A calibration system for soil carbon dioxide efflux measurement chambers: Description and application

• Comparisons have revealed large discrepancies among the many methods for measuring soil CO2 efflux indicating the need for an absolute calibration of methods. This study presents a calibration system, constructed to imitate an area of soil, and its application to two different chamber systems for the measurement Of Soil CO2 efflux: one open and one closed dynamic. Air rich in CO2 was allowed to diffuse through a layer of sand on top of a box of known volume. By measuring the decrease in CO2 Concentration inside the box, the exact CO2 efflux could be calculated. The CO2 efflux rates measured by the chambers could then be compared with the efflux rates calculated from the box. The error of the closed-chamber system ranged from an underestimate of 19% to an overestimate of 21%. The errors were most likely caused by a combination of underestimated chamber volume, causing an underestimation Of CO2 efflux, and turbulence within the chamber, which increased the flax by disturbing the boundary layer above the surface. The open-chamber system always overestimated the CO2 efflux. Disturbing the boundary layer alone was believed to cause a 17% increase in efflux. Increasing negative pressure difference caused a mass flow of CO2-rich air into the chamber. At a pressure difference of -0.15 Pa, the error was 11 to 40%, depending on air-filled soil volume. Accordingly, soil-water content, a parameter to which soil CO2 efflux is often related, was found to substantially affect the measurements made by both tested systems. These results point to the need of calibrating systems used for measuring soil CO2 efflux is measured against a known flux, to elucidate the limits and applicability of each system.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Naturgeografi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Physical Geography (hsv//eng)

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