Geography Reference
In-Depth Information
tribute to soil erosion. On the other hand, introduction into the environment of some element
for which no natural counterbalance exists may have an effect no less profound than, say, ac-
cumulation of phosphates and nitrates in the Chesapeake Bay. A good example is provided by
the kudzu, a fast- growing vine that was let loose in the South and has proceeded to dominate
the natural vegetation over large areas.
Geographically, pollution may originate as a location-specific
point source
or as a larger scale
non-
point source
(sometimes called an
area source
). In the Chesapeake Bay example, a pipe at a sewage
treatment plant that discharges phosphate would exemplify point source. Crop fields in, say, Mary-
land, on which fertilizers that are high in nitrates have been applied, would typify non-point source
or area source.
Spreading the mess
By themselves, pollution sources
per se
generate limited environmental impact. The major
problem, rather, is that pollutants tend not to stay put because they are released within an en-
vironment characterized by several kinds of motion. In other words, nature has mechanisms
that “spread the mess.” As a result, pollution that starts out as a confined geographic event
may end up affecting broad areas and having extensive consequences. Previous chapters have
described these mechanisms in some detail. Here is a brief recap with examples.
The water cycle
The water cycle (see Chapter 8) is a major “culprit” for spreading the mess. Rainfall originates, falls
to earth, and runs off the land to create streams that flow to the sea. In so doing, the water cycle acts
as a pervasive and efficient mechanism that “spreads the mess.”
This process picks up the phosphate discharge, carries it away, and turns a local event (discharge)
intoaproblemofChesapeake-sized proportions.Thisprocessalsoproducesrun-offonanagricultural
field that picks up nitrates from fertilizers and carries them away. And of course, the Chesapeake Bay
does not have
a
tributary, but instead more than a hundred of them, which together collect pollutants
from thousands of point and non-point sources.
