Alpine peatlands: spatially and temporally complex ecosystems with year-round methane cycling activity

Peatlands are well-known emitters of methane. 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 methane dynamics. Furthermore, winter methane dynamics have rarely been studied. We therefore quantified the soil-atmosphere methane flux at an alpine peatland in Austria (1700 m a.s.l), with a focus on the spatial and temporal heterogeneity in this ecosystem. In summer, methane emissions were high (49 mg m 2 h -1 ), whereas in spring, shortly after snowmelt, both methane uptake and emissions were observed at different locations within the alpine peatland. In winter, a local snow-free patch persisted at the peatland due to the year-round influx of 5°C spring water. We compared the methane flux from this snow-free patch to another alpine peatland which also contained such a snow-free area and observed methane emissions at the one peatland (1.2 mg m 2 h -1 ) and methane uptake at the other (−0.06 mg m 2 h -1 ). The input of spring water in combination with the sloping nature of the peatlands resulted in a large spatial heterogeneity, likely as a result of the input of redox-active components such as sulfate by the spring water. The microbial community composition also suggested the presence of active sulfur, iron and methane cycling in the peat soil. Overall, our research shows that alpine peatlands are unique systems due to the year-round spring water throughput, altering biogeochemical cycles and creating local snow-free conditions, with implications for methane cycling.