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Article

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

1
IRD UMR PALOC MNHN/IRD/Sorbonne-Université, 75231 Paris, France
2
LMI PATEO, UGB, BP 234 Saint Louis, Senegal
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UASZ Université Assane Seck de Ziguinchor, BP 523 Ziguinchor, Senegal
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Université de Lorraine, UFR des Sciences Humaines et Sociales, 54015 Nancy, France
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LMI ECLAIRS, UASZ, ENS, BP 5036 Dakar, Senegal
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LaSTEE, Ecole Polytechnique de Thiès, DPA 10 Thiès, Senegal
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ESPACE Lab, Université Côte d’Azur, UFR Espaces & Cultures Campus, 06204 Nice, France
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Université Versailles St Quentin en Yvelines, UFR Sciences Sociales, 78280 Guyancourt, France
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DGPRE, Direction de la Gestion et la Planification des Ressources en Eau, section 2, 20000 Diamniadio, Senegal
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IRD/Laboratoire d’Océanographie Physique et Spatiale (LOPS), IUEM, Univ. Brest, CNRS, IRD, Ifremer, 29280 Plouzané, France
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IRD/IEES; Institut d’écologie et des sciences de l’environnement, 93143 Bondy, France
12
IGE/Université Grenoble Alpes; Institut des Géosciences et Environnement, 38058 Grenoble, France
*
Author to whom correspondence should be addressed.
Water 2020, 12(3), 647; https://doi.org/10.3390/w12030647
Received: 26 January 2020 / Revised: 23 February 2020 / Accepted: 24 February 2020 / Published: 28 February 2020
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. View Full-Text
Keywords: water salinity; inverse estuaries; West Africa; drought; mangrove water salinity; inverse estuaries; West Africa; drought; mangrove
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MDPI and ACS Style

Descroix, L.; Sané, Y.; Thior, M.; Manga, S.-P.; Ba, B.D.; Mingou, J.; Mendy, V.; Coly, S.; Dièye, A.; Badiane, A.; Senghor, M.-J.; Diedhiou, A.-B.; Sow, D.; Bouaita, Y.; Soumaré, S.; Diop, A.; Faty, B.; Sow, B.A.; Machu, E.; Montoroi, J.-P.; Andrieu, J.; Vandervaere, J.-P. Inverse Estuaries in West Africa: Evidence of the Rainfall Recovery? Water 2020, 12, 647. https://doi.org/10.3390/w12030647

AMA Style

Descroix L, Sané Y, Thior M, Manga S-P, Ba BD, Mingou J, Mendy V, Coly S, Dièye A, Badiane A, Senghor M-J, Diedhiou A-B, Sow D, Bouaita Y, Soumaré S, Diop A, Faty B, Sow BA, Machu E, Montoroi J-P, Andrieu J, Vandervaere J-P. Inverse Estuaries in West Africa: Evidence of the Rainfall Recovery? Water. 2020; 12(3):647. https://doi.org/10.3390/w12030647

Chicago/Turabian Style

Descroix, Luc, Yancouba Sané, Mamadou Thior, Sylvie-Paméla Manga, Boubacar D. Ba, Joseph Mingou, Victor Mendy, Saloum Coly, Arame Dièye, Alexandre Badiane, Marie-Jeanne Senghor, Ange-Bouramanding Diedhiou, Djiby Sow, Yasmin Bouaita, Safietou Soumaré, Awa Diop, Bakary Faty, Bamol A. Sow, Eric Machu, Jean-Pierre Montoroi, Julien Andrieu, and Jean-Pierre Vandervaere. 2020. "Inverse Estuaries in West Africa: Evidence of the Rainfall Recovery?" Water 12, no. 3: 647. https://doi.org/10.3390/w12030647

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