Distribuição geoquímica dos metais no material particulado em suspensão - MPS na margem direita da Baia de Marajó, Costa Amazônica, Brasil

Abstract

The Marajó Bay, located in the Amazon region, is one of the largest estuarine systems in Brazil. It is influenced by the Amazon and Tocantins Rivers, with intense hydrodynamics and physico-chemical processes that affect metal distribution. This study aimed to analyze the concentrations and distribution of the elements Al, Fe, Mn, Mg, Zn, Cr, V, Ti, and Ca in suspended particulate matter (SPM) from the right margin of Marajó Bay, correlating the results with environmental factors such as salinity, pH, and local hydrodynamics. Samples were collected at three strategic points— Icoaraci (Point 1), Mosqueiro Island (Point 2), and Colares (Point 3) — during two campaigns carried out between April and May 2023. A Van Dorn bottle was used for surface and 20-meter depth sampling, covering the complete tidal cycle. The particulate material was filtered using cellulose acetate filters (0.45 μm) and analyzed by X-ray fluorescence spectrometry for quantitative determination of the elements. Physico-chemical data such as temperature, pH, salinity, and Eh were obtained using multiparameter probes, and current data using ADCP. Statistical analysis included Kruskal-Wallis tests, Pearson correlations, and boxplots. The results revealed significant variations in SPM concentrations among the sampling points. At Point 3 (Colares), the highest concentrations were observed at the surface (0.278 mg/L), indicating lower hydrodynamic energy and greater deposition of fine sediments, favored by saline intrusion and metal flocculation. Point 1 (Icoaraci) showed the lowest concentrations, suggesting higher sediment removal due to tidal dynamics and river discharge. The Kruskal-Wallis test indicated significant differences among surface samples, especially for Mg, Al, Ti, V, Cr, Fe, and Zn. At depth, only Mg and Zn showed significant variations. Pearson correlations revealed strong associations between Fe, Cr, Mn, and Zn at Point 3, suggesting co-transport of these metals, likely governed by adsorption onto iron and manganese oxides, particularly under low-energy conditions. The observed geochemical behavior highlights that hydrodynamics and saline intrusion are key factors controlling the spatial and vertical distribution of metals in Marajó Bay. It is concluded that Marajó Bay is a highly dynamic estuarine environment, where the deposition and transport of metals in SPM are controlled by both physical processes, such as hydrodynamic variation, and chemical processes, such as flocculation in saline environments. The findings contribute to the understanding of geochemical processes in the Amazon region and provide valuable insights for environmental management and the preservation of local ecosystems.