The positive net radiative greenhouse gas forcing of increasing methane emissions from a thawing boreal forest-wetland landscape.
At the southern margin of permafrost in North America, climate change causes widespread permafrost thaw. In boreal lowlands, thawing forested permafrost peat plateaus ('forest') lead to expansion of permafrost-free wetlands ('wetland'). Expanding wetland area with saturated and warmer organic soils is expected to increase landscape methane (CH4) emissions. Here, we quantify the thaw-induced increase in CH4emissions for a boreal forest-wetland landscape in the southern Taiga Plains, Canada, and evaluate its impact on net radiative forcing relative to potential long-term net carbon dioxide (CO2) exchange. Using nested wetland and landscape eddy covariance net CH4flux measurements in combination with flux footprint modeling, we find that landscape CH4emissions increase with increasing wetland-to-forest ratio. Landscape CH4emissions are most sensitive to this ratio during peak emission periods, when wetland soils are up to 10 °C warmer than forest soils. The cumulative growing season (May-October) wetland CH4emission of ~13 g CH4m-2is the dominating contribution to the landscape CH4emission of ~7 g CH4m-2. In contrast, forest contributions to landscape CH4emissions appear to be negligible. The rapid wetland expansion of 0.26 ± 0.05% yr-1in this region causes an estimated growing season increase of 0.034 ± 0.007 g CH4m-2yr-1in landscape CH4emissions. A long-term net CO2uptake of >200 g CO2m-2yr-1is required to offset the positive radiative forcing of increasing CH4emissions until the end of the 21st century as indicated by an atmospheric CH4and CO2concentration model. However, long-term apparent carbon accumulation rates in similar boreal forest-wetland landscapes and eddy covariance landscape net CO2flux measurements suggest a long-term net CO2uptake between 49 and 157 g CO2m-2yr-1. Thus, thaw-induced CH4emission increases likely exert a positive net radiative greenhouse gas forcing through the 21st century.
Département de Géographie, Université de Montréal & Centre d'études nordiques, 520 Chemin de la Côte Sainte-Catherine, Montréal, QC, H2V 2B8, Canada.
Manuel
M
Helbig
Department of Geography, University of Lethbridge, Lethbridge, AB, T1K 3M4, Canada.
Laura E
LE
Chasmer
Department of Geography, Swansea University, Singleton Park, Swansea, SA28PP, UK.
NatasCha
N
Kljun
Cold Regions Research Centre, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada.
William L
WL
Quinton
Water and Environmental Research Center, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA.|U.S. Geological Survey, Menlo Park, CA, 94025, USA.
Claire C
CC
Treat
Département de Géographie, Université de Montréal & Centre d'études nordiques, 520 Chemin de la Côte Sainte-Catherine, Montréal, QC, H2V 2B8, Canada.
Oliver
O
Sonnentag
D002170:Canada; D002245:Carbon Dioxide; D057231:Climate Change; D008697:Methane; D009656:North America; D012987:Soil / Q000737:chemistry; D066188:Taiga; D053833:Wetlands
D012987:Soil; D002245:Carbon Dioxide; D008697:Methane
boreal forest; carbon dioxide; climate change; eddy covariance; methane; radiative forcing; wetland