Recent Submissions

  • Contribution au recensement de quelques légumineuses spontanées et subspontanées, hôtes de Bruchidae en zone guinéenne au Togo (Coleoptera, Chrysomeloidea)

    Woegan, A.Y.; Glitho, A.I.; Bouchet, F.; Akpagana, K. (1997)
    Un inventaire effectué dans la flore spontanée des Légumineuses des savanes guinéennes du Sud-Togo a permis d'identifier neuf espèces de bruches appartenant à trois genres (Careydon, Conicobruchus et Bruchidius) qui parasitent 12 taxons de Légumineuses.
  • Quelques aspects du beach-rock dans le golfe du Bénin : le cas du Togo

    Blivi, Adoté (1998)
    Les dalles de beach-rock naissent dans les dépôts sédimentaires marins d'âge Holocène et caractérisent les anciennes lignes de rivage. Du fait de l'érosion des plages actuelles qui les recouvraient, elles affleurent en différents points de la côte du golfe du Bénin, jouant par endroits un rôle temporaire de protection naturelle et constituant un handicap pour la pêche traditionnelle. Sur la côte togolaise , elles figurent à différentes attitudes ; dans certaines segments de côte, elles atténuent l'énergie des vagues. Ailleurs elles sont en continuité topographique avec la plage aérienne. Une série de travaux portant d'une part sur les formes et les structures globales a conduit à la connaissance de ces anciennes plages cimentées et d'autre part sur la géométrie, a abouti à la définition de son rôle dans la dynamique côtière.
  • Heavy metals distribution of soils around mining sites of cadmium-rich marine sedimentary phosphorites of Kpogamé and Hahotoé (Southern Togo)

    Gnandi, K.; Tobschall, H.J. (Springer, 2002)
    Metal concentrations of 37 soil samples taken from mining areas (abandoned mine pits and transport routes) in Kpogamé and Hahotoé (southern Togo) range from 0.2-43 ppm for Cd, 15-115 ppm for Pb, 182-1,029 ppm for Cr, 18-356 ppm for Cu, 15-342 pm for Ni, 90-513 ppm for V, 35-536 ppm for Zn, 80-469 ppm for Zr and 266-3,161 ppm for Sr. The tropical alteration of the ore waste plays an important role in the distribution of trace elements in the studied soils. Because the alteration affects the element mobility, generally old abandoned mining areas, which , together with soils near the transport routes, show a higher degree of contamination. Under low pH and oxidising conditions in studied soils Cd, Ni and Zn are generally easily mobilised and are thus available to the environment.
  • The pollution of marine sediments by trace elements in the coastal region of Togo caused by dumping of cadmium-rich phosphorite tailing into the sea

    Gnandi, K.; Tobschall, H.J. (Springer-Verlag, 1999)
    The marine coastal sediments from Togo have been analysed for the trace elements Cd, Cr, Cu, Ni, Pb, Sr, V, Zn and Zr to ascertain the geological impact of dumping of phosporite tailings into the sea. Trace element concentrations ranged from 2-44 ppm for Cd, 22-184 ppm for Cu, 19-281 ppm for Ni, 22-176 ppm for Pb, 179-643 ppm for Sr, 38-329 ppm for V, 60-632 ppm for Zn and 18-8928 ppm for Zr. Regional distribution of trace elements in the marine environment indicates that the concentrations of Cr, Cu, Ni, Pb, V, Sr and Zn increase seawards and along the coastal line outwards of the tailing outfall, whereas Cd and Zr showed reversed spatial patterns. Sorting and transport of phosphorite particles by coastal currents are the main factors controlling the distribution of particle-bound trace metals in the coastal environment. The Cd, Sr and Zn concentrations increase with decreasing grain size. Percolation and shaking experiments were carried out in laboratory using raw phosphate material and artificial sea water. Enhanced mobilization of Cd from phosphorites by contact with the sea water was observed.
  • Morphosedimentary evolution of a delta-sourced, drift-aligned sand barrier-lagoon complex, western Bight of Benin

    Anthony, E.J.; Blivi, A.B. (1999)
    The coast of eastern Ghana and Togo is bounded by a major Holcene sand barrier complex hinged on the Volta Delta to the west and subject to high rates of longshore sand drift (1-1.5 x 10 m³/yr). In spite of its proximity to this major detaic sediment source, this barrier system shows marked longshore variations in progadation following the middle Holocene eustatic sillstand. It is a 'hybrid' system in terms of internal facies composition and plan-view morphology, in that it has evolved from an essentially regressive to a stationary (synonymous with cessation of progradation) system. Both transgressive and barrier-inlet facies have also developed through time and space. These temporal and spatial changes in patterns of development reflect variations in longshore sand transport and deposition over the last 5000 years. Such variations have been controlled by sediment supply from the Volta, by antecedent topography, by lagoonal and river drainage, by sediment cell development and maturation, and in the very recent past, by anthropogenic perturbation. Barrier progradation in the western Bight of Benin diminished considerably or ceased probably as early as 3400 yr B.P. as a single major equilibrium 'drift aligned' bight cell matured, permitting transport of Volta sand toward the rest of the eastern bight in Benin and Nigeria.......
  • The pollution of marine sediments by trance elements in the coastal region of Togo caused by dumping of cadmium-rich phosphorite tailing into the sea

    Tobschall, H.J.; Gnandi, K. (Berlin, Springer, 1999)
    The marine coastal sediments from Togo have been analysed for the trace elements Cd, Cr, Cu, Ni, Pb, Sr, V, Zn and Zr to ascertain the geo-ecological impact of dumping of phosphorite tailings into the sea. Trace element concentrations ranged from 2-44 ppm for Cd, 22-184 ppm for Cu, 19-281 ppm for Ni, 22-176 ppm for Pb, 179-643 ppm for Sr, 38-329 ppm for V, 60-632 ppm for Zn and 18-8928 ppm for Zr. Regional distribution of trace elements in the marine environment indicates that the concentrations of Cr, Cu, Ni, Pb, V, Sr and Zn increase seawards and along the coastal line outwards of the tailing outfall, whereas Cd and Zr showed reversed spatial patterns. Sorting and transport of phosphorite particles by coastal currents are the main factors controlling the distribution of particle-bound trace metals in the coastal environment. The Cd, Sr and Zn concentrations decrease with decreasing grain size in marine coastal sediments, whereas Cr, Cu, Ni and Zn concentrations increase with decreasing grain size. Percolation and shaking experiments were carried out in laboratory using raw phosphate material and artificial sea water. Enhanced mobilization of Cd from phosphorites by contact with the sea water was observed.
  • Sand barrier development in the bight of Benin, West Africa

    Blivi, A.B.; Anthony, E.J.; Oyédé, L.M. (Elsevier, 2002)
    The morphology, sedimentary facies, stratigraphy and development history of re-entrants and sand barriers in Togo and Benin (West Africa) have been analysed from boreholes and field data, and available radiocarbon dates. Re-entrant deposits range from basal Late Pleistocene fluviatile sands into Holocene estuarine and fluvio-deltaic sands. As sea level stabilized between 6000 and 5500 B.P., the "compartmented" coast associated with these reentrants favoured a polycellular longshore drift system. As the latter became infilled throughout the bight of Benin between 6000 and 4000 B.P., the littoral drift system evolved into a unicellular system fed by the Volta delta in Ghana, which has been the major sand source for an almost 300 kin long outer harrier. In spite of the massive and consistent volume of sand drifting eastward (1.2-1.5 x 10'6 m³/yr),progradation slowed down or ceased as equilibrium was achieved between coastal/shoreface geometry and the hydrodynamic regime, resulting in a balance between incoming and outgoing sand, and the downdrift migration of the accumulation sector towards Nigeria. This situation was probably achieved around 1500 to 2500 years ago in Benin, but apparently occurred much earlier in the updrift sector in Togo. This stability has been perturbed by the construction of deepwater ports in 1962 in Cotonon and 1967 in Lome leading to segmentation of the unidirectional drift and spectacular progradation and erosion, respectively, updrift and downdrift of breakwaters.
  • Les déchets miniers phosphatés source de la pollution marine au Togo

    Gnandi, K. (Université de Lomé, 2002)
    L'impact environnemental du rejet dans la mer des déchets miniers issus du traitement des phosphates de Hahotoké-Kpogamé(Togo) a été étudié dans ce manuscrit. Les résultats des analyses chimiques rnontrent de fortes concentrations des éléments Cd (2-44 mg/kg), Cr (1 15-753 mg/kg), Cu (22-184 mg/kg), Ni (19-281 mg/kg), V (38-329 mg/kg), Sr (179-643 mg/kg), Pb (22-176 nig/kg), Zn (60-632 mgikg) et du Zr (18-8928 mg/kg) dans la fraction < 63 um des sédiments marins côtiers. Les concentrations du Cd diminuent du grain grossier (silte) au grain fin (argile), alors que celles du Cr, Cu, Ni, V, Sr, Zn et Pb augmentent lorsque la granulométrie évolue vers le grain fin. Les phénomènes de transport par les courants littoraux, de tri par densité et de sédimentation des particules phosphatées chargées en métaux lourds sont les principaux facteurs de la distribution spatiale des polluants dans les sédiments côtiers. Les concentrations du Cd et du Zr diminuent de la côte vers le large et au fur et à mesure que I'on s'éloigne de I'exutoire des déchets à Gomou Kopé. Celles du Cr, Cu, Ni, V, Zn, Sr et Pb par contre montrent une distribution spatiale contraire, c.a.d qu'elles augmentent de la côte vers le large et au fur et à mesure que l'on s'éloigne de la source. A cause des processus de dispersion des sédiments par les courauts littoraux, un vaste halo geochimique de sédiments hautement pollués s'est constitué autour du point de déversement des déchets miniers. Des essais d'agitation et de percolation du phosphate brut avec de I'eau salée (rapport 1/10) menés en laboratoire montrent qu'une fois le contact eau de mer/phosphate établi il se produit une forte solubilisation des éléments Cd, Ni, Zn, Al et Fe par des processus de désorption causés surtout par la forte salinité de l'eau de mer.
  • The pollution of marine sediments by trace elements in the coastal region of Togo caused by dumping of cadmium-rich phosphorite tailing into the sea

    Gnandi, K.; Tobschall, H.J. (Berlin : Springer, 1999)
    The marine coastal sediments irom Togo have been analysed for the trace elements Cd, Cr, Cu, Ni, Pb, Sr, V, Zn and Zr to ascertain the geoecological impact of dumping of phosphorite tailings into the sea. Trace element concentrations ranged from 2-44 ppm for Cd, 22-184 ppm for Cu, 19-281 ppm for Ni, 22-176 ppm for Pb, 179- 643 ppm for Sr, 38-329 ppm for V, 60-632 ppm for Zn and 18-8928 ppm for Zr. Regional distribution L of trace elements in the marine environment indicates that the concentrations of Cr, Cu, Ni, Pb, V, Sr and Zn increase seawards and aloug the coastal a line outwards of the tailing outfall, whereas Cd and Zr showed reversed spatial patterns. Sorting and transport of phosphorite particles by coastal currents are the main factors controlling the distribution of particle-bound trace metals in the coastal environment. The Cd, Sr and Zn concentrations decrease with decreasing grain size in lnarine coastal sediments, whereas Cr, Cu, Ni and Zn concentrations increase with decreasing grain size. Percolation and shaking experiments were carried out in laboratory using raw phosphate material and artificial sea water. Enhanced inobilization of Cd from phosphorites by coutact with the sea water was observed.
  • Les îlots forestiers au sud du Togo : Dynamique et relations avec les végétations périphériques

    Kokou, K.; Caballé, G.; Akpagana, K.; Batawila, K. (1999)
    Cette étude traite des relations floristiques et dynamiques entre îlots forestiers et végétations périphérique dans la plaine côtière du sud du Togo. Les îlots forestiers sont essentiellement des fôrets sacrées et des forêts "pare-feu" à proximité des villages. Des relations évidentes ont été établies entre les îlots forestiers et les végétations périphériques : 1) phytogéographique, 51,8 % des espéces des îlots et 32,4 % des espèces des végétations périphérique sont d'origine forestière; 2) floristique, 870 espèces ont été recensées dont 649 dans les îlots et 610 dans leurs environs. 373 espèces leur sont communes....

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