João Miguel Dias | University of Aveiro (original) (raw)
Papers by João Miguel Dias
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
Sediment microbial communities are responsible for several ecosystem key-processes such as decomp... more Sediment microbial communities are responsible for several ecosystem key-processes such as
decomposition. However, these communities depend on aerobic respiration making them a source of
CO2 to the atmosphere. Since sediments are a known important carbon sink, it becomes important to
address the factors that modulate sediment respiration and therefore CO2 efflux to the atmosphere.
Therefore, the present work aimed to assess the main factors controlling sediment respiratory activity in
salt marshes. Sediment respiration and several sediment abiotic characteristics were assessed in two salt
marshes from Ria de Aveiro coastal lagoon with contrasting environmental conditions. Sediment
respiration had significant differences across seasons and salt marshes, and different patterns of activity
were found for each salt marsh. Statistical analysis and modelling by Generalized Linear Model (GLM)
revealed that sediment respiration is mostly influenced by organic matter quality (C:N ratio), sediment
temperature and sediment pH. Nevertheless, as temperature appeared to be one of the most important
factors influencing CO2 effluxes from the sediments, its influence during possible global warming
scenarios was focused. The simulations produced by the GLM using the IPCC scenarios projections,
indicated that salt marshes will tend do decrease their CO2 emissions with the increasing temperatures,
reinforcing their role as important carbon sinks. This can be interpreted as an ecosystemic counteract
measure toward a reduction of the increasing temperature by reducing the amounts of greenhouse gas
emissions, namely CO2.
Salt marshes are very important areas for biogeochemical cycling, sediment accretion, pollution f... more Salt marshes are very important areas for biogeochemical cycling, sediment accretion, pollution filtration and retention and erosion and stabilization of the river margins. The high organic matter content in the salt marsh plant sediments along with the radial oxygen diffusion provided by these halophyte root systems gather the ideal conditions for the development of a microbial rhizosphere community. Due to the quick feedback of the microbial communities to an environmental change, these organisms become important monitors for environmental impact assessment. A Salt marsh Sediment Microbial Index (SSMI) that reflected physical-chemical and microbial parameters was applied to plant rhizosphere sediments of five salt marshes from three important water bodies from Portugal. The SSMI revealed to be plant-independent evaluating efficiently the different marshes according to their maturity degree and disturbance influence. Mature salt marshes SSMI classification grouped all the systems at this development stage, while the younger salt marshes are classified in different groups according to their evolution degree. Also the impact degree is reflected at this level discriminating also the more adversely impacted salt marshes. Being a multi-metric index, the SSMI sub-metrics are also susceptible of ecological interpretation, giving important backstage information about the underlying biogeochemical cycling processes.
Nowadays, there is a special concern about the possible impact of sea level rise in hydrodynamic ... more Nowadays, there is a special concern about the possible impact of sea level rise in hydrodynamic patterns of coastal systems and its consequence in contingent ecosystems. In the present work, the effects of sea level rise in residual circulation are analyzed in two of the most important Portuguese coastal systems, Ria de Aveiro lagoon and Tagus estuary. The role of rivers inflow on residual circulation is also analyzed under different sea level scenarios. Several projections of river discharges were considered and two scenarios for sea level were adopted: actual and locally predicted sea level rise. The methodology followed comprises the exploitation of previously validated 2D hydrodynamic numerical models (MOHID) developed for both systems. Results indicate that rivers discharge effect cannot be unconsidered in the long term hydrodynamic analysis for both systems, once residual currents intensity could be at least 40% and even 100% higher in maximum inflow than in typical inflow and no discharges scenarios, respectively. In Tagus estuary, the upper bay is the most affected area in a sea level rise scenario, namely in the upper zone (with extensive intertidal areas) where differences in the residual currents intensity can be higher than 100%. In Ria de Aveiro lagoon, differences between actual and sea level rise could be higher than 80%. Narrow and shallow channels are the most affected areas, revealing the significant impact of sea level rise in the intertidal zones. Consequently, the predicted changes in these systems hydrodynamics could influence the long term transport and their actual equilibrium and, as such, affect the natural state of the contingent biological communities.
Salt marshes are well-known sinks of carbon and nitrogen, incorporating them both into sediment a... more Salt marshes are well-known sinks of carbon and nitrogen, incorporating them both into sediment and
in the halophyte biomass, being key players in the estuarine biogeochemical cycles. Due to aboveground
senescence there will inevitably occur losses of C and N rich detritus, becoming prone to the tidal flooding
and hydrodynamic regime. On the other hand, the ongoing climate change effects, such as sea level rise
(SLR) are known to have influence in the estuarine circulation. The Ria de Aveiro is a mesotidal lagoon
located in the Northwestern Portuguese coast, presenting a very complex geometry and characterized by
large areas of salt marshes and tidal flats distributed along a web of narrow channels. Residual circulation,
tidal asymmetry, tidal dissipation and detritus Lagrangian trajectories 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. The results here discussed show that in the case of Ria
de Aveiro, the examined salt marsh exports about 15 kg C m−2 y−1 and 2 kg N m−2 y−1. Nowadays, Barra
salt marsh presents the highest values of residual circulation, but predictions point out to its reduction
due to SLR scenario. Barra salt marsh shows highly dynamic conditions by being exposed to higher
current velocities, increased erosion rates and longer and more frequent inundation periods. This way,
model results of Lagrangian particles indicate that the detrital particles are highly dispersed, with large
amounts approaching the outer area of the lagoon, a feature that is highly enhanced in the SLR scenario.
These features may have two major implications: (1) enhance the fuelling of secondary production in
the coastal shelf and (2) excessive N exports and possible eutrophication of the coastal area. These two
consequences (positive and negative) acquire even more importance if all the marsh extension along all
the Ria de Aveiro is considered along with its elevated amount of plant-generated detritus. Regarding
the present predictions and concerns on estuarine ecology in a global change framework, it becomes
important to consider these estuarine salt marshes not only as possible nutrient sinks, but also as a
potential N source enhanced by the ongoing climate changes.
Nowadays, there is a special concern about the possible impact of sea level rise in hydrodynamic ... more Nowadays, there is a special concern about the possible impact of sea level rise in hydrodynamic patterns of coastal systems and its consequence in contingent ecosystems. In the present work, the effects of sea level rise in residual circulation are analyzed in two of the most important Portuguese coastal systems, Ria de Aveiro lagoon and Tagus estuary. The role of rivers inflow on residual circulation is also analyzed under different sea level scenarios. Several projections of river discharges were considered and two scenarios for sea level were adopted: actual and locally predicted sea level rise. The methodology followed comprises the exploitation of previously validated 2D hydrodynamic numerical models (MOHID) developed for both systems. Results indicate that rivers discharge effect cannot be unconsidered in the long term hydrodynamic analysis for both systems, once residual currents intensity could be at least 40% and even 100% higher in maximum inflow than in typical inflow and no discharges scenarios, respectively. In Tagus estuary, the upper bay is the most affected area in a sea level rise scenario, namely in the upper zone (with extensive intertidal areas) where differences in the residual currents intensity can be higher than 100%. In Ria de Aveiro lagoon, differences between actual and sea level rise could be higher than 80%. Narrow and shallow channels are the most affected areas, revealing the significant impact of sea level rise in the intertidal zones. Consequently, the predicted changes in these systems hydrodynamics could influence the long term transport and their actual equilibrium and, as such, affect the natural state of the contingent biological communities.
Ocean Dynamics, 2012
The morphologic changes in estuaries and coastal lagoons are very complex and constitute a challe... more The morphologic changes in estuaries and coastal lagoons are very complex and constitute a challenging task in coastal research. The bathymetric changes result from the combined action of tides, waves, rivers discharge and wind stress in the area of interest. Additionally, an accurate knowledge of the sediment transport is essential to achieve a good morphological characterization. This work establishes the influence of the wave climate on the morphodynamics of the Ria de Aveiro lagoon inlet by analysing the numerical results of the morphodynamic modelling system MORSYS2D. The numerical simulations considered a realistic coupled forcing of tidal currents and waves. The computed sediment fluxes and bathymetric changes are analysed and compared with the erosion and accretion trends obtained from the numerical simulations forced only by tidal currents, in order to establish the wave climate influence. The final bathymetry and the corresponding changes are compared with bathymetric data collected through surveys. It is concluded that: (a) the morphodynamics of the study area is dominated by the wave regime in the lagoon inlet and nearshore areas, while in the inner areas is tidally dominated; and (b) the inclusion of the wave regime forcing constitutes an improvement in order to accurately reproduce the local morphodynamics.
Ocean Engineering, 2013
Coastal flooding due to storm surges combined with high tides causes a growing concern, and recen... more Coastal flooding due to storm surges combined with high tides causes a growing concern, and recent legislation requires that European Union countries develop inundation maps for the areas at risk. This paper describes the methodology to generate inundation maps and its application to the Ria de Aveiro, a coastal lagoon exposed to Atlantic storm surges that can exceed 1 m. The maps are based on the application of the shallow water model SELFE, for different return periods and scenarios of sea level rise. A new approach to define the model boundary conditions for different return periods is developed based on the statistical analysis of time series from tidal gauges. This approach considers the effect of storm surges as well as tides and their 18.6 year cycle. The extreme levels obtained with this method converge for the 20 years of available data and are more accurate than the ones obtained with traditional approaches for this limited data set. In addition, the new method provides not only the extreme levels, but also the time series that include them, which are needed to force the hydrodynamic model. The results show that the storm surges affects the entire length of the Ria de Aveiro.
Continental Shelf Research, Jan 1, 2010
Although rising global sea levels will affect the estuarine flooded areas over the coming decades... more Although rising global sea levels will affect the estuarine flooded areas over the coming decades, the local and regional-scale processes will also induce important changes in these coastal systems. The main aim of this work is to investigate possible tidal changes in estuarine systems induced by local geomorphologic modifications, analysing the particular case of Ria de Aveiro which is in risk of inundation. Located in the Portuguese west coast, this tidally driven lagoon has a large area of mostly abandoned salt pans, which are in progressive degradation caused by the lack of maintenance and by the strong currents which erode their protective walls.
Geophysical Journal International, 2006
Electromagnetic fluctuations in the ocean have external sources like ionosphericmagnetospheric cu... more Electromagnetic fluctuations in the ocean have external sources like ionosphericmagnetospheric current systems, and purely internal oceanic sources associated with interaction between water velocity fields and the geomagnetic field, that is, the motionally induced voltage (MIV). During the last decade techniques based on MIV have proven to provide reliable information when applied to the flow monitoring at large oceanic channels. In this paper analysis of data resulting from the implementation of these techniques in a small-scale system, that is, the Ria de Aveiro lagoon (Portugal), is presented.
Geophysical Journal International, 2006
Electromagnetic fluctuations in the ocean have external sources like ionosphericmagnetospheric cu... more Electromagnetic fluctuations in the ocean have external sources like ionosphericmagnetospheric current systems, and purely internal oceanic sources associated with interaction between water velocity fields and the geomagnetic field, that is, the motionally induced voltage (MIV). During the last decade techniques based on MIV have proven to provide reliable information when applied to the flow monitoring at large oceanic channels. In this paper analysis of data resulting from the implementation of these techniques in a small-scale system, that is, the Ria de Aveiro lagoon (Portugal), is presented.
2003 International Conference Physics and Control. Proceedings (Cat. No.03EX708), 2003
Techniques based on motional induced voltage (MIV), which is induced by the water flow across Ear... more Techniques based on motional induced voltage (MIV), which is induced by the water flow across Earth's magnetic field has motivated and increase of interest of oceanographers, regarding studies of large scale ocean flows. The major part of these experiences has been applied to large-scale ocean studies. This technique has been demonstrated during last decade to provide reliable information when applied
Earth and Planetary Science Letters, 2007
On-shore measurements of telluric field oscillations have been used together with electric field ... more On-shore measurements of telluric field oscillations have been used together with electric field acquired in a submarine cable crossing a channel (in Aveiro area) to estimate the water transport through the channel. The on-shore N-S dipole was calibrated by correlating the lunar tidal water transport and the corresponding on-shore motionally tidal electric field. A calibration factor of 7350 m 3 s − 1 for each mV/km, with motionally induced origin, was estimated. Theoretical polarization ellipses of the electric field with tidal origin and telluric field attenuation during inland propagation agreed very well with observed values. The results showed that it is possible to estimate the water transport from on-shore measurements.
Este trabalho apresenta duas novas tecnologias distintas para monitorização de sistemas marinhos ... more Este trabalho apresenta duas novas tecnologias distintas para monitorização de sistemas marinhos e a sua aplicação à Ria de Aveiro: uma tecnologia óptica para medição da temperatura da água e uma tecnologia electromagnética para o cálculo de caudais. A comparação de resultados obtidos através do recurso à tecnologia óptica com resultados de medições efectuadas utilizando tecnologia convencional (STD) mostra que as séries de temperatura da água têm a mesma variabilidade. A análise espectral de dados de diferença de potencial (d.d.p.) obtidos com o cabo eléctrico mostra que o pico de maior energia surge na frequência correspondente à M 2 , a principal componente de maré na Ria de Aveiro, o que mostra que os dados de d.d.p. são sensíveis à maré.
Vaz, N., Mateus, M. and Dias, J.M., 2011. Semidiurnal and spring-neap variations in the Tagus Est... more Vaz, N., Mateus, M. and Dias, J.M., 2011. Semidiurnal and spring-neap variations in the Tagus Estuary: Application of a process-oriented hydro-biogeochemical model.
Continental Shelf …, Jan 1, 2011
Sea level change is an important consequence of climate change due to its impact on society and e... more Sea level change is an important consequence of climate change due to its impact on society and ecosystems. Analyses of tide-gauge data have indicated that the global sea level has risen during the 20th century and several studies predict that the mean sea level will continue to rise during the 21st century, intensifying coastal hazards worldwide. In Portugal, the Ria de Aveiro is expected to be one of the regions most affected by sea level change.
The eastern boundaries of the world’s oceans are among the most productive marine regions owing t... more The eastern boundaries of the world’s oceans are among the most productive marine regions owing to the wind induced coastal upwelling. In this context, changes in coastal upwelling influence chlorophyll-a (Chl-a) concentration along
the Northwest (NW) Iberian Peninsula (IP) coast. This work aimed to evaluate and quantify the influence of meteorological conditions defined by circulation weather types (CWTs) on upwelling and Chl-a variability along the Galician coast. A seasonal (April–September and October–March) characterization of satellite wind-derived upwelling index (UI) and Chl-a concentration was performed dividing the Galician coast into three domains: western (North–south orientation), intermediate (Northeast-Southwest orientation) and northern (West–east orientation) segments. Results revealed that UI and Chl-a concentrations were different among the three coastal segments and seasons. The most favourable upwelling conditions and high Chl-a levels occurred during April–September at western coast. During October–March, high-primary production also occurred and therefore a correlation analysis was performed during winter between Chl-a, UI and discharges of the main rivers. Chl-a and discharges were strongly correlated (0.52 for Minho and 0.31 for Nalon), suggesting that Chl-a during this period was related to signal contamination due to river discharge. The probability that Chl-a or UI exceeded a certain value,
given the occurrence of a specified CWT was computed. Results showed that along the western coastal segment the strongest relations between CWTs, upwelling and Chl-a concentration were obtained during April–September when N and NE occurred, with probabilities higher than 70% for UI and 30% for Chl-a. During winter only the NW type had statistically significant probabilities for UI (50%) and Chl-a (30%). For the intermediate coastal segment during October–March (April–September), when E type occurred, high probabilities of upwelling and Chl-a were observed [100% (66), 50% (25), respectively]. Finally, at the northern coastal segment, Chl-a probability was highest (40–50%) under the S weather type for both seasons.
Suspended sediment concentrations are simulated at Ria de Aveiro, a lagoon located in a temperate... more 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 minimum concentrations were observed near the inlet due to the presence of marine water poor in suspended sediments. When a 0.42 m sea-level rise (an estimate of conditions in 2100) is modelled, a decrease in suspended sediment concentration is observed for the overall study area, as result of an increase in the tidal prism.
The Ria Formosa is a tidal multi-inlet shallow-water coastal lagoon located in the south of Portu... more The Ria Formosa is a tidal multi-inlet shallow-water coastal lagoon located in the south of Portugal, subjected to the dry Mediterranean climate. The tide controls the Ria’s exchange with the adjacent shelf for most of the hydrological year except for isolated torrential run-off events. Episodes of low hypoxia reported in the literature may be related to the lagoon’s flushing time, affecting its shellfish production valued at 20 – 50 million €y-1. Over the past decades several observational and modelling studies presented values for the capacity of the tide to renovate the water inside the Ria. However, these studies lack either the spatial resolution to yield results unaffected by numerical diffusion or analyze a very limited part of the lagoon’s territory. In this work, we use a very-high resolution hydrodynamic model to assess the flushing time exclusively due to tidal forcing inside the Ria Formosa. A bi-dimensional implementation of the finite-volume/finite-difference Eulerian–Lagrangian hydrodynamic and transport model (ELCIRC) was used, allowing for the local refinement of the computational domain, which best suits the lagoon’s complex morphology. The present model configuration was validated for tidal propagation with sea surface elevation collected in 1979/80 at 11 lagoon stations. The validation results show a good agreement between predicted and observed elevations, with root mean square errors lower than 20 cm and skill values higher than 0.98. A set of experiments were carried out by releasing a conservative tracer at different stages of the tide at discrete points of the Ria, where possible environmental hazard hot-spots are located and the flushing e-folding time calculated from the tracer’s dilution. The results are discussed taking into account the propagation of the tide in this multi-inlet, meandering topography. Evidence is presented of topographic trapping due to the complex spatial distribution of the phase lags of the semi-diurnal tidal constituents. This evidence explains the significant increase of the flushing time from the inlets to the head of the channels, thus justifying the use of detailed spatial resolution when modelling such a complex system.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
Sediment microbial communities are responsible for several ecosystem key-processes such as decomp... more Sediment microbial communities are responsible for several ecosystem key-processes such as
decomposition. However, these communities depend on aerobic respiration making them a source of
CO2 to the atmosphere. Since sediments are a known important carbon sink, it becomes important to
address the factors that modulate sediment respiration and therefore CO2 efflux to the atmosphere.
Therefore, the present work aimed to assess the main factors controlling sediment respiratory activity in
salt marshes. Sediment respiration and several sediment abiotic characteristics were assessed in two salt
marshes from Ria de Aveiro coastal lagoon with contrasting environmental conditions. Sediment
respiration had significant differences across seasons and salt marshes, and different patterns of activity
were found for each salt marsh. Statistical analysis and modelling by Generalized Linear Model (GLM)
revealed that sediment respiration is mostly influenced by organic matter quality (C:N ratio), sediment
temperature and sediment pH. Nevertheless, as temperature appeared to be one of the most important
factors influencing CO2 effluxes from the sediments, its influence during possible global warming
scenarios was focused. The simulations produced by the GLM using the IPCC scenarios projections,
indicated that salt marshes will tend do decrease their CO2 emissions with the increasing temperatures,
reinforcing their role as important carbon sinks. This can be interpreted as an ecosystemic counteract
measure toward a reduction of the increasing temperature by reducing the amounts of greenhouse gas
emissions, namely CO2.
Salt marshes are very important areas for biogeochemical cycling, sediment accretion, pollution f... more Salt marshes are very important areas for biogeochemical cycling, sediment accretion, pollution filtration and retention and erosion and stabilization of the river margins. The high organic matter content in the salt marsh plant sediments along with the radial oxygen diffusion provided by these halophyte root systems gather the ideal conditions for the development of a microbial rhizosphere community. Due to the quick feedback of the microbial communities to an environmental change, these organisms become important monitors for environmental impact assessment. A Salt marsh Sediment Microbial Index (SSMI) that reflected physical-chemical and microbial parameters was applied to plant rhizosphere sediments of five salt marshes from three important water bodies from Portugal. The SSMI revealed to be plant-independent evaluating efficiently the different marshes according to their maturity degree and disturbance influence. Mature salt marshes SSMI classification grouped all the systems at this development stage, while the younger salt marshes are classified in different groups according to their evolution degree. Also the impact degree is reflected at this level discriminating also the more adversely impacted salt marshes. Being a multi-metric index, the SSMI sub-metrics are also susceptible of ecological interpretation, giving important backstage information about the underlying biogeochemical cycling processes.
Nowadays, there is a special concern about the possible impact of sea level rise in hydrodynamic ... more Nowadays, there is a special concern about the possible impact of sea level rise in hydrodynamic patterns of coastal systems and its consequence in contingent ecosystems. In the present work, the effects of sea level rise in residual circulation are analyzed in two of the most important Portuguese coastal systems, Ria de Aveiro lagoon and Tagus estuary. The role of rivers inflow on residual circulation is also analyzed under different sea level scenarios. Several projections of river discharges were considered and two scenarios for sea level were adopted: actual and locally predicted sea level rise. The methodology followed comprises the exploitation of previously validated 2D hydrodynamic numerical models (MOHID) developed for both systems. Results indicate that rivers discharge effect cannot be unconsidered in the long term hydrodynamic analysis for both systems, once residual currents intensity could be at least 40% and even 100% higher in maximum inflow than in typical inflow and no discharges scenarios, respectively. In Tagus estuary, the upper bay is the most affected area in a sea level rise scenario, namely in the upper zone (with extensive intertidal areas) where differences in the residual currents intensity can be higher than 100%. In Ria de Aveiro lagoon, differences between actual and sea level rise could be higher than 80%. Narrow and shallow channels are the most affected areas, revealing the significant impact of sea level rise in the intertidal zones. Consequently, the predicted changes in these systems hydrodynamics could influence the long term transport and their actual equilibrium and, as such, affect the natural state of the contingent biological communities.
Salt marshes are well-known sinks of carbon and nitrogen, incorporating them both into sediment a... more Salt marshes are well-known sinks of carbon and nitrogen, incorporating them both into sediment and
in the halophyte biomass, being key players in the estuarine biogeochemical cycles. Due to aboveground
senescence there will inevitably occur losses of C and N rich detritus, becoming prone to the tidal flooding
and hydrodynamic regime. On the other hand, the ongoing climate change effects, such as sea level rise
(SLR) are known to have influence in the estuarine circulation. The Ria de Aveiro is a mesotidal lagoon
located in the Northwestern Portuguese coast, presenting a very complex geometry and characterized by
large areas of salt marshes and tidal flats distributed along a web of narrow channels. Residual circulation,
tidal asymmetry, tidal dissipation and detritus Lagrangian trajectories 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. The results here discussed show that in the case of Ria
de Aveiro, the examined salt marsh exports about 15 kg C m−2 y−1 and 2 kg N m−2 y−1. Nowadays, Barra
salt marsh presents the highest values of residual circulation, but predictions point out to its reduction
due to SLR scenario. Barra salt marsh shows highly dynamic conditions by being exposed to higher
current velocities, increased erosion rates and longer and more frequent inundation periods. This way,
model results of Lagrangian particles indicate that the detrital particles are highly dispersed, with large
amounts approaching the outer area of the lagoon, a feature that is highly enhanced in the SLR scenario.
These features may have two major implications: (1) enhance the fuelling of secondary production in
the coastal shelf and (2) excessive N exports and possible eutrophication of the coastal area. These two
consequences (positive and negative) acquire even more importance if all the marsh extension along all
the Ria de Aveiro is considered along with its elevated amount of plant-generated detritus. Regarding
the present predictions and concerns on estuarine ecology in a global change framework, it becomes
important to consider these estuarine salt marshes not only as possible nutrient sinks, but also as a
potential N source enhanced by the ongoing climate changes.
Nowadays, there is a special concern about the possible impact of sea level rise in hydrodynamic ... more Nowadays, there is a special concern about the possible impact of sea level rise in hydrodynamic patterns of coastal systems and its consequence in contingent ecosystems. In the present work, the effects of sea level rise in residual circulation are analyzed in two of the most important Portuguese coastal systems, Ria de Aveiro lagoon and Tagus estuary. The role of rivers inflow on residual circulation is also analyzed under different sea level scenarios. Several projections of river discharges were considered and two scenarios for sea level were adopted: actual and locally predicted sea level rise. The methodology followed comprises the exploitation of previously validated 2D hydrodynamic numerical models (MOHID) developed for both systems. Results indicate that rivers discharge effect cannot be unconsidered in the long term hydrodynamic analysis for both systems, once residual currents intensity could be at least 40% and even 100% higher in maximum inflow than in typical inflow and no discharges scenarios, respectively. In Tagus estuary, the upper bay is the most affected area in a sea level rise scenario, namely in the upper zone (with extensive intertidal areas) where differences in the residual currents intensity can be higher than 100%. In Ria de Aveiro lagoon, differences between actual and sea level rise could be higher than 80%. Narrow and shallow channels are the most affected areas, revealing the significant impact of sea level rise in the intertidal zones. Consequently, the predicted changes in these systems hydrodynamics could influence the long term transport and their actual equilibrium and, as such, affect the natural state of the contingent biological communities.
Ocean Dynamics, 2012
The morphologic changes in estuaries and coastal lagoons are very complex and constitute a challe... more The morphologic changes in estuaries and coastal lagoons are very complex and constitute a challenging task in coastal research. The bathymetric changes result from the combined action of tides, waves, rivers discharge and wind stress in the area of interest. Additionally, an accurate knowledge of the sediment transport is essential to achieve a good morphological characterization. This work establishes the influence of the wave climate on the morphodynamics of the Ria de Aveiro lagoon inlet by analysing the numerical results of the morphodynamic modelling system MORSYS2D. The numerical simulations considered a realistic coupled forcing of tidal currents and waves. The computed sediment fluxes and bathymetric changes are analysed and compared with the erosion and accretion trends obtained from the numerical simulations forced only by tidal currents, in order to establish the wave climate influence. The final bathymetry and the corresponding changes are compared with bathymetric data collected through surveys. It is concluded that: (a) the morphodynamics of the study area is dominated by the wave regime in the lagoon inlet and nearshore areas, while in the inner areas is tidally dominated; and (b) the inclusion of the wave regime forcing constitutes an improvement in order to accurately reproduce the local morphodynamics.
Ocean Engineering, 2013
Coastal flooding due to storm surges combined with high tides causes a growing concern, and recen... more Coastal flooding due to storm surges combined with high tides causes a growing concern, and recent legislation requires that European Union countries develop inundation maps for the areas at risk. This paper describes the methodology to generate inundation maps and its application to the Ria de Aveiro, a coastal lagoon exposed to Atlantic storm surges that can exceed 1 m. The maps are based on the application of the shallow water model SELFE, for different return periods and scenarios of sea level rise. A new approach to define the model boundary conditions for different return periods is developed based on the statistical analysis of time series from tidal gauges. This approach considers the effect of storm surges as well as tides and their 18.6 year cycle. The extreme levels obtained with this method converge for the 20 years of available data and are more accurate than the ones obtained with traditional approaches for this limited data set. In addition, the new method provides not only the extreme levels, but also the time series that include them, which are needed to force the hydrodynamic model. The results show that the storm surges affects the entire length of the Ria de Aveiro.
Continental Shelf Research, Jan 1, 2010
Although rising global sea levels will affect the estuarine flooded areas over the coming decades... more Although rising global sea levels will affect the estuarine flooded areas over the coming decades, the local and regional-scale processes will also induce important changes in these coastal systems. The main aim of this work is to investigate possible tidal changes in estuarine systems induced by local geomorphologic modifications, analysing the particular case of Ria de Aveiro which is in risk of inundation. Located in the Portuguese west coast, this tidally driven lagoon has a large area of mostly abandoned salt pans, which are in progressive degradation caused by the lack of maintenance and by the strong currents which erode their protective walls.
Geophysical Journal International, 2006
Electromagnetic fluctuations in the ocean have external sources like ionosphericmagnetospheric cu... more Electromagnetic fluctuations in the ocean have external sources like ionosphericmagnetospheric current systems, and purely internal oceanic sources associated with interaction between water velocity fields and the geomagnetic field, that is, the motionally induced voltage (MIV). During the last decade techniques based on MIV have proven to provide reliable information when applied to the flow monitoring at large oceanic channels. In this paper analysis of data resulting from the implementation of these techniques in a small-scale system, that is, the Ria de Aveiro lagoon (Portugal), is presented.
Geophysical Journal International, 2006
Electromagnetic fluctuations in the ocean have external sources like ionosphericmagnetospheric cu... more Electromagnetic fluctuations in the ocean have external sources like ionosphericmagnetospheric current systems, and purely internal oceanic sources associated with interaction between water velocity fields and the geomagnetic field, that is, the motionally induced voltage (MIV). During the last decade techniques based on MIV have proven to provide reliable information when applied to the flow monitoring at large oceanic channels. In this paper analysis of data resulting from the implementation of these techniques in a small-scale system, that is, the Ria de Aveiro lagoon (Portugal), is presented.
2003 International Conference Physics and Control. Proceedings (Cat. No.03EX708), 2003
Techniques based on motional induced voltage (MIV), which is induced by the water flow across Ear... more Techniques based on motional induced voltage (MIV), which is induced by the water flow across Earth's magnetic field has motivated and increase of interest of oceanographers, regarding studies of large scale ocean flows. The major part of these experiences has been applied to large-scale ocean studies. This technique has been demonstrated during last decade to provide reliable information when applied
Earth and Planetary Science Letters, 2007
On-shore measurements of telluric field oscillations have been used together with electric field ... more On-shore measurements of telluric field oscillations have been used together with electric field acquired in a submarine cable crossing a channel (in Aveiro area) to estimate the water transport through the channel. The on-shore N-S dipole was calibrated by correlating the lunar tidal water transport and the corresponding on-shore motionally tidal electric field. A calibration factor of 7350 m 3 s − 1 for each mV/km, with motionally induced origin, was estimated. Theoretical polarization ellipses of the electric field with tidal origin and telluric field attenuation during inland propagation agreed very well with observed values. The results showed that it is possible to estimate the water transport from on-shore measurements.
Este trabalho apresenta duas novas tecnologias distintas para monitorização de sistemas marinhos ... more Este trabalho apresenta duas novas tecnologias distintas para monitorização de sistemas marinhos e a sua aplicação à Ria de Aveiro: uma tecnologia óptica para medição da temperatura da água e uma tecnologia electromagnética para o cálculo de caudais. A comparação de resultados obtidos através do recurso à tecnologia óptica com resultados de medições efectuadas utilizando tecnologia convencional (STD) mostra que as séries de temperatura da água têm a mesma variabilidade. A análise espectral de dados de diferença de potencial (d.d.p.) obtidos com o cabo eléctrico mostra que o pico de maior energia surge na frequência correspondente à M 2 , a principal componente de maré na Ria de Aveiro, o que mostra que os dados de d.d.p. são sensíveis à maré.
Vaz, N., Mateus, M. and Dias, J.M., 2011. Semidiurnal and spring-neap variations in the Tagus Est... more Vaz, N., Mateus, M. and Dias, J.M., 2011. Semidiurnal and spring-neap variations in the Tagus Estuary: Application of a process-oriented hydro-biogeochemical model.
Continental Shelf …, Jan 1, 2011
Sea level change is an important consequence of climate change due to its impact on society and e... more Sea level change is an important consequence of climate change due to its impact on society and ecosystems. Analyses of tide-gauge data have indicated that the global sea level has risen during the 20th century and several studies predict that the mean sea level will continue to rise during the 21st century, intensifying coastal hazards worldwide. In Portugal, the Ria de Aveiro is expected to be one of the regions most affected by sea level change.
The eastern boundaries of the world’s oceans are among the most productive marine regions owing t... more The eastern boundaries of the world’s oceans are among the most productive marine regions owing to the wind induced coastal upwelling. In this context, changes in coastal upwelling influence chlorophyll-a (Chl-a) concentration along
the Northwest (NW) Iberian Peninsula (IP) coast. This work aimed to evaluate and quantify the influence of meteorological conditions defined by circulation weather types (CWTs) on upwelling and Chl-a variability along the Galician coast. A seasonal (April–September and October–March) characterization of satellite wind-derived upwelling index (UI) and Chl-a concentration was performed dividing the Galician coast into three domains: western (North–south orientation), intermediate (Northeast-Southwest orientation) and northern (West–east orientation) segments. Results revealed that UI and Chl-a concentrations were different among the three coastal segments and seasons. The most favourable upwelling conditions and high Chl-a levels occurred during April–September at western coast. During October–March, high-primary production also occurred and therefore a correlation analysis was performed during winter between Chl-a, UI and discharges of the main rivers. Chl-a and discharges were strongly correlated (0.52 for Minho and 0.31 for Nalon), suggesting that Chl-a during this period was related to signal contamination due to river discharge. The probability that Chl-a or UI exceeded a certain value,
given the occurrence of a specified CWT was computed. Results showed that along the western coastal segment the strongest relations between CWTs, upwelling and Chl-a concentration were obtained during April–September when N and NE occurred, with probabilities higher than 70% for UI and 30% for Chl-a. During winter only the NW type had statistically significant probabilities for UI (50%) and Chl-a (30%). For the intermediate coastal segment during October–March (April–September), when E type occurred, high probabilities of upwelling and Chl-a were observed [100% (66), 50% (25), respectively]. Finally, at the northern coastal segment, Chl-a probability was highest (40–50%) under the S weather type for both seasons.
Suspended sediment concentrations are simulated at Ria de Aveiro, a lagoon located in a temperate... more 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 minimum concentrations were observed near the inlet due to the presence of marine water poor in suspended sediments. When a 0.42 m sea-level rise (an estimate of conditions in 2100) is modelled, a decrease in suspended sediment concentration is observed for the overall study area, as result of an increase in the tidal prism.
The Ria Formosa is a tidal multi-inlet shallow-water coastal lagoon located in the south of Portu... more The Ria Formosa is a tidal multi-inlet shallow-water coastal lagoon located in the south of Portugal, subjected to the dry Mediterranean climate. The tide controls the Ria’s exchange with the adjacent shelf for most of the hydrological year except for isolated torrential run-off events. Episodes of low hypoxia reported in the literature may be related to the lagoon’s flushing time, affecting its shellfish production valued at 20 – 50 million €y-1. Over the past decades several observational and modelling studies presented values for the capacity of the tide to renovate the water inside the Ria. However, these studies lack either the spatial resolution to yield results unaffected by numerical diffusion or analyze a very limited part of the lagoon’s territory. In this work, we use a very-high resolution hydrodynamic model to assess the flushing time exclusively due to tidal forcing inside the Ria Formosa. A bi-dimensional implementation of the finite-volume/finite-difference Eulerian–Lagrangian hydrodynamic and transport model (ELCIRC) was used, allowing for the local refinement of the computational domain, which best suits the lagoon’s complex morphology. The present model configuration was validated for tidal propagation with sea surface elevation collected in 1979/80 at 11 lagoon stations. The validation results show a good agreement between predicted and observed elevations, with root mean square errors lower than 20 cm and skill values higher than 0.98. A set of experiments were carried out by releasing a conservative tracer at different stages of the tide at discrete points of the Ria, where possible environmental hazard hot-spots are located and the flushing e-folding time calculated from the tracer’s dilution. The results are discussed taking into account the propagation of the tide in this multi-inlet, meandering topography. Evidence is presented of topographic trapping due to the complex spatial distribution of the phase lags of the semi-diurnal tidal constituents. This evidence explains the significant increase of the flushing time from the inlets to the head of the channels, thus justifying the use of detailed spatial resolution when modelling such a complex system.