Eric Hallot

Habitat Choice by Atlantic Salmon Parr in Relation to Turbulence at a Reach Scale

Abstract The variables commonly used to describe the physical habitat of Atlantic salmon Salmo salar parr are average velocity, water depth, and substrate. A variety of micro- and mesohabitat models have been developed using these variables to assess habitat quality. However, Atlantic salmon parr live in highly turbulent streams and rivers in which intense fluctuations of water velocity occur. Laboratory experiments have shown that turbulence affects the behavior and energetics of fish. Nevertheless, habitat use in relation to the strong temporal variability of velocity in natural environments has rarely been studied. In this study, Atlantic salmon parr habitat was examined in relation to turbulence in the Patapedia River, Quebec. Rather than taking the usual approach of surveying a large population at one point in time, we used an intensive radiotelemetry tracking survey that focused on the habitat use of a few individual fish over an extended period. We analyzed habitat use in relation to several dynami...

The Semois Valley in Southern Ardenne: Short-Wavelength, Large-Amplitude Meanders Incised into a Slaty Basement

The incised meanders of the Semois Valley, in Southern Ardenne, are remarkably elongated, forming a nearly 100-km-long meander belt. Their elongation is conditioned by the relative orientation of the meander loops and the regional slaty cleavage, as theorized by Strahler. These meanders already existed in the Early Quaternary, some cut-off meanders lying more than 100 m above the present floodplain. Although the Quaternary incision rates of the Semois were low (≤0.05 mm/year), several meanders look more entrenched than ingrown, probably because lateral erosion was fairly slow (~0.3–0.5 mm/year), owing to the large quantity of material to evacuate by a rather small river. The combined aesthetic and scientific interests of this particularly well-developed meander belt speak in favour of the preservation of the nicest meanders as geomorphosites.

Cuestas in Gutland (S Luxembourg) and Belgian Lorraine: Evolution of a Structurally Controlled Landscape

The cuesta landscape of Belgian Lorraine and Luxembourg’s Gutland belongs to the north-eastern rim of the Paris Basin, characterized by the wide syncline of the Gulf of Luxembourg. Highlighting the underlying geological structure and lithology, the cuestas were progressively sculpted in close relation with the contrasted evolutions of the Meuse and Rhine river systems. The landscape was established during the Cenozoic in Triassic and Jurassic rocks. These are formed of alternating hard pervious and soft, generally impervious units, the latter with a limited resistance to superficial weathering under the climatic conditions of the Neogene and Quaternary. The hard units frequently appear as thick homogenous layers, not only making the core of the cuestas but featuring also many escarpments. Height and lateral extent of the cuestas are controlled by the thickness of the hard layers and lateral changes in facies, as exemplified in the Middle Liassic sandstone and Triassic rocks. Remnants of an extended Neogene erosional surface cut the cuesta summits at ~400–420 m asl. Later fluvial erosion incised this surface, allowing for the development of lower planation surfaces down to 300 m, including a prominent level at ~350 m. Lower structural surfaces also exist on top of hard layers. Finally, landsliding is shown to participate actively in sculpting the cuesta landscape.