Shallow coastal lagoons driven by tidal processes are extremely dynamic environments prone to continuous natural and anthropogenic pressures. The hydrodynamics of these systems deeply depends on the effect of local morphology on the tidal propagation, so their permanent evolution constantly changes tidal dependent processes. For this reason, the present work aims to review the main characteristics of Ria de Aveiro hydrodynamics, a shallow lagoon located at the Atlantic Coast of Portugal, evaluating its evolution over the last 30 years (between 1987 and 2020) and investigating the main morphological changes in its origin. For this purpose, a comparative analysis is performed to determine the main process, including the observed hydrodynamic changes: Deepening of the inlet channel or of the main lagoon channels. To achieve these goals, the authors explored a remarkable database including bathymetric, tide gauge, and salinity data from 1987 until the present. This analysis is completed by the exploitation of a hydrodynamical model (Delft3D), validated against field data. Several simulations were performed to analyse changes in tidal propagation along the lagoon channels (considering the main semi-diurnal constituent M2), tidal asymmetry, tidal currents, tidal prism, and salinity patterns. The results show that the general deepening of the lagoon observed between 1987 and 2020 led to important changes in the lagoon hydrodynamics, namely the increase/decrease of the M2 constituent amplitude/phase, as well as the increase of tidal currents and salt intrusion within the entire lagoon, with the changes being amplified towards the head of the main channels. Although the inlet deepening partially contributed to the modifications found, the results revealed that the deepening of the main lagoon channels had the most significant contribution to the changes observed during the last 30 years.

The thermal state of the ground governs heat and water exchanges, latent and sensible heat fluxes, plant growth rates, and soil organic matter decomposition and transport (e.g.,

[1] Benthic microbial metabolism and bacterial diagenetic pathways were measured along the southern shelf of Timor-Leste during an upwelling event in the winter SE monsoon season. Vertical profiles of water properties and bottom water nutrient concentrations, and operational ocean modeling showed subsurface upwelling from the Indonesian Throughflow (ITF) along the southern shelf west of longitude 126 25 0 E and surface upwelling at the far eastern end of the shelf. Warm surface waters above the halocline had salinities of 33.6 to 33.9 overlying cooler ITF water with salinities of 34.4 to 34.6. Beneath the zone of subsurface upwelling and stratification, sediment chlorophyll a (range: 2.8-4.4 mg g À1 ) and phaeopigment (range: 4.5-7.0 mg g À1 ) concentrations were sufficient to fuel very rapid rates of benthic oxygen consumption (range: 89.9-142.3 mmol m À2 day À1 ) and dissolved inorganic carbon (DIC) release (range: 108.1-148.9 mmol m À2 day À1 ) across the sediment-water interface, and DIC (range: 94.7-142.5 mmol m À2 day À1 ) and NH 4 + (range: 13.3-19.9 mmol m À2 day À1 ) production from incubated surface (0-10 cm) sediments. Molar ratios of DIC/NH 4 + production were lower (range: 6.6-7.7) in fine-grained sediments under the subsurface upwelling regime than in sandy, possibly scoured sediments under surface upwelling (range: 11.9-21.2) where there was no evidence of benthic enrichment. It is proposed that subsurface upwelling along the widest portions of the shelf stimulates phytoplankton production, leading to deposition of fresh phytodetritus that is rapidly decomposed on the seafloor. These zones of high biological activity may attract and support large populations of pelagic fish and cetaceans that have been caught for centuries along the south coast.

The interaction between tide, river runoff, and wind in coastal lagoons induces complex salinity gradients, which are remarkable when the meteorological forcing is exacerbated. This work aims to characterize the salinity structure under extreme freshwater and wind events in the Ria de Aveiro coastal lagoon (Portugal). The Delft3D model was implemented and validated in 3D mode and used to perform simulations forced with extreme freshwater and wind scenarios. Results show that forcing conditions determine salinity stratification intensity and location. Generally, stratification increases as the freshwater increases, while the salinity intrusion moves downstream. Extreme wind tends to destroy stratification but fails to promote full-depth mixing, which is also dependent on the wind direction, as shown for the Espinheiro channel. The salinity intrusion is also impacted by wind events, being NW storms responsible for an upstream salt transport along the Mira channel and a downstream transport along the Espinheiro channel, and SW storms for an upstream displacement of the salinity intrusion along the São Jacinto channel. Finally, it is observed that the advection of a freshwater plume from the Vouga River into the middle of the São Jacinto channel under high freshwater scenarios causes an unusual local salinity pattern. This plume can either be pushed upstream or prevented from entering the channel, depending on the wind direction.