Transporte de sólidos em suspensão e qualidade da água em Zona Estuarina Amazônica

Abstract

The studies on hydrosedimentological flows in coastal areas are relevant for the maintenance of ecosystem services, development, land use and water resources. An intense erosive process has caused significant hydrological, sedimentometric and water quality changes in the Lower Araguari River and along a stretch of the coast of Amapá, extreme north of Brazil. The main hypothesis of these changes is channel capture of the Araguari river basin by the Amazon River delta, through natural and artificial channels expanding in both directions, with emphasis on the Igarapé Novo - Gurijuba and Urucurituba Channels. The objective of this research was to evaluate the hydrodynamics, solid discharge (QSS) and water quality of channels that connect these two basins, considering aspects of seasonality and semidiurnal tides. Data were collected in two seasonal periods and six sections (Araguari, Igarapé Novo - Gurijuba and Urucurituba). The quantification methods of the parameters were: a) flow measurement with acoustic Doppler profilers (ADCP); b) water sampling in situ for physicochemical analysis and sediment (suspended solids - SS) and c) solids transport calculation (Qss). The results indicated a remarkable seasonal variability and during tidal cycles for most of the water quality parameters (p <0.05). In the dry period, the Igarapé Novo - Gurijuba Channel contributed with a small flow to the Araguari river. In the wet period, this channel diverted 28% of the flow of the Araguari river to the Amazon river, while Urucurituba Channel diverted 72%. In the wet period, the flows increased significantly, and consequently, increased Qss, with the highest expression in the Urucurituba Channel (Qss = 107,982 tons / day). The multiple regression analysis identified that, among other parameters, the distances of the sections measured to the river Araguari and Amazon river are physical gradients significantly influential of the variation of the Qss. Thus, the hypothesis that the Urucurituba channel represents the largest contribution of water and sediments in the Araguari River in relation to the adjacent channel (Igarapé Novo-Gurijuba) was confirmed. We conclude that this process favors space-seasonal intensification of erosive events, SS and water quality (p <0.05), and the rainy season associated with the flood tide effect significantly intensify the Qss of the Amazon River through the interior of the estuary river Araguari. The interactions between the two basins tend to continue to significantly alter water quality, intensifying erosive and depositional processes, affecting the equilibrium ecosystem in the Lower Araguari rive