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.

Freshwater plumes are important flow structures that influence the dynamics and water properties of coastal regions and continental shelves. Turbulence in plume regions is mainly driven by shear instabilities at the interface between plume and oceanic waters, which, in turn, depend on the geometry and outflow of a specific plume region. The Southern Brazilian Shelf presents a highly variable hydrographic distribution modulated by the seasonal wind variation and the freshwater discharge from the La Plata River estuary, which has a significant impact on the continental shelf circulation. This buoyant plume creates strong density gradients and interacts with local water masses resulting in a complex hydrographic pattern. In this study, high resolution hydrography and microstructure measurements were obtained in order to verify the effect of freshwater stratification on vertical mixing in this highly dynamic continental shelf. Results show that the plume is highly stable at southern portions of the shelf, as density displacements, or Thorpe displacements, δ_T, heat diffusivity, K_T, buoyancy flux, B_f, and density gradient ratio, R_p are reduced when compared to the northern areas. Moreover, hydrographic data suggests that the large-scale La Plata River plume has a dynamic mid-field region due to instabilities generated when reaching the shelf break.