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  • 1. Treat, Claire C.
    et al.
    Marushchak, Maija E.
    Voigt, Carolina
    Zhang, Yu
    Tan, Zeli
    Zhuang, Qianlai
    Virtanen, Tarmo A.
    Räsänen, Aleksi
    Biasi, Christina
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kaverin, Dmitry
    Miller, Paul A.
    Stendel, Martin
    Romanovsky, Vladimir
    Rivkin, Felix
    Martikainen, Pertti J.
    Shurpali, Narasinha J.
    Tundra landscape heterogeneity, not interannual variability, controls the decadal regional carbon balance in the Western Russian Arctic2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 11, p. 5188-5204Article in journal (Refereed)
    Abstract [en]

    Across the Arctic, the net ecosystem carbon (C) balance of tundra ecosystems is highly uncertain due to substantial temporal variability of C fluxes and to landscape heterogeneity. We modeled both carbon dioxide (CO2) and methane (CH4) fluxes for the dominant land cover types in a similar to 100-km(2) sub-Arctic tundra region in northeast European Russia for the period of 2006-2015 using process-based biogeochemical models. Modeled net annual CO2 fluxes ranged from --300 g C m(-2) year(-1) [net uptake] in a willow fen to 3 g Cm-2 year(-1) [net source] in dry lichen tundra. Modeled annual CH4 emissions ranged from -0.2 to 22.3 g Cm-2 year(-1) at a peat plateau site and a willow fen site, respectively. Interannual variability over the decade was relatively small (20%-25%) in comparison with variability among the land cover types (150%). Using high-resolution land cover classification, the region was a net sink of atmospheric CO2 across most land cover types but a net source of CH4 to the atmosphere due to high emissions from permafrost-free fens. Using a lower resolution for land cover classification resulted in a 20%-65% underestimation of regional CH4 flux relative to high-resolution classification and smaller (10%) overestimation of regional CO2 uptake due to the underestimation of wetland area by 60%. The relative fraction of uplands versus wetlands was key to determining the net regional C balance at this and other Arctic tundra sites because wetlands were hot spots for C cycling in Arctic tundra ecosystems.

  • 2. Voigt, Carolina
    et al.
    Marushchak, Maija E.
    Mastepanov, Mikhail
    Lamprecht, Richard E.
    Christensen, Torben R.
    Dorodnikov, Maxim
    Jackowicz-Korczynski, Marcin
    Lindgren, Amelie
    Stockholm University, Faculty of Science, Department of Physical Geography. Lund University, Sweden.
    Lohila, Annalea
    Nykänen, Hannu
    Oinonen, Markku
    Oksanen, Timo
    Palonen, Vesa
    Treat, Claire C.
    Martikainen, Pertti J.
    Biasi, Christina
    Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw2019In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 25, no 5, p. 1746-1764Article in journal (Refereed)
    Abstract [en]

    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 (C-14) 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.

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