The coast of Prench Guiana is subjected to the Amazon dispersal system, which is influenced by oceanic currents and trade winds ruled by the position of the Intertropical Convergence Zone. The Sinnamary is one of the major French Guiana rivers. Since 1994, the hydroelectric dam of "Petit Saut" has modified the hydrological regime and the ecological functioning of the estuary. Variations in suspended material (organic and inorganic) concentr&tions, and parllffieters such as salinity, temperature, dissolved oxygen and chlorophyll has been foUowed up trom measurement carried out between December 1996 and February 1998 in the estuary. The load varied seasonally and according to the tide. To establish space-time variability, three. variation factofs (depth, time and tidal variation) have been tested. The effects were significant for síllinity, chlorophyll and the total particulate matter load. Suspended material is four times higher near the bQttom than in the surface, with a 13 % organic matter percentage. Net total particulate material exportation was estimated to 0,05x10(6) t.y-1 for Sinnamary. Modifications of hyçlrological parameters related to petit Saut hydroelectric dam operation mainly affect sediment transport, salinity and oxygen concentration. Significant biological effects are observed in the estuary.
Estuary; Suspended matter; Salinity; Chlorophyll; Tidal cyclo; French Guyana