Environmental Engineering Reference
In-Depth Information
8.6 Coastal Wetlands
Wetland is a generic term grouping together a wide range of inland, coastal and marine habitats that share
a number of common features (Dugan, 1990). A representative definition has been suggested by the RAMSAR
Wetland Convention (RAMSAR, www.ramsar.org): wetlands are “areas of marsh, fen, peatland or water,
whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish
or salt, including areas of marine water, the depth of which at low tide does not exceed six meters.”
Wetlands may be classified into 4 categories in terms of topography and geographic isolation: coastal
(including deltas, tidal marshes, and mangrove swamps), riverine (wetlands along rivers and streams),
wetlands associated with lakes, and inland wetlands. The coastal wetlands could be further classified into
12 sub-categories (RAMSAR, www.ramsar.org): permanent shallow marine waters, marine sub-tidal
aquatic beds, coral reefs, rocky marine shores, sand/shingle/pebble shores, estuarine waters, intertidal
mud/sand/salt flats, intertidal marshes, intertidal forested wetlands, coastal brackish/saline lagoons, coastal
freshwater lagoons, and Karst/subterranean hydrological systems.
World wide, approximately 50% of the wetlands have been destroyed during the past century, largely
due to human activities. Currently, the total global area of wetlands is estimated to be 2.9 million km 2
(Groombridge and Jenkins, 1998). Table 8.6 lists largest wetlands located along major river systems or
coastal wetlands on terrestrial habitats that have little topographic relief.
T able 8.6 Some representative wetland habitats (source: Keddy, 2000 and www.ramsar.org)
Wetland Name
Area (km 2 )
Location
West Siberian Lowlands
Eurasia
780,000-1,000,000
Amazon River
South America
800,000
Hudson Bay Lowlands
North America
200,000-320,000
Mississippi River
North America
86,000
Upper Nile Swamps
Africa
50,000-90,000
Chongming Dongtan Nature Reserve
Shanghai, China
3260
Yellow River Delta National Nature Reserve
Shandong Province, China
1530
Mai Po and Inner Deep Bay Nature Reserve
Hong Kong, China
15
Futian Nature Reserve
Shenzhen, China
3.7
8.6.1 Function of Wetlands
Historically, wetlands had been merely treated as areas that support agriculture, fishery, tourism or
recreation. The importance of wetland's physical and ecological functions has been gradually understood
in recent decades—often as a result of the drastic environmental degradation caused by loss of wetland
habitats. The wetlands between the edge of a water body and the adjacent upland zone provide many
environmental services that include: retaining and conveying flood waters, stabilizing the shoreline against
wind and wave erosion, filtering contaminants and sediments, providing critical habitat and movement
corridors for a wide variety of plants and animals. There is also increasing evidence of the important role
that wetlands play in moderating global warming, by reducing the amount and rate of increase in atmospheric
carbon dioxide and other greenhouse gases. In this section, we illustrate the beneficial functions of wetland
ecosystems with several real-life examples that are particularly relevant to urban development and its
impact on the natural environment.
8.6.1.1 Shoreline Protection
Coastal shorelines are critical interfaces between upland and the littoral zone of the adjacent sea, often
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