Fortnightly variability of total suspended solids and bottom sediments in a macrotidal estuarine complex on the Brazilian northern coast

Abstract

Macrotidal estuaries are highly dynamic and complex environments that need to be understood in many aspects. In this context, the study of sediments is an important tool in the understanding of the processes in estuarine environments. The aim of the present study was to characterize the temporal and spatial distribution of total suspended solids (TSS) and bottom sediments of the Arraial Bay Estuarine Complex and their dynamics under different tidal conditions during different periods. Nine stations were selected within Arraial Bay Estuarine Complex, in Maranhense Gulf, where water samples were collected at two depths in different periods and tide conditions. The following parameters were analyzed: temperature, salinity, turbidity, total suspended solids (TSS), and bottom sediments for grain size analysis, in addition to cross sections to calculate the estuarine flow rate. Temperature, and pH, was within the expected range for the region, with little spatial or temporal variation. The precipitation and the hydrodynamics caused by tidal movements in the region are important controllers of salinity, estuarine flow, TSS and turbidity, which showed spatial and temporal variations. There is a predominance of fine material, mainly composed of silt, which suggests that mangroves are important in the supply and imprisonment of these sediments within the estuarine complex. In addition, tides play an important role in the distribution of suspended and bottom sediments, and in the dynamics of the resuspended one, controlling TSS concentrations and distributions of bottom sediments along the estuarine complex.