Dynamic chamber as a more reliable technique for measuring methane emissions from aquatic ecosystems

Aquatic ecosystems are the largest natural source of atmospheric methane ("CH₄") worldwide. However, the current estimation of CH₄ emissions from aquatic ecosystems still has extensive uncertainty due to large spatiotemporal variations in CH₄ emissions as well as significant uncertainty in measurement methods. In this study, we initially investigated CH₄ fluxes from a simulated eutrophic water body by using static chamber method ("SC") during an incubation period of 36 days. Approximately 23 % of the total flux measurements were unsuccessful because they lacked a linear correlation between the accumulation of CH₄ concentrations and enclosure time. CH₄ fluxes could be achieved for most measurements. However, 5 min after enclosing, the initial CH₄ concentrations measured in the chambers were too high (up to 507.4 ppm) to greatly suppress CH₄ emissions from the diffusion process. Therefore, a dynamic chamber method ("DC") was developed to overcome the shortcomings of the SC. To achieve the DC, air samples must be continuously collected at the inlet and outlet of the dynamic chamber at fixed flow rates. In contrast to the SC, effective CH₄ flux data could be obtained by the DC for each measurement at different frequencies. The DC measured the diel and daily variations in CH₄ fluxes and the displayed CH₄ emissions from the simulated water were highly irregular. The displayed emissions had variations up to more than two orders of magnitude. These results implied that the SC measured few intermittent fluxes that were difficult to represent the actual CH₄ emissions from eutrophic water. The DC developed in this study considers the temporal variations in CH₄ emissions from aquatic ecosystems. Thus, the DC is expected to be applicable in the field flux measurements of CH₄ as well as other greenhouse gases to reduce emissions uncertainties.