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TitleLimited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands
AuthorEstop-Aragonés, C; Cooper, M D A; Fisher, J P; Thierry, A; Garnett, M H; Charman, D J; Murton, J B; Phoenix, G K; Treharne, R; Sanderson, N K; Burn, C RORCID logo; Kokelj, S V; Wolfe, S AORCID logo; Lewkowicz, A G; Williams, M; Hartley, I P
SourceSoil Biology and Biochemistry vol. 118, 2017 p. 115-129, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20170304
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf; html
Subjectssurficial geology/geomorphology; geochemistry; environmental geology; hydrogeology; Nature and Environment; Science and Technology; permafrost; ground ice; peatlands; wetlands; carbon geochemistry; atmospheric geochemistry; sediment geochemistry; climate effects; modelling; carbon dioxide; methane; hydrologic environment; oxygen geochemistry; soil moisture; Climate change; cumulative effects; Atmospheric emissions; Greenhouse gases
Illustrationsschematic representations; tables; time series; bar graphs; plots
ProgramClimate Change Geoscience Permafrost
Released2017 12 24
AbstractPermafrost stores globally significant amounts of carbon (C) which may start to decompose and be released to the atmosphere in form of carbon dioxide (CO2) and methane (CH4) as global warming promotes extensive thaw. This permafrost carbon feedback to climate is currently considered to be the most important carbon-cycle feedback missing from climate models. Predicting the magnitude of the feedback requires a better understanding of how differences in environmental conditions post-thaw, particularly hydrological conditions, control the rate at which C is released to the atmosphere. In the sporadic and discontinuous permafrost regions of north-west Canada, we measured the rates and sources of C released from relatively undisturbed ecosystems, and compared these with forests experiencing thaw following wildfire (well-drained, oxic conditions) and collapsing peat plateau sites (water-logged, anoxic conditions). Using radiocarbon analyses, we detected substantial contributions of deep soil layers and/or previously-frozen sources in our well-drained sites. In contrast, no loss of previously-frozen C as CO2 was detected on average from collapsed peat plateaus regardless of time since thaw and despite the much larger stores of available C that were exposed. Furthermore, greater rates of new peat formation resulted in these soils becoming stronger C sinks and this greater rate of uptake appeared to compensate for a large proportion of the increase in CH4 emissions from the collapse wetlands. We conclude that in the ecosystems we studied, changes in soil moisture and oxygen availability may be even more important than previously predicted in determining the effect of permafrost thaw on ecosystem C balance and, thus, it is essential to monitor, and simulate accurately, regional changes in surface wetness.
Summary(Plain Language Summary, not published)
Permafrost stores globally significant amounts of carbon (C) which may start to decompose as global warming promotes thaw. However, the rate at which this C may be released to the atmosphere is poorly quantified in situ for different permafrost landscapes and disturbances. We used radiocarbon measurements to quantify previously-frozen C release as CO2 under two contrasting conditions: thawed soils exposed to 1) oxic conditions following fires in well-drained forests, and 2) anoxic conditions induced by the collapse of permafrost peat plateaus. No loss of previously-frozen C as CO2 was detected from collapsed peat plateaus, and greater rates of new peat formation resulted in net C uptake over decadal timescales. This contrasted with the potential for substantial contributions of permafrost sources to C loss in well-drained soils following fire. We conclude that changes in soil moisture and oxygen availability determine the effect of permafrost thaw on ecosystem C balance.

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