José Fortes Lopes

Tidal propagation in Ria de Aveiro Lagoon, Portugal

Abstract Ria de Aveiro is a shallow vertically homogeneous lagoon, located in the Northwest of Portugal, connected to the Atlantic through a very narrow artificial channel, and supplied with freshwater by two major rivers, Antua and Vouga. The present study describes the application of a twodimensional depth integrated mathematical model, to predict tide-induced water level and depth mean current for the entire lagoon. The model computes time series of those variables as well as their instantaneous distribution at different times of the tidal cycle. Properties of tides and tidal currents in Ria de Aveiro are characterized and discussed. Special emphasis is given to the study of the hydrodynamic behaviour of the lagoon in extreme conditions of astronomical tide forcing, considering spring and neap tide conditions. Tides propagate from the mouth of Ria de Aveiro and are present in the entire lagoon. The tidal amplitude decreases with the distance from the mouth while the phase lag in the high and low water (which is different) increases. The tidal range increases for the spring tide at the far end of the channels correspond to a local increase of the high tide level, which result in a fortnightly variation of the mean levels at those places.

Implementation and assessment of hydrodynamic, salt and heat transport models: The case of Ria de Aveiro Lagoon (Portugal)

Ria de Aveiro is a shallow coastal lagoon located in the Northwest coast of Portugal. The implementation and the assessment (calibration and validation) of the hydrodynamic, salt and heat transport models for Ria de Aveiro lagoon is presented. During the calibration the models parameters were adjusted to give the best fit of the model results to the field data. The hydrodynamic model calibration was carried out by comparing measured and predicted time series of sea surface elevation for 22 stations. The root-mean square of the difference between those values was determined and harmonic analysis was performed in order to evaluate the model ability to reproduce the tide propagation along the main channels of Ria de Aveiro. Validation of the hydrodynamic model was performed comparing measured and predicted sea surface elevation values for 11 stations, as well as velocities in the main flow direction for 10 stations and water flows for 6 stations. The salt and the heat transport models were calibrated comparing measured and predicted time series of salinity and water temperature for 7 stations. These models were validated comparing the model results with an independent field data set. Results indicate that the hydrodynamic, the salt and the heat transport models for Ria de Aveiro were successfully calibrated and validated.

Hydrological characterisation of Ria de Aveiro, Portugal, in early summer

The hydrologkal features of Ria de Aveiro, a coastal lagoon on the northwest Atlantic coast of Portugal, were investigated in two sampling surveys carried out between 316 and 2416197 and between 2916 and 717197, respectively. There was a significant freshwater inflow into the lagoon during the first survey, especially in the first days, due to the recent rain- falls. Records concerning water level, salinity, temperature and current velocity were performed at several stations located along the four main channels of the lagoon. The type of tide at the mouth was determined and was observed that astro- nomical tide is the main fiorcing agent driving water circulation in Ria de Aveiro. The tide at the mouth is semidiurnal and the tidal wave propagation in the lagoon has the characteristics of a damped progressive wave. Typical estuarine longi- tudinal salinity and temperature gradients connected with the distance to the mouth were identified, whereas vertical and transverse gradients were found unimportant, except in the frontal zone between oceanic and fresh water masses. Accord- ing to the results, even though Ria de Aveiro should be considered as vertically homogeneous, some channels may reveal characteristics of a partially mixed estuary, depending on the freshwater input. 0 1999 Ifremer / CNRS / IRD / Editions scientifiques et medicales Elsevier SAS

Lagrangian transport of particles in Ria de Aveiro lagoon, Portugal

Abstract A two-dimensional vertically integrated hydrodynamic model coupled to a particle tracking model is applied to study the dispersion processes and residence time in Ria de Aveiro lagoon (Portugal). The only dispersion process that is considered in this study is the advection, according to the main characteristics of the local hydrodynamic. The particle tracking model computes the particles position at each time step, using a fourth-order Runge-Kutta integration method. The dispersion of passive particles released along the lagoon and in critical areas are studied in this work. The residence time is also determined for the entire lagoon. The results show that the mixture between particles coming from different channels of the lagoon is negligible in a time scale higher than 2 tidal cycles. The residence time for the lagoon central area is about 2 days, revealing a strong marine influence in this area. At the upper reaches of the channels were found values higher than 2 weeks.

Influence of tides and river inputs on suspended sediment transport in the Ria de Aveiro lagoon, Portugal

Abstract In this work the influence of tides and river inputs on suspended sediment distribution in the Ria de Aveiro, a shallow lagoon situated in the Northwest of Portugal, has been studied. Particular emphasis has been placed on Laranjo Bay, a sub-system of the lagoon from a bio-geophysical point of view. The study is based on both data analysis and sediment transport modelling. Tides are the major factor influencing the hydrodynamics of the lagoon. Their effects are important even at the upper reaches of the different channels, where salinity, temperature and sediment concentrations change during the tidal cycle. Sediment concentration shows both semi-diurnal and fortnightly periodicity. Highest values are found in the northern channels due to erosion induced by high current speeds in shallow areas. Erosion and deposition are the dominant processes determining suspended sediment transport in the lagoon.

Fluxes of bacterioplankton between a tidal estuary and the sea: returning to the "Outwelling Hypothesis"

The tidal dynamics of bacterioplankton communities at the outer part ofa shallow estuary (Ria de Aveiro, Portugal) were studied during 6 tidal cyclesat a fixed sampling site. Bacterial numbers (0.2–8.1 ×109 cells l−1), aminopeptidase activity(189–1662 nmol l−1 h−1),β-glucosidase activity (1.7–67.0 nmoll−1 h−1) and potential glucoseincorporation (0.48–3.99 nmoll−1 h−1) followed a consistent patternof increase during ebb and decrease during flood.Fluxes of bacterioplankton populations and associated heterotrophic activitiesbetween the estuary and the coastal area during a tidal cycle were estimatedfrom the water flux as derived from a two-dimensional vertically-integratednumerical model. The net fluxes estimated for a tidal cycle ranged from−26.0 to −2.5 to × 1016 bacterial cells. The nettidal fluxes of potential heterotrophic activities ranged from −10 to−80 mol h−1 for aminopeptidase, −0.33to −1.10 mol h−1 for β-glucosidase and−0.18 to +0.03 mol h−1 for glucoseincorporation. Net fluxes were generally negative in sign indicating thetransfer of phyto- and bacterioplankton, as well as potential capacities for thedegradation and recycling of organic matter, from the outer estuarinecompartment to the sea.

Salinity modelling accuracy of a coastal lagoon: a comparative river flow analysis of basin model vs. traditional approaches

ABSTRACT Tomas, L.M., Rodrigues, M, Fortunato, A.B., Azevedo, A, Leitão, P.C., Oliveira, A., Rocha, A., Lopes, J.F., Dias, J.M., 2014. Salinity modelling accuracy of a coastal lagoon: a comparative river flow analysis of basin model vs. traditional approaches. 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. 586–591, ISSN 0749-0208.. The main purpose of this study is to investigate the uncertainties in the modelling of salinity fields in the Ria de Aveiro lagoon associated with the estimation of river flow discharges. The prediction of fresh water inputs is necessary to properly implement forcing conditions and consequently to provide accurate forecasts of baroclinic circulation in coastal lagoons. Located in the north-western Portuguese coast, the Ria de Aveiro is a shallow vertically homogeneous mesotidal coastal lagoon with a complex geometry. Although it is tidally dominated, it receives freshwater from five rivers, the Vouga, Antuã, Cáster, Boco and Ribeira dos Moínhos, whose contributions are responsible for the salinity variation within the system. This research concerns the accurate prediction of river flow to be used in the operational forecast system of the lagoon. Given the lack of observed data for river discharges, as there are only two real time measuring stations located in the Vouga and Antuã river basins, but far from the lagoon, alternative estimation approaches are needed. In order to estimate the river discharges for all five rivers, two different approaches were considered: the first estimates the Vouga river flow, the major fresh water source, based on the nearest real time measuring station and estimates the other river flows based on river basin areas proportionality; the second establishes river flows based on the precipitation/river flow relationships for the Vouga and Antuã rivers and on the areas of the other river basins using the SWAT model. The methodology comprises the exploitation of the 3D unstructured-grid hydrodynamic model SELFE, required to adequately simulate the flow and transport of salt in very complex domains such as the Ria de Aveiro. The model is forced by water elevations at the ocean boundary and river flows at the river boundaries, and atmospheric drivers at the surface (wind stress, atmospheric pressure and heat fluxes). The salinity model predictions were compared with data from seven stations, and its accuracy was assessed through Root Mean Square Error (RMSE). The river flows estimated by the first method led to the best fit between observed and predicted salinity.

On the Influence of the Nearbed Sediments in the Oxygen Budget of a Lagunar System: The Ria de Aveiro - Portugal

The filtering capacity of an estuary for both heavy metals and organic micropollutants is largely due to sedimentation. Because sedimentation occurs only for the fraction of contaminant that is adsorbed to particulate matter, the process of sorption (adsorption and desorption) is an essential process. Sediments constitute by far the most important reservoir of nitrogen in shallow systems (Billen & Lancelot,1988). They play two key roles with respect to the plankton system: They act as regenerators of mineral nutrients for the water column, often supplying between 30-70% of nitrogen requirements by phytoplankton. On the other hand, being the only site in coastal marine ecosystems where anaerobic conditions exist, it is, therefore, the local of denitrification, allowing eliminating a large amount of the nitrogen mineralized in the benthos. Sedimentary organic matter is composed of many different size fractions with different degradability (Wijsman, 1999; 2002). Due to the depletion of the degradable organic matter with depth and the preferential degradation of the labile compounds, benthic mineralization rate usually decreases rapidly with depth in the sediment. Consequently, most of the biological activity is restricted to the upper decimetres of the sediment column. Benthic macrofauna plays an important role in early digenesis. Filter feeding organisms, for example, can selectively filter food particles from the water column and thus increase the flux of high quality organic matter to the sediment (e.g. Heip et al., 1995). Additionally, bioturbating and bio-irrigating activity of the macrofauna can increase the transport processes within the sediment (Black, 1997). Conversely, the carbon loading and the effects of benthic mineralization, such as the production of reduced substances and depletion of oxygen, can influence the activity and composition of the benthic community (e.g. Pearson & Rosenberg, 1978). Diagenensis characterises any chemical, physical, or biological changes undergone by sediments after their initial deposition and during and after their lithification (Wijsman, 1999; 2002). Since only a limited number of mathematically formulated problems of organic matter and nutrient diagenesis in sediments can be solved analytically, there has been a shift over the years from a focus on analytical models to numerical models (Berg, 2003). These models are commonly based on mass conservation approaches expressing balances between vertical transport contributions of selected species and biogeochemical interactions between them.