Ce travail de thèse porte sur le devenir du N2 récemment fixé par les diazotrophes dans l’océan oligotrophe de surface.Il apparaît que le N2 récemment fixé est excrété dans le compartiment dissous par tous les diazotrophes marins étudiés et que l'amplitude de cette excrétion dépend d'abord des contraintes environnementales que des diazotrophes impliqués dans la fixation.Le transfert de N2 fixé vers le plancton non-diazotrophe a été quantifié en utilisant une méthodologie innovante (couplage de la spectrométrie de masse à ionisation secondaire à l’échelle nanoscopique (nanoSIMS) et du tri cellulaire par cytométrie en flux). En conditions naturelles, 5 à 20 % du N2 récemment fixé est transféré vers les communautés non diazotrophes, principalement via l’excrétion de NH4+. Ce transfert est deux fois plus efficace lorsque le N2 est fixé par le diazotrophe Trichodesmium que lorsqu’il est fixé par les diazotrophes unicellulaires Crocosphaera ou Cyanothece.L’export du N2 récemment fixé a été évalué en utilisant des larges mésocosmes équipés de pièges à sédiments, déployés dans le lagon de Nouvelle Calédonie, et enrichis en PO43- pour stimuler la fixation de N2. Lors de cette expérience, il a été démontré que la fixation de N2 a alimenté une grande partie de la production primaire nouvelle (>90 %) et que le N2 fixé par les diazotrophes a rapidement été exporté. Cet export a été direct, par la sédimentation des diazotrophes eux-mêmes (représentant ~20 % de la matière particulaire retrouvée dans les pièges au plus fort de l’efflorescence de diazotrophes), et indirect, par le transfert de ~20 % du N2 fixé vers les communautés non diazotrophes qui, à leur tour, ont sédimenté. / This PhD thesis, achieved within the framework of the VAHINE project, focuses on the fate of the recently fixed N2 by diazotrophes in the oligotrophic surface ocean.It appears that the release of the recently fixed N2 in the dissolved pool is a process shared between all diazotrophs tested and that the magnitude of this release depend on the environmental contrains rather than on diazotroph involved in fixation.The transfer of the N2 fixed toward non-diazotroph plankton has been investigated using an innovative methodology (coupling of nano-scale mass spectrometry (nanoSIMS) and cell sorting flow cytometry). It appeared that 5 to 20 % of the recently fixed N2 is transferred toward non-diazotroph plankton, mainly through NH4+ release. This transfer is twice more efficient when the N2 is fixed by the filamentous Trichodesmium compared to Crocosphaera and Cyanothece.Particulate export of the fixed N2 has been investigate in large in-situ mesocosms equipped with sediment traps, deployed in the New Caledonian lagoon and enriched with PO43- in order to stimulate N2 fixation. During this experiment, N2 fixation fueled a large part of the new primary production (>90 %) and that fixed N2 was quickly exported. The export has been direct, through the sedimentation of the diazotrophs themselves, and indirect, through the transfer of ~20 % of the recently fixed N2 toward non-diazotrophic plankton that have, in turn, sedimented.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Iron is a redox active trace metal micronutrient essential for primary production and nitrogen acquisition in the open ocean. Dissolved iron (dFe) has extremely low concentrations in marine waters that can drive phytoplankton to Fe limitation, effectively linking the Fe and carbon cycles. Understanding the marine biogeochemical cycling and composition of dFe was the focus of this thesis, with an emphasis on the role of the size partitioning of dFe (<0.2 jm) into soluble (sFe<0.02 jm) and colloidal (0.02ptm<cFe<0.2 m) size fractions. This was accomplished through the measurement of the dFe distribution and size partitioning along basin-scale transects experiencing a range of biogeochemical influences. dFe provenance was investigated in the tropical North Atlantic and South Pacific Oceans. In the North Atlantic, elevated dFe (>I nmol/kg) concentrations coincident with the oxygen minimum zone were determined to be caused by remineralization of a high Fe:C organic material (vertical flux), instead of a laterally advected low oxygen-high dFe plume from the African margin. In the South Pacific Ocean, dFe maxima near 2000m were determined by comparison with dissolved manganese and 3He to be caused by hydrothermal venting. The location of these stations hundreds to thousands of kilometers from the nearest vents confirms the "leaky vent" hypothesis that enough dFe escapes precipitation at the vent site to contribute significantly to abyssal dFe inventories. The size partitioning of dFe was also investigated in order to trace the role of dFe composition on its cycling. First, the two most commonly utilized methods of sFe filtration were compared: cross flow filtration (CFF) and Anopore filtration. Both were found to be robust sFe collection methods, and sFe filtrate through CFF (10 kDa) was found to be only 74±21% of the sFe through Anopore (0.02pjm) filters at 28 locations, a function of both pore size differences and the natural variability in distribution of 1 OkDa- 0.02 [m colloids. In the North Atlantic, a colloidal-dominated partitioning was observed in the surface ocean underlying the North African dust plume, in and downstream of the TAG hydrothermal system, and along the western Atlantic margin. However, cFe was depleted or absent at the deep chlorophyll maximum. A summary model of dFe size partitioning in the North Atlantic open ocean is presented in conclusion, hypothesizing that a constant dFe exchange between soluble and colloidal pools modulates the constant partitioning of nearly 50% dFe into the colloidal phase throughout the subsurface North Atlantic Ocean, while sFe and cFe cycle independently in the upper ocean. / by Jessica Nicole Fitzsimmons. / Ph.D.

No description available.

Soils are a critical resource for supporting ecosystems, agricultural systems, and human wellbeing. However, these same soils have been degraded by human activities throughout human history. Despite the rapid development of global models that include dynamic changes in land use and land cover (LULC) and biogeochemical processes to assess climate and hydrological impacts, soil properties are often assumed to be spatially or temporally constant. These assumptions can affect the results of model projections, impact assessments and underestimate the human impact on Earth systems. This study reveals the physical impacts of human-altered soil conditions on the global water balance through a meta-analysis study and soil degradation modeling. We link major global LULCs to four hydrologic soil groups: sandy (sand, sandy loam, and loamy sand), loamy (loam, silty loam, and silt)), clayey soils (clay, sandy clay, clay loam, silty clay, and silty clay loam), and sandy clay loam) from 850 to 2015 AD, and identified loamy and clayey soils as the preferred soils for most human land uses. Humans selectively use those soils for intensive agriculture and pasture activities, while grazing occurs on sandier soils. To simulate the impact of human activities on soils, several soil change models were built for soil organic carbon (SOC) content, soil texture (sand, silt, and clay), and soil bulk density from meta-analyses of site observations. The models were applied globally based on the LULC and soil relations, global environmental and soil conditions, and LULC distributions. Pedotransfer functions were applied to estimate soil water-holding capacity using those soil properties, then a Thornthwaite-type water balance model was used to assess the impacts of soil degradation on the global water balance. Results show that under a high-intensity LULC scenario (conventional tillage on croplands and heavy grazing), SOC decreases by 363 Pg and water deficit increases 78 km3 globally. The impacts on SOC and deficit are reduced to 213 Pg and 51 km3, respectively, when reducing land-use intensity by substituting animal ploughing/no-till and light grazing for conventional tillage and heavy grazing. Impacts from other LULC types are identical for these two LULC scenarios. Development of this history between LULC and soil properties allows for improved simulation of human impacts on global water, energy, and biogeochemical cycles. The results of the water balance simulations demonstrate how different soils representations in models can significantly alter the estimates of global evapotranspiration, water deficit, and surplus. This study contributes to developing a better understanding of the processes by which human-induced soil degradation impacts climate/hydrological models and providing a mechanism to better assess the impacts of humans on the Earth system. The outcome will also complement numerous ongoing global studies that evaluate the impacts of climate change on water resources and society. / Graduate / 2023-08-09

Ce travail de thèse porte sur la quantification de la diazotrophie et son influence sur les cycles biogéochimiques dans l'océan de surface Pacifique tropical sud-ouest, une région particulièrement sous-échantillonnée à ce jour. Les objectifs de ce travail étaient (1) de quantifier la fixation de N2 et identifier les principaux acteurs de la diazotrophie dans cette région, (2) d’évaluer l'influence de la fixation de N2 sur la production primaire et sur l'export de carbone, (3) d’identifier les voies de transfert de l’azote fixé dans la chaine trophique planctonique.Il a été mis en évidence que la région du Pacifique tropical sud-ouest était un hot spot de fixation de N2. A l'ouest, les eaux oligotrophes des archipels Mélanésiens présentaient des taux de fixation de N2 élevés et la communauté diazotrophe était dominée par Trichodesmium. A l'est, les eaux ultra-oligotrophes de la gyre du Pacifique sud présentaient des taux de fixation de N2 plus faibles et la communauté diazotrophe était dominée par les UCYN-B.Des bilans d'azote montrent que la fixation de N2 contribuait à plus de 90 % des apports d'azote nouveau dans la couche euphotique, et soutenait donc la quasi intégralité de la production primaire nouvelle. L'étude des voies de transfert de l'azote fixé montre qu’entre 7 et 15 % de la fixation de N2 totale était transféré vers les organismes non-diazotrophes.Ces travaux de thèse démontrent que la diazotrophie soutient la pompe biologique dans l'océan Pacifique tropical sud-ouest, et qu'elle peut jouer un rôle déterminant dans la structure des communautés planctoniques et les cycles biogéochimiques du carbone et de l'azote dans les régions oligotrophes. / This PhD thesis focuses on the quantification of diazotrophy and its influence on biogeochemical cycles in the western tropical South Pacific Ocean, a critically under-sampled region so far. The aim of this work is to (1) quantify N2 fixation and identify the main contributors of diazotrophy in this region, (2) assess the influence of N2 fixation on primary production and carbon export, (3) identify transfer pathways of the fixed nitrogen in the planktonic food web.We have found that the western tropical South Pacific Ocean was a hotspot of N2 fixation. In the western part, the oligotrophic waters of the Melanesian archipelago presented high N2 fixation rates and diazotrophes were dominated by Trichodesmium. In the eastern part, the ultra-oligotrophic waters of the South Pacific gyre presented lower N2 fixation rates, and diazotrophs were dominated by UCYN-B.The nitrogen budgets show that N2 fixation contributed to more than 90 % of the of new nitrogen input in the photic layer. The study of the transfer pathways of the fixed nitrogen has shown that 7 to 15 % of total N2 fixation was transferred to non-diazotrophs.This PhD thesis indicates that diazotrophy sustains the biological pump in the western tropical South Pacific Ocean, and can have a critical influence in the planktonic community structure and in biogeochemical cycles of carbon and nitrogen in oligotrophic regions.

A dinâmica do carbono, nas fases orgânica, inorgânica e gasosa, foi analisada em um ponto na Baía de Caxiuanã e em três pontos no seu afluente Rio Curuá (porções superior, intermediária e inferior) um sistema fluvial de escoamento lento na Amazônia Oriental (Brasil estado do Pará) durante 31 campanhas, de janeiro de 2007 até dezembro de 2009. O objetivo foi avaliar mudanças intra e inter-anuais como função da hidrologia neste preservado rio de água preta. Medições em diferentes profundidades mostraram a formação de estratos físico-químicos, evidenciando o aspecto lêntico nos setores médio e baixo do rio Curuá, com eventos de concentrações extremamente baixas de oxigênio dissolvido durante o período de cheia, como conseqüência da entrada de insumos e da decomposição da matéria orgânica dos ecossistemas terrestres. Devido a esse aspecto, o DOC foi a forma dominante das fases orgânica e inorgânica do carbono, mostrando positiva e significativa correlação com o nível do rio, como resultado de um grande controle de entrada de insumos laterais. As formas particuladas orgânicas não mostraram as mesmas características em nenhum ponto, provavelmente em função da reduzida corrente de água que permite a rápida deposição desses materiais logo após sua entrada no sistema fluvial. As concentrações mais elevadas de CPOC e FPOC observadas na Baía de Caxiuanã parecem ser um sinal da presença de comunidade de fitoplâncton assim como da influência do vento, que ressuspende os sedimentos de fundo nesse ambiente. A concentração de dióxido de carbono exibiu altos valores comparados com a atmosfera, ratificando a bem conhecida característica heterotrófica dos rios amazônicos. Além disso, os baixos níveis de oxigênio observados induziram o consumo de matéria orgânica por bactérias anaeróbias, resultando em altas concentrações de metano, como observado no setor médio do rio Curuá. Assim como ocorreu com as formas particuladas orgânicas, os aspectos ecológicos e geológicos singulares da Baía de Caxiuanã distinguem seu habitat pelos baixos valores de dióxido de carbono quando comparados com a atmosfera, revelando um ambiente com diferente dinâmica biogeoquímica. / Dynamic of carbon, at organic, inorganic, and gas phases, was analyzed in one station at Caxiuanã Bay and three stations on its tributary Curuá River (upper, middle and lower sections) a slow flowing river system in Eastern Amazon (Brazil Pará State) during 31 campaigns, from January 2007 through December 2009. The objective was to evaluate intra and interannual changes as function of hydrology in this undisturbed blackwater river. Measures on different depths showed formation of physicochemical strata, evidencing the lentic aspect on middle and lower sections of Curuá River, with events of extremely low concentrations of dissolved oxygen during high water level, as a consequence of inputs and decomposition of organic matter from terrestrial ecosystems. Due to this aspect, DOC was the dominant form of organic and inorganic carbon phases, showed positive and significant correlation with river stage level for all sites, as result of a large control by lateral inputs. Particulate organic forms did not show the same characteristics in any station, probably as function of reduced water current which enable rapid deposition of these materials soon after their entrance on river system. The higher concentrations of CPOC and FPOC observed at Caxiuanã Bay seem to be a signal of presence of phytoplankton community as well as wind influence which resuspend bottom sediments in this environment. Carbon dioxide concentration on river exhibited higher values compared to atmosphere, ratifying the well-known heterotrophic characteristic of Amazon rivers. Furthermore, observed low levels of oxygen induced organic matter consumption by anaerobic bacteria, resulting in high concentrations of methane, as observed in the middle section of Curuá River. As occurred with particulate organic forms, the singular geologic and ecologic aspects of Caxiuanã Bay distinguish its habitat by low values of carbon dioxide when compared to atmosphere, revealing an environment with different biogeochemical dynamic.

La Méditerranée est caractérisée par une grande variété de régimes trophiques qui s'explique par les apports fluviaux, les ratios azote/phosphore particulièrement élevés dans le bassin oriental, et par les processus hydrodynamiques en particulier le mélange vertical dans les régions situées au nord. Cette thèse qui s'inscrit dans le cadre du projet MerMEX, composante du chantier MISTRALS, a pour objectif l'étude des cycles biogéochimiques en Méditerranée. Elle s'appuie en particulier sur les observations acquises dans le cadre du projet DeWEx et sur la modélisation couplée physique biogéochimie 3D. À l'échelle du bassin et à l'échelle régionale du sous-bassin occidental. La première étude à l'échelle du bassin sur une période de 10 ans a permis d'effectuer une classification de régimes biogéochimiques, en fonction de leurs caractéristiques physiques et biogéochimiques. Les zones oligotrophes présentes au sud du bassin oriental et occidental sont caractérisées par une faible efflorescence et par de grandes profondeurs de nutriclines. Tandis qu'au nord du bassin, au large de Rhodes, en mer Adriatique et dans le bassin Liguro-provençal, le régime oligotrophe estival est suivi en hiver par une dynamique verticale intense, la convection profonde. Cette dernière est considérée comme le moteur de la circulation thermohaline. Elle entraine un enrichissement des eaux de surface en sels nutritifs qui permet une efflorescence rapide et intense au printemps. L'océan Atlantique représente une source de matière organique pour la Méditerranée. Cette mer représente en revanche une source de sels nutritifs pour l'Atlantique. Ensuite, un modèle à très haute résolution a été imbriqué dans le modèle de bassin pour quantifier les processus physiques et biologiques qui déterminent la variabilité temporelle de la disponibilité et de la stœchiométrie des sels nutritifs en Méditerranée nord-occidentale. La convection profonde hivernale entraîne une homogénéisation des propriétés biogéochimiques sur la colonne d'eau, et une stœchiométrie vers des valeurs estivales. Cette région bascule d'un régime d'eutrophie lors de la convection profonde vers un régime oligotrophe après le bloom de printemps. Lors du premier régime la production primaire est dominée par une production nouvelle en surface, alors que lors du deuxième régime la production phytoplanctonique de subsurface est essentiellement régénérée. Les masses d'eau adjacentes à la zone de convection et celles situées au sud sont caractérisées par une dominance de production régénérée toute l'année. Une partie de la matière organique particulaire est exportée en dessous de la couche épipélagique. Cet export de matière organique est variable et est fortement lié à la dynamique verticale des masses d'eau. / The Mediterranean Sea is characterized by various trophic regimes due to river inputs, as well as heterogeneous nitrogen to phosphorus ratios and hydrodynamic processes, in particular vertical mixing. The objective of this thesis that was performed in the framework of the MISTRALS program is the study of the biogeochemical cycles of these various regimes that composed the Mediterranean. It is mainly based on the in situ observations collected during DeWEx project and on 3D physical/biogeochemical modeling at the scale of the entire basin and at the regional of the western sub-basin. The first study is a ten-year basin scale study which allows an ecological classification, giving bioregions in function of their physical and biogeochemical properties. Southern oligotrophic areas in both eastern and western sub-basins are characterized by low efflorescence and deep nutriclines. While in the north, near Rhodes Island, in the southern Adriatic Sea and in the Liguro-Provencal sub-basin, the summer oligotrophic regime is altered annually by intense vertical dynamics, the deep convection. This process is considered as a driving force of the thermohaline circulation and entrains an enrichment of nutrients in surface layer which allows rapid and intense blooms in spring. The Mediterranean receives organic matter from the Atlantic Ocean, while, it is a source of inorganic matter for the Atlantic. In a second part of this thesis, a high resolution model on the western sub-basin was embedded in the basin model to quantify the physical and biological processes that determine the temporal variability of the nutrient stocks and their stoichiometry. The north-western Mediterranean turns from an eutrophic regime during deep convection to an oligotrophic regime after the spring bloom. During the eutrophic regime new production dominates the primary production at the surface while during the oligotrophic regime primary production is essentially associated to subsurface regenerated one. Adjacent water masses of the convection zone and west-southern regions are characterized by a dominance of regenerated production all over the year.

This study examines the relationship between nutrient additions and algae and invertebrate productivity in a nutrient-poor wetland of the Interlake Region of Manitoba, Canada. Alfalfa hay was added to experimental enclosures in May 1992. Alfalfa additions were made in unprocessed and ground forms and consisted of three treatments: ground low, whole low, and whole high. Dissolved oxygen, surface water nutrients, algae standing crop, and invertebrate production were monitored at open marsh sites and in treatment and control enclosures during 1992 and 1993. Stable $ sp{13}$C, $ sp{15}$N and $ sp{34}$S isotope ratios were determined for the alfalfa additions, and for surface water, algae, macrophytes, sediments and invertebrates. / In general, the effects of nutrient additions were confined to 1992. Treatment enclosure dissolved oxygen levels decreased immediately following fertilization, recovering in the low treatments by early June. Low oxygen conditions persisted in whole high enclosures throughout most of 1992. Dissolved and suspended nutrient concentrations, and phytoplankton chlorophyll a increased but, with the exception of dissolved N, were soon lost from the water column. Treatment enclosure epiphytic algae increased while epipelon did not respond to fertilization. The primary effect of fertilization on invertebrate production was an increase in treatment enclosure chironomid larvae during 1992. As with productivity measures, stable isotope ratio values suggested a temporary presence of alfalfa nutrients in the enclosed food webs. Only the isotope ratios of metaphytic algae and snails collected during August 1992 indicated an incorporation of alfalfa nutrients.

Thesis (M.S.)--Indiana University, 2007. / Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Gabriel M. Filippelli, Catherine Souch, Lenore P. Tedesco. Includes vitae. Includes bibliographical references (leaves 80-83).

L’alimentation et l’excrétion constituent deux besoins physiologiques fondamentaux de tout être humain. En analysant leur matérialisation depuis l’échelle cellulaire jusqu’à celle des grands cycles biogéochimiques planétaires, nous proposons de considérer que l’alimentation et l’excrétion humaines participent d’un système dont les modalités de réalisations dans les différentes sociétés humaines permettent de caractériser des régimes socio-écologiques. Nous avons plus particulièrement analysé les systèmes alimentation/excrétion des territoires urbains au regard de leur soutenabilité et proposons une méthodologie de caractérisation fondée principalement sur l’analyse du flux de la substance qui nous paraît la plus pertinente, à savoir l’azote, et sur les modalités de gestion des urines humaines qui représentent près des trois quarts de ce flux. Nous montrons que les systèmes alimentation/excrétion des différentes communautés humaines présentent une très grande variété selon les lieux et époques considérés et proposons de les distinguer entre autres en fonction de leur circularité, c’est-à-dire par le taux de retour sur des sols agricoles des excrétats. En prenant l’agglomération parisienne comme cas d’étude, nous montrons que son système alimentation/excrétion a été de plus en plus circulaire au cours du XIXe siècle, culminant au tout début du XXe siècle aux alentours de 50 % de circularité, avant de se linéariser progressivement au cours du XXe siècle. En ce début de XXIe siècle, nous caractérisons le système alimentation/excrétion de l’agglomération parisienne comme non soutenable car linéaire à plus de 95 %, intensif, inefficace et polluant aux échelles locales et globales. Ces caractéristiques sont généralisées au sein du monde occidental et interpellent sur la possibilité d’une transition socio-écologique vers des systèmes alimentation/excrétion soutenables. Or, depuis les années quatre-vingt-dix, une prise de conscience relative à l’urine a réémergé, principalement en Suède puis dans l’Europe germanique. Elle s’est traduite par de nombreuses réalisations et recherches autour de la séparation à la source des urines. Nous montrons que ce dispositif est actuellement le seul, dans le monde occidental, à avoir permis de nouveau la mise en œuvre de systèmes alimentation/excrétion circulaires. Pouvant être déclinée sous de multiples formes en fonction des contextes, la séparation à la source des urines bénéficie, malgré le verrouillage socio-technique de l’agglomération parisienne autour du tout-à-l’égout, d’un contexte favorable à son développement. Nous avons élaboré un scénario prospectif explorant ainsi la possibilité que l’agglomération parisienne dépasse, en quelques décennies, l’extremum de circularité qu’elle avait connu à la Belle Époque et que les acteurs de ce territoire réalisent, en cohérence avec une transition socio-écologique des autres systèmes énergétiques, hydrauliques et de transport, un régime socio-écologique soutenable de leur système alimentation/excrétion. Cette thèse fait partie du programme de recherche et action OCAPI (www.leesu.fr/OCAPI) / Nutrition and excretion are fundamental physiological needs for all human beings. Analysis of their materiality, from the cellular scale up to the great planetary-scale biogeochemical cycles, shows that nutrition and excretion form a system. The focus of our study is the sustainability of the nutrition/excretion systems of urban areas, which we have sought to assess by analysing substance flows. The most relevant of these substances seems to be nitrogen, so by assessing urban nitrogen flows we can characterise the different possible socioecological regimes and their sustainability. We identify a wide diversity of nutrition/excretion systems depending on the places and eras considered. We propose to distinguish them in terms of their circularity, in other words by the rate at which nitrogen from excreta returns to agricultural land. Using the Paris urban area as our case study, we show that its nutrition/excretion system became increasingly circular in the 19th century, reaching maximum circularity right at the start of the 20th century, before becoming steadily more linear in the course of the 20th century. In these early years of the 21st century, the nutrition/excretion system of the Paris urban area is essentially linear, and still generates significant pollution at both local and global scales. Its environmental footprint is exacerbated by a diet that is very protein rich, mostly animal in origin, and by the non-consumption of a significant proportion of the food produced. All these factors make it unsustainable. These characteristics are found throughout the Western world and raise questions about the possibility of a socioecological transition to sustainable systems of nutrition and excretion. Since the 1990s, initially in Sweden, followed by Nordic and German-speaking Europe, awareness has been growing of the role of urine. Urine is responsible for three-quarters of urban nitrogenous excretions and is a safe substance: following a period of storage, it can be used as agricultural fertiliser. This new awareness has been followed by extensive experimentation and research on urine source separation. We show that this is currently the only method in the Western world to have accomplished a return to circular systems of nutrition/excretion. Urine source separation can be done in multiple ways, depending on circumstances, and conditions in France are favourable to its development, despite the sociotechnical lock-in to mixed sewage management systems. In a forward-looking scenario, we therefore explore the possibility that the Paris urban area could return to, and within a few decades even surpass, the heights of circularity that it attained during the Belle Époque. In that case, alongside a socioecological transition in the other systems – water, energy, transport – the people of this territory could establish a sustainable regime for their system of nutrition/excretion. This thesis is part of the OCAPI research and action programme (www.leesu.fr/OCAPI)