Evaluation of a portable chamber system for soil CO₂ efflux measurement and the potential errors caused by internal compensation and water vapor dilution

抄録

A portable, easy-to-install chamber system for rapid measurements of soil CO₂ efflux is needed for immediate analysis of CO₂ flushes after events such as tillage and grassland renovation. We conducted field measurements and simple simulations to validate the effectiveness of a portable chamber system with an infrared CO₂ gas analyzer (IRGA) and a temperature/humidity sensor (the SIR system). We confirmed that a measurement period of 60-180 s after chamber closure was sufficient for calculation of soil CO₂ efflux. We compared the SIR system with a closed static chamber system and an automated open/closed chamber system. The efflux data obtained with the SIR system were linearly related to the data obtained with the other systems, and the relationships between soil temperature and efflux were similar for the three systems. These results show that the SIR system provided soil CO₂ efflux values with reasonable accuracy relative to the other systems. We also examined how the calculated efflux values were affected by the internal compensation of the IRGA for environmental parameters and water vapor dilution in the chamber. The potential error caused by the default internal compensation of the IRGA was within 3.1% under general environmental conditions. The effects of water vapor dilution were large (>20%) for small CO₂ effluxes. The combined effects of the default internal compensation and water vapor dilution were larger for small CO₂ effluxes than for large CO₂ effluxes, and the effects became larger under conditions of low air pressure. We recommended that accurate environmental compensation and water vapor correction be applied for analysis of small CO₂ effluxes when there is a rapid increase in water vapor, especially under conditions of low air pressure.