Reconstruction of ecohydrological and geochemical changes of the Lac-à-la-Tortue peatland complex, Shawinigan, Québec, in the context of postcolonial human activities

English Abstract:

Ombrotrophic peatlands (bogs) are valuable archives of human activities through atmospheric deposition and past ecohydrological variations. Aside from a native occupation for the past millennia, the Shawinigan region (Quebec) has mainly been affected in the last two centuries by iron mining, agriculture, forestry and industrial development. These types of disturbance can affect ecosystem functioning through changes in drainage, surface vegetation and biogeochemistry. The project aims to evaluate the impact of land use change on recent conditions of a 56 km²-peatland complex east of the city of Shawinigan, using vegetation, hydrology and elemental geochemistry reconstructions.

The peatland complex of Lac-à-la-Tortue, near Shawinigan, is one of the largest in southern Quebec. Four one meter long cores were sampled in open, ombrotrophic sections of the complex, which most likely developed in a paleo-channel of the St. Maurice River and expanded through paludification processes. Ecohydrological changes over the last millennium are reconstructed using loss-on-ignition, plant macrofossil and testate amoeba analyses. Major, trace and lithogenic elements are quantified to track changes in past human activities using ICP-AES and ICP-MS. Chronologies are based on ²¹⁰Pb and ¹⁴C dating.

Preliminary results show various peaks in ash content in the upper 50 cm of the cores, covering the last ~250 years. Given their age and their geochemical composition, these peaks may well be associated with postcolonial human activities.