Geoscience Reference
In-Depth Information
wildlife is the most obvious and perhaps impor-
tant aspect of wetlands. In some American and
African wetlands, for example, millions upon
millions of waterfowl and shorebirds visit briel y
or remain seasonally during annual migrations.
Such dramatic concentrations of wildlife have
attracted hunters since prehistoric times, and
hunting continues to be a major use of wetlands
(Fig. 1-10). Wetlands are, in fact, among the most
productive ecosystems in the world (Niering
1985).
Wetlands also harbor some of the greatest
biodiversity found on the planet. Many aquatic
animals are endemic to isolated wetlands, such
as the hundreds of i sh species found in the
lakes of eastern Africa (Dugan 2005). In other
cases, wetlands represent the last refuges of
animals forced out of other habitats by human
development
-
the Bengal tiger in the Sundar-
bans of India and Bangladesh and the jaguar in
wetlands of South and Central America. Endan-
gered species, such as the whooping crane
(
Grus americana
), are often foremost in the
public eye as symbols for the need to preserve
wetland habitats (Fig. 1-11).
Costanza et al. (1997) attempted to estimate
the economic value of ecosystem services for
major biomes of the world. They identii ed 17
ecosystem services (Table 1-1), many of which
are connected to or interact with wetland envi-
ronments, particularly those involving water,
soil, gases, nutrients and climate. The value of
these services was determined using market and
non-market means, such as the willingness-to-
pay method (see chapter 11). They found that
wetlands in general and estuaries, seagrass/
algae beds, coral reefs, tidal marsh/mangroves,
and swamps/l oodplains in particular have the
highest values for providing a broad array of
ecosystem services. Wetland values are consid-
erably greater, in fact, than tropical forest or
other biomes.
A
B
C
Figure 1-8.
Impact of water diversions in the High
Plains of the central United States. A. Dry channel of the
Arkansas River at Ingalls, southwestern Kansas.
Upstream reservoirs and extraction of water for
irrigation have dried up the river, even in the spring of a
wet year when this picture was taken. B. Center-pivot
irrigation system. The sprayers are set too high for the
winter wheat crop, so that considerable water is lost to
wind drift and evaporation. C. Center-pivot irrigation
system with the sprayers set just above the winter wheat
crop to minimize evaporative loss. Photos by J.S. Aber.
1.2 How much and where
the carbon cycle, which has signii cant implica-
tions for global climate.
The economic benei ts and ecological func-
tions of wetlands are numerous and varied, as
noted above. For many people, nonetheless,
The total coverage of existing wetlands is esti-
mated to range from at least 7 million km
2
to
about 10 million km
2
, or 5-8 percent of the land
