Environmental Engineering Reference
In-Depth Information
Areas of serious concern
Areas of some concern
Stable or nonvegetative areas
Figure 10-10 Natural capital degradation: global soil erosion. (Data from UN Environment Programme and
the World Resources Institute)
is deposited farther down a slope, valley, or plain. In
some places, the loss in crop yields in one area could
be offset by increased yields elsewhere.
These efforts to slow soil erosion are an important
step and, since 1985, have cut soil losses on U.S. crop-
land by about two-thirds. However, effective soil con-
servation is practiced today on only half of all U.S.
agricultural land and on half of the country's most
erodible cropland.
Science Case Study: Soil Erosion
in the United States
Soil in the United States is eroding faster than it forms
on most cropland, but since 1987, erosion has been cut
by about two-thirds.
Bad news. According to the Natural Resources Conser-
vation Service, soil on cultivated land in the United
States is eroding about 16 times faster than it can form.
Erosion rates are even higher in heavily farmed re-
gions. The Great Plains, for example, has lost one-third
or more of its topsoil in the 150 years since it was first
plowed.
Good news. Of the world's major food-producing
nations, only the United States is sharply reducing
some of its soil losses through a combination of plant-
ing crops without disturbing the soil and government-
sponsored soil conservation programs.
Science: Desertification
About one-third of the world's land has lost some
of its productivity from a combination of drought
and human activities that reduce or degrade
topsoil.
In desertification, the productive potential of drylands
(arid or semiarid land) falls by 10% or more because of
a combination of natural climate change that causes
prolonged drought and human activities that reduce
or degrade topsoil. The process can be moderate (a
10-25% drop in productivity), severe (a 25-50% drop),
or very severe (a drop of 50% or more, usually creating
huge gullies and sand dunes). Only in extreme cases
does desertification lead to what we call desert.
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