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La secheresse des annees 1970 a contribue a la degradation de la mangrove en Casamance. Les activites socio-economiques (peche, riziculture...) sont devenues de moins en moins rentables. Pour faire face aux consequences des aleas climatiques, le barrage d’Affiniam fut construit sur le marigot de Bignona. Cependant, a la suite de sa construction, la degradation de la mangrove a semble s’accelerer en amont comme en aval du barrage. Dans ce contexte, la presente etude tente de comprendre cette degradation ainsi que la dynamique de l’ecosysteme autour du barrage. A cet effet, des cartes d’occupation des sols ont ete confectionnees avant et apres la construction du barrage. Des releves de vegetation ont ete faits le long d’un transect de 12 km passant par le barrage. Les resultats montrent que la mangrove a regresse de 55,58% entre 1986 et 2010 autour de l’ouvrage. Sa densite actuelle est de 3869 individus/ha en aval et de 245 individus/ha en amont. La mangrove de la partie aval est moins touchee par la degradation. Cependant, la salinite des eaux peut y atteindre 120 g/l en fin de saison seche, alors que le pH varie entre 6,5 et 7,5. Malgre ce taux de salinite eleve, le pH oscille autour de la neutralite (pH=7). © 2016 International Formulae Group. All rights reserved. Mots cles: Degradation, regression, 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

Dynamique de la mangrove du marigot de Bignona autour du barrage d’Affiniam (Casamance, Sénégal)