Geoscience Reference
In-Depth Information
are found in the subtropical zone, where the
coni guration of terrestrial, hydrological and
local climatic conditions gives rise to wetland
habitats. Many of these subtropical wetlands are
affected by high salinity, especially in the Middle
East, central Asia, and Australia (U.S. Depart-
ment of Agriculture (USDA) 1996).
The general climatic pattern and distribution
of wetlands are inl uenced substantially by the
positions of continents, l ow of ocean currents,
prevailing winds, mountains, and other major
geographic features. For example, the largest
mangrove swamp in the world, the Sundarbans
covering 6000 km
2
(Dugan 2005), is located in
the subtropics of Bangladesh and eastern India,
where monsoons and runoff from the Himalaya
combine to create a vast l oodplain and delta
complex (see chapter 15).
Water supply to wetlands may be reduced by
levees, canals and dams as well as by extraction
of ground water. Filling is another common
means of converting wetlands for building con-
struction, urban expansion, and industrial devel-
opment (Fig. 1-14). Acid rain, shoreline erosion,
and pollution (Fig. 1-15) are further factors
for wetland loss. Such human development
began with the advent of agriculture in the
Neolithic, particularly once early civilizations
arose, and the pace of wetland loss has
1.3 Wetland trends
Humans have modii ed and exploited wetlands
in many ways, most of which have led to loss
of wetland habitats and their conversion to
other land uses and covers. Draining wetlands
is observed globally and for various purposes
-
agriculture, forestry, grazing, peat mining, etc.
Figure 1-14.
Overview of Port Bienville, an industrial
park built on the Pearl River delta in southwestern
Mississippi, United States. A dredged canal provides a
connection via the Pearl River to the Intracoastal
Waterway along the Gulf of Mexico coast. Kite aerial
photo by S.W. Aber, J.S. Aber, and M. Giardino.
Figure 1-15.
Huge chat piles are a legacy of lead-and-zinc mining at Picher, Oklahoma. Considered among the
most seriously degraded sites in the United States, the landscape is essentially destroyed; toxic pollution of ground
and surface water extends many kilometers downstream with severe impacts on human health and wetland
habitats. View toward the southwest; blimp airphoto by J.S. Aber and S.W. Aber.
