Régimes des flux des matières solides en suspension au Cameroun: revue et synthèse à l’échelle des principaux écosystèmes; diversité climatique et actions anthropiques / Regimes of suspended sediment flux in Cameroon: review and synthesis for the main ecosystems; climatic diversity and anthropogenic activities     

《水文科学杂志》2013,58(1)

Abstract

Abstract Since the end of the 1950s, suspended matter measurements have been carried out in the streams and rivers of Cameroon. Despite the fact that these are often point measurements, they provide a framework for a global approach towards studying the regimes of suspended sediment transport in these rivers. The objective here is to assess the intensity of sediment transport and to determine the principal factors which influence it, according to the main climatic units. The influence of human activities is pointed out. It appears that steep slopes, population density, soil cultivation and cattle grazing are the essential factors. The sediment load in these rivers is increasing with latitude with 20–40 g m^-3 at the Equator, 80–100 g m^-3 in the transition zones and 150–160 g m^-3 in the dry tropical zones. The choice of drainage basin size for the characterisation of the rate of effective erosion is indispensable. In fact, in large drainage basins (5 × 10⁴ km²), there is an integration of heterogeneous geomorphological, phytogeographical, pedological and anthropogenic characteristics into average characteristics which do not show the influence of local conditions on sediment transport.  相似文献   

Les camptonites du mont Cameroun,Cameroun, Afrique     

Ismaïla Ngounouno  Bernard Déruelle  Raymond Montigny  Daniel Demaiffe 《Comptes Rendus Geoscience》2006,338(8):537-544

Camptonites have been discovered at Mount Cameroon. They contain phenocrysts of olivine + clinopyroxene + plagioclase ± kaersutite ± bi and ocelli of nepheline or analcite and carbonates. ⁸⁷Sr/⁸⁶Sr_i values are similar to those of the basalts of Mount Cameroon $(\approx 0.7033)$. The camptonites are interpreted as resulting from fractional crystallization of a basaltic magma generated by a low degree of melting of an infra-lithospheric metasomatized mantle tapped by huge lithospheric cracks. To cite this article: I. Ngounouno et al., C. R. Geoscience 338 (2006).  相似文献   

An empirical assessment of the impact of climate change on smallholder agriculture in Cameroon     

Ernest L. Molua   《Global and Planetary Change》2009,67(3-4):205-208

Rainfed tropical agriculture provides important avenue to ascertain the consequences of climate change. This is because reliability of rainfall accounts for much of the variation in agriculture in the region. In addition, the region is already hot and vulnerable from further warming. This study shows from a climate change experiment using Ricardian method in Cameroon that a 7% decrease in precipitation would cause net revenues from crops to fall US$2.86 billion and a 14% decrease in precipitation would cause net revenue from crops to fall US$3.48 billion. Increases in precipitation would have the opposite effect on net revenues. For a 2.5 °C warming, net revenues would fall by US$0.79 billion, and a 5 °C warming would cause net revenues to fall US$1.94 billion. This highlights that agriculture is not only limited by seasonality and magnitude of moisture availability, but also it is significantly impacted by climate change.  相似文献   

Structural features of South-Adamawa (Cameroon) inferred from magnetic anomalies: Hydrogeological implications     

Constant Tatchum Noutchogwe  Fidèle Koumetio  Eliezer Manguelle-Dicoum 《Comptes Rendus Geoscience》2010,342(6):467-474

Structural directions of the southern part of the Adamawa plateau in Cameroon are highlighted by filters applied on the magnetic anomaly map. Determination of the magnitude maxima of (1) the horizontal gradient of the field reduced to the pole, and (2) the analytic signal, allowed a map to be produced showing various lineaments interpreted as the fault system of the studied area. In particular, the faults on the shaded relief map of the horizontal gradient magnitude suggest a slide to the left of the Foumban shear zone in the studied area. Interpretation of the observed anomaly along a profile directed SSE-NNW shows the presence of a magnetized body considered as an intrusion into the granitic basement of probably basaltic volcanic rocks, put in place during the reactivation of the Foumban shear zone. In addition, the observed correlation between the mapped structural directions, the sites of thermo-mineral springs and the hydrographical network shows that the results of this study will be helpful for further hydrogeological research in the studied area.  相似文献   

Fostering women's participation in development through non-governmental efforts in Cameroon     

Lotsmart Fonjong 《The Geographical journal》2001,167(3):223-234

Women constitute 52 per cent of the population of Cameroon and play a very crucial role in the development of society at all levels. Unfortunately, they function from a subordinate position inherent in both traditional and state institutions. Women's empowerment is currently an issue of national concern and both state and international efforts at mainstreaming women in development have so far produced mixed results. The 'grassroots' approach of NGOs has been effective in reaching women at all levels. Activities of NGOs have had far reaching but mixed effects in meeting both practical and strategic gender needs. This paper examines case studies of NGOs and women's empowerment in Cameroon, and highlights their successes, with regard to improved access and welfare and their limitations, with regard to conscientisation, participation and control.  相似文献   

Deep lithospheric structure across the Central African Shear Zone in Cameroon   总被引：1，自引：0，他引：1  

J. Plomerová  V. Babu&#;ka  C. Dorbath  L. Dorbath  R. J. Lillie 《Geophysical Journal International》1993,115(2):381-390

  相似文献   

Les monchiquites de Tchircotché, vallée de la haute Bénoué (Nord du Cameroun)     

Ismaı̈la Ngounouno  Bernard Déruelle  Daniel Demaiffe  Raymond Montigny 《Comptes Rendus Geoscience》2003,335(3):289-296

Dykes of monchiquites of Cainozoic age (37.5±2.3 Ma) are intrusive in Cretaceous sandstones in the Tchircotché area, Upper Benue valley (northern Cameroon). The differentiation of the monchiquites is explained by crystal fractionation of olivine, clinopyroxene, magnetite, ilmenite and apatite. A studied rock has low Sr-isotope ratio $\text{(0.703}\text{69±10)}$, which is similar to those of the alkali basalts of the Cameroon Line. Therefore the continental crust appears to have no significant role in the genesis of the monchiquites.  相似文献   

Perceptions of water in a changing hydrological and ecological context: the case of the Logone flood plains in Cameroon     

JAN WILLEM MOLENAAR†  JOSÉ C M VAN SANTEN‡ 《The Geographical journal》2006,172(4):331-347

We look at the beliefs of the population in North Cameroon concerning water, fish and water spirits in the context of the construction of a dam (1979) and of a flood embankment for a rice irrigation scheme financed by the World Bank. These operations caused a drought that had severe effects on the environment and the inhabitants' economic activities. Acknowledging the new approaches within development and ecological development thinking, we emphasize that local people are part of their environment, and that the environment and people's use of the ecosystem ought to be regarded as a functional unit. Our main argument is that the success of environmental strategies requires that the unequal power relations between the different actors and agencies and the perceptions of policymakers and NGOs be analysed and examined regularly in the course of a project to test their aims and integrity. In addition, the positions of beings and cosmological entities, which in the eyes of the population are 'actors of power to be reckoned with', like the water spirit, should also be included. The hidden agendas of all actors can be as difficult as the water spirit ( Maama Waata ) itself, by which we mean that hidden agendas are equally a part of reality as is the water spirit, even if they are not visible at first.  相似文献   

Palaeomagnetism of the continental sector of the Cameroon Volcanic Line, West Africa   总被引：1，自引：0，他引：1  

R. U. Ubangoh  I. G. Pacca  & J. B. Nyobe 《Geophysical Journal International》1998,135(2):362-374

Measurement of samples from 154 sites in the continental sector of the Cameroon Volcanic Line yielded six palaeomagnetic poles, at 243.6°E, 84.6°N, α ₉₅ = 6.8°; 224.3°E, 81.2°N, α ₉₅ = 8.4°; 176.1°E, 82.0°N, α ₉₅ = 8.5°; 164.3°E, 86.4°N, α ₉₅ = 3.4°; 169.4°E, 82.6°N, α ₉₅ = 4.6° and 174.7°E, 72.8°N, α ₉₅ = 9.5°, belonging to rocks which have been dated by the K–Ar method at 0.4–0.9  Ma, 2.6  Ma, 6.5–11  Ma, 12–17  Ma, 20–24  Ma and 28–31  Ma, respectively. The results are in general agreement with other palaeomagnetic poles from Oligocene to Recent formations in Africa.
  The first three poles for rocks formed between 0.4 and 11  Ma are not significantly different from the present geographical pole. Together with other African poles for the same period, this suggests that the African continent has moved very little relative to the pole since 11  Ma. The other three poles for rocks dated between 12 and 31  Ma are significantly different from the present geographical pole, showing a 5° polar deviation from the present pole in the Miocene and 13° in the Middle Oligocene.  相似文献   

Post-eruptive seismic activity of Mount Cameroon (Cameroon), West Africa: a statistical analysis     

Bekoa Ateba  Nfomou Ntepe   《Journal of Volcanology and Geothermal Research》1997,79(1-2)

Recent seismological studies of the Cameroon Volcanic Line show that Mt. Cameroon is the most active centre, so a permanent seismic network of six seismographs was set up in its region between 1984 and 1986. The network was reinforced with temporary stations up till 1987, and the local seismicity was studied. Here we emphasise a statistical analysis of seismic events recorded by the permanent seismic stations. Four swarms lasting 9 to 14 months are identified at intervals of 2–3 years. Most earthquakes are felt (intensity and magnitude, respectively, less than VI MM and 5) during the first three swarms and a few during repose periods. The main focal regions are the northwest and southeast flanks, the Bimbia and Bioko regions in the South of the volcano. Hypocentres are distributed from the surface to 60 km depth indicating crustal and subcrustal activities. The subcrustal events are observed only in the southeast flank, they are the most regular earthquakes with a monthly frequency of 9 to 15 events. They are characteristic earthquakes with magnitude 2.8 ± 0.1. Between 1984 and 1992, their yearly mean time interval between successive events range from 50 to 86 hours. For that period their occurrence can be modelled as a stationary renewal process with a 3-day period. But the analysis of variance shows possible significant differences among yearly means. A Weibull's distribution confirms that the time intervals between successive deep events are not independent, and in 1993 a swarm of deep earthquakes is recorded, hence a non-loglinear magnitude/frequency relation. The deep seismicity is thought to be associated with a zone of weakness (perhaps a magmatic conduit) and may have some close relationship with the magmatic activity.  相似文献