The influence of local hydrology and seasonality on microbially-mediated methane emissions from a sloping alpine peatland

Recent findings revealed that alpine peatlands are more spatially extensive than previously assumed, reinforcing their importance for carbon storage in alpine ecosystems. Alpine peatlands share certain characteristics with northern peatlands: they have a short growing season, strong seasonality, and are snow-covered for 6 - 9 months per year. While arctic and boreal peatlands are known to emit large amounts of greenhouse gases (GHG), it is still largely unknown to which extent alpine peatlands show different GHG dynamics under climate change and how this links to abiotic and biotic differences like in radiation, soil properties, hydrology and plant community composition.  

In a multidisciplinary study, covering geohydrology, biogeochemistry, microbial ecology, and plant science, we investigate an alpine peatland in Vorarlberg, Austria located at 1670 m a.s.l. altitude on a slight slope of a plain surrounded by mountains up to 2416 m a.s.l. Methane flux measurements with static chambers showed a strong seasonal variation with a surprising switch from methane uptake in certain locations in spring to methane emissions in summer, potentially indicating a large variation in redox conditions with the seasons due to changes in the hydrology. In winter, when the area is covered by >1 m of snow, the sampled alpine peatland remains partly uncovered due to the continuous input of 5°C spring water. This creates a unique environment in which microbial carbon cycling continues at a higher rate than at nearby sites and leads to ongoing methane emissions throughout winter. The strong methane emissions in summer depended strongly on day (high) and night (lower) and short-term weather in the days before/during the measurements, with higher emissions during hot, dry periods compared to colder, rainy periods. In addition, we observed a very large spatial variation, even within the 1 m² scale. This large spatial variation in GHG emissions is supported by a large variation in soil organic carbon and total nitrogen content between locations within the peatland site, as well as variations in the plant community, and seems to be linked to groundwater flows which will be further analysed in upcoming field campaigns.