Search

Sandspits are important natural defences against the effects of storm events in estuarine regions, and their temporal and spatial dynamics are related to river flow, wave energy, and wind action. Understanding the impact of extreme wave events on the morphodynamics of these structures for current conditions and future projections is of paramount importance to promote coastal and navigation safety. In this work, a numerical analysis of the impact of a storm on the sandspit of the Douro estuary (NW Portugal) was carried out considering several mean sea level conditions induced by climate change. The selected numerical models were SWAN, for hydrodynamics, and XBeach, for hydrodynamic and morphodynamic assessments. The extreme event selected for this study was based on the meteo-oceanic conditions recorded during Hurricane Christina (January 2014), which caused significant damage on the western Portuguese coast. The analysis focused on the short-term (two days) impact of the storm on the morphodynamics of the sandspit in terms of its erosion and accretion patterns. The obtained results demonstrate that the mean sea level rise will induce some increase in the erosion/accretion volumes on the seaward side of the sandspit. Overtopping of the detached breakwater and the possibility of wave overtopping of the sandspit crest were observed for the highest simulated mean sea levels. [ABSTRACT FROM AUTHOR]

Estuarine floods are one of the most harmful and complex extreme events occurring in coastal environments. To predict the associated effects, characterize areas of risk, and promote population safety, numerical modeling is essential. This work performs a comparison and a combination of two 2-dimensional depth-averaged estuarine models (based on openTELEMAC-MASCARET and Delft3D hydrodynamic software packages), to develop a two-model ensemble approach that will improve forecast robustness when compared to a one-model approach. The ensemble was applied to one of the main Portuguese estuaries, the Douro river estuary, to predict the expected water levels associated with extreme river discharges in the present-day configuration with the new breakwaters. This is a region that is periodically under heavy flooding, which entails economic losses and damage to protected landscape areas and hydraulic structures. Both models accurately simulated water levels and currents for tidal- and flood-dominated validation simulations, with correlation values close to 1, RMSE below 15%, and small Bias and Skill coefficient close to 1. The two-model ensemble results revealed that the present-day estuarine mouth configuration will produce harsher effects for the riverine populations in case identical historical river floods take place. This is mainly due to the increase in the area and volume of the estuary's sand spit related to the construction of the new breakwaters. [ABSTRACT FROM AUTHOR]

For being densely populated and urbanized, and for concentrating high-value economic activities, estuarine regions have an increased energy demand, which boosts the claim for new, efficient, renewable, and safe energy production. Among these technologies, hydrokinetic energy conversion systems are potentially well-suited for estuaries. However, in the actual context of climate change, it is important to know how changes in mean sea level may affect hydrokinetic energy production. This work proposes a methodology to assess the hydrokinetic energy potential for future scenarios using numerical hydrodynamic modeling techniques. Applied to the Douro estuary, several scenarios considering present conditions, as well as medium (2050) and long-term (2100) predictions under different Shared Socioeconomic Pathways are proposed. The results revealed that the studied region maintains a high dependence on freshwater discharge until 2100, although tidal oscillation is also significantly perceived in the entire estuary. Overall, hydrokinetic power potential will not increase with the mean sea level rise and will instead be considerably lower. Therefore, a decline in the kinetic energy available for exploitation is expected with increasing CO 2 emissions, along with the associated intensification of sea level rise. Results reinforce the need to perform local studies to evaluate future trends in hydrokinetic energy production. • Numerical models are essential tools to represent the main forcings in estuaries. • Combined effects of tide and river flow increase the hydrokinetic energy production. • Hydrokinetic power potential will be considerably lower with the mean sea level rise in climate change scenarios. • Local studies need to be performed to evaluate future trends in hydrokinetic energy exploitation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Integrated Coastal Zone Management / Revista de Gestão Costeira Integrada is the property of Associacao Portuguesa dos Recursos Hidricos and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights: [•] We analyzed the effects of freshwater flow variability on estuarine biogeochemistry. [•] We used a coupled hydrodynamic-biogeochemical model. [•] Different river flow regimes resulting from an upstream dam operation were analyzed. [•] Flow regimes influenced estuarine biogeochemistry and primary production. [•] Results are useful for prediction of changes as a consequence of dam operation. [Copyright &y& Elsevier]

Copyright of Journal of Integrated Coastal Zone Management / Revista de Gestão Costeira Integrada is the property of Associacao Portuguesa dos Recursos Hidricos and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article discusses a study which examined variability in phytoplankton photosynthetic parameters of the Douro estuary in Portugal utilizing data from photosynthesis-irradiance (P-E) incubations. Incubations were performed during seasonal tidal cycles and during monthly surveys conducted along a salinity gradient from December 2002 to December 2003. The authors concluded that variability in the relationship observed between salinity and P-E parameters could be affected by several factors, such as species composition shifts.

Abstract: Freshwater input to estuaries is a fundamental feature of these ecosystems, which may be profoundly altered by river damming as human needs for water consumption, irrigation or energy production increase. The Douro estuary is limited upstream by a dam since 1985, which reduced its length by ca. 60%. Freshwater inputs to the estuary are now irregular and greatly dependent on hydroelectric power demand; values ranging from zero to over 1000m3 s−1, in a matter of hours, especially in summer are common. In the present study, a three-dimensional hydrodynamic model was applied to the Douro estuary. The model was calibrated and validated against water elevation, current velocity, salinity and temperature data. Thereafter, it was used to analyse the effects of different flow regimes and magnitudes on estuarine hydrodynamics and contaminant dispersion. Results obtained suggest that the highly variable flow regimes, currently observed in the Douro, tend to reduce water column stratification and to enhance seawater intrusion, when compared with flow discharges of similar average magnitude, but lower variability. Stable flows seem to be the most effective in dispersing contaminants eventually introduced into the estuary through its small river tributaries. Overall results suggest that flow management may have important effects on estuarine hydrodynamics through non-linear interactions between flow magnitude and variability. [Copyright &y& Elsevier]

Abstract: Ecosystem management and decision making process are dependent of a good knowledge of ecosystem functioning. Conceptual models allow knowledge organization through representation of relationships between variables and processes, facilitating management decisions. In this study, spatial and temporal characterization of key environmental variables, as well as relationships between them, was studied aiming the design of a conceptual model of the Douro estuary. This temperate mesotidal estuary is limited upstream by a hydroelectric power dam that controls freshwater inflow and prevents the propagation of the tide upstream, which, in turn, influences water circulation and biogeochemical dynamics of the system. During one year, from December 2002 to December 2003, water column data were collected monthly at 10 stations along the estuary, during ebb and flood tides. Spatial and temporal variability of water column salinity, temperature, nutrients, phytoplankton biomass, total particulate matter (TPM), phytoplankton primary production (PP), faecal coliform bacteria (FC) and community respiration (CR) were analysed. Salinity stratification was assessed by means of the Estuary Number (Ne) and variation of this index as well as other key characteristics with river flow was analysed. Freshwater discharge controlled salinity stratification and freshwater residence time. Ne indicated that the Douro was stratified for river flows <300m3 s−1, and freshwater residence time was >1day for the same conditions. A decaying exponential relationship between PP and river flow was found, whereas nitrate and TPM increased logarithmically and linearly, respectively, with river flow. Regarding spatial distribution, nitrate and PP decreased downstream, showing that the river was a source of nutrients and phytoplankton, while the opposite trend was found for TPM, FC, ammonium and CR. The latter increase was probably due to untreated sewage discharge in the urbanized middle and lower estuarine stretches. Reduction of nitrate coming from the watershed and of bacterial contamination in the urban stretches of this highly modified water body, according to the European Water Framework Directive, emerges as the main water quality issues for this estuarine ecosystem. [Copyright &y& Elsevier]

Abstract: The pelagic metabolism of the Douro estuary (Portugal) and the factors influencing primary production (PP) and community respiration (CR) in this system were studied during an annual cycle (December 2002–December 2003). Sampling surveys were conducted twice a month during ebb and flood spring tides and water samples were collected for PP and CR assessments at three stations along the estuary (lower, middle and upper stretches). During the study period, PP values were in the range of 4.7–1878.5mgCm−2 d−1 (average, 319.9mgCm−2 d−1). River discharge controlled phytoplankton biomass inputs into the estuary as well as residence time. A decreasing trend in water column PP from the upper to the lower estuary related to higher nitrogen concentrations and phytoplankton biomass from riverine origin was observed. An inverse trend was found for CR, i.e., higher values were found in the lower, more urbanized stretch. During the study period, averaged CR values reached 1154mgCm−2 d−1. In general, heterotrophy dominated the entire estuary, except in the upper stretch from May through July, when increased PP, but also lower CR values were recorded. A positive correlation between chlorophyll a and P max was found which is unusual in coastal ecosystems, where a decreasing trend of the P/B ratio as a function of net primary production is generally observed. This could be explained by the relatively low phytoplankton biomass, preventing intraspecific competition from lowering photosynthetic capacity, on one hand, and the physiology of phytoplankton related to their origin in a semi-lotic (reservoir) ecosystem. No significant differences between tides were observed for all variables, except for the water light extinction coefficient (k) values, reflecting higher turbidity during the ebb. [Copyright &y& Elsevier]

Abstract: The macrobenthic community structure and characteristics of sediments were studied in samples collected seasonally at five stations in the lower mesotidal Douro estuary, Portugal. Sediment characterisation included grain size distribution, total-recoverable metals (Al, Fe, Mn, Zn, Cu, Cr, Pb, Ni and Cd), acid-volatile sulphides (AVS) and simultaneously extracted metals (SEM) and total organic matter contents. Spatial variation surpassed temporal variation both in terms of environmental parameters and community structure. Clear anthropogenic contamination in terms of Zn, Cr, Cu and Pb, and a positive SEM–AVS, indicating the potential bioavailability of these metals, were detected on the north bank of the estuary. Multivariate analysis revealed that in addition to natural sediment characteristics, the anthropogenic metal contamination was influencing the macrobenthic community structure. In fact, greater concentrations of Zn, Cr, Cu and Pb were associated with lower number of species and/or diversity. Finally, the dry weight-normalised metal concentrations appeared as a more useful tool than the SEM–AVS model in predicting disturbance of the macrobenthic community in the studied area. [Copyright &y& Elsevier]

Abstract: In order to assess the variability of phytoplankton, bacteria and viruses, a box model was applied to the mesotidal salt wedge Douro Estuary (NW Portugal). The estuary was divided into boxes with two vertical layers and was driven by salinity and freshwater discharge data acquired during cruises in the spring, summer and fall of 1995. Model runs yielded estimates of the vertical non-advective exchange coefficients for each box, which were then used to establish balance equations for the microbial variables. Such equations allowed calculation of horizontal and vertical fluxes of phytoplankton, bacteria and viruses as well as their respective rates of production or consumption. Bacterial numbers peaked at intermediate salinities (12–18) whereas freshwater phytoplankton biomass decreased linearly with salinity, and estuarine communities increased at intermediate salinities. Virus-like particles had a similar behavior. The lower layer in the Douro Estuary was always a sink for phytoplankton, bacteria and viruses, giving way to negative or close to zero microbial fluxes. In the upper layer of the lower estuary, close to the coastal end where nutrients are abundant, water transparency was high, bacterial generation times were shorter and microbial fluxes were always positive, i.e. net growth occurred. The freshwater end of the estuary was a source of phytoplankton, irrespective of season, whereas it was a source of bacteria and viruses only in summer and spring, respectively. It is suggested that salinity acts as a boundary between different microbial communities, especially on a vertical scale. [Copyright &y& Elsevier]

Studies the relationship between macrobenthic community structure and natural characteristics of sediment and trace metal contamination in the lower Douro estuary in Portugal. Use of an innovative threefold approach, metal normalization to iron and macrobenthic community structure; Detection of a clear signature of anthropogenic contamination; Natural macrobenthic distribution pattern.

Influenced by both marine and river flows, estuaries can present a high potential for hydrokinetic energy exploitation. In this study, the hydrokinetic energy production in the Douro estuary was evaluated through hydrodynamic numerical modelling. The model analysed the tide and river flow, reproduced the combined effects of these two factors on the main current velocity patterns, and identified the estuarine locations with the highest potential for energy exploitation. Given the river's high variability caused by the precipitation patterns in the hydrographic basin area and the river's torrential regime, several discharge scenarios were explored, combining spring and neap tides, and high and low river flows. The results revealed that the region with the highest potential is located in the upper part of the estuary, where the highest-velocity currents were achieved for mid-ebb tide conditions and strong river flows. It was also found that tides reinforce the hydrokinetic energy production during ebb tide, although they are not strong enough to produce high values of hydrokinetic energy, being the river flow the main forcing. This work demonstrates the relevance of choosing parametrized magnitudes that are not dependent on a specific equipment, as well as the importance of a proper characterization of the estuarine hydrodynamic patterns needed to optimize the hydrokinetic energy exploitation. • Numerical models are essential tools to represent the main forcings in estuaries. • Combined effects of tide and river flow increase the hydrokinetic energy production. • Hydrokinetic energy exploitation is optimized with hydrodynamic characterization. • Parametrized magnitudes are important to compare estuarine locations. [ABSTRACT FROM AUTHOR]

An increase in anthropogenic activities in coastal regions can put at risk their flora and fauna and their ecosystem services. Therefore, it is important to evaluate possible impacts. In particular, we need to understand the links between contaminants concentrations and the hydrodynamic patterns of these highly productive regions to anticipate the effects of contaminants in the environment. Towards that aim there is the need to carry out regular campaigns to monitor the evolution of the coastal systems. In this work we analyse in-situ measurements of physico-chemical parameters, and look for possible relations between observed contaminants patterns and estuarine hydrodynamics. Data collected in the Douro estuary, one of the main estuarine regions of the Iberian western coast, revealed the presence of 5 hazardous and noxious substances (HNS), 14 polycyclic aromatic hydrocarbons (PAHs) and 6 trace metals in water and sediment samples. Water temperature and salinity analysis revealed a strong variability, which can affect the water solubility properties and the organisms' tolerance to certain toxins. A relationship between the salinity and the HNS and PAHs concentrations was found, caused by the existence of a salt-wedge that triggers the salting-out effect. Sinker contaminants (PAHs and trace metals) can be re-suspended both during low and high flow conditions associated with the salt-wedge and with strong river flows. Floater contaminants (HNS) are completely depended on the tide, which has the capacity to distribute them through the entire estuary, during low river flow regimes. However, strong river flows, with associated river plumes, can distribute both sinker and floater contaminants to the coastal region trapping them over the inner-shelf. The results clearly show that hydrodynamic patterns are a major driver for contaminants dispersion and pathways in coastal areas, inducing harmful effects to the flora and fauna and, consequently, to the ecosystem services of these regions. Unlabelled Image • Estuarine multidisciplinary characterization based on in-situ measurements is needed. • HNS, PAHs and metals were detected in Douro estuarine water and sediment samples. • The observed high water residence times can increase the contamination effects. • Salt-wedges resuspend sediments and sinker pollutants triggering salting out effects. • Pollutants carried to the coast by high flows can be trapped over the inner-shelf. [ABSTRACT FROM AUTHOR]

Contaminated mullet (Mugil cephalus) from Douro estuary was allowed to depurate in clean water and fed with uncontaminated food. Levels of PCBs and DDTs in muscle and liver, and ethoxyresorufin O-deethylase (EROD) activity were measured at day 0, 21, 120 and 270. In specimens captured in the estuary total PCB and total DDT concentrations were 311 and 65ngg−1 in muscle and 686 and 115ngg−1 in liver, respectively. At day 21, after an initial 10–15 days period of starvation, organochlorines levels increased in both analyzed tissues. Thereafter levels of all PCB congeners and DDT compounds decreased in muscle, and at the end of the 270 days were 49ngg−1 and 13ngg−1, respectively. These decreases were correlated to the lipids consumption. In liver no relationship between those variables was observed, suggesting different elimination processes and eventual exchange of contaminants between muscle and liver. EROD activities decreased in the first days of depuration experiment, but showed no relations with analysed organochlorines. [Copyright &y& Elsevier]