New Tools for Bioindication of Water and Substratum Quality in Streams

Water and stream substratum quality are key factors influencing the composition of aquatic communities. Particularly, stocks of salmonid fishes are in decline and their recruitment rates are strongly dependent on water and substratum quality. In this contribution, two toolboxes for active bioindication of water and substratum quality in streams are presented, the “salmonid egg floating box” (SEFLOB) and the “egg sandwich” (ES). The SEFLOB is a floating box comprising two partitions, one with three replicates for simultaneous bulk exposure of eggs and the other for individual exposure of eggs in a grid. The ES is a toolbox to determine spatially resolved hatching success of salmonid eggs to assess stream substratum quality. It is composed of an egg exposure unit which allows the determination of depth-specific salmonid egg hatching success and a unit for extracting water samples for physico-chemical measurements within the interstitial zone. Both toolboxes were successfully tested under standardized laboratory conditions and in natural and artificially constructed spawning sites of brown trout (Salmo trutta), Danube salmon (Hucho hucho) and grayling (Thymallus thymallus) to assess reintroduction success. The active bioindication approach can be integrated into the holistic Proceeding Chain of Restoration (PCoR) for target-oriented river restoration.