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susceptible to stressors than populations were reproduction and survival are less density
Measurement of stressor effects at the population level is best done by studying populations.
While some use can be made o f field studies such as before and after and control and reference
protocols, the range of substance/stressor concentration may not be wide enough to capture all
the responses or allow the identification of a (NOAEC) for the substance/stressor. One way round this is to conduct controlled experiments under field conditions in micro - or meso-cosms.
A number of procedures have been proposed for these types of tests and there are numerous
examples of their utility (Hill et al. 1994). Most of this work has been carried out in aquatic
systems but some terrestrial systems have also been used. The aquatic systems range from
simple laboratory systems to complex flowing stream systems.
22.214.171.124 EFFECTS OF PESTICIDES IN THE AQUATIC ECOSY STEM
The difficulty of measuring population - or community-level effects is illustrated in the following
discussion of the effects of pesticides in an aquatic ecosystem. The principles in this discussion
illustrate some of the problems and questions which should be addressed in any study designed
to assess the effects of a substance in the environment. This methodol ogy was developed at the
University of Guelph and involves the use of enclosures and micr ocosms as an experimental
technique to assess impact in aquatic ecosystems. Obviously, some of the experimental
procedures do not apply to terrestrial ecosystems. However, the general principles are similar.
Enclosures (limnocorrals) and microcosms ha ve become more widely used as a method or
technique for studying the effects of a variety of substances in aquatic ecosystems. The use of
these enclosures has its basis in two philosophies. The first of these is the perceived need to
assess the effects of a potentially toxic substance in the field — either under actual conditions of
use or under circumstances during which it may come into contact with biota. This philosophy is
based on the dogma (essentially an admission) that one cannot duplicate all e nvironmental
conditions in the laboratory. Laboratory assessments can therefore only act as a guide to
developing hypotheses which must be subjected to testing in field assays. This dogma is widely
accepted and is the raison d'etre for the work of many environmental toxicologists as well as
those in the applied agri cultural sciences.
Historically, these field observations have normally been made after the fact of contamination or
release of a toxic substance. While these studies may have added much t o understanding the
processes whereby such substances distribute in the environment and cause harm, they have done
little to predict or prevent this damage from occurring in the first place. The clear need for
adequate methods, as well as the examples in the systematic field trials of new crop varieties or
agricultural chemicals by agriculturalists, has lead to the development of similar assessments for
environmental stressors. These methods have begun to be accepted by regulatory authorities as
well a s those who use or produce these s...
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- Fall '14
- The Land