Nyong River Research Articles

Diversity and distribution of birds in a Congo Basin wetland: the upstream part of the Nyong River valley in Cameroon along two regions (Centre and East)

Several studies have recently been carried out on the avifauna of Cameroon and have made it possible to update the data for certain regions; however, no recent study has been carried out on the upper valley of the Nyong River, which is a wetland, and therefore the data remains quite old. We carried out a study on the avifauna of this valley and birds were sampled over a period of one year using the mist-netting method. The collected data were analyzed using PAST bio statistical software for the diversity and distribution of the avifauna. A total of 268 individuals belonging to 69 bird species were captured, with a high proportion of passerines (73%) compared with non-passerines. The high diversity of the avifauna is supported by estimated values of diversity indexes which show an absence of supremacy of one species (H’=3.64) and an equal distribution of individuals in their environment (J’=0.86). With the value of the Simpson diversity index of 0.96, our result confirms high diversity within the upper valley of the Nyong River avifauna but it also reveals the abundance of this avifauna. In addition, the Kruskal-Wallis test value of 0.04 showed a significant difference in the distribution of relative abundances of taxa at the areas investigated and that different could be justified by a difference in the physiognomy of their vegetation. This study confirms that the composition as well as the structure of the upper valley of the Nyong River as observed in the field play a main role in the diversity of bird species due to the presence of feeding, resting and nesting areas. Based on our distribution and diversity analysis, the pattern of variation in distribution of birds in this wetland appears to lean on environmental factors and particularly the vegetation, which played the main role with a mixture of poor and good dispersers, migratory and vagrant due to presence of lush vegetation all year round.

Dendrometrical Structure and Physicochemical Analysis of Mangrove Sediments from the Nyong River Estuary (Cameroon, Atlantic Coast)

Mangrove estuaries are not immune to the threats posed by climate and anthropogenic constraints on aquatic environments. In the Nyong River estuary, mangrove ecotone has capital importance for biodiversity conservation due to its localization in the Douala-Edéa protected area. For this study, seven quadrats were delimited in aim to evaluate mangrove structure and assessed his interplay with sediment and water physicochemical characteristics. The study revealed a total of 120 individuals of 4 regularly encountered species over a distance of 14 km: <i>Rhizophora racemosa, Avicennia germinans, Rhizophora harrisonii </i>and <i>Phoenix reclinata</i> palms. The marshy soils under the mangrove have Total Nitrogen percentages varying between 0.04 and 0.68%. Total Organic Carbon (from 2.20 to 8.61%) and Total Organic Matter (from 3.66 to 14.64%) contents have a similar pattern. The ratios of Carbon and Nitrogen (C/N) reflect the presence of organic matter and plant debris over a large proportion of the estuary. The ratio of Nitrogen and Phosphate (N/P) reflects the low availability of nitrogen in relation to phosphorus. The cation elements evolve on average in the order Ca<sup>2+</sup> ˃Mg<sup>2+</sup> ˃Na<sup>+</sup> ˃K<sup>+</sup>. This study provides information that would help explore linkages for future research on biogeochemical balance in mangrove sediment and their implementation.

Biodiversity and the Community Structure of Chromista Cavalier-Smith, 1981 in Nyong and Kienke River Mouths (South-Cameroon)

A survey was undertaken from March to June 2014 on the biodiversity and the community structure of Chromista Cavalier-Smith, 1981 in Nyong and Kienke River mouths (South-Cameroon). In each river, raw waters were collected from upstream to downstream at four sites. Cells were counted using the Malassez cells procedure and species were identified. A total of 10427.1x10<sup>5</sup> cells corresponded to three phyla, eight classes, 23 orders, 32 genera and 40 species (24 freshwater species (60.0% of total species richness and total collection respectively), three marine species (7.5% and 2.4% of the total species richness; and total collection respectively), and one brackish water specialist in Kienke (2.5% and 5.1%), 13 tolerant species (32.5% and 32.6%)). The trophic diatom index revealed undisturbed conditions with no or little alteration of human origin and a low organic pollution (oligotrophic or mesotrophic state) (Nyong: TDI=52.7; Kienke: TDI=69.7; pooled assemblage: TDI=65.0). A low species richness was detected (richness ratio in Nyong: d=0.008; Kienke: d=0.003; pooled rivers: d=0.004), a high species diversity (Shannon index close to maximum) (Nyong: H’=2.742 and H’<sub>max</sub>=2.996; Kienke: H’=2.685 and H’<sub>max</sub>=2.996; pooled rivers: H’=3.245 and H’<sub>max</sub>=3.689), a very low dominance by a few species (Berger-Parker index close to 0) (Nyong: I<SUB>BP</SUB>=0.156; Kienke: I<SUB>BP</SUB>=0.175; pooled rivers: I<SUB>BP</SUB>=0.134), and Hill’s ratio were close to 1 (Nyong: Hill=0.819; Kienke: Hill=0.803; pooled rivers: Hill=0.722). The community was highly even with a high value of the Pielou’s evenness close to 1 (Nyong: J=0.915; Kienke: J=0.896; pooled rivers: J=0.880). Two useful species and one harmful species to fish were rare in Kienke. Species exhibited in Kienke and pooled data in rainy season, a positive global net association while it was negative in Nyong. Assemblage fitted Preston’s model in Nyong with a high environmental constant in the dry season (m’=1.469), low constant in the rainy season (m’=0.947) and the pooled seasons (m’=0.853). In Kienke constants were low (dry season: m’=0.574; rainy season: m’=0.566; pooled seasons: m’=0.581) suggesting a evolved community in less disturbed environments where the majority of species showed moderate abundances. In the dry season, the pooled assemblage functionned on the basis of maintaining a complex information network (close to ecological balance) developed at spatio-temporal scales (ZM model) and it presented a low force of regeneration (fractal dimension of the distribution of individuals among species (1/γ)=0.925<1). The evolved oligotrophic state (close to natural balance) of the chromists’ community should be preserved and protected and the studied rivers classified as reference.

Inventory and Spatial Distribution of Invasive Aquatic Plants in the Lower Part of the Nyong River at Lokoundje in the Ocean Department (South-Cameroon)

The study, conducted from February to June 2020, presents a specific inventory of aquatic invasive plants and a mapping of their distribution gained from field observations and data collection campaigns on the lower part of the Nyong River. Specifically, it was a question of inventorying plant species and geo-referencing their biotopes. Through the results obtained, 12 taxa of aquatic invasive species are present (10 species upstream, 08 in transition, and 02 downstream). Of the 12 species, 10 have an ornamental mode of introduction and 01 is endemic to the environment. In addition, it also emerges from this study that the spatial distribution of the species of aquatic plants designated in the study area presents clusters mainly around the islets represented and on certain parts of the banks of the river.

Mitochondrial DNA Corroborates the Genetic Variability of Clarias Catfishes (Siluriformes, Clariidae) from Cameroon.

The airbreathing walking catfish (Clariidae: Clarias) comprises 32 species that are endemic to African freshwater systems. The species-level identification of this group is challenging due to their complex taxonomy and polymorphism. Prior to this study, the biological and ecological studies were restricted to a single species, Clarias gariepinus, resulting in a biased view of their genetic diversity in African waters. Here, we generated the 63-mitochondrial Cytochrome c oxidase subunit 1 (COI) gene sequences of Clarias camerunensis and Clarias gariepinus from the Nyong River in Cameroon. Both C. camerunensis and C. gariepinus species maintained adequate intra-species (2.7% and 2.31%) and inter-species (6.9% to 16.8% and 11.4% to 15.1%) genetic distances with other Clarias congeners distributed in African and Asian/Southeast Asian drainages. The mtCOI sequences revealed 13 and 20 unique haplotypes of C. camerunensis and C. gariepinus, respectively. The TCS networks revealed distinct haplotypes of C. camerunensis and shared haplotypes of C. gariepinus in African waters. The multiple species delimitation approaches (ABGD and PTP) revealed a total of 20 and 22 molecular operational taxonomic units (MOTUs), respectively. Among the two Clarias species examined, we found more than one MOTU in C. camerunensis, which is consistent with population structure and tree topology results. The phylogeny generated through Bayesian Inference analysis clearly separated C. camerunensis and C. gariepinus from other Clarias species with high posterior probability supports. The present study elucidates the occurrence of possible cryptic diversity and allopatric speciation of C. camerunensis in African drainages. Further, the present study confirms the reduced genetic diversity of C. gariepinus across its native and introduced range, which might have been induced by unscientific aquaculture practices. The study recommends a similar approach to the same and related species from different river basins to illuminate the true diversity of Clarias species in Africa and other countries.

Impact of climate and anthropogenic changes on current and future variability in flows in the Nyong River Basin (equatorial Central Africa)

Abstract Due to climate and environmental changes, sub-Saharan Africa (SSA) has experienced several drought and flood events in recent decades with serious consequences on the economy of the sub-region. In this context, the region needs to enhance its capacity in water resources management, based on both good knowledge of contemporary variations in river flows and reliable forecasts. The objective of this article was to study the evolution of current and future flows in the Nyong River Basin (NRB) in Cameroon. To achieve this, the Pettitt and modified Mann–Kendall tests were used to analyze the hydrometeorological time series in the basin. The SWAT model was used to simulate the future flows in the NRB. During the 1970s, the Nyong basin experienced a joint decrease in rainfall and flow. Despite a general decrease in future precipitation, a significant increase in runoff is expected in this basin, regardless of the period (2022–2060 or 2061–2100), the model (RCA4 or CCCma) and the scenario (representative concentration pathway (RCP) 4.5 or RCP8.5). This increase in flow will be the result of the increase in impervious areas to the detriment of forest in the basin, which will compensate for the drop in precipitation with an increase in runoff.

Two New Species of Annulotrema (Monogenea: Dactylogyridae) Gill Parasites of Brycinus macrolepidotus Valenciennes, 1849 from Nyong River, Cameroon.

Research on gill monogeneans of Characiform has made it possible to find two new species belonging to the genus Annulotrema. The purpose of this paper is to carry out their morphological description. Specimens of Brycinus macrolepidotus were captured in the Nyong River at Akonolinga. Each monogenean was mounted between slide and cover slip in a drop of glycerin ammonium picrate mixture. The sclerotized parts of their haptor and reproductive organs were then drawn and measured. Two new species of Annulotrema were described. Annulotrema ngombiensis n. sp. is morphologically close to Annulotrema tenuicirra Paperna, 1973 and Annulotrema pikei Price, Peebles and Bamford, 1969. However, the new species differs from these other two mainly by the characteristic well-marked terminal cap and the tubiform prostatic reservoir of the accessory part of its MCO, as well as by its dorsal bar with a characteristic triangular piece in the middle of the fork and its ventral bar without filaments. Annulotrema nkengfacki n. sp. is distinguished from all other species previously described as well as from its closest congeners, Annulotrema helicocirra Paperna, 1973 and Annulotrema bouixi Birgi, 1988 by the structure of its MCO whose accessory part is composed of a trapezoid structure surmounted by another which is forked-shaped and by its arched-shaped ventral bar with an inner lining. Brycinus macrolepidotus from Cameroon can harbour two species of Annulotrema, both described in the current study. This result contributes to the knowledge of the species diversity of this genus in the Nyong Basin.

Gill Monogeneans of African Tetra, Brycinus kingsleyae (Günther, 1896), From the Nyong River: Biotope, Distribution and Site Selection

Monogenea is a taxon containing flatworms that are primarily parasites of the skin and gills of fish. The African tetra, Brycinus kingsleyae (Günther, 1896), is a commercial fish species in artisanal fisheries in Southern Cameroon. Although the gill monogeneans of this fish species have been described, no ecological research has been carried out on this component community. The present study was conducted in the Nyong River to provide the first data about some factors that influence the structure of its infracommunities. In dry seasons, 70 fish specimens consisting of 27 males and 43 females of fork length between 9.5 and 14.1 cm were sampled.The analysis of their gill filament number indicated that the gill system of B. kingsleyae is heterogeneous because this factor varies with the length of the fish and depends on the gill arch. The studied guild consisted only of core species: Annulotrema combesi Birgi, 1988, Annulotrema maillardi Birgi, 1988, Annulotrema nyongensis Birgi, 1988, Annulotrema bouixi Birgi, 1988, and Characidotrema regia Birgi, 1988. The number of gill filaments and the parasitic load increased with the fish length, indicating that larger hosts provide a greater diversity of niches for parasites. Monogenean species exhibit various occupation patterns of gill arches, sectors, zones and gender differences in parasitological indices. This study reveals that the host length and sex, filament number, gill arch, sector and zone are largely responsible for structuring the studied component community.

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.

Description of a new species from Clarias maclareni and phylogenetical analysis of Quadriacanthus (Monogenea, Dactylogyridae) species transfers between clariid and non-clariid fish hosts in Cameroon.

Recently in Cameroon, two species belonging to Quadriacanthus: Q. anaspidoglanii Akoumba, Tombi & Bilong Bilong, 2017 and Q. euzeti Nack, Pariselle & Bilong Bilong, 2016 have been recorded on gill filaments of Notoglanidium macrostoma (Siluriformes, Claroteidae) in the Memou’ou River (Nyong Basin) and Papyrocranus afer (Osteoglossiformes, Notopteridae) in Lake Ossa, respectively. These records have been considered the result of lateral transfers from Clariidae to a Claroteidae host for the first case (parasitism of N. macrostoma by Q. anaspidoglanii) and from Clariidae or Bagridae to a Notopteridae host for the second (parasitism of P. afer by Q. euzeti). In this paper, the investigation of interspecific relationships among Quadriacanthus spp. parasitizing Clariidae, Bagridae, Claroteidae and Notopteridae in Cameroon resulted in the record of Q. anaspidoglanii from N. macrostoma, Q. euzeti from P. afer, a new record of Q. levequei Birgi, 1988 from Clarias jaensis in the Nyong River, and the description of Q. barombiensis n. sp. from Clarias maclareni in Lake Barombi Mbo. The newly identified species is characterized by having an accessory piece ending in one small hook and the median expansion of its dorsal bar with two filaments. Phylogenetic analysis based on 28S rDNA sequences confirms that the Quadriacanthus spp. parasitizing gill filaments of non-clariid hosts in Cameroon originate from lateral transfers from clariid fishes, and that Clariidae are ancestral hosts of these monogenean species.

Spatiotemporal Variation of Benthic Macroinvertebrates in Some Tropical Forest Streams of the Nyong Catchment (Cameroon)

With the aim of assessing the benthic macroinvertebrates’ diversity, a study was carried out in some tropical forest streams of the Nyong River catchment in Cameroon from February 2019 to February 2020. A total of 167 samples were carried out from 13 stations during 13 months. Some environmental variables were measured. These parameters varied more or less from station to station but significantly at the temporal level. In this study, 13,690 benthic macroinvertebrates belonging to 4 phyla, 7 classes, 16 orders and 93 families were collected. The benthic macroinvertebrates were more abundant and more diversified in the stations whose waters are well oxygenated and present a moderate current compared to the stations with a very weak current. The diversity varied significantly from 1.33 ± 0.14 bits/ind to 2.00 ± 0.35 bits/ind and the high values were found in stations with multiple substrates and well-oxygenated waters. Temporally, the diversity varied significantly from 1.10 ± 0.16 bits/ind in NM sampling station in February 2020 to 1.87 ± 0.1 bits/ind in the OB sampling station in September. In addition, the settlement was more abundant during the short dry season, more precisely during the month of August (1471 individuals) but richer during the long dry season during the month of February (54 families). The distribution of the abundances of the benthic fauna in the different stations made it possible to identify five typological groups using the rarefaction curves, the ascending hierarchical classification and the principal component analyses. Each of these five groups is characterized by a specific taxonomic richness, composition and abundance.

Mineralogy and geochemistry study of the Nyong River sediments, SW Cameroon: Implications for provenance, weathering, and tectonic setting

Mineralogy and geochemistry study of the Nyong River sediments, SW Cameroon: Implications for provenance, weathering, and tectonic setting

The Multiscale TROPIcal CatchmentS critical zone observatory M‐TROPICS dataset I: The Nyong River Basin, Cameroon

AbstractSimultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast‐changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M‐TROPICS). The data shared by M‐TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse‐gas emissions and carbon budgets from African inland waters. However, long‐term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non‐stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land‐cover and land‐use. The latter highlights the need for longer time‐series and continued support for CZOs particularly in the humid tropics.

Understanding Seasonal and Spatial Variation of Water Quality Parameters in Mangrove Estuary of the Nyong River Using Multivariate Analysis (Cameroon Southern Atlantic Coast)

To evaluate the actual status of water quality and conclude on the mains source of pollution in the Nyong estuary River, seasonal and spatial variation of water quality parameters was interpreted by multivariate statistical techniques (Principal Component analysis). Nine (09) environmental variables were monitored at four surface stations in the estuary for two seasonal cycles. The fieldwork was conducted from 2018 to 2019 during high tide and low tide for each survey. In situ physical parameters were measured for a total of 64 samples (32 samples for each tide). The laboratory works consisted of some physicochemical analyses and processing of these data by descriptive and multidimensional statistical analyses. Temperature, suspended particle matter, nitrate, nitrite and phosphate change significantly in the estuary with season (p p > 0.05). Principal Component analysis found temperature, salinity, pH, ammonium to be the most important parameters contributing to the fluctuations of surface water quality in the Nyong estuary during the dry seasons whereas suspended particle matter, nitrate, and phosphate are the most important parameters contributing to the fluctuation of surface water quality in the Nyong estuary during the rainy seasons. Based on spatial variation, the Principal Component analysis found that, suspended particle matter, nitrate and phosphate contribute to the fluctuation of surface water quality parameters upstream of the estuary while downstream salinity, pH, and ammonium contribute the most to the fluctuation of surface water quality. This study shows us the usefulness of multivariate statistical techniques used in assessing water quality data sets that would help us in understanding seasonal and spatial variations of water quality parameters to manage estuarine systems.

Assessing land use and landscape factors as determinants of water quality trends in Nyong River basin, Cameroon.

Changes in LULC and landscape factors impact water quality at spatial and temporal scales. In this study, we investigated the current status in water quality for sub-watersheds of the southern portion of the Nyong River basin of Cameroon from 1994 to 2014 using the WHO guideline. The trends in the water quality parameters were explored using Mann-Kendall test, and their relationship with changes in LULC and landscape factors were analysed using multiple linear regression and Pearson correlation. The current status in water quality did not exceed the WHO guideline limits for drinking water despite a 16% decrease in forest cover and 10% increase in agricultural areas during the period of record. The concentration and changes in water quality trends varied significantly among the sub-watersheds. The concentration of Ca2+, Mg2+, Na+, SiO2, K+, DOC, SPM and WT showed significantly increasing trends in the Nsimi small sub-watershed, while only Ca2+, Mg2+, Na+ and NO3- showed significantly increasing trends in the large sub-watersheds of Mbalmayo and Olama. A combination of one to five LULC and landscape factors, including changes in urban cover, young secondary forest, slope, elevation and population explained 10 to 70% of the changes in water quality trends at watershed scale. Although the interaction of LULC and landscape factors seems to have low impact on the water quality so far, maintaining greater than 70% forest cover and appropriate fallow farming system is invaluable to protecting water quality in the Nyong River basin in the Congo basin and in other forest-rich regions.

Assessing land use/land cover change impacts on the hydrology of Nyong River Basin, Cameroon

Uncontrolled land use land cover change (LULCC) is impacting watershed hydrology, particularly in tropical watersheds in developing countries. We assessed the extent of LULCC in the southern portion of the Nyong River basin through analysis of three land use maps in 1987, 2000 and 2014. LULCC impact on hydrological variables of the Mbalmayo, Olama, Pont So’o, Messam, and Nsimi sub-watersheds of the southern portion of the Nyong River basin were evaluated by using the linear regression modeling and the Mann-Kendall test. This study reveals that dense forest cover decreased by 16%, young secondary forest increased by 18%, agricultural/cropland increased by 10%, and built-up area/bare soil increased by 3% from 1987 to 2014. The decrease in dense forest cover at 0.6% per year on average was driven by indiscriminate expansion of subsistence agricultural/cropland through shifting and fallow cultivation farming systems. Nonsignificant trends in total discharge, high flows, and low flows were observed in the large sub-watersheds of Mbalmayo and Olama from 1998 to 2013 with LULCC within the watershed. In contrast, significant decreasing trends in stream discharge (up to −5.1% and −5.9%), and significant increasing trends in high flows (up to 2.1% and 6.3%), respectively, were observed in the small sub-watersheds of Pont So’o and Messam from 1998 to 2013, particularly with increase in agricultural/cropland cover and decrease in dense forest cover. However, we found non-significant trends in mean annual discharge and low flows for all and whole watershed with LULCC. The results reveal spatially varying trends of stream discharge, low flows and high flows among the sub-watersheds with LULCC within the study watershed. The results suggest that the impacts of LULCC on watershed hydrology are easily detected in small sub-watersheds than in large sub-watersheds. Therefore, the magnitude of dense forest cover loss must be significantly greater than 16% to cause significant changes and common trends in the hydrology of the sub-watersheds of the southern portion of the Nyong River basin. The Mann-Kendall and Regression approaches show appreciable potential for modelling the impacts of LULCC on the hydrology of the southern portion of the Nyong River basin and for informing forest management.

Preliminary evaluation of Thermo Fisher TaqMan® Triplex q-PCR kit for simultaneous detection of chikungunya, dengue, and Zika viruses in mosquitoes.

Preliminary evaluation of Thermo Fisher TaqMan® Triplex q-PCR kit for simultaneous detection of chikungunya, dengue, and Zika viruses in mosquitoes.

Denudation rates on cratonic landscapes: comparison between suspended and dissolved fluxes, and 10Be analysis in the Nyong and Sanaga River basins, south Cameroon

AbstractSouth Cameroon is located in a tropical and tectonically quiescent region, with landscapes characterized by thick highly weathered regolith, indicative of the long‐term predominance of chemical weathering over erosion. Currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developments with associated needs and increasing pressures on land and natural resources. We analysed two of the main south Cameroon rivers: the Nyong River and Sanaga River. The Sanaga catchment undergoes a contrasted tropical climate from sub‐humid mountainous and humid climate and is impacted by deforestation, agriculture, damming, mining and urbanization, especially in the Mbam sub‐basin, draining the highly populated volcanic highlands. By contrast, the Nyong catchment, only under humid tropical climate, is preserved from anthropogenic disturbance with low population except in the region of Yaoundé (Méfou sub‐basin). Moreover the Nyong basin is dam‐free and less impacted by agriculture and logging.We explore both denudation temporal variability and the ratio between chemical and physical denudation through two catchment‐averaged erosion and denudation datasets. The first one consists of an 11‐year long gauging dataset, while the second one comes from cosmogenic radionuclides [CRNs, here beryllium‐10 (10Be)] from sand sampled in the river mainstreams (timescale of tens to hundreds of thousands of years). Modern fluxes estimated from gauging data range from 5 to 100 m/Ma (10 to 200 t/km2/yr); our calculations indicate that the usual relative contribution of chemical versus physical denudation is 60% and 40%, respectively, of the total denudation. Beryllium‐10 denudation rates and sediment fluxes range from 4.8 to 40.3 m/Ma or 13 to 109 t/km2/yr, respectively, after correction for quartz enrichment. These fluxes are slightly less than the modern fluxes observed in Cameroon and other stable tropical areas. The highest 10Be‐derived fluxes and the highest physical versus chemical denudation ratios are attributed to anthropogenic impact. Copyright © 2016 John Wiley & Sons, Ltd.

The Impact of Climate Variabilities on the Water Resources of Nyong River (Cameroon) during Few Anterior Decades

The Nyong River is situated in south Cameroon. The study of the impact of climate change on the water resource of the River shows that its precipitations and flow rate are decreasing. This negative effect is reinforcing by the fact that the water of the River is collected to feed the population of Yaounde, the political capital of Cameroon and its environs. Given that no action can stop the variability of climate factors, it is necessary to ameliorate the management of water resource of Nyong River.

Mineralogical, geochemical and mechanical characterization of the Ayos (East-Cameroon) lateritic and alluvial clayey mixtures: Suitability for building application

The ferrallitic weathering in South-Cameroon produces a thick soil mantle. However, the high iron content of the clayey materials prevents their efficient use in ceramics. To reduce the iron effect, the Ayos lateritic clays have been mixed with alluvial clays taken from the Nyong River. The results obtained show that the main minerals are Quartz, kaolinite, hematite, goethite and muscovite in lateritic clays and kaolinite, chlorite, quartz, muscovite for the alluvial clays. The chemical compositions indicated that SiO2, Al2O3 and Fe2O3 are the main elements in lateritic clays while in alluvial clays, SiO2 and Al2O3 are predominant. Fe2O3 is less than 2%. The plasticity and ceramic properties are improved with alluvial clays content. The lateritic clays can be used for dense bricks after firing at 1000°C and 1100°C. Mixtures with more than 20wt% of alluvial clays are suitable for dense bricks at all the firing temperatures (900–1100°C). The limiting factor for these mixtures in roofing tiles is their flexural strength.