Sanaga River Research Articles

Ecological concrete by partially substitution of cement with Cameroonian corn stover ash.

This study focuses on the influence of the partial substitution of cement by Cameroonian corn stover ash (CCSA) on the physical and mechanical behavior of concrete. For this, as materials used, one has first the corn stovers coming from the Bandjoun town in the Koung-khi division, in the West region of Cameroon, which are used to obtain the ashes, while the sand used, came from the Sanaga River in the coastal region of Cameroon. In order to obtain the CCSA, the corn stover is calcined in an oven at 600°C for 6h and then characterized; the characterization included infrared spectrometry, X-ray fluorescence spectrometry, fineness of grinding, and absolute density. Four concrete formulations were prepared, according to the amount of CCSA (that is at 0%, 5%, 10% and 15%), in order to carry out tests in the fresh state (slump test, compactness) and in the hardened state, i.e. mechanical tests (compression and bending tests) and physical tests (density test, water absorption, and porosity) after 7, 14, 28 and 60 days. The results of the chemical analyses carried out on the CCSA show that it contains 73.97% of SiO2+Al2O3+Fe2O3, giving it a pozzolanic character in accordance with ASTM C618 standard. The mechanical behavior at an early age (0-28 days) showed a general decrease in strength for concretes containing CCSA. Replacing 10% of the cement with CCSA showed the best mechanical performance (compressive and flexural strength) in the long term (60 days) as compared to the control concrete (with 0% of CCSA). At the same substitution rate the lower absorption and porosity rates were obtained, which are close to those of the control concrete, with relative differences of ±2.43% and ±3.06% respectively.

Physical and Geochemical Characterisation of Pongo Pitti and Bossambo Farm Clays (Littoral Region, Cameroon) for use in Ceramics

The main objective of this work is to discern the physico-chemical and mechanical behavior of the Pongo Pitti and Bossambo Farm clay formations, located on either side of the Sanaga river in the littoral region of Cameroon. To achieve this, two field campaigns and laboratory works were carried out. Four clay materials were collected and brought back to the laboratory. The laboratory investigations involved physico-mechanical and geochemical analyses, followed by ceramic testing. The materials studied have a clayey texture, with clay percentages ranging from 26.89% to 80.3%, silt from 13.2% to 57.6% and sand from 1.58% to 47.26%. The plasticity index ranges from 11.9% to 24.2%. From a geochemical standpoint, the materials studied show a predominance of silica (49.6% to 63.5%), alumina (20.5% to 27.1%) and iron (2.39% to 8.6%), with the SiO2/Al2O3 ratio varying from 1.96 to 3.1. The Al2O3/Fe2O3 ratio is 8.4 for Pongo Pitti clays and 2.9 for Bossambo Farm clays. The geochemical weathering indices (ICV, CIA, PIA, CIW, CIW) show a high degree of weathering, with values in excess of 90%. Alkali and alkaline-earth proportions are lower, and the K2O/Na2O ratio varies between 8.45 and 14.24, showing an enrichment of potassium in relation to sodium. Lantane is the most abundant rare-earth element (323.84 ppm). The REE study shows a predominance of light REEs over heavy REEs (LREE/HREE~4.51) and a negative Europium anomaly. Infrared spectroscopy showed poor kaolinite crystallinity. Mechanically, the specimens studied, fired at temperatures ranging from 950℃ to 1050℃ showed good cohesion and metallic soundness. Linear shrinkage was 4.8%. Mass loss increases with temperature. Its value is 12.5% for Pongo Pitti materials and 8.5% for Bossambo Farm materials. Water absorption decreases with temperature and is 20.27% for Pongo Pitti samples and 15.79% for Bossambo Farm samples. Bulk density increases with temperature (2.11 at 950℃ to 2.51 at 1050℃). Flexural strength increases with temperature and is 6.66 MPa for materials from Pongo Pitti and 8.89 MPa for those from Bossambo Farm. These materials can be used to make fired bricks and roof tiles, and Pongo Pitti materials can be used to make refractory ceramics

Trophic ecology of the African riverine elephant fishes (Mormyridae).

Multiple species of the elephant fishes (Mormyridae) commonly coexist in sympatry in most African tropical rivers and lakes. In this study, we investigated the trophic ecology and potential trophic niche partitioning of eleven mormyrid fish species from the Sanaga River system in Cameroon using the stable isotope composition of carbon and nitrogen in the muscle samples. Albeit most mormyrids mainly feed on invertebrates, we found differences in isotope ratios, and we report signs of the trophic niche partitioning among species. We further found significant differences in isotopic signatures within the Mormyrus genus, suggesting ecological niche diversification among three closely related species. We have also evaluated differences in the isotopic signals between seasons in four species, which could be possibly caused by species migration and/or anthropogenic agricultural activities. To evaluate body shape, we applied geometric morphometric analyses, and we show that most of the species are clearly morphologically separated. We focused on the mormyrid ecomorphology to identify a possible interaction between shape and ecology, and we found a relationship between the δ13C (but not δ15N) isotopic signal and morphology, suggesting their interplay during mormyrid evolution. Overall, we present robust evidence of the trophic niche partitioning within the mormyrid species community, and we integrate trophic ecology with morphometrics, shedding light on the enigmatic evolutionary history of these fascinating African fishes.

Insights into the phylogenetic position of genus Synodontella (Monopisthocotylea) among some other Dactylogyridea gill parasites of African catfishes and the importance of haptoral elements

This work provides new molecular data on seven species representing three genera (Protoancylodiscoides, Schilbetrema and Synodontella) in the order Dactylogyridea. The results help to explain the origin of Synodontella spp. and to elucidate the phylogenetic position of Synodontella in relation to the other genera. The findings also highlight the importance of the haptoral elements in determing phylogenetic relationships between and within Dactylogyridea taxa, which are monogenean parasites of mostly cyprinid fishes in fresh water. A total of 36 catfish specimens representing five species in three genera (Synodontis, Schilbe and Chrysichthys) were collected from two rivers in Cameroon: the Sanaga River (at Edéa and Nachtigal, in the Littoral and Cental regions, respectively) and Boumba River (at Mang-kaka, East Region), and examined for gill parasites. The novel 28S rDNA sequences of seven species belonging to Dactylogyridea were obtained and their phylogenetic relationships inferred. Synodontella resulted as a monophyletic lineage; the samples obtained from the catfish in Cameroon were well-differentiated into two groups. Synodontella appears to be more closely related to Schilbetrema than to the other Dactylogyridea species investigated here. The shape of the ventral bar should be considered an important feature for distinguishing among Dactylogyridea genera. The existence of two or more lineages within the genus Synodontella, as suggested by previous morphological studies, is here molecularly confirmed, indicating speciation as likely an outcome of ecological influences or the phylogenetic relationships among parasites and/or hosts.

Comparative Study of Mortars Made with Sands of Different Geological Origin

The present work is a comparative study of sand mortars from various geological origins to highlight their influence on mortar qualities. Five different sands and the cement CEM II/B–P 42.5R were used to produce mortars with similar water/cement ratios (W/C). These are the “Sanaga” sand from the Sanaga River, the “Wouri” sand from the Wouri River, the Nyambaka basalt sand, the Meiganga granite sand, and the Leboudi gneiss sand. The physical, chemical, and mineralogical features of these sands were used to characterize and classify them. They were then used to formulate mortars, which were analyzed and compared. According to the results of the mortar setting time tests, the initial setting time ranges from 195 minutes for Sanaga sand mortar (MS04) to 210 minutes for gneiss sand mortar (MGN03), passing Wouri sand mortar (MW05) with 200 minutes, basalt sand mortar (MB01) with 198 minutes, and granite sand mortar (MGR02) with 196 minutes. The final setting time ranged from 496 minutes (MGR02) to 510 minutes (MGN03), with an average of 300 minutes added to the initial setting time. The flexural strength tests of the mortars reveal that crushed sands outperform alluvial sands. They range from 1.64 to 2.18 MPa after 2 days, 3 to 3.90 MPa after 7 days, and 7 to 14.84 MPa after 28 days. The results of the compressive strength tests show that quarry sand mortars have greater average compressive strengths than alluvial sand mortars, with basalt sand providing the greatest performance. These strengths range from 6.35 to 10.83 MPa after 2 days, 7.55 to 18.96 MPa after 7 days, and 22.81 to 34.58 MPa after 28 days, with the MB01 being the best sand. These findings reveal that the geological origin of sands, which specifies certain of their physicochemical and mineralogical attributes, has an impact on the properties of mortars. This impact is also influenced by granulometry and organic matter concentration.

Length-Weight Relationship and Condition Factor of Chrysichthys longidorsalis (Risch & Thys Van Den Audenaerde, 1981) Landed at the Sanaga River Basin, Cameroon

Given the lack of adequate information on morphometric characteristics of wild fish in Cameroon, the present research was carried out from November 2019 to October 2020 to analyse length - weight relationship and Fulton’s condition factor of Chrysichthys longidorsalis (Risch & Thys van den Audenaerde, 1981) to provide baseline information for its fishery management and aquaculture development. A total of 451 sampled C. longidorsalis captured from Sanaga River basin of the Centre Region in Cameroon were identified and lengths and weights measured. Mean standard length, total length and total weight of samples were 18.13 ± 7.32 cm, 23.91 ± 9.37 cm and 305.15 ± 315.66 g respectively. The males were longer and heavier than females (p<0.05). High correlation coefficient (>0.9) and coefficient of determination (R2 = 0.9516) revealed strong positive relationship (>95%) between fish standard length and total weight. The growth coefficient (b) values, were less than 3 (2.7234) suggesting a negative allometric growth pattern. Though the condition factor was higher (p<0.05) in males and during the dry season than in females and during the rainy season, the overall value was 5.85 ± 11.44, indicating that the fish had good adaptation to conditions of the Sanaga River basin. This study serves as useful reference for sustainable management and conservation of fish resources in Cameroonian waters.

Biogeography of central African forests: Determinants, ongoing threats and conservation priorities of mammal assemblages

AbstractAimCentral Africa shelters diverse and iconic megafauna, which is threatened by climate and land‐use changes and increased hunting‐induced defaunation. Though crucial for coordinating regional conservation actions, how species assemblages are spatially structured remains poorly understood. This study aims to fill this knowledge gap for mammals across central African forests.LocationTropical moist forests from Nigeria to the Albertine Rift.MethodsAn extensive compilation of forest‐dwelling mammal species lists was made from wildlife and bushmeat‐related surveys across central Africa. A beta‐diversity approach enabling the clustering of surveys composed of similar species was implemented to identify and delimit zoogeographic districts, separately for three well‐documented mammal orders: carnivores, primates and artiodactyls. Random forest classification models were then used to identify the environmental determinants of the district's distribution and to produce a continuous zoogeographic map (and associated uncertainties) critical to assess the conservation status of each district and their ongoing threats.ResultsWhile carnivores do not present a clear spatial structure within central African forests, our findings highlight the structuring role of rivers on both primate and artiodactyl assemblages' distributions. We retained eight and six spatially congruent districts for primates and artiodactyls, respectively. These districts were shaped by the Ubangi‐Congo River system, and the Cross and Sanaga Rivers, with a secondary role of insularity and precipitation identified for primates. Highly threatened districts were highlighted, especially in Nigeria and in the Democratic Republic of Congo, the latter including vast areas that are understudied and poorly represented in the protected area network.Main ConclusionsBeyond refining our understanding of the diversity and uniqueness of mammalian assemblages across central African forests, our map of zoogeographic districts has far‐reaching implications for the conservation of highly threatened taxa, allowing to target species and areas of interest for further sampling, conservation and rewilding efforts.

Epidemiology of epilepsy and relationship with onchocerciasis prevalence in villages of the Ntui Health District of Cameroon

BackgroundA strong association between epilepsy and onchocerciasis endemicity has been reported. We sought to document the epidemiology of epilepsy in onchocerciasis-endemic villages of the Ntui Health District in Cameroon and investigate how this relates to the prevalence of onchocerciasis. MethodsIn March 2022, door-to-door epilepsy surveys were conducted in four villages (Essougli, Nachtigal, Ndjame, and Ndowe). Ivermectin intake during the 2021 session of community-directed treatment with ivermectin (CDTI) was investigated in all participating village residents. Persons with epilepsy (PWE) were identified through a two-step approach: administration of a 5-item epilepsy screening questionnaire followed by clinical confirmation by a neurologist. Epilepsy findings were analyzed together with onchocerciasis epidemiological data previously obtained in the study villages. ResultsWe surveyed 1663 persons in the four study villages. The 2021 CDTI coverage for all study sites was 50.9%. Overall, 67 PWE were identified (prevalence of 4.0% (IQR: 3.2–5.1) with one new-onset case during the past 12 months (annual incidence of 60.1 per 100,000 persons). The median age of PWE was 32 years (IQR: 25–40), with 41 (61.2%) being females. The majority (78.3%) of PWE met the previously published criteria for onchocerciasis-associated epilepsy (OAE). Persons with a history of nodding seizures were found in all villages and represented 19.4% of the 67 PWE. Epilepsy prevalence was positively correlated with onchocerciasis prevalence (Spearman Rho = 0.949, p = 0.051). Meanwhile, an inverse relationship was observed between distance from the Sanaga river (blackfly breeding site) and the prevalence of both epilepsy and onchocerciasis. ConclusionThe high epilepsy prevalence in Ntui appears to be driven by onchocerciasis. It is likely that decades of CDTI have likely contributed to a gradual decrease in epilepsy incidence, as only one new case occurred in the past year. Therefore, more effective elimination measures are urgently needed in such endemic areas to curb the OAE burden.

Design of Controlled Pre-Split Blasting in a Hydroelectric Construction Project

Geologic conditions and design requirements around upstream Nachtigal Falls, in Cameroon, for the hydroelectric construction project on the Sanaga River dictated close control of blasting procedures with very precise geometry to obtain safe and economical excavation lines. Various techniques of pre-split blasting were used in the initial stage of all major excavations. Hole diameters for pre-splitting were 89 mm, and hole spacing ranged from 0.8 to 1m. Explosive charges varied from 1 to 7 kg per hole, and the detonating cord linear charge ranged from 12 to 60g. The contour blasting technique is aimed at controlling overbreak and improving remaining slope stability. Over-break or over-excavation needs to be controlled since its occurrence compromises the operations in terms of safety (instability in the remaining slope; loosening rocks that increase the risk for operational people; an irregular free face for subsequent blasting); and costs (need for reinforcement of the remaining rock structure through costly sustainment systems; increase in concrete volumes in civil works). This paper discusses in detail the design and field implementation of pre-split blasts successfully carried out to achieve clean vertical walls in moderately dipping, though complexly sheared and jointed gneiss. Based on the results of the experiments, we were able to design a pre-splitting pattern both experimentally and in a very cost-effective manner. It is felt that the methods developed on this project could have useful applications on other major construction projects. Doi: 10.28991/CEJ-2023-09-03-05 Full Text: PDF

10World Bank Inspection Panel: The Inspection Panel Report and Recommendation on a Request for Inspection: Republic of Cameroon Nachtigal Hydropower Project (P157734) and Hydropower Development on the Sanaga River Technical Assistance Project (P157733), Report No. Report No. 176365-cm, 27 September 2022

10World Bank Inspection Panel: The Inspection Panel Report and Recommendation on a Request for Inspection: Republic of Cameroon Nachtigal Hydropower Project (P157734) and Hydropower Development on the Sanaga River Technical Assistance Project (P157733), Report No. Report No. 176365-cm, 27 September 2022

Petrography and geochemistry of the Sanaga river sediments, central Cameroon: Constraints on weathering, provenance, and tectonic setting

The Sanaga River (SR), central Cameroon, flows predominantly over metasediments (2.1 Ga), Paleoproterozoic amphibolites and orthogneisses, granitoids from the Adamawa-Yade batholith (AYB), sedimentary clastic rocks of Cretaceous age, and Cenozoic rocks of the Cameroon Volcanic Line. To infer the origin of alluviums and tectonic setting of source rocks, the texture, heavy mineral, major, trace, and rare earth element concentrations of stream sediments were investigated. The very high SiO2/Al2O3 ratios and the ZTR (Zircon-Tourmaline-Rutile) index of SR sediments suggested a high maturity. This interpretation was additionally confirmed by the Th/Sc vs Zr/Sc plot. The Plagioclase- and Chemical Index of Alteration (PIA and CIA) values, the (A-K)-C-N and A–CN–K triangular plots show an intense degree of weathering in the source area. Numerous discrimination diagrams, based on trace elements, indicate that sediments were derived from felsic source rocks mainly granodiorites, granites, and biotite granitoids exposed in the SR watershed. This shows that the metamorphic and volcanic rocks do not significantly contribute to the stream sediments. Paleotectonic investigations using multi-element discrimination plots indicate passive and rift settings for the SR drainage basin. Rift settings were also inferred from downstream sediments of the SR. They are probably related to Proterozoic events including opening of large oceanic basins. The passive and rifted margin settings are supported by the occurrence of rare ophiolitic rocks, which indicate an old oceanic crust.

Rinorea spongiocarpa and Rinorea dimakoensis (Violaceae), new threatened species of forest trees from East and South Regions of Cameroon and Gabon

SummaryTwo tree species are described as new to science: Rinorea spongiocarpa Achound. sp. nov. (placed in Rinorea [unranked] Brachypetalae) and R. dimakoensis Achound. sp. nov. (placed in Rinorea [unranked] Ilicifolieae). Both species occur in Cameroon, south of the Sanaga river, the first from South and East Regions, occurring in evergreen forest from Ngovayang and Lolodorf across the southern plateau to the Dja forest. The second extends also to Gabon, occurring in Cameroon in the northern part of East Region in semi-deciduous forest towards the interface with woodland habitats in the Dimako-Bertoua area. The two species are mapped and illustrated, and their affinities and conservation status according to the 2012 IUCN categories and criteria are discussed. Both R. spongiocarpa and R. dimakoensis are threatened with extinction due to habitat destruction, both are assessed as Vulnerable.

Onchocerciasis in the Ntui Health District of Cameroon: epidemiological, entomological and parasitological findings in relation to elimination prospects

BackgroundDespite decades of community-directed treatment with ivermectin (CDTI), onchocerciasis transmission persists in Cameroon and has been associated with increased risk for epilepsy in endemic communities. We investigated the onchocerciasis situation in the Ntui Health District (a known onchocerciasis focus in Cameroon where the Sanaga River constitutes the main source of black fly vectors) using parasitological, entomological and serological parameters.MethodsIn July 2021, community-based surveys were conducted in four villages (Essougli, Nachtigal, Ndjame and Ndowe). Onchocerciasis was diagnosed via microscopic examination of skin snips. Using rapid diagnostic tests, we screened children aged 3–6 years for Ov16 antibodies as a proxy for recent onchocerciasis transmission. Monthly black fly biting rates were obtained from the two riverside villages (Nachtigal and Essougli) for 12 consecutive months (July 2021 to June 2022) using the human landing catch technique. Some black flies were dissected each month to check for infection.ResultsOverall, 460 participants were recruited; mean age was 32.1 (range: 3–85) years with 248 (53.9%) being males. Among skin snipped participants (n = 425), onchocerciasis prevalence was 14.6%. Participants with epilepsy (n = 25) were more often skin snip positive (45.8% vs 12.7%; P < 0.001) and had higher microfilarial loads (9.2 ± 22.0 vs 0.7 ± 3.5 microfilariae/skin snip; P < 0.001) compared to their peers without epilepsy. Eight (6.5%) of the 123 tested children were Ov16 seropositive. The breeding sites we investigated along the Sanaga River during the current study harbored fewer vectors (annual biting rates reaching 530,322 vs 606,370 in the Mbam River) and exhibited lower black fly infection rates (annual transmission potentials reaching 1479 vs 4488 in the Mbam River) when compared to recent entomological reports in Cameroon.ConclusionDespite substantial biting rates, black fly infection rates (by microscopy) in the Ntui Health District were rather low resulting in overall low transmission potentials in study villages. Thanks to CDTI, O. volvulus infection in both humans and insects is on the decrease. However, there is evidence that O. volvulus is still endemic in these communities. Reducing the vector population will further accelerate onchocerciasis elimination prospects.Graphical

Biodiversity of bottom trawl fishery and left-over marine resources along the Cameroonian coast

The objective of this study was to provide information on the diversity of catches, by-catches and discards by trawlers in the mouths of Sanaga (MSR) and Nyong (MNR) rivers along the coast of Cameroon. Samples were collected on board of a fishing vessel using the bottom trawling technique. Specimens were identified using 2104 and 2016 FAO identification keys. A total of 58 species belonging to 38 families and 5 super-classes were identified. Amongst, 72%, 14%, 10%, 2% and 2% were fish, mollusks, reptiles, crustaceans and cnidarians, respectively. We found 67.1% of marketable fish and shrimp and 32.9% of discards consisting of immature fishes. The MNR was richer in marketable fish species (p=0.0001) and discards (p=0.019) than MSR. The Cameroon coast is rich in biodiversity. However, it is today threatened by marine pollution and the non-respect of trawling which jeopardizes the sustainability of the fishing industry in Cameroon.

Potable Water Supply Deficiency in Yaounde (Centre Cameroon): Challenges and Coping Strategies of the Inhabitants

In most cities in developing countries, dwellers continue facing difficulties in adequately accessing potable water in sufficient quantity for their daily needs. These difficulties are perceived by households each time they fetch drinking water or try to get access to potable water for other household activities. This study aims to assess the problem of potable water supply in the Yaounde III Subdivisions’ neighbourhoods and the coping strategies developed by citizens to meet their needs. To achieve this objective, 300 households were selected and investigated based on purposive and systematic random sampling, particularly in the most densely populated neighbourhoods. We proceeded by identifying the different water supply sources of households for their various needs, and assessing the difficulties encountered in getting water and how they overcome them. Results reveal that in Yaounde III Subdivision only 34.33% of the households are supplied by the Cameroon Water Utilities Corporation (CAMWATER), while 65.67% rely on alternative water supply sources (wells, drillings and springs) without any pre-treatment. Among those connected to CAMWATER network, 46.6% do not have a regular water flow. Results also revealed that water sources were located at reasonable distances (less than 1 kilometre) and that 70% of households take less than 30 minutes to fetch water. Failure in water supply is mainly caused by the insufficient pumping capacity of the existing potable water treatment plants which lead to rationing and shortages, but also to rapid population growth and city extension not followed by the extension of the potable water distribution network. To fill the gap in water supply, it is imperative for public authorities to quickly achieve the project on water supply from the Sanaga River. Also, CAMWATER should extend its distribution network and improve its maintenance system.

Towards the phylogenetic placement of the enigmatic African genus Prolabeops Schultz, 1941.

The small cyprinid genus Prolabeops Schultz, 1941 is restricted to the Nyong and Sanaga River systems in Cameroon. In the past, the genus had been suggested to be either a member of the Labeoninae, Torinae or the Smiliogastrinae mainly on the basis of morphological similarities, and it is nowadays considered as incertae sedis within the Cypriniformes. This study provides the first attempt to reveal the phylogenetic position of Prolabeops using molecular data. For this purpose, the authors sequenced a large fraction of the mitochondrial genome (c. 13,600 bp), including all mitochondrial protein coding genes, of two Prolabeops melanhypopterus specimens and an additional four Enteromius specimens. The large-scale phylogenetic analysis was based on an alignment including all mitochondrial protein coding genes of 902 specimens representing c. 899 cypriniform species. Prolabeops was clearly recovered within the African Smiliogastrinae, forming a weakly supported clade together with Enteromius jae, Enteromius hulstaerti and Barboides gracilis. The study data underline the urgent need of a thorough taxonomic revision of the small African barbs collectively placed in the genus Enteromius.

Mineralogy, geochemistry, and physico-mechanical characterization of basalts, granites, and alluvial sands from Sanaga River (Cameroon): Potential use as construction materials

Mineralogy, geochemistry, and physico-mechanical characterization of basalts, granites, and alluvial sands from Sanaga River (Cameroon): Potential use as construction materials

Geoelectrical imaging and spatial distribution of alluvial materials of the Sanaga River (Cameroon, Central Africa)

Geoelectrical imaging and spatial distribution of alluvial materials of the Sanaga River (Cameroon, Central Africa)

Spatio-temporal assessing rainfall and dam impacts on surface runoff in the Sanaga river basin (transition tropical zone in central part of Cameroon)

Spatio-temporal assessing rainfall and dam impacts on surface runoff in the Sanaga river basin (transition tropical zone in central part of Cameroon)

Evaluation and Mapping of Rainfall Erosivity from Tamsat Satellite Data in the Sanaga River Basin (Srb) in Nachtigal, Cameroon (Central Africa)

Evaluation and Mapping of Rainfall Erosivity from Tamsat Satellite Data in the Sanaga River Basin (Srb) in Nachtigal, Cameroon (Central Africa)