Cette these etudie les effets de la conversion de la foret tropicale en parcelles agricoles, sur les emissions de n2o par les sols. Ce travail est realise a l’echelle du cycle cultural sur le dispositif experimental de combi (littoral guyanais), a l’aide de mesures in situ et de simulations (modele noe) des flux de n2o. La foret tropicale a ete comparee a des parcelles de foret converties en terres agricoles par la methode ‘chop-and-mulch’. La methode de deforestation ‘chop-and-mulch’ associe coupe mecanique de la vegetation, broyage puis enfouissement des residus forestiers dans le sol. Les terres agricoles etaient soient des parcelles de prairie non paturee soient des parcelles cultivees (maïs fertilise/soja) conduites en semis conventionnel (semis apres travail du sol, sans plante de couverture) ou en semis direct (sans travail du sol, avec plantes de couverture).Les principaux resultats de cette etude sont : le sol de la foret tropicale de combi est un faible emetteur de n2o ; la conversion par la methode ‘chop-and-mulch’ de cette foret en prairie ne conduit pas a une augmentation significative des emissions de n2o entre le 19eme et le 31eme mois suivant la conversion ; la conversion de la foret en parcelles cultivees induit une augmentation significative des emissions de n2o due a la fertilisation et a la modification des parametres edaphiques (densite apparente, temperature, humidite volumique) ; la technique sans travail du sol n’engendre pas de flux de n2o significativement plus eleves que la technique avec travail du sol ; l’introduction du phenomene d’hysterese hydrique dans le modele noe presente un reel potentiel pour l’estimation des emissions de n2o in situ. / This study investigates the effects of the conversion of tropical forest to cultivation on soil n2o emissions. The study was carried out over a complete crop cycle at the experimental site combi (french guianese coast). Nitrous oxide fluxes were obtained in the field and by conducting simulations with the noe model. Undisturbed tropical rainforest was compared to rainforest that had been converted to agricultural land using the ‘chop-and-mulch’ method. The ‘chop-and-mulch’ method is a fire-free method used for vegetation clearing combining the mechanical felling of trees with the mulching of small vegetation. Agricultural land included either mowed grassland or soybean/fertilised maize crop rotation. For croplands the two cultivation practices employed were: conventional seeding (using an offset disc harrow, without cover plants) or direct seeding (no till, with cover plants).The main results of this study are: rainforest soil at combi produced low n2o emissions; rainforest converted to mowed grassland using the 'chop-and-mulch’ method did not lead to a significant increase in n2o emissions between the 19th and 31st months after conversion; the conversion of rainforest to croplands induced a significant increase in soil n2o emissions due to the application of fertiliser and the modification of soil parameters (bulk density, temperature, volumetric moisture); n2o emissions from agricultural practices with no-till were no higher than those produced by conventional agricultural practices using an offset disc harrow; and, the introduction of an hydric hysteresis into the noe model constitutes a promising improvement to estimate in situ n2o emissions.

Les plages de sable sont des écosystèmes dynamiques couvrant 70% des côtes mondiales. Ces systèmes abritent un cortège spécifique unique et assurent des fonctions essentielles de nourricerie, de nurserie et d’épuration des eaux. Or à proximité des côtes, la population humaine est en développement constant ce qui accroît les multiples pressions d’origine anthropique sur les écosystèmes côtiers. L’apport en excès de nutriments constitue une menace majeure qui peut se traduire par le développement d’importantes biomasses de macroalgues opportunistes (eutrophisation). La fréquence et l’intensité de ces blooms, communément formés de chlorophycées à court cycle de vie (ulves) et appelés marées vertes (MV), s'amplifient sur les côtes françaises et dans le Monde menaçant le fonctionnement de systèmes prépondérants et uniques.La plupart des études visant à déterminer les effets des MV sur la structure et le fonctionnement d’écosystèmes sédimentaires ont été conduites dans des environnements abrités, micro- ou atidaux. Cette problématique est restée presqu’inexplorée dans des écosystèmes plus dynamiques (systèmes ouverts et macrotidaux) en raison des difficultés de mise en place d’échantillonnage et de détection des effets de stress d’origine anthropique, inhérentes à la variabilité de ces systèmes. Cette thèse a donc eu pour objectif principal de combler ce manque et produire des connaissances en étudiant les réponses in situ des communautés benthiques de plages de sable fin macrotidales en présence ou non de MV. Quatre études ont été menées à différentes échelles spatio-temporelles et en considérant différents compartiments biologiques pour répondre à cette question générale.Ce travail de thèse montre qu’à l’échelle de la région Bretagne (variabilité intégrée sur 2700km de côtes et 7 ans) les communautés benthiques d’écosystèmes dynamiques sont modifiées significativement et de manière conservative par la présence de MV. Ce travail démontre aussi que les marées vertes impactent différemment la faune benthique en fonction du type d’habitat (plages semi-exposées vs. exposées), de la profondeur (mediolittoral vs. infralittoral), et du compartiment biologique (macrofaune benthique vs. juvéniles de poissons plats). Ces comparaisons ont permis d’identifier la faune benthique de médiolittoral inférieur des plages exposées comme étant le système le plus affecté par les MV. L’étude des variations à fine échelle spatio-temporelle de ce dernier montre que les caractéristiques faunistiques (uni- et multi-variées) sont modifiées le long d’un gradient de couverture d’algues vertes. Par exemple, la β-diversité décroît significativement le long de ce gradient. Afin d’explorer les processus pouvant expliquer ces modifications, et déterminer si ces changements ont des répercussions sur le fonctionnement de l’écosystème « plage de sable », les effets de l’accumulation d’ulves sur le réseau trophique à différent(e)s niveaux/échelles ont été mesurés. Les résultats de cette étude montrent qu’une importante biomasse d’ulves induit un changement de la structure entière du réseau trophique et une modification importante du fonctionnement trophique des plages. Les expérimentations menées au cours de cette thèse montrent que les changements observés sont induits par des effets directs (consommation de débris d’ulves) et indirects (modifications d’autres sources de nourriture) de la présence des MV.Cette thèse propose un cadre de travail visant à mieux détecter les effets de stress anthropiques sur la structure et le fonctionnement d’écosystèmes dynamiques. Dans un contexte de changement global forçant les écosystèmes à faire face à de multiples stress, cette approche pourrait se révéler particulièrement utile pour démêler, comprendre et prédire les effets de perturbations induites par les activités humaines sur le fonctionnement des écosystèmes et constituer une aide à la gestion de ces environnements particuliers. / Highly dynamic systems, often considered as resilient systems, are characterised by abiotic and biotic processes under continuous and strong changes in space and time. Because of this variability, the detection of overlapping anthropogenic stress is challenging. Coastal areas harbour dynamic ecosystems in the for of open sandy beaches, which cover the vast majority of the world’s ice-free coastline. These ecosystems are currently threatened by increasing human-induced pressure, among which mass-development of opportunistic macroalgae (mainly composed of Chlorophyta, so called green tides), resulting from the eutrophication of coastal waters. The ecological impact of opportunistic macroalgal blooms (green tides, and blooms formed by other opportunistic taxa), has long been evaluated within sheltered and non-tidal ecosystems. Little is known, however, on how more dynamic ecosystems, such as open macrotidal sandy beaches, respond to such stress. This thesis assesses the effects of anthropogenic stress on the structure and the functioning of highly dynamic ecosystems using sandy beaches impacted by green tides as a study case. The thesis is based on four field studies, which analyse natural sandy sediment benthic community dynamics over several temporal (from month to multi-year) and spatial (from local to regional) scales. In this thesis, I report long-lasting responses of sandy beach benthic invertebrate communities to green tides, across thousands of kilometres and over seven years; and highlight more pronounced responses of zoobenthos living in exposed sandy beaches compared to semi-exposed sands. Within exposed sandy sediments, and across a vertical scale (from inshore to nearshore sandy habitats), I also demonstrate that the effects of the presence of algal mats on intertidal benthic invertebrate communities is more pronounced than that on subtidal benthic invertebrate assemblages, but also than on flatfish communities. Focussing on small-scale variations in the most affected faunal group (i.e. benthic invertebrates living at low shore), this thesis reveals a decrease in overall beta-diversity along a eutrophication-gradient manifested in the form of green tides, as well as the increasing importance of biological variables in explaining ecological variability of sandy beach macrobenthic assemblages along the same gradient. To illustrate the processes associated with the structural shifts observed where green tides occurred, I investigated the effects of high biomasses of opportunistic macroalgae (Ulva spp.) on the trophic structure and functioning of sandy beaches. This work reveals a progressive simplification of sandy beach food web structure and a modification of energy pathways over time, through direct and indirect effects of Ulva mats on several trophic levels. Through this thesis I demonstrate that highly dynamic systems respond differently (e.g. shift in δ13C, not in δ15N) and more subtly (e.g. no mass-mortality in benthos was found) to anthropogenic stress compared to what has been previously shown within more sheltered and non-tidal systems. Obtaining these results would not have been possible without the approach used through this work; I thus present a framework coupling field investigations with analytical approaches to describe shifts in highly variable ecosystems under human-induced stress.

<p> In the study area, the South Saskatchewan River has a sandy bed (mean diameter .3mm) with irregularly-shaped braid bars termed sand flats. These range in length from 50 to 2000 m. The river has an average discharge of 220m^3/sec, with a mean annual flood of 1450 m^3/sec. The river has been dammed upstream of the study area since 1965, but little downcutting has occured. </p> <p> Ripples, sand waves and dunes are the equilibrium bedforms present . Ripples and dunes are well known , but sand waves are long , low bedforms with superimposed ripples, lack scour troughs, and occur at lower flow velocities than dunes . Foreset-type bars are also present , but are not equilibrium forms . They result from flow expansion around older topography. They occur at (1) channel junctions, (2) channel bends, (3) areas of channel widening, (4) places of vertical flow expansion . They deposit planar crossbeds. </p> <p> Large areas of the river have many sand flats with no major channels, and may even lack minor channels. These areas are termed sand flat complexes. Where a major channel curves around a sand flat complex, a large diagonal bar is deposited. It is mainly on the tops of these bars where new sand flats form. </p> <p> The major channels rarely exceed 5 m in depth, but may be 150m wide. They are floored by sinuous-crested dunes with sand waves and ripples along their margins. The dunes build up during floods (2 m maximum amplitude). Large dunes occur in the deeper channels. </p> <p> Three different morphologies of small sand flats, symmetric, asymmetric and side, have been recognized. Each type forms from a bar which becomes partly immobilized where it becomes emergent. The remainder of the bar front continues to advance around this emergent nucleus. The different morphologies result because of the control exerted by preexisting deposits on the shape of the initial bar. </p> <p> Larger sand flats lack these morphologies because they have been extensively modified. The major processes of modification are vertical, lateral, and upstream accretion by bars; linking of sand flats by bars; erosional action. The variable morphologies of larger sand flats reflect only their latest modification. The stratification of sand flats is mainly planar crossbed sets deposited by the bars. </p> <p> During the winter, a 60cm thick layer of ice covers the entire system. The sand flats are immobilized because their top layers of sediments are frozen. In some places, their surfaces are disrupted by fluid escape caused by high pore pressures generated by freezing. Flow proceeds down the channels under the ice. Rafting of cobbles and scouring around grounded ice blocks takes place at breakup. </p> <p> The facies sequences resulting from sedimentation in the river are mainly sandy. Those which are deposited by channels consist dominantly of trough crossbeds, but lone planar crossbed sets may be present, deposited by large bars. Facies sequences which include sand flat deposits have several sets of planar crossbeds stacked on top of one another. All sequences have a zone of small crossbeds and ripple cross-lamination near the tops, resulting from shallow water deposition. They are capped by one-half metre of muddy flood-plain deposits. </p> / Thesis / Doctor of Philosophy (PhD)

The discursive and critical positions of the ‘classic’ nineteenth-century novel, particularly the woman’s novel, in the field of adaptation studies have been dominated by long-standing concerns about textual fidelity and the generic processes of the text-screen transfer. The sociocultural patterns of adaptation criticism have also been largely ensconced in representations of literary women on screen. Taking a decisive twist from tradition, this thesis traces the evolution of representations of masculinity in the malleable characters of Rochester and Heathcliff in film and television adaptations of Charlotte Brontë’s Jane Eyre and Emily Brontë’s Wuthering Heights between 1939 and 2009. Concepts of masculinity have been a neglected area of enquiry in studies of the ‘classic’ novel on screen. Adaptations of the Brontës’ novels, as well as the adapted novels of other ‘classic’ women authors such as Jane Austen, George Eliot and Elizabeth Gaskell, increasingly foreground male character in traditionally female-oriented narratives or narratives whose primary protagonist is female. This thesis brings together industrial histories, textual frames and sociocultural influences that form the wider contexts of the adaptations to demonstrate how male characterisation and different representations of masculinity are reformulated and foregrounded through three different adaptive histories of the narratives of Jane Eyre and Wuthering Heights. Through the contours of the film and television industries, the application of text and context analysis, and wider sociocultural considerations of each period an understanding of how Rochester and Heathcliff have been transmuted and centralised within the adaptive history of the Brontë novel.