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Tidal estuaries are regarded as highly important ecosystems, mostly due to their high primary productivity and associated role as carbon sinks. In these ecosystems, primary productivity is mainly due to the photosynthetic carbon fixation by phytoplankton and microphytobenthos. The productivity of the two communities has been mostly studied separately, and directly comparable estimates of their carbon fixation rates in the same estuary are relatively scarce. The present study aimed to characterize the spatio-temporal variability of the productivity of phytoplankton and microphytobenthos in a tidal estuary, the Ria de Aveiro (Portugal). The productivity of the two communities was determined using a common methodological approach, based on measurements of in vivo chlorophyll fluorescence, allowing the estimation of the annual ecosystem-level budget for carbon fixation by the two groups. Productivity rates were determined based on synoptic in situ measurements of absolute rates of electron transport rate of photosystem II, using Pulse Amplitude Modulation fluorometry. Chlorophyll fluorescence indices were accompanied by measurements of salinity, temperature, water turbidity, solar irradiance, and planktonic and benthic microalgal biomass. Measurements were carried out hourly, along four spring-neap tidal cycles distributed along 1 year, on three sites of the estuary. The most pronounced trends in the spatio-temporal variability of the photophysiology and productivity of the two communities were the following: (i) maximum biomass and productivity were reached later for microphytobenthos (summer-autumn) than for phytoplankton (spring-summer); (ii) the absorption cross-section of PSII was generally higher for phytoplankton; (iii) the two groups showed a similar photoacclimation state, but microphytobenthos appeared as high light-acclimated when compared to phytoplankton. Biomass-specific productivity was on average higher for phytoplankton than for microphytobenthos, averaging 68.0 and 19.1 mg C mg Chl a–1 d–1, respectively. However, areal depth-integrated production rates were generally higher for the microphytobenthos than for the phytoplankton, averaging 264.5 and 140.0 mg C m–2 d–1, respectively. On an annual basis, phytoplankton productivity averaged 49.9 g C m–2 yr–1 while the productivity of microphytobenthos averaged 105.2 g C m–2 yr–1. When upscaling to the whole estuary, annual primary production rates of phytoplankton and microphytobenthos reached 4894.3 and 7534.0 t C yr–1, respectively, representing 39.4 and 60.6% of the combined total of 12428.3 t C yr–1 determined for the two communities in the Ria de Aveiro.

Drowning accidents followed by the disappearance of the body are particularly distressing events. When such tragedy strikes, Search and Rescue Operations are usually deployed to recover the body. The efficiency of such efforts can be enhanced by timely data and appropriate data integration tools, such as operational prediction systems relying on numerical models or other data sources. In this paper, we propose four stages for Search and Rescue Operations after drowning accidents and briefly address the critical role of ocean observations at each stage, as well as the relevancy of available computational resources. The potential of the combination of different data sources on the state of the sea to provide better insight into Search and Rescue Operations is discussed. This work is a challenge to oceanographers, data scientists and relevant marine stakeholders to produce knowledge and tools to support Search and Rescue Operations after drowning accidents.

Costa, S.; Picado, A.; Vaz, N.; Coelho, C.; Portela, L., and Dias, J.M., 2018. Climate change effects on suspended sediment dynamics in a coastal lagoon: Ria de Aveiro (Portugal). In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 521–525. Coconut Creek (Florida), ISSN 0749-0208. Coastal systems are very important interface areas between land and sea, subject to constant changes motivated by both natural and anthropogenic factors. In addition to the increasing modifications imposed by human activities, natural processes are also being altered as a result of climate change. Important consequences of climate change in coastal systems are sea level rise (SLR) and changes in freshwater discharge, due to modifications in rainfall patterns and air temperature. The aim of this work was to assess the impact of climate changes on the suspended sediment dynamics i...

It is of global interest, for the definition of effective adaptation strategies, to make an assessment of climate change impacts in coastal environments. In this study, the salinity patterns adjustments and the correspondent Venice System zonations adaptations are evaluated through numerical modelling for Ria de Aveiro, a mesotidal shallow water lagoon located in the Portuguese coast, for the end of the 21st century in a climate change context. A reference (equivalent to present conditions) and three future scenarios are defined and simulated, both for wet and dry conditions. The future scenarios are designed with the following changes to the reference: scenario 1) projected mean sea level (MSL) rise; scenario 2) projected river flow discharges; and scenario 3) projections for both MSL and river flow discharges. The projections imposed are: a MSL rise of 0.42 m; a freshwater flow reduction of ∼22% for the wet season and a reduction of ∼87% for the dry season. Modelling results are analyzed for different tidal ranges. Results indicate: a) a salinity upstream intrusion and a generalized salinity increase for sea level rise scenario, with higher significance in middle-to-upper lagoon zones; b) a maximum salinity increase of ∼12 in scenario 3 and wet conditions for Espinheiro channel, the one with higher freshwater contribution; c) an upstream displacement of the saline fronts occurring in wet conditions for all future scenarios, with stronger expression for scenario 3, of ∼2 km in Espinheiro channel; and d) a landward progression of the saltier physical zones established in the Venice System scheme. The adaptation of the ecosystem to the upstream relocation of physical zones may be blocked by human settlements and other artificial barriers surrounding the estuarine environment.

Cohesive sediments play an important ecological role in coastal systems, affecting light penetration in the water column and consequently the local biogeochemical processes. The main aim of this work is to study the water-column light extinction coefficient (k) dependence on cohesive sediment dynamics within Ria de Aveiro lagoon under sea level rise and extreme freshwater discharges events. A coupled estuarine hydrodynamic and transport model is explored, following previous modeling frameworks developed for the Ria de Aveiro. Three scenarios were simulated: a reference scenario (SC1), wherein present hydrodynamic, mean sea level and present freshwater discharges were used to simulate present hydrodynamic and cohesive sediments; a scenario considering local projections of sea level rise of 0.42 m (SC2); and a third one corresponding to maximum freshwater inflow for the lagoon's tributaries (SC3). Results show higher concentrations of cohesive sediments near the rivers mouths, gradually decreasing toward the lagoon's inlet. From SC2 scenario was found that the effect of sea level rise in sediment dynamics and in water-column light extinction coefficient is not significant. However, the tidal prism increase in this case induces a dilution of the sediments concentration from fluvial origin and consequently a slightly k decrease. Contrarily, in SC3 scenario, the extreme freshwater inflow enhances the cohesive sediment concentration in the entire lagoon, limiting the light penetration in the water column. In summary, extreme river discharge events have a highest impact on water-column light penetration in Ria the Aveiro than predicted sea level rise.

Vaz, L.; Serodio, J., Mateus, M., Dias, J.M., and Vaz, N., 2016. Primary production of the benthic microalgae in the bottom sediments of Ria de Aveiro Lagoon. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 178–182. Coconut Creek (Florida), ISSN 0749-0208. The Ria de Aveiro is a mesotidal coastal lagoon located in the north coast of Portugal. It has a complex irregular geometry characterized by large intertidal areas and several freshwater tributaries, which are the main sources of nutrients into the lagoon. The dynamics between the tidal propagation and the landward nutrient sources modulates the primary production within the lagoon. Here, primary production may have two main contributors: the chlorophyll in the water column and the benthic microalgae in the bottom sediments. In this work, a new methodology to compute microalgae in the b...

Longo, R.S., Picado, A., Vaz, N. and Dias, J.M., 2016. Biological response of a coastal plain estuary to torrential episodes: a modelling study. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 78–82. Coconut Creek (Florida), ISSN 0749-0208. Estuaries are highly dynamic systems with an important impact on biogeochemical cycles and primary production, which may be affected and modified in a climate change context, namely due to extreme rainfall events. This study aims to research chlorophyll-a (Chl-a) and nutrients dynamics in the Tagus estuary under extreme freshwater discharge in a climate change context, using a 2D biophysical model. Three scenarios were set changing the inputs from the main tributaries – Tagus and Sorraia rivers. First, a scenario with one day of extreme discharge for both rivers was considered. Next, and in order to un...

The Douro is one of the largest rivers of the Iberian Peninsula, representing the most important buoyancy source into the Atlantic Ocean on the northwestern Portuguese coast. The main goal of this study is to contribute to the knowledge of physical processes associated with the propagation of the Douro River plume. The general patterns of dispersion in the ocean and how the plume change hydrography and coastal circulation were evaluated, considering the main drivers involved: river discharge and wind. Coastal models were implemented to characterize the propagation of the plume, its dynamics, and its impact on coastal circulation. Different numerical scenarios of wind and river discharge were analyzed. The estuarine outflow is sufficient to generate a northward coastal current without wind under moderate-to-high river discharge conditions. Under easterly winds, the propagation pattern is similar to the no wind forcing, with a northward current speed increasing. A southward coastal current is generated only by strong westerly winds. Under upwelling-favorable (northerly) winds, the plume extends offshore with tilting towards the southwest. Southerly winds increase the velocity of the northward current, being the merging of the Douro and Minho estuarine plumes a likely consequence.

This work studies the influence of the Tagus estuary, Portugal, on the near coastal system using a model application to describe the main physical and biogeochemical processes in the Region of Freshwater Influence (ROFI). It was used as nested modeling approach, downscaling the solution for the general circulation from a larger domain model (the Portuguese coast), to the local Tagus estuary domain. The model is evaluated during a very dynamic and biologic productive period of the year, corresponding to the winter and early summer (January–May 2007). Also during this period, there is a strong freshwater inflow into the Tagus estuary, which in turn modulates the estuarine outflow to the Tagus ROFI. The results focus on water temperature and chlorophyll and a skill assessment was made, given the lack of data required to perform a thorough validation. Simulation results reveal an adequate reproduction of the vertical thermal structure and chlorophyll concentrations. While a fairly reasonable agreement is seen for water temperature, showing no significant thermal stratification at the study area (average surface-to-bottom difference ranging from 1.3 °C to 1.6 °C), chlorophyll vertical profiles show some differences between the model results and the measurements. Maximum model bias for surface temperature is 1.4 °C and ranges from 1 to 2 mg m− 3 for chlorophyll, revealing an underestimation of the predicted chlorophyll and surface temperature for the area in the vicinity of the Tagus mouth. The general trends of surface chlorophyll and surface water temperature are satisfactorily reproduced by the model.

The northwestern coast of the Iberian Peninsula is characterized by a high primary production mainly supported by coastal upwelling, creating an extraordinary commercial interest for fisheries and aquaculture. Considering chlorophyll- a (Chl- a ) as an indicator of primary production, its spatio-temporal variability was researched in this study in the surface water of this upwelling region from 1998 to 2007. Satellite derived Chl- a , Sea Surface Temperature (SST) and Ekman transport data as well as the inflow of the main rivers discharging into the study area were used to investigate the origin of the Chl- a concentration. Empirical Orthogonal Function (EOF) analysis of weekly Chl- a images was performed, as well as correlation analysis between Chl- a concentration, Ekman transport and river discharge. EOF results suggest that the highest Chl- a concentration occurs near the coast up to 60 km offshore. The interannual variability of Chl- a , SST and Ekman transport was also studied considering summer and winter months. Generally, 2005, 2006 and 2007 were the most productive years during the summer months with high Chl- a concentrations along the coast associated to the strong upwelling conditions observed. Otherwise, 1998 seemed to be the most productive year during winter. The absence of upwelling favorable conditions together with localized low SST and considerable discharges, suggests that the high Chl- a concentrations observed during this period are mainly due to the entrance of nutrients through river runoff. However, in winter, high concentrations of colored dissolved organic matter (CDOM), associated with river runoff, are present in the ocean surface, leading to an erroneous strong signal of the satellite. During winter correlations of 0.58 and 0.49 were found between Chl- a concentration and Douro and Minho discharges, respectively, evidencing that high Chl- a concentration was related with river runoff. Otherwise, during summer, Chl- a and Ekman transport exhibited a correlation of − 0.38 indicating that high Chl- a is associated to upwelling events. In summary, it was found that the spatio-temporal variability of Chl- a along the northwestern coast of Iberian Peninsula exhibited the clear influence of upwelling events during summer. Conversely, the variability during winter was mainly due to entrance of nutrients through the rivers discharge which flow into the area.

The Minho River discharge is recognized as particularly important in driving the circulation and hydrography of Rias Baixas, which are highly productive fishery and aquaculture regions extremely sensitive to environmental characteristics. The intrusion of the Minho River plume inside these Rias can reverse the normal circulation pattern and affect the macronutrient concentrations, imposing a control on new production within the estuarine environment. Consequently, detailed knowledge of the propagation of the plume in this zone facilitates largely the management of many exploited and protected local species. Thus, the main purpose of this work is to study the propagation and influence of Minho estuarine plume in Rias Baixas circulation and hydrography through the development and validation of an application of MOHID numerical model including a local coastal nesting configuration fed by Minho River discharge predicted by an estuary model. The nesting configuration and the Minho estuary model were validated and then applied to research the role of the wind and Minho River discharge effects on the circulation reversal. The spring of 1998 was chosen as the validation period for Minho estuarine plume propagation, considering there were field data available for this period confirming the intrusion of the Minho River plume in Rias Baixas and reversing the normal circulation pattern. Predictions replicate accurately the hydrodynamics and thermohaline patterns in Minho estuary and Rias Baixas under these conditions showing that the developed model application reproduces the dynamics of the coupled estuarine-near coastal systems under research. Results showed that a buoyancy intrusion caused by the Minho River reverses the normal estuarine salinity longitudinal gradient and estuarine circulation of the Rias de Vigo and Pontevedra. Moreover, it was found that a continuous moderate Minho River discharge combined with southerly winds is enough to reverse the Rias Baixas circulation pattern, reducing the importance of the occurrence of specific events of high runoff values.

Plecha, S., Picado, A., Chambel-Leitao, P., Dias, J.M., Vaz, N., 2014. Study of suspended sediment dynamics in a temperate coastal lagoon: Ria de Aveiro (Portugal). In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 604–609, ISSN 0749-0208. Suspended sediment concentrations are simulated at Ria de Aveiro, a lagoon located in a temperate climate area in the northwest of Portugal. The fine-grained suspended sediment concentration is analyzed using the numerical model MOHID (www.mohid.com) and spatial maps of instantaneous and maximum concentration and also temporal variability at specified locations are analyzed in order to characterize the influence of the tide and sea level conditions in the suspended sediment concentrations within the lagoon. The highest suspended sediment concentrations were found in upstream areas during ebb conditions due to the river's proximity, while the ...

The Tagus Estuary is the largest estuarine system in the Iberian Peninsula. Located in a heavily populated metropolitan area (Lisbon), the estuary-coastal continuum is subject to significant natural variability (e.g., tidal variations, winds, river inflow, etc.) and human pressures (e.g., sewage outflow, infrastructures, coastal reclamation, dredging, etc.). Since the 1980s, the estuary has been a natural laboratory for a great number of multidisciplinary studies, but also a numerical laboratory to test models and to develop new ideas and numerical methodologies. Hydrodynamic and biogeochemical models have been used ever since to ascertain the main spatial and temporal features of the Tagus system, connecting its dynamic to its biogeochemical cycles, providing numerical tools used to increase knowledge and to manage the estuary and nearby coastal waters. The main objective of this paper is to present a synopsis of the scientific output related to numerical studies in the Tagus system, by reviewing more than fifty papers published over the past four decades. Our work provides a historical background and description of the numerical models implemented to address estuarine hydrodynamics, nutrient uptake, primary production, light availability, seasonal and annual cycles and the link between physical, biological and chemical estuarine oceanography.

Different characteristics of Spartina maritima found in two distinct salt marshes located in different estuaries were analysed through interpretation of their local hydrodynamic patterns, as well as the impact of sea level rise on physical processes and consequently on plant dynamics and salt marshes stability. These salt marshes are situated in two of the most important Portuguese coastal systems, Tagus estuary (Rosário salt marsh) and Ria de Aveiro lagoon (Barra salt marsh), which are dominated by physical processes that induce strong tidal currents. They were monitored during one year and plant and sediment samples of S.maritima were collected quarterly in order to determine the vegetation coverage, above and belowground biomass, organic matter and sediment moisture. Residual circulation, tidal asymmetry and tidal dissipation were determined from numerical modelling results of the MOHID 2D model that was applied to each coastal system, considering the actual sea level and a sea level rise (SLR) scenario.Results suggest that the different characteristics found for Spartina maritima in the Rosário and the Barra salt marshes may be related with the diverse hydrodynamic conditions identified for each salt marsh. Consequently, the exploration of SLR scenario predictions indicates how these salt marshes could evolve in the future, showing that the important changes in these hydrodynamic parameters under climate change context might induce significant modifications in the salt marshes dynamics and stability. SLR scenario could lead to changes in nutrients and sediments patterns around the salt marshes and thus vegetation coverage percentage would be affected. Additionally, as a consequence of flood duration increase, sediment moisture will increase causing a stress condition to plants. Hence, the ratio below/aboveground biomass might increase, becoming critical to plants survival under conditions of accelerated sea level rise. Accordingly, both SLR and expected changes in vegetation coverage percentage in controlling salt marshes evolution have important implications in their stability and consequently in coastal management. These conditions are unlikely to be unique to these salt marshes and it is suggested that similar analyses are replicated for other tidally dominated systems to improve understanding and characterization of their dynamics and stability under climate change context. This work was been supported by FCT in the framework of the research projects PTDC/AAC-CLI/104085/2008 – ECOSAM: Effects of Carbon Dioxide increase on Salt Marshes, LTER/BIA-BEC/0063/2009 – LTER-RAVE: Long term monitoring in the Ria de Aveiro and PTDC/MAR/107939/2008 – DyEPlume: Estuarine Dynamics and Plume Propagation in the Portuguese coast, co-funded by COMPETE/QREN/UE. The second author is supported by the Ciência 2008 Program, financed by the Portuguese Science Foundation. Authors would like to thank to the anonymous reviewers that contributed for this paper improvement, as well as to colleagues whose help was essential for carrying out this work, especially Ana Azevedo, Leandro Vaz, Magda Sousa and Renato Mendes. Thanks for all the support and availability. published

The finding of human remains in aquatic environments is usually attributed to causes such as work-related or recreational accidents, suicides, discarded homicide victims, and natural disasters. When the point and date of entry in the water is unknown, these findings pose serious challenges to forensic analysis given the difficulty to estimate the drift of the body. In this context, the information retrieved from cases where the point of entry and body recovery sites are known, as well as the timing, is significant. Two drowning accidents in marine coastal waters were analyzed. In both cases the post-mortem submersion interval (PMSI) is known, as well as the accident (point of entry) and body recovery sites. Accumulated degree days (ADD) was estimated in both cases using satellite sea surface temperature data. In both cases the bodies were recovered in the vicinity of the accident site (~2 km in case 1 and less than 1 km in case 2). Results were interpreted in terms of oceanographic conditions, physical settings and ADD. The results provide some relevant clues on the fate of human cadavers in coastal marine environments that can be used by officials and agencies involved in the recovery of bodies, as well as by forensic investigators when dealing with these findings.

The role of river discharge, wind and tide on the extension and variability of the Tagus River plume was analyzed from 2003 to 2015. This study was performed combining daily images obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor located onboard the Aqua and Terra satellites. Composites were generated by averaging pixels with the same forcing conditions. River discharge shows a strong relation with the extension of the Tagus plume. The plume grows with the increasing river discharge and express a two day lag caused by the long residence time of water within the estuary. The Tagus turbid plume was found to be smaller under northerly and easterly winds, than under southerly and westerly winds. It is suggested that upwelling favoring winds provoke the offshore movement of the plume material with a rapidly decrease in turbidity values whereas downwelling favoring winds retain plume material in the north coast close to the Tagus mouth. Eastern cross-shore (oceanward) winds spread the plume seaward and to the north following the coast geometry, whereas western cross-shore (landward) winds keep the plume material in both alongshore directions occupying a large part of the area enclosed by the bay. Low tides produce larger and more turbid plumes than high tides. In terms of fortnightly periodicity, the maximum plume extension corresponding to the highest turbidity is observed during and after spring tides. Minimum plume extension associated with the lowest turbidity occurs during and after neap tides.

The Tagus estuary is a mesotidal estuary located on the Western Portuguese coast, and is characterized by large areas of salt marshes (17.24 km2) and tidal flats distributed along the margins. Halophyte vegetation in this system concentrates heavy metals during the growing season and subsequently releases these metals to the environment following senescence. Although there currently there are no metal discharges to the estuary, this was not true in the past, and there are still large amounts of legacy metals within the system. The results presented here show that marshes in the Tagus estuary, can export metal contaminants at the rate of 162 Zn kg m2 y− 1, 26 Cu kg m2 y− 1, 28 Pb kg m2 y− 1 and 1 Cd kg m2 y− 1. Eddies are generated inside the estuary during frequent flood events, enhancing erosion and transport of particles. During neap tide periods plant detritus is mostly retained in the inner estuary in the vicinity of the marsh source; during spring tides, however, export to the main channel and to the ocean is significantly increased. Sea level rise (SLR) and/or expected increase in the frequency of flood events will increase detrital movement within the estuary and discharges of metal contaminated particles to the ocean shelf. This research highlights the capacity of the present estuary to moderate fluxes of legacy metals to the ocean, but also calls for efforts to reduce present contaminant inputs from the watershed to mitigate contaminant transport to the ocean in the future.

Picado, A., Alvarez, I., Vaz, N., and Dias, J.M., 2013. Chlorophyll concentration along the northwestern coast of the Iberian Peninsula vs. atmosphere-ocean-land conditions. In: Conley, D.C., Masselink, G., Russell, P.E. and O’Hare, T.J. (eds.), Proceedings 12 th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 2047-2052, ISSN 0749-0208. The aim of this work is to investigate the relationship between the atmosphere-ocean-land conditions and chlorophyll a (Chl-a) formation along the northwestern coast of the Iberian Peninsula. Spatial and temporal distribution of Chl-a concentration, sea surface temperature, surface winds and rivers discharge were analyzed from 1998 to 2007, using remote sensing data. Generally, the Chl-a concentrations are higher near the coast showing a seasonal variability. In fact, along the coast there are higher Chl-a concentrations during the dry season (April to September) which can be associated to the upwelling favorable conditions (southward winds). These favorable conditions are related to the presence of cold nutrient-rich water which upwells towards the surface layers enhancing the primary production. During winter months, the wind pattern is usually upwelling unfavorable (northward winds); however high Chl-a concentration also occurs near the coast. These high values could be related to the inland nutrients input through rivers discharge and winter upwelling events. Afterwards, correlation coefficients were computed between Chl-a and upwelling index, SST and rivers discharges. Between June to September chlorophyll and upwelling index are positively correlated, increasing southward (0.58 to the south of the study area). During winter, the correlation coefficient between chlorophyll and rivers discharge is 0.75 in the northern region of the study area. Therefore, during summer months the chlorophyll variations could be explained mainly by the frequent upwelling events, whereas during winter months, high chlorophyll concentration near coast depends on rivers discharges.

The Minho River, situated 30 km south from the Rias Baixas, is the most important freshwater source flowing into the Western Galician coast. This discharge is particularly important in driving the circulation and hydrography of this coastal region. To study this important issue, numerical modeling may constitute an important tool being used to understand the coastal plume effects under different conditions. The main purpose of this study is to implement and validate a marine model able to reproduce the propagation of the Minho estuarine plume. The chosen period for the validation was the spring of 1998, because a high Minho River discharge was reported as well as favorable wind patterns to spread the river plume towards the Rias Baixas. The numerical model MOHID was used through a downscaling approach with a three-level one-way nested scheme. The numerical predictions show good agreement with the observed water level in the entire domain. Also, the measured components of the velocity are well represented by the model, as well as the observed pycnocline, which is predicted for the observed depth. According to the model results, a buoyancy intrusion caused by the Minho river reverses the normal estuarine salinity longitudinal gradient of the Rias de Vigo and Pontevedra. Otherwise, this pattern is not observed in the Ria de Arousa. All these patterns are corroborated by in situ measurements. In summary, the validation results show that the model adequately reproduces the hydrodynamic and thermohaline patterns of the Western Galician coast. published

This work investigates the recent morphological changes at the inlet of a complex coastal system (Ria de Aveiro lagoon, Portugal). This study was carried out using bathymetric data analysis and numerical simulations obtained with the 2DH morphodynamic modelling system MORSYS2D. The present simulations considered only tidal forcing, and a sensitivity analysis was performed by tuning the formula used to compute the sediment transports. A non-uniform sediment grain size distribution for the Ria de Aveiro inlet is considered in the numerical simulations, based on surveys performed in this area. The model results are analysed to assess if they resemble the observed trends of erosion and deposition, as calculated from bathymetric data. A quantitative analysis of the differences between the bathymetric changes obtained through surveys and the numerical results over a period of 3 years considering different sediment transport formulations shows that the formulations of Ackers and White (1973) and Engelund and Hansen (1967) are the ones that best describe the morphodynamic changes driven by tides in the Ria de Aveiro inlet.

The hydrography of the Espinheiro channel, an estuarine tidal channel located within Ria de Aveiro (Portuguese northwest coast), is investigated using the analysis of a thermohaline variables data set as function of two main forcing factors: incoming river flow and tide. Salinity and water temperature vertical profiles were measured twice a month from September 2003 to September 2004 at ten stations along the channel. Furthermore, in order to characterize the upper fluvial region of the channel in terms of these variables, thermohaline properties and current speed were also measured during two tidal cycles at an anchor station near the channel's head. The salinity distribution along the channel is closely related to the incoming river flow and tidal propagation. The water temperature distribution is related to the freshwater temperature seasonal variations and, due to the shallowness of the study area, is also related to the meteorological conditions. Empirical Orthogonal Functions (EOFs) are used to study the salinity and water temperature variations along the channel. The analysis reveal that the first EOF accounts for 87 and 97% of the total variance in vertically average salinity and water temperature, respectively. The temporal variation of the first EOF of the mean salinity and water temperature (PC1) is well correlated to the freshwater inflow (− 0.86) and freshwater temperature (0.79), respectively. Formation of strong salinity gradients has been found in a region between 7 and 8 km from the lagoon's mouth. These strong gradients migrate within a region of about 1 km depending on the tidal regime: neaps or springs and its formation is related to changes in the channel's morphology (depth and width).

Estuaries are interface areas between rivers and the coastal sea. They also receive point discharges of contaminants which can affect estuarine biogeochemistry. The study of residual circulation in estuaries is a key issue since it is related to the transport and dispersal of dissolved and non-dissolved substances. This study investigates the residual flows in a coastal plain estuary (the Tagus estuary, Portugal) taking into account the major forcing factors: tide, river discharge and wind stress. The methodology used is the implementation of a high resolution estuarine model in a 2D mode to simulate the tidal dynamics of the estuary. Tidal flows were calculated by tidally-averaging the flow currents along the whole estuary. The complex bathymetry of the estuary, tides, river discharge and wind stress modulate the residual flow in the Tagus estuary. The combine effect of the tide and river discharge creates preferential corridor flows in the deeper areas of the estuary. On the other hand, wind intensity and direction generate changes in residual currents in the shallow areas near the south shore of the estuary. River runoff changes the residual current intensity from values higher than 0.3 ms-1 (high discharge) to values of about 0.05 ms-1 (low discharge). The wind direction also induces changes in the residual flow patterns, inducing a rotation of the residual flow, according to the wind direction. Thus, the estuarine model of the Tagus estuary is a tool that sheds new insight about its fundamental hydrodynamics processes and consequently about the long term circulation patterns.

The Douro is one of the longest rivers in the Iberian Peninsula and represents the most important freshwater input into the Atlantic Ocean in the northwestern Portuguese coast. In order to fill the gaps on the comprehension of the spatial variability of the Douro estuarine plume, an innovative methodology was applied to observe and characterize this plume and its spatial and temporal variability. Using images of normalized water-leaving radiance at 555 nm from MODIS (Moderate Resolution Imaging Spectroradiometer) in combination with long-term concurrent wind, tidal and river discharge data (2003-2011), this work evaluates the effect of the main drivers (river discharge, wind and tide) on the plume features. Expected strong relationships between river discharge and turbid levels were detected. A circular pattern is well distinct off Douro estuary when the flow exceeds 500 m3 s-1. Under upwelling favorable winds and high river discharge regime, an offshore expansion is observed. During southerly winds, there is a plume confinement to the coast. Easterlywinds produce a bulge formation with an offshore detachment from the coast while westerly winds tend to confine freshwater close to the shoreline and decrease the cross-shore advection. Under high river discharges, a remarkable tidal influence in the near-field regions is observed close to the coast and near the river mouth.

The influence of freshwater flow on bacterial communities in the estuarine system Ria de Aveiro (Portugal) was investigated at two sites differently impacted by river inputs, representative of the marine and brackish water zones of the estuary. Sampling events were clustered based on hydrological features. The hydrodynamic was simulated with a Lagrangian model and related to microbiological parameters. Estuarine bacteria responded to different freshwater regimes developing distinct patterns of abundance and activity at the marine and brackish water zones. A circulation pattern induced by high river inflow produced vertical stratification in the marine zone, promoting a seaward flux of bacterioplankton, and stimulating the import of riverine phytoplankton and particle-attached bacteria to the brackish water zone. Advective transport and resuspension processes contributed to a 3-times increase in abundance of particle-attached bacteria during intense freshwater inputs. Additionally, bacterial activity in the estuary was controlled by inorganic nitrogen, responding to different freshwater inputs, which, in association with different prevailing sources of organic substrates induced significant changes in bacterial production. The dynamic and main controlling factors of bacterial communities are clearly impacted by freshwater inputs. Therefore, significant changes in the recycling of nutrients by microbial activities can be expected from alterations in freshwater inputs either related to global climate change or regional hydrological regimes.

The buoyancy generated by the Minho estuarine plume can flood the Rias Baixas for long periods, reversing the normal salinity gradients. Thus, the main purpose of this work was to study the propagation of Minho estuarine plume to the Rias Baixas, establishing the wind and river discharge conditions in which this plume affects the circulation and hydrography features of these coastal systems as well as the plume characteristics under the most probable forcing conditions, through the application of the numerical model MOHID. For this purpose, several scenarios with different river discharges and wind were simulated. The numerical results revealed that the Minho estuarine plume responds rapidly to wind variations and is influenced by coastline geometry. Under Minho River discharges higher than 700 m 3 s − 1 and weak northward winds (3 m s − 1 ) the circulation patterns of the Rias de Vigo and Pontevedra are reversed. On the other hand, moderate northward winds (6 m s − 1 ) combined with Minho River discharges higher than 200 m 3 s − 1 , 300 m 3 s − 1 and 700 m 3 s − 1 reverse the circulation pattern of the Rias de Vigo, Pontevedra and Arousa, respectively. Under the same conditions, the water exchange between Rias Baixas was analyzed using a particle-tracking model following the trajectories of particles released close to the Minho River mouth. Over 5 days, under Minho River discharges higher than 2100 m 3 s − 1 combined with northward winds of 6 m s − 1 , an intense water exchange between Rias was observed. However, only 20% of the particles found in Ria de Pontevedra come directly from the Minho River.

Numerous studies based on tide gauge records demonstrated the sea level rise on the Portuguese coast during the last century. Different climatic models predict a mean sea level rise for this coast ranging between 0.28 m and 0.42 m, for the period 2091–2100 relative to 1980–1999. Thus, the potential evaluation of the sea level rise impact on the Portuguese coast becomes critical, especially in sensitive areas as estuaries. The main aim of this work is to evaluate hydrodynamic changes in the Douro estuary induced by the sea level rise. A baroclinic finite volume numerical model was implemented to the Douro estuary in a 2D mode. The model calibration was performed comparing predicted and observed sea surface elevation time series for several stations. The tidal input at the ocean open boundary forces the 2D hydrodynamic model considering actual and future mean sea levels. At the landward boundary the model is forced with the freshwater discharge. The research explores changes in current velocity and amplitude and phase differences of the main diurnal and semi-diurnal tidal constituents along the estuary. The results suggest local significant changes in the Douro hydrodynamics in response to the sea level rise. Nevertheless, the differences don't affect the general estuary’s circulation. Concerning the main tidal constituents, the amplitude increases and the phase decreases, revealing that the tide tends to propagate faster upstream and with higher tidal ranges. Owing to the increasing of the amplitude and the water level, the current velocity values tend to decrease in the estuary, mainly near the low-lying areas. published

Storm surges are a hazardous phenomenon, since they may flood large coastal areas, causing socio-economical and habitation losses. Thus, the study of their characteristics and effects in coastal regions is crucial to prevent their negative consequences. This work aims at assessing the storm surges impact in the hydrodynamics of a tidal lagoon located in the north-western Portuguese coast (Ria de Aveiro). Storm surge amplitudes of 0.58 m, 0.84 m and 1.17 m for 2, 10 and 100 return periods, respectively, were determined adjusting the annual maximum amplitudes to a Generalized Extreme Value (GEV) distribution. To assess the hydrodynamic changes in the Ria de Aveiro under storm surge conditions, numerical modeling simulations were carried out, considering four scenarios: a single astronomical tidal forcing (reference) and astronomical tide plus 2, 10 and 100 years return period surges. Maximum levels and velocities for the entire lagoon and the tidal prism for the main cross-sections were determined and compared with the reference scenario. Generally, the model results suggest that during storm surge events the maximum levels increase in whole domain, with the largest increase found for the 100 return period storm surge scenario (1.17 m). The most significant changes occur at the main channels head for all scenarios, revealing that these regions are the most vulnerable to marginal flooding. Also, storm surges induce higher velocities and tidal prisms in the lagoon, increasing the marginal risk of erosion, as well as the salinization of the lagoon marginal lands. published

Measurements of velocity and salinity near the mouth and head of the Espinheiro channel (Ria de Aveiro lagoon, Portugal) are used to study the local variation of physical water properties and to assess the balance, under steady conditions, between the seaward salt transport induced by river discharge and the landward dispersion induced by various mixing mechanisms. This assessment is made using data sampled during complete tidal cycles. Under the assumption that the estuarine tidal channel is laterally homogeneous and during moderate tidal periods (except for one survey), currents and salinity data were decomposed into various spatial and temporal means and their deviations. Near the channel's mouth, the main contributions to the salt transport are the terms due to freshwater discharge and the tidal correlation. Near the channel's head, this last term is less important than the density driven circulation, which is enhanced by the increase in freshwater discharge. The remaining terms, which are dependent on the deviations from the mean depth have a smaller role in the results of salt transport. The computed salt transport per unit width of a section perpendicular to the mean flow is in close agreement to the sum of the advective and dispersive terms (within or very close to 12%). An imbalance of the salt budget across the sections is observed for all the surveys. Considerations are made on how this approach can inform the management of hazardous contamination and how to use these results to best time the release of environmental flows during dry months.

The main goal of this study is to use an integrated ecosystem model to study the role of physical, chemical and environmental parameters on the biogeochemistry of the Tagus estuary, the main estuarine system in Portugal. This work was developed as part of EU-funded INSEA project and tried to accomplish two major aims: (1) the development and implementation of a coupled modeling system capable of reproducing all the major characteristics both in physical and biological environments, and (2) to create a coastal management system based on the efficient integration of observations and biophysical models. Our results suggest that both aims were met. In this study we have used a 2D hydrodynamic application coupled to a complex ecological model presented in a companion paper which captures the state of the art of marine ecological models, and also developed during the project. Special emphasis is given to the processes governing temporal and spatial patterns of both phytoplankton and bulk properties, and the physical–biological interactions shaping their variability. The results shown in this paper are indicative of a reasonable performance of the model. It captures the complexity of the Tagus estuary and provides reasonable estimates of the biomass trends of a highly dynamic and interactive community.

A 3D baroclinic model (Mohid) is used to perform hindcast simulations in a tidal channel: the Espinheiro Channel (Portugal). These simulations are conducted for four distinct periods where markedly different river discharge and tides occurred, and the outputs are compared to time series measurements and synoptic thermohaline data. The model reveals its ability in reproducing observed temporal variability in sea level height and along-channel velocity, presenting skill coefficients higher than 0.85. The model qualitatively reproduces along-channel thermohaline distributions at three different vertical levels, during low-to-medium river inflow, underestimating the salinity stratification when the river flow is high (higher than 100 m 3 s - 1 ). In general, the trends inferred from the observations are reproduced by the numerical model. The cross-sectional tidally averaged structure of salinity and longitudinal velocity analyzed near the channel's mouth reveals ebb residual currents at the south shore and flood residual currents at the north shore under low-to-medium river discharge. When the river discharge is high (higher than 100 m 3 s - 1 ), the channel is almost laterally homogeneous in terms of salinity and residual velocity presenting a two-layer structure with flood currents near the bottom and ebb currents at the top layer. The salt transport was also analyzed and follows the same patterns found in the cross-sectional residual velocity. Close to the channel's mouth, the water exchange is mainly driven by the tidal forcing, except under high river flow events when the freshwater extends its influence from the channel's head to its mouth.

This work presents results from two complementary and interconnected approaches to study water temperature and salinity patterns in an estuarine tidal channel. This channel is one of the four main branches of the Ria de Aveiro, a shallow lagoon located in the Northwest coast of the Iberian Peninsula. Longitudinal and cross-sectional fields of water temperature and salinity were determined by spatial interpolation of field measurements. A numerical model (Mohid) was used in a 2D depth-integrated mode in order to compute water temperature and salinity patterns. The main purpose of this work was to determine the horizontal patterns of water temperature and salinity in the study area, evaluating the effects of the main forcing factors. The field results were depth-integrated and compared to numerical model results. These results obtained using extreme tidal and river runoff forcing, are also presented. The field results reveal that, when the river flow is weak, the tidal intrusion is the main forcing mechanism, generating saline and thermal fronts which migrate with the neap/spring tidal cycle. When the river flow increases, the influence of the freshwater extends almost as far as the mouth of the lagoon and vertical stratification is established. Results of numerical modelling reveal that the implemented model reproduces quite well the observed horizontal patterns. The model was also used to study the hydrology of the study area under extreme forcing conditions. When the model is forced with a low river flow (1 m3 s−1) the results confirm that the hydrology is tidally dominated. When the model is forced with a high river flow (1,000 m3 s−1) the hydrology is dominated by freshwater, as would be expected in such an area.

Coastal upwelling is one of the best studied oceanographic phenomena because of its effects on primary production. The western coast of the Iberian Peninsula has high biological diversity, mainly due to this primary production. In this study, the response of salinity and temperature to the occurrence of upwelling was analysed at the Ria de Vigo– and Ria de Aveiro–ocean boundary over the course of a year. Both systems were influenced by similar external forcing, but the response of thermohaline properties differed. Salinity and temperature were dependent on external forcing throughout the water column at Ria de Aveiro, whereas near-bed measurements revealed the presence of upwelled water at Ria de Vigo. Eastern North Atlantic Central Water was observed during spring–summer (summer) at the southern (northern) mouth of Ria de Vigo, but it was not observed at Ria de Aveiro. This difference may be due to the shallowness and narrowness of the Ria de Aveiro mouth, which can limit the entrance of ocean water. The trends found are unlikely to be unique, suggesting that geomorphologic characteristics of system–ocean boundaries determine how physical processes occurring in adjacent coastal areas impact estuarine properties.