Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw

• Published in: Global change biology Vol. 25; no. 5; pp. 1746 - 1764
• Main Authors: Voigt, Carolina, Marushchak, Maija E., Mastepanov, Mikhail, Lamprecht, Richard E., Christensen, Torben R., Dorodnikov, Maxim, Jackowicz‐Korczyński, Marcin, Lindgren, Amelie, Lohila, Annalea, Nykänen, Hannu, Oinonen, Markku, Oksanen, Timo, Palonen, Vesa, Treat, Claire C., Martikainen, Pertti J., Biasi, Christina
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.05.2019
• Subjects: Arctic region; Atmosphere; Biogeochemistry; Carbon 14; Carbon dioxide; Carbon dioxide emissions; carbon sinks; Climate Research; Climate Science; climate warming; CO2; Curve fitting; Dissolved organic carbon; Dynamics; Earth and Related Environmental Sciences; Ecosystems; Environmental monitoring; Gases; Geovetenskap och miljövetenskap; Geovetenskap och relaterad miljövetenskap; Greenhouse effect; greenhouse gas; greenhouse gas emissions; Greenhouse gases; Groundwater table; Klimatforskning; Klimatvetenskap; Melting; mesocosm; Mesocosms; Methane; methane oxidation; monitoring; Natural Sciences; Naturvetenskap; Oxidation; Peat; Peatlands; Permafrost; Permafrost thaws; permafrost-carbon-feedback; Radiocarbon dating; Radiometric dating; radionuclides; Soil; Soil dynamics; Soil layers; Stocks; Thawing; Vegetation; Water table; Arctic region; permafrost-carbon-feedback; CO2; climate warming; mesocosm; greenhouse gas; methane oxidation
• ISSN: 1354-1013; 1365-2486; 1365-2486
• DOI: 10.1111/gcb.14574

Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long‐term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4) to the atmosphere, but how much, at which time‐span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant–soil systems (mesocosms) allowed us to simulate permafrost thaw under near‐natural conditions. We monitored GHG flux dynamics via high‐resolution flow‐through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10–15 cm of permafrost under dry conditions increased CO2 emissions to the atmosphere (without vegetation: 0.74 ± 0.49 vs. 0.84 ± 0.60 g CO2–C m−2 day−1; with vegetation: 1.20 ± 0.50 vs. 1.32 ± 0.60 g CO2–C m−2 day−1, mean ± SD, pre‐ and post‐thaw, respectively). Radiocarbon dating (14C) of respired CO2, supported by an independent curve‐fitting approach, showed a clear contribution (9%–27%) of old carbon to this enhanced post‐thaw CO2 flux. Elevated concentrations of CO2, CH4, and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH4 in the peat column, however, prevented CH4 release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost–carbon feedback by adding to the atmospheric CO2 burden post‐thaw. However, as long as the water table remains low, our results reveal a strong CH4 sink capacity in these types of Arctic ecosystems pre‐ and post‐thaw, with the potential to compensate part of the permafrost CO2 losses over longer timescales. Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long‐term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4) to the atmosphere, but how much, at which time‐span and as which gaseous carbon species is still highly uncertain. A novel experimental approach using intact plant–soil systems (mesocosms) allowed us to simulate permafrost thaw under near‐natural conditions. We show here that peatlands may strengthen the permafrost–carbon feedback by adding to the atmospheric CO2 burden post‐thaw.