Geochemical tracers of recharge-discharge functions in southern Quebec
aquifer-peatland systems
Miryane Ferlatte1, Marie Larocque1, Vincent Cloutier2
1Université
du Québec à Montréal, Département des Sciences de la Terre
du Québec en Abitibi-Témiscamingue, Campus d’Amos,
Groupe de recherche sur les eaux souterraines
2Université
Abstract
In areas where peatlands are abundant, they are likely to play a significant role in the hydrological and
hydrogeological dynamics of a watershed. However, the processes behind aquifer-peatland interactions
are not well understood. The objective of this study was to identify geochemical tracers to be used by
catchment management authorities to assess the hydrogeological role of peatlands in southern Quebec,
hence promoting sustainable management of groundwater resources. Twelve peatland profiles
instrumented with piezometers were investigated in the Abitibi and Centre-du-Quebec regions of southern
Quebec. The two regions have contrasted climate, geology and geomorphology. Abitibi peatlands are
found on esker slopes while Centre-du-Quebec peatlands are depression wetlands. Variations of hydraulic
heads, as well as variations of inorganic and organic composition of water from the superficial aquifer,
peat pore water and groundwater from beneath the peatland suggest a variety of possible flow
connections: groundwater inflow from the superficial aquifer, lateral outflow of peat pore water to the
superficial aquifer and vertical peat pore water flow percolating down through the underlying mineral
sediments. Only limited indications of vertical groundwater from beneath the peatland have been
observed. The first component (PC1) of a principal component analysis is characterized by elements
typical of groundwater, and represents the primary control of the geochemical variation in peat pore water.
Total dissolved solids (TDS) are highly correlated with PC1 scores and indicate probable zones of
groundwater inflow through the peat at thresholds above ~14 mg/l. Diffusion calculation shows that the
diffusion process alone cannot explain the composition of most peat pore water samples. This is a strong
indication of a groundwater upward flow discharging from the mineral deposits beneath the peatland
(when measured concentrations are higher than simulated concentrations) or of a peat pore water
downward flow recharging the underlying mineral waters (when measured concentrations are lower than
simulated concentrations). This study shows that a majority of the studied peatlands are long-term storage
systems receiving lateral contributions from a superficial aquifer. Some peatlands provide water laterally to
the superficial aquifer, some receive groundwater vertically and some lose water to the underlying
deposits. All of these exchanges are important components in the sustainability of peatland hydrological
functions.
Keywords: peatlands, groundwater, geochemistry, hydrological functions, southern Quebec
Technical theme: Groundwater-Surface Water Interactions and Ecohydrology
1
miryanef@gmail.com, (514-987-3000, poste 1515)