A model of recent sedimentation in the Cananeia–Iguape estuary, Brazil

Abstract

Coastal systems, in particular estuaries, are the first depositional environment to receive sediments transported by rivers to the coastal ocean. As a consequence of the geochemical processes involved, a part of the sediment may be deposited in the estuary and the remainder flows into the ocean, being transported and deposited under the influence of tides and maritime currents. This study was carried out in the Cananeia–Iguape estuary on the southern coast of São Paulo state, Brazil. The vertical distribution of 210Pb and 137Cs in sediments has been used as a tool for estimating the sedimentation rates in the coastal environment. Concentrations of 210Pb and 137Cs, as well as heavy metals (lead, zinc, copper) were determined in four sediment cores collected in the Cananeia–Iguape estuary. The estimated sedimentation rates were from 5.3 mm yr−1 to 12.7 mm yr−1. The highest sedimentation rate obtained for Valo Grande corresponds with an accelerated expansion of the sand and clay banks of the Mar Pequeno channel, a growth of the mangrove areas, and a decrease in the depth of the main channel of navigation, a fact that has been affecting the navigation in the area very seriously. The data obtained for the metals showed a sedimentary dynamics in agreement with that obtained in the studies of sedimentation rates, thus contributing to the understanding of the hydrodynamic mechanisms of the system.