Download Evolution of high marshes in the St. Lawrence freshwater

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EVOLUTION OF HIGH MARSHES IN THE ST. LAWRENCE FRESHWATER
ESTUARY AND PROTECTION STRATEGIES FOR AT-RISK SPECIES
WITHIN A CLIMATE CHANGE PERSPECTIVE
VULNERABILITIES, IMPACTS AND ADAPTATION
PROGRAM : ECOBIOCC
PROJECT START AND END DATES
JUNE 2011 • OCTOBER 2013
INFORMATION
Robert Siron
[email protected]
514-282-6464
www.ouranos.ca
PRINCIPAL INVESTIGATOR
CONTEXT
Photo : Najat Bhiry, Université Laval
The tidal marshes of the St. Lawrence River freshwater estuary are home to various
endemic plants, some of which are currently at risk. Among these plants, three are
designated as endangered in Quebec and are subject to conservation plans, i.e. Victorin's
water hemlock, Parker's pipewort and Victorin's gentian. Limited in scope, the habitat of
these species on the banks of the St. Lawrence is subject to the phenomena of erosion
and submersion during strong storms. Climate change, both under way and anticipated,
could accentuate these phenomena and thus habitat loss for these species. To date, the
impact and, above all, the causes of these phenomena in the freshwater estuary remain
poorly documented. This is thus the first detailed study on this topic. The marshes under
study were selected in order to be representative of various sectors of the freshwater
estuary. From upstream to downstream, they are the marshes of
Saint-Augustin-de-Desmaures, Beaumont, Château-Richer and Isle-aux-Grues.
Najat Bhiry,
Université Laval
OTHER PARTICIPANTS
• Environment Canada
• Ministère du Développement durable, de
l’Environnement, de la Faune et des
Parcs
FUNDED BY
OBJECTIVES
www.ouranos.ca
• Document the dynamics of the marshes under study.
• Identify the primary factors of their evolution in order to enable the MDDEFP to adapt
its preservation strategies for endangered or vulnerable species and its biodiversity
conservation strategies for the sectors under study.
METHODOLOGY
• Multidate analyses of aerial photographs and orthophotographs;
• Recurring geomorphological surveys;
• Vegetation surveys and habitat characterizations for the three endangered plant
species under study;
• Analyses of photographic, meteorological and tidal databases;
• Bivariate statistical analyses aimed at documenting links between the variables under
study and erosion, and thus identifying the factor(s) responsible for high marsh erosion.
REFERENCE
Bhiry N. et al. 2013 Évolution des hauts marais de l’estuaire d’eau douce du Saint-Laurent
et stratégies de protection des espèces en situation précaire dans une perspective de
changements climatiques. Final report for Ouranos.
http://www.ouranos.ca/media/publication/241_RapportBhiry2013.pdf
See overleaf for
results.
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EVOLUTION OF HIGH MARSHES IN THE ST. LAWRENCE FRESHWATER
ESTUARY AND PROTECTION STRATEGIES FOR AT-RISK SPECIES
WITHIN A CLIMATE CHANGE PERSPECTIVE
RESULTS
The primary results demonstrate that the erosion of the high
marshes in the freshwater estuary is approximately several
cm/month in all sites and was caused by various phenomena.
During the project, two phenomena caused a more significant
decline of the anti-erosion embankments. One phenomenon
corresponds to hurricane Irene, which was characterized by
strong winds (> 62 km/h) and abundant precipitation (80
mm). The second phenomenon relates to the "ice-out" in April
2012, which contributed to the erosion of the high marshes by
ripping out rafts of vegetation. During the summer and
autumn of 2012, the decline of the embankment was less
significant than in 2011, probably due to more stable and less
rainy meteorological conditions. In addition, an analysis of
historical changes to the sites under study over a 50-year
period revealed a slight decrease in the surface area of the
upper schorre, i.e. the upper intertidal area of the saltmarsh,
generally accompanied by an increase in the surface area of
the lower schorre. In three of the four sites, a lateral inland
displacement of the upper schorre was also observed. In
addition, two of the three endangered plant species targeted
by the project appear more vulnerable to high marsh erosion,
i.e. Victorin's gentian and Victorin's waterhemlock, which
grow in proximity to or on both sides of the anti-erosion
embankment.
Integrating the results by means of statistical analyses also
made it possible to establish significant links between the
"freeze-up" duration, embankment height, submersion
frequency and embankment erosion. Similarly, the results
demonstrate that the combination and simultaneity of certain
key climate variables (e.g. the cumulative effect of wind
strength and intensity, precipitation and high water levels)
may lead to significant erosion of the embankment (Figure 1).
Si/Ss : Lower schorre/upper schorre;
Sg/sf : Coarse sediments/fine sediments.
The variables in bold were identified as the primary
variables exacerbating erosion of the high-marsh
embankment. The accompanying arrows and their number
indicate the observed trends: Increased erosion, 
decreased erosion and,  no trend.
The thick yellow arrows illustrate how the combination and
simultaneity of certain variables may lead to erosion of the
embankment.
Figure 1. Conceptual model showing the principal documented geomorphological, ecological (plant-related),
meteorological and hydrodynamic variables with a potential influence on erosion in the high marshes of the St.
Lawrence freshwater estuary.
BENEFITS FOR ADAPTATION
This project made it possible to:
 During the selection of the priority sites requiring protection in connection with the review of the MDDEFP's
endangered species conservation plans, underscore the importance of taking into account the surrounding
environments and characteristics due to which certain marshes are currently less affected by erosion, in order to
protect endangered marshes.
 Provide important information, thereby giving specialists better tools with which to model marsh evolution based on
climate change with a view to protecting at-risk environments.
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