A comparison of habitat diversity and interannual habitat dynamics in actively and passively restored mountain rivers of
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FORM AND FUNCTION
A comparison of habitat diversity and interannual habitat dynamics in actively and passively restored mountain rivers of Germany Sonja C. Ja¨hnig • Armin W. Lorenz Rainer R. C. Lorenz • Jochem Kail
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Received: 31 December 2011 / Accepted: 21 July 2012 / Published online: 20 September 2012 Springer Science+Business Media B.V. 2012
Abstract We compared habitat diversity and morphodynamics of ‘actively’ restored reaches (including removal of bank fixation, widening and large wood placement) with ‘passively’ restored reaches (abandonment of channel maintenance) and adjacent nonrestored control reaches in medium-sized Central
Guest editors: A. Elosegi, M. Mutz & H. Pie´gay / Form and function: channel form, hydraulic integrity, and river ecosystem functioning Sonja C. Ja¨hnig and Armin W. Lorenz contributed equally to this study. S. C. Ja¨hnig (&) Biodiversity and Climate Research Centre (BiK-F) & Senckenberg Research Institute and Natural History Museum, Department of River Ecology and Conservation, Clamecystr. 12, 63571 Gelnhausen, Germany e-mail: [email protected] A. W. Lorenz Department of Aquatic Ecology, Faculty of Biology, University of Duisburg-Essen, Universita¨tsstr. 5, 45141 Essen, Germany R. R. C. Lorenz Lorenz TexResearch GmbH, Schmaxbruch 35b, 41334 Nettetal, Germany J. Kail Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Mu¨ggelseedamm 310, 12587 Berlin, Germany
European mountain rivers. Habitat diversity and river morphology were mapped in two consecutive years and changes in habitat composition (channel features, substrates) and morphological changes (active depth and width) were quantified. In both years, habitat diversity was generally higher in the restored reaches compared to their non-restored counterparts, and significantly differed between restoration approaches, with average values in actively restored reaches being about 60% larger than in passively restored reaches. Channel feature composition differed significantly, both between restored and unrestored reaches, and between restoration approaches, whereas substrate composition was similar in all investigated reaches, indicating that restoration had a higher effect on mesohabitat than on microhabitat conditions. Interannual habitat dynamics in respect to channel feature composition were larger in the actively restored compared to the passively restored reaches, while substrate composition remained fairly constant in all reaches. Regarding morphodynamics, changes in depth and width of actively restored reaches differed significantly from changes in passively restored ones in three of the four elements compared. Our findings imply increased habitat richness, diversity and habitat dynamics in the restored reaches, especially in actively restored ones. Analysis of discharge data suggests that flood events exceeding critical shear stress of the bed material, and the time span since restoration determine the potential for morphological changes.
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Keywords Active restoration Passive restorati
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