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Holocene dynamics in subarctic peat plateaus of west-central Canada: Vegetation succession, peat accumulation and permafrost history
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Dynamics in vegetation, permafrost and peat and net carbon accumulation rates throughout the Holocene have been studied in two subarctic peat plateaus of west-central Canada through plant macrofossil analysis, geochemical analyses and AMS radiocarbon dating. Peatland formation at the studied sites began around 6600-5900 cal yr BP as a result of paludification of upland forests. Permafrost aggradation probably occurred 5600-4500 cal yr BP when Sphagnum fuscum became established and rootlet layers started to appear. Alternating layers of Sphagnum fuscum and rootlet peat throughout most of the peat profiles are indicating relatively dry surface conditions, suggesting that permafrost conditions have remained stable since the peat plateau stages were initiated. Local fires have occurred in the peatlands, but most fires did not cause degradation of the permafrost. However, lower peat and net carbon accumulation rates are recorded from rootlet layers containing charcoal. The long-term peat and net carbon accumulation rates for both studied peat profiles are 0,30-0,31 mm/yr and 12,5-12,7 gC/m2yr. Accumulation rates are variable depending on peat plateau stage. Peat accumulation rates are in general 4-5 times higher in S. fuscum than in rootlet stages, and net carbon accumulation rates are 3-4 times higher. Therefore even though Sphagnum peat makes up a majority of the peat profile depth, rootlet peat stages can represent most of the time since the peatland was initiated. The gross stratigraphy and plant macrofossil analyses show that there have been no wet phases, indicating permafrost collapse, since the peat plateau stages were initiated. This suggests that subarctic peat plateaus with alternating Sphagnum fuscum and rootlet peat layers have been acting as long-term net carbon sinks, accumulating carbon which has been incorporated into the permafrost, throughout most of the Holocene. High and stable carbon/nitrogen ratios throughout most of the profiles suggest that decomposition has not occurred in the perennially frozen peat. Since the peat plateaus are characterized by no decay in the permafrost and dry surface conditions, methane emissions are negligible from these ecosystems. In a future warmer climate carbon that has been stored under permafrost conditions can be remobilized. The warming may cause drier surface conditions resulting in increased emissions of carbon dioxide or, alternatively, permafrost collapse resulting in wetter surface conditions and increased methane emissions.

Place, publisher, year, edition, pages
Stockholm: Institutionen för naturgeografi och kvartärgeologi , 2007. , 70 p.
Keyword [en]
peatlands, permafrost, carbon accumulation, fire, subarctic, Holocene
National Category
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-7299OAI: oai:DiVA.org:su-7299DiVA: diva2:198010
Supervisors
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2010-08-18Bibliographically approved
List of papers
1. Long-term stability of permafrost in subarctic peat plateaus, west-central Canada
Open this publication in new window or tab >>Long-term stability of permafrost in subarctic peat plateaus, west-central Canada
2008 (English)In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 18, no 4, 589-601 p.Article in journal (Refereed) Published
Abstract [en]

Long-term vegetation succession and permafrost dynamics in subarctic peat plateaus of west-central Canada have been studied through detailed plant macrofossil analysis and extensive AMS radiocarbon dating of two peat profiles. Peatland inception at these sites occurred around 5800-5100 yr BP (6600-5900 cal. BP) as a result of paludification of upland forests. At the northern peat plateau site, located in the continuous permafrost zone, palaeobotanical evidence suggests that permafrost was already present under the forested upland prior to peatland development. Paludification was initiated by permafrost collapse, but re-aggradation of permafrost occurred soon after peatland inception. At the southern site, located in the discontinuous permafrost zone, the aggradation of permafrost occurred soon after peatland inception. In the peat plateaus, permafrost conditions have remained very stable until present. Sphagnum fuscum-dominated stages have alternated with more xerophytic communities characterized by ericaceous shrubs. Local peat fires have occurred, but most of these did not cause degradation of the permafrost. Starting from 2800-1100 yr BP (2900-1000 cal. BP) consistently dry surface conditions have prevailed, possibly related to continued frost heave or nearby polygon crack formation.

Keyword
peatlands, peat plateau, permafrost, fire, macrofossils, vegetation succession, radiocarbon dating, subarctic, Canada, Holocene
Identifiers
urn:nbn:se:su:diva-16208 (URN)10.1177/0959683608089658 (DOI)000256882300008 ()
Available from: 2009-01-26 Created: 2009-01-26 Last updated: 2017-12-13Bibliographically approved
2. Holocene peat growth and decay dynamics in sub-arctic peat plateaus, west-central Canada
Open this publication in new window or tab >>Holocene peat growth and decay dynamics in sub-arctic peat plateaus, west-central Canada
2009 (English)In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 38, no 1, 13-24 p.Article in journal (Refereed) Published
Abstract [en]

Peat and net carbon accumulation rates in two sub-arctic peat plateaus of west-central Canada have been studied through geochemical analyses and accelerator mass spectrometry (AMS) radiocarbon dating. The peatland sites started to develop around 6600–5900 cal. yr BP and the peat plateau stages are characterized by Sphagnum fuscum peat alternating with rootlet layers. The long-term peat and net carbon accumulation rates for both profiles are 0.30–0.31 mm/yr and 12.5–12.7 gC/m2yr, respectively. These values reflect very slow peat accumulation (0.04–0.09 mm/yr) and net carbon accumulation (3.7–5.2 gC/m2yr) in the top rootlet layers. Extensive AMS radiocarbon dating of one profile shows that accumulation rates are variable depending on peat plateau stage. Peat accumulation rates are up to six times higher and net carbon accumulation rates up to four times higher in S. fuscum than in rootlet stages. Local fires represented by charcoal remains in some of the rootlet layers result in very low accumulation rates. High C/N ratios throughout most of the peat profiles suggest low degrees of decomposition due to stable permafrost conditions. Hence, original peat accretion has remained largely unaltered, except in the initial stages of peatland development when permafrost was not yet present.

Identifiers
urn:nbn:se:su:diva-18787 (URN)10.1111/j.1502-3885.2008.00048.x (DOI)000262635900002 ()
Available from: 2009-02-03 Created: 2009-02-03 Last updated: 2017-12-13Bibliographically approved

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