Coastal Zone is a transitional environment between continent, sea and atmosphere; being well diversified and highly productive. Brazil’s northern coast estuaries are very complex and dynamical ecosystems which are highly influenced by seasonal variances, water and solid discharges from regional drainages, tide, wind, and current. Marajo Island, the world’s biggest river-estuarine island, presents tropical and wet climate, and influence from a strong mesotidal regime (2 – 4m of amplitude), its east margin is surrounded by tidal channels which are important for exchange of sediments and nutrients, these are influenced by regional hydrodynamic and hydrology, which compose this work’s objective. The study area covers three tidal channels belonging to Soure (Pesqueiro channel) and Salvaterra (Jubim and Limão channels) cities. This work, as a whole, has been realized through three campaigns (two for analyzing dry season and one for the rainy), along the spring tide on channels’ outfall and inward, about 13 hours (a tide cycle). The following equipment were used: CTD, OBS and currentmeter, fixed near the channels’ bottom to estimate the salinity, temperature, surface oscillation, turbidity, current intensity and its components. During the dry season, the highest values of salinity were obtained in Pesqueiro channel, followed by Jubim and Limão; as in the rainy season the order was reversed, showing a likely salt concentration on thinner channels. The most intense temperature values, on sampling period, were registered at the channels’ outfall, due to a relatively lower vegetable cover than inside the channel, at the highest solar intensity times. Also at the outfalls, have been found the highest values of turbidity, when the tidal moments were more intense (flood tide and ebb tide), in other words, the current intensity was higher. The magnitude of the longitudinal velocity’s component has obtained higher data than the transversal component, due to its orientation be the same of the channel’s preferential flow; both the components, predominantly, were more intense during the ebb tide moment. In relation to the delay that the tide has, between the sampling stations in each channel, depending on the distance between them, it was possible to allege that the channels’ inward tide takes less time, during the rainy season, to present the same conditions found at their outfall; and, provided this prognosis, it’s possible to interfere, creating containment measures, if there is some kind of contamination in area.
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