Report on Harmonisation of freshwater biological methods

enthic algae in the reach, but results may not be sensitive to subtle water qualitychanges because of habitat variability between reaches. Species composition ofassemblages from a single habitat potentially reflect water quality differences betweenstreams more precisely than multihabitat sampling, but impacts in other habitats in thereach may be missed (Barbour et al, 1999).16. The sampling frequency for phytobenthos monitoring varies from annually inFrance, every 3 years in Austria and 4 years in Romania.17. Barbour et al. (1999) recommended that single habitat sampling should be usedwhen biomass of periphyton is assessed. In other circumstances the use ofmultihabitat sampling may be more appropriated. The only references for biomassquantification relate to the assessment method developed by Norway, which isperformed in a single substratum, in riffle conditions.18. The level of taxonomic resolution used in the assessment methodologies based inphytobenthos is the species or species groups. Only Slovenia uses a higher taxonomiclevel, which varies from species to family or higher taxonomic level. Forphytobenthos most of the indices require species-level identification, although somecan be used with genera, or a mixture of genera and species. Some taxa are difficult toidentify and in these cases the taxa have been pooled into “paired taxa”.19. Despite the complexity of diatoms identification, this is costly and timeconsuming process and hence, the lowest taxonomic level is often preferable,providing a better ecological resolution, especially for definition of referenceconditions. This problem will be enhanced if the monitoring programmes includediatoms and non-diatoms groups.20. The identification process is based on a European Standard EN 14407 (2004)Water quality: Guidance standard for the identification, enumeration andinterpretation of benthic diatom samples from running water. This standardestablishes methods for identification and enumeration of relative proportions ofdiatom taxa on prepared slides and of data interpretation relevant to assessment ofwater quality in rivers and streams. It is suitable for use with indices and assessmentmethods based on the relative abundance of taxa.71