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› › › › › › › › › › › › › › › › › › COMPLETED PROJECT › › › › › › › › › › › › › › › › › 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. › › › › › › › › › › › › › › › › › › › COMPLETED PROJECT (CONT’D) › › › › › › › › › › › › 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. ››››››››››››››››››››››››››››››››