Global sea levels are expected to rise as a result of climate change, which will lead to the inundation and erosion of low lying coastal areas and accelerate the intrusion of seawater into sub-surface sediments. Many of the UK’s legacy nuclear facilities are located in close proximity to the shore, raising questions regarding the potential mobilisation of radionuclides during sea level rise. Here batch and column experiments were used to simulate and investigate the effect of these processes on the mobilisation of key radionuclides Tc, 90Sr and U from oxic and reduced sediments under sea level rise scenarios. Strontium-90 was rapidly mobilised from exchangeable surface sites from oxic sediments during inundation and erosion scenarios with seawater (≈ 60%). Strontium release was driven by ion exchange between Sr90 and Mg2+ cations present in high concentrations in seawater. Uranium release from oxic and reduced sediments was kinetically controlled, characterised by slow release from a range of binding sites, promoted by the formation of U-carbonate complexes. Uranium mobilisation was slower from reduced sediments compared with oxic sediments under seawater flow conditions; therefore reduced sediments would act as a longer term source of U to marine environments. Release was more extensive from initially nitrate reducing sediments (53%) compared with extensively iron reducing sediments (38%), with the difference in release explained by the longer contact period of U(VI) with the iron reducing sediment relative to the nitrate reducing sediment which would lead to slower desorption. Additionally, U(IV) species would be released more slowly than U(VI) species sorbed to the sediments. The release of Tc was dependent on sediment re-oxidation coupled with the oxidation of Tc(IV) to Tc(VII). Batch experiments showed that only a small proportion of Tc was rapidly (within 5 days) released from the sediments into seawater and groundwater which suggests that the majority of any Tc(IV) contamination will be released slowly as the seawater plume migrates through the sediments. Technetium release was slowest, and ultimately limited to the greatest extent (17%), in initially Fe-reducing sediments, when they were re-oxidised in seawater. Thus the cycling of iron and the impact of the water chemistry on iron mineralogy were important for hindering Tc release. Column experiments showed that iron minerals were less effective at retarding Tc release under flow-through conditions. Kinetically controlled and solubility limited Fe dissolution led to on-going Tc release from the sediments, i.e. the retarding effect of iron phases was temporary and significantly more Tc was mobilised (79-93%) compared with the batch experiments (17-45%). This study has shown for the first time that radionuclides will be released from reduced and oxic sediments as a result of future sea level rise. Contaminated sediments have the potential to act as a secondary source of radionuclide contamination entering the marine environment from coastal nuclear sites. This information is essential when siting new nuclear facilities and when developing effective remediation, decommissioning and management strategies for legacy coastal sites.

<p>Inorganic chlorine (Clinorg) is generally considered to be inert and has been used as a tracer for groundwater movements. This assumption is thereby fundamental for current knowledge about soil biogeochemistry. However, recent work showed that Clinorg can be retained, i.e. immobilised, in soil, which contradicts the previous assumptions. The aim of this laboratory study was to investigate if the processes that immobilise Clinorg in soil are affected by molecular oxygen (O2), and if the immobilisation occurs in the top soil layer only or also further down were the soil structure is different from the upper soil layer. Two experimental set-ups have been established. In the first experiment regarding the O2 regime (OXANIS), the immobilisation of Clinorg was studied in soil under oxic and anoxic conditions, respectively. In a second incubation study (SOLIS) the immobilisation was studied under oxic conditions in different layers of a coniferous forest soil. To investigate the immobilisation of Clinorg, a method using radiolabelled chloride 36 (36Clinorg) was applied. The use of radiolabelled chloride is an excellent and reliable method for studying transformation processes in soil systems. The results of the laboratory study showed that Clinorg retention rates under oxic conditions were much higher than retention rates under anoxic conditions, indicating an important role of O2. Furthermore, the immobilisation of Clinorg occurred in all soil layers were oxygen is provided, but rates were highest in the top soil layer (organic layer, O-horizon). Clearly, O2 influenced the net Clinorg retention, but additional studies are required to identify the processes behind this result. The calculated immobilisation rates for Clinorg in the three soil horizons correspond to the amount of organic material detected in the different soil horizons indicating a strong connection between the occurrence of organic matter in soil and the immobilisation of Clinorg.</p>

Inorganic chlorine (Clinorg) is generally considered to be inert and has been used as a tracer for groundwater movements. This assumption is thereby fundamental for current knowledge about soil biogeochemistry. However, recent work showed that Clinorg can be retained, i.e. immobilised, in soil, which contradicts the previous assumptions. The aim of this laboratory study was to investigate if the processes that immobilise Clinorg in soil are affected by molecular oxygen (O2), and if the immobilisation occurs in the top soil layer only or also further down were the soil structure is different from the upper soil layer. Two experimental set-ups have been established. In the first experiment regarding the O2 regime (OXANIS), the immobilisation of Clinorg was studied in soil under oxic and anoxic conditions, respectively. In a second incubation study (SOLIS) the immobilisation was studied under oxic conditions in different layers of a coniferous forest soil. To investigate the immobilisation of Clinorg, a method using radiolabelled chloride 36 (36Clinorg) was applied. The use of radiolabelled chloride is an excellent and reliable method for studying transformation processes in soil systems. The results of the laboratory study showed that Clinorg retention rates under oxic conditions were much higher than retention rates under anoxic conditions, indicating an important role of O2. Furthermore, the immobilisation of Clinorg occurred in all soil layers were oxygen is provided, but rates were highest in the top soil layer (organic layer, O-horizon). Clearly, O2 influenced the net Clinorg retention, but additional studies are required to identify the processes behind this result. The calculated immobilisation rates for Clinorg in the three soil horizons correspond to the amount of organic material detected in the different soil horizons indicating a strong connection between the occurrence of organic matter in soil and the immobilisation of Clinorg.

This study explored the effects of seasonal variability on the geochemistry of sinking pthesiss and on the nitrogen cycle of the Cariaco Basin. Pthesis fluxes were measured at the base of the euphotic zone (the depth of 1% of photosynthetically active radiation - PAR) with drifting sediment traps during months of upwelling and non-upwelling regimes from March 2007 to November 2009. Flux estimates were analyzed in the context of seasonal variations in sea surface temperature, primary productivity, and chlorophyll a concentrations using data generated by the CARIACO Time-series Program as well as satellite data. Additionally, nine years (1996-2000 and 2004-2007) of nutrients, phytoplankton taxonomy and δ15N of sinking pthesis data within the twilight zone (225 m) from the CARIACO Time-series Program were examined. Results showed that the flux of organic matter responded to changes in surface chlorophyll a but not to primary production. Sinking organic matter decreased by an order of magnitude from the base of the euphotic zone to the oxic-anoxic interface; most of the organic matter produced in surface waters was remineralized before leaving the upper 50-100 m. Lithogenic material often represented a large fraction of the flux. Isotopic analyses showed that 13C/12C ratios of sinking organic carbon were enriched (~-19‰) during the upwelling period and depleted during relaxation (~-23‰). This reflects seasonal changes in inorganic carbon utilization by phytoplankton and suggests that the δ13C of organic carbon in Cariaco sediments can be used as a proxy for carbon fixation by primary producers. The δ15N of the settling flux was influenced by the strength of the upwelling and the presence of the nitrogen fixer Trichodesmium thiebautii in the basin in different seasons; the 15N/14N ratio of sinking nitrogen reflects both imported and local nitrogen fixation signals. This result argues against previous interpretations of the δ15N from the basin's sedimentary record, which suggested that the nitrogen isotopic composition of flux is influenced by denitrification at the oxic-anoxic interface. Dissolved gas samples from the Cariaco eastern and western sub-basins from September 2008 (non-upwelling) and March 2009 (upwelling) were studied to assess the production of biogenic nitrogen gas through mass spectrometric N2/Ar ratiometry. Excess nitrogen gas indicated that upwelling affects the intensity of denitrification at the oxic-anoxic interface. In four of the six stations the concentration of biogenic nitrogen gas at the oxic-anoxic interface was 2.7-6.1 µM N higher during the upwelling period than during the relaxation season (p< 0.001), implying that denitrification in the basin was stimulated by the vertical flux of organic matter and/or the ventilation of the oxic-anoxic interface by oxygenated and nutrient-rich intermediate Caribbean waters.

In this thesis I will use a ‘men’s rights’ influencers fanbase as an example of a new generation of people who values toxic and traditional masculinity. I will do so by doing a critical discourse analysis on 1200 comments from the platform Reddit, using Fairclough's three-dimensional model as inspiration. Furthermore, to deepen the analysis I have chosen to analyze the comments in relation to parasocial relationships, hegemonic masculinity as well as the concepts of traditional and toxic masculinity. I found through my analysis that the fanbase views the influencer as a form of ‘beacon of truth’, and made a plethora of external references in regards to the movie 'The Matrix’. Moreover, the fans articulate masculinity in a way where ‘strength’ is prevalent, and is in line with traditional and toxic masculinity - whilst holding the influencer as a form of ideal of this form. In the discussion I draw parallels to how referencing the Matrix as a concept could speak of a mistrust towards the government, and how the countermovement to ‘modern’ masculinity could result in dangerous practices. To conclude, I highlight how there is still more research to be done on the field of alternative influencers and what consequences this ‘countermovement’ may have.

Les écosystèmes côtiers sont des milieux complexes au sein desquels les communautés microbiennes, jouant un rôle majeur dans leur fonctionnement et leur maintien, s’adaptent et sont tolérantes à des conditions environnementales fluctuantes. En effet, au rythme des marées et de l'activité de la macrofaune, des oscillations oxie/anoxie influencent la composition et la dynamique des communautés microbiennes et par conséquent leur implication métabolique. Afin d’appréhender le devenir du pétrole dans ces écosystèmes, il est donc indispensable d’apporter des connaissances sur l’écologie des microorganismes intervenant dans son élimination, notamment dans des conditions oscillantes anoxie/oxie. Ainsi, ce travail de thèse a eu pour objectif de décrypter l’assemblage de communautés microbiennes hydrocarbonoclastesde sédiments intertidaux soumises à des oscillations anoxie/oxie en présence de pétrole lors d’une expérience en bioréacteurs. Les réponses écologiques des communautés bactériennes globales et de micro-organismes sulfato-réducteurs en conditions oscillantes ont pu être décrites en comparaison avec celles obtenues en conditions d’oxie ou d’anoxie permanentes, par l’analyse des données obtenues par séquençage haut-débit des gènes de l’ARN 16S et dsrB au niveau transcriptionnel. Ces études comparatives ont mis en évidence des profils écologiques en réponseaux conditions oscillantes, pouvant être répandus dans différents environnements marins côtiers. En réponse à ces conditions particulières, de nombreux microorganismes semblent avoir le potentiel à tolérer et/ou s’adapter aux différentes conditions d'oxygénation. Cette capacité d’acclimatation rapide des communautés bactériennes aux conditions oscillantes se sont accompagnées de capacités de dégradation équivalentes ou supérieures dans ces conditions par rapport à la condition d’oxie permanente montrant l’influence des oscillations anoxie/oxie sur le devenir du polluant dans les environnements pollués soumis à ces conditions. / Coastal ecosystems are complex environments in which microbial communities, playing a major role in their functioning and maintain, are tolerant and adapt to changing environmental conditions. Indeed, the tides and the macrofauna’s activity generate oxic/anoxic oscillations which influence the composition and dynamics of microbial communities and consequently their metabolic in volvement. To understand the fate of oil in these ecosystems, it is essential to provide knowledge on the ecology of microorganisms involved in these systems, taking into account anoxic/oxicoscillating conditions. Thus, this thesis aimed to decipher the organization of hydrocarbonoclastic microbial communities inhabiting intertidal sediments, when they are subjected to anoxic/oxic oscillations in an experiment in bioreactors with oil addition. Ecological responses of bacterial communities and sulfate-reducing microorganisms in oscillating conditions have been described comparing with those obtained with permanent oxic or anoxic conditions, using high-throughputsequencing analyses of the 16S rRNA and dsrB genes at the transcriptional level. These comparatives studies have highlighted ecological profiles in response to the oscillating conditions, which can be prevalent in different coastal marine environments. In response to these particular conditions, many organisms seem to have the potential to tolerate and / or adapt to the different conditions of oxygenation. This rapid acclimation capacity of bacterial communities tothese changing conditions have been accompanied by equivalent or greater degradation capacity under these conditions compared to the permanent oxic condition, showing the influence of the anoxic/oxic oscillations on the fate of pollutant in environments subjected tothese conditions.

In Australia, significant effort goes into reducing the amount of nitrogen and phosphorus entering inland waters from point sources. However, little is known of the extent to which riparian organic matter may act as a source of these nutrients. Also, whilst the relationships between the nitrogen, phosphorus and carbon cycles are broadly known, there is little quantitative data regarding the release of these elements from Australian riparian organic matter and their subsequent microbial mineralisation within aquatic environments. In particular, comparatively little is known of their comparative role in nutrient and organic matter cycling within anoxic zones, and the influence that different riparian organic matter may have on stream water quality. This lack of such data presently hampers the ability of water managers to make educated decisions regarding the management of riparian zones in Australia. In order to improve understanding in this area, a combination of laboratory and in situ experiments were carried out in order to compare the abiotic release and aerobic/ anaerobic mineralisation of leaf derived dissolved organic carbon (DOC), dissolved nitrate/nitrite (NOx) and soluble reactive phosphorus (SRP) under different environmental conditions. Four plants common to Australian riparian zones were investigated: two native species, Eucalyptus camaldulensis (gum) and Phragmites australis (common reed), and two exotic species, Salix babylonica (willow) and Lolium multiflorum (rye grass). After 30 days, formaldehyde inhibited 1g willow and rye grass extracts contained the most SRP (0.7 mg/L), whilst gum extracts contained 0.3 mg/L and common reed 0.1 mg/L of SRP.Willow and rye grass abiotically released twice as much NOx than gum and common reed, although concentrations were only between 0.05-0.1 mg/L. Gum and common reed released the most DOC per gram of leaf matter (14 and 12 mmol/g of leaf matter respectively), but based on the initial carbon content of each leaf type, the largest percentage contributor of DOC under abiotic conditions was common reed and rye grass (both 38% mass/mass), with gum (33% mass/mass) and willow (30% mass/mass) being smaller contributors. The most bioavailable DOC was released by rye grass and common reed, with between 83 and 94% of this DOC microbially mineralised after 30 days in oxic conditions. When conditions were not inhibited, microbial growth was evident almost immediately in willow, rye grass and common reed leaf extracts. However, microbial growth was suppressed for the first 48 hours in gum leaf extracts. After this suppression period, the rate of DOC mineralisation was equal in willow and gum leaf extracts (0.1 day-1). Under anoxic conditions, the rate and extent of DOC mineralisation of willow and gum leaves depended on the type of electron acceptor provided. Added nitrate and iron III enhanced the mineralisation of both willow and gum leaves relative to no terminal electron acceptors (from zero to 0.01-0.04 and 0.002- 0.004 moles/day respectively), but added sulphate only enhanced the mineralisation of gum leaves (0.04 moles/day). When no additional electron acceptors were provided, particulate leaf mineralisation was more extensive under oxic than anoxic conditions. However, the mineralisation of leaf derived DOC were the same regardless of oxygen availability, and after 35 days in either condition the percentage of leaf DOC mineralised for each leaf type was of the order common reed > rye grass > willow > gum. All the leaf types tested were able to sustain the caddis fly larvae Triplectides australis under controlled laboratory conditions, and survival rates were high using all four leaf types as a food source. Triplectides australis did not significantly increase the amount of DOC released from each type of leaf matter, but they did consistently increase the proportion of simple carbohydrates present within the DOC fraction. The results of these experiments suggest that changes to riparian vegetation, particularly from the native to exotic species used in this study, will inherently alter in-stream concentrations of dissolved carbon and nutrients (particularly SRP). This potentially will affect in-stream, hyporheic and subsurface processes, particularly in areas where surface water flow is low and riparian leaf inputs are high.

Les écosystèmes marins côtiers sont constament soumis à des pollutions, notamment aux hydrocarbures, du fait de leur localisation et de leurs caractéristiques environnementales. Le rôle clé des microorganismes dans la dégradation de ces polluants est aujourd’hui très bien décrit. Toutefois, les conditions d’oxygénation fluctuantes dans ces environnements côtiers, dues aux marées et aux activités de bioturbation de la macrofaune, influencent les communautés microbiennes.Ainsi, ce travail de thèse a eu pour objectif de caractériser, l’assemblage de communautés microbiennes hydrocarbonoclastes de sédiments marins côtiers soumises à des oscillations oxie/anoxie en présence de pétrole lors d’une expérience en bioréacteurs. L’adaptation des bactéries marines hydrocarbonoclastes notamment des genres Alcanivorax et Cycloclasticus vis-à-vis de ces variations d’oxygène a pu être investiguée par oligotypage. Des écotypes ont été identifiés en fonction des conditions d’oxygénation démontrant ainsi les capacités d’adaptation aux conditions oscillantes d’oxygène de ces deux genres. La structure des communautés archéennes (séquençage des transcrits du gène de l’ARNr 16S) n’a pas montré de modification évidente liée aux conditions d’oxygénation démontrant ainsi des capacités d’adaptation et/ou de résistance plus importantes chez ces microorganismes comparées aux communautés bactériennes. Enfin, les analyses métagénomiques ont mis en évidence une réponse fonctionnelle spécifique aux oscillations oxie/anoxie. Ainsi, ces travaux de thèse apportent de nouvelles connaissances sur l’influence des variations d’oxygénation sur les communautés microbiennes et par conséquent sur la dégradation des hydrocarbures au sein des écosystèmes marins côtiers. / Coastal marine ecosystems are constantly subject to pollution, particularly hydrocarbons, because of their location and their environmental characteristics. The key role of microorganisms in the degradation of these pollutants is now well described. However, fluctuating oxygenation conditions in these coastal environments, due to tides and macrofauna bioturbation activities influence microbial communities.Thus, this thesis work aimed to characterize the assembly of microbial hydrocarbonoclastic communities of coastal marine sediments subjected to oxic/anoxic oscillations in the presence of oil during a bioreactor experiment. The adaptation of MOHCB, particularly of Alcanivorax and Cycloclasticus genera, to these oxygen variations has been investigated by oligotyping. Ecotypes were identified according to the oxygenation conditions demonstrating adaptation capacities of these two genera to the oscillating oxygen conditions. The structure of archaeal communities (16S rRNA transcript sequencing) did not show any modification related to the oxygenation conditions thus demonstrating greater adaptation and/or resistance capacities in these microorganisms compared to the bacterial communities. Finally, metagenomics analyses revealed a specific functional response to oxic/anoxic oscillations. Thus, this thesis provides new insights into the influence of oxygenation variations on microbial communities and consequently on the degradation of hydrocarbons in coastal marine ecosystems.

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