High nitrous oxide production from thawing permafrost

Permafrost soils contain nearly twice as much carbon as the atmosphere(1). When these soils thaw, large quantities of carbon are lost, mainly in the form of methane and carbon dioxide(1-9). In contrast, thawing is thought to have little impact on nitrous oxide emissions, which remain minimal following the summer thaw(4). 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 mu g Nh(-1) kg(-1), they were 18 mu g Nh(-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.