Year-round methane cycling activity in a European alpine peatland with large spatial and temporal variability

Abstract. Peatlands are well-known emitters of methane (CH₄). European alpine peatlands share certain characteristics with boreal peatlands, despite being located at temperate latitudes, such as a strong seasonality with snowfall in winter and a short summer and growing season. Unlike boreal peatlands, they experience relatively large temperature fluctuations between day and night and are more likely to be sloping. It is unknown how these factors affect CH₄ dynamics. Furthermore, winter CH₄ dynamics have rarely been studied. We quantified the soil-atmosphere CH₄ flux at an alpine peatland in Austria (1670 m a.s.l), with a focus on the spatial and temporal heterogeneity in this ecosystem. In summer, CH₄ emissions were high (0.7–206 mg m² h^-1), whereas in spring, shortly after snowmelt, both CH₄ uptake and emissions were observed at different locations within the alpine peatland (ranging from -4 mg m² h^-1 to 11 mg m² h^-1). In winter, a local snow-free patch persisted at the peatland due to the year-round influx of 5 °C spring water. Both CH₄ uptake and emission were observed in winter, with emissions also observed at snow-covered locations (fluxes ranging from -41 mg m² h^-1 to 6 mg m² h^-1). The spatial heterogeneity in summer was further investigated by high resolution chamber measurements and soil analyses of temperature, carbon and nitrogen content, and 16S rRNA analyses of the microbial community. These showed a grouping that likely resulted from the input of redox-active components by the spring water that entered the peatland in a non-uniform pattern, which was revealed by soil temperature measurements. Overall, our research shows that alpine peatlands are unique systems with complex spatial and temporal patterns, which have strong implications for soil microbiology and CH₄ cycling.