Radioanalytical assessment of sedimentation rates in Guajara Bay (Amazon Estuary, N Brazil). A study with unsupported 210Pb and 137Cs modeling

Guajara Bay is an integral part of the Amazon Estuary system, and functions as the main receiver of urban and industrial wastes from the city of Belem, capital city of PA State (N Brazil). There is a lack of knowledge regarding quantitative measures of sedimentation, such as sedimentation rates, in the literature for this area of the Amazon Estuary. This study aimed the evaluation of recent (time range of 100 years) sedimentation rates in three sediment profiles collected in the coastal system of Guajara Bay with a radioanalytical approach of unsupported 210Pb and 137Cs modeling. The mean sedimentation rates for the cores obtained were 0.85 ± 0.12 cm year-1 for Anadim core, 1.02 ± 0.17 cm year-1 for Outeiro core and 0.53 ± 0.04 cm year-1 for Tucunduba core. With the use of three models of sedimentation rate models, it was observed that Anadim and Outeiro core presented constant sedimentation rates for the evaluated time range, but Tucunduba did not. This difference in sedimentation rates was probably due to their different sampling locations that present diverse hydrodynamic regime, with deposition of fine sediments in the upper area of the bay and stronger fluvial currents in the southernmost region. (author)