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1. Dynamique de la mangrove et perceptions locales dans le Département d’Oussouye (Basse-Casamance, Sénégal) entre 1972 et 2018

Author

El Hadji Balla Diéye, Tidiane Sané, Boubacar Solly, Boubacar Demba Ba, Ngor Ndour, Oumar Sy, Mamadou Thior, Victor Mendy, El Hadji Sidy Babacar Tall, Catherine Mering, and Amadou Tahirou Diaw

Subjects
mangrove, dynamics, management, mapping, lower-casamance, senegal, Agriculture
Abstract

Mangrove dynamics and local perception in the Department of Oussouye (Basse-Casamance, Senegal) between 1972 and 2018. In Lower-Casamance, the mangrove is a particular ecosystem that is home to many resources and remains the seat of the main rural activities. In the Oussouye area, this mangrove has experienced a significant decline during the 1970s and 1980s. The study of its spatio-temporal dynamics, using geomatics tools coupled with field surveys, made it possible to apprehend its decline between 1972 and 1994 of -42 %; and its positive evolution of +22.44 % between 1994-2018. The factors behind the decline during the 1970s and 1980s were mainly the rainfall deficit, with the consequences of salinization and acidification of the land, and the weakness of natural regeneration. The study also showed that anthropogenic actions such as cutting wood for various reasons and stilt roots have long harmed mangrove ecosystems. The recovery observed in recent decades is to be seen in the context of the return of rainfall to a better situation and the awareness of the populations of the strategic and important role of the mangrove.

Published
2022
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2. Inverse Estuaries in West Africa: Evidence of the Rainfall Recovery?

Author

Luc Descroix, Yancouba Sané, Mamadou Thior, Sylvie-Paméla Manga, Boubacar Demba 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 Ali Sow, Eric Machu, Jean-Pierre Montoroi, Julien Andrieu, and Jean-Pierre Vandervaere

Subjects
water salinity, inverse estuaries, west africa, drought, mangrove, Hydraulic engineering, TC1-978, Water supply for domestic and industrial purposes, TD201-500
Abstract

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.

Published
2020
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4. Le Conflit Politico-Militaire en Casamance, un Facteur Déterminant dans la Mise en Valeur des Terres de la Commune de Niaguis (Ziguinchor – Sénégal) sans titre

Author

Victor Mendy, Mamadou Thior, and Oumar Sy

Subjects
General Arts and Humanities, General Social Sciences
Abstract

La Casamance, de façon générale, tient sa particularité à l’égard du reste du Sénégal à son milieu physique surtout. Certaines formations végétales comme la palmeraie sont presque une spécificité de la région et d’autres comme la mangrove y sont en abondance. Les conditions climatiques ont favorisé le développement de l’agriculture dans cette région, qui s’est épanouie depuis des siècles. Cependant, depuis 1982, le conflit armé a occasionné l’abandon de zones de cultures, ce qui a accentué la précarité socioéconomique des populations. Cette contribution a pour objectif de décrire la situation agricole dans la commune de Niaguis avant, pendant et après la période de hautes tensions. L’approche adoptée est une combinaison de méthodes: les enquêtes de terrains et l’usage des Systèmes d’Information Géographique (SIG).

Published
2023

5. Dynamique de la mangrove et perceptions locales dans le Département d’Oussouye (Basse-Casamance, Sénégal) entre 1972 et 2018

Author

Amadou Tahirou Diaw, Catherine Mering, El Hadji Sidy Babacar Tall, Victor Mendy, Mamadou Thior, Oumar Sy, Ngor Ndour, Boubacar Demba Ba, Boubacar Solly, Tidiane Sané, and El Hadji Balla Diéye

Subjects
General Agricultural and Biological Sciences, General Environmental Science
Abstract

En Basse-Casamance, la mangrove constitue un écosystème particulier qui abrite de nombreuses ressources et reste le siège des principales activités rurales. Dans la zone d’Oussouye, cette mangrove a connu une régression importante au cours des décennies 1970 et 1980. L’étude de sa dynamique spatio-temporelle, à partir des outils de la géomatique couplés à des enquêtes de terrain, a permis d’appréhender son déclin, entre 1972 et 1994 de -42 % ; et son évolution positive de +22,44 % entre 1994-2018. Les facteurs à l’origine de la régression durant les années 70 et 80 sont principalement le déficit pluviométrique avec comme conséquences la salinisation et l’acidification des terres, et la faiblesse de la régénération naturelle. L’étude a aussi montré que les actions anthropiques telles que la coupe du bois pour diverses raisons et des racines échasses ont longtemps porté préjudice aux écosystèmes de mangrove. La reprise constatée au cours des dernières décennies est à replacer dans le contexte du retour de la pluviométrie à une situation meilleure et à la prise de conscience des populations du rôle stratégique et important de la mangrove.

Published
2022

6. Inverse estuaries in West Africa : evidence of the rainfall recovery ?

Author

Ange-Bouramanding Diedhiou, Victor Mendy, Julien Andrieu, Awa Diop, Djiby Sow, Yancouba Sané, Mamadou Thior, Jean-Pierre Vandervaere, Arame Dièye, Bamol Ali Sow, Jean-Pierre Montoroi, Safietou Soumaré, Yasmin Bouaita, Marie-Jeanne Senghor, Luc Descroix, Saloum Coly, Alexandre Badiane, Sylvie-Paméla Manga, Bakary Faty, Joseph Mingou, Eric Machu, Boubacar Demba Ba, ORSTOM, Université Assane SECK de Ziguinchor (UASZ), Laboratoire d'Algèbre, de Cryptologie, de Géométrie Algébrique et Applications (LACGAA), Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD), Patrimoines Locaux et Gouvernance (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Patrimoines locaux, Environnement et Globalisation (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU), Patrimoines et Territoires de l'eau (LMI PATEO), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Université de Lorraine - UFR Sciences humaines et sociales - Metz (UL UFR SHS), Université de Lorraine (UL), LMI ECLAIRS, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Université Côte d'Azur (UCA), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Direction de la Gestion et la Planification des Ressources en Eau (DGPRE), Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Études des Structures, des Processus d’Adaptation et des Changements de l’Espace (ESPACE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Sorbonne Université (SU)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), and UFR Sciences humaines et sociales - Metz [Université de Lorraine] (UL UFR SHS)

Subjects
Wet season, lcsh:Hydraulic engineering, 010504 meteorology & atmospheric sciences, [SDE.MCG]Environmental Sciences/Global Changes, Geography, Planning and Development, drought, 010501 environmental sciences, Aquatic Science, water salinity, 01 natural sciences, Biochemistry, West africa, lcsh:Water supply for domestic and industrial purposes, lcsh:TC1-978, Dry season, West Africa, 14. Life underwater, mangrove 1 Problematics, 0105 earth and related environmental sciences, Water Science and Technology, Hydrology, lcsh:TD201-500, geography, mangrove, geography.geographical_feature_category, Estuary, 15. Life on land, 6. Clean water, State of the Art, Salinity, Fresh water, 13. Climate action, inverse estuaries, Period (geology), Environmental science, Mangrove
Abstract

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&ndash, 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&ndash, 10 km downwards from the upstream estuary entry, during the dry season, to a location 40&ndash, 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 km&sup2, 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.

Published
2020

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