Water management that alters riverine ecosystem processes has strongly influenced deltas and the people who depend on them, but a full accounting of the trade-offs is still emerging. Using palaeoecological data, we document a surprising biogeochemical consequence of water management in the Colorado River basin. Complete allocation and consumptive use of the river's flow has altered the downstream estuarine ecosystem, including the abundance and composition of the mollusc community, an important component in estuarine carbon cycling. In particular, population declines in the endemic Colorado delta clam, Mulinia coloradoensis, from 50-125 individuals m(-2) in the pre-dam era to three individualsm-2 today, have likely resulted in a reduction, on the order of 5900-15 000 tCyr(-1) (4.1-10.6 mol Cm-2 yr(-1)), in the net carbon emissions associated with molluscs. Although this reduction is large within the estuarine system, it is small in comparison with annual global carbon emissions. Nonetheless, this finding highlights the need for further research into the effects of dams, diversions and reservoirs on the biogeochemistry of deltas and estuaries worldwide, underscoring a present need for integrated water and carbon planning.

Les historiens et archéologues ont efficacement mis à profit les travaux réalisés dans le domaine des SIG pour répondre à leurs propres problématiques. Pour l'historien, un Système d’Information Géographique est avant tout un outil de compréhension des phénomènes sociaux.De nombreuses sources géohistoriques sont aujourd'hui mises à la disposition des chercheurs: plans anciens, bottins, etc. Le croisement de ces sources d'informations diverses et hétérogènes soulève de nombreuses questions autour des dynamiques urbaines.Mais les données géohistoriques sont par nature imparfaites, et pour pouvoir être exploitées, elles doivent être spatialisées et qualifiées.L'objectif de cette thèse est d'apporter une solution à ce verrou par la production de données anciennes de référence. En nous focalisant sur le réseau des rues de Paris entre la fin du XVIIIe et la fin du XIXe siècles, nous proposons plus précisément un modèle multi-représentations de données agrégées permettant, par confrontation d'observations homologues dans le temps, de créer de nouvelles connaissances sur les imperfections des données utilisées et de les corriger. Nous terminons par tester le rôle de référentiel géohistorique des données précédemment qualifiées et enrichies en spatialisant et intégrant dans le modèle de nouvelles données géohistoriques de types variés (sociales et spatiales), en proposant de nouvelles approches d'appariement et de géocodage / The increasing availability of geohistorical data, particularly through the development of collaborative projects is a first step towards the design of a representation of space and its changes over time in order to study its evolution, whether social, administrative or topographical.Geohistorical data extracted from various and heterogeneous sources are highly inaccurate, uncertain or inexact according to the existing terminology. Before being processed, such data should be qualified and spatialized.In this thesis, we propose a solution to this issue by producing reference data. In particular, we focus on Paris historical street networks and its evolution between the end of the XVIIIth and the end of the XIXth centuries.Our proposal is based on a merged structure of multiple representations of data capable of modelling spatial networks at different times, providing tools such as pattern detection in order to criticize, qualify and eventually correct data and sources without using ground truth data but the comparison of data with each other through the merging process.Then, we use the produced reference data to spatialize and integrate other geohistorical data such as social data, by proposing new approaches of data matching and geocoding

Geographic Information Systems (GIS) have demonstrated their utility in predictively modeling the location of archaeological sites, and providing a framework for cataloging sites eligible for heritage management status. The intent of this GIS-based study is to begin to create a geohistorically organized database of information culled from historic documents and archaeological excavation. In this case study of postbellum land tenure in Hillsborough County, Florida, a GIS-based approach is used to demonstrate the impacts of federal and state land ownership policy decisions during the Reconstruction Era and beyond. GIS data are also used to reveal information about how people use their allotted environment to non-verbally communicate their perceptions of the world and their place in it. Finally, GIS are shown to be ideally suited for allowing multi-scalar, diachronic comparisons of archaeological sites and materials. This research was conducted according to the concepts of Actor-Network-Theory (ANT), which assumes there is a generalized symmetry between the agency of human actors and non-human actants (i.e. it does not assume the primacy of human intentional action). ANT accepts that materials can carry non-verbal messages (e.g. colors, aromas, tactility), which affect how humans interact, communicate, and organize themselves in space. ANT allows for the use of scales based on human action, and analyses that are based standardized metrologies. Finally, ANT obviates being limited to strict categories of macro- and micro-, by accepting that networks may bridge both. This research shows that two rural communities have undergone similar growth trajectories, with a historically black community having experienced some setbacks in the early 20th century. However, the results show that the rural African American community was not more subdivided than the neighboring Euro-American community, contrary to initial expectations. Additionally, there is a suggestion that communities may move socially important buildings such as churches schools to the community center or periphery, depending on the intended recipient of the message. The study also documents the centralization, concentration, and clustering of the county's African American population through time.

La guerre du Việt Nam mit la forêt au coeur des enjeux militaires. Nées des controverses sur lesconséquences environnementales des épandages d’herbicides, des hypothèses ont émergé sur les impacts decette pratique : différentiels selon les unités paysagères, aggravés par les perturbations anthropiques antérieureset postérieures à la guerre. Relevant de la biogéographie, l’analyse géohistorique confronte des sources souventdivergentes et privilégie les princeps pour reconstituer, à des dates clés, les paysages d’une province au coeurdu conflit. L’état actuel de partition en trois unités – plaine, collines et montagnes – révèle le lien entreperturbation et accessibilité. Circa 1954, les pratiques précoloniales et coloniales avaient déjà perturbé lesécosystèmes, de manière croissante des montagnes vers la plaine. Les impacts d’une guerre dirigée contre lemilieu furent directs et indirects. Après-guerre, ils furent aggravés par les pratiques civiles, qui bloquèrent lareconquête spontanée et provoquèrent déboisements et déforestations ; la pression s’accrut dans les collines etles montagnes, plus affectées par la guerre. Depuis circa 1990, les décisions politiques ont placé officiellementla forêt entre protection et développement mais elles se heurtent aux nécessités du développement économique.La reconquête, dirigée, accélérée par la plantation d’espèces à croissance rapide, est engagée dans dessylvosystèmes perturbés et épargnés par la guerre. Aujourd’hui, dans les trois unités paysagères, les zonesdéfoliées ne sont pas identifiables : cicatrisation, poursuite du recul des forêts surtout ont fait leur oeuvre.Restent visibles les géofaciès de cratères et les anciennes bases militaires américaines. La conjugaison desperturbations empêche l’identification du strict impact actuel de la guerre et relativise celui-ci ; plus affaiblissont les sylvosystèmes de la plaine qui, moins touchés, subissent une forte pression séculaire. / The Việt Nam war put the forest at the heart of military stakes. The controversies over the environmentalconsequences of herbicide spraying inspire the hypothesis that the impacts of this practice are differentialaccording to landscape units, worsened by the human disturbances prior to and after the war. Coming underbiogeography, the geohistorical analysis compares sources, that are often divergent, and favors primary ones toreconstruct, at key dates, the landscapes of a province at the heart of the conflict. The present state of partitioninto three units – plain, hills and mountains – reveals the link between disturbance and accessibility. Circa1954, the precolonial and colonial practices had already disturbed ecosystems increasingly from the mountainsto the plain. The impacts of a war against the environment were direct and indirect. In the post-war years, theywere worsened by the civilian practices, which inhibited spontaneous reforestation and provoked forestimpoverishment and deforestation; the pressure increased in the hills and mountains, which were more affectedby the war. Since circa 1990, the political decisions have officially put the forest between protection anddevelopment but they come up against the necessities of economic development. Managed, accelerated by theplantation of fast-growing species, the reforestation is started in some sylvosystems, that were disturbed orspared by the war. Today, in the three landscape units, the defoliated areas are not identifiable because ofhealing and, above all, continuation of forest decline. Geofacies of craters and former American military basesremain visible. The combination of disturbances prevents from identifying the strict present impact of the warand puts this one into perspective; more weakened are the plain sylvosystems, which were less hit but suffer astrong secular pressure.

Bon nombre d’agglomérations s’engagent vers un urbanisme marqué par la notion de ville durable et par les thèmes de cadre de vie, de nature en ville, de mixité sociale et d’identité territoriale. Dans cette perspective, les entités urbaines, au site originel lié à l’eau, trouvent dans leurs milieux fluviaux et humides des terrains d’application et d’expérimentation idoines et y développent de vastes projets urbains que l’on se propose d’analyser par la notion de « requalification urbaine ». La diversité des politiques, perçue à travers l’étude des villes péri-franciliennes, en éclaire les manifestations concrètes, la diversité, mais aussi les travers éventuels.Mais, le caractère récent de la redécouverte de l’eau en ville, qui succède à une longue phase de dénigrement, requiert une approche géohistorique des liens entre la ville et ses milieux d’eau afin d’inscrire la démarche de requalification dans une politique patrimoniale pérenne qui privilégie l’idée de trajectoire paysagère. Il en ressort, par le biais de l’étude d’Amiens et d’Orléans, des configurations singulières entre le façonnement des milieux humides et l’histoire des cités.Les jeux d’acteurs, essentiellement publics, engagés dans la requalification urbaine des lieux d’eau, y seront également mis en évidence car les particularités fonctionnelles de ces zones humides bousculent les outils et procédures de gestion urbaine ainsi que les modes de gouvernance. Il s’agit dès lors de cerner la place des lieux d’eau dans les stratégies politiques urbaines, d’en décrire les traductions spatiales et d’en révéler le potentiel d’attractivité par le biais des campagnes de communication et d’animation. / Many agglomerations are engaged in sustainable urban policies, focusing on lifestyle, development of green space, social melting-pot and local identity. With these objectives in mind urban areas, originally built beside water, find ready-made sites in their catchment area rivers and wetlands to apply and experiment large projects. These will be studied under the name of “urban requalification”. The diversity in policy approach, evident amongst the greater metropolitan area of Paris, shows variability in the concrete manifestations and end results.The recent re-discovery of waterways in the city comes after many years of planners turning their back on it. Therefore a geohistorical approach to the links between the city and it’s wetlands is required. This will allow the urban requalification process to be integrated into a perennial heritage strategy which prioritises a focus on landscape. This study, of Amiens and Orleans situation, highlights the singular configuration between the landscaping of the wetland and the history of urban centres.The interaction between the different actors, essentially within the public sector sphere, engaged in urban requalification of wetlands will be examined. In fact, the specificity of wetlands functions obliges a reassessment of the tools and procedures of urban management as well as the various modes of governance. Consequently the place of water in urban strategy needs to be defined, the translation onsite described and the attractiveness potential through communication campaigns and public events outlined.