Is what has been measured of any direct relevance to the success of the macrophyte in its particular environment?

The Danube is the second-longest river in Europe that is subjected to various man-made alterations, including those related to hydro-power plants. We surveyed and analyzed the presence and abundance of macrophytes in the main channel from 2582 river kilometers (rkm) to 171 rkm. We also assessed selected habitat parameters in the sampled river stretches. Sixty-eight different plant species were recorded along the entire course. Among neophytes, we found Elodea nuttallii, E. canadensis, Vallisneriaspiralis and Azolla filiculoides. Based on similarity analysis, we distinguished 15 plant communities, most of which were defined as associations, which were classified into 5 alliances and represented three vegetation classes, namely vegetation of rooted hydrophytes Potamogetonetea, the vegetation of pleustophytes Lemnetea and vegetation of marshes Phragmitetea. The number and abundance of plant species, as well as plant communities recorded in single stretches, varied along the course. Canonical correspondence analysis (CCA) revealed that environmental parameters explained 21% of plant species composition. CCA runs with neophytes explained 41% of the variance, and current velocity, water transparency, species number and bank structure were significant variables. The present study revealed that the free-running sections of the river are poor in number and abundance of plant species, whereas impounded reaches mainly show an opposite result.

The EU water framework directive (WFD) is intensively connected with other European legal regulations and supporting documents. This close interrelationship calls for deeper considerations when WFD is implemented in locations of high conservation value, e.g. Natura 2000 sites. A comprehensive, but specific comparison of the goals of WFD with the aims of habitats directive (HD) and birds directive (BD) provides a sensitive overview on their peculiarities, with an outlook on potential synergies and conflicts. The sometimes complex guidance for solving complicated situations in the practical application of these differing legal provisions is also described. The representation of requirements for Natura 2000 sites as part of river basin management plans, and related up-to-date experience are given special attention. Finally recommendations and conclusions provide the reader with a complete view of this challenging chapter in European Policy. In the end, considerably more synergies than conflicts are identified between the objectives of WFD, HD and BD. Whenever conflicts should arise these directives prevent derogating from their requirements by cross-references. Therefore, firm and timely coordination between water and nature conservation authorities is necessary.