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Over the next century society will be facing significant increases in temperature and sea-level, which pose a growing threat to low-lying coastal communities. To protect these communities, adaptation strategies are needed that will be sustainable not only in the immediate future, but throughout the next century and beyond. Recent events like the tsunami in Southeast Asia and Hurricane Katrina in Louisiana have illustrated how vulnerable and vastly under-prepared many coastal regions are for storm and natural disaster events. This paper uses the Bay of Fundy as a case study to explore the feasibility of using coastal salt marsh restoration as a tool to adapt to sea-level rise and mitigate climate change. In particular, the ability of marshes to self-adapt to changes in sea-level, their function as a buffer of coastal processes, their cost-effectiveness relative to traditional, static, man-made defences, and their ability to accumulate carbon are explored. Using these attributes of salt marshes, it may be possible to increase the protective capacity of a coastline by increasing the amount of salt marsh through restoration projects. The viability of salt marsh restoration projects in the Bay of Fundy is briefly considered.
Au cours des prochains siecles, la societe devra faire face a des augmentations significa-tives de la temperature et du niveau de la mer, ce qui constitue une menace grandissante pour les communautes etablies dans les zones cotieres de faible elevation. Afin de proteger ces communautes, les strategies d'adaptation qui seront deployees devront non seulement repondre aux besoins a court et moyen terme, mais offrir une solution durable bien au-dela du prochain siecle. Des evenements recents, tels que le tsunami dans le sud-est de I'Asie et I'ouragan Katrina en Louisiane, illustrent bien a quel point plusieurs regions cotieres sont vulnerables et nettement mal preparees pour faire face a des evenements tels que tempetes et catastrophes naturelles. Dans cet article, les auteurs presentent de la situation a la baie de Fundy comme etude de cas pour examiner la faisabilite de la restauration des marais salins cotiers comme outil d'adaptation a la hausse des niveaux de la mer et d'attenuation des effets des changements climatiques. On se penche plus precisement sur la capacite qu'ont les marais a s'adapter aux changements du niveau de la mer, a leur fonction de zone tampon dans les processus cotiers, a leur rapport cout-efficacite comparativement aux defenses artificielles, traditionnelles et statiques construites, enfin, on evalue leur capacite a accumuler le carbone. Par le biais des proprietes des marais salins, il est envisageable d'accroitre la capacite protectrice du littoral par I'augmentation du nombre de marais salins a I'aide de projets de restauration. La viabilite des projets de restauration des marais salins de la baie de Fundy est examinee brievement.
Keywords:
Climate change, sea-level rise, adaptation, mitigation, salt marsh restoration
Introduction
Climate change poses increasing risks to many low-lying coastal communities that are ill-prepared for the inevitable global rise in sea-level. Nearly two-thirds of the world's largest cities and 20% of global population inhabit coastal areas, and risks will be exacerbated in the future given projections of population growth rates above world averages along coasts (IPCC, 2001a). This situation, coupled with limited progress mitigating greenhouse gas (GHG) emissions, has increased the need for consideration of climate change adaptation strategies.
People have been coping with dynamic coastal processes for thousands of years; however, the 21st century will likely pose a unique and largely unprecedented challenge. Traditional strategies for adapting to sea-level rise have included the building of seawalls, dykes, and levees. We have already witnessed the catastrophic failure of a levee system in Louisiana during Hurricane Katrina (2005); storm events of this kind will prove even more devastating in light of rising sea levels in the future. The effect of the 2004 Asian Tsunami is further evidence of coastal community vulnerability to extreme weather events and natural disasters. Most recently (May 2008), Cyclone Nargis ravaged coastal Burma (also known as Myanmar) leaving an estimated 62,000 people dead or missing. The United Nations fears that the death toll is greater than 100,000 and media reports estimate that 2,000,000 survivors have seen their homes and farms washed away.
One lesson that can be derived from these recent disasters is the critical role of coastal wetlands in protecting inland areas. In the case of Louisiana, the loss of wetlands has been a longstanding trend. From 1978 to 2000, 77.4 [km.sup.2]/year were lost, and it is estimated that an additional 1,329 [km.sup.2] of wetland will be lost before 2050 (Barras et a/., 2003). The deterioration of Louisiana's wetlands has undermined their vital function of buffering storm surge and flood events, as evidenced by the height and destruction caused by Hurricane Katrina's storm surge (Day et al., 2007). In the case of the Asian Tsunami and Cyclone Nargis, evidence suggests that coastal communities with intact mangrove forests experienced significantly less destruction to human life and infrastructure than those without (Kathiresan and Rajendran, 2005; Vermaat and Thampanya, 2006; Anon, 2008).
The restoration of coastal ecosystems is not a new idea. Research and restoration of coastal wetlands has been ongoing on the Pacific Coast in California (Callaway and Zedler, 2004; Simenstad et al., 2006), on the Gulf Coast in the Mississippi Delta (Day Jr. et al., 2005; Simenstad et al., 2006), on the north eastern coast of the U.S.A. (Hinkle and Mitsch, 2005), and in the U.K. (French, 2006). This research has helped to inform the case for restoration in the Bay of Fundy; however, the Bay of Fundy presents unique conditions not seen in previous research. These include the significant role of ice in shaping marsh morphology (van Proosdij, 2006), the Bay's macrotidal regime, and the upper Bay's turbid waters with high amounts of suspended sediment (Ollerhead et al., 2005).
This paper explores the potential for using coastal wetlands as an adaptive tool for dealing with climate change and sea-level rise, with particular focus on salt marshes in the Bay of Fundy in the Canadian Maritimes (Figure 1). The potential impacts of climate change and sea-level rise are explored before considering the qualities of salt marshes that make them appropriate as an adaptation and mitigation strategy. Finally, the causes of global wetland loss are examined to better understand global trends before turning attention to the specific conditions of the Bay of Fundy that make it suitable for restoration projects.
[FIGURE 1 OMITTED]
Climate Change and Sea-Level Rise
The earth's is now warming as a direct result of significant increases in greenhouse gas (GHG) emissions that are of anthropogenic origin (Mehdi et al., 2006; IPCC, 2007). From 1850 - 1899 to 2001 - 2005 the global total temperature increase has been 0.76[degrees]C (IPCC, 2007). In Canada, the six warmest years on the instrumental record have been recorded during the past decade and trends of warming are expected to continue for decades to come (Mehdi et al, 2006; IPCC, 2007). The IPCC predicts an average global increase in surface temperature of between 1.1 and 6.4[degrees]C by 2099 depending on emissions (IPCC, 2007).
These forecasts have a variety of possible consequences, but among the most wide-reaching is a predicted rise in sea-level. The IPCC forecasts a global mean sea-level rise of between 18 and 59 cm by 2099 (IPCC, 2007). In addition to gradual succumbing of coast lands, the rise in sea-level will exacerbate impacts of storm events because of increasing heights of accompanying storm surges. The consequences of increasing mean sea-level and heightening storm surge events are a serious matter for many populated coastal areas of the world. For example, it was estimated by Titus et al. (1991) that if no action is taken, a 1 m rise in sea-level would result in the loss of over 36,000 [km.sup.2] of coastal land in the United States, much of which is densely populated.
One of the coastal, low-lying regions of particular concern in Canada is the Maritimes, situated along its east coast, where sea-level rise has both a eustatic and isostatic component. The eustatic component of sea-level rise is associated with the change in the volume of water in the ocean caused by thermal expansion and addition of melted glacier and ice cap water. In the Maritimes, the isostatic component of sea-level rise is caused by the lowering of coastal land relative to the sea due to glacial regression on the interior of the continent. The immense weight of ice-age glaciers had caused the coastal regions of the continent to bulge upward, but as this weight diminishes, it causes crustal subsidence (lowering of the land) in peripheral regions, including the Maritimes (McCulloch et al., 2002).
For example, Halifax, NS experienced a 35 cm rise in sea-level over the last century, 20 cm of that rise attributed to isostatic change and the remaining 15 cm attributed to eustatic change (McCulloch et al., 2002; Desplanque and Mossman, 2004). The potential rise in eustatic sea-level predicted by the IPCC over the next century (9 to 88 cm by 2100) coupled with continuing isostatic subsidence, paint an ominous picture for low lying regions of the Maritimes. A recent report from Environment Canada (2006), although focused on the Northumberland Strait, strongly suggests that relative sea-level in the area will rise by 50 to 60 cm ([+ or -] 35 cm) over the course of this century. Even these estimates are likely conservative given the real possibility of accelerated ice-sheet disintegration this century (Hansen, 2007). Either way, adaptation to sea level rise is both necessary and inevitable.
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