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11.
J Kantoussan JM Ecoutin R Laë OT Thiaw L Tito de Morais 《African Journal of Marine Science》2018,40(2):175-185
This study examines the effects of increasing salinity on fish assemblage structure in the Casamance Estuary, Senegal, using a series of indices. The study data were derived from commercial fishery surveys conducted between April and July 2005. Analysis of within-trophic-group diversity in the Casamance Estuary shows a significant drop in the diversity of apex predators in the upper, more saline reaches of the estuary. By contrast, primary consumers adapted well to salinity changes and exhibited higher taxonomic diversity in the upper reaches of the estuary than in the lower reaches. The findings also indicate decreases in average sizes of the landed species and the trophic levels among fish catches in the direction of the upper reaches. However, the catch per unit effort (CPUE) was globally higher in the upstream area of the estuary as compared with the downstream area. This increasing CPUE trend from the lower towards the upper reaches is attributed to (i) the high primary productivity in the upper Casamance Estuary; (ii) the increasing abundance of euryhaline fish species in an upstream direction; and (iii) ‘telescoping’ of the food chain through the presence of mostly herbivorous fishes in the upper reaches. Such a situation likely facilitated high fish production in the upstream area of the estuary, though multimetric indices indicated unfavourable living conditions for many fish taxa in this area. 相似文献
12.
J.M. Ecoutin M. Simier J.J. Albaret R. Laë L. Tito de Morais 《Estuarine, Coastal and Shelf Science》2010
To investigate the changes in the fish assemblage of the Sine Saloum estuary (Senegal) over a 10-year period, it was surveyed during a complete hydrological cycle (three principal hydro-climatic seasons) first in 1992 and then in 2002–2003. The sampling protocol for the two surveys was identical, using the same sampling technique, the same collection periods, and the same sampling stations. 相似文献
13.
The aim of this paper is to show the contribution of geography to the study of pastoral mobility. While pastoralists of Ferlo,
Senegal, have become semi-sedentary, little is known about the mobility of their livestock. In this paper, pastoral mobility
is analysed using GPS measurements of cattle movements made by a pastoralist from 1997 to 2000. Based on data from 3 years,
a quantification of the extent of movements and mappings of the patterns are made. The results show that cattle walk about
5000 km on an annual basis, and while a great deal of the mobility can be characterised as daily circular movements between
the camp and watering points, occasional transhumance is still used to make the most of variable resources. 相似文献
14.
Mamadou Adama Sarr Philippe Gachon Ousmane Seidou Christopher Robin Bryant Jacques André Ndione Jacques Comby 《水文科学杂志》2013,58(9):1538-1549
AbstractDaily precipitation data from 31 Senegalese stations spanning the period from 1950 to 2007 were used to examine the inter-annual variations of seven rainfall indices: the annual mean precipitation (MEAN); the annual standard deviation of daily precipitation (STD); the frequency of wet days (Prcp1); the maximum number of consecutive dry days (CDD); the maximum 3-day rainfall total (R3D); the wet day precipitation intensity (SDII); and the 90th percentile of rain-day precipitation (Prec90p). The indices were spatially averaged over three agro-climatic regions in Senegal. Trends in the time series of the averaged indices were assessed using both visual examination and a modified version of the Mann-Kendall (MM-K) test. Initially negative significant trends in all seven indices suggest gradually drier conditions over the three agro-climatic regions between 1950 and 1980. In contrast, no significant trends, or even positive significant trends, were observed from the mid-1980s to 2007. The MM-K test was applied to all available data (1950–2007) and the period from 1971 to 2000. While several indices were found to have significant trends towards drier conditions for the 1950–2007 period, only PRCP1 showed a positive significant trend for the 1971–2000 period. The MM-K test did not detect a significant trend for the other indices. It was found that the rainfall deficit and therefore drought is no longer intensifying, and that the region may even become wetter. However, the period covered by the observations is still too short to resolve the question of whether there is now a trend towards wetter conditions.
Editor Z.W. Kundzewicz; Associate editor K. Hamed 相似文献
15.
《International Geology Review》2012,54(9):1073-1086
Field studies in the Palaeoproterozoïc Daléma basin, Kédougou-Kéniéba Inlier, reveal that the main tectonic feature comprises alternating large shear zones relatively well-separated by weakly deformed surrounding rock domains. Analysis of the various structures in relation to this major D2 phase of Eburnean deformation indicates partitioning of sinistral transpressive deformation between domains of dominant transcurrent and dominant compressive deformation. Foliation is mostly oblique to subvertical and trending 0–30° N, but locally is subhorizontal in some thrust-motion shear zones. Foliation planes of shear zones contain a superimposed subhorizontal stretching lineation which in places cross-cuts a steeply plunging stretching lineation which is clearly expressed in the metasedimentary rocks of weakly deformed surrounding domains. In the weakly deformed domains, the subhorizontal lineation is absent, whereas the oblique to subvertical lineation is more fully developed. Finite strain analyses of samples from surrounding both weakly deformed and shearing domains, using finite strain ratio and the Fry method, indicate flattened ellipsoid fabrics. However, the orientation of the long axis (X) of the finite strain ellipsoid is horizontal in the shear zones and oblique within the weakly deformed domains. Exceptionally, samples from some thrust zones indicate a finite strain ellipsoid in triaxial constriction fabrics with a subhorizontal long axis (X). In addition, the analysis of the strain orientation starting from semi-ductile and brittle structures indicates that a WNE–ESE (130° N to 110° N) orientation of strain shortening axis occurred during the Eburnean D2 deformation. 相似文献
16.
AbstractIn Senegal, magnetotellurie (MT) method has been used in an attempt to resolve the principal structural features by their electrical response. On the basis of numerical modelling of data, an unified model of possible crustal structure is presented for the West african margin. The results are in agreement with other independent geophysical and geological information. 相似文献
17.
西非塞内加尔盆地是全球近期油气勘探最活跃的前缘盆地之一。基于盆地最新的油气藏数据和勘探成果,应用石油地质综合研究和含油气系统分析的方法,研究了塞内加尔盆地的油气分布规律和主控因素,以成藏组合为评价单元,评估了待发现油气可采资源量,并探讨了盆地油气资源潜力和未来的勘探领域。研究表明,盆地发育3套含油气系统,志留系含油气系统、盐下三叠系含油气系统和白垩系含油气系统,白垩系含油气系统是最重要的含油气系统。区域上,盆地的油气主要分布于毛里塔尼亚次盆和北部次盆;层系上,油气主要储集于上白垩统赛诺曼阶、下白垩统阿尔比阶和中新统;埋深上,盆地油气储量集中分布于1 500~2 000 m和2 000~2500 m。油气富集的主要控制因素是生储盖的有效配置、优质的储层和圈闭及盐活动。资源评价结果表明,塞内加尔盆地待发现石油、天然气和凝析油的可采资源量分别为1 5083×106 bbl、363 Tcf(万亿立方英尺)和3270×106 bbl,合计7 8879×106 boe油当量,最具勘探潜力的成藏组合是上白垩统赛诺曼阶成藏组合和下白垩统阿尔比阶成藏组合。 相似文献
18.
Trends of biomass production and land processes in the Sahel have been widely studied since the droughts of 1970s. Satellite data have been an important source of information because of limited in situ data. Previous studies relied on the assumed existence of a relationship between vegetation productivity and the NDVI, in particular the annually integrated NDVI (iNDVI). This study examines this assumption and its limitations, based on in situ time series measurements of biomass, species composition, NDVI and soil moisture at the Dahra test site in northern Senegal. It is shown that, there are large differences between the NDVI – vegetation productivity relationships, and these differences can be linked to species composition. There is moderate correlation between NDVI and above-ground net primary productivity (ANPP) at the peak season (r2 = 0.39). In particular, the species Zornia glochidiata is characterized by high peak NDVI and low ANPP, compared to other common species such as Cenchrus biflorus and Aristida adscensionis. It is concluded that spatial and temporal variations in species dominance is likely to add noise to the relationship between NDVI and biomass. However, the seasonal cyclic fraction of the NDVI – “small seasonal integral” – reduces such noise. 相似文献
19.
fil. dr. GUNNAR JOHNSSON 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):99-103
Johnsson, G.: Localities visited on Excursions during the Nordic Symposium on Frozen Ground Morphology. Geografisk Tidskrift 82: 99–103. Copenhagen, October 15, 1982. The localities showing periglacial phenomena of various kinds that were demonstreated on September 7, 8 and 10 during the frozen ground symposia are described in this report with text and illustrations. The objects demonstrated were, i.a., periglacial valleys formed chiefly through gelifluction, an ice-wedge cast with infilling of lime, large ice-wedge casts of the most common type in south Sweden, lateglacial aeolian sand underlain by wind eroded stones and boulders, fossil periglacial ground surfaces with overlying sand with small ice-wedge casts and asymmetrical periglacial valleys. 相似文献
20.
Abstract Knowledge of the natural resources of a country is essential for the assessment of its development possibilities. This is particularly true for the evaluation of groundwater resources in a country like Uruguay, where less than 5 per cent of the potential is exploited and this in an inefficient way, and where no drastic future increase in demand is predicted. In the present paper the generalized hydrogeological model of the country was reconstructed, and recharge values, obtained by an approach adapted from nearby areas, were introduced. 相似文献