Auto-épuration du milieu marin. Quelques remarques méthodologiques

Outfall at sea of sewage from Abidjan requires information about the die-off of bacteria in the sea. The method of determination is described and validity of data is analysed. These preliminary results point out some features about the choice of methodology

La pollution bacterienne de la lagune et de la mer autour d'Abidjan

The total coliforms, fecal coliforms and fecal streptococci were counted over 1 year at 33 stations in the Ebrié Lagoon near Abidjan (Ivory Coast). Most of the waters show high numbers of bacteria, (D category of the American standards). For the sea-beaches, high numbers of fecal germs are found where the human population is abundant

Mineralogical attenuation for metallic remediation in a passive system for mine water treatment

Passive systems with constructed wetlands have been consistently used to treat mine water from abandoned mines. Long-term and cost-effective remediation is a crucial expectation for these water treatment facilities. To achieve that, a complex chain of physical, chemical, biological, and mineralogical mechanisms for pollutants removal must be designed to simulate natural attenuation processes. This paper aims to present geochemical and mineralogical data obtained in a recently constructed passive system (from an abandoned mine, Jales, Northern Portugal). It shows the role of different solid materials in the retention of metals and arsenic, observed during the start-up period of the treatment plant. The mineralogical study focused on two types of materials: (1) the ochre-precipitates, formed as waste products from the neutralization process, and (2) the fine-grained minerals contained in the soil of the wetlands. The ochre-precipitates demonstrated to be poorly ordered iron-rich material, which gave rise to hematite upon artificial heating. The heating experiments also provided mineralogical evidence for the presence of an associated amorphous arsenic-rich compound. Chemical analysis on the freshly ochre-precipitates revealed high concentrations of arsenic (51,867 ppm) and metals, such as zinc (1,213 ppm) and manganese (821 ppm), indicating strong enrichment factors relative to the water from which they precipitate. Mineralogical data obtained in the soil of the wetlands indicate that chlorite, illite, chlorite–vermiculite and mica–vermiculite mixedlayers, vermiculite, kaolinite and goethite are concentrated in the fine-grained fractions (<20 and <2 μm). The chemical analyses show that high levels of arsenic (up to 3%) and metals are also retained in these fractions, which may be enhanced by the low degree of order of the clay minerals as suggested by an XRD study. The obtained results suggest that, although the treatment plant has been receiving water only since 2006, future performance will be strongly dependent on these identified mineralogical pollutant hosts.Fundação para a Ciência e a Tecnologia (FCT

RAINFALL AND SALINITY OF A SAHELIAN ESTUARY BETWEEN 1927 AND 1987 CRO-DT (Centre de Recherches Océanographiques de Dakar-Thiaroye)/ISRA (Institut Sénégalais de Recherches Agricoles) BP 2241, Dakar (Senegal)

ABSTRACT Pagès, J. and Citeau, J., 1990. Rainfall and salinity of a Sahelian estuary between 1927 and 1987. J. Hydrol.,. The Saloum river (Sénégal, West Africa) is an inverse estuary, with salinities of more than 80 g 1-l reached 100 km from the sea. Monthly salinity measurements have been done 120 km inland since 1927. Seasonal salinity increase (during dry season) proceeds at a constant rate ( N 0.3 g I-&apos; d-&apos;). This would indicate that evaporating water masses are shallow (average depth N 0.4m). Since 1950, annual maximum and minimum salinities have been increasing, with decreasing rains, at a rate of about 1.3 g I-&apos; per year. Across the 1927-1987 period, both yearly extremes are well correlated with rainfall in the previous years, indicating a &quot;memory&quot; spanning three years or less. We have computed a water budget as a function of rainfall with three different hypotheses about the extent of the evaporating surfaces. Comparison with actual data indicate that about 60% of the lowlands are evaporating as shallow open waters would. We discuss the implications of these results for the possible future of the estuaries in the region, especially in the &quot;green-house effect&quot; hypothesis

Variations climatiques récentes en Afrique de l’Ouest et au Nord-Est du Brésil

Nos recherches ont pour but la création de fichiers de données, pour une surveillance de la Zone Intertropicale de Convergence (ZITC), et l’étude de paramètres physiques qui lui sont liés : position en latitude, à 28 ouest, du maximum de nébulosité, et anomalies de température de surface de la mer dans l’Atlantique intertropical ; températures radiatives et discontinuités thermiques en Afrique de l’ouest ; répartition et fréquence d’apparition des amas convectifs (cumulonimbus) de 50 est à 50..