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  to ecology
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Workshop sessions

Topic 5. Linking hydromorphology and ecology (more general issues and concepts, within context of reference conditions).

a) Klement Tockner, IGB, Berlin.

Hydrogeomorphic linkages and feedbacks in highly dynamic fluvial systems.

Highly dynamic fluvial ecosystems are particularly sensitive to environmental changes and are now rare landscape features throughout Europe. Therefore, a key challenge in river management is to link flood protection and nature restoration, in particular by gaining a better understanding of the complex linkages and feedbacks between fluxes of water, sediments, nutrients, organic matter, and organisms in dynamics fluvial systems. Based on ongoing research along near-natural river systems, I will discuss ecological and geomorphic thresholds in dynamic systems, quantify reciprocal coupling of aquatic and terrestrial food webs, present concave and convex islands as key ecological nodes along river corridors, and suggest functional indicator for assessing the hydroecological integrity of dynamic fluvial ecosystems. Finally, I will provide an overview of the multiple pressures that threaten fluvial ecosystems at the local, regional and continental scale.

b) Steve Ormerod and Ian Vaughan, Cardiff University.

Towards improved quantitaive links between hydromorphology and ecology.

A recent extensive review of the literature has illustrated that:

1. Processes linking the distribution and abundance of river organisms and hydromorphological character are generally well understood, but poorly quantified;
2. The consequences of hydromorphological modification for river organisms and ecosystems are poorly quantified;
3. Regulatory agencies require improbed quantitative tools to discharge their responsibilities under current legislation.

In this contribution, we outline the review findings, and illustrate some initial attempts to use large data sets to address some of the shortfalls using available information.

c) Richard Johnson, Swedish Agricultural University, Uppsala.

Spatial congruency and response of taxonomic groups in streams to gradients in resource and habitat characteristics.

Understanding patterns in taxonomic congruency and the importance of environmental variables as drivers of these patterns are prerequisites for analyzing declines in regional species pools. Using data on fish, invertebrate, macrophyte and benthic diatom assemblages from high quality sites, Mantel tests and principal components analysis failed to reveal strong diversity gradients in lowland or mountain streams. Composition of other taxonomic groups were, however, better predictors of assemblage diversity than interactions with environmental variables lending support to the importance of species interactions for spatial coherence (usually > 50% of the variance in diversity of one organism group could be explained by the presence of another organism group). Including complete gradients (high and low quality sites), regression showed that composition of benthic diatom assemblages in lowland streams and invertebrate assemblages in mountain streams were the best predictors of changes nutrient concentrations. By contrast, macrophyte richness in lowland and invertebrate composition in mountain streams were better predictors of changes in habitat. Correlation indicates that macrophyte assemblages in lowland streams and fish assemblages in mountain streams may function as surrogate indicators for the diversity of other taxonomic groups.

Topic 6. Ecologically-based river restoration