Environmental Engineering Reference
In-Depth Information
to pollution or subtle effects of contaminants on individual organisms that, if
continued in the medium and long term, will feed through into ecological
effects at a population level. So there are circumstances where we can detect
subtle effects of pollution on field populations. An understanding of the
conditions necessary to achieve this, combined with an appreciation of the
reasons why this is sometimes not possible, leads us to the conclusion that it is
likely that there are many other aquatic locations where pollution is having
adverse ecological effects but where we are not able to detect them using
currently available methods.
What effects do we expect pollution to have on ecosystems?
It is helpful to begin by identifying the sorts of ecological change that we
expect to observe when an ecosystem is exposed to a damaging pollutant.
Fig. 7.1 shows a model for the effects of pollution on a community. Except in
extreme environments, where few species can survive because of physical
stress, we would expect a reasonably diverse community of organisms to be
present at an unpolluted site. If this area becomes polluted, some or all of the
species present may migrate out of the area, be killed or fail to reproduce,
leading to reduced diversity. If the pollution event is transitory, the community
will recover in time. But if the pollution source is continuous, or the pollutant
persists in the environment (in sediments, for example), then these pollution
sensitive species will be unable to recolonise. In the case of severe pollution,
Pollution event
Reduction or elimination of some species
Yes
Does pollution
remain high?
No
No
Was competition
strong?
Yes
New species can colonise.
Species composition altered.
Diversity remains high.
Diversity
permanently
reduced
Figure 7.1. Schematic diagram showing the possible impacts of pollution on
a community. If interspecific competition was strong, the result can be altered
community composition but unchanged diversity.
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