Science of Water : Concepts and Applications

Water Pollution 215
humans depend on various human-made water treatment processes to restore water to potable and
palatable condition. However, it should be pointed out that Nature, as Hercules pointed out, is not
defenseless in its fi ght against water pollution. For example, when a river or stream is contaminated,
natural processes (including dilution) immediately kick in to restore the water body and its contents
back to its natural state. If the level of contamination is not excessive, the stream or river can restore
itself to normal conditions in a relatively short period. In this section, Nature’s ability to purify and
restore typical river systems to normal conditions is discussed.
In terms of practical usefulness the waste assimilation capacity of streams as a water resource
has its basis in the complex phenomenon termed stream self-purifi cation. This is a dynamic phenomenon
refl ecting hydrologic and biologic variations, and the interrelations are not yet fully understood
in precise terms. However, this does not preclude applying what is known. Suffi cient knowledge is
available to permit quantitative defi nition of resultant stream conditions under expected ranges of
variation to serve as practical guides in decisions dealing with water resource use, development, and
management (Velz, 1970).
BALANCING THE “AQUARIUM”
An outdoor excursion to the local stream can be a relaxing and enjoyable undertaking. In contrast,
when you arrive at the local stream, spread your blanket on the stream bank, and then look out upon
the stream’s fl owing mass and discover a parade of waste and discarded rubble bobbing along the
stream’s course and cluttering the adjacent shoreline and downstream areas, any feeling of relaxation
or enjoyment is quickly extinguished. Further, the sickening sensation the observer feels is not
lessened, but worsens as he scrutinizes the putrid fl ow more closely. He recognizes the rainbowcolored
shimmer of an oil slick, interrupted here and there by dead fi sh and fl oating refuse, and the
slimy fungal growth that prevails. At the same time, the observer’s sense of smell is alerted to the
noxious conditions. Along with the fouled water and the stench of rot-fi lled air, the observer notices
the ultimate insult and tragedy: The signs warn, “DANGER—NO SWIMMING or FISHING.” The
observer soon realizes that the stream before him is not a stream at all; it is little more than an unsightly
drainage ditch. The observer has discovered what ecologists have known and warned about for years,
that is, contrary to popular belief, rivers and streams do not have an infi nite capacity for pollution.
Before the early 1970s, disgusting occurrences such as the one just described were common
along the rivers and streams near main metropolitan areas throughout most of the United States.
Many aquatic habitats were fouled during the past because of industrialization. However, our
streams and rivers were not always in such deplorable condition.
Before the Industrial Revolution of the 1800s, metropolitan areas were small and sparsely populated.
Thus, river and stream systems in or next to early communities received insignifi cant quantities
of discarded waste. Early on, these river and stream systems were able to compensate for the
small amount of wastes they received; when wounded (polluted), Nature has a way of fi ghting back.
In the case of rivers and streams, Nature provides fl owing waters with the ability to restore themselves
through a self-purifi cation process. It was only when humans gathered in great numbers to
form great cities that the stream systems were not always able to recover from having received great
quantities of refuse and other wastes.
What exactly is it that man does to rivers and streams? As stated earlier, Halsam points out that
man’s actions are determined by his expediency. In addition, what most people do not realize is that
we have the same amount of water as we did millions of years ago, and through the water cycle, we
continually reuse that same water—water that was used by the ancient Romans and Greeks is the
same water we are using today. Increased demand has put enormous stress on our water supply. Man
is the cause of this stress. Thus, what man does to rivers and streams is to upset the delicate balance
between pollution and the purifi cation process. That is, we tend to unbalance the aquarium.
As mentioned, with the advent of industrialization, local rivers and streams became deplorable
cesspools that worsened with time. During the Industrial Revolution, the removal of horse manure