Geochemistry of suspended particulate matter in a tropical estuarine system, southeastern Brazil

Abstract

The aim of this study is to assess the variation of the geochemistry of suspended particulate matter (SPM) in the tropical estuarine system composed of the adjacent Piraquê-Açu and Piraquê-Mirim (ES) rivers using SPM sampled with sediment traps (45 µm mesh) installed in the drainage channels. We collected SPM during different tidal stages and seasonal periods and analysed the metals using inductively coupled plasma mass spectrometry according to EPA 3051A, the mineralogy using X-ray diffraction, the particle size using laser ray diffraction, and organic matter (OM) using calcination. The traps collected enough SPM to perform analyses for each sampling period. The SPM consists of silt size particles, and the percentage of OM is between 20 and 40%. The particles are dominated by kaolinite and quartz, and gibbsite, haematite, goethite, and pyrite are also present. These materials are found in the Barreiras Formation, through which the drainage system cuts. The metal concentrations were higher in the summer: Al (3208.32 g kg-1), Pb (28.05 mg kg-1), Mn (676.35 mg kg-1), Cr (136.12 mg kg-1), and Cu (13.76 mg kg-1). The Piraquê-Açu River had higher metal concentrations than the Piraquê-Mirim River, and the geochemical indices of both rivers indicate that they naturally contribute to the estuarine system of the Piraquê-Açu and Piraquê-Mirim rivers (SEPAPM). However, anthropic interferences influence these indices at the confluence of the two channels.