Recent sedimentation rates in the Caravelas estuary (Bahia, Brazil) using unsupported 210Pb and 137Cs modeling

The Caravelas estuary is located in a zone of the Brazilian coast (Southern Bahia State) which has been submitted to different kinds of land uses during the last 50 years. This zone has an important ecological role, due to its mangroves and its location next to Abrolhos coral reef, the most important in the Southern Atlantic Ocean. Pb-210 and Cs-137 dating methods, accompanied by a sedimentological study, were applied to sediment cores in order to establish sedimentation rates and identify historical trends of land use and erosive processes. Sedimentation rates were established according to the "Constant Rate of Supply" (CRS) Pb-210 dating model, which was preferred rather than the "Constant Initial Concentration" (CIC) model. Corrected sedimentation rates obtained from Pb-210 dating were corroborated through a second independent radionuclide tracer such as Cs-137. The sedimentation rates obtained according to the CRS model for the cores were 1.07 +/- 0.13 cm yr(-1) for T#2 (inner sector), 0.65 +/- 0.06 cm yr(-1) for T#5 and 0.85 +/- 0.09 cm yr(-1) for T#8 (outer sector). The difference in sedimentation rates among the sampling sites could be due to hydrodynamic processes and could be related to the tendency of increase of erosive processes, conditioned by the changes in the landscape and land use to, which this region has been submitted.