C. Andrade

The sedimentary record of recent (last 500 years) environmental changes in the Seixal Bay marsh, Tagus estuary, Portugal

The inner Tagus estuary is essentially a sedimentation basin that receives cohesive sediment from terrestrial, marine, biological and anthropogenic sources. Three short cores from one site in a marsh area of this estuary (Seixal Bay) were analysed for sedimentary, geochemical and micropalaeontological contents (benthic foraminifera and nannoplankton). The length of the cores represents about half a millennium of sedimentation. Textural analysis suggests a highly uniform mud sedimentation for most of the cores but geochemical, mineralogical and micropaleontological results indicate climatic and environmental changes and anthropogenic disturbance. Three Foraminifera zones were identified. The lower part of the lower zone indicates sedimentation in an open channel or a lower domain of an exposed high-energy sandflat. Sediments of the upper part of the lower zone and of the middle zone were deposited in a lower-energy environment, probably associated with a sheltered, vertically aggrading mudflat located within the Seixal Bay. Biological and mineralogical indicators suggest that periods of total or partial closure of this bay occurred. Clay minerals indicate that drier and colder conditions prevailed in the lower half of this zone evolving gradually to a wetter and warmer environment towards the top. The upper zone indicates persistence of low-energy sedimentation and evolution towards the present salt-marsh conditions. Anthropogenic pollution is clear in geochemical proxies at the top of the sedimentary column and was used for dating purposes.

Anthropogenic influence in the Sado estuary (Portugal): a geochemical approach

Two areas of salt marsh in the Sado estuary – Faralhao, on the industrialized north margin and Malha da Costa, on the south bank, sheltered by a uninhabited sand spit – have been cored to study the geochemical signature of anthropogenic activity in recent (19th century onwards) intertidal sediments. Short cores were taken from each site from both the high and low marsh and were studied for texture, organic matter, pH, carbonates and geochemistry, including the heavy metals Cu, Pb and Zn. The marsh sediments are free of carbonate bioclasts and quite uniform in texture, consisting of acid to neutral clayey silt in addition to organic matter, which is higher in the top 20 cm. The vertical concentration profiles of heavy metals indicates enrichment in the top 30 cm of the sediment of the high marsh, in contrast with underlying high and low marsh sediment that has concentrations of metals at both studied sites similar to the Average Shale international reference/ continental crust sediments. The geochemical signal of anthropogenic influence in the marsh sediment was determined to have commenced from 1900-1920 using the sedimentation rates derived from 210Pb and 137Cs analyses. Spatial contrast in contamination levels was found within the estuary, with sediments of the Faralhao marsh showing higher enrichment factors of all metals. The anthropogenic increase of the supply of metal to the Sado estuary resulted from extensive exploitation of pyrite ore in the drainage basin until the1960’s; since that time, the sediments record a break in metal input, which resulted from a decline of the mining industry. However, in the marsh located closer to the industrial area (Faralhao) this break is followed by a local increase of heavy metal fluxes, which is interpreted as the result of intensification of anthropogenic influence. The comparison of metal concentrations in marsh sediments with target values established in quality guidelines indicates the studied area to be of environmental concern.

Sedimentary structure of the Nazaré coastal dunes (Portugal)

The internal structure of costal dunes located south of Nazaré was analyzed using Ground Penetrating Radar. These coastal dunes comprise stabilized dunes, located in the inner part of the dune field, and foredunes, both separated by a dry dune slack. The radargram analysis allowed the identification of five bounding surfaces that define six main aeolian sand units. The Units I, II, III and IV correspond to the progradation of foredunes seaward (NW), while Units V and VI represent the migration of a parabolic dune and a blowout, respectively, to southeast. A strong reflector separating Units I, II and III from Unit V is interpreted as a paleosoil, suggesting a break in aeolian sedimentation of unknown duration, but with sufficient time for soil development. The absent of the paleosoil over the Unit IV leave some doubts in relation to its relative age, although is indicative of the occurrence of an erosive event. Radar stratigraphic analysis provided a relative chronology of units that will be used as a framework for selecting sampling points for future absolute dating and sedimentological studies.

Effect of inlet morphology and wave action on pollutant pathways and sediment dynamics in a coastal stream

Hydrodynamics and water renewal of intermittent coa stal streams are highly variable, at various time scales, due to the very active morphod ynamic behavior of their inlets. Due to this strong dynamics, the pathways of water-born e materials – and the consequences of contaminated discharges – can depend strongly on the morphology and environmental conditions. Predicting the fate of contaminants in these systems requires coupled numerical models accounting for the major physical and water quality processes. We aim at improving the understanding of the impact of inlet morphology and wave action on the pollutant and sediment pathways of th ese small coastal systems, based on a suite of calibrated and validated coupled models. T wo analyses, based on particle simulations, are presented to assess sediment dynam ics and pollutant pathways for several conditions. Results show that waves have a major effect on the fate of waterborne materials in the estuary. Wave-induced curren ts sweep away materials coming out of the estuary, while wave-induced setup has a prof ound effect on tidal propagation, water levels and velocities in the estuary, promoti ng he upstream transport of pollutants. 1 National Laboratory for Civil Engineering, Av. do B rasil, 101, 1700-066 Lisbon, Portugal; {aoliveira, afortunato, mguerreiro, xbertin, nbrune au, mfrodrigues, pfreire, lsimoes, gdodet, amendes}@lnec.pt. 2 Faculdade de Ciências da Universidade de Lisboa, Ca mpo Grande, Ed. C6, 1749-016 Lisboa, Portugal; {rtaborda, candrade, amasilva, cm antunes}@fc.ul.pt. 3 CIMA, Universidade do Algarve, Campus de Gambelas, Ed. 7, 8005-139 Faro, Portugal; cloureiro@ualg.pt.