Scientific base and modular concept for comprehensive assessment of streams in Switzerland

There is a difficult polarity between reality and ecologically desirable go als of stream ecosystem management in Switzerland. Most streams are exposed to a variety of impacts. Due to a high intensity of anthropogenic activity there is a high pressure on land and water use. Essential water uses have to be guaranteed. On the other hand there is also a strong need to preserve or restore (bring back ecological integrity) or rehabilitate streams (brin g back 'relative ecological integrity'). Stream assessment should, therefor e, produce sound data suitable for characterizing the ecological condition of streams and for supporting their sustainable management. The methods sho uld include a system approach as the basic unit and sound scientific princi ples of ecological integrity emphasizing habitat connectivities. The method s should allow: . the condition of streams to be rationally described and j udged, . identification of different kind of impacts on a stream, . verific ation of the effects of water protection measures, . identification of suit able future actions in the context of a whole stream system. In order to co ver the various requirements a modular concept for stream system-oriented a nalysis was developed. Altogether nine modules are elaborated. Each module deals with specific stream features (two hydrodynamic and ecomorphological modules, five biological modules, two chemical and ecotoxicological modules ). Single modules, several modules, or all of them may be applied, dependin g on the purpose of the analysis. For each module a cost-effective survey p rocedure (rapid method) and a progressively more rigorous method providing more detailed information is suggested. Based on the result of the analysis , stream rehabilitation concepts can then be elaborated in cooperation with managers, river engineers and biologists.