ABSTRACT
The aim of biological methods of evaluating water quality is to detect any physical or chemical degradation of the environment by studying the composition of the settlement, its species richness, and the appearance or disappearance of species. Biological methods of evaluating pollution with recourse to biochemistry and ecotoxicology measure either the trophic state of an environment or the degree of species sensitivity to pollution. Biocoenotic methods are based on the preponderant role of ecological factors in the dynamics of communities. Communities are considered the synthetic expression of various environmental factors, and their structure consequently reflects the physicochemical characteristics of each environment. A biological indicator corresponds to a population or set of populations indicating the state of an environment by their qualitative and/or quantitative characteristics. Methods of evaluation by species or biological indicators are based on the succession of algae, macrophytes, invertebrates, or fish downstream of a polluting effluent.
