The peat bog’s age



The process begun in order to create an ecological reserve in the Grande plée Bleue incited in 2008 the Quebec department of Sustainable Development, Environment and Parks to mandate, as a first step, the department of Geography and the Laval University Centre d’études nordiques (Northern Studies Center) in Québec to carry out a research. The following text is a simplifying summary of the two reports produced by the team of searchers following the two research periods done on field and in laboratory. Besides, we invite you to read both reports revealing with details the results of this research; to do so, just click on the tab DOCUMENTATION and select the two titles. We must remind us that 80% of the peat bogs existing before European colonization vanished or have been badly perturbed, that is giving to the Grande plée Bleue such an importance in matter of conservation, education and scientific knowledge.


Picture by Jean-Paul DOYON

Picture by Jean-Paul DOYON


First report produced by Martin LAVOIE and Élisabeth C. ROBERT, May 2009:


Étude paléoécologique de la tourbière de la Grande plée Bleue
(Paleoecological study of the Grande plée Bleue peat bog)


The mandate received from the Department was to carry out a paleoecological* study, more precisely to reconstitute the different steps of development from its very beginning in a specific part of the peat bog.

The first visit on the site took place in June and the next one in August 2008. The area previously chosen was located in a part of the lower flat land (platiere) presumably older, near the centre and structured by ponds, therefore closer to the original point where the peat bog first appeared.

Two profiles (GPB-1 and GPB-2) 30 cm distant from each other have been done using the core drill sampling technique with segments of 50 cm, alternating in two holes perforated at a distance of 10 cm for each profile. A total of 63 levels have been analyzed.

The different layers of peat noted are: wood and herbaceous peat, wood and sphagnum peat, herbaceous and sphagnum peat, sphagnum peat, sphagnum and wood peat. One of the characteristics of a peat bog is the organic residues preservation on a long term because of a scarce oxidation due to the air rarity.

The vegetal and fossils samples (macroremains) can be identified and counted and their laboratory analysis helps to know the age of the bog, its very beginning and growth (dynamic), at least in the samplings proximity. A core drill sampling reaching a depth of 450 cm revealed a date back to 8 340 years and 3 main periods dividing the peat bog development.

Zone I: depth of450-438 cm, dated from 8 340 and 8 190 years before today and that we can identify as belonging to the initial forest, existing during a short period of time (around 150 years), though already in a bog formation process, 8 300 years ago. This forest is constituted with balsam fir, white birch, tamarack and black spruce.

Zone II: depth of 438-420 cm, dated from 8 190 and 7 890 years before today, a transition period while the initial forest characterized by balsam fir and birch disappeared when the tamarack and the black spruce still exist.

Zone III: depth of 420-0 cm, a period of 7 890 years before today till now, with an ombrotrophic peat bog, subdivided in 7 strata (layers) including the acrotelm.

The evidences made at the end of this first study analysis help to deduce that the Grande plée Bleue have been formed to the detriment of the original forest and in a relative short period of time after the retirement of the interior sea, made with the melting ice cover that began at the end of the icy period, about 10 000 years ago.
The present peat bog could actually be the merging of several bog areas to form a single one during its evolution. Another conclusion was that the bog evolution have not been determined by climatic events (exogenous) but rather in an autogenous process (by itself), by spatial progression, and that the ponds would have been formed about 1 000 years ago.

Yet, another study was necessary to be able to confirm the first conclusions and new hypothesis.



Second report produced by Martin LAVOIE, Élisabeth C. ROBERT and Julien COLPRON-TREMBLAY, August 2010:


Étude paléoécologique de la tourbière de la Grande plée Bleue – Origine et mode de formation
(Paleoecological study of the Grande plée Bleue peat bog – Origin and type of formation)

The same methodology as the one adopted for the first study have been used for this one. The first sampling site revealing the presence of an ancient forest, it was indicating that the very starting point of the peat bog have not been reached yet; therefore, the sampling had to be located closer to the oldest site of the bog birth, near the limits of the ponds, in order to obtain a more precise date. Samples have then been taken in July, August and October 2009 in a point identified as GPB-3. We must remember that the ombrotrophic peat bogs generally take form in small depressions badly drained. Segments having a length of 50 cm have been taken in holes with a depth of 244 to 395 cm and 37 samples were collected in the 3 zones characterizing the bog different periods of evolution. The age confirmed in laboratory for the first deposit on the sedimentary layer after the retirement of the Goldthwait Sea was 9 460 years before today.

Zone I: From the basis made of clay sediments and characterized by dominating herbaceous species; with a probable not very deep pond surrounded by willows and near a forest of balsam fir and white birch, existing during a short period of 3 centuries.

Zone II: The poor minerotrophic peat bog, at a depth of 383—370 cm, between 9 130 and 8 360 years before today.

Zone III: The ombrotrophic peat bog, at a depth of 370-250 cm, between 8 360 years ago and now.

This second sampling then confirmed the old age of the peat bog, older than the other bogs previously studied. The spatial growth of the Grande plée Bleue would have followed the model showing a vertical and lateral development, starting, or from a single original point, or from several points that met together.

This peat bog has other very particular characteristics: the quick installation of ombrotrophic conditions, the stability on a long period of time of its flora and the fact that it shelters an exceptional number of ponds. We cannot though assert at which speed growth and when all these ponds took shape, more studies in this field would be innovating.





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