排序方式： 共有15条查询结果，搜索用时 31 毫秒
1.
Nicolas Baghdadi Gilles Grandjean Didier Lahondère Philippe Paillou Yannick Lasne 《Comptes Rendus Geoscience》2005,337(8):719-728
The potential of radar imagery in geological exploration was investigated at a study site in Mauritania (Akjoujt region). Compared with optical images, the results obtained show how radar imagery can help not only in detecting surface geological structures such as dykes and veins, but also mapping subsurface structures beneath a shallow layer of sand (palaeochannels). The mapping potential was found to be much better at long wavelengths than at short ones (L-band, compared with C- and X-band). As for optical images, their contribution is much more limited in the mapping of surface geological structures, and inappropriate for detecting subsurface structures. We conclude that spatial remote sensing enables the improvement of existing geological maps and the optimization of cartographic surveying. To cite this article: N. Baghdadi et al., C. R. Geoscience 337 (2005). 相似文献
2.
Pieter J.C. Honkoop Eilke M. Berghuis Sander Holthuijsen Marc S.S. Lavaleye Theunis Piersma 《Journal of Sea Research》2008,60(4):255-263
The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass (Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km2 of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m− 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m− 2) than seagrass meadows (30.0 g AFDM m− 2). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m− 2 and seagrass meadows 6.9 g AFDM m− 2. As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass. 相似文献
3.
This paper deals with the periodic fluctuation of precipitation at three meteorological stations (Atar, Chenguitti, and Akjoujt) in the Adrar and Inchiri provinces in northern Mauritania and its links with sea surface temperature (SST). Trends for these three meteorological stations were evaluated using the Mann–Kendall (MK) nonparametric test, regression analysis, and autocorrelation for persistence analysis. The MK test showed a significant decreasing trend for Akjoujt and an insignificant trend for the other rainfall time series. However, the decreasing linear regression trends were highly significant for the different time series. On the other hand, persistence analysis indicated the presence of a linear Markov type. The cycles found by power spectrum analysis ranged from 0.5 years to about 11 years. The possibility of a connection between precipitation in this region and sunspot numbers was suggested. SST of the Atlantic Ocean, Indian Ocean, and Mediterranean Sea have significant cross-correlations with precipitation in the study area. The El Niño-Southern Oscillation effect was found to be marginal. 相似文献
4.
Maritime governance stakes are important in West Africa, if only due to the dominant role of fisheries, which coastal populations mainly depend on. In this context, with reference to the fishery sector mostly studied in two countries (Guinea and Mauritania), this paper aims to identify and synthesize the challenges to be met towards developing the governance of marine spaces. To this end, the analysis is based on field knowledge, which provides input into a grid set according to the various integration levels of the concept of ICZM. This paper thus reports the major methodological obstacles to be overcome, commensurate to the stakes insofar as marine policies can and must contribute to the economic and social development of this region. 相似文献
5.
《Geodinamica Acta》2013,26(5):389-400
Despite its capital importance, the genesis of endoreic water table depressions in Western sub-Sahelian Africa is not well known yet. It is the case of the Trarza Aquifer, which is the main resource of drinkable water for Nouakchott. While water needs are growing steadily, global warming is threatening this resource. The genesis of piezometric depression is the object of this study, which analyses it in the light of the hydrochemistry of the western border of the Trarza aquifer, which is located in proximity of the Atlantic Ocean and its salt wedge. The hydrochemical facies of groundwater in the Idini pumping site, 60 km East of Nouakchott, and that of a Nouakchott to the Senegal River transect, should be categorised into 3 groups: 1) chloro-sulfated 2) sulfato-chlorinated and chloro-bicarbonated. Such facies, which are also sodocalcic, indicate that mineralization is of mixed origin (marine and continental). After reviewing the main mathematical models for piezometric depression, the present study attempts a conceptualization of the piezometric evolution of this phreatic aquifer (Continental Terminal) during the Quaternary. It highlights the dominant role of evaporation in the evolution of the water table of the Trarza aquifer, whose impact is similar to the one of the Quaternary marine level increase. 相似文献
6.
《Marine Policy》2014
The new protocol signed in July 2012 by the European Union and Mauritania under the existing Fisheries Partnership Agreement did not produce the expected results. The main component of this protocol consisted of the access rights for 300,000 t/yr of small pelagics. During the first five months after the signature of the protocol, no EU pelagic trawlers used the opportunities created by the protocol. Only after the formal approval of the protocol by the European Council in December 2013, some eastern EU member states started sending their pelagic trawlers back to Mauritania. This resulted in a utilisation of the protocol of 54% for the whole of 2013. Although the EU repeatedly stated that the €70 million/yr paid under the protocol provided good value for money, this assertion was hard to maintain considering the limited utilisation of the agreement. The paper analyses why the EU concluded an agreement with Mauritania that was not wanted by their industry and that was therefore only partially used in the end. It describes the decision making process inside the EU; the different parties involved and their different objectives. It is concluded that the EU decision making process suffers from a lack of transparency and that the combination of a business agreement with development aid resulted in an agreement which did not attain either of the stated objectives. It is proposed that in future the two aspects are clearly separated, and that the development component is extended to other countries in West Africa, including those that have no fish to sell to the EU. 相似文献
7.
Abstract Comprehensive geological, hydrogeological and hydrogeochemical investigations were carried out in the south of Hodh El Chargui (southeast Mauritania). Obtaining a hydrogeological conceptual model is crucial for groundwater resources development and management. This is especially true in developing countries and in the rural areas of sub-Saharan Africa. The chosen areas are represented by lithologies referring to a long geological time frame, dating from the Upper Neoproterozoic to the Quaternary age. We developed a methodology in order to identify sites that were suitable for the realization of productive, protected and correct wells to supply safe water to the rural community. A multicriteria approach to studying hydrogeology was used in the project area. In order to identify some main areas in which to carry out pilot interventions, criteria relating to water accessibility and availability, and to hydrogeological and water quality, were considered. Moreover, during the project, it was possible to transfer know-how and hand over responsibilities to the local population and bodies. Citation Ghiglieri, G. & Carletti, A. (2010) Integrated approach to choosing suitable areas for the realization of productive wells in rural areas of sub-Saharan Africa. Hydrol. Sci. J. 55(8), 1357–1370. 相似文献
8.
The 500 km2 of tidal flats at the Banc d'Arguin, Mauritania, are a wintering site for over 2 million shorebirds, making this one of the areas with the highest density of shorebirds in the world. In earlier studies, it was found that these huge numbers of birds are dependent on a rather low biomass of benthic animals. To explain this paradoxical situation, we hypothesized that the earlier assessments of biomass in late winter and early spring do not reflect a year-round situation. Benthic biomass may be high when the birds arrive in autumn to be subsequently grazed down in the course of winter. To test this hypothesis, we have determined benthic biomass in September 1988. The result has been compared with a biomass value obtained in February–April 1986 with the same methods and at the same stations. These two biomass values do not differ significantly; so our hypothesis has to be rejected. It has to be admitted, however, that our experimental design cannot discern between differences due to the year of sampling and those due to the season. 相似文献
9.
The Reguibat Shield comprises a western “Archaean terrane” and eastern “Eburnean terrane” juxtaposed during the early Palaeoproterozoic Eburnean Orogeny. Metasedimentary rocks of probable Palaeoproterozoic age are preserved as flat-lying klippen (Kediat Ijil and Guelb Zednes) and steep imbricate zones (El Mahaoudat range and Sfariat Belt). These are interpreted to record a phase of thrust tectonics that emplaced a continental margin succession onto a composite Archaean foreland prior to ca. 2.06 Ga sinistral transcurrent deformation. Together, these events reflect partitioned Eburnean transpression. 相似文献
10.
体征表征动物个体的健康状况,影响个体的体型及其生殖价值。乌贼(Sepia officinalis)营终生一次繁殖产卵,但性腺发育成熟个体的体征变化过程尚未可知。为此,本研究利用残差指标分析方法,对毛里塔尼亚外海分布的乌贼成熟个体的体征及其与体型、摄食强度关系进行了分析研究。结果显示,乌贼雌性成熟个体胴长范围为138~323 mm,雄性成熟个体胴长范围为135~343 mm;两者胴长呈单峰值区间分布,体质量与胴长呈显著的幂函数关系,幂函数拟合b值小于3。雌性、雄性成熟个体的体征存在一定的波动变化但不显著,在功能性成熟产卵期仍保持较好状态。同时,体征与胴长没有显著的函数关系,但是与胃饱满度密切相关,胃饱满度越高、体征越好;并且雌性、雄性成熟个体的空胃率比较低,在14%~34%之间。结果表明,毛里塔尼亚外海乌贼成熟个体保持个体生长,通过正常的摄食活动保持较好的体征。 相似文献