The Brazilian Equatorial Margin, located in North-Northeast region of Brazil, has great ecological and economic importance. Inserted in that place, there is the Maranhão Continental Shelf (MCS) with its surrounding coast so variated, and the estuary of Turiaçu’s river (MA) with its biological significance, high tide amplitude and tidal power. Therefore, the objective of this work was to evaluate the variation of physico- chemical parameters in a stretch of equatorial margin, since Turiaçu River estuary until the break of MCS, according to spatiality, seasonality and tidal influence. The sampling was done in wet (january/2018), transitional (july/2018) and dry season (october/2018). The physicochemical
parameters investigated were temperature (°C), pH, electric conductivity
(mS/cm), turbidity (NTU), total dissolved solids (g/L), dissolved oxygen (mg/L) and
salinity. They were obtained in situ by a multiparameters probe Horiba U50. In the estuary, the sampling lasted a tide cycle (~13 hrs), occurring the acquisition of water samples halfhourly and in the shelf it was instantaneously. The statistical treatment of data was done by ANOVA two-way test, and if significant differences were found, the Tukey’s test was executed. Pearson’s correlation was realized to examine the correlation between the studied paramers, in agreement with seasonality. The temperature varied from 27.1°C to 32.4°C, reflecting equatorial characteristic of studied area, understanding the seasonality influenced
this parameter. The pH values were between 5.24 and 9.88, the study area was considered, predominantly, a basic environment, as well as this parameter presented spatial and seasonal variation. It had local significant differences and strong negative correlation (r = -0.95) with total dissolved salts (TDS) and electrical conductivity (EC). Solely in the middle of estuary, a high tidal influence in this parameter was observed. The DO ranged from 0.26 mg/L to 10.57 mg/L, occurring seasonal and spatial variation. This parameter was the most
influenced by the tide. Turbidity ranged from 0 NTU to >1000 NTU revealing the
characteristic of white waters estuary. The values of this parameter exceed the equipment detection range and was frequent in wet season. The significant differences did not occurred. The EC, TDS and salinity ranged, respectively, from 0.039 mS/cm to 57.2 mS/cm, 0.025 g/L to 78.3 g/L and 0 to 38.1. The correlation between these three parameters is positively very strong (r = 0,99), having the same seasonal and spatial behaviors, data fluctuation with tide and significant differences. It was perceived seasonal, spatial and tidal influence in these parameters. Therefore, it was concluded that, all parameters showed
seasonal and spatial variation and the estuary’s data, it was evident the tidal influence in all x f the studied parameters, except temperature. This study contributed to the scientific knowledge regarding the Turiaçu River’s estuary and MCS.
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