The dynamics of a frictionally-dominated Amazonian estuary

Abstract

(Praça do Oceanográfio, 191, SP, Brasil) 4 Centro de Pesquisas Aquáticas do Instituto de Pesquisas Científicas e Tecnológicas do Estado do Amapá (Rodovia Juscelino Kubitschek, km 10, 68903-000 Macapá, AP, Brasil)Corresponding author: nilsasp@ufpa.br A B S T R A C TThe hydrodynamics, morphology and sedimentology of the Taperaçu estuary were investigated. This is one of several estuaries located within the largest mangrove fringe in the world, bordering the Amazon region, subject to a macrotidal regime and regionally atypical negligible fresh water supply. The results reveal widespread sand banks that occupy the central portion of the estuarine crosssection. Well-sorted very fine sandy sediments of marine origin prevail. Shorter flood phases, with substantially higher current velocities, were observed in the upper sector of Taperaçu, as expected for a shallow, friction-dominated estuary. However, ebb domination can be expected for estuaries with large associated mangrove areas and substantial estuarine infilling, both of which situations occur on the Taperaçu. The tidal asymmetry favoring flood currents could be the result of the absence of an effective fluvial discharge. Furthermore, it was observed that the Taperaçu is connected by tidal creeks to the neighboring Caeté estuary, allowing a stronger flux during the flood and intensifying the higher flood currents. As a whole, the results have shown a complex interaction of morphological aspects (friction, fluvial drainage, connections with neighbor estuaries, infilling and large storage area) in determining hydrodynamic patterns, thus improving the understanding of Amazon estuaries. R E S U M OA hidrodinâmica, morfologia e sedimentologia do estuário do Taperaçu foram investigadas. Este é um entre vários estuários do litoral amazônico que integram a maior extensão contínua de manguezais do mundo, apresentando uma descarga de água doce muito reduzida, atípica para a região. Os resultados revelam grandes bancos arenosos que ocupam em grande parte a porção central do estuário. Areias muito finas e bem selecionadas de origem marinha prevalecem. Fases de enchente mais curtas, com velocidades de corrente substancialmente mais altas, são observadas na porção superior do estuário, como esperado para um estuário raso e dominado por fricção. Por outro lado, uma vazante mais intensa poderia ocorrer como resultado de grandes áreas de manguezais associadas e intenso preenchimento estuarino, sendo que ambas as condições são observadas no Taperaçu. Neste caso, a prevalência da enchente parece estar associada à ausência de uma descarga fluvial efetiva. Além disso, alguns canais de maré conectam o Taperaçu com seu vizinho estuário do Caeté, o que contribuiria para o domínio de enchente. Como um todo, os resultados demonstram uma complexa interação de aspectos de configuração (fricção, drenagem fluvial, conexões com estuários vizinhos, preenchimento e grandes áreas intermareais) na determinação dos padrões hidrodinâmicos, contribuindo para o entendimento dos estuários da região ...

Relationships between copepod community structure, rainfall regimes, and hydrological variables in a tropical mangrove estuary (Amazon coast, Brazil)

“…1), the Taperaçu has 21 km 2 of surface water and a catchment area of approximately 40 km 2 , but no effective source of freshwater. A recent study conducted in this estuary indicates that the system is characterized by discreet vertical gradients in hydrological parameters (Asp et al 2012). The main hydrodynamic feature is a semidiurnal tidal range of about 5 m, which may reach 6 m during the equinoctial spring tides (DHN 2008).…”

“…It is classified as a shallow (mean depth = 4.2 m), permanently open estuary, with many sandbanks running down the middle, high turbidity (mean 378.1), and strong tidal currents of up to 2.04 m s -1 (Asp et al 2012). Delimited by the Atlantic Ocean and the Maiaú Bay and Caeté estuary (Fig.…”

Observation of an Estuarine Turbidity Maximum in the Highly Impacted Capibaribe Estuary, Brazil

“…Such conditions are unfavorable to the formation of ETM. The eastern shores of Pará seem to present favorable conditions for the formation of ETM, and a single survey carried out in the Caeté estuary has shown a feature in the longitudinal distribution of SPM which fits in with what is expected of an ETM (ASP et al, 2012), even though it has not yet been assessed.…”

Hydrodynamic connectivity between two macrotidal Amazonian estuaries

“…Asp et al (2012) studying the Taperaçu and Caeté estuaries found out that there is a connection between the estuaries through the Taici channel. Their findings have motivated further investigation and therefore the development of the present study ( Figure 1).…”

“…The Taperaçu estuary presents 21 km² of water surface and a catchment area of approximately 40 km², without an effective fresh water source (Asp et al, 2012). On the other hand, the Caeté River has a basin of around 2,000 km², with fresh water discharge in the order of 40 m³.s -¹ (Souza Filho et al, 2009;Pereira et al, 2009).…”