Die vorliegende Arbeit unterbreitet einen Vorschlag, wie der Umgang mit der Ausnahmeregelung der weniger strengen Umweltziele nach Art. 4.5 der EU-Wasserrahmenrichtlinie (WRRL) für den ökologischen Zustand von Fließgewässern aussehen kann. Dazu wird ein Verfahren ausgearbeitet, das es erlaubt, in mehrfach belasteten Fließgewässern den bestmöglichen ökologischen Zustand zu identifizieren. Das Verfahren bezieht sowohl Elemente der Bewertung von Ökosystemstrukturen, -funktionen als auch der Bereitstellung von Ökosystemleistungen ein und verfolgt einen adaptiven Managementansatz. Anhand einer Fallstudie wird aufgezeigt, dass auch ein weniger strenges Umweltziel ambitioniert ist und eine Vielzahl an Renaturierungsmaßnahmen erfordert, wenn alle Bestimmungen in und Handreichungen zur WRRL ernst genommen werden.

The cumulative dissertation at hand addresses the question of how promising the successful implementation of the WFD is. Since research on implementation deficits has so far mainly considered national and sub-national levels, regional and local scales are taken centre stage within the dissertation. The Hase river catchment, which is located in one of Germany s most intensive livestock areas, serves as an example. The thesis shows that the procedural character of the WFD and regulative uncertainties give way to interpretation and action leeway, which will be pivotal to judgement on implementation success at lower levels. Moreover, the consistent operationalisation of nitrate limits in particular has led to major difficulties during implementation in Germany from which restraints can be expected for the preparation of river basin management plans and the program of measures. As to the regional level, implementation restraints also upraise due to socio-economic dependencies from agriculture and a high identification of the regional population with this economic sector have placed agriculture in a powerful position. In conclusion, one can state that various implementation restraints occur and the cause of these can be found at all scales European, sub-national and regional. The results of this dissertation concerning the multi-level system reveal that the relationship and interaction of the various scales will be given increased attention during the implementation process of European environmental policy. Besides the national and sub-national scale, the regional and local levels will be of equal importance. The question of suitable scales for implementation decisions and measures also offers pivotal approaches to undertake future research. Further research needs occur with new regional studies at national and international scales, with regard to the future of water protection in the course of the reform of German federalism and the current debate on climate change.