Rainwater Chemistry and Wet Deposition over the Equatorial Forested Ecosystem of Zoétélé (Cameroon)

Within the framework of IDAF (IGAC DEBITS AFRICA: International GlobalAtmospheric Chemistry/DEposition of Biogeochemically Important TraceSpecies/Africa) network, data analysis is realised on precipitation chemical composition collected in Zoétélé, in Southern Cameroon. This station, located atabout 200 km from the Atlantic Ocean, is representative of a so-called `Evergreen Equatorial Forest' ecosystem. An automatic wet-only precipitation collector was operated at the station from 1996 to 2000. The rainfall regime, associated with eastward advection of moist and cool monsoon air masses, amounts to an average of 1700 mm/year. Inorganic and organic content of the precipitation were determined by IC in 234 rainfall events, representing a total 4,583 mm of rainfall from an overall of 7,100 mm.The mean annual precipitation chemistry and wet deposition fluxes characteristic of an African equatorial forest are quantified. Typical atmospheric gases and particles sources influence the precipitation chemical content and the associated deposition of chemical species. Indeed, hydrogen concentration is the highest (12.0 eq.L^–1) of the IDAF measurements, leading to acid rains with a low mean pH 4.92. The mineral species are dominated by nitrogenous compounds (NH₄ ⁺:10.5 and NO₃ ^–: 6.9 eq.L^–1), Ca²⁺ (8.9 eq.L^–1) and SO₄ ^{2 –} 5.1 eq.L^–1. Relationship between Ca^{2 +} and SO₄ ^{2 –} indicated aterrigeneous particulate source and an additional SO₄ ^{2 –} contributionprobably due to swamps and volcano emissions. Na⁺ and Cl^–concentrations, around 4.0 eq.L^–1, seem very low for this site,accounting for the marine source. Besides, strong correlations between NH₄ ⁺/K⁺/Cl^– indicate the biomass burning originof these species. Accordingly, precipitation chemistry in Zoétéléis influenced by three major sources: biogenic emissions from soil and forest ecosystems, biomass burning from savannah, and terrigenous signature from particles emissions of arid zones; and three minor sources: marine, volcano and anthropogenic. In spite of the relatively low concentration of all these elements, the wet deposition is quite significant due to the high precipitation levels, with for example a nitrogenous compounds deposition of 34 mmol.m^–2.yr^–1.     

Démantèlement des paysages cuirassés anciens en zones forestières tropicales d'Afrique centrale : formation d'accumulations ferrugineuses actuelles en bas de versantOld ferricrete landscape dismantling in Central Africa rain forest zone: formation of the present downslope iron accumulations

Present downslope iron accumulations were investigated in the rainforest zone in southern Cameroon. Six clay and Fe-hydroxide dominated patterns have been identified and occur on the lower part of hill slopes. They can be subdivided in three different sequences, related to gentle, moderate or steep slopes. They are discontinuous with respect to the dismantling zone of the old ferricrete cap formed at Cretaceous period. They show a gradual development from a soft Fe-crust (carapace) to a vesicular facies that will, with time, cover the whole landscape again. To cite this article: É. Temgoua et al., C. R. Geoscience 334 (2002) 537–543.     

Hydrogeochemical controls and usability of groundwater in the semi-arid Mayo Tsanaga River Basin: far north province,Cameroon

Deuterium, δ ¹⁸O, major ions and dissolved silica in groundwater from semi-arid Mayo-Tsanaga river basin in the Far North Province, Cameroon were used to trace hydrogeochemical processes that control their concentrations and to explore for usability of the water. Electrical conductivity ranges from 57–2,581 μs/cm with alternating low and high values along the hydraulic gradient. Waters from piedmont alluvium show low concentrations in major cations, which peak in Mg within basalt, Na within plain alluvium, and Ca within basalt and the sandy Limani-Yagoua ridge. The initial dominant groundwater composition is CaHCO₃, which did not evolve within the basalt and piedmont alluvium, but evolved to NaHCO₃ in the granite and plain alluvium. The main processes controlling the major ions composition include the following: (1) dissolution of silicates and fluorite; (2) precipitation of fluorite and carbonate; (3) cation exchange of Ca in water for Na in clay; (4) and anthropogenic activities. The δD and δ ¹⁸O ratios vary from −35 to 0.7 and −5.3 to 1.1‰, respectively. The lowest and highest isotope ratios are observed in groundwater within the downstream sandy Limani-Yagoua ridge and the upstream graintes respectively. Variation in isotope ratios depends on altitude effect of −0.48‰ per 100 m between 600 and 850 m asl, and on evaporation, which had insignificant effect on the water salinity. Seventy percent of the groundwater shows poor drinking quality and 90% is suitable for irrigation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Les orthogneiss calco-alcalins de Foumban–Bankim : témoins d'une zone interne de marge active panafricaine en cisaillement

The mylonitic rocks of the Central Cameroonian Shear Zone (Foumban–Bankim sector) are mainly ancient magmatic rocks emplaced in an internal zone of a Pan-African active margin. They display calc-alkaline affinities with granitoids of northern Cameroon, but differ by their higher K contents and shoshonitic nature. This spatial distinction in pre- to syn-orogenic magmatism permits to define a north to south potassium increase trend, compatible with the existence of a northern Pan-African subduction zone. The shearing evolution of this margin is marked by the superposition of two mylonitic foliations and the occurrence of unusual δ-type porphyroclasts. This suggests the interference of two shearing phases operating in opposing sense at a constant direction, under deep and shallow metamorphic conditions, respectively. To cite this article: E. Njonfang et al., C. R. Geoscience 338 (2006).     

Geochemistry and geochronology of the ~620 Ma gold-associated Batouri granitoids,Cameroon

The Batouri gold mining area in southeastern Cameroon is part of the Adamawa–Yadé Domain of the Central African Fold Belt (Pan-African). It is underlain by a variety of granitic rocks, including alkali-feldspar granite, syeno-monzogranite, granodiorite, and tonalite. Geochemical data suggest that these rocks formed by differentiation of I-type tonalitic magma under oxidizing conditions in a continental volcanic arc setting. U–Pb dating of zircons from gold-associated monzogranite-granodiorite at Kambélé gave concordant ages of 619 ± 2 and 624 ± 2 Ma, while Ar–Ar dating of alkali-feldspar granite yielded a non-plateau maximum age of 640–620 Ma. These ages imply that the Batouri granitoids were emplaced during the collision of the West African Craton and the Congo Craton.

The geochemical characteristics of the Batouri granitoids as well as their oxidized state (magnetite series) are typical of gold-associated felsic rocks in subduction settings elsewhere. The similarities in age, composition, and geochemical affinities of these granitoids with those reported from other localities in the Adamawa–Yadé Domain reinforce the earlier assumption that the granitic rocks of this domain represent parts of a regional-scale batholith, with commonly small-scale, high-grade auriferous quartz veins in structurally favourable sites. The spatial and temporal association of gold mineralization and the Batouri granitoids may suggest potential for regional-scale, high-tonnage, granite-related gold ore.     

The relationship between herders and trees in space and time in northern Cameroon

Extensive herding is an important activity in northern Cameroon, in terms of both the local social economy and local land management. However, this activity is strongly linked to the availability and accessibility of fodder resources. Due to territorial processes, such as land clearance and wood harvesting, this resource is receding and pasturelands are becoming fragmented. Herders are facing new challenges to secure their livelihoods, and, in this context, fodder trees are emerging as a key resource, allowing herds to subsist up to the end of the dry season. Increasingly, trees are playing a significant part in the herders' strategies to feed their herds in time and space and to 'root' their activities to particular lands. This trend requires an analysis of the importance of fodder trees in the definition of territorial strategies operated by herders in northern Cameroon, in the context of various herding systems (nomadic herding, agro herding using transhumance, and settled agro herding). A discussion of herding strategies needed to address the decreasing access to fodder resources highlights the problems of current extensive herding systems and leads to proposed alternatives.     

Expanding horizons: Women’s voices in community-driven development in the Cameroon grasslands

Communities are increasingly becoming development spaces where members are dynamic actors in fashioning issues of common interest. This paper explores women’s efforts at building social capital for communitarian ventures in selected rural localities of the Cameroon grasslands. It is argued that effective participation in raising livelihoods and infrastructure provisioning is facilitated through women’s social networks (njangis). The paper situates the gender concerns in community participation, rekindled through village development associations (VDAs) – crucial in needs identification, prioritization and execution of identified projects. Based on focused field studies in selected localities, it is established that due to their low social status, workloads and tight schedule, women remain on the sidelines of the leadership in VDAs. However, women’s in-cash or in-kind contribution remains crucial to the successful implementation of projects. Enhancing female participation hinges on efforts at erasing cultural stereotypes that project women as domestic workers, improving literacy, increased access to productive resources especially land, direct support to women’s agricultural activity and improved rural infrastructure (roads, water supply, and electricity) that is compromising women’s participation and empowerment drive.     

Climate variability and maize production in Cameroon: Simulating the effects of extreme dry and wet years

The effects of interyear variability of extreme rainfall events on maize yields at locations in Cameroon, in central‐west sub‐Saharan Africa were investigated through a simulation assessment combining a weather generator with a crop growth model. This study analyzes the potential of using dry/wet year predictions to reduce risk in subsistence agricultural production associated with climate variability at the site level. Weather data sets from eight provincial study localities were classified into three precipitation scenarios – dry (lower threshold), normal and wet (upper threshold) years. According to the modelling results, there is a less than 12 per cent variance in mean maize yields across six out of the eight localities when planting occurs in March, May and August. The variance is equivalent to approximately 100–300 kg per ha, which represents a significant amount of food in the household security of the majority impoverished sectors of rural and urban society, and which could greatly impact the socioeconomic activities of the entire populace. The results lead to the conclusion that all extreme dry and wet years are not equal in terms of their regional manifestation. This calls for precise monthly and sub‐seasonal local level forecasts and the effective dissemination of this information to farming communities in Cameroon, thereby facilitating the adaptive management of indigenous cropping practices and reducing their vulnerability to climate related disasters.     

Geochemical composition of dykes along the Cameroon Line (CL): Petrogenesis and similarities with the Central Atlantic Magmatic Province

We report whole-rock geochemistry and Sr–Nd–Pb isotopic compositions of mafic dykes intruded in the Precambrian granito-gneissic basement complex, exposed at Nyos, Batibo, Dschang and Foumban on the Cameroon Line. The dykes are alkaline (Batibo), transitional (Foumban), and subalkaline (Nyos, Batibo and Dschang) with SiO₂ of 45–54 wt% and MgO of 2–9 wt%, similar to dykes reported in other areas of the Cameroon Line (CL) and the Central Atlantic Magmatic Province (CAMP). The abundances of rare earth elements (REE) and the Primitive Mantle normalised patterns for the Nyos, Batibo and Dschang dykes are similar to those of MORB, indicating that the dykes formed at shallower depths by a higher degree of partial melting relative to the Foumban dykes and the alkaline lavas of the CL. The transitional basaltic dykes with steeper REE patterns have their sources at deeper levels in the lithospheric mantle, possibly the garnet-spinel transition zone and were generated by a lower degree partial melting of the lithospheric and plume components. The Nyos and Batibo subalkaline dykes show similar isotopic compositions with a spectrum extending from depleted (DMM-like) to enriched (EM1-like) mantle, indicating the similarity in their source components. The Dschang dykes show distinct isotopic characteristics with relatively unradiogenic Nd-Pb isotope compositions compared to the Batibo and Nyos dykes. The Foumban transitional dykes with characteristic wide ranges in Sr-Nd-Pb isotopic compositions reveal varying contributions from enriched mantle components (EM1 and EM2) in addition to its plume signature similar to those of CL lavas. The Nyos and Batibo dykes alongside other dykes on the CL have low TiO₂ abundances (<2 wt%), negative PM-normalised Nb-anomalies, and moderately to strongly enriched REE patterns, and isotopic composition that overlaps with those of CAMP, suggesting a similar lithospheric origin.     

Institutional dimensions of the developing REDD+ process in Cameroon

The reducing emissions from deforestation and forest degradation (REDD+) initiative has emerged in recent years as a mechanism to simultaneously address climate change, biodiversity, and poverty reduction challenges at the margins of tropical forests. Congo Basin countries, including Cameroon, have embraced the opportunities that REDD+ provides, with great expectations. Yet, it needs to be investigated whether the enabling institutional environment, which is required for implementing REDD+, is present. Understanding is still limited on how to build adequate and strong institutional relations that could shape the reforms towards the establishment of efficient emissions reductions schemes. Furthermore, uncertainty remains on the operational mechanisms of REDD+, suggesting that, to catalyse effectiveness, there is a need to come up with a governance model nested in relevant policy frameworks. This study builds on a modified ‘4Is’ framework – Institutions, Interests, Ideas and Information – to analyse REDD+ and explore stakeholders' perceptions on the local forest governance potential. A structural implementation model to optimize the effectiveness of REDD+ is developed. Findings suggest that governments need to review existing policies to take into account participation, local people rights, and information access as a way to stimulate actors' willingness to contribute to emissions reductions and carbon stock increases under REDD+ regimes.