Salt Fluxes in a Complex River Mouth System of Portugal

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

Towards operational modeling and forecasting of the Iberian shelves ecosystem

There is a growing interest on physical and biogeochemical oceanic hindcasts and forecasts from a wide range of users and businesses. In this contribution we present an operational biogeochemical forecast system for the Portuguese and Galician oceanographic regions, where atmospheric, hydrodynamic and biogeochemical variables are integrated. The ocean model ROMS, with a horizontal resolution of 3 km, is forced by the atmospheric model WRF and includes a Nutrients-Phytoplankton-Zooplankton-Detritus biogeochemical module (NPZD). In addition to oceanographic variables, the system predicts the concentration of nitrate, phytoplankton, zooplankton and detritus (mmol N m(-3)). Model results are compared against radar currents and remote sensed SST and chlorophyll. Quantitative skill assessment during a summer upwelling period shows that our modelling system adequately represents the surface circulation over the shelf including the observed spatial variability and trends of temperature and chlorophyll concentration. Additionally, the skill assessment also shows some deficiencies like the overestimation of upwelling circulation and consequently, of the duration and intensity of the phytoplankton blooms. These and other departures from the observations are discussed, their origins identified and future improvements suggested. The forecast system is the first of its kind in the region and provides free online distribution of model input and output, as well as comparisons of model results with satellite imagery for qualitative operational assessment of model skill.publishe

Assessment of coastal management options by means of multilayered ecosystem models

This paper presents a multilayered ecosystem modelling approach that combines the simulation of the biogeochemistry of a coastal ecosystem with the simulation of the main forcing functions, such as catchment loading and aquaculture activities. This approach was developed as a tool for sustainable management of coastal ecosystems. A key feature is to simulate management scenarios that account for changes in multiple uses and enable assessment of cumulative impacts of coastal activities. The model was applied to a coastal zone in China with large aquaculture production and multiple catchment uses, and where management efforts to improve water quality are under way. Development scenarios designed in conjunction with local managers and aquaculture producers include the reduction of fish cages and treatment of wastewater. Despite the reduction in nutrient loading simulated in three different scenarios, inorganic nutrient concentrations in the bay were predicted to exceed the thresholds for poor quality defined by Chinese seawater quality legislation. For all scenarios there is still a Moderate High to High nutrient loading from the catchment, so further reductions might be enacted, together with additional decreases in fish cage culture. The model predicts that overall, shellfish production decreases by 10%–28% using any of these development scenarios, principally because shellfish growth is being sustained by the substances to be reduced for improvement of water quality. The model outcomes indicate that this may be counteracted by zoning of shellfish aquaculture at the ecosystem level in order to optimize trade-offs between productivity and environmental effects. The present case study exemplifies the value of multilayered ecosystem modelling as a tool for Integrated Coastal Zone Management and for the adoption of ecosystem approaches for marine resource management. This modelling approach can be applied worldwide, and may be particularly useful for the application of coastal management regulation, for instance in the implementation of the European Marine Strategy Framework Directive

Turbidity under changing physical forcing over two contrasting locations of seagrass meadows

Seagrass meadows support a range of ecosystem functions in coastal lagoons, from habitat and shelter of invertebrates and fishes to stabilizing sediments, serving at the same time as important ecological quality status indicators due to their sensitivity to water quality parameters. Seagrass meadows are recognized as one of the most productive ecosystems on Earth. Those in mesotidal mid-latitude lagoons with low flushing times primary production are greatly affected by turbidity. Here, we investigate the physical controls of turbidity in Ria de Aveiro, Portugal, by simulating its response to varying conditions of tidal and river forcing. A 2-dimensional hydrodynamic and transport model developed and calibrated for this coastal lagoon was forced with tide at the inlet, wind and river inflow. The tidal flow was found to be the main driver of changes in turbidity with river-borne plumes assuming some relevance during extreme events. The turbidity response for scenarios of increasing storm-driven events and mean sea level was compared between two existent seagrass patches and the differences in the turbidity conditions put in context of their relevant physical mechanisms. A difference in response was shown to exist between the two patches, mainly attributable to the tide which resuspends the spatially-varying sediments deposited seasonally by river inflow.The European Commission, under the 7th Framework Programme, supported this study through the collaborative research project LAGOONS (contract n°283157).The Portuguese Foundation for Science and Technology (FCT) also supported this study through the research projects DyEPlume (PTDC/MAR/107939/2008) and LTER-RAVE (LTER/BIA-BEC/0063/2009) co-funded through European Union (COMPETE, QREN, FEDER) and national FCT/MCES (PIDDAC), as well through the PhD grant SFRH/BD/84613/2012 (A. Azevedo).publishe

Summary of tidal and river discharge conditions during the survey periods.

<p>Summary of tidal and river discharge conditions during the survey periods.</p

Profiles of non-tidal velocity at stations A and B.

<p>Profiles of non-tidal velocity at stations A and B.</p

Profiles of non-tidal salinity at stations A and B.

<p>Profiles of non-tidal salinity at stations A and B.</p

Salt transport in the Espinheiro channel [kgm⁻¹s⁻¹].

<p>Letters (a) to (g) refer to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047349#pone.0047349.e012" target="_blank">Equation 6</a> salt transport terms.</p

The Espinheiro channel showing the survey locations A and B.

<p>The Espinheiro channel showing the survey locations A and B.</p

Contour figures of salinity as a function of the non-dimensional depth (<i>Z</i>) and time for all survey periods.

<p><i>H</i> and <i>L</i> indicate the local high and low-water. (a) 21/02/2002 (station A); (b) 28/02/2002 (station A); (c) 15/01/2004 (station B); (d) 16/06/2004 (station B); (e) 27/08/2004 (station B); (f) 03/12/2004 (station B).</p