Pollution Monitoring by Bottom
Invertebrates
T. W. BEAK, President
T. W. Beak Consultants Ltd.
4999 St. Catherine Street
Montreal, Canada
INTRODUCTION
If a body of natural water, be it a river, a lake or part of the ocean, is
grossly polluted, it is not difficult to establish this fact by chemical or biological
measurements. It is more difficult to measure small changes in pollution whether
they be from positive purity to very slight pollution, or from a seriously polluted
state to a slightly less polluted one. It is in these circumstances when one wishes
to measure small insidious changes in pollutional status that toe biological method
and particularly the bottom macro-invertebrates are a valuable tool.
As an example, if DO is below two mg/l, BOD is 20 mg/l or more, or there
are significant amounts of toxic materials, it is not difficult to define a river or
lake as polluted. Supposing, however, one finds DO values which are lower than
in toe natural unpolluted state, but still well above generally accepted danger
limits, e. g. five mg/l and we know that there are a large number of exotic chemicals which are difficult to analy2e in small concentrations, how are we to measure whether or not these circumstances have a pollutional significance? How are
we to know whether, over a long period, beneficial species of fish and other animals will slowly disappear from the environment. Sampling of bottom invertebrates can be helpful in these circumstances.
At toe other extreme we may have to deal with a river or lake which we know
is grossly polluted. Efforts to reduce this pollution may be in hand, yet toe variations in the usual chemical parameters, due to variations in flow and in discharge of effluent, may be such that it is difficult to tell whether an overall improvement is taking place. Again, a study of toe bottom macro-invertebrates
may give a useful indication of this.
The really experienced biologist can, by studying an adequate set of samples
from any water body, form a reasonably good estimate of its pollutional status,
provided he knows toe water body reasonably well. However, toe principal value
of toe biological measurement of water pollution is to monitor change, whether
it be for better or worse. A gradual disappearance of sensitive species, or toe slow
re-appearance of species which have hitherto been absent from an environment,
are a sure sign that there is a deterioration in the first instance and an improvement in the second. In spite of the sophistication of modern methods of chemical
analyses, the biological method is invaluable for monitoring gradual change in
toe environment.
SEARCH FOR INDICATOR SPECIES
The search for indicator species has been as great a drawback to biological
measurement of pollution as toe study of alchemy was to medieval chemistry. By
toe same token it encouraged much research which has proved valuable in unin-
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