Considerazioni sull'applicazione dell'indice diatomico ICMi (Intercalibration Common Metric Index) nell'Italia nord- occidentale

Within the framework of the European Directive 2000/60/CE (WFD) we evaluated the ecological status of some of the most important rivers in the North-West Italy (Aosta Valley, Liguria and Piedmont), through diatom community analysis and the application of the main European diatom indices. The main aim of this research was the evaluation of the ICMi reliability in our regions through the comparison with other accomplished European diatom indices. Starting from 2008, we analysed diatom communities detected in 200 samples, coming from those stretches included in the Regional Environment Protection Agencies (ARPA) monitoring programs, representing 7 different hydroecoregions (HERs) and the 7 river macrotypes identified in the North-West regions (included in Alpine, Central, Mediterranean). In total, we identified 305 taxa, with the presence of some allochthonous species and new records for Italy. Through the comparison with other European indices we pointed out that ICMi index generally tends to overestimate river quality, especially sites assigned to the Central and Mediterranean typology. Indeed, reference values for the Ecological Quality Ratio (EQR) calculation are too low and, as a consequence, EQR often exceeded 1 and ICMi final results are too often very good. Moreover, some frequently recorded species (allochthonous taxa, teratological forms and recently described species) are not included in the calculation of the index lowering its reliability.