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A palaeoenvironmental study of a palaeochannel within the lower alluvial floodplain of the Allier River, France, has been carried out at a high temporal resolution. Research was based upon a multi-proxy approach using different sedimentological (magnetic susceptibility, sediment texture and loss on ignition) and palaeoecological (pollen, non-pollen palynomorphs (NPPs), diatoms – indicators). The palaeochannel was dated from six radiocarbon dates and spans from the second to the eleventh century AD. The cultural landscape history of this floodplain and the progressive hydrological disconnection of the palaeochannel between the Antiquity and the early Middle Ages could be reconstructed according to several characteristic environmental phases. Co-inertia analysis linking pollen, NPPs and diatom corroborated the significant co-structure of these proxies and allowed to distinguish functional palaeoecological groups in terms of landscape openness, on-site aquatic and hygrophilous vegetation, riparian woodland, soil moisture and grazing pressure. Results obtained underpin the importance of grazing as a major agent of landscape change in floodplains, especially since the ninth century AD, when the clearance of the riparian woodland is attested. Gallo-Roman and Late-Antiquity land-use systems, on the contrary, allowed for the preservation of riparian fluvial landscapes. [ABSTRACT FROM PUBLISHER]

Man-induced channel changes within Alpine alluvial rivers are investigated. For the middle Arve river, a series of long profiles surveyed between 1856 and 1981 show deep and rapid degradation since the beginning of the 1950s. This tendency is related to gravel extraction, weir construction, and embankment, and is shown to characterize Alpine rivers. [ABSTRACT FROM AUTHOR]

The historical trend of aggradation in stream beds of Europe's mountain and piedmont areas has been reversed since the beginning of the twentieth century to a general tendency towards narrowing and incision. After an overview of some causes and geomorphological effects of river bed incision, and a description of some case studies in alpine rivers, this paper aims to assess how the phenomenon affects the ecosystems of alluvial plains. The questions addressed are, in particular, the effect of river bed incision on sediment redistribution during floods, habitat diversity and the water table; and the consequences of these changes for the distribution and diversity of biological communities. The effect of incision on floodplain vegetation, instream invertebrate communities, groundwater and former channel ecosystems and fish communities are considered. It has been found that incision rarely affects the biocoenoses directly, but indirect changes in habitat conditions are significant. At the scale of the whole hydrosystem, thepredicted impact of incision is a decrease in habitat heterogeneity,and, thereby, in biodiversity. At the ecosystem scale, the negative effect on biodiversity is higher in habitats that are less connected to the running water of the river. [ABSTRACT FROM AUTHOR]