Circulação e transporte de materiais na região portuária do complexo estuarino de São Marcos (CESM) - Maranhão, BRASIL.

Abstract

Knowledge of hydrosedimentological behavior in coastal areas is very relevant for the maintenance of ecosystem services, development, land use and water resources. In the set of coastal environments and port logistics, there is the Port Complex of São Luís-CPSL, the largest and most important port complex on the North-Northeast coast (composed of 4 main ports) and the second in Latin America, with regard to to the flow of loads. In order to understand how hydrodynamic circulation and water bodies influence the transport of materials and constituents in the São Marcos Estuarine Complex (CESM), a characterization was carried out based on data analysis (conservative and non-conservative, speed and direction of currents) off the CPSL. The two campaigns (spatial and temporal approach) took place in 2017, covering the different periods (spring tide and square tide) and stages (flood and ebb) of the tide and in different seasonal regimes and fluvial discharge conditions (rain and end of rain). The equipment used for data acquisition was the ADCP, CTD and a van Dorn bottle. Through the data on the thermal and saline structures observed at CESM, cooler and more saline waters (𝑆a = 30.8) were observed in the rainy season, characterizing a Coastal Water (CW) and in the end of the rainy season it was observed if less saline and warmer waters, featuring an Estuarine Water (EW) (𝑆a=25.8), which resulted in percentages of fresh water (31%) and residence time (2 hours) higher in this period. The current intensities showed a maximum value of around 2.3 m s-1 that occurred in both tides and seasonal periods. The longitudinal component was more intense in the ebb (1.56 m s-1 in Mooring I and 1.13 m s-1 in Mooring II). MPS concentrations were high (> 550 mg L-1 ), with average values of approximately 200 mg L-1 and higher concentrations in the rainy season. Even so, the environment showed high concentrations of dissolved oxygen (OD>200 µmol kg-1 ). The highest flows occurred in the rainy season (33000 m³s-1 ) and at the end of the rainy season they were lower (27400 m³s-1 ), with 60% of the load balance values showing an import behavior, in both seasonal periods. The total water volume ranged from 107 m3 to 109 m3 , being higher during the rainy season. The variability of the average suspended sediment flows was 1243.99 Ton.h-1 in the rainy season and 741.65 Ton.h-1 at the end of the rainy season, both at low tide, with percentages above 80% of this. material being retained in the innermost radials of CESM, close to the berths of the Port of Itaqui. In any case, it is worth emphasizing that the MPS flows associated with the variability of environmental conditions and climate changes shape the estuarine region, requiring continuous monitoring due to potentially harmful activities, such as possible nautical accidents or oil spills or any contaminants in the water. region that results in destruction of the environment and the coastal region. The results presented emphasized how complex and dynamic the São Marcos estuarine system is, with regard to understanding the changes that occur in hydrodynamic and material transport in estuaries governed by macro tides located at the Amazon Semi-Arid interface.