High nitrous oxide production from thawing permafrost

Abstract

The impact of thawing permafrost on the nitrogen cycle is uncertain. Laboratory experiments using permafrost cores from northeast Greenland reveal that rewetting of thawed permafrost increases nitrous oxide production over 20-fold. Permafrost soils contain nearly twice as much carbon as the atmosphere1. When these soils thaw, large quantities of carbon are lost, mainly in the form of methane and carbon dioxide1,2,3,4,5,6,7,8,9. In contrast, thawing is thought to have little impact on nitrous oxide emissions, which remain minimal following the summer thaw4. Here, we examined the impact of thawing on nitrous oxide production in permafrost cores collected from a heath site and a wetland site in Zackenberg, Greenland. Rates of nitrous oxide production in the heath soil were minimal, regardless of the hydrological conditions. Although rates of nitrous oxide production in the wetland soil were low following thawing, averaging 1.37 μg N h−1 kg−1, they were 18 μg N h−1 kg−1 for permafrost samples following thawing, drainage and rewetting with the original meltwater. We show that 31% of the nitrous oxide produced after thawing and rewetting a 10-cm permafrost core—equivalent to 34 mg N m−2 d−1—was released to the atmosphere; this is equivalent to daily nitrous oxide emissions from tropical forests on a mean annual basis 10. Measurements of nitrous oxide production in permafrost samples from five additional wetland sites in the high Arctic indicate that the rates of nitrous oxide production observed in the Zackenberg soils may be in the low range.