Macrophytes and diatoms – major results and conclusions from the STAR project Karel Brabec 1, * & Krzysztof Szoszkiewicz 2 1 Institute of Botany and Zoology, Faculty of Science, Masaryk University, Kotlarska 2, 611 37, Brno, Czech Republic 2 Department of Ecology and Environmental Protection, Agricultural University of August Cieszkowski, ul. Pia ˛ tkowska 94C, 61-691 Poznan, Poland (*Author for correspondence: E-mail: brabec@sci.muni.cz) Key words: Water Framework Directive, aquatic plants, assessment Abstract The interactions between sensitivity and variability of macrophyte and diatom communities were evaluated as a research support of methodologies required by the Water Framework Directive. Slope and shading were identified as additional typological parameters improving links between unimpacted macrophyte communities and running water types. Two other studies demonstrated indication value of macrophytes for assessment of nutrient enrichment and hydromorphological degradation. The special exercises were realized within the STAR project to evaluate sources of variability/uncertainty in assessment methods based on macrophytes and diatoms. Sampling period and shading of the site were found as major factors affecting variability in macrophyte assessment results. Uncertainty of diatom assessment is predominantly associated with selection of site, substrate type and taxonomic identification. Further extension of indication systems and definition of macrophyte/diatom-specific typology of running waters are considered as the main aims of subsequent investigations. Introduction Aquatic macrophytes and algae are primarily sensitive to human impacts changing the light and nutrient regimes, physical characteristics of habi- tats and organic matter spiralling (Murphy, 1998). Agriculture, forest management, urban develop- ment, river regulation and other activities affect aquatic primary production and structure of autotrophic communities. Macrophyte communi- ties can be viewed as indicators of flow conditions, but they can also act as factor affecting flow sig- nificantly or they are utilised as the substrate by algae and macroinvertebrates. Scale of response varies from short-term con- ditions existing at microhabitat through response to characteristics of channel or riparian zone to large-scale changes in watershed. Phytobenthos is usually considered as early warning indicator while macrophytes due to their longer life cycles and tolerance to short-term changes of environmental conditions indicate more persistent impairment. Aquatic plants are considered as valuable indicators of ecological status and their monitor- ing is required by Water Framework Directive (Council of the European Communities, 2000). General advantages of using macrophytes for assessment are that they are stationary, are visible by naked eye, relatively low manpower demands, quantity can be expressed as cover and in some cases remote sensing bring information about quantity of macrophytes. Advantages of diatoms are well-established relationships with certain stressors (particularly eutrophication), they are Hydrobiologia (2006) 566:175–178 Ó Springer 2006 M.T. Furse, D. Hering, K. Brabec, A. Buffagni, L. Sandin & P.F.M. Verdonschot (eds), The Ecological Status of European Rivers: Evaluation and Intercalibration of Assessment Methods DOI 10.1007/s10750-006-0097-0