LAUSR

Abstract As part of our program to reconstruct the inter-dune depression's history in western Senegal and the diatom microflora inventory in Senegal, a 125 cm long core was taken from Mbao pond in the suburbs of Dakar. Diatoms were present only in the upper half of the core but their abundance remained poor to medium. However, an inventory of a total of 92 species and varieties belonging to 39 genera was determined. The most represented genera were Eunotia and Nitzschia (13 species each), with Pinnularia (9 species). The microflora is characterized by a dominance of epipelic, epiphytic and aerophytic species. Specific diversity was low and unevenly distributed throughout the core. Based on the diatom assemblages and lithological data, the following conclusions could be drawn: The absence of diatoms at the base of the core (zone O) is due either by their mechanical destruction by an agitated depositing environment, or by dissolution after their deposit. The base of the diatom section of the core or zone A is characterized by an association of very shallow freshwater aquatic environment with acidic pH; The upper part (zone B) is marked by the disappearance of acidophilic species and the development of mesosaprobic and meso-eutrophic alkaliphile species, linked to organic pollution caused by human influences, resulting in eutrophication of the waters of the pond. The dominant species have a great capacity of adaptation to the high concentrations of dissolved substances, following a strong evaporation as a result of a deficit of rainfall.