The Amazon estuary is influenced by the tide and river discharge systems variations that
modify the currents and contribute with inputs of suspended particulate matter (SPM)
resulting in morphological changes along the river. The quantification of these parameters
provides an understanding of the rates of export and import of materials or volume and its
implications in the estuarine geomorphology. The aim of this study is to evaluate the
hydrodynamic, volume transport and SPM in different periods in Jacaré Grande, Pará and
Tocantins rivers. Speed and current direction, tide, turbidity, volume transport and SPM data
were collected over a tide cycle in the dry (2012) and rainy (2013) periods. The Pará river the
exported volume in both periods, while the Tocantins river imported during the dry period
and the exported in the rainy period. The Jacaré Grande river, influenced by the Amazon
river, imported in the rainy season and exported in the dry period. The analysis of the volume
transport methods showed a trend of export toward Amazon river and Marajó Bay in the dry
season and only toward the Marajó Bay during the rainy season. SPM values were higher in
the rainy season and descending from Jacaré Grande river to the Tocantins river in dry and
rainy season, respectively. Turbidity followed the same trend of SPM with tide, with
maximum values during the flood. SPM transportation methods showed similar values and
the same direction. The Jacaré Grande river served as an exporter during the dry period and as
an exporter in the dry period, the Para river as an exporter in both periods and the Tocantins
river in the dry season as an importer and as an exporter during the rainy season. The system
formed by the three rivers showed the same trend of export in both periods, with two
exportation routes in the dry season (Amazon river and Marajó Bay), and only one
exportation route in the rainy period (Marajó Bay). Annually the system exports between 5
and 7.2 million tons and possibly the Marajó Bay receives 3.7 to 5.8 million tons. The volume
transported to the ocean can be much higher. SPM flows, associated with the variability of
environmental conditions, molds the estuary, as seen in the mouth of the Tocantins river and
Guajará Bay. Thus, it important a continuous monitoring due to the potential boating
accidents, oil spills or any contamination in the region that can result in damage the
enviroment.
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