The redox potential of soil as an additional factor describing the variability of methane fluxes from a wetland during dry conditions: a case study for Biebrza National Park, Poland

In the years 2013–2018, continuous measurements of methane fluxes (FCH4) were carried out in the Biebrza National Park wetland. The results, similar to those from other stations in mid-latitudes, showed a clear annual variability of FCH4 in wet years (2013 and 2014) with minimum values in winter and intense methane emissions to the atmosphere from April to September (up to +0.35 gCH4·m-2·day-1). In dry years (2017 and 2018) in turn, the annual variability was clearly disturbed due to lower groundwater levels. Parallel to FCH4, the variability of the parameters describing the properties of soil, such as soil temperature and groundwater level, and, starting from 2017, the oxidation and reduction (redox) potential, was measured. The aim of the study is to perform a comparative analysis of the variability of FCH4 under typical and reduced soil moisture conditions, as well as an analysis of the temporal variability of the redox potential measured at five depths as a parameter supporting the analysis of the variability of methane fluxes in dry years. In such years, the occurrence of intense but short-term methane release was observed in April–May (up to + 0.1 gCH4·m-2·day-1), then a rapid decrease in the FCH4 value with the groundwater level falling to values close to those of winter and an irregular appearance of elevated FCH4 values in the period from June to November.