Lake Alaotra (Madagascar) is not about to disappear.: Hydrological and sediment dynamics of an environmentally and socio-economically vital wetland.

Abstract : Lake Alaotra is the largest lake in Madagascar (456 km2). It is surrounded by marshland and irrigated perimeters of great economic value forming the “main rice granary” of the country. The basin also has an heritage and ecological value as a wetland protected by the Ramsar Convention (1971) and is home to a number of threatened endemic species. In reality the “lake” is just a vast shallow pool that seems doomed to silt up as the surrounding basin is affected by very strong erosion, the marks of which can be seen in the landscape («lavaka» or «tevana»). If Lake Alaotra is a transitional form destined to disappear, the question remains of how fast this will happen. In spite of repeated cries of alarm in the Malagasy media and also a few scientific affirmations, the silting up of the lake is not obvious. In a first approach, a critical analysis of arguments backing the hypothesis of rapid sedimentation in the lake is addressed. Subsequently, new data collected highlight the processes that effectively limit sedimentation, ranked from upstream to downstream these are: sand deposits by the overflows into the lacustrine plain, buffering by the aquatic vegetation in the marshes, resuspension of fine particles by wind and waves and their discharge related to currents and a probable subsidence. Significant sedimentation in the lake itself has not been shown, quite the opposite. Finally, local planning options are discussed. Priority must be given to improved land management in the catchment which affects both the large rice perimeters and the lake itself.
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Submitted on : Friday, March 2, 2018 - 9:27:21 AM
Last modification on : Thursday, June 20, 2019 - 1:02:24 AM

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Luc Ferry, Michel Mietton, Laurent Touchart, Olivier Hamerlynck. Lake Alaotra (Madagascar) is not about to disappear.: Hydrological and sediment dynamics of an environmentally and socio-economically vital wetland.. Dynamiques Environnementales - Journal international des géosciences et de l’environnement, Presses universitaires de Bordeaux, 2014, Chemins et territoires de l'eau dans les pays de la ceinture tropicale. Ressources et patrimoines, pp.104-123. ⟨http://www.pub-editions.fr/index.php/revues/dynamiques-environnementales.html⟩. ⟨hal-01122412v2⟩

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