EXERCISE 28
Effect of Sewage Outfall
on a Stream Ecosystem
Human activity has affected profoundly streams
and lakes in all parts of the world. Streams have
been subjected to additions of gross amounts of
domestic sewage, industrial effiuents (e.g., wastes
from tanneries, pulp mills, creameries, steel mills,
and chemical factories), agricultural wastes, oil
spills, mining wastes, urban runoff, radioactive
materials, pesticides, waste heat, and numerous
other pollutants, often because it was considered
expedient and economical to have the unwanted
materials carried away ("out of sight") by the
flowing water. Likewise, under the guise of
"progress," streams have been channelized, stabilized, dewatered (for irrigation), and superwatered (artificially increased flow for drinking
and power plant needs). In most cases, the effects
on the aquatic biota are insidiously cumulative.
In some cases, the effects are readily apparent
[e.g., acid mine drainage; see Parsons (1968)], but
in others the effects accumulate more slowly [e.g.,
accumulations of trace metals; see Whitton and
PROCEDURES
Say (1975)]. In all cases, a longitudinal gradient
develops below the point of insult and, given
enough time (distance) without further insult, the
stream ecosystem generally recovers to a state of
well-being.
In this exercise, we shall examine the effects of a
sewage outfall on a stream ecosystem. Select a
site, preferably on a small stream, into which
sewage is being discharged. In most areas of the
United States, this sewage will have already
undergone primary and/or secondary treatment
[e.g., Bolton and Klein (1971) and Rohlich and
Uttormark (1972)]. Nevertheless, exercise health
precautions when collecting and analyzing samples from such areas; for example, keep hands
away from face and wash thoroughly after handling samples. Select sample sites immediately
above and below the sewage outfall. In addition,
a few sites 1 km apart above and 2 km apart
below the outfall should delineate the longitudinal changes.
1. Describe the physical and topographic characteristics of the sample sites (see
Exercise 5). Make a sketch of the area and locate the sample sites.
2. Attempt to determine the amount, type, and frequency of sewage discharge into the
stream.
3. At each site measure the following:
a. Water temperature (see Exercise 2).
b. pH (see Exercise 8).
345
Effect of Sewage Outfall
on a Stream Ecosystem
Human activity has affected profoundly streams
and lakes in all parts of the world. Streams have
been subjected to additions of gross amounts of
domestic sewage, industrial effiuents (e.g., wastes
from tanneries, pulp mills, creameries, steel mills,
and chemical factories), agricultural wastes, oil
spills, mining wastes, urban runoff, radioactive
materials, pesticides, waste heat, and numerous
other pollutants, often because it was considered
expedient and economical to have the unwanted
materials carried away ("out of sight") by the
flowing water. Likewise, under the guise of
"progress," streams have been channelized, stabilized, dewatered (for irrigation), and superwatered (artificially increased flow for drinking
and power plant needs). In most cases, the effects
on the aquatic biota are insidiously cumulative.
In some cases, the effects are readily apparent
[e.g., acid mine drainage; see Parsons (1968)], but
in others the effects accumulate more slowly [e.g.,
accumulations of trace metals; see Whitton and
PROCEDURES
Say (1975)]. In all cases, a longitudinal gradient
develops below the point of insult and, given
enough time (distance) without further insult, the
stream ecosystem generally recovers to a state of
well-being.
In this exercise, we shall examine the effects of a
sewage outfall on a stream ecosystem. Select a
site, preferably on a small stream, into which
sewage is being discharged. In most areas of the
United States, this sewage will have already
undergone primary and/or secondary treatment
[e.g., Bolton and Klein (1971) and Rohlich and
Uttormark (1972)]. Nevertheless, exercise health
precautions when collecting and analyzing samples from such areas; for example, keep hands
away from face and wash thoroughly after handling samples. Select sample sites immediately
above and below the sewage outfall. In addition,
a few sites 1 km apart above and 2 km apart
below the outfall should delineate the longitudinal changes.
1. Describe the physical and topographic characteristics of the sample sites (see
Exercise 5). Make a sketch of the area and locate the sample sites.
2. Attempt to determine the amount, type, and frequency of sewage discharge into the
stream.
3. At each site measure the following:
a. Water temperature (see Exercise 2).
b. pH (see Exercise 8).
345