Mudflats and mud suspension observed from satellite data in French Guiana

The littoral of French Guiana is characterized by the north-westward migration of large mud banks along shore and by high suspended particulate matter concentrations (SPMC) coming from the Amazon River. A correspondence function is established between in situ optical data and SPMC measurements obtained from three coastal surveys on the Kaw River, the Mahury estuary, and the adjacent continental shelf, respectively. This function is applied to SPOT satellite images to estimate SPMC distributions near the sea surface on five dates between 1998 and 2001. Two typical situations have been observed: the mud suspensions are generally confined near the coast by a strong north-westward coastal current, while in one case (SPOT scene of 2 July 2001) the turbid plumes, probably resulted from the wave action on the mud banks, are directed seaward. SPMC varies from more than 300 mg l−1 adjacent to the intertidal zone to a few mg l−1 offshore. Turbid plumes are observed downstream, with regard to the Guyana Current, of small islands along the coast. Mud undulations are observed on the emergent surface of the mudflats, parallel to the crest waves and characterized by a wavelength of 200–1000 m. These structures are interpreted to form by wave action on the soft mudflat surface. Mangrove colonization of the mudflat follows these primary topographic structures.