The return of degraded stream ecosystems by using positive impacts from near-natural sections: a new practical guide for restorations.

Streams in North Rhine- Westphalia ( Germany) are frequently impacted by hydromorphological degradation leading to a loss of sensitive species and a reduction in diversity. These findings mean that the final objective of the European Water Framework Directive to achieve the good ecological status will be failed for a large number of streams. In a holistic approach, a new concept, considering the cost efficiency, has been developed to enhance habitats by morphological changes. This guide serves as a basis for stream restoration projects. The theoretical background is that near-natural sections influence adjacent sections of medium habitat quality positively by migration of type-specific sensitive organisms. The preconditions are a local taxa richness in the catchment area, the reduction of nutrients and organic matter, and the guarantee of free movement. This so-called 'spreading effect' can be measured upstream and downstream. The length of by these means valourized sections depends on the stream type and on the biological quality component. [ABSTRACT FROM AUTHOR]