Bastos L.,University of Porto |
Bio A.,University of Porto |
Pinho J.L.S.,University of Minho |
Granja H.,University of Porto |
And 2 more authors.
Estuarine, Coastal and Shelf Science | Year: 2012
The Douro estuary sand spit (NW Portugal) is an important natural defence against the impact of storm events. Aiming to improve navigation safety, a breakwater was built to stabilise the spit. In 2001, a monitoring programme was set up to understand the dynamics of the sand spit and, later, to evaluate breakwater efficiency on stabilising the spit's shape and volume. Nine years of periodic, accurate 3D digital elevation models obtained from kinematic differential Global Positioning System surveys were used to assess spatial and temporal changes in the spit morphology before and after the breakwater construction. Temporal and spatial spit dynamics were further related to river discharge flows, wave action and wind energy. Although the breakwater had a stabilising effect on most of the spit's area and volume, it caused a clear change in the morphology of the spit's head and in the previously observed patterns of erosion and accretion. Before breakwater construction, erosion was significantly correlated with extreme river discharge and wind conditions; accretion was significantly correlated with extreme wind conditions; and spit area and volume at 1-2 m elevation with extreme wave conditions. After breakwater construction, these correlations were not found, but the eastern (inland) face of the spit and particularly its southern part became more susceptible to the observed extreme river discharge flows, wave and wind conditions. The instability in the SE part of the spit may pose a threat to an existing local Nature Reserve. Furthermore, before breakwater construction, the spit often breached during severe floods favouring river discharges. The strengthening of the spit after breakwater construction may reduce the likelihood of breaching and lead to more severe flood effects in the estuary. © 2012 Elsevier Ltd.
Palma C.,IH Instituto Hidrografico |
Oliveira A.,IH Instituto Hidrografico |
Valenca M.,IH Instituto Hidrografico |
Cascalho J.,University of Lisbon |
And 4 more authors.
Marine Pollution Bulletin | Year: 2013
The Azores Platform and the Irving and Great Meteor seamounts south of the archipelago (38°N-29°N) have rarely been studied geochemically, a fact which is surprising given that they represent the south-eastern limit of region V outlined in the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR Convention). The main aim of the present work was therefore to characterise the spatial variability of major and minor elements in deep-sea sediment cores from these two regions. XRD and geochemical analyses revealed that whereas the Azores Platform sediments are composed of a mixture of biogenic and detrital volcanic material, those at the seamounts are characterised by carbonated biogenic remains. The latter sediments were found to contain very low amounts of volcanic or hydrothermal detrital material, being almost entirely comprised of CaCO3 (more than 80%). © 2013 Elsevier Ltd.
Palma C.,IH Instituto Hidrografico |
Lillebo A.I.,University of Aveiro |
Borges C.,IH Instituto Hidrografico |
Souto M.,EMEPC Task Group for the Extension of the Continental Shelf |
And 3 more authors.
Marine Pollution Bulletin | Year: 2012
This study provides data concerning the hydrography and water chemistry of the Atlantic region between 29-38° N and 27-31° W, and establishes background values for dissolved Cu, Cd, Pb and As. Three water masses were identified: the Eastern North Atlantic Central Water (ENACW), the Mediterranean Water (MW) and the North Atlantic Deep Water (NADW). The ENACW exhibits a clear meridional gradient of temperature and salinity, with comparatively high values at the southern sites and lower values on the Azores platform. The ENACW, which includes the euphotic zone, also had comparatively high concentrations of oxygen and lower concentrations of nutrients and metals. The Cu, Cd and Pb results suggest that new background concentrations for OSPAR Region V (the Wider Atlantic) should be established as follows: 0.15-13. nM for Cu, 0.05-1.4. nM for Cd and 0.03-5. nM for Pb. The background concentrations of As for OSPAR Region V should be 7-28. nM. © 2012 Elsevier Ltd.