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Sep 12, 2016Keywords:
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Dynamique de la mangrove du marigot de Bignona autour du barrage d’Affiniam (Casamance, Sénégal)
Abstract
La sècheresse des années 1970 a contribué à la dégradation de la mangrove en Casamance. Les activités socio-économiques (pêche, riziculture...) sont devenues de moins en moins rentables. Pour faire face aux conséquences des aléas climatiques, le barrage d’Affiniam fut construit sur le marigot de Bignona. Cependant, à la suite de sa construction, la dégradation de la mangrove a semblé s’accélérer en amont comme en aval du barrage. Dans ce contexte, la présente étude tente de comprendre cette dégradation ainsi que la dynamique de l’écosystème autour du barrage. A cet effet, des cartes d’occupation des sols ont été confectionnées avant et après la construction du barrage. Des relevés de végétation ont été faits le long d’un transect de 12 km passant par le barrage. Les résultats montrent que la mangrove a régressé de 55,58% entre 1986 et 2010 autour de l’ouvrage. Sa densité actuelle est de 3869 individus/ha en aval et de 245 individus/ha en amont. La mangrove de la partie aval est moins touchée par la dégradation. Cependant, la salinité des eaux peut y atteindre 120 g/l en fin de saison sèche, alors que le pH varie entre 6,5 et 7,5. Malgré ce taux de salinité élevé, le pH oscille autour de la neutralité (pH=7).
© 2016 International Formulae Group. All rights reserved.
Mots clés: Dégradation, régression, amont, aval, Casamance
English Abstract
Dynamics of the mangrove ecosystem around the Affiniam dam (Casamance, Senegal) on the Bignona backwater. The drought in the 1970s has contributed not only to the mangrove system degradation but also to the decrease of socio-economic profits for rural communities (fishing, rice production...). To accommodate to the adverse weather conditions, the Affiniam dam was built on the backwater of Bignona. However, its construction significantly reduced and degraded the mangrove system affecting the upstream as well as the downstream parts of the dam. To understand the causes of the environmental deterioration and the dynamics of the ecosystem around the dam, maps of the lands used before and after construction of the dam were made and vegetation inventory were conducted along a 12 km transect across it. The results of this study showed that the mangroves decreased by 55.58% between 1986 and 2010 in the area surrounding the dam with a current density of 3869 individuals/ha downstream and 245 individuals/ha upstream. The downstream portion of the mangroves where the tides are still effective is less affected by the process of environmental deterioration. However, water salinity can reach 120 g/l at the end of the dry season while water pH can vary between 6,5 and 7,5. Despite this high rate of salinity, the pH oscillates around 7 (neutral pH).
© 2016 International Formulae Group. All rights reserved.
Keywords: Degradation, regression, upstream, downstream, Casamance
