Consequences of fluvial maintenance operations on the sediment morphodynamic and the associated BIOdiversity in the mosaic of MAREAU-aux-prés islands.

Abstract : The Mareau-aux-Prés islands are characterized by a multiple channel pattern affected by an incision of the main channel of 0.6m between 1979 and 2002. In this area, natural limestone riffles influence the morphology and spatial distribution of vegetated islands, secondary channels and alluvial bars. The latter bars are colonized by woody pioneer trees, such as native black poplar (Populus nigra L.). Within these islands, the central 3 ha sandy-gravelly bar is currently beeing surveyed since 2007. In a first study from 2007 to 2012, a multidisciplinary approach has been conducted to understand sediment dynamics and morphological evolution into an island style, mainly governed by sedimentary vertical accretion and presence of woody pionner vegetation (Wintenberger et al. 2015a,b). In september 2012, the vegetation of such island was uprooted and the bar level lowered in order to maintain the flow capacity of the river. A new sandy-gravelly bar appeared in spring 2013, ideal field support for studying long-term ecological issues. A second research programme from 2013 to 2015 was conducted in a multidisciplinary approach, focusing on physical and biological compartments. Field measurements on annual basis were performed on hydro-sedimentary processes to compare with the 2007-2012 period. Biotic components focus on colonization dynamics by Populus nigra seedlings (studying small-scale spatial genetic structure), by native and invasive flora (through seed bank and summer inventories), by community assemblages of ground beetles Coleoptera Carabidae, and on the consequence of the modification of the feeding habitat by the European beaver (as the central island constituted the main source of wood). A new project (2016-2019) has been elaborated, allowing to follow this long term survey, and also incorporating new technologies, such as satellite remote sensing. References : Wintenberger, C., et al. 2015a. Geomorphology, 246 : 305-320 Wintenberger, C., et al. 2015b. Geomorphology 248 : 185-204