Understanding greenhouse gas emissions from stored organic carbon is an increasingly important area in gas flux science. Melt of permafrost layers, caused by rising global temperatures, threatens to contribute more to atmospheric CO2 concentrations than previously thought. These large permafrost melt driven emissions of greenhouse gases also have the potential to cause accelerated global warming because of global climate feedback loops.
The use of closed chamber systems is prevalent in greenhouse gas flux measurements from permafrost layers. Many closed chamber systems contain a infrared gas analyzer (IRGA) sensors, however, these tend to be costly and limiting to the operator. A recent branch in gas flux research focuses on designing closed chamber systems that yield accurate and reproducible results using an automated interface; which omits the requirement for an operator to oversee the experiment, as with the use of IRGAs. Automation also allows for more measurements to be recorded over longer periods of time, such as an entire day, to account for dynamic factors including respiration trends and air temperature fluctuations.
In a study conducted by Gagnon et al. (2016), an automated closed-chamber apparatus was developed, containing low-cost sensors and microcontrollers. The goal of the research project was to determine whether the lower-budget systems generated results comparable to more costly IRGA sensors.
The study site selected is located within a continuous permafrost zone of Salluit, Quebec, Canada, see Figure 1. Four automated chambers (ACs) were designed using opaque polyvinyl chloride (PVC) tubing and supported with steel-based platforms (Figure 2). Carbon dioxide sensors were installed in each chamber and were powered by solar batteries. Automated measurements were recorded using microcontrollers (Figure 3), while IRGAs were circulated between all chambers to obtain reference CO2 measurements.
The results obtained from the CO2 sensors were linearly correlated with the IRGA reference measurements, and the overall trends using both sensoring techniques were similar. The data collected by the CO2 sensors was 6.0 ± 1.6% higher than the data collected by the IRGAs. Therefore it is stated by Gagnon et al. that the CO2 sensors produced accurate results.
The CO2 sensors cost less than $100 USD each, compared to several hundred of dollars for the IRGAs. The IRGAs also require constant supervision and are incompatible with microcontrollers, thus restricting the sensors to measure only one site at a time. The chambers using CO2 sensors are more easily transferred from one site to another and can measure more sites at once with the use of a microcontroller. The design of the ACs contributed to the overall success of the project, however, it is proposed that further work be done to optimize the chamber design for maximum efficiency and increased accuracy. Completing such a project is valuable to the scientific community, as sensors that come at a low cost and generate accurate results can be built into closed chamber systems for continued research of greenhouse gas fluxes from permafrost zones.