Geography Reference
In-Depth Information
Going Global: Multiple Sources Affect an Entire
Population
The Chernobyl and Exxon Valdez accidents discussed earlier in the chapter illustrate how a one-time
point-source release of pollutants in a dynamic environment can have wide-ranging effects. More ser-
ious, however, is a case of on-going discharge from multiple-point sources, which generate potential
for negative human impact on a global environmental scale. “Potential?” No, scratch that. At least
two phenomena have already sprung forth: acid rain and global warming.
Raining acid
Acid rain
is precipitation that has an unusually high acid content. It has been identified as a
major cause of forest demise in various parts of the world, and also of contamination of lakes
and estuaries.
The principal cause of this phenomenon is the burning of fossil fuels to operate motor vehicles, man-
ufacturing facilities, and electrical utility plants (see Figure 18-4). A lesser but important cause is the
smelting of ores that contain sulphur. Two unfortunate by-products are sulfur dioxide and nitrogen
dioxide. When sulfur dioxide interacts with atmospheric moisture, it transforms into a dilute solution
of sulfuric acid, a very corrosive substance. Nitrogen dioxide is transformed into nitric acid, which is
not particularly corrosive, but is harmful to organic matter.
The range of impacts
After sulfur dioxide and nitrogen dioxide have formed in the atmosphere, they may remain there for
long periods and be carried by the wind far from their source areas. Ultimately, they fall to earth
with snow, sleet, hale, or rain. Even dew may bring them to Earth. Thus, though the phenomenon
is popularly called acid rain, it would be more properly called
acid precipitation
or
acid deposition
.
Whatever the label, negative impacts may be manifested in the following ways:
Terrestrial impacts:
Terrestrial impacts concern vegetation and soil. After acid precipit-
ation has seeped into the ground, it may be taken up by the root systems of plants. If a suf-
ficient amount of acid is taken in, even as small dosages over a long period, the stress may
be sufficient to kill individual trees and perhaps destroy entire forests. Obviously, the effects
