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Mapping groundwater recharge in Africa from ground observations and implications for water security
No full textGroundwater forms the basis of water supplies across much of Africa and its development is rising as demand for secure water increases. Recharge rates are a key component for assessing groundwater development potential, but have not been mapped across Africa, other than from global models. Here we quantify long-term average (LTA) distributed groundwater recharge rates across Africa for the period 1970-2019 from 134 ground-based estimates and upscaled statistically. Natural diffuse and local focussed recharge, where this mechanism is widespread, are included but discrete leakage from large rivers, lakes or from irrigation are excluded. We find that measurable LTA recharge is found in most environments with average decadal recharge depths in arid and semi-arid areas of 60 mm (30-140 mm) and 200 mm (90-430 mm) respectively. A linear mixed model shows that at the scale of the African continent only LTA rainfall is related to LTA recharge-the inclusion of other climate and terrestrial factors do not improve the model. Kriging methods indicate spatial dependency to 900 km suggesting that factors other than LTA rainfall are important at local scales. We estimate that average decadal recharge in Africa is 15 000 km(3) (4900-45 000 km(3)), approximately 2% of estimated groundwater storage across the continent, but is characterised by stark variability between high-storage/low-recharge sedimentary aquifers in North Africa, and low-storage/high-recharge weathered crystalline-rock aquifers across much of tropical Africa. African water security is greatly enhanced by this distribution, as many countries with low recharge possess substantial groundwater storage, whereas countries with low storage experience high, regular recharge. The dataset provides a first, ground-based approximation of the renewability of groundwater storage in Africa and can be used to refine and validate global and continental hydrological models while also providing a baseline against future change
Biochar as a strategy to manage plant diseases caused by pathogens inhabiting the soil : a critical review
No full textThe current agricultural scenario faces a range of challenges, with phytosanitary ones being paramount. In most cases, plant diseases are treated with chemicals; however, they cause environmental pollution and face the acquired resistance of pathogens. Alternatively, biochar is a valuable tool for inducing the systemic resistance of plants since it is an effective and widely used resource to improve the physical, chemical, and biological attributes of the soil, consequently providing an adequate environment for healthy plant development. The effectiveness of the application of biochar in the control of plant diseases has been attributed to its alkaline pH, which contributes to the growth of beneficial microorganisms and increases the availability of nutrients, and to its porous structure, which provides a habitat and protection for the development of the soil microbiome. Therefore, the combined effect of improvements to soil attributes through biochar creates its role in controlling pathogens. This review assesses the beneficial and potential effects of biochar in agricultural soils, as well as showing the positive effects of biochar in the management of soil pathogens. Besides, we deeply evaluate twenty papers that used biochar as a strategy to manage plant diseases caused by pathogens inhabiting the soil in different soil-pathogen-plant systems. Among these studies, 70 % validate biochar as a strategy for the management of plant diseases; 10 % of studies showed that the efficiency of biochar as a disease management tool depends on the type of feedstock, and 20 % of studies describes that the biochar is not a management tool for suppressive diseases, caused by Pythium ultimum and Rhizoctonia solani in some host plants. The biochar is a strategy to manage plant diseases caused by pathogens inhabiting the soil, due different mechanisms as fungitoxic effect of biochar, sorption of allelopathic and phytotoxic compounds that can harm the plant, induction of plant resistance, increase of activities and abundance of beneficial microorganism's, changes in soil quality as nutrient availability and abiotic conditions
Tropical Indian Ocean and ENSO relationships in a changed climate
No full textWe explore the current (1958-2005 period) and near future (2006-2050 period) teleconnections between El Nino Southern Oscillation (ENSO), Indian Ocean Basin Mode (IOBM), and Indian Ocean Dipole (IOD) as simulated in historical and Representative Concentration Pathway (RCP8.5) simulations of 32 coupled models that participated in the phase five of Coupled Model Intercomparison Project (CMIP5). A set of 16 CMIP5 models out of 32 models, which perform best to simulate tropical climate variability in recent decades, is first selected using a robust method based on the Empirical Orthogonal Function analysis for detailed analysis. Most of these models show modest capability in reproducing the seasonal cycle of ENSO types in the current period. Further, amplitude of Indian Ocean (IO) modes is overestimated by the 16 models along with large inter-model spread. Based on these results, a subset of 9 models is formed, which simulate a realistic seasonal phase-locking of ENSO for a robust assessment of future teleconnections. No significant change in El Nino amplitude is detected in near future. However, the IOBM is projected to be weaker during late spring and early summer. The IOD is projected to be stronger during boreal summer in the future relative to the current period. We also investigate if there are any changes from historical to RCP 8.5 simulations in the strength of the IO negative feedback on ENSO with a multiple linear regression approach. The IO negative feedback strengthens significantly in the RCP8.5 scenario due to the increasing role of IOBM in speeding the transition from El Nino to La Nina, despite its reduction of amplitude. In contrast, IOD loses its predictive value in the future projections
Neurodevelopmental assessment at one year of age predicts neuropsychological performance at six years in a cohort of West African children
No full textRural children from Benin, west Africa were evaluated with the Mullen Scales of Early Learning (MSEL) at one year of age and then at six years with the Kaufman Assessment Battery for Children (KABC-II), the visual computerized Tests of Variables of Attention (TOVA), and the Bruininks-Oseretsky Test (BOT-2) of motor proficiency (N = 568). Although both the MSEL and KABC-II were available to the assessors in French, instructions to the mother/child were in local language of Fon. Mothers were evaluated with the Edinburgh Postpartum Depression Scale (EPDS), Caldwell HOME Scale, educational level and literacy, and a Socio-Economic Scale - also in their local language (Fon). After adjusting for maternal factors, MSEL cognitive composite was correlated with KABC-II with moderate effect sizes, but not with TOVA scores. Overall eta-squared effect for the multivariate models were moderately to strongly correlated (.07 to .37). Neurodevelopmental assessments in early childhood adapted cross-culturally are predictive of school-age neuropsychological cognitive ability
On the threshold of release of confinement in an epidemic SEIR model taking into account the protective effect of mask
No full textWe present a classic SEIR model taking into account the daily movements of individuals in different places. The model also takes into account partial confinement of individuals. This model is coupled with a model of protection against the epidemic by the use of masks. We are studying the effects of combined confinement and protection measures on the dynamics of the epidemic. We consider a constant proportion of asymptomatic people. We assume that symptomatic infected people may change their urban travel behavior due to the disease which causes them to travel less to places where they used to move and to stay at home more often. We present a sensitivity study with respect to the parameters. We show that the combination of the use of masks with almost complete release of confinement makes it possible to avoid the occurrence of a secondary peak of the epidemic. The model predicts that a total release of confinement can be successful for an epidemic of R0=2.5 if on average a proportion of 60% of the population wears masks of 60% efficacy. However, if 10% of the population remains confined, the same goal can be achieved with a proportion of 80% of the population wearing masks with efficacy of the order of 40%
Molecular detection of microorganisms in lice collected from farm animals in Northeastern Algeria
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Les leçons du programme de lutte contre les vecteurs du paludisme par aspersions intradomiciliaires de DDT ou de dieldrine dans la zone pilote de Bobo-Dioulasso : échec ou succès ?
No full textPendant cinq ans, à partir de 1953, un grand programme d'aspersions pariétales intradomiciliaires s'est déroulé dans la zone pilote de Bobo-Dioulasso avec du DDT ou de la dieldrine (DLN) avec une évaluation conceptuellement entomologique et parasitologique [18].
Par rapport à la zone témoin, le DDT a induit une réduction d'environ 95 % et 67 % du taux de piqûres d'Anopheles gambiae, respectivement à l'intérieur et à l'extérieur des maisons. Mais du fait de son action irritante, le DDT a augmenté de cinq fois le coefficient d'exophagie de ce vecteur. La DLN n'a eu aucun impact sur le taux de piqûres d'An. gambiae aussi bien à l'intérieur qu'à l'extérieur, vu la résistance de l'espèce anophélienne à cet insecticide. L'indice sporozoïtique d'An. gambiae a été réduit de 96 % dans les zones traitées au DDT et de 70 % dans le secteur traité à la DLN.
Le DDT a réduit de 98 % et de 91 % le taux de piqûres d'Anopheles funestus, respectivement dans les maisons traitées et à l'extérieur. Avec la DLN, ces réductions ont été respectivement de 98 % et 97 %. L'indice sporozoïtique d'An. funestus a été réduit de 95 % dans les zones traitées au DDT.
La lutte antivectorielle a permis de réduire la transmission due à An. gambiae et An. funestus de quelques 99,8 % dans les villages traités au DDT par rapport aux villages témoins. La DLN a permis de réduire de 99,9 % la transmission due à An. funestus, mais quasiment pas celle due à An. gambiae. La lutte antivectorielle basée sur les aspersions intradomiciliaires de DDT ou de DLN a permis de réduire de 99,9 % la transmission des Plasmodium humains assurée par les deux vecteurs majeurs, An. gambiae et An. funestus dans les villages de la zone pilote.
Chez les enfants de 2-9 ans l'indice splénique a été de 84,3 % (n= 979) en zone témoin et 44,4 % (n=8920) en zones traitées (différence : -47,3 %), la prévalence plasmodiale a été de 60,6 % (n=946) en zone témoin et 38,0 % (n=7242) en zones traitées (différence : – 37 %) mais les indices gamétocytiques sont restés aux mêmes niveaux (3,28 %, n = 946 en zone témoin et 3,04 %, n = 7242 en zones traitées) indiquant le maintien du "réservoir de virus" et des possibilités de transmission.
Par rapport à la zone témoin, "l'indice de contamination nouvelle" a été significativement moindre chez les nourrissons de 0-3 mois et de 4 à 6 mois dans les villages traités au DDT mais pas chez les nourrissons 7 à 12 mois démontrant que la lutte antivectorielle avait eu une certaine efficacité dans la prévention de l'infection plasmodiale mais "tous les nouveau-nés étaient infectés dans l'année", donc la transmission de P. falciparum n'avait pas été complètement stoppée.
Les aspersions intradomiciliaires avec le DDT ont été d'une grande efficacité dans la réduction de la transmission mais les vecteurs sont restés présents et la transmission, même fortement réduite, s'est maintenue de sorte que dans l'optique de l'éradication, le programme avait été considéré comme un "semi–échec" avec la décision d'adopter un changement complet de stratégie de lutte contre le paludisme et de se centrer sur la chimiothérapie de masse plutôt que sur la lutte antivectorielle.
Ces opérations de lutte antivectorielle d'aspersions pariétales de DDT peuvent être considérées comme un succès entomologique, avec ses limites indiquées par le maintien d'un certain niveau de transmission et des indices spléniques et plasmodiques ainsi que d'une incidence observée chez les nourrissons. Cinquante ans après, en l'absence de vaccins, cette recommandation de lutte intégrée et coordonnée contre les vecteurs et les Plasmodium est toujours d'actualité en bénéficiant, entre autres, des moustiquaires imprégnées et des traitements à base d'artémisine
Impact of traditional processing on proximate composition, folate, mineral, phytate, and alpha-galacto-oligosaccharide contents of two West African cowpea (Vigna unguiculata L. Walp) based doughnuts
No full textDoughnuts made from cowpea, a highly nutritious pulse, are frequently consumed in West Africa. As processing may affect their nutritional composition, cowpea processing into two doughnut types (ata and ata-doco) was characterized, and samples collected from 12 producers in Cotonou, Benin. Proximate composition, folate, mineral, phytate, and alpha-galacto-oligosaccharide contents were determined in the raw material, intermediate products, and doughnuts. Mass balance was assessed during ata production to monitor folate and alpha-galacto-oligosaccharides distribution, and to determine what steps most influenced their concentration. Ata was prepared with dehulled-soaked seeds, and ata-doco with whole or partially dehulled, non-soaked and dry-milled seeds. After both types of doughnuts production, lipid content increased by 11-33 times compared with raw seeds, due to oil absorption during deep-frying. Milling led to an increase of iron content by 50-57 % (ata) and 21-75 % (ata-doco production). Alpha-galacto-oligosaccharide contents decreased by 22-57 % after whipping during ata-doco, but not during ata production. The mass balance assessment showed significant reductions of folate (-50 %) and alpha-galacto-oligosaccharides (-33 %) after dehulled seed washing and soaking during ata production. This study showed that the impact of traditional processing on the nutritional value of cowpea-based doughnuts is strong, but highly variable depending on the doughnut type and producers' practices