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The effects of climate and environmental change are likely to exacerbate water stress in Africa over the next five decades. It appears obvious, therefore, that large river basins with considerable total renewable water resources will play a prominent role in regional cooperation to alleviate the pressure of water scarcity within Africa. However, managing water resources in the large river basins of Africa involves problems of data paucity, lack of technical resources and the sheer scale of the problem. These river basins are located in regions that are characterized by poverty, low levels of economic development and little food security. The rivers provide multiple goods and services that include hydro-power, water supply, fisheries, agriculture, transportation, and maintenance of aquatic ecosystems. Sustainable water resources management is a critical issue, but there is almost always insufficient data available to formulate adequate management strategies. These basins therefore represent some of the best test cases for the practical application of the science associated with the Predictions in Ungauged Basins (PUB). The thesis presents the results of a process-based hydrological modelling study in the Congo Basin. One of the primary objectives of this study was to establish a hydrological model for the whole Congo Basin, using available historical data. The secondary objective of the study was to use the model and assess the impacts of future environmental change on water resources of the Congo Basin. Given the lack of adequate data on the basin physical characteristics, the preliminary work consisted of assessing available global datasets and building a database of the basin physical characteristics. The database was used for both assessing relationships of similarities between features of physiographic settings in the basin (Chapters 3 and 4), and establishing models that adequately represent the basin hydrology (Chapters 5, 6, and 7). The representative model of the Congo Basin hydrology was then used to assess the impacts of future environmental changes on water resources availability of the Congo Basin (Chapter 8). Through assessment of the physical characteristics of the basin, relationships of similarities were used to determine homogenous regions with regard to rainfall variability, physiographic settings, and hydrological responses. The first observation that comes from this study is that these three categories of regional groups of homogenous characteristics are sensible with regards to their geographical settings, but the overlap and apparent relationships between them are weak. An explanation of this observation is that there are insufficient data, particularly associated with defining sub-surface processes, and it is possible that additional data would have assisted in the discrimination of more homogenous groups and better links between the different datasets. The model application in this study consisted of two phases: model calibration, using a manual approach, and the application of a physically-based a priori parameter estimation approach. While the first approach was designed to assess the general applicability of the model and identify major errors with regard to input data and model structure, the second approach aimed to establish an understanding of the processes and identify useful relationships between the model parameters and the variations in real hydrological processes. The second approach was also designed to quantify the sensitivity of the model outputs to the parameters of the model and to encompass information sharing between the basin physical characteristics and quantifying the parameters of the model. Collectively, the study’s findings show that these two approaches work well and are appropriate to represent the real hydrological processes of Congo Basin. The secondary objective of this study was achieved by forcing the hydrological model developed for the Congo Basin with downscaled Global Climate Model (GCMs) data in order to assess scenarios of change and future possible impacts on water resources availability within the basin. The results provide useful lessons in terms of basin-wide adaptation measures to future climates. The lessons suggest that there is a risk of developing inappropriate adaptation measures to future climate change based on large scale hydrological response, as the response at small scales shows a completely different picture from that which is based on large scale predictions. While the study has concluded that the application of the hydrological model has been successful and can be used with some degree of confidence for enhanced decision making, there remain a number of uncertainties and opportunities to improve the methods used for water resources assessment within the basin. The focus of future activities from the perspective of practical application should be on improved access to data collection to increase confidence in model predictions, on dissemination of the knowledge generated by this study, and on training in the use of the developed water resources assessment techniques.

Cercopithecus mitis is a polytypic, pan-African guenon species with a complex evolutionary history. The Lomami River Blue Monkey, C. m. heymansi, occurs within the Tshuapa-Lomami-Lualaba (TL2) Conservation Landscape and exhibits high pelage variation. Previous studies have shown discordance between the mitochondrial and Ychromosome gene trees of C. m. heymansi. The objectives were to test the phylogenetic pattern found in the mtDNA tree using a larger sample size of C. m. heymansi, determine the genetic diversity of the population, and hypothesize methods of speciation. While many species within the C. mitis radiation depict paraphyly, I determined that C. m. heymansi forms highly supported monophyletic clades in both mtDNA and Ychromosome gene trees. These results suggest that C. m. heymansi is a distinct lineage within the C. mitis radiation. Future genomic analyses are important in resolving the evolutionary history of this population and discerning its taxonomic classification and conservation value. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

A comprehensive hydrological study of large watersheds in Africa e.g. the Congo basin and the Nile basin has not been vigorously pursued for various reasons. One of the major reasons is the lack of adequate modeling tools that would not be very demanding in terms of input data needs and yet inclusive enough to cover such wide extents (over 3 million square kilometers for the Congo basin). Using a coupled run of the Community Atmospheric model (CAM3) and Community Land Model (CLM3) components of the Community Climate System of Models (CCSM), this study looks into the spatial and temporal variation of precipitation and river runoff in the Congo basin in the light of increasing trends in deforestation of the tropical forests. The effect of deforestation on precipitation and runoff is investigated by changing the land cover-type from the current configuration of broadleaf evergreen/deciduous, non-Artic grass and corn to a mostly grass type of vegetation. Discharge simulation for the river Congo is centered at the point of entrance to the Atlantic Ocean. Although the CLM3 does not presently simulate the observed river runoff to within at least one standard deviation it gives an opportunity to iteratively improve on the land surface parameterization with a possibility of future accurate prediction of mean monthly river runoffs under varying climate scenarios and land use practices. When forced with the National Center for Environment and Prediction (NCEP) re-analysis data the CLM3 runoff simulation results are relatively more stable and much closer to the observed. An improved CLM3 when coupled to CAM3 or other Global Climate Models is definitely a better tool for investigative studies on the regional hydrological cycle in comparison to the traditional methods. There was a slight reduction in rainfall in the first experiment which mimicked a severe form of deforestation and a slight increase in rainfall following low level of deforestation. These changes in rainfall were however statistically insignificant when compared to the control simulation. There was notable heterogeneity in the spatial distribution of the changes in rainfall following deforestation.

Doctorat en philosophie et lettres / info:eu-repo/semantics/nonPublished

La zone intertropicale est une zone clé du climat mondial, dans la mesure où ce secteur joue un rôle essentiel dans le cycle du carbone à l’échelle globale, via la pompe du carbone par la productivité primaire, elle-même accrue dans les grandes cellules d'upwelling côtières. L’objectif principal de ce travail était de discuter la variabilité climatique haute fréquence ayant affecté l'Océan Atlantique Est tropical au cours des derniers 45 000 ans à l’échelle orbitale et sub-orbitale. Notre étude a ainsi mis en évidence les connexions liant le domaine océanique et le domaine continental (panaches fluviatiles) à travers la comparaison entre les conditions hydrologiques de surface reconstruites par les assemblages phytoplanctoniques microfossiles (kystes de dinoflagellés : principaux outils de cette étude) et la variabilité de la mousson africaine déduite de données géochimiques sédimentaires disponibles sur les 3 carottes d’étude, situées au large du Congo ainsi que dans le Golfe de Guinée. Ce travail de thèse a également permis de réaliser un travail approfondi de mise à jour de la base de données dinokystes modernes et des données environnementales qui leurs sont associées (température et salinité de surface, productivité primaire, mais aussi nouveaux ajouts : densité de l’eau, saisonnalité, ou encore anomalies de températures par rapport à la moyenne des températures calculée selon un axe latitudinal), afin de pouvoir quantifier les paramètres hydrologiques sur les carottes d’étude via la fonction de transfert dinokyste développée pour l’Océan Atlantique tropical. Les assemblages dinokystes ont révélé une grande sensibilité aux effets de la précession, avec des environnements chauds et soumis à de fortes décharges fluviatiles observés en contexte de minima de l'indice de précession, en particulier durant la dernière déglaciation, configuration amplifiée par le maximum d’obliquité. Les résultats issus de la fonction de transfert démontrent le rôle primordial du fleuve Congo dans l'évolution de la productivité primaire au cours du temps, via l'apport massif de nutriments, ainsi que via des mécanismes d'upwelling générés par l'activité du fleuve en elle-même. / The intertropical area is a key domain for the knowledge of past global climate, with indeed a prevalent role regarding of carbon cycle; high productive conditions in this area being induced by the large eastern boundary upwelling cells. The main purpose of this work consisted in discussing the high frequency climate variability that occurred in the eastern tropical Atlantic Ocean over the last 45,000 years. This area then permitted to highlight land-sea linkages through the relationships existing between marine environments as deduced from microfossil assemblages (dinoflagellate cysts: main proxies of this study) and the African monsoon as reconstructed through river-plume activity, thanks to three cores located off the Congo river mouth and in Gulf of Guinea. Furthermore, this work permitted to deeply update the tropical dinocyst modern database used by the dinocyst-based transfer function method developed for the Tropical Atlantic Ocean (new modern sites and new environmental datasets : SST, SSS, net primary productivity, upwelling activity, seasonality). Dinocyst assemblages revealed a strong influence of precession effects, with warmer and wetter periods reconstructed during minima of precession, especially during the last deglaciation, strongly enhanced by the obliquity maximum. Dinocyst-based transfer function results also highlighted the prevalent role of the Congo River on past primary productivity evolution through strengthened terrigenous inputs to the ocean but also through river-induced upwelling mechanism.

Le complexe des lobes terminaux du système turbiditique du Congo, localisé à 760 km des côtes de l’Afrique Equatoriale et à 5000 m de profondeur, constitue un système sédimentaire unique pour étudier les transferts de matière organique dans l’Océan Atlantique. En effet, ce complexe, d’une superficie de 3000 km² environ, est actuellement le réceptacle final des apports turbiditiques, initiés dans le canyon du fleuve Congo. Cette thèse, qui s’inscrit dans le cadre du projet ANR-Congolobe, a pour objectif d’apporter des connaissances sur la composition biogéochimique de ces apports et d’apporter des conclusions sur leur(s) origine(s), leur distribution et leur devenir dans les sédiments. Pour ce faire, neuf carottes d’interface (~20 cm) et une carotte longue (~900 cm) prélevées en différents sites du complexe des lobes ont été étudiées. La stratégie employée a consisté (1) à réaliser une description des faciès et de la granulométrie des sédiments, (2) à réaliser une étude géochimique globale et moléculaire sur ces mêmes sédiments (%Corg, C/N, δ13Corg et δ15N, 137Cs, acides gras, tétraéthers) (3) à confronter les données acquises avec celles obtenues sur les sources initiales marines et terrestres par un modèle de mélange binaire (δ13Corg) et par une analyse discriminante (acides gras), (4) à considérer un site spécifique en tant que référence temporelle, (5) à combiner les données acquises à tous les sites dans une analyse multivariée pour appréhender le devenir de cette région à l’échelle millénaire. Tous les marqueurs considérés ont révélé que les sédiments des lobes constituent un véritable puits de matière organique particulaire terrigène en provenance du Congo. Les concentrations en carbone organique sont élevées dans les sédiments argilo-silteux (~3 à 5 %). 70 à 80 % de ce carbone organique dérive du fleuve et consiste en des débris végétaux et en de la matière organique altérée issue de l’érosion des sols, alors que les 20 à 30 % restants consistent en une matière organique marine très dégradée. Une analyse plus détaillée des biomarqueurs lipidiques suggère que la matière organique apportée par les turbidites est peu réactive, néanmoins, l’analyse des acides gras a permis de détecter la présence de composés marins frais dans certains échantillons. Une conclusion importante de cette étude est que tous les résultats portant sur la composition et la distribution de la matière organique dans les sédiments sont en accord avec les modalités de dépôt turbiditique (rapidité du transfert, fréquence des apports, épaisseur des dépôts) ainsi qu’avec les propriétés granulométriques des sédiments. Ces caractéristiques physiques permettent d’expliquer que la matière organique soit exceptionnellement bien préservée dans les couches anoxiques des sédiments, une observation valable à l’échelle des millénaires qui soulève l’intérêt de prendre en compte la région des lobes pour comprendre le devenir de la matière organique terrestre dans l’océan global. / The terminal lobe complex of the Congo deep-sea fan, which is a unique region to study the transfer of organic matter from the land to the Atlantic Ocean, is located 760 km off the Equatorial African coast and at 5,000 m depth. This region covers 3000 km2 and is the terminal receptacle of the particulate organic matter provided by turbidity currents originating from the Congo River canyon. This thesis is part of the Congolobe ANR-project and aims at providing information on the biogeochemical composition of these organic matter inputs to study their origin, distribution and fate in lobe complex sediments. Nine short sediment cores (~20 cm) and one long core (~900 cm) were collected in different sites of the lobes complex for different sediment analyses. The strategy of the study consists of the following five analytical steps: (1) to achieve a facies and granulometry description of the sediments; (2) to study the global and molecular geochemical characteristics of the sediments (%OC , C/N, δ13Corg, δ15N, 137Cs, fatty acids and tetraethers); (3) to compare these data to data from marine and terrestrial end-members using a binary mixing model (δ13Corg) and a discriminant analysis (fatty acids); (4) to consider a specific site as a time reference and (5) to discuss the fate of the sedimentary organic matter at the millennium time scale of the overall area by combining different data in a multivariate analysis. All the different proxies used in this study revealed that lobe sediments could be a sink for organic inputs from the Congo River. Organic carbon concentrations are high in silty-clay sediments (~3 to 5 %). Over the study region, 70 to 80 % of the organic carbon originate from the Congo River and consist of vegetal detritus and soil derived-OM. The remaining 20 to 30 % consists of highly degraded organic matter. A more detailed lipid biomarker analysis shows that the organic matter is poorly reactive; however, fatty acid analyses reveal the presence of fresh planktonic compounds in some samples. An important finding of this study is that the composition and the distribution of the organic matter in sediments are consistent with turbiditic deposition patterns (e.g., rapidity of transfer, frequency and thickness of deposits) as well as with the granulometry properties of the sediments from the terminal lobe complex. Due to the specific sediment characteristics, organic matter is exceptionally well preserved in the anoxic sediment layers, reaching back to millennial time scales. Hence, studying the lobe complex area is of great interest for a better understanding of the fate of terrestrial organic matter in the global ocean.

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