A new generation of indicators: the example of the invertebrate multimetric index I2M2

Abstract

Benthic macroinvertebrates are known to be good indicators of the nature and intensity of disturbances to which aquatic ecosystems are subjected. Since 1992, the Normalized Global Biological Index (IBGN) has been used to assess the ability of the environment to host macroinvertebrates by taking into account their variety, their sensitivity to pollution and the most biogenic habitats. But in 2000, the European Water Framework Directive (WFD) sets new rules for the evaluation of the quality of the environment making the IBGN non-compliant and thus imposing the development of a new sampling protocol and a new index: the I2M2 multimetric index. This index is made up of 5 metrics and was designed to respond significantly to 17 pressure categories linked to water quality and habitat degradation. It is expressed in terms of deviation from the reference and its class boundaries are defined for each type of watercourse. The I2M2 exhibits robust average discrimination efficiency greater than 80% for the pressure categories considered (68-97%) where the IBGN demonstrated significantly lower performance with an average discrimination efficiency of about 65% (53-90%).