Temporal Variability of Suspended-Solids Concentration in the Estuarine Channel of Patos Lagoon, Southern Brazil

Rafael André Ávila,Osmar Olinto Möller,Priscila Mulattieri Suarez Orozco,Mauro Michelena Andrade

doi:10.3390/w13050646

Rafael André Ávila, Osmar Olinto Möller + Show 2 more

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https://doi.org/10.3390/w13050646

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Abstract

The assessment of suspended-solids dynamics is crucial for the effective monitoring of estuarine environments. As the recurring in-situ sampling is usually problematic, the calibration of the backscattering from acoustic Doppler profilers has shown to be a reliable technique to estimate the suspended-solids concentration (SSC) in estuaries and rivers. In this study, we obtained a linear model that provides SSC estimates for the estuarine channel of Patos Lagoon by calibrating turbidity and acoustic data with in-situ concentration samples. The model output was analyzed in terms of its relationship with estuarine hydrodynamics and temporal variability. In this estuary, the supply of suspended solids is known to be due the runoff from its main tributaries, but also through the exchanges between the estuary and the coastal ocean. Both sources provide sediments and organic solids which affect water quality, geomorphology, and harbor operations. Results show that SSC is strongly linked to estuarine hydrodynamics, where concentrations increase with streamflow. During outflow periods, higher concentrations are associated with river runoff, whereas with inflow conditions they are induced by southern and southwesterly winds. However, relationship between SSC and streamflow is asymmetrical, meaning that the largest concentrations are majorly linked to outflow currents and downstream transport.

Highlights

Suspended solids, known as suspended matter, are a common element of aquatic environments, but they are of particular importance in estuaries
Acoustic Signal Backscattering Calibration The conditions observed during the three-day field survey to collect turbidity data for the calibration of the acoustic data are displayed as ensemble averages of streamflow velocity, Acoustic backscattering (AB), salinity, and turbidity profiles (Figure 3)
Turbidity was considerably low close to the surface (∼5 FTU), but it exponentially raised towards the bottom, a pattern followed by the backscattering

Summary

Introduction

Known as suspended matter, are a common element of aquatic environments, but they are of particular importance in estuaries. It must be conducted periodically to accurately encompass the suspended-solids variability associated with local hydrodynamics Given this inherent difficulty, the use of surrogate techniques by means of Acoustic Doppler Profilers (ADPs) is usually more suitable and effective. Backscattering is a measure of the spreading and attenuation of the acoustic signal as it travels along the water It is generated by suspended particles, but it depends on water density and instrument-specific parameters such as frequency, power, transducer size, and slant angle [11]. When taking these factors into consideration, the interaction between suspended solids and the acoustic signal is proportional to their concentration, allowing reliable estimates [12]

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