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Notes
- Abstract:
- Coastal wetlands, which are comprised of marshes, swamps, mangroves and other coastal plant communities, provide a large number of goods and services that contribute to the economic welfare of the local and global communities (Millennium Ecosystem Assessment, 2005). Examples of ecosystem services include the protection of shorelines from erosion, storm buffering, sediment retention, water quality maintenance, nutrient recycling, preservation of biodiversity, provision of natural environmental amenities, climate regulation, carbon sequestration, as well as cultural heritage and spiritual benefits (Larson et al., 1989; Barbier, 1991; Williams, 1990; Barbier et al., 1997; Brouwer et al., 1999; Woodward and Wui, 2001; McLeod et al., 2005; Brander et al., 2006). However, coastal wetlands are declining rapidly. Recent estimates indicate that approximately 1% of the global coastal wetland stock was lost each year in the late 20th century (Nicholls, 2004; Hoozemans et al., 1993).
The causes of wetland loss are numerous and often complex.5 The rapid loss of the global coastal wetland stock in the 20th century was primarily caused by direct land reclamation. While significant losses due to human actions are likely to continue in the future, it is projected that stresses on wetland areas may be further aggravated in the 21st century due to climate change. Wetlands face a number of hazards including rise in sea-level, increased atmospheric concentration of carbon dioxide, rise in air and water temperature, and changes in the frequency and the intensity of precipitation and storm patterns (Alongi, 2008).
Among these various natural threats of a changing climate, the threat posed by the rise in sea level has received increased attention (Titus, 1988; Hoozemans et al., 1993; Nicholls et al., 1999; Nicholls, 2004; Alongi, 2008).6 In combination with human activities, it is estimated that a 1 m global-mean sea level rise (SLR) could threaten half of the world’s coastal wetlands, which are designated as wetlands of international importance, while those that survive could be substantially changed (Hoozemans et al., 1993; Nicholls et al., 1999).
Since periodic flooding is the essential characteristic of coastal wetlands, sea-level rise (henceforth SLR) can disrupt wetlands in three significant ways: inundation, erosion, and salt water intrusion. The natural impact of SLR causes coastal wetlands to migrate to upland areas. The net change in the area of total wetlands depends on the slopes of the wetlands and characteristics of these areas. If the land has a constant slope all the way through the wetlands and the upland areas, then the area lost to wetlands drowning in the sea may be equal to the area acquired by the landward encroachment of high tides.7 If the slope above is steeper than the wetlands, then the SLR causes a net loss of wetland area. However, wetland migration is only possible if the adjacent upland areas are not developed, otherwise all the wetlands may be lost (Titus, 1988).
Understanding the impact of SLR on coastal wetlands must therefore take into account factors that affect the ecological balance of the wetland ecosystem such as the history of sea levels in regard to the development of coastal gradients, relative geomorphic and sedimentologic homogeneity of the coast, the coastal processes including the tidal range and its stability, the availability of fresh water and sediment, and the salinity of soil and groundwater (Belperio,
1993; Semeniuk, 1994; Blasco et al., 1996; Alongi, 2008). Even though location-specific studies
are needed to define the specific details, experts and scientists agree that adaptation of
wetlands to future sea-level rise depends on its success in landward progression and is
conditioned by the availability of adequate and suitable space for expansion/ migration, and a
rate of sea level rise that is not greater than the rate at which wetlands can migrate. ( English )
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