DIN CEN/TR 16151:2011-06

Multimetric indices belong to the generally used tools for classification of quality of freshwater and brakish water ecosystems (flowing waters, still waters, transitional waters, wetlands). A multimetric index combines several single metrics, the results of which will finally form a multimetric result. Thus, multimetric indices integrate several attributes of a community ("metrics") to describe and evaluate a status. Different metric categories (for example, taxa diversity, sensitive and tolerant species, trophic structures) reflecting different environmental conditions are combined to form a multimetric index. Multimetric indices can be applied to different aquatic ecosystems (flowing waters, still waters, transitional waters, wetlands) as well as various biological quality components (fish, benthic invertebrates, macrophytes, phytoplankton, pyhtobenthos). They are flexible with regard to the composition of the metrics, as different metrics are suitable for evaluation of different ecosystems or different stressors. In the last years, a large amount of multimetric indices has been developed and is now used especially with the aim of implementation of the Water Framework Directive. It is expected that many existing multimetric indices are adjusted and many new indices will be developed in the next years. In order to improve comparability between multimetric evaluation methods, the method of the development and use of a multimetric index is described. Differentiation between two methods for calculation of multimetric indices is made: the "general method" and the "stressor-specific" method. The "general method" determines different metrics using the list of species. The metric results may be compared individually with the corresponding metric values under reference conditions. From this comparison, a value is determined for every metric. These values are subsequently used to calculate the multimetric index. The "stressor-specific method" chooses a series of metrics based on their suitability to detect a certain stressor. As a result, the values of the metrics which aim at a single stressor, are firstly calculated to achieve a value representing the intensity of this stressor. The evaluation results for all stressors are finally calculated to achieve a multimetric index. The results of a multimetric index may be visualized on various levels: the top level displays the ecological status class, the second level (in the case of the stressor-specific method) the results of the stressor-specific modules (quality classes "organic contamination" and "degradation of the flowing waters morphology") and the third level the results of the single metrics. The preparatory works have been developed by NA 119-01-03-05-06 AK "Biologisch-ökologische Gewässeruntersuchung" ("Biological ecological analysis of water") of NA 119-01-03 AA "Wasseruntersuchung" and has been funded by the Länderfinanzierungsprogramm "Wasser, Boden und Abfall" (federal funding programme "Water, soil and waste").