Diatoms from Alto Adige/Südtirol (Northern Italy): characterization of assemblages and their application for biological quality assessment in the context of the Water Framework Directive

The Water Framework Directive 2000/60/EC (WFD) requires the analysis of biological elements of aquatic ecosystems to assess water quality. Diatoms are the component of the periphyton most commonly used to classify lotic environments. Within the context of the WFD the concept of ‘reference conditions’ was introduced and biological quality of watercourses is expressed as Ecological Quality Ratio (EQR). This study was carried out in Alto Adige/Sudtirol (Province of Bolzano-Bozen, northern Italy), belonging to the Alpine eco-region, and to the hydro-ecoregion Inner Alps. During 2006–2009, epilithic diatoms were sampled from monitoring and reference sites of seven stream types. Diatom assemblages were analysed with TWINSPAN and CCA analyses to investigate species association and distribution in relation to stream characteristics. Altitude and geology resulted to be the most important factors influencing diatom assemblage composition, and were used to describe new stream types. Indicator species analysis was used to characterize reference assemblages. The biological quality of watercourses was assessed using different diatom indices: Specific Pollution sensitivity Index (IPS), Eutrophication and Pollution Index with Diatoms (EPI-D), Trophic Index (TI). We tested also the Intercalibration Common Metric index (ICM)