Use of multitracers for the study of water mixing in the Paraiba do Sul River estuary

Multitracers were used to study water mixing in the Paraiba do Sul River estuary region in August 2007 (dry season) and March 2008 (rainy season) and to evaluate the reach of the river plume in the direction of the open ocean. Two sampling campaigns were carried out, each in a different season. Based on these results, it was possible to conclude that the multitracers used in this study (salinity, Si, Ba and U, as well as the radium isotopes Ra-223, Ra-224, Ra-226 and Ra-228) presented satisfactory results toward defining the plume reach and determining the residence time and water-mixing processes in the estuary. A strong correlation was observed between tracers and the distance to the coast. During the low river water discharge period, the riverine water took about 10 days to reach open ocean waters (salinity 35). During the rainy period this value decreased to 6 days. Based on the radium results, it was possible to calculate diffusion coefficients (K-h) of 23 km(2) d(-1) and 38 km(2) d(-1) for Ra-224 and Ra-223, respectively, during the dry season (winter). Values of 65 km(2) d(-1) and 68 km(2) d(-1) for Ra-223 and Ra-224, respectively, were found for the rainy period (summer). (C) 2009 Elsevier Ltd. All rights reserved.