Long-term spatial C accumulation patterns in ombrotrophic peatlands of the Eastmain region, Quebec, Canada

Simon van Bellen, Ph.D. student

Chaire de recherche DÉCLIQUE1 / Institut des Sciences de l’Environnement and GEOTOP
Université du Québec à Montréal, 201 Avenue Président-Kennedy, Montréal, Qc, H2X 3Y7,
van_bellen.simon@courrier.uqam.ca

Pierre-Luc Dallaire, Master student

Chaire de recherche DÉCLIQUE / Département de Géographie and GEOTOP, Université du
Québec à Montréal, 201 Avenue Président-Kennedy, Montréal, Qc, H2X 3Y7

Michelle Garneau, Professor

Chaire de recherche DÉCLIQUE / Département de Géographie and GEOTOP, Université du
Québec à Montréal, 201 Avenue Président-Kennedy, Montréal, Qc, H2X 3Y7,

1 Chaire DÉCLIQUE (Dynamique des Écosytèmes tourbeux et changements CLImatiQUEs)

Besides excellent archives of environmental change, northern ombrotrophic peatlands
constitute an important global stock of organic carbon (C). We aim to reconstruct Holocene
rates of C accumulation linked to paleoenvironmental changes focused on fire events and
hydroclimatic variations. The three studied mires (1.7-2.7 km2) are located in the Eastmain
region (James Bay) around 52ºN. As forest fires are frequent in boreal Quebec, recurrent
burning may have affected long-term peat C accumulation. We hypothesize that Quebec
boreal peatlands have been less vulnerable to burning than the forested mires of western
Canada because of their wetness and unforested vegetation cover.

Reconstructed Holocene C accumulation rates were based on peat volume calculations
combined with age-depth models and peat density analyses. Peat volumes were obtained by
manual probing and ground-penetrating radar analyses, after which data interpolation using
ArcGIS was performed. Multiple cores were sampled and analyzed in laboratory to determine
the concentration of organic carbon in peat deposits and for reconstruction of vegetation
succession, water table fluctuations and charcoal influx as indicator of fire events.
Radiocarbon dating provided chronologies of the reconstructed changes.

Results show an important lateral expansion of peat in the early stages of Holocene peatland
development. Peat accumulation slowed down from around 4500 cal yrs BP in LLC bog,
whereas in MOS and STE bogs the onset of accumulation slowdown was delayed. A
comparable slowdown of carbon sequestration starting 4500 cal yrs BP has been reported
from peatlands in both eastern and western boreal Canada, possibly indirectly forced by
Neoglacial cooling.

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