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correction of the Multi-Spectral Instrument (MSI)-SENTINEL-2 imagery over inland and sea waters from SWIR bands. Remote Sensing of Environment, Elsevier, 2018, 204, pp.308-321 A B S T R A C TRemote sensing of inland and sea waters depends on the quality of the retrieval of the water-leaving radiance from the top-of-atmosphere measurements. The water-leaving radiance can be difficult to observe due to the reflection of direct sunlight on the air-water interface (sunglint) in the direction of the satellite field of view. The viewing geometry of Sentinel-2 satellite (European Space Agency) makes it vulnerable to sunglint contamination. In this paper, an original method is proposed to correct Sentinel-2-like imagery for sunglint contamination. The sunglint contribution is first estimated from the shortwave-infrared (SWIR) part of the spectrum and then extrapolated toward the near-infrared and visible bands. The spectral variation of the sunglint signal is thus revisited for a wide spectral range (from 350 to 2500 nm). The bidirectional reflectance distribution function related to the sunglint is shown to vary by > 28% from the SWIR to the blue bands of Sentinel-2. The application of the proposed algorithm on actual Sentinel-2 data demonstrates that sunglint patterns are satisfactorily removed over the entire images whatever the altitude of the observed target. Comparison with in situ data of water-leaving radiances (AERONET-OC) showed that our proposed algorithm significantly improves the correlation between satellite and in situ data by 55% (i.e., from R 2 = 0.56 to R 2 = 0.87). In addition, the discrepancies between satellite and in situ measurements are reduced by 60%. It is also shown that the aerosol data provided by the Copernicus Atmosphere Monitoring Service (CAMS) can be safely used within the proposed algorithm to correct the Sentinel-2-like satellite data for both sunglint and atmospheric radiances. Improvements of the proposed method potentially rely on simultaneous retrievals of the aerosol optical properties. The proposed method is applicable to any satellite sensor which is able to measure in SWIR spectral bands over aquatic environments.

The hierarchical branching nature of river networks can have a strong influence on the assembly of freshwater communities. This unique structure has spurred the development of the network position hypothesis (NPH), which states that the strength of different assembly processes depends on the community position in the river network. Specifically, it predicts that 1) headwater communities should be exclusively controlled by the local environment given that they are more isolated and environmentally heterogeneous relative to downstream reaches. In contrast, 2) downstream communities should be regulated by both environmental and dispersal processes due to increased connectivity given their central position in the riverscape. Although intuitive, the NPH has only been evaluated on a few catchments and it is not yet clear whether its predictions are generalizable. To fill this gap, we tested the NPH on river dwelling fishes using an extensive dataset from 28 French catchments. Stream and climatic variables were assembled to characterize environmental conditions and graph theory was applied on river networks to create spatial variables. We tested both predictions using variation partitioning analyses separately for headwater and downstream sites in each catchment. Only 10 catchments supported both predictions, 11 failed to support at least one of them, while in 7 the NPH was partially supported given that spatial variables were also significant for headwater communities. We then assembled a dataset at the catchment scale (e.g. topography, environmental heterogeneity, network connectivity) and applied a classification tree analysis (CTA) to determine which regional property could explain these results. The CTA showed that the NPH was not supported in catchments with high heterogeneity in connectivity among sites. In more homogeneously connected catchments, the NPH was only supported when headwaters were more environmentally heterogeneous than downstream sites. We conclude that the NPH is context dependent even for taxa dispersing exclusively within streams.

Abstract. The spatial and temporal coverage of the Landsat satellite imagery make it an ideal resource for the monitoring of water temperature over large territories at a moderate spatial and temporal scale at a low cost. We used Landsat 5 and Landsat 7 archive images to create the Lake Skin Surface Temperature (LakeSST) data set, which contains skin water surface temperature data for 442 French water bodies (natural lakes, reservoirs, ponds, gravel pit lakes and quarry lakes) for the period 1999-2016. We assessed the quality of the satellite temperature measurements by comparing them to in situ measurements and taking into account the cool skin and warm layer effects. To estimate these effects and to investigate the theoretical differences between the freshwater and seawater cases, we adapted the COARE 3.0 algorithm to the freshwater environment. We also estimated the warm layer effect using in situ data. At the reservoir of Bimont, the estimated cool skin effect was about −0.3 and −0.6 • C most of time, while the warm layer effect at 0.55 m was negligible on average, but could occasionally attain several degrees, and a cool layer was often observed in the night. The overall RMSE of the satellite-derived temperature measurements was about 1.2 • C, similar to other applications of satellite images to estimate freshwater surface temperatures. The LakeSST data can be used for studies on the temporal evolution of lake water temperature and for geographical studies of temperature patterns. The LakeSST data are available at https://doi.org/10.5281/zenodo.1193745.

The role of the south-western Alps as a corridor for Mediterranean trout (Salmo trutta complex Linnaeus, 1758) was evaluated in order to understand the influence of the last glacial events in shaping the spatial distribution of the genetic diversity of this salmonid. For this, the allochthonous hypothesis of a man-mediated French origin (19th century) of the Mediterranean trout inhabiting the Po tributaries in the Italian side of the south-western Alps was tested. A total of 412 individuals were analysed at the mitochondrial control region. The phylogenetic classification was carried out by using a Median-Joining Network analysis. Mismatch pair-wise analysis, molecular dating and Kernel density distribution analysis of the main mitochondrial lineages were evaluated to compare past demographic dynamics with the current spatial distribution of genetic diversity. The main outcomes resulted strongly in agreement with a biogeographic scenario where the south-western Alps acted as a unidirectional corridor that permitted the colonization of the upper Durance (Rhône River basin) by trout from the Po River basin. Therefore, the Mediterranean trout should be considered as native also along the Italian side of the south-western Alps and the allochthonous hypothesis should be rejected.

Juvenile roach were always more abundant in the less modified section (BPS) of the river than in the other sections (RES and TAIL). While the original primary river channel was directly impacted by the flash flood, no significant difference in otolith shape was observed before or after the flash flood. Our results suggest that this part of the reach provides refuge habitats used by fish during high flow events. K E Y W O R D SCyprinidae, flood event, Lower Rhône River, otolith morphometry | INTRODUCTIONThe channelisation and regulation of large rivers have severely impacted fluvial morphology and processes by changing natural hydrological and sedimentary regimes which contribute to the high ecological value of large floodplains (Bravard & Petts, 1996;Poff et al., 1997). The length and habitat heterogeneity of riverine ecotones have been reduced (Schiemer, Zalewski, & Thorpe, 1995;Tockner & Stanford, 2002) and the spatial and temporal patterns of hydrological connectivity have been highly altered (Pringle, 2003;Ward & Stanford, 1995). Populations of highly mobile organisms like fish, which use distinct habitats during their life cycle, have been seriously affected.Major changes in fish assemblages in large European rivers such as the Danube (Balon, Crawford, & Lelek, 1986; Holcik, 1988), the Rhine (Cazemier, 1988;Lelek, 1989) or the Rhône (Pattee, 1988;Persat, 1988) resulted from the 19th century river straightening, the channelisation and the construction of successive diversion dams (mainly during the 20th century) which have created new artificial environments. On the Rhône River, a typical hydropower scheme includes a reservoir (RES) created by the diversion dam built on the upper part of the river, a canal which redirects the main river flow to a power plant, and a bypassed old river that spans for several kilometres. Typically, the tailrace (TAIL) and the bypassed sections (BPS) converge in the downstream RES formed by next diversion dam (see Figure 1). Most of the time, the BPS receives a low minimum instream flow and overflows occur at the dam when river discharge exceeds the capacity of the hydropower plant. However, these released flows (discharge from the dam) are generally lower than the initial discharge prior to the

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