Temporal and Spatial Variability Scales of Salinity at a Large Microtidal Estuary

The Río de la Plata is a large fluvial–estuarine–sea system discharging into the southwestern Atlantic Ocean, which has relevant features such as high fluvial discharge, microtidal astronomical tidal scales, a relevant meteorological tide, and a strong atmospheric forcing effect, due to its large width. The objective of this study is to advance the understanding of the estuarine hydrodynamics and salt transport, as well as discussing the main characteristics of the spatiotemporal variability of the salinity field. To achieve this, the results of a 3D model of the Río de la Plata and its maritime front were used, simulating an extensive period of 10 years. In this study, the model was validated using vertical salinity profiles collected at different locations in the estuary. The temporal variability of the salinity stratification was characterised at different temporal scales: annual, monthly, and storm. At the same time, the influences of fluvial flow and winds were determined. The correlation analysis between fluvial flow and the salinity field showed that high annual fluvial flows generate an extension of the freshwater area, with larger longitudinal salinity gradients and a shift of the salinity front towards the ocean. The tendency at the monthly scale is not as clear as that observed at the annual scale. The results show that the effect of a storm coming from the northwest is quite similar to that of storms coming from the southwest, especially in the central and southern zones of the Río de la Plata, where mixing increases and stratification decreases, according to the intensity of the storm. The effect of south–southeasterly storms increases the mixing process and reduces stratification; the opposite effect was identified with respect to northeasterly storms, under the influence of which the stratified area increases. Synthesising the obtained results, a global zonification of the vertical salinity stratification for the Río de la Plata is proposed.

Comprehensive bathymetry and intertidal topography of the Amazon estuary

The characterization of estuarine hydrodynamics primarily depends on knowledge of the bathymetry and topography. Here, we present the first comprehensive, high-resolution dataset of the topography and bathymetry of the Amazon River estuary, the world's largest estuary. Our product is based on an innovative approach combining spaceborne remote sensing data, an extensive and processed river depth dataset, and auxiliary data. Our goal with this mapping is to promote the database usage in studies that require this information, such as hydrodynamic modeling or geomorphological assessments. Our twofold approach considered 500 000 sounding points digitized from 19 nautical charts for bathymetry estimation, in conjunction with a state-of-the-art topographic dataset based on remote sensing, encompassing intertidal flats, riverbanks, and adjacent floodplains. Finally, our estimate can be accessed in a unified 30 m resolution regular grid referenced to the Earth Gravitational Model 2008 (EGM08), complemented both landward and seaward by land (Multi-Error-Removed Improved-Terrain digital elevation model, MERIT DEM) and ocean (General Bathymetric Chart of the Oceans version 2020, GEBCO_2020) topographic data. Extensive validation against independent and spatially distributed data, from an airborne lidar survey, from ICESat-2 altimetric satellite data, and from various in situ surveys, shows a typical vertical accuracy of 7.2 m (riverbed) and 1.2 m (non-vegetated intertidal floodplains). The dataset is available at https://doi.org/10.17632/3g6b5ynrdb.2 (Fassoni-Andrade et al., 2021).

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

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.

Comprehensive bathymetry and intertidal topography of the Amazon estuary

The characterization of estuarine hydrodynamics primarily depends on the knowledge of bathymetry and topography. Here we present the first comprehensive, high-resolution dataset of the topography and bathymetry of the Amazon River estuary, the world's largest estuary. Our product is based on an innovative approach combining space-borne remote sensing data, an extensive and processed river depth dataset, and auxiliary data. Our goal with this characterization is to promote the database usage in studies that require this information, such as hydrodynamic modeling or geomorphological assessments. Our twofold approach considered 500'000 sounding points digitized from 19 nautical charts for bathymetry estimation, in conjunction with a state-of-the-art topography dataset based on remote sensing, encompassing intertidal flats, riverbanks, and adjacent floodplains. Finally, our estimate can be accessed in a unified 30 m resolution regular grid referenced to EGM08, complemented both landward and seaward with land (MERIT DEM) and ocean (GEBCO2020) topography data. Extensive validation against independent and spatially-distributed data, from an airborne LIDAR survey, from ICESat-2 altimetric satellite data, and from various in situ surveys, shows a typical accuracy of 8.4 m (river bed) and 1.2 m (non-vegetated inter-tidal floodplains). The dataset is available at http://dx.doi.org/10.17632/3g6b5ynrdb.1 (Fassoni-Andrade et al., 2021).

Development of a methodology to allocate mixing zones of industrial discharges in estuaries - Desarrollo de una metodología para delimitar zonas de mezcla de vertidos industriales en estuarios

The main objective of the present study is to make a step forward in the assessment of mixing zones of single-port industrial discharges in estuaries by developing and implementing a stepped methodology according to the significance of the considered discharge. Thereby, this methodology establishes where a mixing zone is required and determines its size and acceptability for each point discharge based on numerical models and mathematical tools. Thus, in this thesis a “Stepped Approach” has been developed to document the policy decision tree (methodology) that may be adopted by Member States and/or Industries when setting Mixing Zones (MZs) under Directive 2008/105/EC and Directive 2013/39/EU. The structure of the thesis is organized in six chapters as follows: - Chapter 1. Introduction. This chapter has introduced the reader in all other chapters of the thesis. Firstly, the motivations for research, explaining their importance and the reasons that led to the development of this thesis, are displayed. Secondly, the general aim of the thesis is presented and, finally, the organization of this thesis is explained. - Chapter 2. State of the Art. With the general aim in mind, a literature review is carried out in this chapter in order to evaluate the different methodological approaches used in daily practice around the globe, to state the contemporary issues in estuarine physics (hydrodynamics and mixing) and, finally, to gather the available numerical tools used to study estuarine hydrodynamics and mixing. This review highlights the strengths and deficiencies found in current approaches and allows the definition of the final objectives of the present work. - Chapter 3. Overall Methodology. In this chapter, the developed methodology, involving five steps, has been described. In Step 1, we collect the required information about the study area and the toxicant discharges. Step 2 identifies the significance of the discharge or discharges in the study zone. Next, Step 3 evaluates the effect generated by discharges and delimitates MZs from a simplified calculation that takes into account fixed conditions. Step 4 evaluates the effect generated by discharges and delimitates MZs during the driest year according to the river flow. Finally, in Step 5, we ’reevaluate’ the effect generated by discharges and ’redelimitate’ MZs according to a real case of dilution taking into account the variability of the environmental forcings. - Chapter 4. Numerical Tools. In this chapter, a review of the used numerical models and all the self-developed mathematical tools for integrating, transferring, communicating and plotting the required and obtained information along the overall methodology is presented. - Chapter 5. Results: Application to Suances Estuary. The implementation/application to Suances Estuary of the developed methodology in Chapter 3, using the proposed numerical tools described in Chapter 4, is presented. - Chapter 6. Conclusions and Future Research Topics. At the end of the document the conclusions of the present work are presented together with some proposals for future research topics that may complement the present study and the proposed methodology. Lastly, all the contributions made by this thesis were itemized.