Environmental Engineering Reference
In-Depth Information
predominate. The adaptation of plants to desert conditions varies. For example, the
saguaro cactus develops a widely spreading root system; the mesquite has roots that may
reach depths of over 50 m; many cacti and agaves store water in their roots, stems and
leaves. Some plants reduce water loss through evaporation by controlling their stomata,
while others have long dormant periods, growing and flowering briefly and irregularly
when moisture is available (Plate 27.4). Some species of plants avoid excessive exposure
to the sun and drying winds by growing largely underground.
DESERT SOILS
The soils associated with desert conditions are typically little weathered, and lacking in
humus. In the most extreme cases, no true soil exists, but, even where sufficient plant
growth does occur to provide a surface accumulation of plant debris and a food base for
soil fauna, the lack of leaching and chemical weathering leaves soils relatively infertile.
Salinity may be a problem where the rock type produces saline ground water, or where
salty sea water seeps into aquifers, as it does in many coastal areas. Winds blowing from
the sea also may introduce salt. Constant evaporation from the surface draws water from
the lower layers of the soil and leads to the accumulation of salts in the upper horizons. If
the parent material is rich in sodium salts, solonetzic soils may develop. Practically no
leaching occurs, so, even though the salt is soluble, it accumulates in the soil.
Plate 27.2 Desert vegetation in the southern Kalahari. Small
amounts of vegetation survive on moisture provided by the
alluvial fan emerging from the valley in the background.
Photo: Peter Smithson.
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