Linking peat fires presence to carbon accumulation patterns under Holocene climate regimes in boreal peat bogs of the James Bay region, Québec, Canada
Simon van Bellen1 Michelle Garneau2 Yves Bergeron3
1 GEOTOP/Institut des sciences de l’environnement, Université du Québec à Montréal, C.P. 8888, Succursale Centre-Ville, Montreal, Qc H3C 3P8
2 GEOTOP/Département de géographie, Université du Québec à Montréal, 201 Avenue Président- Kennedy, Montréal, Qc, H2X 3Y7
3 NSERC Chaire industrielle CRSNG – UQAT – UQAM en aménagement forestier durable, Université du Québec en Abitibi- Témiscamingue, 445 boul. de l'Université, Rouyn-Noranda, Qc, J9X 5E4
Holocene-scale changes in peat fire regimes of ombrotrophic peatlands are studied by the analysis of peat cores. The aim of the project is to improve the comprehension of peat fire regimes and their influence on peat carbon accumulation under long-term variations in climate.
The peat bogs studied (1.7-2.7 km2) form sensitive records of climate variations because of their dependence on precipitation as a water source. In each of the three bogs one central, deep core (3.0-5.0 m) and eight shallower (0.6-2.8 m) cores were taken, creating a total of 12 transects along a forest/peatland gradient. The analyses of macro-charcoal fragments (>355 μm) on lateral, shallow cores located along the forest/peatland gradient indicate variations in peat fire regimes. The combination of AMS radiocarbon dating and loss-on-ignition analyses results in global models of long-term rates of horizontal and vertical accumulation of peat. In addition, high-resolution records of past vegetation (plant macrofossil analysis) and paleo-water table depths (the application of a transfer function to past testate amoebae assemblages) from the deepest cores provide an image of variations in growth conditions.
Present results show a pattern of lower carbon accumulation rates starting between 4000 and 3000 BP with a gradual increase in bog water tables and an increase in herbaceous vegetation while drier Sphagnum moss species diminish. However, the high presence of large macro-charcoal fragments around the same period shows that the occurrence of peat fires may be the result of specific climate variables that may not be detectable by testate amoebae analyses nor plant macrofossil analyses. The preliminary results are in correspondence with previous research, that showed that wet depressions may well be more susceptible to local burning due to lower water retention abilities. Cooler and wetter conditions have previously been reported in Québec as the Neoglacial period that started around 3400 BP.
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