L’anticipation et l’adaptation de nos sociétés aux bouleversements résultants du changement climatique sont aujourd’hui des questions majeures guidant les activités humaines et l’action publique. Néanmoins, la prévision reste un défi essentiel en raison des fortes incertitudes existantes et il est primordial de continuer à progresser dans la compréhension des mécanismes à l’origine de ces bouleversements. Au sein du cycle hydrologique, le réservoir de surface (incluant les lacs, les rivières et les plaines d’inondation) occupe une place importante car il est l’une des principales ressources en eau des écosystèmes et des populations. Or, la dynamique des stocks d’eau de surface est toujours mal connue aux échelles régionale et globale, du fait de l’absence de mesures pluriannuelles d’extension et de hauteur d’eau des zones inondées, et de la prise en compte limitée de ces variables dans les modèles hydrologiques et hydrodynamiques. La télédétection spatiale offre désormais la possibilité d’effectuer un suivi des stocks d’eau de surface en utilisant la complémentarité entre l’imagerie multi-spectrale, permettant de cartographier les étendues inondées, et l’altimétrie radar fournissant des séries temporelles de hauteur d’eau des hydro-systèmes continentaux. L’objectif de ma thèse est de tirer le meilleur parti de la complémentarité entre les différents types d’observations spatiales pour évaluer les ressources en eau du réservoir de surface et mesurer la dynamique des transferts d’eau des continents aux océans, et son impact sur la zone côtière en utilisant les concentrations de matières en suspension comme traceur des masses d’eau. Depuis le milieu des années 1990, la multiplication des missions multi-spectrales à moyenne résolution (< 1 km de résolution spatiale) et des altimètres radars à haute précision (comprise entre 10 et 30 cm) permet de réaliser un suivi hebdomadaire à mensuel des volumes d’eau de surface dans les grands bassins fluviaux. / The anticipation and adaptation of our societies to the upheavals resulting from climate change are today major issues guiding human activities and public action. Nevertheless, the forecast remains a key challenge because of the strong uncertainties that exist and it is essential to continue to progress in understanding the mechanisms behind these upheavals. Within the hydrological cycle, the surface reservoir (including lakes, rivers and floodplains) occupies an important place as it is one of the main water resources of ecosystems and populations. However, the dynamics of surface water stocks are still poorly known at the regional and global scales, due to the absence of multi-year measures of extension and water depth of the flooded areas, and the limited consideration of these variables in hydrological and hydrodynamic models. Satellite remote sensing now offers the possibility of monitoring surface water stocks by using the complementarity between multispectral imagery, allowing to map flooded areas, and the radar altimetry providing time series of water depths of continental hydro systems. The aim of my thesis is to make the most of the complementarity between the different types of spatial observations to evaluate the water resources of the surface reservoir and to measure the dynamics of water transfers between land and ocean, and its impact on the coastal zone using suspended particulate matter as tracer of water bodies. Since the mid-1990s, the multiplication of multispectral missions with medium resolution (<1 km of spatial resolution) and high-precision radar altimeters (between 10 and 30 cm) makes it possible to carry out weekly-to-monthly monitoring of volumes surface water in large river basins.

Estuarine circulation and its associated transport processes drive the environmental integrity of many near-shore habitats (the coastal ocean, rivers, estuaries and emergent wetlands). A thorough understanding and consideration of this circulation is, therefore, vital in the proper management of these habitats. The aim of this study is to bring together theory and new satellite observations in the Columbia River Estuary to increase our understanding of estuarine circulation and transport. Surface reflectance measurements gathered by the Moderate Imaging Spectroradiometer (MODIS) are first compared to in situ observations to develop an empirical model for remotely derived surface turbidity. Results indicate that MODIS data significantly correlate with in situ measurements of turbidity throughout the CRE (R2 = 0.96). Remote estimates of turbidity are then used to explore the physical processes that drive their spatial distribution. Although the response to different hydrodynamic conditions varies throughout the system, global levels of turbidity are most sensitive to fluvial and tidal inputs and increase during spring tides and high river flow. As a result, the turbidity field has temporal cycles that are consistent with the frequency of these processes. The location of the estuarine turbidity maximum (ETM) is highly dynamic and typically migrates downstream as the tidal velocity or river flow increases. The ETM becomes trapped near the Megler Bridge (river kilometer 20), however, and the presence of strong topography in this region suggests there exists an interaction between bottom topography and sediment transport. A 2-D semi-analytical model, developed herein from the simplified Navier-Stokes equations, confirms that topographic features exhibit substantial influence on longitudinal turbidity distributions. The model considers the coupled, tidally-averaged velocity (composed of gravitational circulation, internal tidal asymmetry, and river flow) and salinity fields and assumes a condition of morphodynamic equilibrium to estimate the distribution of sediment for arbitrary channel configurations. Model simulations demonstrate that topographic highs tend to increase local seaward sediment fluxes, and that topographic lows increase local landward sediment fluxes. Sediment flux convergence near topographic highs compresses the local turbidity distribution, whereas flux divergence near topographic lows dilates the distribution and, under appropriate conditions, produces multiple ETMs. In summary a combination of the model and satellite data has given valuable new insights into the sediment dynamics of estuarine environments; in particular, both show that turbidity distribution and ETM location vary considerably with tidal and river flow conditions, fluctuating on a variety of timescales, and are heavily influenced by bottom topography.

In the restoration of tidal wetland ecosystems, potential drivers of plant community development range from biotic controls (e.g. plant competition, seed dispersal) to abiotic controls (e.g. tidal flooding, salinity levels). How these controls influence the success of tidal wetland restoration are only partly understood, but have important implications for wetland habitat recovery. Specifically, the extent to which the existing native and non-native seed banks in tidally reconnected wetlands interact with these controls is not clear, yet the potential success of passive restoration methods depends upon this understanding. For a 54-year chronosequence of eleven tidal wetland restoration sites in the Lower Columbia River of western Oregon, USA, it was hypothesized that native plant species and soil properties would show trends approaching reference levels within 3 to 20 years post-restoration and that lower elevation wetland areas within restored sites would exhibit a greater native species abundance and similarity to reference sites, compared with restored high elevation wetland areas. Results indicated that plant species richness, soil organic matter, bulk density, pH, and salinity conditions among the restoration sites reached reference wetland ranges within 3-6 years post-tidal reconnection. The mid-low marsh elevation zones (<2.5 m) recovered native plant cover within 3-6 years post-tidal reconnection, while high marsh elevation zones (>2.5 m) remained dominated by nonnative species Phalaris arundinacea and Juncus effusus subsp. effusus. To investigate the mechanisms driving these non-native plant invasions, it was ii hypothesized that native and non-native wetland plant community distributions would be reflective both of their abundance in the seed bank and of their germination tolerance to wetland tidal flooding and salinity conditions. Using a factorial study design of three tidal conditions by three salinity levels, these hypotheses were tested in the greenhouse. Overall, non-native seeds were found to significantly outnumber native seeds in both seed banks. In the greenhouse, P. arundinacea and J. effusus were found to germinate more readily out of the seed bank under freshwater high-marsh flooding (1 hour a day) treatments as compared to oligohaline (3 ppt) mid-low marsh flooding (3-6 hours twice a day) treatments and to brackish salinity (10 ppt) treatments. Dominant native wetland species, Carex lyngbyei and Schoenoplectus lacustris, germination were not found to vary significantly among the treatments (p > 0.10). These results indicate that the salinity and flooding gradients within these restored marshes suppress germination of the non-native species in the low-mid marsh but not in the high marsh, where they are likely able to outcompete the native species due to their dominance in the seed bank. The implications of these results for passive tidal wetland restoration efforts are that both seed bank composition and species-specific tolerances to restored tidal flooding and salinity gradients are key mechanisms driving native and nonnative plant community development and resilience.

Knowledge of the interactions among species and communities is vital for their management and protection. Increasingly, the role of marine protected areas in this regard is being recognised, primarily because of the potential for previously-harvested species to increase in density and biomass, and the linkages among species to be restored. Monitoring and research was conducted within and surrounding two marine reserves on the east coast of the North Island of New Zealand – Te Tapuwae o Rongokako, near Gisborne, and Te Angiangi, south of Napier. The aim was to describe the biological characteristics of spiny lobsters (Jasus edwardsii) in the absence of fishing, and to describe the effects of fishing and protection on lobster populations and the communities of which they are a component. Diver and pot surveys showed that lobsters were significantly more abundant within the reserves than in the surrounding fisheries and that the populations were comprised of a larger proportion of legal-sized individuals. Higher female fecundity within Te Tapuwae o Rongokako Marine Reserve compared with the surrounding fishery was proposed to be primarily a result of increased availability of large males within the reserve. The impact of the fishery on lobsters was also evidenced in the lower tail width to carapace length ratio of the fished population compared to the population within Te Tapuwae o Rongokako Marine Reserve, due to the minimum legal size for Jasus edwardsii in New Zealand being based on tail width. The largest tagging study ever to be conducted in a New Zealand marine reserve showed that sublegal male lobsters within Te Tapuwae o Rongokako Marine Reserve were growing on average faster than the same sized individuals outside the reserve, potentially as a result of the effects of handling and / or size-selective fishing. A decrease in growth rate over time was recorded in male lobsters within the reserve, which coincided with an increase in catch per unit effort and may indicate that density-dependent effects are operating. Distinct seasonal movements of tagged lobsters were recorded, with the vast majority of movements taking place within reefs. Where the boundaries of the reserve crossed reef habitat, significant movement of lobsters across the boundaries occurred. Lobsters within Te Tapuwae o Rongokako Marine Reserve not only exhibited cannibalistic behaviour but foraged during the day, including on intertidal reef platforms at high tide, potentially as a behavioural response to increased competition for food – behaviour not previously reported for this species. Outside the reserve, lobster bait apparently provided an alternative protein source but despite this supplementation of diet, these lobsters were in poorer nutritional condition, as evidenced by their lower body weights relative to carapace length and tail width for both sexes. Lobsters outside the reserve were also significantly more affected by a bacterial infection associated with handling, than lobsters within the reserve. These findings have significant implications for fisheries management and for the design and management of marine protected areas (MPAs). This study demonstrates that many of the biological parameters used in evaluating harvest strategies in the New Zealand lobster fishery may be biased unless collected from populations with a natural size structure, such as may occur within marine protected areas.

En la presente tesis se aborda el desarrollo de un modelo de calidad del agua orientado al estudio de sustancias prioritarias y peligrosas teniendo en cuenta los efectos de la dinámica sedimentaria a fin de facilitar la gestión de zonas estuarinas. Además, con el objeto de poder llevar a cabo la integración del modelo desarrollado dentro de un Sistema de Información Geográfica, se establecen los procedimientos metodológicos necesarios. La conjugación de estas tareas permitirá fusionar los beneficios de ambos instrumentos bajo un único entorno a fin de obtener una herramienta de gestión de vertidos que aporte respuestas técnicas tomando en consideración las exigencias legislativas de la normativa vigente. / This thesis tackles the development of a water quality model devoted to priority and hazardous substances considering, as well, the effects derived from the sedimentary dynamics with the aim to simplify the management of estuarine areas. Moreover, with the aim to integrate this model into a Geographical Information System, the required methodological procedures are established. The combination of both tasks will allow the integration of the benefits from both tools within a unique environment that will allow the discharges management providing technical answers taking into consideration the legislative requirements.

River export has a strong influence on the productivity of coastal waters. During storm events, rivers deliver disproportionate amounts of nutrients and organic matter to estuaries. Anthropogenic changes to the land use/cover (LULC) and water use also have a strong influence on the export of nutrients and organic matter to estuaries. This study specifically addressed the following questions: 1) How does river water chemistry vary across LULC patterns in the Mission and Aransas river watersheds? 2) How do fluxes of water, nutrients, and organic matter in the rivers vary between base flow and storm flow? 3) How do variations in nutrient/organic matter concentrations and stable isotope ratios of particulate organic matter (POM) in Copano Bay relate to river inputs? Water was collected from the Mission and Aransas rivers and Copano Bay from July, 2007 through November, 2008 and analyzed for concentrations of nitrate, ammonium, soluble reactive phosphorus (SRP), dissolved organic nitrogen, dissolved organic carbon, particulate organic nitrogen, particulate organic carbon (POC), and the stable C and N isotope ratios of the POM. The first half of the study period captured relatively wet conditions and the second half was relatively dry compared to long term climatology. Riverine export was calculated using the USGS LOADEST model. The percentage of annual constituent export during storms in 2007 was much greater than in 2008. Concentration-discharge relationships for inorganic nutrients varied between rivers, but concentrations were much higher in the Aransas River due to waste water contributions. Organic matter concentrations increased with flow in both rivers, but POM concentrations in the Aransas River were two fold higher due to large percentages of cultivated crop land. Values of [delta]¹³C-POC show a shift from autochthonous to allochthonous organic matter during storm events. Following storm events in Copano Bay, increases and quick draw down of nitrate and ammonium concentrations coupled with increases and slow draw down of SRP illustrate nitrogen limitation. Organic matter concentrations remained elevated for ~9 months following storm events. The [delta]¹³C-POC data show that increased concentrations were specifically related to increased autochthonous production. Linkages between LULC and nutrient loading to coastal waters are widely recognized, but patterns of nutrient delivery (i.e. timing, duration, and magnitude of watershed export) are often not considered. This study demonstrates the importance of sampling during storm events and defining system-specific discharge-concentration relationships for accurate watershed export estimation. This study also shows that storm inputs can support increased production for extended periods after events. Consideration of nutrient delivery patterns in addition to more traditional studies of LULC effects would support more effective management of coastal ecosystems in the future. / text

The respective kinetics of bacterial leucine aminopeptidase and [beta]-glucosidase activities were investigated to improve understanding of factors controlling activity and hydrolytic capacity in estuarine organic-poor sands. Depth distributions of enzyme activity and bulk organic matter content were determined in sediments of Aransas Bay and Copano Bay Texas, to investigate enzyme dynamics as related to the geochemical properties of the sediment. Vertical profiles of activity in sediment showed that the enzymes were more active at the surface and that the potential hydrolysis rate of leucine aminopeptidase was higher than that of [beta]-glucosidase. Vertical patterns of enzyme activity correlated (weakly) with variations in sediment organic matter (TOC, TN, and carbohydrates) content. Enrichments of sediment samples with monomeric organic compounds and inorganic nutrients did not affect leucine aminopeptidase and [beta]-glucosidase activities in short- and long-term incubations. Enzyme activity was independent of nutrient availability and suggested that microbial communities were not nutrient-limited. Time-course assays of bacterial hydrolysis of TOC, TN, and carbohydrates provided information about how substrate limitation may affect enzyme activity. Positive correlations between bulk TOC and TN content and enzyme activity indicated enzyme dependence on polymeric substrate content. Induction of enzyme activity after sediment enrichments with specific labile compounds confirmed the importance of available organic substrate to enzyme hydrolysis efficiency. A kinetic approach established the occurrence of enzyme inhibition and its effects on enzyme hydrolytic capacity. The addition of a specific-enzyme substrate to sediment samples modified enzyme parameters and indicated that a substrate-reversible type of inhibitor could reduce enzyme hydrolytic capacity. The addition of polyphenol, as a natural inhibitor of enzyme activity, to the sediment resulted in a concomitant reduction of leucine aminopeptidase activity and ammonium regeneration rate, and thus demonstrated a close coupling between enzyme activity and sediment ammonium regeneration. These research results demonstrate the dynamic nature of the hydrolytic enzymes, provide information about the mechanisms of induction and inhibition of activity, and demonstrate some implications of reducing the hydrolytic capacity to organic matter decomposition and nutrient regeneration rates. / text

Η οικολογία και η δυναμική της εγκατάστασης εξετάστηκαν για τέσσερα μεσογειακά παράκτια είδη: Diplodus vulgaris, Diplodus sargus, Oblada melanura και Diplodus annularis. Η διερεύνηση τους έγινε με υποδιαίρεση της βενθικής ιχθυονυμφικής τους φάσης σε έξι οντογενετικά στάδια βάσει χρωματικών πρότυπων που εμφάνιζαν διαδοχή και ήταν χαρακτηριστικά για κάθε είδος. Η συλλογή δεδομένων έγινε για κάθε οντογενετικό στάδιο με στρωματοποιημένη δειγματοληψία, με τις στρώσεις να αποτελούν συνδυασμό τύπου υποστρώματος και βάθους στην παράκτια περιοχή ανατολικά των εκβολών του Αχελώου, από βάθος 0 έως 5m. Τα δεδομένα συλλέχθηκαν με απ’ ευθείας παρατηρήσεις με χρήση καταδυτικής συσκευής. Υπολογίστηκαν οι πυκνότητες κάθε οντογενετικού σταδίου στους διάφορους τύπους υποστρώματος και βάθη μέσα στο έτος. Η κατανομή των πυκνοτήτων αυτών έδωσε στοιχεία για τις οικολογικές προτιμήσεις των βενθικών ιχθυονυμφών και των νεαρών, καθώς και για τους ρυθμούς μεταμόρφωσης κάθε είδους. Επίσης ελέγχθηκε το πρότυπο συμπεριφοράς των ιχθυονυμφών του μελανουριού κατά την εγκατάσταση τους, μ’ επινόηση ειδικής μεθοδολογίας κι ενός δείκτη που απέδωσε ποσοτικά τις διάφορες εκφάνσεις της συμπεριφοράς. Σύμφωνα με τ’ αποτελέσματα της εργασίας, φάνηκε ότι ο σαργόπαπας και ο σαργός εγκαθίστανται την κρύα περίοδο του έτους, ενώ το μελανούρι και ο σπάρος τη θερμή. Όλα τα είδη εμφάνισαν γρηγορότερο ρυθμό μεταμόρφωσης κατά τα πρώτα στάδια, ενώ τα είδη που εγκαταστάθηκαν το καλοκαίρι είχαν συνολικά γρηγορότερους ρυθμούς μεταμόρφωσης από τα χειμερινά. Τα είδη εμφάνισαν διαφοροποίηση στη χρονική και χωρική κατανομή τους ώστε να ελαττώνονται οι ανταγωνιστικές δράσεις. Το είδος με τη μακρύτερη χρονική παρουσία ήταν ο σαργόπαπας (10 μήνες), ο οποίος εμφάνισε ευρύτητα ως προς τις οικολογικές του απαιτήσεις διασπειρόμενος σ’ όλο το εύρος βάθους και τύπους υποστρώματος, εκτός του αμμώδους. Στον αντίποδα, το μελανούρι είχε τη μικρότερη συνολική παρουσία (4 μήνες) και απόλυτη εξάρτηση από σκληρό υπόστρωμα. Ο σαργός κι ο σπάρος έδειξαν ενδιάμεσες οικολογικές απαιτήσεις με προτίμηση στα σκληρά υποστρώματα και στα φανερόγαμα αντίστοιχα. Κανένα είδος δεν έδειξε προτίμηση σε αμμώδεις βυθούς. Ιδιαίτερο οικολογικό ρόλο εμφάνισε το ρηχότερο τμήμα της παράκτιας ζώνης και οι μεταβατικές ζώνες διαφορετικών υποστρωμάτων. Οι βενθικές ιχθυονύμφες του μελανουριού επέδειξαν τάση παραμονής για μέρες με μικρές ομάδες σε σημεία του υποστρώματος. Στα επόμενα στάδια σχημάτισαν μεγάλες ομάδες με μικρότερη εξάρτηση από το υπόστρωμα. / The ecology and dynamics of settlement process were studied for four sparids (Diplodus vulgaris, D. sargus. D. annularis and Oblada melanura), in a coastal littoral in western Hellas. The benthic larval phase of each species was divided in six ontogenetic stages, according to specific patterns in appearance that followed a sequence. Preliminary observations showed non homogeneous distribution of the larvae in the area, so stratified sampling was applied. Strata represented the different substratum types accounted in each of the three depth zones of 0-1m, 1-2m and 2-5m. Data concerned abundances of each ontogenetic stage in each stratum during a 15 month interval and they were collected by visual census. Moreover, data on site-attachment ontogenetically depended behavior of benthic larvae of O. melanura were also collected. The later behavior was studied via an index devised for quantifying different expressions of residence behavior. Two of the studied species (D. vulgaris and D. sargus), settled during the cold period of the year while the other two settled during summer. Metamorphosis rates were faster at the first ontogenetic stages for all species, while they were faster in total for the summer species. Temporal and spatial distribution of the species was arranged in order to minimize competition. D. vulgaris and D. sargus settled in the same substratum types in different periods and O. melanura and D. annularis settled during the same period in different substrata. D. vulgaris remained in the nursery area the longest period, exhibiting the broadest ecological requirements, being distributed in different substrata and depths. O. melanura remained half as long in the nursery area, exhibiting the narrowest ecological requirements, staying always over hard substratum in shallow waters. The other two species exhibited intermediate conditions, with D. sargus preferring hard substratum and D. annularis, seagrass beds. None of the studied species preferred soft substratum. The shallowest part of the littoral appeared to be very important for three species (D. vulgaris, D. sargus, O. melanura) and the transition zones (between two different substrata), for all four of them. Benthic larvae of Oblada melanura commenced settlement in small shoals that resided for varying number of days in specific sites over stones or rocky substratum. Gradually as metamorphosis proceeded they became more kinetic forming larger shoals that expanded their home range.

Historical environmental changes in two shallow, unstratified, estuaries in Buzzards Bay, Massachusetts are compared, using three diatom paleo-production indicators: sedimentary biogenic silica (BSi), BSi flux and ratio of Centric to Penate diatoms. Both estuaries were exposed to pollution. New Bedford Harbor (NBH) has a history of intensive nutrient loading and industrial pollution, while the control site, Apponagansett Bay, has lower levels of nutrient loading. Consideration of local precipitation history and diatom parameters suggests that salinity-driven changes in diatom production are negligible. Over the past &sim;350 yrs, BSi concentrations and fluxes are higher in NBH. Thus, overall diatom production is sensitive to nutrient enrichment and less responsive to industrial pollutants. The relationship between the C/P ratio and environmental conditions is not as clear, possibly due to its dependence on eelgrass abundance. The uniqueness of this study lies in its use of the parameters combined, as well as its geographic setting.

South African estuaries have high biodiversity value and provide many benefits to society, including food, real estate, a place for recreation and economic enterprise. However, they are facing growing human pressures such as urban encroachment, development in river catchments and interference in hydrological cycles. This dissertation provides an exploratory study of the environmental history of the Mgeni River Estuary, KwaZulu-Natal in an attempt to improve the understanding of the forces that drive environmental change. Through the application of the techniques and methodologies of environmental history, it explores the dynamics, characteristics and impacts of human interaction with the Mgeni River Estuary over time. It focuses on the emergence of a capitalist! industrial society in the twentieth century as this period has been characterised by the most significant environmental alteration and degradation. With the aid of the techniques and methodologies employed, the study highlights a complexity of natural and human events that have altered the estuary over time. Comparative analysis of aerial photographs between 1937 and 1996 reveals that physical changes to the estuary were linked to prevalent social and economic activities. The study describes cultural beliefs, modes of resource use and the political economy as significant and interwoven factors that facilitate environmentally intrusive activities. The study has provided insights into the complexity of factors that influence the rate and extent of change of an estuarine system. It concludes that to improve the understanding of the causes of environmental change, it is necessary to look further than the physical impacts on the environment to the attitudes and beliefs that underlie them. While the solutions to the problems facing the Mgeni River Estuary are not easily at hand, such analysis should assist policy makers and managers in finding a way to initiate more sustainable estuarine development in the future. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.