Geography Reference
In-Depth Information
20
Wetlands conservation
Max Wade
and
Elena Lopez-Gunn
(Gleich 1993). According to the Ramsar
classification, there are marine, coastal, inland and
man-made types, subdivided into thirty categories
of natural wetland and nine humanmade ones,
such as reservoirs, barrages, and gravel pits (Dugan
1993). The International Wetlands Research
Bureau has established a wetland database. In
relation to natural wetlands, the World
Conservation Monitoring Centre (Groombridge
1992) summarises the extent of different types
relative to latitude (Figure 20.1). Surveys have
established the extent of wetlands, both past and
present, in different areas of the world, leading to
the compilation of inventories of wetland sites,
particularly for plants, birds and mammals, and
investigations into physical, chemical and
biological processes. Collectively, these have
developed a real insight into wetland ecology.
Wetlands epitomise the problem of trying to
classify ecosystems and habitats. While mangroves,
for example, meet the criteria set for wetlands,
SETTING THE SCENE
Wetlands represent only 6 per cent of the Earth's
surface, but it is believed that in 1900 this
percentage might have been twice as much
(Barbier
et al
. 1994). Wetlands include a wide array
of habitats, ranging from fens and marshes to
mangrove forests and rice paddies, and are
considered one of the most threatened landscapes
in the world (Gardiner 1994). A simple definition
is 'land with soils that are permanently flooded'
(Williams 1990: p. 1).The Ramsar Convention, an
international treaty to conserve wetlands, defines
wetlands as: '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 metres.' This encompasses a wide range
of habitats, the main types being shown in Box
20.1 based on just one recognised classification
Box 20.1
A classification of wetland habitats
drainage from surrounding mineral soil and usually
supports marsh-like vegetation.
Marsh
A frequently or continually inundated wetland
characterised by emergent herbaceous vegetation
adapted to saturated soil conditions. In European
terminology, a marsh has a mineral soil substrate and
does not accumulate peat.
Swamp
A wetland dominated by trees or shrubs (US
definition). In Europe, a forested fen would easily be
called a swamp. In some areas, wetlands dominated by
reed grass are also called swamps.
Fens
A peat-accumulating wetland that receives some
Bogs
A peat-accumulating wetland that has no
significant inflows or outflows and supports acidophilic
mosses, particularly spaghnum.
Peatland
A generic term for any wetland that
accumulates partly decayed plant matter.
Source: Gleick 1993.
