Soil CO2 efflux represents a significant portion of the global carbon cycle. Accurate estimates of soil CO2 flux across a wide range of spatial and temporal scales remain important inputs to global climate models. One common approach to estimate CO2 efflux from soils is a closed-chamber system, where a sealed chamber is deployed on the surface for a short period of time and the CO2 efflux is calculated from the rate of CO2 increase measured by a gas analyzer during the measurement. Validation of soil flux systems can be challenging due to large variation in natural environments. Here we describe a controlled flux chamber designed to validate soil CO2 efflux systems against a known and constant flux. We compare results between the widely used LI-8100A soil flux system and a new soil flux chamber for the LI-6800 portable photosynthesis system. Additionally, the importance of an automatic actuation system to seal the chamber is discussed in the context of pressure-induced artifacts in the flux measurement.
Results/Conclusions
In a controlled environment, consisting of a uniform sandy soil with an independently calculated flux, both the LI-8100A and LI-6800 soil flux systems report CO2 efflux values similar to the independently calculated flux. Repeatability between both systems was comparable, with no significant differences in the final CO2 efflux calculated from either measurement system. We additionally demonstrate large pressure perturbations in the soil when a sealed chamber is placed on the soil surface. In actuated chambers, the pressure perturbation is greatly reduced. The implications of this result on the measured efflux values is discussed.