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10 Arid and semi-arid environments
Causes of soil degradation Water erosion accounts for about 60% of soil degradation. There are many types of erosion including surface, gully, rill and tunnel. Acidification is the change in the chemical composition of the soil, which may trigger the circulation of toxic metals. Eutrophication (nutrient enrichment) can degrade the quality of ground water. Groundwater over-abstraction can lead to dry soils. Salt-affected soils are typically found in marine-derived sediments, coastal locations and hot arid areas where capillary action brings salts to the upper part of the soil. Atmospheric deposition of heavy metals and persistent organic pollutants can make soils less suitable for sustaining the original land cover and land use. Climate change will probably intensify the problem. It is likely to affect hydrology and hence land use.
Human activities
Human activities have often led to degradation of the world’s land resources. Damage has occurred on 15% of the world’s total land area. While severely degraded soil is found in most regions of the world, the negative economic impact of soil degradation is most severe in those countries most dependent on agriculture for their incomes. Table 10.1 Human activities and their impact on soil erosion Action
Effect
Removal of woodland or ploughing of established pasture
The vegetation cover is removed, roots binding the soil die and the soil is exposed to wind and water. Slopes are particularly susceptible to erosion.
Cultivation
Exposure of bare soil surface before planting and after harvesting. Cultivation on slopes can generate large amounts of runoff and create rills and gullies.
Grazing
Overgrazing can severely reduce the vegetation cover and leave the surface vulnerable to erosion. Grouping of animals can lead to trampling and creation of bare patches. Dry regions are particularly susceptible to wind erosion.
Roads or tracks
Reduced infiltration can cause rills and gullies to form.
Mining
Exposure of bare soil leads to rapid erosion.
10.4 Sustainable management of arid and semi-arid environments Sustainable development is a process by which human potential (quality of life) is improved and the environment (resource base) is used and managed sustainably to supply humanity on a long-term basis.
Essential oils in the Eastern Cape, South Africa
Sustainable development meets the needs of the present generation without compromising the ability of future generations to meet their own needs.
Revised
Global pattern
About 65% of the world production of essential oils occurs in developing countries such as India, China, Brazil, Indonesia, Mexico, Egypt and Morocco. However, the USA is also a major producer of essential oils such as peppermint and other mints.
Paper 2 Advanced Physical Geography Options
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