Approche décisionnelle géospatiale et multicritère dans l’identification des zones potentielles de recharge des eaux souterraines : cas du bassin versant du Mayo Bocki au Nord Cameroun

La présente étude a été effectuée pour déterminer les zones potentielles de recharge des eaux souterraines. Pour ce faire, la démarche  méthodologique était basée sur l’analyse multicritère associée aux techniques géospatiales. Les données utilisées étaient entre autres les images  satellitaires, les fonds cartographiques, les données pluviométriques et les niveaux statiques. Ces données ont permis d’exprimer sous forme de  carte thématique les facteurs régissant la recharge (pente, drainage, lithologie, fracturation, sol, pluviométrie et occupation du sol). L’analyse de  sensibilité par suppression d’un paramètre a permis d’établir l’ordre d’influence suivant : Lit > Sol > AACH > Df > Pl > Pe > Dd > OS. Le croisement de  tous ces paramètres après pondération a conduit à l’élaboration de la carte qui montre que les zones à ort potentiel occupent 3 % de la zone d’étude  pendant que les zones de faible à faible potentialité sont de l’ordre de 58 % dans le bassin. Les zones à potentialité moyenne quant à elles  représentent 39%. Ce support cartographique constitue indéniablement un outil d’aide à la décision pour les gestionnaires de l’eau.   This study was carried out to determine potential groundwater recharge areas. To do this, the methodological approach was based on multi-criteria  analysis associated with geospatial techniques. The data used were, among others, satellite images, base maps, rainfall data and static levels. These  data made it possible to express in the form of a thematic map the factors governing the recharge (slope, drainage, lithology, fracturing, soil,  rainfall and land use). The sensitivity analysis by deletion of a parameter made it possible to establish the following order of influence: Lit > Sol  > AACH > Df > Pl > Pe > Dd > OS. The crossing of all these parameters after weighting led to the development of the map of potential recharge zones  which revealed that the zones with high potential occupy 3% of the study zone while the zones with low to low potentiality are around 58% in  the basin. Areas with average potential represent 39%. This cartographic support is undeniably a decision-making tool for water managers

Postharvest Adaptation Strategies to the Effects of Temperature Variations and Farmer-Miller Practices on the Physical Quality of Rice in Cameroon

In order to develop simple and adaptable measures to reduce the impact of changing climatic con ditions and poor postharvest practices on grain quality, data on temperature and postharvest practices were collected and correlated with physical grain quality parameters for 3 rice devel opment hubs (Ndop, Lagdo and Mbam) in Cameroon. Inter-annual variations in temperature and thermal amplitudes were the highest in Ndop followed by Mbam and the least in Lagdo. When the same rice variety was grown in the hubs and milled with a laboratory hand dehusker, the mean chalky score was highest in Ndop (18%) and least in Mbam (11%). In addition, Ndop recorded higher grain fissures and broken fractions compared to Mbam or Lagdo. Positive correlations were observed between thermal amplitudes, grain fissures and the proportion of broken fractions. However, rice milled using commercial mills located in the hubs recorded the highest broken frac tions in Mbam (54% - 63%), followed by Lagdo (43% - 52%) and the least in Ndop (35% - 38%). The type of mills in the hubs was responsible for these differences as Mbam had only Engelberg types mills that recorded higher broken fractions than in Ndop where only rubber roll mills were present (P < 0.05). Lagdo had a mixture of Engelberg and rubber roll mills and recorded interme diate broken fractions. Proper parboiling, recovery and processing of poorly filled and immature grains during parboiling and processing of low-grade and fine broken rice into product generally accepted by the local population were demonstrated as simple adaptation strategies to mitigatethe adverse effects of changing climatic conditions and poor postharvest practices on the physical quality of rice especially in sub-Saharan African countries

Transient fertilization of a post-Sturtian Snowball ocean margin with dissolved phosphate by clay minerals

Marine sedimentary rocks deposited across the Neoproterozoic Cryogenian Snowball interval, ~720-635 million years ago, suggest that post-Snowball fertilization of shallow continental margin seawater with phosphorus accelerated marine primary productivity, ocean-atmosphere oxygenation, and ultimately the rise of animals. However, the mechanisms that sourced and delivered bioavailable phosphate from land to the ocean are not fully understood. Here we demonstrate a causal relationship between clay mineral production by the melting Sturtian Snowball ice sheets and a short-lived increase in seawater phosphate bioavailability by at least 20-fold and oxygenation of an immediate post-Sturtian Snowball ocean margin. Bulk primary sediment inputs and inferred dissolved seawater phosphate dynamics point to a relatively low marine phosphate inventory that limited marine primary productivity and seawater oxygenation before the Sturtian glaciation, and again in the later stages of the succeeding interglacial greenhouse interval

Comparative Analysis for Estimating Hydraulic Conductivity Values to Improve the Estimation of Groundwater Recharge in Yaoundé-Cameroon

Climate change will deeply affect the precipitation and evapotranspiration around the world. The sustainability of groundwater resources is crucial for regional and local communities, which is intimately tied to the changing recharge rate. To accurately assess the recharge rate, different methods were used to estimate hydraulic conductivity of an unconfined aquifer in this study. Particle size method with four empirical formulae, together with in-situ aquifer tests and the inverse modelling techniques were integrated to evaluate their potential for the determination of hydraulic conductivity of unconsolidated aquifer materials in order to improve groundwater recharge estimation. Results showed a wide disparity between the granulometric estimates of the hydraulic conductivity and the in-situ and modelling techniques. Slug test values range from 5.13 x 10-6 m/s to 4.96 x 10-5 m/s whereas the infiltration test (Porchet method) results vary from 1.91 x 10-7 m/s to 1.16 x 10-6 m/s. The simulated hydraulic conductivity values range from 2.54 x 10-7 m/s to 6.36 x 10-7 m/s, with a decreasing trend in the northeast-southwest (NE-SW) direction. The infiltration method appeared to be better than the granulometric one in the estimation of the vertical hydraulic conductivity within the unsaturated zone of porous formations. This study also pointed out that within an anisotropic formation, the hydraulic conductivity ratio (Kv/Kh) should not always be taken as equal to 10. Specific tests should be implemented to access this value in a given aquifer.The inverse modelling results showed the net recharge values varying from 68.5 mm/yr to 180 mm/yr. The modelling technique appears to be consistent with the in-situ estimates. Therefore, the application of groundwater modelling tool in this study has shown excellent promise for characterizing the spatial distribution of hydraulic conductivity and net recharge values within the targeted aquifer system

Comparative Analysis for Estimating Hydraulic Conductivity Values to Improve the Estimation of Groundwater Recharge in Yaoundé-Cameroon

Climate change will deeply affect the precipitation and evapotranspiration around the world. The sustainability of groundwater resources is crucial for regional and local communities, which is intimately tied to the changing recharge rate. To accurately assess the recharge rate, different methods were used to estimate hydraulic conductivity of an unconfined aquifer in this study. Particle size method with four empirical formulae, together with in-situ aquifer tests and the inverse modelling techniques were integrated to evaluate their potential for the determination of hydraulic conductivity of unconsolidated aquifer materials in order to improve groundwater recharge estimation. Results showed a wide disparity between the granulometric estimates of the hydraulic conductivity and the in-situ and modelling techniques. Slug test values range from 5.13 x 10-6 m/s to 4.96 x 10-5 m/s whereas the infiltration test (Porchet method) results vary from 1.91 x 10-7 m/s to 1.16 x 10-6 m/s. The simulated hydraulic conductivity values range from 2.54 x 10-7 m/s to 6.36 x 10-7 m/s, with a decreasing trend in the northeast-southwest (NE-SW) direction. The infiltration method appeared to be better than the granulometric one in the estimation of the vertical hydraulic conductivity within the unsaturated zone of porous formations. This study also pointed out that within an anisotropic formation, the hydraulic conductivity ratio (Kv/Kh) should not always be taken as equal to 10. Specific tests should be implemented to access this value in a given aquifer.The inverse modelling results showed the net recharge values varying from 68.5 mm/yr to 180 mm/yr. The modelling technique appears to be consistent with the in-situ estimates. Therefore, the application of groundwater modelling tool in this study has shown excellent promise for characterizing the spatial distribution of hydraulic conductivity and net recharge values within the targeted aquifer system

Shallow groundwater quality evolution after 20 years of exploitation in the southern Lake Chad: hydrochemistry and stable isotopes survey in the far north of Cameroon

International audienc