Study of a calibration system for soil respiration measurement chambers

Abstract

Purpose. Soil respiration measurement is an important component of the global carbon cycle assessment. To effectively validate the measurement performance of the monitoring instruments and provide accurate carbon flux data, a new flux-monitoring gas-chamber calibration system was investigated. Method. In an environmentally controlled laboratory, a concentration calculation calibration system, mass calculation calibration system, and flow calculation calibration system were used to quantify soil CO2 emissions. The measurement performance of the soil-respiration monitoring gas chamber was investigated, and the strengths and weaknesses of each calibration system were examined. Results. The unsteady-state flow chamber and steady-state chamber measurements had fewer errors and provided better results than the unsteady-state nonflow chamber. The measured values of the closed chamber were low, whereas the measured values of the open chamber were occasionally high and low. For calibration systems, the concentration calculation system is easy to operate; however, the reference flux values are unstable, and the mass calculation system allows for different gas transport mechanisms. However, it is complex to operate and it is difficult to control the air pressure in the diffusion chamber. The calibration process of the flow calculation system was stable and easy to operate; however, the experimental time was long, and the CO2 gas consumption was high. However, for the calibration effect, the optimal calibration system was the flow-meter algorithm. Conclusion. This study proposes a better calibration method for the soil CO2 flux gas chamber, which is conducive to improving the measurement accuracy of the instrument, and provides new ideas for the calibration of other environmental gas monitoring instruments.