Standardized total biological index

The Total Biological Index Standardized or IBGN is a standardized method used in ecology applied in order to determine the biological quality of a River. The method uses the determination of the macro Invertébré S of Fresh water. The index, of a value from 0 to 20, is based on the presence or the absence of some Taxon S Bioindicateur S polluo-sensitive such as the Plécoptère S or polluo-resistant. More generally, any modification of the composition of the alive communities lodged by an aquatic environment, is not only the proof of a disturbance, but is also characteristic of a Polluant given (and even of its concentration).
The essential interest of the use of IBGN is that it makes it possible to characterize the disturbance of a medium (watery) by its effects and not by its causes. For example, it is the only means of proving a last Pollution (reduction in the number of individuals or disappearance of certain species of Insecte S), which a physicochemical analysis of the Eau does not allow.

The evaluation of the quality of the medium is founded on the analysis of the settlements of certain benthic macro-invertebrates (pledged with the substrate). The repertory of the organizations retained for the calculation of IBGN contains 138 tax. The taxonomic unit selected is the family, except for some groups for which it is the junction or the class. Among the 138 Taxon S, 38 of them set up 9 indicating groups.

The results obtained spread out of 0 (very bad biological quality) to 20 (very biological good quality). The method being standardized, it can be useful is to compare two sites (or more) between them if it were applied correctly to each site, that is to say to evaluate a modification in the time of the biological quality of water on the level of a single site.

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