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The distribution and environmental state of vegetated islands within human-impacted European rivers

Authors

  • LUISA FERNANDA RICAURTE,

    1. Department of Aquatic Ecology, EAWAG, Swiss Federal Institute of Aquatic Sciences and Technology, Duebendorf, Switzerland
    2. ETH-Zurich, IBZ, Institute of Integrative Biology, Zurich, Switzerland
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  • SARAH BOESCH,

    1. Department of Aquatic Ecology, EAWAG, Swiss Federal Institute of Aquatic Sciences and Technology, Duebendorf, Switzerland
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  • JUKKA JOKELA,

    1. Department of Aquatic Ecology, EAWAG, Swiss Federal Institute of Aquatic Sciences and Technology, Duebendorf, Switzerland
    2. ETH-Zurich, IBZ, Institute of Integrative Biology, Zurich, Switzerland
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  • KLEMENT TOCKNER

    1. Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany
    2. Institute of Biology, Freie Universität, Berlin, Germany
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Luisa Fernanda Ricaurte, Department of Aquatic Ecology, EAWAG, Swiss Federal Institute of Aquatic Sciences and Technology, Duebendorf, Switzerland.
E-mail: luisa.ricaurte@eawag.ch

Summary

1. Vegetated islands within river corridors are pivotal landscape features and are among the first to disappear as a consequence of flow regulation and channelisation. However, how vegetated islands vary along human-impacted rivers is poorly understood.

2. We carried out a detailed analysis of the contemporary distribution, diversity and environmental state of vegetated islands within 12 human-impacted European rivers, using 75 Landsat 7 ETM+ satellite images (1999–2002), historical maps, DEM data and landscape metrics. We tested whether channel fragmentation, catchment land use and the environmental state of fringing floodplains determine the spatial patterns of the islands. We also analysed the historical change of islands within selected sections of the Upper Danube, Upper Rhine and Olt rivers.

3. We identified 2771 islands in the contemporary landscape, varying from 0.06 to 9828 ha. Islands covered up to 21% of the active channel area and contributed up to 32% of the total riparian ecotone length. Island density ranged from 0.06 islands per river-km (River Sava) to 1.6 islands per river-km (River Tagliamento). River regulation has led to a marked loss of island density: 94% in the Upper Danube, 93% in the Upper Rhine, and 69% in the Olt. The environmental state of the islands was significantly less altered by human activity than of their fringing floodplains; 93.4% of the vegetated islands exhibited a near-natural state, while 86% of the fringing floodplains were expansively converted to agricultural and urban land uses.

4. Our results highlight the ubiquitous presence of vegetated islands, their sensitivity to river regulation and their pivotal role for the future restoration and management of river corridors.

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