Impact of marine influence and cultivation on the diatom flora of Thiaroye Pond, Dakar, Senegal

Abstract

During a limnological and palaeolimnological study of the western part of the Great Coast of Senegal, an analysis of diatoms was carried out in Thiaroye Pond in the suburbs of Dakar. Current diatom flora in the water and on floating plants, and subfossil flora in two cores were sampled in 1996 and 2003. A total of 104 species and varieties, belonging to 38 genera were identified, 61 in the current environment and 87 from the cores. The genera most represented were Nitzschia (16 species), Eunotia (9 species), Amphora and Pinnularia (7 species each). The most frequently and regularly observed freshwater species were Cyclotella meneghiniana, Diadesmis confervacea, Eunotia pectinalis and Nitzschia amphibia, with marine to brackish-water forms occasionally being present. The proximity of the pond to the Atlantic Ocean had a dual effect on the diatom assemblage. Marine to brackish-water diatoms were transferred by wind and birds, and salinity increased over time, due to the rising level of saline groundwater. The alkalinity of the pond increased over time, due to the progressive destruction of the natural vegetation of the pond as a consequence of cultivation.

Keywords:

• acidity
• alkalinity
• land use
• saline water intrusion
• salinisation
• shallow fresh water