Assess the impact of climate change on high marshes in the freshwater estuary and develop strategies for protecting species in precarious situations

Context and project description

The marshes along the river in the Québec City region shelter some 20 plant species in precarious situations that could be threatened by climate change. This includes the Victorin’s fringed gentian and Victorin’s water hemlock, two plants designated as threatened in Quebec that only grow in the freshwater and brackish estuary of the St. Lawrence. With several other species associated with that habitat, they could well pay the price of global warming, following a rise in water level, increased ice movement, and greater exposure to waves.

This project, which spanned a two-year period (2011-2012), helped provide a better understanding of the dynamics of the marshes of the St. Lawrence fresh-water estuary through an in-depth study of four sites. At each of those sites, a multi-date analysis of aerial photographs and orthophotos, a characterization of the vegetation and monthly geo-morphological surveys were carried out. The evolution of the high marsh was monitored using reference pegs placed at the foot of the erosional slope marking the boundary with the low marsh. Some meteorological data (precipitation, wind force and intensity, etc.) was also analyzed

Results

The main results show that erosion of the high marshes of the fresh-water estuary is around several centimeters per month at all sites and that it was caused by various phenomena, including tropical storm Irene, which featured strong winds (> 62 km/h) and heavy precipitation (80 mm). The second phenomenon is connected with the ice departure in April 2012, which contributed to the erosion of the high marsh by tearing up rafts of vegetation. The historical evolution of the sites under study highlighted a decrease in the surface area of the high marsh, typically accompanied by an increase in that of the low march. The marshes’ exposure to storm winds, the slope height, the vegetation density and the length of the freeze-up season are among the factors that appear to influence the erosion rate the most.

The results of these studies will provide possible solutions for developing strategies to protect species in precarious situations. For instance, we could place priority on sites that are best situated to resist the assault of the elements, or give preference to sectors where fairly large natural environments still exist above the shoreline to allow habitats to replenish. 

Consult the report in PDF format to learn more about this project:

Evolution of high marshes in the St. Lawrence freshwater estuary and protection strategies for at-risk species within a climate change perspective

Participating departments

Government of Canada

  • Environment and Climate Change Canada

Government of Quebec

  • Ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques
  • Fonds vert Québec-consortium Ouranos (PACC-26)

Other partner

  • Centre for Northern Studies, Université Laval