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Nurseries in estuary ecosystems represent essentials areas to the renewal of adult populations. They provide resources needed to the juveniles' growth and are characterized by higher survival rates compared to other habitats, partly because of a reduced pressure from predation. Furthermore, estuarine systems are under numerous anthropic pressures which disturb the nursery's functioning, consequently decreasing favourable habitats to juveniles' settlement. To improve knowledge on these nurseries, it is key to understand juveniles' spatio-temporal dynamics and its associated mechanisms. In order to answer this problematic, fish communities in the Seine estuary are studied integrating multidimensional aspects, spatial scales and temporal evolution. This work is supported by a 14 years-long survey of fish communities conducted by Ifremer since 1995. It explores various biotic scales from the whole community to intra-specific relationships as well as inter-specific interactions between juveniles populations. Geostatistical developments provide a diverse set of analysis for the integration of the spatial dimension, which completes the multivariates approaches that characterize the communities and their dynamics.The Seine estuary shelters four specific assemblage, each containing juveniles. Two of them possess numerous species with an economic interest and a large proportion of juveniles in two distinct areas (pelagic and benthic). However, the decreases in chlorophyll a and turbidity seem to have impacted juveniles' densities and the occurrence of both assemblages. Functional analysis of species assemblages also indicates a reduction of planktivorous taxa such as herring and sprat. Despite physical changes in the estuary caused by the harbour's development, sole, plaice and dab juveniles are occurring in three assemblages covering distinct habitats also stable in time. Each species follow its own spatial dynamic, not showing a common one that would be govern by environmental or human-induced changes. Nonetheless, a linear model of coregionalization describing spatial interactions between biotic and abiotic variables allowed to defined two scales of spatial structures; fine (6km) and medium (12km), highlighting scale-dependent relations between flatfish juveniles and environment. Therefore, environmental variables such as salinity, which were not structuring the density of juveniles, are empathised. The importance of interspecific relationships attested in our work along with the scale dependency at which they are considered reinforce the need for an explicit integration of biotic variables and spatial dimensions when modelling flatfish distributions within estuarine systems.; Les zones de nourriceries en milieu estuarien représentent des espaces essentiels au renouvellement de populations adultes. Elles fournissent les ressources nécessaires à la croissance des juvéniles et sont caractérisées par des taux de survie des juvéniles supérieurs à ceux observés dans d'autres habitats, entre autre du fait d'une pression de prédation réduite. Par ailleurs, les milieux estuariens sont soumis à de nombreuses pressions anthropiques qui impactent le fonctionnement des zones de nourriceries, et réduisent ainsi les habitats favorables à l'installation des juvéniles. Afin d'améliorer les connaissances de ces zones, il est essentiel de comprendre la dynamique spatio-temporelle des juvéniles et les processus associés. Pour répondre à cette problématique, les communautés de l'estuaire de Seine sont étudiées au travers de méthodes intégrant implicitement aspects multidimensionnels, échelles spatiales et évolutions temporelles Ces travaux s'appuient sur 14 années de suivi des communautés halieutiques grâce aux campagnes NOURSEINE de l'Ifremer depuis 1995. Les travaux menés explorent différentes échelles biotiques allant de l'ensemble de la communauté jusqu'aux relations intra-spécifiques, en passant par les interactions inter-spécifiques entre populations de juvéniles. Des développement géostatistiques fournissent une diversité d'analyses afin d'approcher la dimension spatiale, complétant les approches multivariées qui caractérisent les communautés et leur dynamique.L'estuaire de Seine présente quatre assemblages spécifiques contenant chacun des populations de juvéniles. Deux d'entre eux présentent de nombreuses espèces d'intérêt économique et une forte richesse en juvéniles dans deux zones distinctes (pélagique et benthique). Cependant, les diminutions en concentration de chlorophylle a et de turbidité semblent avoir affectées les densités de juvéniles et la présence de ces deux assemblages. L'analyse fonctionnelle des assemblages d'espèces montre également la diminution des densités des taxons planctonophages tels que le hareng et le sprat. En dépit des modifications physiques de l'estuaire du fait de l'extension portuaire, les juvéniles de sole, de plie et de limande sont présents dans trois assemblages couvrant des habitats distincts et stables dans le temps. Chaque espèce suit sa propre dynamique spatiale, et aucune d'elles ne montre une dynamique commune qui serait gouvernée par des changements environnementaux et d'origine anthropique. Néanmoins, un modèle linéaire de corégionalisation, décrivant les interactions spatiales entre variables biotiques et abiotiques a permis de définir deux échelles de structurations spatiales, à fine échelle (6km) et à moyenne échelle (12km), mettant en évidence des relations dépendantes des échelles spatiales entre les juvéniles de poissons plats et l'environnement. Ainsi, des variables environnementales, telles que la salinité, qui n'étaient jusque-là pas structurantes de la densité dans les résultats, sont mises en avant. L'importance des relations inter-spécifiques démontrées par nos travaux ainsi que la dépendance des relations avec l'environnement aux échelles auxquelles elles sont considérées, appuient la nécessité d'intégrer explicitement les variables biotiques et la dimension spatiale dans la modélisation de distributions de poissons plats, dans les milieux estuariens.

This numerical modeling study (i) assesses the influence of the sediment erosion process on the sediment dynamics and subsequent morphological changes of a mixed-sediment environment, the macrotidal Seine estuary, when non-cohesive particles are dominant within bed mixtures (non-cohesive regime), and (ii) investigates respective contributions of bedload and suspended load in these dynamics. A three dimensional (3D) process-based morphodynamic model was set up and run under realistic forcings (including tide, waves, wind, and river discharge) during a 1-year period. Applying erosion homogeneously to bed sediment in the non-cohesive regime, i.e., average erosion parameters in the erosion law (especially the erodibility parameter, E0), leads to higher resuspension of fine sediment due to the presence of coarser fractions within mixtures, compared to the case of an independent treatment of erosion for each sediment class. This results in more pronounced horizontal sediment flux (two-fold increase for sand, +30% for mud) and erosion/deposition patterns (up to a two-fold increase in erosion over shoals, generally associated with some coarsening of bed sediment). Compared to observed bathymetric changes, more relevant erosion/deposition patterns are derived from the model when independent resuspension fluxes are considered in the non-cohesive regime. These results suggest that this kind of approach may be more relevant when local grain-size distributions become heterogeneous and multimodal for non-cohesive particles. Bedload transport appears to be a non-dominant but significant contributor to the sediment dynamics of the Seine Estuary mouth. The residual bedload flux represents, on average, between 17 and 38% of the suspended sand flux, its contribution generally increasing when bed sediment becomes coarser (can become dominant at specific locations). The average orientation of residual fluxes and erosion/deposition patterns caused by bedload generally follow those resulting from suspended sediment dynamics. Sediment mass budgets cumulated over the simulated year reveal a relative contribution of bedload to total mass budgets around 25% over large erosion areas of shoals, which can even become higher in sedimentation zones. However, bedload-induced dynamics can locally differ from the dynamics related to suspended load, resulting in specific residual transport, erosion/deposition patterns, and changes in seabed nature.

International audience; Productive and ecologically highly valuable ecosystems, macrotidal estuaries are also characterised by complex habitat and connectivity dynamics driven by tidal and freshwater influence. Organisms living in these constantly changing systems have to match their movement patterns to the shifting habitat mosaic using available windows of connectivity to access habitat patches of interest. This appears particularly important for the juvenile stages of many fish species colonising shallow and intertidal areas of the estuaries as summer nurseries. We apply tools from landscape ecology to investigate the estuarine habitat and connectivity dynamics on the example of juvenile seabass (Dicentrarchus labrax). We test under which conditions spatio-temporal bottlenecks to estuarine nursery colonisation may emerge for this species in a human-modified estuary. Combining a hydrodynamic model of the Seine estuary with remote sensing data allows us to capture structural changes in habitat availability and connectivity at the estuarine scale and at a fine spatio-temporal resolution. With chronological least-cost modelling of successive tidal steps, we assess patterns of nursery accessibility and estimate tidal colonisation fronts for different mobility scenarios. We show that, at certain hydrological conditions, tidal water level variation causes local disruptions of habitat availability and connectivity, creating temporary bottlenecks for seabass juveniles’ movement. Fish mobility appears determinant for their vulnerability to these connectivity disruptions. Our approach allows for quantitative assessment and visualisation of riverscape complexity related to tidal dynamics. It is applicable to other highly dynamic ecosystems, where the mobile nature of connectivity and habitats needs to be integrated into conservation and management planning.

International audience; Coastal and estuarine nurseries are composed of habitats with different biotic and abiotic features. Quantifying the contribution of different habitats within nurseries to juvenile fish feeding would help identify those that are essential in the completion of their life cycle, by providing food resources that maximise growth and survival. Essential habitats for four bentho-demersal fish species (whiting, sea bass, plaice and common sole) in an estuarine nursery were identified using gut contents and stable isotopes. Habitats differed in isotopic ratios and benthic communities. The estuarine gradient defined the macrofauna communities and sources of organic matter used by primary consumers. Trophic niche overlaps and trophic contribution of habitats highlighted that the species used both intertidal and subtidal habitats as feeding grounds. Flatfish were local feeders and fed on prey available mainly in the habitat in which they were caught, suggesting feeding behaviour that required little energy for movement. Sea bass were concentrated in upstream habitats, with intertidal mudflats contributing for nearly half of its diet. Whiting had an ubiquitous feeding strategy, suggesting that it may target prey with the most energetic gain in the habitats. Hence, habitats were used simultaneously during the same season or asynchronously throughout the year by the juvenile fish studied, suggesting no preference for a specific habitat at the community scale. Finally, both trophic tracers demonstrated the trophic importance of intertidal mudflats, especially for the sea bass and common sole, with contributions up to the half and two-third of their diet respectively.

Peu étudié par le passé, le mobilier en plomb romain découvert dans l’estuaire de la Seine possède un vaste potentiel de recherche. Les problématiques liées à la compréhension des pratiques artisanales, de la circulation du métal dans la région et des pratiques funéraires calètes et véliocasses touchent ici des collections archéologiques anciennes et récentes. Une approche pluridisciplinaire mêlant archéologie et archéométallurgie est susceptible de répondre à ces questions, qui s’inscrivent dans une dynamique de recherche commune à plusieurs laboratoires français et allemands.Coordination du PCR : Malina Robert (Université de Nantes & Caux Seine Agglo).

This study used a hydrodynamic and sediment transport process-based model to simulate maintenance dredging in a macrotidal estuary: the Seine Estuary. This sandy-muddy estuary allows access to two major ports (Le Havre and Rouen). The model accounts for sand and mud dynamics and was previously validated for turbidity and morphodynamic coupling. Dredging is schematised as a physical process responding to simulated seabed evolutions. In coherence with port practices, (i) numerical dredging is conducted when sediment depositions exceed nautical depth limits determined by port authorities; (ii) dredged sediment are released in the water column above dumping sites. The model successfully reproduced the amount of sand and mud dredged in harbors and fairways (7MT/year) without any drift along 10 years. Moreover, the dredged quantities appeared to be considerably higher than the estuarine turbidity maximum (ETM) mass, which was successfully simulated by the model. The model was used to study relationships between maintenance dredging requirements and hydro-meteorological forcings. Dredging requirements are related to forcings in different ways depending on the exposure of dredged areas to waves, currents and ETM. Le Havre harbor and fairway are sensitive to storms, as 75% of the dredging activity is due to waves higher than 1m. The entrance of Rouen fairway equally responds to tidal range, river discharge and waves. Variabilities in dredging requirements differ depending on the type of sediment. For instance, at the entrance of the Seine navigation channel, mud dredging is strongly correlated to tidal range and secondarily to river discharge, while sand dredging is dominantly related to waves. A specific simulation (not including local wind-induced circulation) showed that the low contribution of waves to mud dredging was explained by materials in suspension hauled off-site. This process is induced by westerly winds that occurred together with waves. On the other hand, mud dredging increases with tidal amplitude in areas of intense tidal currents, and presents a counter clock-wise hysteresis with tidal amplitude, which can be compared to the one followed by the ETM mass. In addition, the dependence of mud dredging on river discharge appears to be related to the proximity of the ETM, the main source of fine sediment, which location shifts downwards when river discharge increases. At an inter-annual scale, variability in the temporal distribution of hydrometeorological forcings leads to 50% variation of annual dredged masses. In conclusion, this study has improved the understanding of the estuarine dynamics responsible of maintenance dredging.

International audience; Phytoplankton primary production varies considerably with environmental parameters especially in dynamic ecosystems like estuaries. The aim of this study was to investigate short-term primary production along the salinity gradient of a temperate estuary over the course of 1 year. The combination of carbon incorporation and fluorescence methods enabled primary production estimation at short spatial and temporal scales. The electron requirement for carbon fixation was investigated in relation with physical-chemical parameters to accurately estimate primary production at high frequency. These results combined with the variability of the photic layer allowed the annual estimation of primary production along the estuary. Phytoplankton dynamics was closely related to salinity and turbidity gradients, which strongly influenced cells physiology and photoacclimatation. The number of electrons required to fix 1 mol of carbon (C) was ranged between 1.6 and 25 mol electron mol C−1 with a mean annual value of 8 ± 5 mol electron mol C−1. This optimum value suggests that in nutrient replete conditions like estuaries, alternative electron flows are low, while electrons transfer from photosystem II to carbon fixation is highly efficient. A statistical model was used to improve the estimation of primary production from electron transport rate as a function of significant environmental parameters. Based on this model, daily carbon production in the Seine estuary (France) was estimated by considering light and photic zone variability. A mean annual daily primary production of 0.12 ± 0.18 g C m−2 day−1 with a maximum of 1.18 g C m−2 day−1 in summer was estimated which lead to an annual mean of 64.75 g C m−2 year−1. This approach should be applied more frequently in dynamic ecosystems such as estuaries or coastal waters to accurately estimate primary production in those valuable ecosystems.

The dynamics of Suspended Particulate Matter (SPM) in macrotidal estuaries is highly variable both spatially (from the fluvial compartment to the estuary mouth) and temporally (from the second to several years), but it is essential to understand and quantify the sedimentary dynamics of estuarine environments. With the development of high-frequency measurement networks around the world, the main objective of this study is to qualify the turbidity measurements acquired by a high-frequency measurement network (SYNAPSES network) located on the Seine estuary (i) in terms of monitoring the SPM dynamics from the fluvial compartment to the turbidity maximal zone (TMZ) and (ii) in terms of estimation of the SPM fluxes on different spatio-temporal scales of the Seine estuary. Data acquired from the SYNAPSES network and complementary in situ campaigns (81 days of 12 h - OBS-3+/YSI/LISST 100X-C / ADCP 600 kHz) on four stations from the fluvial estuary of the Seine Estuary to the turbidity maximal zone, are an extremely rich and unique dataset on estuarine environments. The variability in the relationship between turbidity measurements [NTU] and SPM concentration measurements [g.L-1] on each campaign, reveals the effect of (i) the internal sensor technology and (ii) the variability of the particle inherent optical properties (median diameter D50, dry density rho and scattering efficiency Qc) on the sensitivity of different optical sensors. The analysis of the in situ and the SYNAPSES data allowed to calibrate the turbidity measurements in mass concentration, with a validated relationship on the annual cycle, specific to each of the stations and reduced uncertainties. After a study of the SYNAPSES station representativeness across the section, the instantaneous fluxes of SPM are estimated (i) from the SPM concentration and liquid flow data acquired by the ADCP on the global section and (ii) from the SPM concentrations of the SYNAPSES network coupled to the hydrodynamic model MARS-3D (estimation of the liquid flow). Comparisons of SPM fluxes in situ to those estimated by the combination SYNAPSES/MARS-3D allow to propose a specific coefficient for each of the SYNAPSES network stations, xith the aim of adjusting the SPM instantaneous fluxes estimated from the SYNAPSES network to the in situ reality, with reasonable uncertainties. the tools and approaches developed in the PhD thesis on the Seine estuary can be applied to other macrotidal estuaries to estimate sedimentary fluxes., La dynamique des Matières en Suspension (MES) dans les estuaires macrotidaux est fortement variable à la fois spatialement (du compartiment fluvial à l'embouchure de l'estuaire) et temporellement (de la seconde à plusieurs années), mais reste primordiale pour comprendre et quantifier la dynamique sédimentaire des environnements estuariens. Avec le développement croissant des réseaux de mesures haute-fréquence à l'échelle internationale, l'objectif principal de cette étude est de qualifier et de valoriser les mesures de turbidité acquises par un réseau de mesures haute fréquence (réseau SYNAPSES) implanté d'amont en aval sur l'estuaire de la Seine (France) à la fois (i) en matière de suivi de la dynamique des MES du compartiment fluvial au bouchon vaseux et (ii) en matière d'estimation des flux de MES sur différentes échelles spatio-temporelles de l'estuaire de la Seine. Les données acquises à partir du réseau SYNAPSES et des campagnes in situ (81 journées de 12 h - OBS-3+/YSI/LISST 100X-C/ADCP 600 kHz) sur quatre stations réparties de l'estuaire fluvial à la zone du bouchon vaseux, constituent un set de données extrêmement riche et unique sur les domaines estuariens. La variabilité des relations, établies entre les mesures de turbidité [NTU] et les mesures de concentrations en MES [g.L-1] sur chacune des campagnes de l'échelle tidale à annuelle, met en évidence l'effet (i) de la technologie interne du capteur et (ii) de la variabilité des propriétés optiques inhérentes des particules (diamètre médian D50), densité sèche rhô et efficacité de diffusion Qc) sur la sensibilité des différents capteurs optiques. L'analyse conjointe des données in situ et des données SYNAPSES a permis de calibrer les mesures de turbidité en concentration massique, avec une relation validée sur le cycle annuel, spécifique à chacune des stations et des incertitudes minimisées. Après une étude de la représentativité des stations du réseau vis-à-vis de la section, les flux instantanés de MES sont estimés (i) à partir des données de concentrations en MES et de débits acquis par l'ADCP sur l'intégralité de la section et (ii) à partir des concentrations ponctuelles en MES du réseau SYNAPSES couplées au modèle hydrodynamique MARS-3D. Les comparaisons des flux de MES in situ par rapport à ceux estimés par la combinaison SYNAPSES/MARS-3D permettent de proposer un coefficient spécifique à chacune des stations du réseau SYNAPSES, dans le but d'ajuster les flux instantanés de MES estimés, avec leurs incertitudes, à partir du réseau SYNAPSES à la réalité in situ. Les outils et les démarches développés dans la thèse sur l'estuaire de la Seine pauvent être appliqués à d'autres estuaires macrotidaux pour estimer les flux sédimentaires.

The dynamics of Suspended Particulate Matter (SPM) in macrotidal estuaries is highly variable both spatially (from the fluvial compartment to the estuary mouth) and temporally (from the second to several years), but it is essential to understand and quantify the sedimentary dynamics of estuarine environments. With the development of high-frequency measurement networks around the world, the main objective of this study is to qualify the turbidity measurements acquired by a high-frequency measurement network (SYNAPSES network) located on the Seine estuary (i) in terms of monitoring the SPM dynamics from the fluvial compartment to the turbidity maximal zone (TMZ) and (ii) in terms of estimation of the SPM fluxes on different spatio-temporal scales of the Seine estuary. Data acquired from the SYNAPSES network and complementary in situ campaigns (81 days of 12 h - OBS-3+/YSI/LISST 100X-C / ADCP 600 kHz) on four stations from the fluvial estuary of the Seine Estuary to the turbidity maximal zone, are an extremely rich and unique dataset on estuarine environments. The variability in the relationship between turbidity measurements [NTU] and SPM concentration measurements [g.L-1] on each campaign, reveals the effect of (i) the internal sensor technology and (ii) the variability of the particle inherent optical properties (median diameter D50, dry density rho and scattering efficiency Qc) on the sensitivity of different optical sensors. The analysis of the in situ and the SYNAPSES data allowed to calibrate the turbidity measurements in mass concentration, with a validated relationship on the annual cycle, specific to each of the stations and reduced uncertainties. After a study of the SYNAPSES station representativeness across the section, the instantaneous fluxes of SPM are estimated (i) from the SPM concentration and liquid flow data acquired by the ADCP on the global section and (ii) from the SPM concentrations of the SYNAPSES network coupled to the hydrodynamic model MARS-3D (estimation of the liquid flow). Comparisons of SPM fluxes in situ to those estimated by the combination SYNAPSES/MARS-3D allow to propose a specific coefficient for each of the SYNAPSES network stations, xith the aim of adjusting the SPM instantaneous fluxes estimated from the SYNAPSES network to the in situ reality, with reasonable uncertainties. the tools and approaches developed in the PhD thesis on the Seine estuary can be applied to other macrotidal estuaries to estimate sedimentary fluxes., La dynamique des Matières en Suspension (MES) dans les estuaires macrotidaux est fortement variable à la fois spatialement (du compartiment fluvial à l'embouchure de l'estuaire) et temporellement (de la seconde à plusieurs années), mais reste primordiale pour comprendre et quantifier la dynamique sédimentaire des environnements estuariens. Avec le développement croissant des réseaux de mesures haute-fréquence à l'échelle internationale, l'objectif principal de cette étude est de qualifier et de valoriser les mesures de turbidité acquises par un réseau de mesures haute fréquence (réseau SYNAPSES) implanté d'amont en aval sur l'estuaire de la Seine (France) à la fois (i) en matière de suivi de la dynamique des MES du compartiment fluvial au bouchon vaseux et (ii) en matière d'estimation des flux de MES sur différentes échelles spatio-temporelles de l'estuaire de la Seine. Les données acquises à partir du réseau SYNAPSES et des campagnes in situ (81 journées de 12 h - OBS-3+/YSI/LISST 100X-C/ADCP 600 kHz) sur quatre stations réparties de l'estuaire fluvial à la zone du bouchon vaseux, constituent un set de données extrêmement riche et unique sur les domaines estuariens. La variabilité des relations, établies entre les mesures de turbidité [NTU] et les mesures de concentrations en MES [g.L-1] sur chacune des campagnes de l'échelle tidale à annuelle, met en évidence l'effet (i) de la technologie interne du capteur et (ii) de la variabilité des propriétés optiques inhérentes des particules (diamètre médian D50), densité sèche rhô et efficacité de diffusion Qc) sur la sensibilité des différents capteurs optiques. L'analyse conjointe des données in situ et des données SYNAPSES a permis de calibrer les mesures de turbidité en concentration massique, avec une relation validée sur le cycle annuel, spécifique à chacune des stations et des incertitudes minimisées. Après une étude de la représentativité des stations du réseau vis-à-vis de la section, les flux instantanés de MES sont estimés (i) à partir des données de concentrations en MES et de débits acquis par l'ADCP sur l'intégralité de la section et (ii) à partir des concentrations ponctuelles en MES du réseau SYNAPSES couplées au modèle hydrodynamique MARS-3D. Les comparaisons des flux de MES in situ par rapport à ceux estimés par la combinaison SYNAPSES/MARS-3D permettent de proposer un coefficient spécifique à chacune des stations du réseau SYNAPSES, dans le but d'ajuster les flux instantanés de MES estimés, avec leurs incertitudes, à partir du réseau SYNAPSES à la réalité in situ. Les outils et les démarches développés dans la thèse sur l'estuaire de la Seine pauvent être appliqués à d'autres estuaires macrotidaux pour estimer les flux sédimentaires.

The mysid Neomysis americana (S.I. Smith, 1873), native from the East coast of North America, was recorded for the first time in European waters in The Netherlands 8 years ago. This species was observed for the first time on the French coast in the Seine estuary (Normandy) in 2017. As for The Netherlands, this species has probably been introduced on the French coast by shipping in ballast waters., Le mysidacé Neomysis americana (S.I. Smith, 1873), espèce originaire de la côte est d’Amérique du Nord, a été signalé pour la première fois dans les eaux européennes aux Pays-Bas il y a 8 ans. Cette espèce a été observée pour la première fois sur les côtes françaises dans l’estuaire de la Seine (Normandie) en 2017. Comme pour les Pays-Bas, cette espèce a probablement été introduite sur la côte française avec le transport maritime dans des eaux de ballast.

International audience; The objective of this study is to analyze the impact of hydrological variability influenced by climatic phenomena upon the sedimentary exchange between the turbidity maximum (TM) and a river mouth intertidal mudflat. This study, carried out over a period of 10 years (1997–2006) in the Seine Estuary (France), is specifically focused on two extreme periods: a wet one from 2001 to 2002 and a drier one from 2005 to 2006. This study is based on an original approach combining data gathered via low-altitude remote sensing with altimeter readings and ground-level measurements.During this 10 year period, we observed a link between climate change and the sedimentary processes on the mudflat surface. The modifications of sedimentary processes are mainly connected to the multiannual variability of hydrological flow rates that control the positioning of the turbidity maximum, the source of the sedimentary material deposited in this intertidal zone. The TM at the mouth of the Seine estuary is well developed; its maximum mass is estimated to be between 300,000 tons and 500,000 tons (Avoine et al., 1981) with maximum concentrations in the surface waters ranging from 1 to 2 g ∙ l− 1 (Le Hir et al., 2001). Most of the fine particles stored within the TM have been found to originate from within the catchment area (Dupont et al., 1994). In the Seine estuary, the dynamics of the estuarine TM, in response to hydrodynamic forcings, have been previously described (Avoine et al., 1981) and modeled (e.g. Brenon and Le Hir, 1999, Le Hir et al., 2001). The TM is upstream of the northern mudflat when the river flow is low (< 450 m ∙ s− 1) and nearby the study area when the river flow is higher. Thus during wet periods, the sedimentation rates increase by + 17 cm ∙ y− 1, while during the drier one (when the turbidity maximum is located upstream of the estuary) we observed an erosion rate of 7.6 cm ∙ y− 1. Sedimentation events in the mudflat resulting from spring tides are less frequent during dry periods, and they deposit a smaller quantity of sediment (− 23% of total deposition mass per event). Because of the lower flow rates coupled with the impacts of local development, the flood tides have become dominant. This contributes to the addition of sandy or silty sediments on the mudflat, of which the slope has increased 450% over 8 years caused by erosion.

Despite being highly exposed to various anthropogenic and environmental pressures, estuaries are productive and important areas for the maintaining of marine resources. The Seine estuary is a largely altered ecosystem, particularly after Port 2000’s construction. Two spatial ecosystem models (1996-2002 and 2005-2012) using the Ecopath modelling approach have been built. They aimed to estimate the contribution of the various estuarine habitats to the global food web functioning and the impact of the various recent infrastructures. These models are relying on a particular structure, including sedentary trophic group which are associated to a particular habitat and mobile trophic group, corresponding to the top predators. The predator-prey relationships are modelling following a density dependence hypothesis which takes account of the predators’ opportunism and the adaptation. The two models highlighted the structuring role of the benthic communities and the high attractiveness of the Northern and Southern areas in terms of nursery. A predation report has been shown from downstream to upstream and from subtidal areas to intertidal areas during the second time period. Finally, Ecosystem Network Analysis indicated a maturity decrease and an increase of stress in this already stressed estuary.; Les estuaires sont des milieux productifs, important pour le maintien des ressources marines et très exposés aux pressions anthropiques et environnementales. L’estuaire de Seine est un écosystème fortement altéré, notamment suite à la récente construction de Port 2000. Deux modèles écosystémiques (1996-2002 et 2005-2012) spatialisés utilisant l’approche Ecopath ont été construits afin d’estimer la contribution des différents habitats estuariens au fonctionnement du réseau trophique ainsi que l’impact de ces aménagements. Ces modèles s’appuient sur une structure particulière incluant des groupes trophiques sédentaires liés aux habitats et des prédateurs supérieurs mobiles. Les relations prédateurs-proies sont modélisées selon une hypothèse de densité dépendance permettant de prendre en compte l’opportunisme et l’adaptation des prédateurs. Ces modèles ont mis en évidence le rôle structurant des communautés benthiques ainsi que l’attractivité des zones Nord et Sud de l’estuaire malgré les pressions anthropiques. Un report de prédation vers l’aval et les zones intertidales a été observé durant la seconde période. Différents indicateurs de santé des écosystèmes ont également mis en évidence une diminution de la maturité et une augmentation du stress de cet estuaire déjà fortement stressé.

00000; International audience; During 2002–2005, a new container terminal in the commercial harbour of Le Havre, named “Port2000”, was built on the northern flank of the Seine estuary, northern France. This extension is already known to have modified the estuary current and sediment dynamics, as well as reducing biomass of the suprabenthos assemblage, for the whole downstream part of the system. However, studies on other biotic communities were largely inconclusive, and an ecosystem-wide analysis was still lacking. Here, we performed a before/after study of ecosystem dynamics of the different habitats of the Seine estuary, using a Linear Inverse Modelling technique (LIM-MCMC) to estimate all flows occurring in the food web. Ecological Network Analysis indices were calculated, summarising ecosystem functioning traits and giving indications about the habitat health status. Results showed that the southern flank (FS, Fosse Sud) exhibits all characteristics to be considered as the least stressed habitat of the estuary: system activity and functional specialisation of flows were stable between periods, ecosystem recycling processes and detrital dynamics were also stable; an increase in trophic specialisation (decrease in system omnivory) was the only change confirming a general ecological succession. The northern flank (FN, Fosse Nord), where the actual terminal was built, showed a food web with increased importance of lower trophic levels (increased detritivory and carbon recycling), increased stability and flow efficiency, but possibly regressed to a previous step in ecological succession. In the central navigation channel (CH), patterns of network indices were overall inconclusive and the general image is one of a constantly shifting food web, a condition possibly caused by the year-round dredging activities. The functioning of the Seine estuary – especially of FN and FS – seems to have been modified by the combination of harbour construction and the related mitigation measures. Network indices partially captured this combination of changes and, although not fully operational yet, they are promising tools to comply with the European Union mandate of defining ecosystem health status.

Concentrations of volatile hydrogen sulfide (H2S), carbonyl sulfide (OCS), methane thiol (MeSH), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) in the Seine estuary (France) were investigated in spring 2005 using samples collected from the first meter beneath the surface. Levels of dissolved metals (Ag, Cd, Cu, Zn, Ni, Co, Pb), suspended particulate matter, and particular organic carbon were also assessed. Maximum concentrations were 0.80 nM for H2S, 0.64 nM for OCS, 3.06 nM for MeSH, 11.06 nM for DMS, and 1.18 nM for DMDS, and different features were observed for the five volatile reduced sulfur compounds (VRSCs). Experiments were conducted to determine silver-VRSC conditional stability constants. Major interactions were observed between H2S and Ag, which may partially account for the absence of volatile H2S at the lowest salinities. OCS, MeSH, and DMS did not interact with Ag, as revealed by their insignificant K' values. Variations in concentrations along the salinity gradient may be explained by the influence of phytoplanktonic compounds.

International audience; The Marais Vernier is the largest freshwater wetland in the Seine Estuary in northern France. It is in a heavily urbanized and industrialized region and could be affected by atmospheric deposition and by fluvial input of contaminants in water diverted from the Seine River. To evaluate contaminant histories in the wetland and the region, sediment cores were collected from two open-water ponds in the Marais Vernier: the Grand-Mare, which was connected to the Seine by a canal from 1950 to 1996, and the Petite Mare, which has a small rural watershed. Diversions from the Seine to the Grand-Mare increased sedimentation rates but mostly resulted in low contaminant concentrations and loading rates, indicating that the sediment from the Seine was predominantly brought upstream by tidal currents from the estuary and was not from the watershed. Atmospheric sources of metals dominate inputs to the Petite Mare; however, runoff of metals from vehicle-related sources in the watershed might contribute to the upward trends in concentrations of Cr, Cu, and Zn. Estimates of atmospheric deposition using the Petite Mare core are consistent with measured deposition in the region and are mixed (similar for Hg and Pb; larger for Cd, Cu, and Zn) compared with deposition estimated from sediment cores in the northeastern United States. A local source of PAHs in the watershed of the Petite Mare is indicated by higher concentrations, higher accumulation rates, and a different, more petrogenic, PAH assemblage than in the Grand-Mare. The study illustrates how diverse sources and transport pathways can affect wetlands in industrial regions and can be evaluated using sediment cores from the wetland ponds.

The Seine estuary (France) is currently one of the world's most contaminated estuaries, due in particular to its high cadmium and lead content. Proper understanding of contaminant transfer, transformation and retention mechanisms throughout the estuary and up to the adjacent marine zone require a range of studies involving data collections, experiments, and modeling tool. A multivariable transport model (SiAM-3D) was used to simulate dissolved and particulate transport and it is applied to several calculation grids; a speciation model (MOCO) was used to select key species and obtain a schematic system representation. The coupled model for Cd and Pb was compared with field measurements. The complementary character of various tools (model applied to annual time scale, in situ measurements and experiments) allowed to explore and quantify various hypotheses on the high dissolved cadmium concentrations observed during low river flow. The target is to achieve a compromise between acceptable computing times and adequate result accuracy. Although particle and contaminant behaviour is globally well-reproduced by the coarse grid, calculation errors relating to bayward fluxes and stocks deposited inside the estuary were highlighted after comparison with the fine grid.

Semi-diurnal and fortnightly surveys were carried out to quantify the effects of wind- and navigation-induced high-energy events on bed sediments above intertidal mudflats. The mudflats are located in the upper fluvial part (Oissel mudflat) and at the mouth (Vasiere Nord mudflat) of the macrotidal Seine estuary. Instantaneous flow velocities and mudflat bed elevation were measured at a high frequency and high resolution with an acoustic doppler velocimeter (ADV) and an ALTUS altimeter, respectively. Suspended particulate matter concentrations were estimated by calibrating the ADV acoustic backscattered intensity with bed sediments collected at the study sites. Turbulent bed shear stress values were estimated by the turbulent kinetic energy method, using velocity variances filtered from the wave contribution. Wave shear stress and maximum wave-current shear stress values were calculated with the wave-current interaction (WCI) model, which is based on the bed roughness length, wave orbital velocities and the wave period (T-S). In the fluvial part of the estuary, boat passages occurred unevenly during the surveys and were characterized by long waves (T-S > 50 s) induced by the drawdown effect and by short boat-waves (T-S < 10 s). Boat waves generated large bottom shear stress values of 0.5 Nm(-2) for 2-5 min periods and, in burst of several seconds, larger bottom shear stress values up to 1 N m(-2). At the mouth of the estuary, west south-west wind events generated short waves (T-S < 10s) of H-S values ranging from 0.1 to 0.3 m. In shallow-water environment (water depth < 1.5 m), these waves produced bottom shear stress values between 1 and 2 N m(-2). Wave-current shear stress values are one order of magnitude larger than the current-induced shear stress and indicate that navigation and wind are the dominant hydrodynamic forcing parameters above the two mudflats. Bed elevation and SPM concentration time series showed that these high energy events induced erosion processes of up to several centimetres. Critical erosion shear stress (tau(ce)) values were determined from the SPM concentration and bed elevation measurements. Rough tau(ce) values were found above 0.2 N m(-2) for the Oissel mudflat and about 1 N m(-2) for the Vasiere Nord mudflat. These results demonstrate the advantages of combining the measurement of instantaneous velocity and bed elevation to determine in situ the erosion and deposition processes as a function of bottom shear stress variations. (c) 2006 Elsevier Ltd. All rights reserved.

International audience; The Chinese mitten crab Eriocheir sinensis H. Milne Edwards, 1853 is a native crab of East Asia. It is predominant in freshwater but migrates seawards to breed. It was found in Normandy, for the first time, in 1943 (Hoestlandt, 1943, 1948). Seventy-one years of observations along the Normandy coast and in the Seine estuary, as well as in the ship-canals and inner seaport of Le Havre, have recorded a total of 65 crabs at 33 locations. The observation of an E. sinensis juvenile in mussel beds along the Calvados coast indicates that this habitat can be a favourable location for larval settlement.

Seine estuary is one of the most polluted in the northern hemisphere largely due to its urban and agricultural activities of its watershed. Despite this the copepod E. affinis represents 90% of zooplankton biomass in the Seine estuary. The aim of the thesis was to develop a new bioassay Survival Growth copepod with the copepod E. affinis on various environmental matrices. Initially, the bioassay was developed using sediments spiked with molecules representative models of estuarine contamination (APs, PAHS and PCBs) before being validated on natural sediments of the Seine estuary. The bioassay was applied in solution 4-NP and PCB 126 and Vibrio anguillarum from the Seine estuary. A multi-generational exposure protocol was applied under the same conditions for three generations. The results showed an effect on larval development after 6 days of exposure to sediments. In solution, similar results were obtained, including, retarded growth after two days of exposure to 4-NP and PCB 126 correlated with chitobiase activity levels. However, at the end of the experiment the result is not observed. At exposition with Vibrio anguillarum, increased activity was recorded chitobiase the first days, involving an increase in growth in the sixth day. As part of the multi-generational experimenting, the copepod appears to be stabilizing at the third generation., L’estuaire de Seine est l’un des plus pollués de l’hémisphère nord dû notamment à ses activités urbaines et agricoles de son bassin versant. Malgré cela le copépode E. affinis représente 90 % de la biomasse zooplanctonique en estuaire de Seine. L’objectif de la thèse était de développer un nouveau Bio-essAi Survie Croissance copépode (BASIC) à l’aide du copépode E. affinis sur différentes matrices environnementales. Dans un premier temps, le bio-essai a été mise au point à l’aide de sédiments enrobés avec des molécules modèles représentatives de la contamination estuarienne (APs, HAPS et PCBs) avant d’être validé, par la suite, sur des sédiments naturels de l’estuaire de Seine. Le bio-essai à ensuite été appliqué en solution au 4-NP et au PCB 126 et sur Vibrio anguillarum issus de l’estuaire de Seine. Un protocole d’exposition multi-générationnel a été appliqué dans les mêmes conditions pendant trois générations. Les résultats recensés ont montré un effet sur le développement larvaire lors des expositions après 6 jours d’expositions à des sédiments enrobés. Dans le cadre des expositions en solution, des résultats similaires ont été obtenus, notamment, un retard de croissance après deux jours d’exposition au 4-NP et au PCB 126 corrélé avec les niveaux d’activité chitobiase. En revanche, à la fin de l’expérimentation ce résultat n’est plus observé. Lors des expositions à Vibrio anguillarum, une augmentation de l’activité chitobiase a été enregistrée les premiers jours de l’exposition, impliquant une augmentation de la croissance au sixième jour. Dans le cadre des expérimentions multi-générationnelle, le copépode semble se stabiliser à la troisième génération.

Since the mid 19th century, Seine Estuary has been subject of heavy human interference to facilitate the deep draft navigation (channelization, embankments, and dredging) affecting the natural flooding regime of riparian ecosystems. The same time, floodplain has also been the subject of management in order to allow (1) agriculture land use and (2) the exploitation of alluvial materials (extraction aggregates). The present study aims (i) to determine whether the current state of anthropized riparian ecosystems of the lower Seine valley requires and authorizes the restoration of a functioning considered as acceptable for riparian ecosystems, and (ii) to monitor the functioning of reconstituted soil following the filling of gravel-pit using dredged sediments in the floodplains of the Seine Estuary.The first part of the thesis is devoted to diagnose the current state (morphology and functioning) of soils in riparian ecosystems and follow their potential capacity to remove nitrogen during experiments microcosms. The main results of morphology and functional measurements (in situ and ex situ) show that soils in riparian ecosystems cannot be grouped according to their degree of connectivity. Functional measurements showed that low connected sites remains favorable to the sink of carbon and nitrogen removal. Then, I assessed the effect of flood duration due to the daily water fluctuation versus river floods on N removal in riparian soils, a microbially-mediated soil process, through two experiments studies. The first of two studies showed that the daily water fluctuation has a significant effect on the improvement of purifying capacity of soils. The second study showed that disconnected soils have found their normal functions after a change of water regime. Also, it suggests that between 3- and 7-day long waterlogging is needed in the disconnected soils for it to exhibit a significant denitrification level.The second part of the thesis focused in the evaluation of success of the restoration experience following the filling of gravel-pit using dredged sediments. Overall, the results obtained in this part show that (1) the diachronic monitoring of soil characteristics is not efficient to assess if typical wetland soil characteristics are reached in reconstituted soils in a short duration of follow and (2) the functional approach (in situ and ex situ) relative to soil respiration, mineralization of C and N and denitrification appear to be a good tool for evaluating., Depuis le milieu du 19ème siècle, l’estuaire de la seine a fait l’objet de lourds aménagements pour autoriser la navigation de bateau à fort tirant d’eau jusqu’à Rouen (chenalisation, endiguements, dragage) impactant les écosystèmes rivulaires en les déconnectant souvent du fleuve. Dans le même temps, la plaine alluviale de l’estuaire de Seine a également fait l’objet d’aménagements pour permettre (1) l’utilisation agricole des sols (drainage) et (2) l’exploitation des matériaux alluvionnaires (extraction de granulats). L’étude présentée ici a pour objectifs (i) de déterminer si l'état actuel des écosystèmes rivulaires anthropisées de la basse vallée de Seine nécessite et autorise, la restauration d'un état et d’un fonctionnement considérés comme écologiquement acceptables pour un écotone rivulaire, et (ii) de suivre le fonctionnement d’un sol reconstitué suite au comblement d’une ballastière à l’aide de sédiments de dragages au sein de la plaine alluviale de l’estuaire de la Seine.La première partie de la thèse est consacrée à diagnostiquer l’état actuel (morphologie et fonctionnement) des sols des écosystèmes rivulaires et de suivre leurs potentialités en terme de capacités épuratrices vis-à-vis de l’N lors d’expérimentations en microcosmes. Les résultats sur la morphologie et le fonctionnement (in situ et ex situ) montrent que les sols des écosystèmes rivulaires ne peuvent pas être regroupés selon leurs degrés de connectivité. Les mesures fonctionnelles ont montré que les sites moins connectés au fleuve restent favorables à l’expression de la fonction de stockage de carbone et à la dénitrification. J’ai ensuite testé expérimentalement l'effet d’une durée d’inondation attribuable aux variations journalières de niveaux d’eau versus les crues du fleuve sur la fonction épuratrice vis-à-vis de l’azote des sols d'écosystèmes rivulaires par voie bactérienne, à travers deux études expérimentales. La première a mis en évidence que les inondations journalières de niveau d’eau a un effet significatif sur l’amélioration de pouvoir épurateur des sols. La seconde étude a montré que les sols actuellement déconnectés retrouvent leurs fonctions normales après une modification de régime hydrique. De plus elle suggère que le temps nécessaire pour qu’un sol déconnecté retrouve un niveau significatif de dénitrification est de 3 à 7 jours d’engorgement en eau.La seconde partie de la thèse s’est principalement intéressée à l’évaluation du succès d’une expérience de restauration suite au comblement d’une ballastière avec de sédiments de dragages. L’ensemble des résultats obtenus dans cette partie montrent que (1) l’approche pédologique et écologique employée n’a pas été suffisante pour évaluer le succès de la restauration sur une courte durée de suivi et que (2) l’approche fonctionnelle (in situ et ex situ) relative à la respiration du sol, à la minéralisation du C et de l’N et à la dénitrification semble être pertinente pour l’évaluation.

Scientific fisheries surveys routinely identify a large diversity of commercial and non-commercial benthic megainvertebrates that could provide useful information for Marine Strategy Framework Directive (MSFD) descriptors. Species is obviously the basic taxonomic level to which most ecological studies and theories refer. Identification at this level of organization is indeed always preferred over any other taxonomic level. Nevertheless, aggregation of species to higher taxonomic levels may be unavoidable sometimes, since errors of identification are known or suspected to occur in many surveys. Using analyses of taxonomic sufficiency (identification of organisms at various taxonomic resolutions) and groups of morphospecies (taxa identified easily by non-experts on the basis of evident morphological traits), this study aims to quantify the loss of ecological information incurred by partial identification of benthic megafauna in bottom trawl surveys in order to put such data to good use. The analyses were conducted on five scientific surveys representing a large range of geographical areas (from 150 km(2) to 150 000 km(2)) and environmental conditions. Results show that genus, family and, particularly, morphospecies are good surrogates for species identification in community analyses. We suggest that bottom trawl surveys can provide reliable megafauna data that may usefully complete those obtained by grab surveys. The use of morphospecies could lead to new strategies, combining different datasets to provide indicators for MSFD descriptors (e.g. D6). (c) 2013 Elsevier Ltd. All rights reserved.

International audience; An epidemiological survey was conducted in the Seine estuary and in two smaller and relatively preserved estuaries on the French Atlantic coast in order to estimate the occurrence of liver lesions in European flounder, Platichthys flesus, and also to seek putative risk factors for the recorded pathologies. Four hundred and seventy-eight fish of both sexes and of different size ranges were sampled in the three studied areas, 338 of which in the Seine estuary. All fish were examined for histopathological liver lesions, while DNA adducts and otoliths were analyzed on a subsample. Five categories of hepatic lesions were recorded with the following prevalence for the Seine estuary: 36.7 % inflammations, 8 % parasites (mainly encysted nematodes), 6.5 % foci of cellular alteration (FCA), 5.3 % foci of necrosis or regeneration (FNR), and 1.5 % tumors. Inflammation occurrence increased according to age, contrary to parasitic infestations and FCA which were more prevalent in young fish, notably those of < 1 year old (group 0). Tumors were only observed in females of more than two winters. Females exhibited a higher prevalence of tumors (3.0 %) and FCA (6.5 %) than males (0 and 2.6 %, respectively). Parasitic and infectious lesions and FNR were equally distributed in males and females. The prevalence of FNR was also shown to vary according to sampling season, with significantly more occurrences of liver necrosis in the fish collected in summer than in spring. Spatial differences were observed with a higher occurrence of encysted parasites in flounders from the upper Seine estuary, while inflammations predominated in flounders living downstream. Temporal trends were also noted, with an increased prevalence of parasitic infestations, inflammations, and FCA in the 2002-2003 period in comparison to the 1996-1997 one. The three flounder populations from the Seine estuary (Normandy), Ster estuary (Brittany), and Bay of Veys (Normandy) showed different spectra of hepatic lesions. Flounders from the Bay of Veys had relatively few liver lesions as compared to flounders from the two other estuaries. Flounders from the Ster estuary exhibited the highest prevalence of parasites (37.2 %) and inflammations (51.1 %). Finally, FCA and liver tumors occurred at very similar levels in both flounder populations from the Seine and the Ster estuaries. Group 0 flounders inhabiting the upper Seine estuary were more prone to parasitic and pre-neoplastic hepatic lesions and had higher levels of liver DNA adducts than the older ones living downstream. It was postulated that group 0 European flounders may serve as valuable bioindicators for assessing the quality of estuarine waters and the health status of euryhaline fish populations.

International audience; A sensitivity study is performed to investigate the importance of multiphysics and multiscale couplings for modelling wave height in the outer Seine estuary (English Channel), the harbour of Le Havre and its new infrastructures Port 2000. Multiphysics coupling focuses on the effects of the tide in terms of time-varying water depths and currents on wind-generated surface-gravity waves. Simulations are based on the coupling of phase-averaged wave-propagation modules with circulation modules. This coupling is evaluated by comparing numerical results of the significant wave height with field data collected in November 2008 at two wave buoys moored in the access channel to Le Havre harbour. Predictions confirm a periodic local increase reaching 30 % of the wave height induced by current refraction. Multiscale coupling focuses on the importance of nested computational domains for predicting wave heights in the inner basin of Port 2000. A phase-resolving wave module is set up at this ultimate scale. Need of coupling this module with simulations at the scale of the outer Seine estuary is evaluated by comparing wave-agitation modellings driven by spatially-uniform and spatially-varying forcings with measurements in the inner basin. This comparison highlights the sensitivity of predictions to the directions of waves approaching the harbour entrance.

L’estuaire de Seine est un continuum entre l’amont (le bassin versant et ses apports) et l’aval (la baie de Seine et le bassin oriental de la Manche). Cependant, selon leurs perceptions, scientifiques, gestionnaires ou aménageurs considèrent différentes limites de cet espace d’interface diversifié en habitats naturels mais qui sont tous fortement anthropisés. La phase de dégradation de l’estuaire de la Seine a commencé au milieu du 19ème entraînant une réduction de la qualité des eaux, de la contamination de l’écosystème et la réduction des surfaces de l’estuaire, notamment par atterrement de surfaces industrialo-portuaires. Depuis les années 1980, plusieurs indicateurs de qualité montrent son amélioration mais d’autres contaminants demeurent préoccupants, tels que le PCB et le HAP, des perturbateurs endocriniens. En dépit de tout cet ensemble d’aménagements et donc, de contraintes anthropiques s’ajoutant aux contraintes naturelles, les espèces estuariennes apparaissent résistantes et l’estuaire de la Seine est encore riche de son milieu vivant et de sa diversité. Après une phase d’amélioration de la connaissance sur la structure et le fonctionnement de l’écosystème de l’estuaire de la Seine (Phases 1 à 3 du programme Seine-Aval), l’ambition du programme est de voir s’améliorer la restauration des fonctionnalités de l’estuaire. Les projets d’aménagement actuels continuent de maintenir la compartimentation de l’estuaire et sont encore appréhendés de façon trop autonome. Il faut soutenir la réalisation d’un plan de Gestion Globale de l’Estuaire de la Seine et passer d’une vision sectorielle à une vision globale. D’ailleurs, les écologues ne peuvent que partager cette vision écosystémique prônant une approche spatio-temporelle holistique donc globale. The estuary of the Seine is a continuum between its upstream part (the watershed and its input in the hydrological system) and the downstream part (the Seine Bay and the eastern part of the English Channel). However, according to, their sensitivities, scientists, administrators or policy makers consider various limits of this interface constituted of diversified natural heritage environments but strongly made man modified. The degradation of the Seine estuary began in the middle of 19th with the decreasing of the water quality, the contamination of the ecosystem and the reduction of the intertidal surfaces by the silting of industrial and harbour surfaces. Nevertheless, since the 1980’s, several indicators show the improvement of the estuary quality but other contaminants remains important, i.e. PCB, PAH, and endocrine biomarkers … In spite of all these natural and anthropogenic constraints, the Seine estuary shows remaining high specific and habitat diversities. After a phase of increasing of the knowledge on the structure and the functioning of the Seine ecosystem (Phases 1 - 3 of the Seine-Aval programme), the ambition of the programme is to restore the estuarine functionalities. But the nowadays harbour projects continue to maintain the existing ecological compartments of the Seine estuary and are still studied independently. It is necessary to support the promotion of a Global Management Plan of the Seine Estuary, and to surpass the sector-based vision to a global vision. Moreover, the ecologists can share this ecosystem-based management, i.e. a global holistic spatio-temporal approach.

Cette contribution interroge la réalité socio-naturelle de l’estuaire de la Seine que construisent les expériences nautiques de loisir. On s’intéresse en particulier aux médiations que produisent les spots de pratique. En quoi ces médiations territoriales et ces constructions esthétiques donnent-elles accès ou font-elles écran à une conscience du milieu estuarien ? L’article montre un estuaire morcelé, très inégalement fréquenté, et propose une typologie des principales formes de spots à l’œuvre. La mer, la Seine urbaine et la Seine des îles façonnent trois rapports aux eaux turbides du fleuve : quels sont-ils ? L’hétérogénéité des usages et des perceptions s’explique par la gestion multiscalaire de l’espace estuarien et par les horizons d’attente dans lesquels s’inscrivent les pratiques. Ce que font les publics dans la nature permet ainsi de comprendre les perceptions de l’environnement et d’interroger à nouveaux frais la gestion des écosystèmes, qu’il s’agisse de mesures compensatoires, de mesures de protection ou d’actions de reconquête. This article explores the socio-natural reality of the Seine river estuary that has been constructed by the practice of water sports. We were particularly interested in the mediations produced by these practices. How do territorial mediations and aesthetic constructions provide access to or serve as a screen for an awareness of the estuary environment? The article shows a fragmented estuary, very unevenly visited, and proposes a typology of the principal forms of sport. The ocean, the urban Seine and the Seine around the islands have three distinct relationships with the turbid waters of the river: what are they? The heterogeneity of usages and perceptions can be explained by the multiscalar management of the estuary space and by the horizons of expectation for the various sports practices. Understanding what the public does in nature thus provides insight into perceptions about the environment and suggests new questions about the management of ecosystems, whether this concerns measures of compensation, protection or recovery.

International audience; The present study aimed to develop a method of quantification of heat shock protein transcript levels in the estuarine copepod Eurytemora affinis. For that, the full-length cDNA of the 78-kDa glucose-regulated protein (Ea-grp78) and the cytosolic 90-kDa heat shock protein (Ea-hsp90A) from this species have been cloned. These cDNA revealed, respectively, 2,370 and 2,299 bp with 1,971 and 2,124 bp open reading frames encoding 656 and 707 amino acids. Main features, sequence identities and phylogenetic analysis with other species were described. Then, the expression profiles were analysed using reverse transcription/real-time quantitative PCR method from copepods subjected to different thermic and osmotic stresses in laboratory, and from copepods directly sampled into the natural population of the Seine Estuary (France) along a salinity gradient. Thermic shock (7.5°C, 22.5°C and 30°C during 90 min) significantly induced increases of transcript quantities ranged between 1.7- and 19.7-fold the levels observed in control conditions (15°C). Hypo- and hyper-osmotic shocks (salinities of 1 and 30 during 90 min) caused a 2-fold induction of Ea-hsp90A transcript level in comparison to controls (salinity of 15) whereas no significant change was measured for Ea-grp78. On the other hand, similar expression profiles were observed for the two transcripts after 72 h of exposition to salinities of 1 and 25 with a significant 2-fold induction observed for the lower salinity. To finish, strong expression inductions of both Ea-grp78 and Ea-hsp90A genes were observed in field copepods sampled at low salinity during the campaigns of June 2009 and May 2010. These results tend to show that the low salinity and the increase of temperature seem to have a synergic effect on stress condition of copepods.

Sp. Iss. SI Proceedings of the Seventh International Symposium on Flatfish Ecology, Part I; Estuaries and coastal waters are essential nursery habitats for many marine species, and especially for flatfishes. Thus, investigating how anthropogenic disturbances affect the quality of these habitats is of major importance to understand their consequences on the population renewal of marine species. The aim of the present study was to analyse the effects of estuarine habitat degradation on the population of the common sole in the Eastern Channel, a key species in the fish community and fisheries in this area. We especially focused on the drastic drop in the surface area and on the low water quality of the Seine estuary, the main river of the Eastern Channel. A geographic Information System (GIS) was used to develop quantitative maps of sole nursery habitats in the Eastern Channel by using a habitat suitability model based on bathymetry and sediment structure. This approach indicated that juvenile densities are low in the Seine estuary with regards to other nursery sectors. Then, thanks to historical maps of the Seine estuary, habitat suitability maps were built for key dates in the modifications of this estuary since 1850. This backward predictive approach suggests that habitat loss in the Seine estuary has led to a 42% decrease of its nursery capacity. As the density of juvenile sole in the Seine estuary is low in comparison to other sectors, this represents only a 3% loss at the sole population scale, in the Eastern Channel. However, when we assumed that prior to anthropogenic disturbance the juvenile density in the Seine estuary might have been equivalent to the current density of adjacent sectors with higher quality, the loss in abundance could be nearly 23% (8-36%). Results suggest that the loss in habitat surface combined with habitat degradation has led to an important loss in the contribution of the Seine estuary nursery to the whole sole population in the Eastern Channel. (C) 2009 Elsevier BM. All rights reserved.

International audience; This article presents numerical simulations for the turbidity maximum (TM) in the Seine estuary using a 2-D vertical width-integrated two-phase flow model. The results are in rather good agreement with observations in a natural environment. The displacement of the TM is reproduced and a concentrated particles layer is observed on the numerical results. These results highlight the interest of this innovative approach for sediment transport simulations in estuary: no erosion or deposition laws are imposed

International audience; This study presents an original work on measurements of stable and radioactive iodinated species in the Seine estuary (France), with estimates fluxes of volatile gaseous species from water to the atmosphere. Various iodinated compounds were identified in water and air in particular 131I in water, what is unusual. Concentrations and behaviour of iodinated elements in the Seine estuary seem similar to what has been observed in other European estuaries. MeI (Methyl Iodide) and Total Volatile Iodine (TVI) fluxes from water to air vary between 392 and 13949 pmol m-2 d-1 and between 1279 and 16484 pmol m-2 d-1, respectively. Water to air flux of TVI for the Seine river was estimated in the range 4-46 kg y-1. Measurements of 131I in water varying between 0.4 and 11.9 Bq m-3. Fluxes of 131I from water to atmosphere are in the range 2.4 × 105-1.3 × 107 Bq y-1, close to an annual discharge of 131I by a nuclear reactor. © 2008 Elsevier Ltd. All rights reserved.

International audience; The Seine estuary (France) is one of the world's macrotidal systems that is most contaminated with heavy metals. To study the mercury-resistant bacterial community in such an environment, we have developed a molecular tool, based on competitive PCR, enabling the quantification of Gram-negative merA gene abundance. The occurrence of the Gram-negative merA gene in relation with the topology (erosion/deposit periods) and the mercury contamination of three contrasted mudflats was investigated through a multidisciplinary approach and compared with a non-anthropized site (Authie, France). The higher abundance of the Gram-negative merA gene in the Seine estuary mudflats indicates a relationship between the degree of anthropization and the abundance of the merA gene in the mudflat sediments. In the Seine mudflats, the maxima of abundance are always located in fresh sediment deposits. Therefore, the abundance is closely related with the hydrosedimentary processes, which thus seem to be determining factors in the occurrence of the Gram-negative merA gene in the surface sediments of the Seine's mudflat.

In tide-dominated systems, fine-grained deposits occur in intertidal areas of inner estuaries as loci of convergence of fluvial and marine material. Even in the vicinity of estuaries, mud deposits are rare on open sandy beaches. This study focuses on temporary occurrences of muddy sediments on marine beaches along the Calvados coastline in Normandy, adjacent to the macrotidal Seine estuary (France). Clay mineralogy, majoreminoretrace elements and radionuclides were used as particulate markers to determine the provenance of the mud deposits. The fine fraction, defined here as particles

Measurements of polycyclic aromatic hydrocarbons (PAHs) were carried out from 2001 to 2003 in various environmental compartments (ambient air, atmospheric deposition, soils, sediments, runoff, and surface waters) in the Seine Estuary. The goal of this study was to identify the importance of atmospheric fluxes to occurrence of PAHs in the estuary, and to estimate the major pathways of their transport and accumulation within this ecosystem. The annual atmospheric inputs in the estuary ranged from 2.5 to 16 kg for the first sampling year, which is high when compared to those calculated for other European locations. In parallel, PAH transport from the atmosphere to the watershed outlet was investigated for two rural and urban small experimental watersheds within the Seine Estuary. In rural areas, atmospheric inputs are higher than exported loads by surface water and PAHs are accumulating in soils. The inverse occurs in urban areas, where the contribution of atmospheric deposition is negligible compared with PAH exported loads by runoff. These results allowed us to establish a mass balance for PAHs on the scale of the Seine Estuary, and to determine the dynamics of PAH transport. This study highlights the role of the atmospheric compartment in the transfer of contaminants and the importance of the local PAH inputs within the Seine Estuary.

The Seine estuary, one of the largest estuaries of the European northwest continental shelf, is subjected to numerous anthropogenic influences. Here we present an assessment of the microbial faecal contamination of the estuary water. The most vulnerable areas were defined on the basis of the fluxes of indicator organisms and the occurrence of Salmonella and Cryptosporidium sp. and Giardia sp. (oo)cysts. The microbial quality of the water changes from upstream to downstream: in the upstream area, contamination by faecal-indicator bacteria and Salmonella occurs during periods of high flow; in the urbanized area, mid-way between the uppermost areas of the estuary and its mouth, discharge from a wastewater treatment plant and a tributary degrade water quality; at the estuary mouth, the accumulation of microorganisms attached to particles in the maximum turbidity zone, particularly Clostridium perfringens spores and oocysts of Cryptosporidium, is accompanied by inputs of ThC and Escherichia coli from tributaries. In some areas, significant strong relations are observed between Salmonella, (oo)cysts of protozoan, and levels of faecal indicators.

International audience; During the 2001–2002 hydrological cycle, 8,000 tons P year−1 (44% as particulate phosphorus) originating from the Seine basin entered the Seine estuary. P content in suspended sediments (SS) is 2.9 g P kg−1 (80% as inorganic form) at Poses (the upstream limit of the Seine estuary). During the transfer from Poses to Caudebec (the limit of saline water intrusion), Particulate Inorganic Phosphorus (PIP) in SS decreases by 40% whereas Particulate Organic Phosphorus (POP) remains stable. This decrease is explained as the result of (i) a dilution by SS poorer in P, originating from storage zones (mudflats) within the estuary, and (ii) a loss of P by sedimentation, especially in the Rouen harbour where 15% to 20% of SS are yearly trapped and extracted. Downstream, in the turbidity maximum of the estuary, P content in SS is twice as low as at Poses (1.5 g P kg−1, 70% as inorganic form). PIP content is fairly homogeneous both vertically and throughout an annual survey. On the other hand, POP varies by season. Higher POP content is observed during vernal period with phytoplankton accumulation. In a salinity gradient from 0 to 30 (PSS78), PIP content further decreases by 30%. POP does not vary much in this gradient, leading to the assumption that PIP is submitted to desorption in response to the dilution by marine waters (poor in orthophosphates). Using 32P isotopic method, we establish a mathematical formulation of P exchangeable between the suspended solid and water phases of the Seine estuary. Particulate P in the turbidity maximum zone is shown to represent a possible source of dissolved P, available for algal growth in the Seine Bight. Instead of playing a role of nutrient retention, the turbidity maximum zone of the Seine estuary could favour coastal eutrophication.

In the macrotidal Seine estuary where growing mud deposits occurred in the mouth and in the bay of Seine, the identification and quantification of sources of fine material have been undertaken on three hundred superficial samples using particulate markers. A great "chemical and mineralogical identity card" of muddy sediments in the continuum Seine-bay of the Seine contributes new information on: dilution of fine material in the bay of the Seine, penetration of marine fine-grained sediments in the estuary and in the small rivers adjacent to the bay, and local and punctual fossil contribution.The determination of particulate mixing (PCA, mixing equations) shows that the recent fine sedimentation is the composite mixing of four sources (marine, riverine, fossil, estuarine) at long time scale (several decades). The mixing is more complex at short time scale (seasonal, instantaneous), with the input of secondary sources., Dans l'estuaire à fortes marées de la Seine où les vases s'étendent de plus en plus vers l'aval, l'identification et la quantification des sources de particules ont été entreprises sur trois cents échantillons superficiels par l'utilisation de marqueurs particulaires. Une "carte d'identité chimique et minéralogique" complète des sédiments fins de l'ensemble du continuum Seine-baie de Seine apporte de nouvelles informations sur : la dilution des apports fluviatiles en baie de Seine, la pénétration de particules fines marines dans l'estuaire et les petits cours d'eau côtiers, et l'apport local et ponctuel par érosion de matériel fossile.La résolution du mélange particulaire (ACP, équations de mélange) montre qu'à long terme (plusieurs décennies), la sédimentation fine actuelle correspond au mélange composite de quatre sources (marine, fluviatile, fossile, estuarienne). A court terme (saisonnier, évènementiel), le mélange est encore plus complexe, marqué par certaines sources secondaires.

Using recent indices developed, in part, for use under the European Water Framework Directive (AMBI, BENTIX, BOPA BQI, I2EC and the trophic index ITI), the ecological quality status of two highly contaminated environments-the Bay of Seine and the Seine estuary (Eastern English Channel)-was determined on several spatial and temporal scales. Data from 604 observations gathered over a 14-year period (1988-2002) were analyzed, and the results used to show the relationship between biotic indices, environmental variables and classic descriptors (e.g., number of species, total abundance, dominance index, ES(50) and Shannon/Brillouin diversities). Though the specific ecological quality (EcoQ) values calculated with the various indices were different, the overall trend of the results was similar. Synthesizing the values produced by the six indices used in the study allowed attribution of a high to good EcoQ status to the Bay of Seine and a moderate EcoQ to the estuary. The mesh size used when processing samples was proved to have no effect in winter on the EcoQ values for either body of water. (c) 2006 Elsevier Ltd. All rights reserved.

The aim of this study is to analyse and to quantify the fine particles transfer (i.e.< 63 μm) in the marine part of the man-altered macrotidal Seine estuary (France) by (i) an analysis of a two year time-series of altimeter data, which reveals the bed elevation variations on an intertidal mudflatd located at the Seine mouth and (ii) measurements of the concentration of suspended particulate matter (SPM) contained within the turbidity maximum (TM). The results of this analysis reveal that sedimentation on the mudflat is mainly controlled by the dynamics of the TM such that during the largest spring tides (i.e. tidal ranges > 7.1 m). Then, deposition of SPM from the turbidity maximum becomes important, allowing fine particles to settle on the mudflat, where the current velocities are low (< 0.4 m s− 1). On tides of lower range (< 7.1 m) bed elevation levels suggest that erosion of the mudflat surface dominates, however dewatering processes also occur in the soft mud deposits resulting in compaction. During periods of wave activity and periods of increasing river discharge, the mudflat surface experiences rapid erosion. These periods of erosion (sudden or progressive) imply a transfer of fine-grained material from the mudflat surface back into the TM.The long term (∼ 22 months), high frequency (1 measurement every 10 min) and high resolution (0.6 mm) dataset obtained from the altimeter allows quantification of the volume of material exchanged between the intertidal area and the estuarine standing stock of SPM. The maximum of deposition on the studied mudflat during the study was of 27 cm, with highest deposition occurring after the periods of highest river flow and implying that between 25 and 40% of the maximum estimated mass of SPM held within the estuarine TM (300,000–500,000 T) had been temporarily deposited on the mudflat. Likewise following periods of resuspension by wave activity, bed elevations reduced by an order of ∼ 1 cm, suggesting a release of between 1–1.5% of the TM load from the mudflat back into suspension.The study shows that lateral exchanges of sediment between the intertidal reaches of the estuary and the water column are an important part of the sediment budget, and that the supply of sediment available for deposition (i.e. the TM) has a causal relationship with sedimentation rates experienced by intertidal mudflats.

Coastal fish populations settle more or less frequently, at various stages, estuarine systems. Tidal marshes are one of the components of these mosaics of habitats. The first part of this work describes fish assemblages through the utilisation of these systems by fishes analysed in order to propose a revised functional classification of ecological guilds. T h i s new classification is used to compare fish communities of four estuarine systems in the western coast of France: the Mont Saint- Michel Bay, the Saint-Brieuc Bay, the Loire estuary and the Aiguillon Bay. The second part aims at characterizing the nursery function as defined by Beck et al. (2001). Acombinative approach based on gut content analysis, and stable isotope analysis shows that Yo Y s e a bass (Dicentrarchus labrax) that are caught in tidal marshes feed actively in situ and that the salt marsh preys contribute significantly to the first year food resources. An examination of the microstructure of the Yo Y sea bass otoliths using SEM shows characteristic marks, which are interpreted as fingerprints of the passage in the salt marsh. The microstructural analysis showed that sea bass recruits in estuarine areas after variable length of time (33 days to 126 days) spent in marine waters during migration from spawning areas to estuaries. After entry into estuarine complexes, growth rate increases. Microchemical analysis of the whole otolith using ICPMS technology revealed characteristic signatures of each of the studied estuarine systems. This suggests that the chemical composition of trace elements in the otoliths can be used as a chemical tag of fish. After a synthesis of this combinative approach, a reflection is committed concerning the efficiency of these approach in order to advise managers. The same though is engaged to evaluat the sustainabilityof these studies that mix strong field investments and theoretical ecology (guilds, life history traits, etc.)., Les populations de poissons côtiers colonisent de manière plus ou moins fréquente et à diverses écophases les écosystèmes estuariens. Les marais salés constituent un des nombreux éléments de ces mosaïques d'écosystèmes. La première partie de ce travail consiste en une approche descriptive de la composition des assemblages piscicoles au travers de l'analyse des guildes écologiques, et débouche sur la définition et la validation de guildes colonisatrices. Elles sont définies puis critiquées au travers de l'étude des populations de poissons présentes dans quatre systèmes estuariens de la façade ouest de la France : baie du Mont Saint-Michel, baie de Saint-Brieuc, estuaire de la Loire et baie de l'Aiguillon. La seconde partie s'intéresse à la caractérisation de la fonction de nourricerie de ces écosystèmes chez les juvéniles de bars européens (Dicentrarchus labrax) au travers de la définition proposée par Beck et al. (2001). Une approche combinée, basée sur des études de contenus stomacaux et sur l'analyse des rapports isotopiques des muscles de juvéniles capturés dans les marais salés, montre que les poissons s'alimentent activement dans ces systèmes et que les proies consommées in situ contribuent de manière significative à la première année de croissance. Une étude des microstructures des otolithes par MEB révèle la présence de marques spéciales qui peuvent être attribuées au passage dans les marais salés. L'analyse microstructurale montre que le recrutement des jeunes bars est étalé dans le temps avec des migrations marines plus ou moins longues (de 33 à 126 jours). Une fois installés dans les systèmes estuariens, leur croissance s'accélère. Une analyse microchimique des otolithes par ICPMS révèle des compositions caractéristiques de chacune des nourriceries estuariennes. Ceci suggère que les compositions en éléments traces peuvent être utilisées comme signature chimique discriminante chez les poissons. Enfin, après un bilan de cette approche combinée, une réflexion est engagée concernant l'efficacité de ces analyses dans le conseil aux gestionnaires. Une réflexion similaire est menée concernant la pérennité et la reproductibilité de telles études qui mélangent de forts investissements de terrain et de l'écologie théorique (guildes, traits d'histoire de vie,...).

The mouth of the Seine has been undergoing intense morphological changes for decades, because of containment work to improve access to the ports of Rouen and Le Havre. A significant trend is the progradation of the downstream estuary. Simultaneously, the surface area of the intertidal mudflats tends to decrease. The estuary's sediments are composed of silt and fine sand (respectively transported from the river Seine and the open sea). Their distribution is linked to the hydrodynamic characteristics of the estuary and may display layered vertical structures. To understand the estuary's morphological changes, a morphodynamic ditigal model is developed from a validated (3D) model of silty sediment transport. A model of suspended fine sand transport as well as a bathymetric readjustment module are developed. The sediment's erodability takes into account the proportions of sand and silt; two erosion regimes are recognized (respectively non-cohesive and cohesive). The sediment is discretised into fine layers (~ mm) and the consolidation of the silty layers is simulated. Thus, the erodability of the superficial layers depends upon the relative concentration of silt (i.e., between the grains of sand). Simulations performed for an arbitrary initial condition of the sediment bed show that the model reproduces a realistic distribution of the silt and sand. The main morphodynamic trends, such as progradation and the rotating of banks at the river mouth, are qualitatively reproduced. The results show that sand and silt contribute in a specific way to the morphological changes., L'embouchure de la Seine a subi des évolutions morphologiques fortes depuis plusieurs décennies, en raison de travaux d'endiguement pour améliorer les accès aux ports de Rouen et du Havre. Une tendance importante est la progradation de l'estuaire aval. Simultanément, la superficie des vasières intertidales tend à diminuer. Les fonds de l'estuaire sont composés de vase et de sable fin (respectivement transportés depuis la rivière de Seine et depuis le large). Leurs distributions sont liées aux caractéristiques hydrodynamiques de l'estuaire et peuvent présenter des structures verticales litées. Pour comprendre les évolutions morphologiques de l'estuaire, un modèle numérique morphodynamique est développé, à partir d'un modèle (3D) validé de transport de sédiments vaseux. Un modèle de transport de sable fin en suspension, ainsi qu'un module de réactualisation bathymétrique sont développés. L'érodabilité du sédiment tient compte des proportions de sable et de vase ; deux régimes d'érosion sont distingués (resp. non-cohésif et cohésif). Le sédiment est discrétisé en couches fines (~ mm) et la consolidation des couches vaseuses est simulée. Ainsi, l'érodabilité des couches superficielles dépend de la concentration relative de vase (i.e. entre les grains de sable). Des simulations réalisées pour une condition initiale arbitraire du fond sédimentaire montrent que le modèle reproduit une répartition réaliste des vases et des sables. Les principales tendances morphodynamiques, comme la progradation et la rotation des bancs à l'embouchure, sont qualitativement reproduites. Les résultats montrent que sables et vases contribuent de manière spécifique aux évolutions morphologiques.

International audience

Concentrations of Cd, Cu, Ni, Pb and Zn were determined in bulk atmospheric deposition collected at five stations in the Seine River basin (France), to evaluate sources and fluxes of atmospheric trace metals. Bulk deposition (wet + dry) was sampled weekly from March 2001 to February 2002 for 4 sites and from March to December 2001 for the last one. The concentrations of the elements in bulk deposition (dissolved + particulate form) followed the order: Zn > Pb > Cu > Ni > Cd. Concentrations of Zn, Pb and Ni were highly correlated with one another, suggesting a common source, related to the combustion of coal and heavy fuel. Metal concentrations in bulk deposition did not exhibit a high degree of temporal variability over the annual cycle and were not obviously related to meteorological parameters (rainfall, wind). Estimates of the total annual direct atmospheric deposition of metals to the Seine Estuary ranged from 16 kg yr− 1 for Cd to 5600 kg yr− 1 for Zn. Loadings of Cd, Cu and Ni from direct atmospheric inputs were less than 1% of those contributed by the Seine River and loadings of Pb and Zn represented 1.27% and 1.56% of the Seine contribution. Direct atmospheric inputs are negligible compared to fluvial inputs, but the indirect atmospheric deposition to the estuary was not estimated. Based on these results, trace metal concentrations in Paris have decreased by a factor of 4.6 for Zn and by a factor of 50 for Ni from 1988 to 2001. Of particular interest is the continued decrease in bulk deposition of Pb during this period, underlining the impact of policy initiatives concerning the reduction of lead on emissions in France.

The speciation and partition of mercury in a macrotidal estuary (Seine estuary, France) was studied in order to explore the role of the high turbidity zone (HTZ) in mercury transfer to the adjacent coastal waters. Water and particles were analyzed to determine the concentrations of various mercury species, including monomethylmercury and the inorganic fraction. The exchangeable particulate mercury, which varies with salinity, and the mercury fraction associated with the amorphous oxyhydroxides were evaluated. The distribution of dissolved mercury species during early mixing suggests non-conservative behavior of organically bound mercury at the head of the estuary. Mercury in the particles covaried positively with suspended particulate matter concentrations up to a threshold, which constitutes the typical mercury load of particles and deposited sediments of the HTZ. This distribution pattern is well explained by a dilution model: a slowly settling, low metal population of particle, characterized by relatively invariant turbidity, becomes admixed with a variable amount of higher metal content particles derived from the resuspension in the HTZ. In addition, in the HTZ, which acts as a degradation reactor for particulate organic matter, particulate mercury concentrations increase with increasing C:N ratios and amorphous oxyhydroxides particles. Mercury reaches the estuarine HTZ mainly associated with the riverine and marine particles, including organic matter and oxyhydroxides, which are temporarily trapped in the HTZ and mixed with autochthonous HTZ particles. The largest particles periodically settle and undergo diagenetic reactions and resuspensions, which lead to their mercury enrichment. Depending upon hydrodynamic conditions, mercury escapes seaward as fine particulate within the plume, partially associated with the oxyhydroxides. A surface complexation model reproduces most of the partitioning observed. In the dissolved phase the model simulation suggests that a very strong ligand must be present to explain the field observations.

This paper is the first to describe the spatio-temporal changes of mesozooplankton in the Seine estuary. Monthly samples were collected along the estuary in 1996 in order to analyse the seasonal changes of the mesozooplankton community and to identify the major environmental parameters that may influence the spatial distribution of zooplankton in this megatidal estuary. Statistical analysis (canonical correspondence analysis) showed that salinity was the main factor correlated with the longitudinal distribution of zooplankton. Marine species (Temora longicornis, barnacle larvae...) were located in the outer part of the estuary, while more oligohaline species (Eurytemora affinis) were recorded in the inner part of the estuary. A mixed zone was characterised by the presence of the neritic copepods Acartia spp. and Eurytemora affinis. The marine species (e.g. T longicornis, Oikopleura dioica, Barnacle larvae) showed maximum abundance at the end of spring (June) while the most abundant estuarine species, E. affinis, peaked in late winter-spring and declined with the onset of summer. This copepod dominated the estuarine zooplankton throughout the year, and found in the Seine estuary very high favourable conditions to exhibit ultimate abundances (> 190 000 ind m(-3)) which is one order of magnitude higher than those found in other European estuaries. It represented the main prey for major planktonivorous species such as suprabenthic and fish species located living in the upstream zone of the Seine estuary. (C) 2002 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS. All rights reserved., Des prélèvements mensuels ont été réalisés en 1996 afin d’analyser les changements temporels de la communauté mésoplanctonique estuarienne et d’identifier les principaux paramètres responsables de la distribution spatiale du zooplancton dans cet estuaire mégatidal. Des analyses statistiques (analyse canonique des correspondances) ont montré que la salinité est le principal facteur contrôlant la distribution spatiale du zooplancton. Une zone intermédiaire comporte un assemblage faunistique composé d’espèces néritiques comme les copépodes du genre Acartia et le copépode oligohalin Eurytemora affinis. Les espèces marines (e.g. T. longicornis, Oikopleura dioica, larves de cirripèdes) atteignent leur maximum d’abondance à la fin du printemps (juin) alors que le copépode prépondérant dans l’estuaire, E. affinis, a un maximum à la fin de l’hiver et au début du printemps. Son abondance commence à décliner dès l’été. Cependant, ce copépode domine la communauté mésozooplanctonique estuarienne toute l’année et trouve, dans l’estuaire de la Seine, des conditions de développement très favorables puisque les densités maximales dépassent 190 000 ind m–3, soit un ordre de grandeur plus élevé que dans les autres grands estuaires européens. Il est la proie favorite de nombreuses espèces planctonophages et suprabenthiques ainsi que des poissons fréquentant cette partie amont de l’estuaire de la Seine.

In this report, nutrient concentrations and fluxes are evaluated at the Caudebec station in the Seine estuary; with a mean river flow of 413 m3/s, the values of mean interannual fluxes are 46 300 t per year for silicium, 90 700 t per year for total nitrogen and 11 000 t per year for total phosphorus ; since 1984, there is a decrease of phosphate fluxes (3 % per year) and an increase of total nitrogen fluxes (2 % per year)., Dans ce rapport sont évalués les concentrations et les flux de sels nutritifs à la station de Caudebec dans l'estuaire de la Seine; les flux moyens interannuels, correspondant à un débit de 413 m3/s, sont de 46 300 t par an pour le silicium, 90 700 t par an pour l'azote total et 11 000 t par an pour le phosphore total ; depuis 1984, les flux de phosphate diminuent de 3 % par an et les flux d'azote total augmentent de 2 % par an.