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In-Depth Information
more than 100 metres deep were dug by hand nearly two centuries ago through hard
Nubian Sandstone to provide reliable water for humans and their herds during the
sixteen-day journey by camel from Kufra Oasis in Libya to Ounianga in Chad. In fact,
the Nubian Sandstone is the largest groundwater aquifer in the world (Alker,
2008
,
extending across 2 million km
2
in the Sahara and Arabia, with an estimated storage
of 150,000 km
3
of groundwater. Unfortunately, the water in this aquifer is being
used today at a rate far in excess of any replenishment from precipitation on distant
mountains. The last episodes of groundwater recharge of this aquifer were in the late
Pleistocene and early Holocene, so current use amounts to mining a non-renewable
resource.
A number of other major desert aquifers, such as the Ogallala Aquifer in the
United States (Reilly and Franke,
1999
; Bartolino and Cunningham,
2003
)andthe
Great Artesian Basin in central Australia, are also being used to excess, which will
require new adaptive strategies in the future. The Great Artesian Basin covers an
area of 1.7 million km
2
(660,000 sq miles) and is the largest and deepest artesian
basin in the world. (Artesian water is confined groundwater flowing under pressure
from a recharge zone of higher elevation to an outlet in a series of springs situated
at lower elevations). The Ogallala Aquifer, also known as the High Plains Aquifer,
is a vast shallow aquifer some 450,000 km
2
(174,000 sq miles) in area that underlies
eight states in the Great Plains region (South Dakota, Nebraska, Wyoming, Colorado,
Kansas, Oklahoma, New Mexico and Texas) and supports more than a quarter of all
irrigated farmland in the United States. It is at present suffering severe depletion and
increasing groundwater pollution, which is a major cause of concern.
A number of small towns have been built in remote and arid parts of Arabia,
Australia and China on sites rich in minerals, petroleum and natural gas. All of these
settlements use substantial quantities of water for industrial and domestic purposes.
Much of this water comes from fossil groundwater - a non-renewable resource. In
some towns, such as the gold-mining town of Kalgoorlie in western Australia, water
needs to be brought in from much further away by pipeline, a process likely to
accelerate in the future as other mining towns are built in desert areas.
4.3 Adaptations of plants to life in deserts
Desert plants have adapted to the low and erratic rainfall regime in a variety of ways,
but the two primary needs are to minimise unnecessary water loss through evaporation
while retaining or being able to acquire enough water to allow photosynthesis to
proceed efficiently (Evenari et al.,
1971
; Ozenda,
1977
; Evenari et al.,
1985
;Evenari
et al.,
1986
;Guninetal.,
1999
).
The
succulents
retain water in their roots, stems and leaves, and they include the
Euphorbias
of the deserts of Eurasia and the cacti of the American deserts (
Figure 4.3
).
Despite its name, the Barbary Fig (or prickly pear) is not native to north-west Africa
