Euro-limpacs Deliverables

ABSTRACT - DELIVERABLE 95

Report - Testing the concept of habitat dynamics

In large parts of Europe hydromorphological alteration is the main stressor affecting rivers. Alterations include channel straightening, dam construction, disconnection of the river from its floodplain, and alteration of riparian vegetation. These changes also affect wetlands and lakes in the associated floodplain through, for example, a lowering of the groundwater level, increased siltation or changes in inundation regime (Hansen, 1998). Under predicted future climate conditions further stresses will be introduced including the combined effect of changes in precipitation and climate−induced changes in land−use patterns. These in turn may cause changes in catchment hydrology that will affect sediment transport and channel morphology, inundation frequency and extent, and impact aquatic ecosystems at both catchment and habitat scale.

In task 2 ?Hydromorphological changes and aquatic and riparian biota? the question is addressed of how the distribution of taxa at the habitat scale is controlled by the environmental conditions at the catchment scale. Characteristic taxa to be used as response parameters to hydrological and morphological structures were therefore identified in task 1. These now called indicators of hydromorphology reflect key hydromorphological conditions at the catchment scale and were studied in task 2 in detail at the habitat scale. The habitats necessary for the occurrence of the indicator species was derived from information of pre− and post−restoration conditions. Hydromorphological restoration more often reduced habitat dynamics and offered the opportunity to extract the knowledge needed on the relation between habitat dynamics and species occurrences.

The objective was to determine the effects of hydromorphological measures on the structure and functioning of the instream communities. The key questions were: “What are the positive and negative effects of individual hydromorphological measures (=changes) on the instream functioning and indicators” and “What is the role of discharge and thus habitat dynamics upon these measures”.

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