Inverse Estuaries in West Africa: Evidence of the Rainfall Recovery?

Inverse Estuaries in West Africa: Evidence of the Rainfall Recovery?

In West Africa, as in many other estuaries, enormous volumes of marine water are entering the continent. Fresh water discharge is very low, and it is commonly strongly linked to rainfall level. Some of these estuaries are inverse estuaries. During the Great Sahelian Drought (1968–1993), their hyperh...

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Bibliographic Details
Published in:Water (Basel) Vol. 12; no. 3; p. 647
Main Authors: Descroix, Luc, Sané, Yancouba, Thior, Mamadou, Manga, Sylvie-Paméla, Ba, Boubacar Demba, Mingou, Joseph, Mendy, Victor, Coly, Saloum, Dièye, Arame, Badiane, Alexandre, Senghor, Marie-Jeanne, Diedhiou, Ange-Bouramanding, Sow, Djiby, Bouaita, Yasmin, Soumaré, Safietou, Diop, Awa, Faty, Bakary, Sow, Bamol Ali, Machu, Eric, Montoroi, Jean-Pierre, Andrieu, Julien, Vandervaere, Jean-Pierre
Format: Journal Article
Language:English
Published: MDPI AG 01-03-2020
MDPI
Subjects:
Africa
drought
Droughts
Environmental aspects
Environmental Sciences
Estuaries
Fresh water
Global Changes
History
inverse estuaries
mangrove
Mangrove swamps
Measurement
Natural history
Salinity
water salinity
west africa
Africa
water salinity
drought
State of the Art
West Africa
mangrove 1 Problematics
inverse estuaries
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Summary:In West Africa, as in many other estuaries, enormous volumes of marine water are entering the continent. Fresh water discharge is very low, and it is commonly strongly linked to rainfall level. Some of these estuaries are inverse estuaries. During the Great Sahelian Drought (1968–1993), their hyperhaline feature was exacerbated. This paper aims to describe the evolution of the two main West African inverse estuaries, those of the Saloum River and the Casamance River, since the end of the drought. Water salinity measurements were carried out over three to five years according to the sites in order to document this evolution and to compare data with the historical ones collected during the long dry period at the end of 20th century. The results show that in both estuaries, the mean water salinity values have markedly decreased since the end of the drought. However, the Saloum estuary remains a totally inverse estuary, while for the Casamance River, the estuarine turbidity maximum (ETM) is the location of the salinity maximum, and it moves according to the seasons from a location 1–10 km downwards from the upstream estuary entry, during the dry season, to a location 40–70 km downwards from this point, during the rainy season. These observations fit with the functioning of the mangrove, the West African mangrove being among the few in the world that are markedly increasing since the beginning of the 1990s and the end of the dry period, as mangrove growth is favored by the relative salinity reduction. Finally, one of the inverse estuary behavior factors is the low fresh water incoming from the continent. The small area of the Casamance and Saloum basins (20,150 and 26,500 km² respectively) is to be compared with the basins of their two main neighbor basins, the Gambia River and the Senegal River, which provide significant fresh water discharge to their estuary.
ISSN:2073-4441
2073-4441
DOI:10.3390/w12030647