G. Blake: A New Methodology Concept in Aquatic Ecotoxicology
99
What are the application limits of outdoor microcosms and mesocosms?
Too large systems are difficult to handle, expensive and hard to duplicate. As for
mathematical models, the increased validity gives rise to extreme complexity,
making it difficult to exploit the results.
The use of mesocosms has definite advantages:
• in a natural ecosystem:
possibility of using radioactive tracers,
better control of sampling and of ecosystem representativity,
• better control of experimental conditions,
evaluation possibility ...
• in laboratory experiments (cultures, monospecific breeding):
mingling of several selected species with visualization of their relationships,
•
populations whose densities are more representative of the medium
(plankton, invertebrates ... ),
more faithful to the natural behavior of organisms,
experiments over several seasons or even longer,
•
complexity close to that of a natural system,
truer distribution and chemical forms of the pollutant introduced ...
A certain number of constraints must be respected, and physical models can have
their disadvantages as well:
The biological populations of mesocosms show more stability in their
evolution, since the accumulation of organic matter leads to a greater
variety of heterotrophic populations.
Mesocosms require a very ponderous follow-up procedure of their
biological populations.
In fact, it is by an integrated approach, combining monospecific tests, laboratory
and outdoor microcosms, that one can best integrate the different levels of
biological and ecological information that can result in a more realistic approach
of the multispatial and multi temporal dimension of ecological risk evaluation
(Fig. 2).
3 CONCLUSION
As we know, biological tests constitute a partial method for learning about the real
consequences of xenobiotic impact on aquatic ecosystems. Current procedures
involve searching for and following, through systems of various and complex
dimensions and structures, the effects of a whole range of contamination by a
toxic, primarily via a key process (energy exchanges: respiration and photosynthetic activity).
99
What are the application limits of outdoor microcosms and mesocosms?
Too large systems are difficult to handle, expensive and hard to duplicate. As for
mathematical models, the increased validity gives rise to extreme complexity,
making it difficult to exploit the results.
The use of mesocosms has definite advantages:
• in a natural ecosystem:
possibility of using radioactive tracers,
better control of sampling and of ecosystem representativity,
• better control of experimental conditions,
evaluation possibility ...
• in laboratory experiments (cultures, monospecific breeding):
mingling of several selected species with visualization of their relationships,
•
populations whose densities are more representative of the medium
(plankton, invertebrates ... ),
more faithful to the natural behavior of organisms,
experiments over several seasons or even longer,
•
complexity close to that of a natural system,
truer distribution and chemical forms of the pollutant introduced ...
A certain number of constraints must be respected, and physical models can have
their disadvantages as well:
The biological populations of mesocosms show more stability in their
evolution, since the accumulation of organic matter leads to a greater
variety of heterotrophic populations.
Mesocosms require a very ponderous follow-up procedure of their
biological populations.
In fact, it is by an integrated approach, combining monospecific tests, laboratory
and outdoor microcosms, that one can best integrate the different levels of
biological and ecological information that can result in a more realistic approach
of the multispatial and multi temporal dimension of ecological risk evaluation
(Fig. 2).
3 CONCLUSION
As we know, biological tests constitute a partial method for learning about the real
consequences of xenobiotic impact on aquatic ecosystems. Current procedures
involve searching for and following, through systems of various and complex
dimensions and structures, the effects of a whole range of contamination by a
toxic, primarily via a key process (energy exchanges: respiration and photosynthetic activity).