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Actiuni asupra solului




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Swamps, deserts, and submerged coastal lands are naturally inaccessible; surface mines, waste-disposal sites, and municipal landfills are waste areas created by human activity. The land reclaimed fr
om such areas has been used for agricultural and forest crops, recreation, wildlife, and industrial or residential development.
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par }{ b f102 fs18 RECLAMATION OF NATURALLY INACCESSIBLE AREAS
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par }{ f102 fs18 Naturally inaccessible areas
are frequently the result of moisture extremes. Wet areas must be either drained or land-filled. Drainage (see drainage systems) is accomplished in several ways: by building a system of channels, by laying drainage pipes, and by pumping. In many cases emb
a
nkments must be constructed to keep water out of the reclaimed areas. landfill operations require large quantities of suitable fill material such as sand, which is often obtained by dredging adjacent areas. Water is supplied to arid areas either by pumpin
g it from underground sources or by transporting it through an irrigation system.
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par Reclamation of wetlands has significantly enhanced the well-being of several nations. The Netherlands is an outstanding example. Over a period of centuries the amount of arab
le land has been significantly increased by the construction of dikes, enclosing portions of the shallow coastal waters, which are then drained off. The Zuider Zee project, the first phase of which was a 29-km (18-mi) dike completed in 1932, has created n
early 200,000 ha (500,000 acres) of polders, which is land reclaimed from the sea. Because much of this land is below sea level, continuous pumping is required to maintain the desired water-table level.
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par Considerable areas in salt marshes have also been rec
laimed in eastern England by constructing embankments that separate the marshes from the sea and draining the marshes both with ditches inside the embankments and through tidal sluices. Because the marshes are above sea level, pumping is not needed. Land
reclaimed from the sea has such a high salt level that only salt-tolerant vegetation can be planted during the first few years. However, after several years, rain leaches out most of the sodium ions and soil conditions improve.
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par An example of large-scale re
clamation of freshwater marshes is the drainage in the 1930s of the Pontine Marshes of Italy, a 75,000-ha (195,000-acre) region of dunes and marshes about 70 km (45 mi) southwest of Rome. The project not only opened new land for settlement and agriculture
but also helped control malaria, a product of the marshes.
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par Reclamation of wetlands has been less actively pursued in the United States, because such areas are highly productive habitats for fish, shellfish, birds, and wildlife. Reclamation of arid lands,
however, has been a major goal of the U.S. Bureau of Reclamation. The Lower Colorado River Project has transformed desert areas, such as the Imperial Valley of California, into some of the most productive cropland in the world.
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par The Dutch experience also p
oints a warning, however. Although Dutch farmers have wrested some of the world's highest yields from their reclaimed lands, they have done so at considerable expense. The annual cost of drainage and dike repairs exceeds $400 million; runoff from fertiliz
e
rs and pesticides adds to the burden of water pollution; the constant pumping has compressed polder soils, causing them to sink while, at the same time, it is feared that sea levels may be rising. In consequence, in 1993 the Netherlands government announc
ed plans to reverse the reclamation process, returning over 240,000 ha (600,000 acres) to marsh, lake, and forest.


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