Some Important Biological Effects of
Pollution Often Disregarded in
Stream Surveys
CLARENCE M. TARZWELL and ARDEN R. GAUFIN
Chief and Biologist
Biology Section
Environmental Health Center, Public Health Service
Cincinnati,  Ohio
The complexity of the pollution problem is being constantly intensified by the ever-increasing variety of pollutants that are added to streams.
Due to the fact that pollutants, domestic and industrial, represent only
a portion of the many factors which determine stream environments,
the same pollutant may not bring about similar conditions in different
streams. The character of the watershed, including soil type, amount
and type of ground cover, and land uses; the amount, seasonal distribution, and type of precipitation; the frequency of floods and the amount
of erosion; and the character of the stream banks, bottom materials,
gradient, and stream flow are all of importance. These and other factors
determine stream characteristics, environmental conditions, the aquatic
biota, and in large part the effects of different polluting substances.
Some  Biological  Effects  of  Pollutants
Pollutants may alter the stream environments and thereby affect
aquatic life in a number of ways. These environmental changes may
include an increase in stream temperatures; changes in the character of
the stream bottom; increase in turbidity; changes in the content of dissolved oxygen; increase in dissolved nutrients; production of undesirable
growths; deposition of sludge beds; and the addition of toxic wastes.
The degree or extent of the effect of these changes on aquatic life varies
with the type and amount of the pollutant and the character of the
receiving water. It is the purpose of this paper, therefore, to point out
some of the possible effects of pollution on aquatic life and to indicate
pertinent ecological conditions which should be noted in stream surveys.
Water used for cooling purposes in industrial processes may become
so hot and be of such quantity that it may substantially raise the temperature of the receiving stream.  The addition of a waste or wash water
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