Environmental Engineering Reference
In-Depth Information
selection (an evolutionary response) results in a genetically
different population.
What community level effects can be produced?
Once populations of sensitive species are affected, changes
in communities can result. In general, communities become
less diverse because of the loss of some sensitive species.
Shifts in community composition also occur in which toler-
ant species become more abundant, while the more sensitive
species decline. Community-level effects are most com-
monly studied in benthic communities that are composed
largely of polychaete worms and bivalve mollusks that live
in the sediments and cannot move away quickly. A useful
approach devised by Peter Chapman is to measure concen-
trations of contaminants in the sediments, the toxicity of the
sediments (by sediment toxicity tests), and the benthic com-
munity structure. This is referred to as the sediment quality
triad. While it cannot indicate which particular contami-
nants are responsible for toxicity, it is very useful for com-
paring different areas or changes in a given area over time.
Contaminated sites tend to have multiple contaminants that
may interact in different ways. Because of these interactions,
it is very difficult to predict biological effects based only on
knowledge of the types and concentrations of contaminants
at a particular site.
What can marine organisms to do defend themselves
against toxic effects?
Animals have enzyme systems that can detoxify organic chem-
icals and break them down. These are discussed in Chapter 8.
Over the long term, chemicals can select for individuals that
are more tolerant, and thus evolution of more tolerant popula-
tions may take place.
Search WWH ::
Custom Search