G. Blake: A New Methodology Concept in Aquatic Ecotoxicology
97
reconstituting a structure and a systemic functioning sufficiently
complex to validate the results of biotests and to reveal valid information
on an ecological scale. In our opinion, this approach can only be
supplied by a laboratory or outdoor microcosm scale.
Justifying the use of large reconstituted systems is particularly worthwhile for
ecosystem divisions that require a minimum size to be considered valid:
the case of sediments that, in insufficient amounts, might show reactivities more linked to wall effects (oxido-reduction artefacts) than to their
own specific mechanisms (decomposing organic matter, water-sediment
exchanges, bioturbation ... );
the case of biological organisms that require a space (or a time) that
cannot be easily simulated in limited laboratory conditions: long-lived
organisms (invertebrates and fish, vascular plants, ... ). These organisms,
by their ecological role, necessarily affect the future of ecosystems.
The variety of physical factors over a period of years lead to responses from the
community of organisms that no sophisticated laboratory arrangement could
reproduce; these conditions can only be reproduced by transposing ecological
systems in a real situation. Such variations of the medium are also the source of
different evolutionary possibilities of the contaminant agent, and we were able to
verify that the specific physicochemical characteristics of the chemical compound
reveal themselves in these conditions:
revelation of the transient nature of a solvent that will be very quickly
eliminated from an aquatic ecosystem into which it was introduced and
verification that it is but slightly harmful to biological communities;
on the other hand, the general distribution of a highly hydrosoluble
compound with repercussions on those compartments with important
exchange capacities, etc ...
2
SOME ADVANTAGES AND DISADVANTAGES OF
OUTDOOR MICROCOSMS AND MESOCOSMS
Various parameters, controlled or not, can take place in micro and mesocosm
experiments and can limit the validity of the results. In large reservoirs, it was
possible to follow their evolution for two to three years parallel to that of the
ecosystems they were supposed to represent, and, in this case, the results are very
favorable. In the case of microcosms, the ecological drift of the system can be
reproduced much more often and must be watched.
In the case of laboratory microcosms with a high degree of environmental control,
there must be the same procedure as that followed in mathematical modeling, i.e.
one must intervene by varying, during the validation phase, the physicochemical
factors and thereby follow the effects of this variation on the microcosm ([6]). In
this way, the microcosm undergoes a sensitivity analysis; at the same time its range
of application is also validated, as can be done for a mathematical model.
97
reconstituting a structure and a systemic functioning sufficiently
complex to validate the results of biotests and to reveal valid information
on an ecological scale. In our opinion, this approach can only be
supplied by a laboratory or outdoor microcosm scale.
Justifying the use of large reconstituted systems is particularly worthwhile for
ecosystem divisions that require a minimum size to be considered valid:
the case of sediments that, in insufficient amounts, might show reactivities more linked to wall effects (oxido-reduction artefacts) than to their
own specific mechanisms (decomposing organic matter, water-sediment
exchanges, bioturbation ... );
the case of biological organisms that require a space (or a time) that
cannot be easily simulated in limited laboratory conditions: long-lived
organisms (invertebrates and fish, vascular plants, ... ). These organisms,
by their ecological role, necessarily affect the future of ecosystems.
The variety of physical factors over a period of years lead to responses from the
community of organisms that no sophisticated laboratory arrangement could
reproduce; these conditions can only be reproduced by transposing ecological
systems in a real situation. Such variations of the medium are also the source of
different evolutionary possibilities of the contaminant agent, and we were able to
verify that the specific physicochemical characteristics of the chemical compound
reveal themselves in these conditions:
revelation of the transient nature of a solvent that will be very quickly
eliminated from an aquatic ecosystem into which it was introduced and
verification that it is but slightly harmful to biological communities;
on the other hand, the general distribution of a highly hydrosoluble
compound with repercussions on those compartments with important
exchange capacities, etc ...
2
SOME ADVANTAGES AND DISADVANTAGES OF
OUTDOOR MICROCOSMS AND MESOCOSMS
Various parameters, controlled or not, can take place in micro and mesocosm
experiments and can limit the validity of the results. In large reservoirs, it was
possible to follow their evolution for two to three years parallel to that of the
ecosystems they were supposed to represent, and, in this case, the results are very
favorable. In the case of microcosms, the ecological drift of the system can be
reproduced much more often and must be watched.
In the case of laboratory microcosms with a high degree of environmental control,
there must be the same procedure as that followed in mathematical modeling, i.e.
one must intervene by varying, during the validation phase, the physicochemical
factors and thereby follow the effects of this variation on the microcosm ([6]). In
this way, the microcosm undergoes a sensitivity analysis; at the same time its range
of application is also validated, as can be done for a mathematical model.