Bilan et dynamique des interactions rivières-lac(s)-aquifères dans le bassin hydrologique du lac Tchad: Approche couplée géochimie et modélisation des transferts

Lake Chad Basin (LCB) is a 2.5 billion km2 closed drainage basin, located in the center of Africa. Surface waters (rivers and lake) are unequally distributed and highly variable. The lake Chad, which shows strong surface variations, enhances the climatic variations over the LCB. The multi-layer aquifer system of the LCB is composed of two geologic units (the quaternary (Q) and the Continental Terminal (CT)) containing large water resources. They could imbalance the increasing freshwater scarcity in the area but their recharge needs to be constrained. The understanding of surface water variability and ground water recharge is essential to support water management in the area. In this work, we tried to quantify the hydro(geo)logical response of the LCB to climatic variability by combining geochemical and modeling approaches. Samplingof water reservoirs (surface, Q and CT aquifers) have been carried out between 2011 and 2013. Lake Chad levels modeling between 1955 and 2011 was calibrated from hydrological, chemical and isotopic data. It allows to disentangle evaporation from transpiration and from infiltration. Transpiration, neglected in previous studies, accounts for 15 % of the total evapotranspiration and is particularly high in the Archipelagos. Based on the chlorine dynamic in the LCB, a transit time of 10 yr from the upper basin to the lower rivers, a short renewal rate of lake waters and infiltration of lake waters toward the aquifer are estimated. The detection of thermonuclear 36Cl together with the stable isotopic composition of groundwaters allow to draw the present-day recharge distribution in the Quaternary aquifer. We show that present-day recharge occurs in 60 % of the groundwater sampled but is confined to the vicinity of surface waters. An evaporationbetween 85 and 98 % of lake waters in the surrounding of Lake Chad is estimated by the comparison of model-calibrated infiltration rates with groundwater geochemical data. Groundwaters with a contrasted geochemical signature are stored in the center of the piezometric depressions, suggesting no present-day recharge in these enigmatic groundwater features. Although it would require further investigation, the recharge of these waters could be related to the African Humid Period. The deep waters of the CT, with water ages of 300 000 yr, show geochemical patterns indicative of an old and humid recharge period. These original data on the multi-layer aquifer of the LCB give new insights into paleorecharge in the Sahelian band. GCM paleoclimatic simulations over the last millennium have been introduced in a rainfallrunoff model (GR2M), coupled with our lake level model. This preliminary approach shows the difficulty to reconcile lake level records from paleohydrological modeling.Le bassin endoréique du lac Tchad (BLT) couvre 2,5 millions de km2 au centre de la zone sahélienne. La distribution en eau de surface (rivières et lac) y est très inégale et variable dans l’espace et dans le temps. Le lac Tchad, dont la surface enregistre de fortes variations, agit comme un amplificateur des variations climatiques sur le BLT. Le système aquifère multicouche du BLT est composé de deux formations (le quaternaire (Q) et le continental terminal (CT)) qui contiennent d’importantes ressources en eau. Ces dernières pourraient répondre à la pression croissante sur la ressource en eau dans le bassin, mais leur recharge doit être évaluée. La compréhension de la variabilité hydrologique de surface et de la recharge des aquifères est donc un enjeu sociétal. Au cours de cette thèse, nous avons cherché à quantifier la réponse hydro(géo)logique du BLT aux variations du climat, par un couplage entre traceurs géochimiques et modélisation, à différentes échelles de temps.Un bilan hydrologique, chimique et isotopique, calé à partir des données disponibles entre 1955 et 2011, permet de distinguer les flux d’évaporation, de transpiration et d’infiltration qui affectent la surface du lac. La transpiration, jusqu’alors négligée dans le bilan hydrologique, contribue à environ 15 % de l’évapotranspiration, elle est particulièrement importante dans la zone des archipels. La dynamique du chlore dans le BLT met en évidence un temps de transfert entre le bassin amont et les rivières autour de 10 ans, un renouvellement des eaux du lac très rapide et une infiltration de 200 mm an¡1 vers l’aquifère quaternaire. Le couplage d’un modèle pluie-débit (GR2M) et du modèle de lac, forcé par des simulations paléoclimatiques de GCM sur le dernier millénaire, met en évidence, dans une démarche exploratoire, la difficulté de la comparaison modèle-données dans les reconstitutions paléohydrologiques. La cartographie de la recharge moderne de l’aquifère quaternaire est obtenue par l’interprétation de la présence ou de l’absence de 36Cl thermonucléaire dans les eaux. La distribution du 36Cl thermonucléaire et des isotopes stables de l’eau montre une recharge récente dans 60 % de l’aquifère quaternaire, essentiellement liée aux interactions avec les eaux de surface. A partir de l’infiltration obtenue par le modèle de lac et des données géochimiques de la nappe quaternaire, la reprise évaporatoire actuelle sur les pourtours du lac Tchad est évaluée entre 85 et 98%.Des eaux géochimiquement contrastées par rapport aux eaux de surface sont observées dans le coeur des dépressions piézométriques de l’aquifère quaternaire, ne suggérant aucune recharge actuelle au sein de ces structures hydrogéologiques particulières. La période de recharge de ces eaux reste énigmatique mais serait liée à la Période Humide Africaine. La composition géochimique propre aux eaux du CT suggère un temps de résidence des eaux dans l’aquifère supérieur à 300 000 ans. Ces données originales sur les aquifères du BLT pourraient servir à mieux contraindre la paléorecharge en zone sahélienne

De <i>novo </i>transcriptomes of 14 gammarid individuals for proteogenomic analysis of seven taxonomic groups

Gammarids are amphipods found worldwide distributed in fresh and marine waters. They play an important role in aquatic ecosystems and are well established sentinel species in ecotoxicology. In this study, we sequenced the transcriptomes of a male individual and a female individual for seven different taxonomic groups belonging to the two genera Gammarus and Echinogammarus: Gammarus fossarum A, G. fossarum B, G. fossarum C, Gammarus wautieri, Gammarus pulex, Echinogammarus berilloni, and Echinogammarus marinus. These taxa were chosen to explore the molecular diversity of transcribed genes of genotyped individuals from these groups. Transcriptomes were de novo assembled and annotated. High-quality assembly was confirmed by BUSCO comparison against the Arthropod dataset. The 14 RNA-Seq-derived protein sequence databases proposed here will be a significant resource for proteogenomics studies of these ecotoxicologically relevant non-model organisms. These transcriptomes represent reliable reference sequences for whole-transcriptome and proteome studies on other gammarids, for primer design to clone specific genes or monitor their specific expression, and for analyses of molecular differences between gammarid species

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P &lt; 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Lake(s), rivers and groundwater dynamics and interactions in the Lake Chad Basin : geochemical tracers and modeling

Le bassin endoréique du lac Tchad (BLT) couvre 2,5 millions de km2 au centre de la zone sahélienne. Le lac Tchad agit comme un amplificateur des variations climatiques sur le BLT tandis que le système aquifère multicouche contient d'importantes ressources en eau. La réponse hydro(géo)logique du BLT aux variations du climat est étudiée par un couplage entre traceurs géochimiques et modélisation. Un bilan hydrologique, chimique et isotopique permet de distinguer les flux d'évaporation, de transpiration et d'infiltration à la surface du lac. La transpiration, jusqu'alors négligée, contribue à environ 15% de l'ET. La dynamique du chlore dans le BLT suggère un temps de transfert dans le bassin amont autour de 10 ans, un renouvellement rapide des eaux du lac et une infiltration de 200 mm an-1. Le couplage d'un modèle pluie-débit (GR2M) et du modèle de lac, forcé par des simulations paléoclimatiques de GCM sur le dernier millénaire, montre la difficulté de la comparaison modèle-données dans les reconstitutions paléohydrologiques. La cartographie de la recharge moderne de l'aquifère quaternaire est obtenue par l'interprétation des teneurs en 36Cl thermonucléaire dans les eaux. Une recharge récente, proche des eaux de surface, est mise en évidence dans 60% de l'aquifère quaternaire et la reprise évaporatoire actuelle en bord du lac Tchad est évaluée entre 85 et 98%. Les eaux géochimiquement contrastées des dépressions piézométriques ne signent pas de recharge actuelle. La composition géochimique propre aux eaux du CT suggère un temps de résidence supérieur à 300 000 ans. Ces données originales pourraient servir à mieux contraindre la paléorecharge en zone sahélienne.Lake Chad Basin (LCB) is a 2.5 billion km2 closed drainage basin, in the center of Africa. Lake Chad enhances the climatic variations over the LCB while the multi-layers aquifer system contains large water resources. The hydro(geo)logical response of the LCB to climatic variability is studied by combining geochemical and modeling approaches. The lake Chad levels modeling, calibrated from hydrological, chemical and isotopic data, allows to disentangle evaporation from transpiration and from infiltration. Transpiration, neglected in previous studies, accounts for 15% of the total ET. From the chlorine dynamic in the LCB, a transit time of 10 yr in the upper basin, a short renewal rate of lake waters and their infiltration toward the aquifer are estimated. GCM paleoclimatic simulations over the last millennium were introduced into a rainfall-runoff model (GR2M) and the lake level model. It shows the difficulty to reconcile lake level records from paleohydrological modeling. The detection of thermonuclear 36Cl together with stable isotopic composition of groundwaters allow to draw the present-day recharge distribution in the Quaternary aquifer. Present-day recharge occurs close to surface waters in 60% of the groundwater sampled and an evaporation between 85 and 98% of waters in the surrounding of Lake Chad is estimated. Groundwaters with a contrasted geochemical signature are stored in the center of the piezometric depressions, suggesting no present-day recharge. The deep waters of the CT, with water ages of 300 000 yr, show geochemical patterns indicative of an old and humid recharge period. These original data give new insights into paleorecharge in the Sahelian band

Lake(s), rivers and groundwater dynamics and interactions in the Lake Chad Basin : geochemical tracers and modeling

Le bassin endoréique du lac Tchad (BLT) couvre 2,5 millions de km2 au centre de la zone sahélienne. Le lac Tchad agit comme un amplificateur des variations climatiques sur le BLT tandis que le système aquifère multicouche contient d'importantes ressources en eau. La réponse hydro(géo)logique du BLT aux variations du climat est étudiée par un couplage entre traceurs géochimiques et modélisation. Un bilan hydrologique, chimique et isotopique permet de distinguer les flux d'évaporation, de transpiration et d'infiltration à la surface du lac. La transpiration, jusqu'alors négligée, contribue à environ 15% de l'ET. La dynamique du chlore dans le BLT suggère un temps de transfert dans le bassin amont autour de 10 ans, un renouvellement rapide des eaux du lac et une infiltration de 200 mm an-1. Le couplage d'un modèle pluie-débit (GR2M) et du modèle de lac, forcé par des simulations paléoclimatiques de GCM sur le dernier millénaire, montre la difficulté de la comparaison modèle-données dans les reconstitutions paléohydrologiques. La cartographie de la recharge moderne de l'aquifère quaternaire est obtenue par l'interprétation des teneurs en 36Cl thermonucléaire dans les eaux. Une recharge récente, proche des eaux de surface, est mise en évidence dans 60% de l'aquifère quaternaire et la reprise évaporatoire actuelle en bord du lac Tchad est évaluée entre 85 et 98%. Les eaux géochimiquement contrastées des dépressions piézométriques ne signent pas de recharge actuelle. La composition géochimique propre aux eaux du CT suggère un temps de résidence supérieur à 300 000 ans. Ces données originales pourraient servir à mieux contraindre la paléorecharge en zone sahélienne.Lake Chad Basin (LCB) is a 2.5 billion km2 closed drainage basin, in the center of Africa. Lake Chad enhances the climatic variations over the LCB while the multi-layers aquifer system contains large water resources. The hydro(geo)logical response of the LCB to climatic variability is studied by combining geochemical and modeling approaches. The lake Chad levels modeling, calibrated from hydrological, chemical and isotopic data, allows to disentangle evaporation from transpiration and from infiltration. Transpiration, neglected in previous studies, accounts for 15% of the total ET. From the chlorine dynamic in the LCB, a transit time of 10 yr in the upper basin, a short renewal rate of lake waters and their infiltration toward the aquifer are estimated. GCM paleoclimatic simulations over the last millennium were introduced into a rainfall-runoff model (GR2M) and the lake level model. It shows the difficulty to reconcile lake level records from paleohydrological modeling. The detection of thermonuclear 36Cl together with stable isotopic composition of groundwaters allow to draw the present-day recharge distribution in the Quaternary aquifer. Present-day recharge occurs close to surface waters in 60% of the groundwater sampled and an evaporation between 85 and 98% of waters in the surrounding of Lake Chad is estimated. Groundwaters with a contrasted geochemical signature are stored in the center of the piezometric depressions, suggesting no present-day recharge. The deep waters of the CT, with water ages of 300 000 yr, show geochemical patterns indicative of an old and humid recharge period. These original data give new insights into paleorecharge in the Sahelian band

Holocene North African Climate

During the Holocene, that is, the last 11,500 years, the North African climate has undergone significant changes. While the Sahara is now the largest desert on Earth, there used to be a “Green Sahara” at the beginning of the Holocene. It resulted from significant precipitations that were linked to the northward shift of the inter-tropical convergence zone, which was caused by the increase in summer insolation in the northern hemisphere. Holocene lacustrine deposits from Hassi El Medjna, Gran..

Climat de l’Afrique du Nord pendant l’Holocène

Dépôts lacustres holocènes de Hassi El Medjna, Grand Erg Occidental, Algérie Au cours de l’Holocène, c’est-à-dire les 11 500 dernières années, le climat de l’Afrique du Nord a connu d’importants changements.Alors qu’aujourd’hui le Sahara est le plus vaste désert du monde, il y avait un « Sahara Vert » au début de l’Holocène, du fait d’importantes précipitations liées à la migration vers le Nord de la zone de convergence intertropicale, sous l’effet d’une augmentation de l’insolation estivale ..

Campaspe Catchment SW and GW Data (2016-2017)

This dataset is made available with a Creative Commons, Attribution license 4.0 International License. Copyright Flinders UniveristyThe dataset consists of Campaspe River discharge data as well as Campaspe river and groundwater geochemical data (major ions, water stable isotopes, 222 Radon) measured by our team between 2016 and 2017. The dataset also contains a link to all relevant information regarding the numerical model

Suprapermafrost groundwater transfers high concentrations of aged dissolved organic carbon to Greenlandic rivers

International audienceClimate change is rapidly altering northern watersheds by disrupting large amounts of water and materials stored in glaciers, snow cover and permafrost. Permafrost thaw enhances the connectivity between surface and deeper water pathways and increases the suprapermafrost groundwater (SPGW) contribution to Arctic river discharge. SPGW, which can originate from permafrost thaw or infiltrated rain waters, participates to the transfer of water and carbon in Arctic catchments. However, the coupling of the water and carbon cycles in SPGW are not quantified, while it can modulate the permafrost climate feedback. Here, we investigate the origin and water transit time of SPGW and quantify and characterize dissolved organic matter (DOM) in the Zackenberg valley (Northeastern Greenland). We aim to quantify SPGW fluxes contribution to river water and carbon exports. In August 2021, we collected water samples from the glacio-nival Zackenberg river, its tributaries and a small nival headwater stream (Graense). SPGW was sampled from wells along transects from soils to river channels. Water samples were analysed for water isotopes (2H, 18O), dissolved gases (222-Rn, SF6, CFCs), dissolved organic carbon (DOC) concentration, radiocarbon ages (Δ 14 C), and DOM optical properties. A significant contribution of young-SPGW to rivers is estimated from dissolved gases. Contrasted DOC concentrations, DOM properties and Δ 14 C are observed between SPGW, hyporheic and river waters, with consistently higher concentrations and older DOC in subsurface flows. DOM optical properties evolve significantly from soils to rivers and along stream channels. Hyporheic waters displayed an enrichment in proteinaceous organic compounds illustrating their role as hotspots for microbial activity where intense DOM processing occurs. This dataset provides unique insights into SPGW role in hydrological and biogeochemical cycles in Arctic permafrost ecosystems

Dilution of reactive plumes: evolution of concentration statistics under diffusion and nonlinear reaction

International audienceConcentration fields of solutes in porous media often exhibit large fluctuations, driven by physical and chemical heterogeneity from the pore to the Darcy scale. For many applications, ranging from reactive transport modeling to toxicology, the knowledge of mean concentrations is not sufficient, and quantifying concentration variability is necessary. The probability density function Highlights • We introduce a general framework quantifying the link between concentration PDFs and spatial concentration profiles. • We derive a dynamical equation for the evolution of the concentration PDF under diffusion and nonlinear reaction in 1D. • We derive analytical predictions for the concentration PDF and its moments using a weakcoupling approximation