Geoscience Reference
In-Depth Information
1
Wetland overview
1.1 Introduction
the Earth's system. Wetland components include
water, soil, vegetation, and wildlife. Since the
i rst human hunter-gatherers camped by springs
and shores, people have utilized, modii ed,
exploited or impacted wetlands in various ways.
Moreover, the early establishment of human set-
tlements and subsequent expansion were based
on irrigated agriculture along major river l ood-
plain valleys
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Nile (Fig. 1-3), Tigris-Euphrates,
Niger, Indus, Mekong, etc.
Wetlands continue to be essential for modern
human society; they represent the primary
sources of fresh water for people in most places
around the world. Wetlands minimize l ooding
and storm damage, nourish i sheries (Fig. 1-4),
produce fur-bearing animals, sustain irrigated
agriculture, support herding and grazing (Fig.
1-5), recharge aquifers, provide shipping water-
ways (Fig. 1-6), supply hydropower, grow timber,
yield fossil fuels (Fig. 1-7), are incubators for
gemstones, and provide many other resources.
These functions are clearly evident, as they
inl uence the daily lives of people living in and
deriving economic benei ts from wetlands.
In spite of local recognition of wetland func-
tions and values, however, the larger regional
and global signii cance of wetlands is more
difi cult for many people to fathom. What is
economically benei cial in upper portions of
drainage basins
-
irrigation, timber harvesting,
hydroelectric power, recreation and other
human uses
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is often deleterious for down-
stream inhabitants of wetlands and coastal
Wetland. The name summons immediate images
or experiences to most people
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from the endless
sand beach of Padre Island, Texas (Fig. 1-1), to
wildlife in the Okavango Delta of Botswana
(Fig. 1-2), to the deadly Great Grimpen Mire,
as described in the Sherlock Holmes tale,
The
Hound of the Baskervilles
by Sir Arthur Conan
Doyle:
Rank weeds and lush, slimy water plants send an
odour of decay and a heavy miasmatic vapor into
our faces, while a false step plunged us more than
once thigh-deep into the dark, quivering mire,
which shook for yards in soft undulations around
our feet.
Whether real or i ctional, wetlands have con-
spicuous roles in the physical, biological and
cultural geography of the world. Wetlands are
places where the ground is generally saturated
or l ooded for extended periods during the
growing season such that distinctive soils form
and specialized vegetation grows under condi-
tions in which oxygen is depleted or absent.
Such environments include marshes, fens, bogs,
and swamps (see chapter 2). Wetlands occur at
the conl uence of unique terrestrial, hydrological
and climatic conditions that give rise to some of
the most biodiverse regions of the world. They
also play a vital role in the cycling and storage
of key nutrients, materials and energy through
