Investigation of physical properties and suspended particulate matter discharge in a macrotidal estuary at the Amazon-semiarid transition zone

Abstract

This study evaluated the hydrodynamic circulation and discharge of Suspended Particulate Matter (SPM) in the Arraial-São José Estuarine Complex (ASJEC) located at the Amazon-semiarid interface, northeastern Brazil. Quasi-synoptic data were collected in the rainy and dry seasons of 2017 under spring tide conditions. For each sampling event, two mooring stations (one downstream [S-A] and one upstream [S-B]) were deployed during a complete tidal cycle. The physical characteristics in the rainy and dry seasons enabled dividing the estuarine complex into zones, with a mixing zone/coastal zone interface and a tidal river zone/mixing zone interface. The estuary is vertically quasi-homogeneous, indicating conditions of high vertical instability. The currents at the stations were more intense during the flood tide, demonstrating the importance of the marine component in the region. The estuarine system ranged from partially mixed to well mixed at both stations in the rainy season and was well mixed at both stations in the dry season. Total salt transport was towards the upstream portion of the estuary, suggesting the accumulation of matter in the ASJEC, most likely associated with the entrance of marine waters. The input of coastal water in the ASJEC intensifies the baroclinic pressure gradient, which creates a hydraulic barrier, indicating that SPM discharges from the continental drainage to the estuary and is interrupted from the estuary to the adjacent continental shelf.