|
| | | Linking holocene carbon accumulation patterns to peat fire occurrence in boreal bogs, northern Quebec, Canada
Simon van Bellen1, Michelle Garneau2, Yves Bergeron3
1 GEOTOP / Institute of Environmental Science, Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville, Montreal, Qc, H3C 3P8, Canada (van_bellen.simon@courrier.uqam.ca)
2 GEOTOP / Department of Geography, Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville, Montreal, Qc, H3C 3P8, Canada
3 NSERC UQAT/UQAM chair in sustainable forest management, Université du Québec en Abitibi-Témiscamingue, 445 boul. de l'Université, Rouyn-Noranda, Qc, J9X 5E4, Canada
In order to improve the comprehension of peatland carbon dynamics and the possible influence of fire occurrence, three ombrotrophic peatlands of the James Bay region were studied. In the boreal region, fire is a major forest disturbance factor with a mean frequency of 1 event every 100 years. It is hypothesized that fires are less frequent in eastern Canadian peatlands than those of western continental Canada due to the general absence of trees. In each studied bog, a core in the deepest section and 8 cores at short transects along the forest/peatland gradient were sampled. AMS 14C dating and loss-on-ignition analyses were used to determine peat and carbon accumulation rates. Past fire occurrence was estimated using macro-charcoal analyses on the shallow cores. In addition, plant macrofossil and testate amoebae analyses were performed on the central cores in order to reconstruct vegetation succession linked to water table fluctuations (Booth, 2008). Results show mean LORCA of 15.2 g m-2 y-1, varying from 10.4 to 22.8 g m-2 y-1. A general decline in carbon accumulation rate started around 4000 cal BP with the lowest values between 2200 and 700 cal BP. This period is also characterized by an increasing concentration of macro-charcoal, indicating peat combustion or fire events near the peatland. However, plant macrofossil analyses performed at 1-cm interval failed to identify important changes in vegetation assemblages in horizons where charcoal shows maximum values. This can suggest that burning was not local or that burning was not intense enough to induce significant changes in vegetation. The plant macrofossil and testate amoebae reconstructions show a long-term rise in water tables and an increased abundance of Cyperaceae and lawn/hollow Sphagnum spp. since 2600 cal BP. This paleoenvironmental shift can be associated to the Neoglacial cooling which was characterized by year-round cooler and wetter winter conditions with a more frequent intrusion of unstable, dry air masses during the fire season (Carcaillet and Richard, 2000).
Reconstructed carbon and charcoal accumulation rates from one core show low C accumulation rates between 2200 and 500 cal BP. Charcoal is abundant during the same period. As a direct link could not be established, an allogenic factor, e.g. climate, may have driven both patterns.
Booth, R. K. 2008. Testate amoebae as proxies for mean annual water-table depth in Sphagnum-dominated peatlands of North America. Journal of Quaternary Science 23, 43-57.
Carcaillet, C. and Richard, P. J. H. 2000. Holocene changes in seasonal precipitation highlighted by fire incidence in eastern Canada. Climate Dynamics 16, 549-559.
Cliquer ici pour visualiser le poster
Retour à l'index des résumés |
|  |
|
| |
