High release of strong greenhouse gas nitrous oxide found from northern peatlands at permafrost thaw

The study was published in the journal Proceedings of the National Academy of Sciences.

The authors used 16 mesocosms -- 80 cm long, intact peat columns with natural vegetation -- collected in a subarctic peatland in Finnish Lapland, to directly measure N₂O emissions from thawing permafrost during a 33-week experiment. For this experiment, the mesocosms were set up in a climate-controlled chamber, mimicking natural temperature, moisture and light conditions. Sequential top-down thawing of the mesocosms -- first of the seasonally thawing active layer and then the permafrost part -- allowed the authors to directly assess N₂O dynamics under near-field conditions.

The highest post-thaw emissions occurred from bare peat surfaces, which are commonly found in permafrost peatlands. For these surfaces, permafrost thaw resulted in a five-fold increase in emissions. The emission rates measured from these surfaces matched rates from tropical forest soils, the world's largest natural terrestrial N₂O source. The presence of vegetation cover in the mesocosms lowered thaw-induced N₂O emissions by approximately 90%. Water-logged conditions completely suppressed the N₂O emissions. A vulnerability assessment indicated that areas with high probability for N₂O emissions cover approximately one fourth of the Arctic. According to the authors, the Arctic N₂O budget will depend strongly on future moisture and vegetation changes. However, the authors state that the Arctic will likely become a substantial source of N₂O when permafrost thaws.

The study was carried out by researchers of the Department of Environmental and Biological Sciences at the University of Eastern Finland, in cooperation with colleagues from Lund University, Sweden.

The research was funded by the Nordic Center of Excellence DEFROST, and supported by the European Union project PAGE21, the Academy of Finland (project CryoN), and JPI Climate project COUP.