Hydrodynamics and Bio-Optical Assessment of Two Pristine Subtropical Estuaries in Southern Brazil

Abstract

A B S T R A C TMeasuring small-scale physical processes and how they affect the spatial patterns of sea water's optical constituents plays a key role in understanding the functioning of complex coastal ecosystems such as estuaries. The spatial variations of physical and ---ine System, located on the Southern Brazilian coast. Both sub-estuaries were classified as Type 1a, wellmixed with low stratification. The salinity variations are in phase with the water level, and the tidal propagation is well represented by a standing wave. The vertical velocity profiles showed little vertical shear, and the intensity of the u-component of the velocity varied semi-diurnally. The upper estuary salt transport was dominated by tidal diffusion in an unstable water column. The optical environment presented a mixed dominance of optically active substances, as indicated by the absorption coefficients of dissolved and particulate matter. The colored dissolved organic matter (CDOM) showed overall conservative behavior and was dominant in light absorption below 550 nm in the Medeiros, while nonalgal particles play the most important role in light absorption in the Itaqui in the blue absorption band. The phytoplanktonic contribution is prominent in the red domain and increases as a function of saline intrusion. However, due to the influence of freshwater discharge and the re-suspension of bottom sediments induced by physical processes, the concentrations of the optical components in the water column do not generally have any simple relationships between them. R E S U M OA quantificação de processos de transporte de pequena escala e a compreensão de como eles afetam o padrão espacial dos constituintes ópticos da água são peça chave no funcionamento de um ecossistema costeiro. A variação espacial e local de propriedades físicas e bio-ópticas da água foi analisada durante um ciclo de maré de sizígia do verão austral, bem como as estimativas do transporte advectivo e dispersivo de sal na secção transversal da boca dos subestuários Mederiros e Itaqui. Si sul do Brasil, e também integram a reserva da b salinidade componente u de velocidade variou semidiurnamente. O transporte de sal estuário água instável dominância com dominância da luz abaixo de 500 nm em Mede partículas Contudo, devido à influência da descarga de água doce e a ressuspensão de sedimentos induzida por processos físicos as concentrações dos componentes ópticos na colu ' .

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