E-mail : yann.arlen-pouliot.1@ulaval.ca

Recent dynamics of structured peatlands in Québec's upper boreal forest
Supervisor :
Serge Payette  

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Several studies conducted in northern Québec indicate that 20th-century lake levels are higher than those of the preceding centuries due to an increase in precipitation following the Little Ice Age (Bégin, 2001, Quarternary Research; Payette & Delwaide, 2004, Ecological Monographs; Payette & Filion, 1993, Boreas). It is likely that this increase in precipitation has also elevated peatland water tables. This inference is supported by a phenomenon that is occurring in structured peatlands, called "aqualization", which describes a process in which peatland ponds increase in size and new ponds develop in depressions.  The growth of these ponds can destroy the patterned structure of the peatlands through the merging of small ponds. It is common to find subfossil wood of significant size buried in the peat or submerged in the ponds. These trees established during a less humid period and died due to the rise of the water table. The objectives of this research are: 1. to evaluate the spatial arrangement of ponds and strings within the structured peatlands, 2. to evaluate the recent changes in the accumulation rate of organic matter in the hummocks, hollows, and strings in relation to the changing precipitation regime, and 3. to determine the effects of climate and topography on the stratigraphy and lateral growth of structured peatlands. We are also dating subfossil wood,  obtained from the bottom of the ponds, which have been identified as trees on the historical aerial photographs. Tree growth rates, as well as the interdating of individuals, will be accomplished by counting and measuring the annual rings of the subfossil wood. Variations in the accumulation rate of the peat will be determined by dating tree seedlings, as the peat accumulation process gradually buries the stems of the seedlings allowing the accumulation rate to be measured. All of the seedlings originating from seeds within a 5 m wide longitudinal transect will be identified, georeferenced with a theodolite, and sampled. The position of the peatland surface will be marked on the sampled stem allowing the peat accumulation rate to be calculated for the duration of each seedling's life by counting annual rings. The stratigraphy of the peatland will be analyzed by obtaining peat cores every 25 m along a longitudinal transect,  as well as from cores obtained along one to three transversal transects. The description of the stratigraphy will includes the degree of decomposition, the color and vegetation composition of the organic matter, as well as the granulometry of the underlying inorganic sediments. Peat samples of 1 cm in thickness will be obtained from the base of the peatland and at 50 cm intervals along the core for 14C dating. Although we know that precipitation has increased over the last two centuries, more research is required in order to have a better understanding of the precipitation regime’s dynamics over the last several hundred, and if possible, several thousands of years, in northern Québec. Although Québec's northern peatlands are spatially important, their potential in the domain of paleohydrology have not yet been fully explored. Furthermore, our understanding of how these peatlands affect the hydrologic balance of a watershed such as the LaGrande hydroelectric complex is not complete. To our knowledge, no studies have evaluated the ecological impact of the increase in aquatic surface area of these peatlands.   Furthermore, the morphogenesis of the ponds and strings in the structured peatlands are still subject to debate  (Seppälä & Koutaniemi, 1985, Boreas).

Publication

Arlen-Pouliot, Y., Bhiry, N., 2005. Palaeoecology of a palsa and a filled thermokarst pond in a permafrost peatland, subarctic Québec, Canada. The Holocene, 15: 408-419.