Hoe staat het er twintigjaar later voor?

Kris van Looy, Wendy Liefveld, Gijs Kurstjens & Jasper Hugtenburg

rivierherstel, doelsoorten, hydrodynamiek, connectiviteit

Het uitgevoerde natuurherstel langs Maas en Rijntakken heeft ertoe geleid dat de belangrijkste doelsoorten uit veel soortgroepen terugkeren, zoals stroomdalplanten, libellen, sprinkhanen, prikken, stroommossels, mét daarbij de kritische soorten van de top van de voedselpiramide. Een aantal groepen, zoals dagvlinders, kriebelmuggen en steenvliegen, laat echter nog geen duidelijk herstel zien. Gerichte monitoring van de natuurontwikkeling langs Maas en Rijntakken, samen met de monitoringresultaten voor specifieke ingrepen, geeft inzicht in de sleutelfactoren voor succes. In dit artikel willen we het rivierherstel, en de succes- en faalfactoren daarvan voor het gebied van onze grote rivieren, nader analyseren.

Room for large rivers and ecological restoration programs

Kris van Looy, Wendy Liefveld, Gijs Kurstjens & Jasper Hugtenburg

River restoration, river species, hydrodynamics, natural flooding, connectivity

With this contribution, documented river restoration project evaluations in time for the Rhine-Meuse delta are gathered and analysed. Comparison of presence of target species in different taxonomic groups between the period before nature development (1980-1993) and the period of nature development (1994-2009), reveals that many critical target species recolonized. The restored network of large core areas and smaller stepping stones appear to contribute to the connectivity for a large group of species. For example, a spectacular expansion along the large rivers is visible for the river-bound plant species.
Aquatic insects of both stagnant and running waters have increased sharply. Grasshopper species have benefited from the large areas of natural grazed landscape, and are gradually colonizing nature reserves throughout the entire river area. The common species show an exponential increase in abundance thanks to the natural grazing management. This also leads to a large increase in breeding birds along the rivers, for which the insects are basic food. Several critical species groups for habitat quality, such as butterf lies and stonef lies are not responding up till now. Also for specific river restoration measures, like side-arm reconnection, restoration of tidal connection, novel bank protection techniques, the quality and success is measurable in the diversity of flow and habitats realised. For the identified issues of habitat quality, more attention is needed for the restoration of hydromorphological conditions of overbank and in-stream sedimentation, and of specific habitats of the large alluvial rivers, such as low dynamic grassland and lower f loodplain wetlands. The combination of space and time gradually brings about the nature targets, in accordance with the space requirements of the critical species. Nevertheless, management corrections are needed to support the quality demands for specific habitats and species groups.

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