Abstract
This paper that serves as a prelude to a series of papers on the theme ‘Pesticide stress in freshwater ecosystems’,
has three main objectives. First it outlines the importance of ecological expertise assessing the risks of discharge of
pesticides into aquatic environments; second, it discusses possible contributions of ecotoxicological experiments
to ecological theory; and third, it advocates the need for an integrative approach in stress-ecology. This approach is
based on descriptive ecology, experimentation in the laboratory and in model ecosystems, and on the development
of computer simulation models.
Abbreviations: Assessment factor – Factor in ecotoxicological assessment for extrapolation of laboratory single
species toxicity data to field populations and communities; EC50 – Concentration of a toxicant in an environmental
medium expected to produce a certain effect in 50% of the test organisms in a given population; NOEC – No-
Observed Effect Concentration: Highest concentration or amount of a toxicant in the test system that causes no
observable biological effects to the target organism; Mesocosm – see Model ecosystem; Microcosm – see Model
ecosystem; Model ecosystem – Man-made study system containing associated organisms and abiotic components
that is large enough to be representative of a natural ecosystem, yet small enough to be experimentallymanipulated.
Mesocosms are larger outdoor model ecosystems, while microcosms are the smaller, and generally indoor, model
ecosystems; Semi-field study – Experiment performed in model ecosystems or in field enclosures