The comparison of two chamber designs for measurements of methane fluxes from a Wetland Research Park

Naturally occurring, biologically productive wetlands are significant greenhouse gas contributors, producing roughly 25% of the world’s methane stock. This is a concern to scientists on a global scale, as methane has a Global Warming Potential (GWP) 25x greater than that of CO2. It is imperative to gas flux science to understand the contribution that wetlands makes to the global greenhouse gas (GHG) budget, and to work on developing the most accurate, precise and efficient methods of gas flux measurements.

Figure1

Figure 1

A study was conducted by Waletzko and Mitsch on a Wetland Research Park in central Ohio, in which methane emissions from the Oletangy River Wetland Research Park (ORWRP) (please see Figures 1 and 2) were measured using different chamber designs. Two basic chamber designs were explored for this study, both measuring methane emissions over a 10 month study. The designs were selected based upon previous work conducted by Livingston and Hutchinson (2000) and on follow up studies conducted by Levy et al. (2012) and Pihlatie et al. (2013). In these studies, suggestions were made for designing chambers that take into account parameters such as venting, volume to base area ratios and temperature control. There have been many designs used in experiments, however to date, few have actually been compared. This was the goal of the Waletzko and Mitsch study.

Figure2

Figure 2

The design of both chambers included a polyvinylchloride (PVC) frame with a high density polyethylene (HDPE) base. The first chamber design contained a plastic bag chamber. The second design contained a rigid plastic chamber. Please see Figure 3 below. Gas samples were extracted from the chambers using syringes and were analyzed on a Shimadzu gas chromatograph.

Figure 3

Figure 3

Statistical analysis shows there was no significant difference in the data collected from both chamber designs. The data analysis accounted for environmental changes such as atmospheric temperature, soil moisture, dissolved organic carbon (DOC) and biological oxygen demand (BOD), which all affect methane production. Accounting for these factors ensured that the results would be equivalent in their analysis. It was suggested that further designs be explored to regulate sampling time and sampling methods. It was found that a time lapse of 33 minutes occurred between collecting samples at a particular site, and a time lapse of 73 minutes occurred during the collection of samples between sites. As chamber design has a negligible impact on the methane flux measurement, the installation of an automated measuring system would further increase the accuracy and reproducibility of results by reducing this time lapse.

As both the bag and rigid chamber methods yielded statistically similar results, it was recommended that the selection of chamber design be made based on ease of use, efficiency and durability. It was also recommended that continued monitoring be conducted over a longer period of time, to account for seasonal and annual fluctuations in biological productivity and hence in methane production. This research is important to the scientific community as these results illustrate that chamber design does not change flux measurements in wetland environments. Research groups continuing work in this field are able to employ different chamber designs and obtain comparable results.