Bibliographies: 'Processus estuaire' – Grafiati (2024)

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Dans la région de Trois-Pistoles, l’action des vagues est moins importante en raison de la prédominance que prennent le glaciel et la marée dans le transport des sédiments littoraux de cette région. La disparité et le mauvais triage des sédiments de surface montrent que plusieurs processus sédimentologiques contribuent à la répartition des sédiments récents. L’influence de la marée dont le marnage atteint 5 m et celle des glaces flottantes dont l’activité dure environ 100 jours par année sont des processus relativement bien connus. L’analyse de l’action des vagues est basée sur le modèle de mise en mouvement des sédiments mis au point par KOMAR et MILLER (1975) en utilisant les données de vagues enregistrées au large de Trois-Pistoles. L’action prédominante des vagues consiste davantage à brasser les sédiments qu’à les trier à cause du balancement de la marée. La formation de nombreuses flèches dans la région montre cependant que les vagues d’intensité plus forte réparties sur de longues périodes contribuent à la construction des formes d’accumulation dans la région. Le rôle que jouent les vagues à l’interface entre les sédiments récents et les argiles de la mer de Goldthwait reste à déterminer.

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RÉSUMÉ À plusieurs endroits, le couvert glaciel des rivages de l'estuaire du Saint-Laurent contient des débris grossiers. Un relevé des cailloux à la surface de la glace a été fait dans quatre sites. On y a mesuré plus de 300 cailloux pesant entre un kilo et une tonne. Dans les sites étudiés, les cailloux de petite taille (1 à 20 kg) prédominent avec 60 %; les cailloux de 20 à 50 kg comptent pour 25 %; les autres ont un poids supérieur à 50 kg. Dans trois des sites étudiés, la débâcle est survenue le lendemain des observations. Les cailloux à la surface de la glace ont donc été évacués au large et vers l'aval sur des distances qui ont pu atteindre 30 km avant d'être délestés. La puissance des vagues et la vélocité des courants étant relativement modestes sur les estrans du Saint-Laurent estuarien, une grande partie des sédiments grossiers excède leur compétence; les matériaux au-dessus de 10 cm sont donc exclusivement déplacés par les glaces. Le relevé des cailloux à la surface du couvert glaciel renseigne utilement sur la charge sédimentaire des glaces et aide à quantifier le processus.

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RÉSUMÉ De larges plates-formes littorales ceinturent l'île aux Coudres, dans le moyen estuaire du Saint-Laurent. Le substrat rocheux est constitué de microgrès et de schistes à forts pendages. L'environnement océanographique est caractérisé par un régime marégraphique semi-diurne macrotidal, des eaux saumâtres, de forts courants de marée généralement parallèles aux rivages, et des vagues relativement importantes du sud-ouest et du nord-est suivant l'axe du Saint-Laurent. Une saison glacielle de 4 mois environ permet le développement d'un pied de glace en hiver. Des profils topographiques levés tout autour de l'île ont permis de mettre en évidence certains faits: 1) les plates-formes les moins exposées, du côté nord, sont étroites, en pente forte, relativement élevées et contiguës à une falaise rocheuse parfois vive; il semble qu'elles résultent d'un recul, sous l'action des agents littoraux, de l'escarpement rocheux correspondant au front des nappes appalachiennes; 2) les plates-formes des deux extrémités exposées de l'île accusent un degré de destruction plus avancé que les autres; 3) des niveaux préférentiels d'aplanissem*nt sont décelables statistiquement et peuvent être corrélés avec des modes dans la courbe de distribution de la fréquence des niveaux d'eau. Les plates-formes de l'île aux Coudres évoluent sous les conditions hydrodynamiques actuelles, mais il s'agit de paléoformes rajeunies qui correspondraient à la surface Micmac. La cryoclastrie, l'érosion glacielle et l'altération superficielle des formations schisteuses et microgréseuses sont considérées comme des agents majeurs dans les processus d'érosion en relation avec les marées.

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Abstract. The incomplete spatial coverage of CO2 partial pressure (pCO2) measurements across estuary types represents a significant knowledge gap in current regional- and global-scale estimates of estuarine CO2 emissions. Given the limited research on CO2 dynamics in large estuaries and bay systems, as well as the sources of error in the calculation of pCO2 (carbonic acid dissociation constants, organic alkalinity), estimates of air–sea CO2 fluxes in estuaries are subject to large uncertainties. The Estuary and Gulf of St. Lawrence (EGSL) at the lower limit of the subarctic region in eastern Canada is the world's largest estuarine system, and is characterized by an exceptional richness in environmental diversity. It is among the world's most intensively studied estuaries, yet there are no published data on its surface-water pCO2 distribution. To fill this data gap, a comprehensive dataset was compiled from direct and indirect measurements of carbonate system parameters in the surface waters of the EGSL during the spring or summer of 2003–2016. The calculated surface-water pCO2 ranged from 435 to 765 µatm in the shallow partially mixed upper estuary, 139–578 µatm in the deep stratified lower estuary, and 207–478 µatm along the Laurentian Channel in the Gulf of St. Lawrence. Overall, at the time of sampling, the St. Lawrence Estuary served as a very weak source of CO2 to the atmosphere, with an area-averaged CO2 degassing flux of 0.98 to 2.02 mmol C m−2 d−1 (0.36 to 0.74 mol C m−2 yr−1). A preliminary analysis revealed that respiration (upper estuary), photosynthesis (lower estuary), and temperature (Gulf of St. Lawrence) controlled the spatial variability in surface-water pCO2. Whereas we used the dissociation constants of Cai and Wang (1998) to calculate estuarine pCO2, formulations recommended for best practices in open ocean environments may underestimate pCO2 at low salinities, while those of Millero (2010) may result in overestimates.

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In tide-dominated estuaries, maximum-turbidity zones (MTZs) are common and prominent features, characterized by a peak in suspended-sediment concentration (SSC) associated with estuarine processes. The Brazilian Amazon coast includes many estuaries, experiencing macrotidal conditions. MTZs are expected to occur and are crucial for sediment delivery to the longest continuous mangrove belt of the world. The area is under influence of the Amazon River plume (ARP), the main SSC source, as local rivers do not deliver substantial sediment supply. To assess the processes that allow the ARP to supply sediment to the estuaries and mangrove belt along the Amazon coast, the results from previous individual studies within five Amazon estuaries (Mocajuba, Taperaçu, Caeté, Urumajó and Gurupi) were compared with regards to SSC, salinity, morphology and tidal propagation. This comparison reinforces that these estuaries are subject to similar regional climate and tidal variations, but that their dynamics differ in terms of distance from the Amazon River mouth, importance of the local river sediment source, and morphology of the estuarine setting. The Urumajó, Caeté and Gurupi are hypersynchronous estuaries where perennial, classic MTZs are observed with SSC > 1 g·L−1. This type of estuary results in transport convergence and MTZ formation, which are suggested to be the main processes promoting mud accumulation in the Amazonian estuaries and therefore the main means of mud entrapment in the mangrove belt. The Mocajuba and the Taperaçu estuaries showed synchronous and hyposynchronous processes, respectively, and do not present classic MTZs. In these cases, the proximity to the ARP for the Mocajuba and highly connected tidal channels for the Taperaçu estuary, assure substantial mud supply into these estuaries. This study shows the strong dependence of the estuaries and mangrove belt on sediment supply from the ARP, helping to understand the fate of Amazon River sediments and providing insights into the mechanisms providing sediment to estuaries and mangroves around the world, especially under the influence of big rivers.

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Estuaries are defined as the areas between rivers and the ocean that have unique ecological characteristics, a wealth of flora and fauna, and are essential to both biodiversity and hydrological processes. Aquatic ecosystems depend on their biological traits as well as their physical and chemical qualities. The objective of the current study was to identify seasonal variations in the physico-chemical parameters of Tamil Nadu's Nandalar Estuary. The physico-chemical characteristics of the Nandalar Estuary were recorded which have an impact on the estuarine environment. Future analyses of the ecological, biological, and cultural elements of estuarine species as well as the allowable limit of fisheries and aquatic life would benefit from preliminary data on the physico-chemical parameters in this Nandalar estuary area.

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Abstract. The French coast facing the Bay of Biscay (North-East Atlantic) is characterised by the presence of small macrotidal and turbid estuaries, including the Charente, which is geographically located between the two large estuaries of the Gironde and the Loire (south-west France). Multi-year, multi-site and high-frequency water quality surveys have shown that the Loire and, to a lesser extent, the Gironde suffer from summer hypoxia. These observations raised the question of the possible occurrence of hypoxia, particularly in one of these small estuaries, the Charente, which flows into the Bay of Marennes-Oléron, the first oyster-farming area in France. Unlike its two large neighbours, the Charente estuary is not continuously monitored, although it is subject to similar climatic changes and anthropogenic pressures, making it impossible to assess potential risks to the ecosystem. Here we present a first study of dissolved oxygen in the Charente estuary based on a combination of longitudinal studies along the estuary axis and instrumented sites to determine the intensity and spatial extent of deoxygenation. Temperature, dissolved oxygen and conductivity sensors were deployed at several sites during the summers of 2018, 2019 and 2020 to record temperature, salinity and dissolved oxygen every 15 min. The high-frequency dataset is compared with a long-term low-frequency dataset (1975–2022; 8–12 measurements per year) to determine whether or not there is a deterioration in the oxygenation of the Charente estuary. The high-frequency dataset shows a high variability in dissolved oxygen (DO) with a clear influence of the tidal cycle. During summer, DO concentrations are often below 5 mg L−1 and sometimes even below 2 mg L−1, indicating the presence of a summer estuarine oxygen minimum zone with an extension along the estuarine axis of about 20–25 km. Temperature is the main factor controlling DO in the Charente estuary, which limits preventive management strategies and, in the context of global warming, raises questions about the long-term suitability of estuarine conditions for the needs of the biological communities, particularly migratory fish.

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Abstract. Alluvial river estuaries consist largely of sand but are typically flanked by mudflats and salt marshes. The analogy with meandering rivers that are kept narrower than braided rivers by cohesive floodplain formation raises the question of how large-scale estuarine morphology and the late Holocene development of estuaries are affected by cohesive sediment. In this study we combine sand and mud transport processes and study their interaction effects on morphologically modelled estuaries on centennial to millennial timescales. The numerical modelling package Delft3D was applied in 2-DH starting from an idealised convergent estuary. The mixed sediment was modelled with an active layer and storage module with fluxes predicted by the Partheniades–Krone relations for mud and Engelund–Hansen for sand. The model was subjected to a range of idealised boundary conditions of tidal range, river discharge, waves and mud input. The model results show that mud is predominantly stored in mudflats on the side of the estuary. Marine mud supply only influences the mouth of the estuary, whereas fluvial mud is distributed along the whole estuary. Coastal waves stir up mud and remove the tendency to form muddy coastlines and the formation of mudflats in the downstream part of the estuary. Widening continues in estuaries with only sand, while mud supply leads to a narrower constant width and reduced channel and bar dynamics. This self-confinement eventually leads to a dynamic equilibrium in which lateral channel migration and mudflat expansion are balanced on average. However, for higher mud concentrations, higher discharge and low tidal amplitude, the estuary narrows and fills to become a tidal delta.

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AbstractSmall estuaries in Mediterranean climates display pronounced salinity variability at seasonal and event time scales. Here, we use a hydrodynamic model of the Coos Estuary, Oregon, to examine the seasonal variability of the salinity dynamics and estuarine exchange flow. The exchange flow is primarily driven by tidal processes, varying with the spring–neap cycle rather than discharge or the salinity gradient. The salinity distribution is rarely in equilibrium with discharge conditions because during the wet season the response time scale is longer than discharge events, while during low flow it is longer than the entire dry season. Consequently, the salt field is rarely fully adjusted to the forcing and common power-law relations between the salinity intrusion and discharge do not apply. Further complicating the salinity dynamics is the estuarine geometry that consists of multiple branching channel segments with distinct freshwater sources. These channel segments act as subestuaries that import both higher- and lower-salinity water and export intermediate salinities. Throughout the estuary, tidal dispersion scales with tidal velocity squared, and likely includes jet–sink flow at the mouth, lateral shear dispersion, and tidal trapping in branching channel segments inside the estuary. While the estuarine inflow is strongly correlated with tidal amplitude, the outflow, stratification, and total mixing in the estuary are dependent on the seasonal variation in river discharge, which is similar to estuaries that are dominated by subtidal exchange flow.

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Abstract. Rivers and estuaries are flanked by floodplains built by mud and vegetation. Floodplains affect channel dynamics and the overall system's pattern through apparent cohesion in the channel banks and through filling of accommodation space and hydraulic resistance. For rivers, effects of mud, vegetation and the combination are thought to stabilise the banks and narrow the channel. However, the thinness of estuarine floodplain, comprised of salt marsh and mudflats, compared to channel depth raises questions about the possible effects of floodplain as constraints on estuary dimensions. To test these effects, we created three estuaries in a tidal flume: one with recruitment events of two live vegetation species, one with mud and a control with neither. Both vegetation and mud reduced channel migration and bank erosion and stabilised channels and bars. Effects of vegetation include local flow velocity reduction and concentration of flow into the channels, while flow velocities remained higher over mudflats. On the other hand, the lower reach of the muddy estuary showed more reduced channel migration than the vegetated estuary. The main system-wide effect of mudflats and salt marsh is to reduce the tidal prism over time from upstream to downstream. The landward reach of the estuary narrows and fills progressively, particularly for the muddy estuary, which effectively shortens the tidally influenced reach and also reduces the tidal energy in the seaward reach and mouth area. As such, estuaries with sufficient sediment supply are limited in size by tidal prism reduction through floodplain formation.

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Cette these porte sur la modelisation numerique tridimensionnelle du transport en suspension des sediments cohesifs en estuaire. Dans un premier temps, le modele numerique telemac-3d, qui simule les ecoulements tridimensionnels en riviere et en mer, a fait l'objet de nouveaux developpements afin de representer les processus propres aux sediments fins (phenomene de floculation, mouvements de la creme de vase, consolidation du fond vaseux). L'etude d'un estuaire schematique a montre les capacites du code a simuler les phenomenes caracteristiques des environnements estuariens: propagation de la maree, intrusion saline et formation du bouchon vaseux. Le modele a alors ete applique a un cas reel: l'estuaire de la loire. Le bouchon vaseux reproduit par le modele presente des caracteristiques (position dans l'estuaire, deplacements au cours de la maree) similaires a celles observees en nature. Le modele de creme de vase a aussi ete teste et il s'est avere utile pour une bonne representation de la dynamique sedimentaire estuarienne

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Les estuaires assurent une production élevée et le transfert d'une grande quantité de matière organique (MO) du continent vers l'océan. Une étape importante pour comprendre les échanges de MO à l'interface continent - océan, le long de la côte française de la Manche Orientale, est d'établir un bilan de MO dans les trois plus grands estuaires : la Canche, l'Authie et de la Somme. Dans ce but, il a été réalisé une description sédimentologique et biologique du sédiment de surface et une caractérisation élémentaire et isotopique distinguant l'origine de la MO sédimentaire. La caractérisation du sédiment de surface a été réalisée, de l'étage proche subtidal à supratidal, le long de transects transversaux au fleuve, constituant un réseau de 36, 37 et 39 stations respectivement pour l'estuaire de la Canche, de l'Authie et de la Somme. A partir de cette approche cartographique, un transect représentatif dans l'estuaire de la Canche et de l'Authie a été sélectionné, dans le but de quantifier la minéralisation benthique de la MO sédimentaire, le long du gradient tidal et finalement d'établir un bilan de la dégradation de la MO à l'échelle de l'estuaire. A partir de la caractérisation sédimentologique et biologique du sédiment de surface, le paysage estuarien a été défini selon quatre faciès biosédimentaires : les bancs et plateformes sableuses, les vasières, le bas et le haut des prés salés. Il a été démontré que la répartition de la MO à l'échelle de l'estuaire est contrôlée par la distribution de ces différents faciès biosédimentaires. En effet, les sédiments sableux sont soumis à des contraintes hydrodynamiques importantes dans lequel le dépôt de la MO est limité. En revanche, la MO se dépose préférentiellement dans les lieux où les sédiments fins s'accumulent tels que les vasières et les prés salés. Ces deux environnements sédimentaires sont soumis à des contraintes hydrodynamiques plus faibles, plus particulièrement les prés salés, où la végétation favorise le dépôt et limite la remise en suspension de la MO sédimentaire. En effet, les fortes quantités de MO sédimentaire mesurées dans les prés salés sont issues de la contribution des halophytes en C3 dominant le haut des prés salés. Néanmoins, notre étude montre que la MO déposée le long du gradient tidal est aussi dépendant de l'apport de MO particulaire provenant des communautés phytoplanctoniques fluviatiles et marines/estuariennes. De plus, cette étude a mis en évidence des différences géomorphologique avec un état de maturité des prés salés avancée dans l'estuaire de la Canche, une progradation du pré salé en rive dans l'estuaire de l'Authie et une régression du pré salé, en rive nord dans l'estuaire de la Somme, issu d'un comblement avancé. A l'immersion et à l'émersion, les vasières et les prés salés ont une contribution plus importante que les sédiments perméables à la minéralisation benthique. Paradoxalement, le bilan de la minéralisation benthique, relève une contribution non négligeable des sédiments perméables dans l'estuaire de l'Authie, étant donné leur vaste répartition à l'échelle de l'estuaire. Il a été démontré que la variation spatiale de la minéralisation benthique repose sur les caractéristiques sédimentologiques des faciès biosédimentaires mais aussi sur les facteurs biologiques tels que la macrofaune benthique, le microphytobenthos et le système racinaire des halophytes. Cette thèse contribue à une meilleure définition du rôle des estuaires picards dans le cycle de la MO et permet un premier pas vers la quantification d'un bilan de MO dans les trois principaux estuaires de la Manche Orientale
Estuaries ensure a high production and transfer a large amount of organic matter (OM) from continent to ocean. To understand OM exchanges at the continent-ocean interface along the eastern English Channel coast, it is primordial to establish a mass balance OM budget in the three main estuaries : the Canche, the Authie and the Somme estuaries. In this frame, the sedimentary OM distribution and origin were studied by coupling a sedimentological description of surficial sediments and an elemental and isotopic characterization of the sedimentary OM. Such approach was carried out from near from subtidal to supratidal stages, along transects transversal to the main river channel, resulting in a sampling of 36, 37 and 39 stations respectively from the Canche, the Authie and the Somme estuaries. Based on this mapping approach, a representative transect was selected in the Canche and the Authie estuaries in order to quantify the sedimentary OM benthic mineralization along the tidal gradient and finally to establish an OM mineralization budget at the estuarine scale. Based on the sedimentological and biological characterization of sediments, the estuarine landscape was described according to four biosedimentary facies : sand flats, mud flats, low and high marshes. This study evidenced that the distribution of OM at the estuary scale is mainly controlled by the distribution of these biosedimentary facies. Indeed, sand flats are subject to intense hydrodynamic conditions in which sedimentary OM deposition is limited. On the other hand, OM is preferentially deposited in fine-grained sediments such as mud flats and salt marshes. Both of these sedimentary environments are subjected to lower hydrodynamic conditions, especially salt marshes, where vegetation enhances deposition and limits the resuspension of sedimentary OM. Indeed, the high quantities of sedimentary OM measured in salt marshes mainly originate from C3 halophytes dominating high marsh areas. Nevertheless, our study also evidenced that the deposition of sedimentary OM along the tidal gradient depends on the contribution of particulate OM from fluvial and marine/estuarine phytoplankton communities. Moreover, this study has demonstrated that various evolutions of the geomorphological features, with a mature salt marsh present in the Cancheestuary, a seaward prograding salt marsh on the north shore of the Authie estuary, a salt marsh retreat on the north shore of the Somme estuary resulting from an advanced sand infilling. The OM benthic mineralization campaigns demonstrated that during immersion and emersion periods, mud flats and salt marshes are the main contributors to total OM mineralization along the tidal gradient in contrast to sand flats. The spatial variation mainly depended on the sedimentological characteristics of each of biosedimentary facies but also on biological factors such as benthic macrofauna, microphytobenthos and root system of halophytes. The OM mineralization budget at the estuarine scale showed a significant contribution of sand flats in the Authie estuary given their wide distribution. This thesis contributes to a better definition of the role of "Picard" estuaries in the OM cycling and allows a first step towards the quantification of a mass balance OM budget in the three main estuaries of the eastern English Channel coast

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La problematique de cette these engagee dans le cadre du programme seine-aval, est de comprendre et de caracteriser les mecanismes d'envasem*nt de l'estuaire macrotidal de la seine. La cartographie de la couverture sedimentaire de rouen jusqu'a la baie de seine est presentee. Dans l'embouchure, les facies sedimentaires etaient grossiers au xixeme siecle et envases actuellement. Une interpretation de l'evolution a l'echelle du siecle est proposee. Une etude faciologique des depots est realisee. Les modalites de la sedimentation sont etudiees sur une courte echelle de temps. La variation de la nature des sediments superficiels est d'occurrence saisonniere. Le depot vaseux, d'extension maximale en crue, est partiellement remanie et deplace en etiage. L'etude du comportement mecanique des vases permet d'identifier les processus d'erosion. Les vases acquierent rapidement de fortes valeurs de cohesion et sont difficilement erodables par les seuls courants de maree. Les caracteristiques hydrosedimentaires des masses d'eau sont decrites. Le role des courants de maree dans la formation des structures turbides et le role du chenal nord dans le stockage et le transfert des mes sont etudies. L'etude morphosedimentaire de la vasiere nord a ete entreprise. Son fonctionnement hydrosedimentaire est etroitement lie aux crues, aux tempetes et a la divagation du chenal nord. L'etude geochimique des sediments fins et des mes a ete initiee. Elle caracterise un pole continental, un pole marin et des sources intra-estuariennes de particules. L'envasem*nt actuel de l'estuaire de la seine est incontestable mais fluctuant. Il est lie au cycle complexe des particules fines, partiellement stockees en etiage, en partie expulsees en crue et deposees dans les faibles profondeurs. Les caracteristiques rheologiques et mineralogiques de ces vases expliquent leur preservation partielle. La partie superficielle des vases est remaniee ulterieurement et en partie reintroduite au sein de l'estuaire.

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La migration des bancs de vase observée le long des côtes Guyanaises génère des problématiques de navigation, particulièrement pour l'unique port de commerce de Guyane localisé dans l'estuaire du Mahury. La dynamique hydrosédimentaire de cet estuaire mésotidal et l'influence des bancs sur cette dernière sont très peu renseignées. Les principaux résultats de cette étude mettent en évidence l'importance relative du débit et des courants de marée sur la dynamique des sédiments fins. Bien que l'asymétrie de la marée soit dominée par le flot, les courants de jusant sont prédominants en saison humide et équivalents aux courants de flot en saison sèche. La dynamique des sédiments fins est gouvernée par la remise en suspension, bien que des épisodes de stratification puissent fortement atténuer la turbulence durant les premières heures du jusant. Les flux résiduels de sédiments sont généralement orientés vers l'amont durant la saison sèche et vers l'aval en saison humide, excepté lorsque les débits sont inférieurs aux moyennes saisonnières. L'évolution des fonds de l'estuaire sur 20 ans indique néanmoins une stabilité des dépôts et souligne la capacité de l'estuaire à évacuer les sédiments apportés durant la phase d'envasem*nt. L'interdépendance entre l'estuaire du Mahury et le banc de Kaw sera ainsi soumise à discussion. Elle permettra d'évaluer la capacité du banc de Kaw à influencer la sédimentologie de l'estuaire et inversem*nt d'évaluer la capacité de l'estuaire à perturber la migration du banc
The mud banks migration observed along the Guyanese coastline generates navigating issues, especially for the unique harbor of French Guiana located in the Mahury Estuary. The hydro-sedimentary dynamic of this mesotidal estuary and the influence of the mud banks migration is poorly documented. The main results have brought to light the relative importance of the river discharge and tidal currents on the fine sediment dynamics. Even though the tidal asymmetry is dominated by the flood, the ebb currents are predominant during the wet season and are equivalent to the flood currents during the dry season. The fine sediment dynamics are mainly governed by the resuspension even though some stratification events can highly damp turbulence during the first hours of the ebb. The residual fluxes of sediment are generally landward during the dry season and in the wet season when river discharges are lower than the seasonnal averages. However, the bathymetric evolution over 20 years indicates the stability of the deposits and underlines the estuary's capacity of flushing sediments brought from the mud bank. The interdependence between the Mahury Estuary and the Kaw mudbank will therefore be subject to discussion. It will allow us to evaluate the mud bank influence on the estuarine sedimentology or, inversely, evaluate the capacity of the estuary to interfere with the mud bank migration and slowing down its progression with the currents

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Le modèle input-output régional environnementalisé développé dans la thèse de M. Cordier suggère qu’il serait possible de restaurer 25% des surfaces naturelles de nourriceries de poissons détruites dans l’estuaire de la Seine entre 1834 et 2004. Le modèle suggère que la mesure de restauration pourrait augmenter de 15% à 23% la biomasse de soles produite dans l’estuaire par rapport à une situation sans mesure. Quant à l’effet des coûts de restauration sur les agrégats macroéconomiques (PIB, emploi, etc.), il génère une diminution qui ne dépasse pas 0,5% par rapport à une situation sans mesure. Le modèle montre cependant que trois secteurs sont particulièrement touchés par la mesure, leur bénéfice étant considérablement réduit. Cela indique le compromis à réaliser entre les objectifs écologiques à long terme et les objectifs économiques sectoriels à court terme. La quantification des compromis par le modèle constitue un atout utile aux processus de décision participatifs multicritère / The regional green input-output model developed in Mateo Cordier's PhD shows that it seems possible to restore 25% of the natural areas of fish nurseries destroyed in the Seine estuary between 1834 and 2004. The model suggests that the restoration measure could increase between 15% and 23% the biomass of sole generated by the estuary compared to a situation without measure. Regarding the impact of restoration costs on macro-economic indicators (GDP, employment, etc.), it generates a decrease that does not exceed 0,5% compared to a situation without measure. However, the model shows that three sectors are particularly impacted by the measure. Their benefits are considerably reduced. This shows the trade-off that occurs between ecological targets on the long run and economic targets on the short run. The quantification of such trade-offs in the model is particularly useful to public participation in decision-making.
Doctorat en Sciences agronomiques et ingénierie biologique
info:eu-repo/semantics/nonPublished

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Les forçages hydrodynamiques influençant les vasières intertidales de l'estuaire de Seine ont été calculés dans le système Seine. Ces forçages induisent des érosions de plusieurs millimètres à plusieurs centimètres. La connaissance des processus d'érosion/dépôt a permis la réalisation d'un modèle semi-empirique 1DV de l'évolution des vasières intertidales. Les processus de floculation et de défloculation des matières en suspension (MES) naturelles de l'estuaire de Seine ont été étudiés en laboratoire. Les tests cinétiques effectués à partir du suivi annuel des MES ont permis d'évaluer les paramètres de contrôle de ces processus. Une hiérarchisation est proposée, désignant l'intensité turbulente, la concentration et la qualité des MES comme prépondérants. Un modèle multiclasse de floculation des MES naturelles a été développé. La comparaison de ce modèle aux cinétiques expérimentales a permis d'évaluer l'évolution de l'efficacité de collision selon la nature des MES
Hydrodynamic forcing parameters that influence intertidal ares have been determined in the Seine estuary. These parameters induce sediment erosion, ranging from few millimeters to several centimeters per tide. The knowledge of erosion and deposition mechanisms has led to the development of a semi-empirical 1DV numerical model, simulating the evolution of intertidal areas. Flocculation/deflocculation processes have been studied in lab from natural suspended particulate matter (SPM). Kinetic tests have been carried out with SPM sampled in the Seine estuary. This study has permitted to classify the controlling parameters, representing turbulence, SPM concentration and quality as the predominant parameters. A flocculation numerical model has been developed to simulate the dynamics of natural particles. The comparison of the experimental results and the simulation results allowed evaluating the variability of the collision efficiency as a function of SPM characteristics

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Tableau d'honneur de la Faculté des études supérieures et postdorales, 2014-2015
Les canyons et chenaux sous-marins sont formés par des courants de densité subaquatiques et sont les principaux conduits par lesquels les sédiments continentaux atteignent les milieux marins profonds. Plusieurs canyons et chenaux sous-marins incisent les marges de l’estuaire et du golfe du Saint-Laurent jusqu’à une profondeur de ≥ 300 m. Des données hydroacoustiques et sédimentologiques récemment acquises ont permis d’analyser en détail la morphologie et les processus sédimentaires tardi-quaternaires qui ont modifié l’architecture de ces systèmes turbiditiques. Quatre types de systèmes turbiditiques ont été identifiés en fonction de leur source respective de sédiments. Un premier type de système, alimenté par la dérive littorale, a été cartographié dans les secteurs de Sept-Îles, Les Escoumins et Tadoussac. La formation et l’évolution de ces trois systèmes semblent être étroitement liées à un apport sédimentaire provenant de l’érosion des rives avoisinantes. Vers la mi-Holocène, alors que la charge sédimentaire provenant des rivières a drastiquement diminué, l’érosion des fronts deltaïques a vraisemblablement contribué à alimenter ces systèmes turbiditiques. L’activité gravitaire est aujourd’hui dominée par des mouvements de masse qui permettent le transfert sédimentaire vers le niveau de base. Un second type de canyon a été découvert dans le secteur de Pointe-des-Monts. Bien qu’il ne reçoive pas d’apport sédimentaire, ce dernier est le seul où des formes en croissant, probablement associées à des courants supercritiques, ont migré récemment. Leur activité holocène peut être expliquée par des mouvements de masse épisodiques et des courants quasi-continus d’origine hydrodynamique se déplaçant sur le plancher marin. Des données sédimentologiques suggèrent que ces courants d’origine hydrodynamique seraient responsables de la formation des canyons. Deux autres types de chenaux et canyons ont été identifiés dans l’estuaire, soit des systèmes reliés aux rivières et aux glaciers. Ces deux types de systèmes ont été actifs majoritairement au début de l’Holocène, alors que la charge sédimentaire transportée vers l’estuaire était plus importante, permettant la génération de courants hyperpycnaux. Ainsi, cette recherche a permis de démontrer la variabilité morphologique des canyons et chenaux de l’estuaire et du golfe du Saint-Laurent ainsi que les différentes phases d’activité et types de processus gravitaires qui ont mené à la formation de systèmes turbiditiques dans un contexte tectonique et climatique similaire.
Submarine canyons and channels are formed by subaqueous sediment density flows and are the main conduits through which continental sediments reach deeper sedimentary basins. Numerous submarine canyons and channels incise the margins of the Estuary and Gulf of St. Lawrence, to a depth of ≥ 300 m. Multibeam bathymetry, acoustic backscatter, seismic reflection and sedimentological analysis have allowed examining in great detail the morphology and the late-Quaternary sedimentary processes within these systems. Four types of submarine fans were identified based on their respective source of sediment. A submarine fan located in ≤ 60 m deep in the Sept-Îles sector has illlustrated the role of longshore drift on the formation and evolution of such systems. Longshore drift, through submarine transverse bars and coastal sand bars, forced the formation of a submarine fan near 5 ka BP. Its activity is now dominated by the passage of low density/intensity flows forming sandwaves on the edge of the coastal shelf and high energy flows (probably slope failures) that allow the accumulation of sediment on the deeper submarine fan. Two other systems fed by longshore drift were identified in the Tadoussac and Les Escoumins sectors, where similar recent episodic activity has been described. A second type of canyon system was discovered in the Pointe-des-Monts sector. These canyons are sediment-starved and yet, they are the only systems in which crescentic bedforms recently migrated upslope. Their short- and long-term activity can be explained by slope failures and quasi-continuous hydrodynamic processes along the seafloor. Sedimentological data suggest that quasi-continuous flows of hydrodynamic origin are responsible for the formation of the canyons. Two other types of channels and canyons were identified in the St. Lawrence: systems fed by rivers and glaciers. Both types of systems were active mainly in the early-Holocene, when sediment supply to the St. Lawrence was greater. When sediment supply drastically diminished during mid-Holocene, erosion of deltaic fronts likely led to an increase in longshore-drift transport and the formation and/or continuated activity of the Sept-Îles and Les Escoumins systems.

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Au cours de ce travail, j’ai réalisé une série d'études dans le bassin du Changjiang (Yangtze), afin de mieux comprendre l'influence de ces effets.Tout d'abord, l'exploitation du barrage des Trois Gorges (TGD) a modifié la composition géochimique des sédiments en aval. Depuis 2003, les sédiments venant des hauts bassins ont été en grande partie retenus en amont, tandis que les sédiments précédemment déposés dans le bassin moyen-inférieur ont été progressivement remis en suspension. Ces processus expliquent l’évolution géochimique des sédiments exportés vers la mer de Chine. En deuxième partie, une étude systématique démontre que les compositions isotopiques en lithium des phases dissoutes et particulaires se comportent de façon conservative dans la zone de mélange de l'estuaire du Changjiang. Cependant, les phases échangeables ne représentent qu'une faible quantité de Li, ce qui explique son impact négligeable dans cette zone. Troisièmement, Cette étude confirme que dans les grands bassins versants, l'altération chimique peut réagir rapidement à de grandes amplitudes climatiques. Ceci est particulièrement bien illustré, dans la carotte CM97, par la période du Younger Dryas. Depuis 2 000 ans, les δ7Li des argiles s’accentuent clairement par rapport à la période précédente, à cause de l'érosion des sols de plaines induite par l'homme. En résumé, ces résultats apportent de nouveaux éclairages sur l'interprétation des proxys et sur la réponse de l'altération chimique aux variations climatiques, ce qui est essentiel pour mieux quantifier l’impact du l’altération continentale sur les climats passés et futurs de notre planète
In order to better understand the weathering-climate feedback, a series of studies was carried out in the Changjiang (Yangtze) Basin. First, the operation of the Three Gorges Dam (TGD) changed downstream sediment geochemical compositions. Before 2003, large amounts of upstream-derived sediments deposited and experienced further weathering in the mid-lower basin. Since 2003, strong riverbed sediment resuspension changed the roles of the mid-lower reaches from important sinks to major sources of sediments delivered to the sea. As a consequence, an intensified weathering intensity of downstream sediment was observed.Second, dissolved δ7Li exhibit a conservative behavior in the Changjiang Estuary. During the process of SPM transported offshore, weathering product flocculated and deposited, while primary minerals resuspended. The combined effect resulted in the UCC-like SPM δ7Li values. There is a Li isotope fractionation between the dissolved load and exchangeable phase. However, this process shows negligible impact on δ7Li of dissolved load and particulates. Third, weathering response to climate is complex in large river basins. During the Younger Dryas, the positive excursion of clay δ7Li is consistent with enhanced incongruent weathering, in response to temperature cooling. The minor variation of clay δ7Li at 11 – 2 ka likely indicate stable weathering and mile climate variation. Over the last 2 kyr, the fluctuation of clay δ7Li is mostly caused by intensification of human activities. In summary, this thesis sheds new lights on the weathering-climate feedback over geologic past, and provides perspectives on how human activities affect natural processes

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De leur source continentale à leur lieu de stockage ultime, les particules sédimentaires détritiques vont être produites en fonction de la nature et de l'intensité des processus continentaux : climat, contexte géodynamique. Sur les plates-formes, elles vont subir l'action des agents hydrodynamiques, vont se déplacer, constituer des corps sédimentaires qui seront préservés ou non selon la nature et l'intensité des processus : agitation s.l., apports sédimentaires, création d'espace par subsidence et variation du niveau marin... Enfin, dans les domaines océaniques profonds, elles vont se déposer.
L'objectif des travaux présentés dans ce mémoire est, par une approche sédimentologique, de reconstituer les conditions environnementales, tant sur les continents que sur les plates-formes, ayant conduit aux dépôts étudiés. Sur cette base, nous avons entrepris des études sur des dépôts du Pléistocène en mer du Nord ainsi que dans les mers de Chine de l'Est et du Sud. Cette époque, par sa proximité, permet des études à très haute résolution temporelle tandis qu'elle est caractérisée par des oscillations climatiques et eustatiques importantes et rapides. De plus, les dépôts les plus récents portent la trace de l'Homme.
Sur la plate-forme, l'étude des grands corps sableux, bancs et très grandes dunes, a permis de préciser les mécanismes de leur mise en place. A court terme, même dans les environnements dominés par la marée, l'importance de phénomènes sporadiques tels que les houles de tempêtes, a été démontrée. Ils impriment aux formes et à la structure des fonds marins leur marque tandis que les agents tidaux sont les pourvoyeurs du matériel sédimentaire. A plus long terme, ce ne sont plus les agents dynamiques qui conditionnent la préservation des corps sédimentaires mais la création d'espace disponible et l'importance des apports sédimentaires. Au niveau de l'estuaire de l'Authie, des séries de carottages nous ont aidé à mesurer les conséquences du mouvement vers le nord des divers ensembles sédimentaires sur le type de sédiment rencontré ainsi que sur les modifications d'un espace naturel convoité par l'Homme.
Dans les bassins profonds, en mer de Chine du Sud, nos études ont permis de préciser les sources du matériel sédimentaire et son transport en faisant la part des contributions éolienne, fluviatile et marine. L'étude des caractères sédimentologiques de la fraction détritique a permis également d'étudier la balance ntre l'érosion et l'altération sur les zones émergées ainsi que de voir quelle est la réponse des marqueurs détritiques aux changements climatiques globaux depuis 2 millions d'années.

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Scylla serrata is a portunid crab which can attain a weight of over 2 kg and a carapace width exceeding 250 mm. It is distributed throughout the Indo-West Pacific extending down the east coast of Africa, and both the east and west coasts of Australia. In Australia it is commonly known as the mud crab because it occurs within muddy, mangrove-lined bays and estuaries. Mud crabs are generalist predators eating most small, slow moving animals which they can catch, but they are also vigorous scavengers. Being scavengers, they are readily caught in baited traps set by commercial and recreational fishers, and are the stock for these popular fisheries. Female crabs spawn offshore and larvae spend a period in the plankton where they develop into postlarvae or megalopae...
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment
Science, Environment, Engineering and Technology
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Abstract:

The Lingding Estuary is one of the main parts of the whole Pearl River Delta, which lies in the South Sea, China. It is about 60 km wide from Hong Kong in the east to Macao in the west and the water areas are approximately 2110 km2. The process of suspended sediment movement is influenced by many factors, such as the estuarine geometry, tidal range and ravine flows etc.. In this paper, large scale hydrological observations in the Lingding Estuary have been respectively carried out in July, 2003. Based on these data, characteristics of temporal and spatial variation of suspended sediment concentration (SSC) in the Lingding Estuary are studied. The research result shows that SSC changes with the variation of tide current and runoff, the sediment re-suspension is often occurred 1–2 hour following the flood or ebb tide. The maximum turbidity appears near the gauging station V3. In the flood dominant stage, the sediments move towards the mainland, while during the ebb sediments move down.

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Ling Ding Yang (LDY) estuary is one of the main parts of the whole Zhujiang estuary, which lies in the south sea, China. It is about 60km wide from Hong Kong in the east to Macao in the west and the water areas are approximately 2110 km2. The mixing process of salt water and fresh water in the estuary is influenced by many factors, such as the estuarine geometry, tidal range and ravine flows, etc. In this paper, based on the data from the tidal gauge stations and synchronously surveyed data during July 2003, a study on the temporal and spatial distribution characteristics of salinity was made. According to the observation data, in wet season, the fresh water and salt water mixes with the N parameter between 0.21 and 1.63. The distribution of salinity concentration in the east part of LDY is due to coriolis’ force. The salinity concentration decreases from the sea to the estuary, and there exists apparent division point, Nei Lingding Island. To the south of Nei Lingding Island, it is almost partially mixed, and to the north of Nei Lingding Island, it belongs to highly stratification. At the same time, the stratification parameter and the vertical mean velocity in wet season are compared. The N parameter changes with the velocity of tide flow in a tidal cycle. The value of N in a flood tide is usually larger than that is in an ebb tide. That is to say, the mix intensity is much bigger in the flood tide.

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This paper presents two non-intrusive techniques to measure the time evolution of the vertical profile of concentration during batch settling test. The first one is a Magnetic Resonant Imaging (MRI) vertical prototype used on Gironde estuary. The second is an X-ray ‘home-made’ prototype used on Seine estuary. Both are used to observe the sedimentation and the consolidation processes of natural cohesive sediments. They provide the movement of the supernatant/suspension interface and the isoconcentration lines of the process. A space-time based method is proposed to close the governing equation.

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Estuaries trap much of the fine sediment delivered to them by rivers. This phenomenon presents challenges to the US Army Corps of Engineers (USACE) navigation mission, which maintains navigable waterways for waterborne commerce through estuarine regions. The USACE Regional Sediment Management Program and the USACE Norfolk District are conducting a regional sediment transport modeling study to identify cost-effective sediment management schemes in the James River, a tributary estuary of Chesapeake Bay. A key element of the sediment transport modeling study is the definition of cohesive sediment transport processes, such as erosion and settling velocity. This report describes field-based measurements of cohesive sediment erosion and settling velocity conducted in November 2017. The team conducted erosion testing on 15 cores collected throughout the tidal system. Additionally, two anchor stations were occupied to measure tidal variations in vertical distributions of suspended sediment concentration, particle size, and settling velocity. Recommended cohesive sediment transport parameters were developed from the field measurements.

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Submerged aquatic vegetation (SAV) growing in estuarine and coastal marine systems provides crucial ecosystem functions ranging from sediment stabilization to habitat and food for specific species. SAV systems, however, are sensitive to a number of environmental factors, both anthropogenic and natural. The most common limiting factors are light limitation, water quality, and salinity, as reported widely across the literature. These factors are controlled by a number of complex processes, however, varying greatly between systems and SAV populations. This report seeks to conduct an exhaustive examination of factors influencing estuarine and coastal marine SAV habitats and find the common threads that tie these ecosystems together. Studies relating SAV habitats in the United States to a variety of factors are reviewed here, including geomorphological and bathymetric characteristics, sediment dynamics, sedimentological characteristics, and water quality, as well as hydrologic regime and weather. Tools and methods used to assess each of these important factors are also reviewed. A better understanding of fundamental environmental factors that control SAV growth will provide crucial information for coastal restoration and engineering project planning in areas populated by SAVs.

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Salmonid species are critically important ecologically, socially, and economically for North American coastal regions. Alterations to the structure (e.g., channelization) and function (e.g., sediment transport) of estuaries, rivers, and streams have greatly impacted these species, many are now listed as federally threatened or endangered. As part of environmental compliance procedures and policy, the U.S. Army Corps of Engineers (USACE) is required to assess the impacts and/or benefits of proposed water resource projects (e.g., levee maintenance, ecosystem restoration, etc.) to the environment. The USACE is required to predict and quantify environmental benefits using models to justify federal investment in ecosystem restoration projects. The purpose of this effort is to develop a general model or model framework that can be used during the USACE planning process that will serve as a unified standard Salmonid model. The primary purpose of the model will be to project future environmental benefits that will result from proposed restoration measures. Additionally, the model needs to be sensitive to different combinations of restoration measures in order to assist the USCAE in the planning and decision making process. This report presents the results of the first phase of model development using the mediated model development process.

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Cruise AL534/2 is part of a multi-disciplinary research initiative as part of the JPI Oceans project HOTMIC and sought to investigate the origin, transport and fate of plastic debris from estuaries to the oceanic garbage patches. The main focus of the cruise was on the horizontal transfer of plastic debris from major European rivers into shelf regions and on the processes that mediate this transport. Stations were originally chosen to target the outflows of major European rivers along the western Europe coast between Malaga (Spain) and Kiel (Germany), although some modifications were made in response to inclement weather. In total, 16 stations were sampled along the cruise track. The sampling scheme was similar for most stations, and included: 1) a CTD cast to collect water column salinity and temperature profiles, and discrete samples between surface and seafloor, 2) sediment sampling with Van Veen grab and mini-multi corer (mini-MUC), 3) suspended particle and plankton sampling using a towed Bongo net and vertical WP3 net, and 4) surface neusten sampling using a catamaran trawl. At a subset of stations with deep water, suspended particles were collected using in situ pumps deployed on a cable. During transit between stations, surface water samples were collected from the ship’s underway seawater supply, and during calm weather, floating litter was counted by visual survey teams. The samples and data collected on cruise AL534/2 will be used to determine the: (1) abundance of plastic debris in surface waters, as well as the composition of polymer types, originating in major European estuaries and transported through coastal waters, (2) abundance and composition of microplastics (MP) in the water column at different depths from the sea surface to the seafloor including the sediment, (3) abundance and composition of plastic debris in pelagic and benthic organisms (invertebrates), (4) abundance and identity of biofoulers (bacteria, protozoans and metazoans) on the surface of plastic debris from different water depths, (5) identification of chemical compounds (“additives”) in the plastic debris and in water samples.