Most of the published models using the GM underestimated cumulative annual F soil by 55% to 361%, while the Chamber model closely approximated cumulative F soil (0.6% error). Surprisingly, the SF 6 model combined with the GM underestimated F soil by 32%. Differences between in situ models could stem from the Chamber model implicitly accounting for production of soil CO 2 , while the conservative tracer model does not. Therefore, we recommend using the GM only after calibration with chamber measurements to generate reliable long‐term ecosystem F soil measurements. Accurate estimates of F soil will improve our understanding of soil respiration's contribution to ecosystem fluxes.