ALGAE FOR MONITORING RIVERS Identification versus counting protocols as sources of uncertainty in diatom-based ecological status assessments Maria Kahlert • Martyn Kelly • Raino-Lars Albert • Salome ´ F. P. Almeida • Toma ´s ˇ Bes ˇta • Sau ´l Blanco • Michel Coste • Luc Denys • Luc Ector • Marke ´ta Fra ´nkova ´ • Das ˇa Hlu ´ bikova ´ • Plamen Ivanov • Bryan Kennedy • Petr Marvan • Adrienne Mertens • Juha Miettinen • Joanna Picinska-Faltynowicz • Juliette Rosebery • Elisabet Torne ´s • Sirje Vilbaste • Andrea Vogel Received: 27 January 2010 / Accepted: 17 May 2011 / Published online: 3 May 2012 Ó Springer Science+Business Media B.V. 2012 Abstract In 2009, seventeen analysts participated in a pan-European diatom ring-test (intercalibration), analyzing nine samples from seven countries follow- ing the European standard EN 14407. The objective of this exercise was to agree on practical conventions on diatom identification to facilitate future intercalibra- tion work and to assess the extent to which national differences in sample analysis (counting protocol and identification conventions) contribute to variability in EU-level comparisons of diatom-based methods. Dif- ferences in the reported taxa lists were large, but not a major source of variation in values of a common metric (the phytobenthos Intercalibration Common Metric, ICM). Therefore, every country can apply its own identification conventions for national assess- ments, and still be fairly confident that the ICM reflects the national classification of its streams. Part of the index variation was due to differences in counting protocols and care should be taken when handling broken valves, girdle views and small taxa. More work at both national and European level is needed to provide a harmonized way of using diatoms for ecological status assessments in the future. Electronic supplementary material The online version of this article (doi:10.1007/s10750-012-1115-z) contains supplementary material, which is available to authorized users. Guest editors: L. Ector, D. Hlu ´bikova ´ & L. Hoffmann/ Proceedings of the 7th International Symposium ‘‘Use of Algae for Monitoring Rivers’’, Luxembourg, November 23–25, 2009 M. Kahlert (&) Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, P.O. Box 7050, 750 07 Uppsala, Sweden e-mail: Maria.Kahlert@slu.se M. Kelly Bowburn Consultancy, 11 Monteigne Drive, Bowburn, Durham DH6 5QB, UK R.-L. Albert Á J. Miettinen Ecomonitor Ltd., La ¨nsikatu 15, 80110 Joensuu, Finland S. F. P. Almeida Department of Biology, GeoBioSciences, GeoTechnologies and GeoEngineering (GeoBioTec) Research Unit, University of Aveiro, 3810-193 Aveiro, Portugal T. Bes ˇta Department of Botany, Faculty of Science, University of South Bohemia, Branis ˇovska ´ 31, 370 05 C ˇ eske ´ Bude ˇjovice, Czech Republic S. Blanco Department of Biodiversity and Environmental Management, University of Leo ´n, 24071 Leo ´n, Spain M. Coste Á J. Rosebery Water Quality and Wastewater Department, Irstea, 50, Avenue de Verdun, Gazinet, 33612 Cestas Cedex, France L. Denys Research Institute for Nature and Forest (INBO), Kliniekstraat 25, 1070 Brussels, Belgium 123 Hydrobiologia (2012) 695:109–124 DOI 10.1007/s10750-012-1115-z