Rainfall and salinity of a sahelian estuary between 1927 and 1987

The Saloum river (Senegal, West Africa) is an inverse estuary, with salinities of more than 80 gl-1 reached 100 km from the sea ... Since 1950, annual maximum and minimum salinities have been increasing, with decreasing rains, at a rate of about 1.3 gl1-1 per year. Across the 1927-1987 period, both yearly extremes are well correlated with rainfall in the previous years, indicating a "memory" 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 "green-house effect" hypothesi

Foraminifères et thécamoebiens de l'estuaire hyperhalin du fleuve Casamance (Sénégal)

Une cinquantaine d'espèces de Foraminifères et 8 espèces de Thécamoebiens ont été reconnues dans l'estuaire de la Casamance. La répartition de ces microorganismes permet d'établir une zonation écologique de cet estuaire hyperhalin. Un suivi des peuplements sur près de 2 ans a permis de mettre en évidence un cycle saisonnier avec augmentation de la proportion des formes hyalines en aval d'Adéane, pendant la saison des pluies. Mais ce cycle est masqué par une évolution de plus grande ampleur, probablement en relation avec l'évolution climatique actuelle qui affecte l'ensemble de la région. #Ammotium salsum et #Ammonia tepida sont les espèces les plus résistances. #A. tepida$ peut se développer dans les stations les plus en amont, à condition que la salinité soit comprise entre 35 et 50 °/°° pendant plus de 3 mois. (Résumé d'auteur

Distribution of carbon in a tropical hypersaline estuary, the Casamance (Senegal, West Africa)

The Casamance estuary, on the coast of Senegal, is an inverse hypersaline estuary : salinity increases landward, and dry season salinity values are up to 172 psu due to the evaporation of seawater. Dissolved inorganic carbon (DIC) concentrations decreased landward as a negative linear function of salinity. Thermodynamic modelling and the absence of CaCO3 in the sediments indicate that this loss of DIC was not due to calcite precipitation in the main water body. The intermost, almost landlocked, waters contained high phytoplankton biomass ... and high concentrations of allochthonous dissolved organic carbon. Photosynthetic uptake of DIC and subsequent particulate organic carbon sedimentation is proposed as hypothetical explanation of the relationship between DIC and salinity; localized overheating in shallow waters might also be involved. (D'après résumé d'auteur