Here we present an experimental campaign delving into the complex interplay between sand dune morphology and tidal current dynamics. Employing particle image velocimetry (PIV) measurements, we conducted diverse series of laboratory flume experiments to scrutinize the hydrodynamic influence of dunes on steady currents, both aligned and opposed to the dune asymmetry. Our experiments sought to replicate the hydrodynamics occurring over the tidal dune field of the Goulet de Brest, located in Brittany, France. The Goulet hosts well-formed and highly dynamic dunes shaped by intense tidal currents. Notably, these currents exhibit a distinctive asymmetry, with ebb flows prevailing towards the southwest in contrast to the opposite flood flows. The resulting tidal asymmetry is vividly mirrored in the dune profiles, showcasing an accentuated asymmetry in the southeast part of the field, where dunes grow taller in shallower waters. Conducted in a bidirectional current-permitting flume, each experimental series encompassed varied hydrodynamic conditions, such as ebb and flood, aligned or opposed to the dune asymmetry, and different bottom roughnesses. We utilized sediment mixtures that were progressively coarser, transitioning from a smooth to a fully rough flow regime. The PIV flow measurements provided unprecedented spatial resolution, slightly larger than 1 mm, and temporal resolution sampling data at a frequency of 200 Hz. These measurements were taken at the central dune crest and along the neighboring trough. At the inlet, lower-frequency point measurements were conducted using a Vectrino-II ADV Nortek, ensuring the stability of inlet currents during different PIV acquisitions. Analysis of the collected data unveiled a rich tapestry of turbulent processes and boundary layer dynamics. The identified detachment and reattachment points of the boundary layer, along with their spatio-temporal oscillations, revealed an intermittent advection of coherent turbulent structures downstream from the dune crest proceeding further downward along the lee side in the boundary layer and upward in the water column up to the free surface. These deepened our understanding of the intricate interactions between boundary layer dynamics and turbulence. Additionally, by scrutinizing the vertical current profile along the dune, we estimated the equivalent bottom roughness and local shear stresses, providing crucial insights into the drag imposed by the dunes, with potential implications for sediment transport processes. In essence, this dataset stands as a cornerstone in unraveling the intricate relationship between tidal dune morphology and coastal current dynamics. It underscores the potential of PIV measurements for investigating such large-scale phenomena under controlled conditions. Furthermore, the collected database can inform the development, validation, and sensitivity analysis of new numerical models aiming at the investigation of those fine-scale processes taking place at the interface of sand dunes and tidal current which control sediment transport and thus shape coastal areas.

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With the growing number of sensors technologies, the production of numerous types of data allows finer observations of our environment. Among them, time series represent a valuable heritage by the time spent on their recording and the information they contain. However, the analysis of time series produced by a monitoring network generally requires preprocessing steps to separate data with meaningful information from sensors' dysfunctions or measurement particular conditions. In this context, outliers are already well studied and several methods are already developed to identify them. In this paper, we propose a complementary method to identify buffered data. Buffered data are characterized by a lower amplitude than the rest of the time series and can be naturally caused (groundwater influence for example) or caused by measurement defects (sensor covered by sediment movements). The necessity to identify buffered signals came with the use of data coming from several databases with different level of qualification. Buffered signals are not necessarily filtered with conventional preprocessing methods and can affect the analysis when not related to the studied phenomena. The identification method proposed in this study relies on a normalized diurnal range index. It was developed on surface river temperature time series recorded in metropolitan France to cover a wide variety of regional climates and measurement environments. The method is able to highlight buffered data inside a time series. Furthermore, it is able to separate (naturally caused or not) occasional or regular buffered signal periods in a time series. The study then uses preprocessed time series to analyze the distribution of regular buffered data according to the season of occurrence and a climate typology

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Coastal marine sediments can be either major scrubbers or eutrophication contributors to surface waters. Standard methods for direct measurement of nutrient fluxes at the sediment-water interface do not consider hydrodynamic forcing although several ex-situ studies suggest that sediment resuspension can dramatically increase dissolved fluxes. We provide a new model to quantify dissolved phosphate (PO4$^{3−}$) resuspension flux (J$_R$) based on physical representation of its identified components: diffusion stimulation by exposure of deeper sediment layer with higher PO4$^{3−}$ concentration in the porewater (J$_D$), pore water mixing with overlying water (J$_M$) and net adsorption/desorption from suspended sediments (J$_K$). This approach was applied to field data from a Seine intertidal mudflat periodically submitted to millimetric erosion. On a tidal scale, the model output reveals a J$_R$ of 272.3 ± 360.0 μmol m$^{-2}$ h$^{-1}$ (± 52% from parameter uncertainty), well above flux calculated by application of Fick's first law (0.15 ± 0.85 μmol m$^{-2}$ h$^{-1}$) or by ex situ core incubation (40.8 μmol m$^{-2}$ h$^{-1}$). Iron bound phosphorus within suboxic layers buffers PO4$^{3−}$ concentrations in superficial sediments leading to negligible contributions of J$_D$ and J$_M$ to total fluxes. Conversely, J$_K$ appears to be the main exchange pathway, even though improvements in turbidity measurement would allow this term to be defined more precisely. Correction required to enhance and control model robustness are described. These results show the importance of considering the dissolved PO4$^{3−}$ resuspension flux in dynamic environments.

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Based on a search of publications in the scientific literature as well as international reports available online, I draw up a list of 25 documents which include cross-references to the terms offshore wind farms (OFW), and nonindigenous species (NIS). This review shows that no relationship has yet been clearly established between the implementation of OFWs and the colonization of NIS on turbine foundations and scour protections. Evidence for such an effect needs to be documented and confirmed in the future.

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<div><p>To identify short-term changes (14-69 days) in the adult abundance of two closely related shallow-burrowing bivalves (Ruditapes spp.), a series of observations and displacement assessments were made during the 2014-2018 period. This study was initiated to estimate the natural displacement of clams in a high-energy hydrodynamic tidal regime along the western coast of Cotentin in Normandy, France (western basin of the English Channel, northeastern Atlantic). The raking of several different surfaces and sediment types at successive periods separated by about one month shows clam displacement in most of the selected quadrats. The mean abundance displacement derived from all the observations carried out in 2014, 2016 and 2018 is estimated at 1.8 ind•m -2 mo -1 , a value that should be compared with the mean density of between 2.0 and 12.5 ind•m -2 along the western coast of Cotentin. These displacements are confirmed with experiments using clams marked with an inox metal washer and detected with a Minelab Sovereign GT multi-frequency metal detector. During the course of the experiments, about 20% of the clams show a displacement. Most of the displacements are moderate, being less than 2 m, but some clams could be displaced by more than 20 m.</p></div>

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ABSTRACT Despite the valuable palaeoecological and palaeoenvironmental information provided by vertebrate tracks, those made in semi‐liquid sediments have been largely overlooked because they are assumed to be preserved as a mass of disrupted sediment and to have a low preservation potential. Nevertheless, understanding their mechanisms of formation, infilling and preservation is crucial since they could be more abundant in the fossil record than expected or be misinterpreted as other soft‐sediment deformation structures. To solve these aspects, this study analyses consecutive cross‐sections performed along a human track made by a shod foot in semi‐liquid sediments in the upper intertidal flats of the Bay of Mont‐Saint‐Michel (north‐west France) and monitored until its complete burial. These were compared with cross‐sections of tracks made in a flume tank. Cross‐sections reveal that the sediment structures associated with these tracks reflect the mechanism of their formation and infilling, and even the footstep dynamics. These structures comprise: (i) marginal rims that developed at both sides of tracks during foot penetration; (ii) upward deformation structures produced during foot withdrawal; (iii) a syn‐track infilling , which almost entirely fills the tracks during the withdrawal, formed by sediment collapsed from the track walls or by liquefied sediment; (iv) a post‐track infilling that fills the tracks completely during their subsequent flooding. This work demonstrates that these tracks have a high preservation potential in tidal settings, especially if they are made after the peak of a spring tide period, and undergo desiccation and consolidation during neap tides, which prevents their erosion and favours their burial by sediment. The identification of the above‐mentioned structures in fossil counterparts provides useful palaeoenvironmental information, because they allow discriminating these tracks from those made in sediments with less water content and from other soft‐sediment deformation structures (i.e. convolute bedding and balls‐and pillows) with which they share strong resemblances.

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