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The coastal flanks of Mt Etinde is wedged between the sea and the southwestern slope of Mt Cameroon. The only fresh water resources available for multipurpose uses in this area are mountain springs and streams that drain volcanic materials. To access the sources, processes and assess the ecological risk associated with hydrochemicals and heavy metals in these mountain water resources, 18 water samples were collected in different seasons at 4 locations between may 2009 and december 2010 for major ions and heavy metals determination. The sampled waters ranged from neutral to slithly alkaline, weakly mineralized and dominated by Ca–Mg–HCO3 water type irrespective of season. The hydrochemical ratios revealed ions chemistry mostly influenced by geogenic source of silicate rock weathering and atmospheric inputs. Sampled waters had low concentration of heavy metals which are less mobile in the aqueous phase, controlled by hydraulic condition. Geochemical processes of mineral dissolution and reverse ion exchange coupled with hydrodynamic processes of flushing at the weathering front and soil leaching are the main controls on the water chemistry in the area. Despite agricultural and other anthropogenic activities, quality indices in the study area indicate the absence of anthropogenic inputs. Key words: Major ions, heavy metals, rocks weathering, soil leaching, water quality assessment.

The regional Quaternary aquifer of the Lake Chad Basin represents a major resource crossing several countries in the Sahel region. It is intensively used for many purposes, including drinking water supply, domestic uses, breeding and irrigation. However, this resource already undergone the climate change effects and the strong pressure of human activities. For instance, some authors shown that in Cameroon, the NO3- contents have increased by a factor of six between 1993 and 2013. It is therefore urgent to propose pragmatic water management strategies in this region, which will be based on a total understanding of the aquifer functioning. To achieve this objective, major ions chemistry and isotopic tools were combined. It is the first time that a such multi-proxy study is conducted in the region. Chemical analyses revealed that the geogenic influence is marked by dissolution, hydrolysis of silicate minerals, and possible cation exchanges. The nitrates content up to 1500 mg/l confirm the high impact of anthropogenic activities on this resource. Water stable isotopes show the contribution of surface water in addition to actual rainwater, in the recharge of the aquifer while 3H and 14C highlight that the Quaternary aquifer gathers both recent and old groundwater (~1500 years). Above all, these radioactive tracers helped to identify the different flow paths: a shallower one (under an active recharge from river and rainwater), a deep one (with the lowest concentrations in 3H and 14C, more protected from surface pollutants and dominated by geogenic processes) and an intermediate level attesting a mixing between the deep and shallower levels. Finally, thanks to δ15N-NO3 and δ18O-NO3 three main sources of nitrates were identified: (i) deposits of nitrogenous organic matter (animal excrement, manure, household waste); (ii) naturally synthesized nitrate in the soil; and (iii) nitrate from nutrients of the paleo-sea. A conceptual model of the regional Quaternary aquifer can then now be proposed in 02 points: (i) the existence of distinct flow paths with the deep one which is strategic especially for drinking purpose and (ii) the dependence of the aquifer to perennial rivers.

This work explores the possibility of using Mine tailing (MT) as a feedstock in the synthesis of phosphate geopolymer binder. MT was activated at different concentrations of phosphoric acid (4, 6, 8, 10 and 12 M). The modification of the Si/Al weight ratio was done by the incorporation of 5, 10, 15, 20 and 25 wt% of calcined kaolinite (CK). After 28 days of curing, the products obtained were analyzed using XRD, FTIR, compressive strength and water absorption. The results of the XRD and FTIR analyses reveal a partial dissolution of the crystalline phase of iron oxide in this medium and the formation of aluminium phosphate hydrate as new crystalline phase. The optimum values of compressive strength (45.5 MPa) and water absorption (3.0 %) show that the binder obtained by activation with 6 M phosphoric acid and 10 wt% CK incorporation can be used in the manufacture of structural materials. Acid activation of MT thus appears as an innovative way to recycle these fine wastes in the synthesis of geopolymer.

This paper investigates the resistance of alkali-activated binder from volcanic ash (VA) + Municipal Solid Waste Incinerator Fly Ash (MSWI-FA) system exposed into sulphuric acid solution and artificial seawater at 56 days. The effect of these aggressive media on the physical, structural, mechanical and microstructural properties of alkali-activated mortars was discussed. The degradation was studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The decrease of compressive strength after 56 days was 9.10%, 22.08%, 32.5% in artificial seawater, 2% H2SO4 and 4% H2SO4, respectively. The loss of strength in both media is primarily due to the fact that the water molecules present in these media penetrated into the pore cavities between binders and aggregates, making them weak. In an acidic medium, it is also due to the decalcification and depolymerization reactions whereas in seawater medium, it is attributed to the movement of content ions and probable formation of Friedel’s salt. The results disclose that VA + MSWI-FA based alkali activated materials resist better in seawater than in sulphuric acid solution. Synergistic use of volcanic ash and MSWI-FA for construction materials through alkaline activation looks like the upcoming trend to valorize these wastes.

The Mungo River and its tributaries represent the major sources of water supply for agriculture and drinking purposes for the Douala city and the south western agricultural region of Cameroon. In this study, the surface water hydrochemistry was investigated at 12 locations to determine the hydrochemical and heavy metals characteristics and to assess the suitability for drinking and irrigational purposes. Results of water samples collected along the main channel and tributaries showed that the major ions were dominated by Ca2+ > Na+ > Mg2+ > K+ > NH4+ and > HCO3- > SO42- > Cl- > F- > PO43- , with concentrations varying between 0 to 60 mg/l. Heavy metal concentrations were relatively weak, dominated by Fe > Mn > As > Cd > Zn > Se. The main hydrochemical facies types revealed primarily 52% Ca-Na-HCO3 and 48% Ca-Mg-HCO3. Base on Gibbs diagram and relative ion ratios, the hydrochemical characteristics are derived from weathering of silicate rocks and atmospheric source. The influence of anthropogenic factors including agro-industrial activities on the hydrochemical characteristics was less marked. The chemical composition of the water samples was compared with the drinking water standards and only the concentration of Fe was above the WHO guide limits in a single sample at Passi. The evaluation of the water quality for irrigation showed that 95% of water samples are suitable for irrigation in almost all soil types. According to the water quality index (HPI, HEI and Cd), this water is considered of excellent quality for consumption. The results provide a preliminary database for sustainable management of water resource in the Mungo River basin.

A major flood event occurred on 21 August 2020 in the densely populated Makèpè Missokè neighborhood in the city of Douala (Cameroon, Africa). Nearly 2210 buildings and 12,376 victims spread over 82 hectares were affected. A 2D HEC-RAS model is applied to simulate and characterize this event. A cross analysis of flood depth and flow velocity is used to classify the flood risk and identify areas exposed from low to high hazard. The simulations provide detailed information on the flood characteristics (extent, depth, velocity, arrival time, and duration). The simulated maximum water surface profiles are consistent with the floods marks with differences ranging from 0.02 m to 0.44 m, indicating a good agreement between the observed and simulated water levels at the peak flow (NSE = 0.94, Erel = 0.92, RMSE = 0.21 m). The maximum inundation level is 4.48 m and the flow velocity is globally low at less than 1 m/s. The average flood arrival time and duration are 5 h and 26 h, respectively, for a threshold height of 0.5 m. These results indicate a fast mobilization of the major river channel for the evacuation of this flood. The level of accuracy of the developed model of the 21 August 2020 flood event is appropriate for flood hazard assessment in the city of Douala and is designed to find operational application in future events.

The Ekomedion two-mica granite, southwestern Cameroon, has potential for uranium and molybdenum mineralization. Here, we present LA-ICP-MS U–Pb ages, Lu–Hf isotope characteristics, trace element concentrations and Ti-geothermometry of zircon from this granite hosting U–Mo mineralization in pegmatitic pods. The majority of zircon are CL-dark though some CL-bright cores were also identified. U–Pb zircon age data range from 121 ± 3 to 743 ± 11 Ma with only 5 of 34 ages being near concordant. The concordant mean age of 603 ± 12 Ma is similar to ages of granitic intrusions along the Central African Shear Zone in Cameroon. Apparent ages with mean of 261 ± 6 Ma reveal open system behavior with respect to Pb and/or U. Zircon eHfi values range from − 20.3 to − 0.3. This implies that U–Mo was remobilized during partial melting of the surrounding gneiss. Zircon Th/U > 0.1 as well as an increasing Hf with decreasing Th/U indicates that fractional crystallization was the main factor that controlled U–Mo mineralization in pegmatitic pods. Y and Y/Ho ratios cluster from 29 to 33 close to the chondritic ratio of 28 and indicate fractionation of Y and Ho with low F contents during the earliest stages of crystallization. Late stage accumulation of F-rich magmatic-hydrothermal fluids impacted U–Mo mineralization as a ligand. Zircon contains a prominent negative Eu anomaly pointing to a fractionating system rich in plagioclase. Calculated Ti-in-zircon temperatures span 672 °C to 1232 °C with the temperatures at the high end reflecting interference from mineral inclusions in the zircon grains while the lower temperature values are linked to crystallization.

In this work, municipal solid waste incinerator fly ash (MSWI-FA) was used as precursor to alter the reactivity of low reactive volcanic ash (VA) for alkali-activated cement synthesised. The effects of various proportions of MSWI-FA (0, 5, 10, 15 and 20%) on the final properties of the inorganic polymer are reported. The increase in MSWI-FA content increases the heat of reaction in MSWI-FA as the result of the reaction between the amorphous alumina-silica and the Ca-rich precursor. Isothermal conduction calorimetry, FTIR, XRD SEM/EDS, and physico-mechanical analyses were used to follow up the different formulations. New crystalline phases, namely Margarite (CaAl2 (Al2Si2)O10(OH)2, PDF#04-013-3004), Mordernite-(Ca) ((Ca, Na2, K2)(Al2 Si10 O24)·7H2O, PDF#00-011-0155) and Thernadite (Na2SO4, PDF#01-074-2036) confirm the good reactivity. The SEM/EDS exhibited the coexistence of C–S(-N-A)–H and N-A-S-H gels in binary system alkali-activated. The compressive strength and bulk density ranged from 9.38 to 21.07 MPa and from 1.56 to 1.77 g/cm3, respectively. These results indicated the possibility to use VA and MSWI-FA to synthesize room temperature alkali-activated matrices applicable in the manufacture of structural and functional materials. MSWI-FA appears energy-efficient and sustainable solution for the improvement of the volcanic ash based alkaline activated materials.

A survey using the electrical resistivity and test pit methods is carried out in the Douala subbasin in order to investigate the sub-surface layering and evaluate the thickness of each layer through the variation of the resistivity with the depth. Applying the Schumberger array, a total of 48 vertical electrical sounding is conducted along 8 profiles directed W-E and using traditional method, 25 test pits with depth between 15 and 19 meters are done. Qualitative interpretation is carried out through the resistivity and test pit maps. The test pit maps reveal the presence of the following layers: The first layer of thickness varies from 0.2 to 2.0 m (average of 1.9 m). The thickness of the second layer varies between 0.2 and 4.0 m with an average of 2.8 m. The thickness of the third layer is between 2.0 and 4.0 m with an average of 3.8 m. That of the fourth and fifth layers ranges respectively between 4.0 and 6.0 m (average of 5.4 m) and between 2.0 and 6.0 m with an average of 4.4 m. Isoresistivities maps from resistivities computed for different AB/2 values (1.5; 4.4; 13.5; 19; 27.5; 58 m) are generally characterized by the apparent resistivities which define many domains in function of the AB/2 values. The superficial layer is characterized by electric resistivity values ranging from 720 to 2073 Ωm for AB/2 = 1.5 m and probably represents pedologic materials. For other values of AB/2, resistivity varies from 253 to 32,381 Ωm (AB/2 = 4.4 m), 0.1 to 1838 (AB/2 = 13.2 m) with an average of 341 Ωm, 0.3 to 1608 Ωm (AB/2 = 19 m) with an average of 279 Ωm, 6.4 to 1427 Ωm (AB/2 = 27.5 m) with an average 291 Ωm, and 19.7 to 3555 Ωm (AB/2 = 58 m) with an average of 850 Ωm. These different values of resistivity represent the sedimentary materials.

International audience; Hydrological models are important tools for the simulation of water storage and hydrological fluxes in large basins and complex river systems. The hydrological models can compensate the lack of observed data in ungauged basins. In this study, the hydrological model of large basins MGB (for Model of Large Basins in Portuguese) is used to evaluate the hydrological processes of the Ogooué River Basin (ORB), which has been mostly unmonitored for about three decades. Simulations were carried out over an 18-year period from 1998 to 2015 using TRMM 3B42 daily rainfall data from the Tropical Rainfall Measurement Mission (TRMM) as forcing and in situ and altimetry-based river discharges from Envisat, Saral Altika and Jason-2 for calibration and validation. The results of the model were in good agreement with the flows measured at stations upstream and downstream of the Ogooué basin (Nash-Sutcliffe Efficiency (NSE) > 0.56 for all calibration gauges). The MGB model efficiently describes the seasonal and interannual variations of the flow in the Ogooué River and its major tributaries which were found to be highly correlated to the rainfall (r ranging from 0.72 to 0.90 and 0.56 to 0.87 at seasonal and interannual time-scales respectively). Interannual variations of precipitation and river discharge of the ORB are linked to the El Niño Southern Oscillation (ENSO) in the tropical eastern Pacific Ocean and southeastern tropical Atlantic Niño. Also, the Ogooué River discharge was found to be strongly correlated with Sea Surface Temperature (SST) at annual and semi-annual time-scales.

This study investigates the dominant orientations of lineament features and the relationship between these trends and the spatial orientation of tectonic structures in the transition zone of the Congo craton and the Pan African belt in South Cameroon area. Landsat 8 OLI/TIRS and hill-shaded images, constructed from 30 m-resolution SRTM-DEM data, were used for automatically extracting and mapping geological lineaments. Lineament features were analyzed by means of azimuth frequency and length density distributions. Three major sets of lineaments trending W–E, ENE-WSW and WNW-ESE are identified in the South Cameroon area. These trends are probably related to repeated reactivation of pre-existing crustal structures during Eburnean and Pan-African tectonic episodes. The lineaments were formed under the compressional tectonic stress regimes generated during these tectonic events.

12 pages; International audience; This study interprets 11 years (2006 to 2016) and 6 months (March to August in 2017) of respectively monthly and daily isotopic (δD and δ18O) monitoring of rain at Douala (Cameroon), a humid tropical station in Western Africa. The main scope is to analyze the climate controls on precipitation isotopes at different timescales. Firstly, we examine the annual cycles of δ18O. Over the 11 years of survey, the annual cycle exhibits a W shape that is quite reproducible from year to year, with two minima in spring and autumn periods. Based on back trajectory calculations and remote sensing observations of water vapor isotopic composition, we show that the observed depletion in spring and autumn is due to strong convective activity along air mass trajectories. The same effect of convective activity can be observed at the daily timescale. At seasonal and daily time scales, the isotopic composition is also strongly tied to the convective organization and cloud types. More depleted precipitation is associated with larger areas of high clouds. Very low to low clouds are observed in July-August, mid-level to high clouds are dominant in June and high to very high clouds characterize March-April-May, thus explaining the enriched (depleted) values in summer (spring). Finally, this paper highlights the importance of large scale meteorological conditions controls on precipitation stable isotope composition in the Gulf of Guinea.

Background: In Cameroon, the practice of market gardening exposes both the farmers and consumers to a certain number of health-related hazards. Environmental health risks associated to this activity showed that it was responsible for the increased of transmission risk of the human and animal intestinal worms. Methods: The epidemiology of soil borne diseases associated with urban agriculture was furthermore considered in three market garden sites of the city of Yaounde (Tsinga, Nkolondom, Nkolbisson). From October to December 2016, water and soils from rivers, wells and furrows were analysed for physicochemical characteristics and parasite identification using Kato-Katz and Formol-Ether methods. Results: Means of water parameters and parasite composition varied per locations and environments in the 82 samples analyzed. Ranges of mean temperature, pH, electrical conductivity, turbidity and color of water samples were 25.2-25.5°C (), 6.53-7.01 UC, 308-502 µS.cm-1, 637-1,300 FTU and 2,451-6,422 Co-Pt, respectively. Soil parasites consisted of 3 protozoans (Entamoeba histolytica, Sarcocystis sp. and Giardia intestinalis) and 11 helminths (Fasciola hepatica, Diphyllibotrium latum, Ascaris lumbricoides, Trichuirus trichiura, Ancylostoma sp., Trichostrongylus sp., Schistosoma mansoni, Schistosoma sp., Paragonimus westermanii, Strongyloides stercoralis and Hymenolepis nana). Conclusion: The presence of viable helminths suggests that harmful soil pathogens such as protozoans and helminths can spread through market gardening. This reminds on the need to find better ways to alleviate the control of intestinal parasitic infections which, nevertheless, are classified as neglected tropical diseases.

The study of changes in rocks due to interaction with hydrothermal fluids at active volcanoes provides insights into wall rock alteration associated with ore deposits formed in the geological past. Therefore, the nature of mineral alteration and chemical changes experienced by wall rocks can be investigated at eruptive sites on active volcanoes and the results used to better constrain ore-forming processes. In this study, we investigated the alteration at eruptive sites at Mount Cameroon volcano. These eruptive vents lie along NE-SW-trending fissures that define the Mount Cameroon rift. The vents are surrounded by cones composed largely of pyroclastic materials and to a lesser extent lava. Fumaroles (volcanic gases) rising through the vents during and after the 1999 eruption have resulted in the alteration of the pyroclastic robble along the fissures and the inner walls of the cones. Consequently, altered basaltic materials are covered with thin films of reddish, yellowish to whitish secondary minerals. These coatings result from an interaction between the surfaces of the basaltic glass with volcanically-derived acidic fluids. Petrographic investigations and XRD analysis of the basalts have identified primary mineral phases, such as olivine, pyroxene (mainly augite) and feldspars. Alteration products revealed include ubiquitous silica as well as gypsum, magnetite, feldspar, alunite and jarosite. Jarosite occurrence indicates that SO2 is the primary volcanically-derived acid source involved in coating formation. High contents of sulfur identified in the basalts indicate that melts at Mount Cameroon can be sulfur saturated as backed by previous melt inclusion data. Whole rock geochemical analysis shows a gain in silica in the altered samples and this ties with the mass balance calculations although minor gains of Al2O3, , MgO, MnO, CaO and K2O are shown by some samples.

We used high-resolution gravity data to analyse crustal structure beneath the Bangui Magnetic Anomaly (BMA) and the Chad Basin within the North-Central African region. Moho depths and effective elastic thickness values, calculated respectively by a regularized non-linear inversion method and by analysis of the coherence function between gravity and topography, have been interpreted with reference to seismic data , previous gravity studies and regional geology . Our aim is to determine the crustal architecture and to analyse its mechanical behaviour. Estimated Moho depths range from 30 to 43 km in the North-Central African region. Beneath the uplift zones (Adamawa-Yade plateau, Ouaddai, Tibesti, Hoggar, Tuareg shield) and the Congo Craton , the Moho depths range between 35 and 37 km. These values can be interpreted by tectonic and seismic events recorded along the regional shear zones; but also to the remobilization of the Precambrian basement. Analysis of the coherence function between the Bouguer gravity and the topography shows two different domains of rigidity: the highest values (100 km e values in Cameroon compared to others regions (Chad, Central African Republic, Niger, Egypt, Algeria) show the magnitude of these events on the crustal architecture. This being defined by the presence of cratonic cores, the Cameroon Volcanic Line (CVL) and hot spots as well as large regional shear zones, explain the fact that thermo-tectonic and seismic events that occurred at the northern edge of the Congo Craton in Cameroon, are more intense than in the Central African Republic. So according to the geodynamic process in Cameroon and Central African Republic, related to the hot spots along the CVL, thermo-tectonic and seismic events recorded along the regional shear zones (Sanaga Shear Zone and the Central Cameroon Shear Zone) and the Congo Craton, the BMA is associated to two different geotectonic contexts. The sources of the BMA are closely linked to the Congo Craton; they bottom should not exceed −37 km depth. The present results agree with previous studies which allow us to understand the evolution of the Saharan metacraton and the preservation of cratonic remnants (Murzuq, Al-Kufrah, Chad); similarly the estimated Moho depths is an important step that would serve as an input to model the sources of the Bangui Magnetic Anomaly.

The Bangui Magnetic Anomaly (BMA) is one of the largest magnetic anomalies in the world whose origin is still not known. This research investigated the crustal thickness , Curie depths and thermal structures in the Central African sub-regions – Cameroon, Central African Republic and adjacent countries – which are largely characterized by the Bangui Magnetic Anomaly. To achieve a better understanding and clearer idea of the location of the possible sources of the BMA, analyses of geothermal structures were conducted. Two potential methods were used: gravity to evaluate the crustal thickness and magnetics for geothermal analysis. Spectral analysis of gravity data shows that crustal thickness range between 14 and 55 km. The highest depths were found in Central African Republic. The lower values of crustal thickness were obtained in South-Chad basin with a minimum of roughly 14 km. Geothermal analysis is carried out using the Curie point depth, thermal gradient and heat-flow evaluations. The results show that the BMA is related to a thick crust of roughly 40 km. Depth to the bottom of possible sources does not exceed the lower crust. The mean Curie point depth estimated is 38 km with an error of ±2 km. Geothermal results also show the difference in the thermal behaviour between the crust in the Pan African and Precambrian domain. The mobile zone which constitutes the Pan African domain is associated with a thin crust of high heat-flow values of 65 mW/m 2. However, the Precambrian domain beneath the BMA is associated with a thick crust with lower heat-flow values (roughly 45 mW/m2). The difference between crustal thickness and Curie point depths shows that all the sources of the BMA are crustal. The present results are in favour of a geological origin for the Bangui Magnetic anomaly.

This study presents the ore texture, mineralogy and whole rock geochemistry of iron occurrence from the Edea North area located at the upper limit of the Nyong Unit, part of the Congo craton. This iron mineralization is of magnetite quartzite type enclosed by metamorphic rocks of the granulite facies. Two main facies have been identified over the study area including the banded and the massive facies. The mineralogical set of these facies is in majority represented by magnetite, quartz and pyroxene martite in addition to minor biotite, apatite, and amphibole. Magnetite presents as irregular and elongated minerals which can contain quartz inclusions of various shapes and sizes, as blasts clustering, around pyroxenes and isolated xenomorphic magnetite minerals in the silicate phases. Quartz varies from fine to coarse-grained and ribbon quartz. This indicates re-crystallization and deformation during metamorphism. Electron microprobe analysis on magnetite and martite show Fe2O3 contents that vary between 96.11 and 99.76. Whole rock chemical data showed that Fe-contents are as high as 62.9 wt%. The SiO2 content varies between 33.8 wt% and 51.2 wt%. Iron oxides and SiO2 are negatively correlated. Moreover, the low positive correlations between Al2O3 and HFSE, and LILE suggest a contribution of clastic materials in the protolith of studied materials. The samples show low contents of V, Cr, Ba, Zr with respect to igneous rocks. This may infer a sedimentary origin for the studied rocks; furthermore, these materials may have undergone hydrothermal alteration. The REE patterns reveal enrichment in LREE compared to HREE. Some samples show positive Eu (1.82) and other negative anomalies Eu (0.54 to 0.97). The lack of Ce anomalies suggests that the depositional environment of the Edea North iron occurrence was anoxic or suboxic. Overall, the Edea North iron occurrence may have undergone significant input from hydrothermal sources with imprints of the clastic during its deposition.