Abstract
Dynamic accumulation chamber methods have been extensively used to estimate the total output of CO 2 released from active volcanic area. In order to asses the performance and reliability of a closed dynamic system several tests were carried out with different soil permeabilities and soil CO 2 fluxes. A special device was used to create a constant one-dimensional CO 2 flux through a soil column with a known permeability. Three permeabilities were investigated, ranging between 3.6 × 10 − 2 and 3.5 × 10 μm 2, as were several CO 2 fluxes (ranging between 1.1 × 10 − 6 and 6.3 × 10 − 5 kg m − 2 s − 1 ). The results highlight that the accuracy of soil CO 2 flux measurements strictly depends on the soil gas permeability and the soil CO 2 flux regimen. Generally chamber measurements underestimate CO 2 fluxes at low soil permeability and low soil CO 2 fluxes, whereas appreciable overestimations occur for high permeability soil, especially for high soil CO 2 fluxes. Other tests carried out with different settings for the measurement device, such as the chamber volume and the flux of the pump used to recirculate air through the chamber and the gas analyzer (recirculation flux), revealed a strong dependence of the closed dynamic chamber measurements on the recirculation flux. Low recirculation fluxes (0.2–0.4 l min − 1 ) decreased the performance of the measurement system, causing underestimations of the actual soil CO 2 flux, whereas higher values (0.6–1.0 l min − 1 ) resulted in overestimations, especially for elevated soil CO 2 fluxes. An empirical equation was deduced to allow accumulation chamber fluxes to be calculated very accurately based on soil gas permeabilities measured in the field.
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