Federico Vilas

Geochemistry of Major and Trace Elements in Sediments of the Ria de Vigo (NW Spain): an Assessment of Metal Pollution☆

Ria de Vigo is a funnel-shaped, fault-bounded coastal embayment in Galicia, NW Spain. There are a number of important centres of population and industrial activity along its margins, which serve as sources of pollution. Sixty-six subtidal sediment samples have been collected in the Ria. The samples have been subjected to a total digestion technique and analysed for major and trace elements (Al, Fe,Ti, Mn, Cu, Pb, Cr, Zn, Co, As, Ni, Cd and Sr). Variations of absolute metal concentrations reflected variations in textural and/or carbonate and organic matter content. Geoaccumulation indexes and enrichment factors have been calculated to assess whether the concentrations observed represent background or contaminated levels. It is proved that the choice of the background plays an important role in the interpretation of the geochemical data. PCA was a very useful tool to define background values for metals in the Ria de Vigo area. These values were similar to regional values given by other authors. It is concluded that the Ria is slightly to moderately polluted for some of the studied metals. The spatial extent of pollution was examined, and it was found that the most polluted area is located in the inner and southern parts of the Ria.

Subantarctic macrotidal flats, cheniers and beaches in San Sebastian Bay, Tierra Del Fuego, Argentina

Abstract San Sebastian Bay is a large, semicircular coastal embayment situated on the Atlantic coast of Tierra del Fuego, Argentina. It is a high-energy, subantarctic environment with a tidal range of 10.4 m, influenced by large waves of Atlantic and local origin and swept by constant, strong westerly winds. A 17 km long gravel spit protects the Northern part of the Bay giving rise to a gradient in sedimentary processes. From south to north, are seven distinct sedimentary environments. Coastal sedimentation started at least 5200 years before present (BP) and a rapid progradation related to a relative sea-level drop has infilled about 6 kilometres of the Bay with a sedimentary sequence 10–11 m thick. 14-C dating of unabraded shells in the Chenier ridges of the relict part of the complex allows for a precise reconstruction of the stages of the progradation, that has slowed from 2.35 m/year at 5000 years BP to 0.6 m/year at present. The possible causes of the sea-level drop are discussed.

Diagenesis and anthropogenesis of metals in the recent Holocene sedimentary record of the Ría de Vigo (NW Spain)

To contribute to establishing a historical baseline for future evaluations of the environmental quality of the Ría de Vigo (NW Spain), we report metal contents determined in eight gravity cores obtained at representative locations in 1990 - before the installation of any wastewater treatment plants - and in fractions thereof that were obtained by the BCR sequential extraction method. The results suggest that early diagenesis had been influenced by both hydrodynamic conditions and organic matter input (the latter especially in areas devoted to mariculture), and that anthropogenic inputs had also affected the concentrations and between-fraction distribution of Cu, Pb, Zn and other metals in surficial sediments.

The Corrubedo beach-lagoon complex, Galicia, Spain: Dynamics, sediments and recent evolution of a mesotidal coastal embayment

Abstract The Corrubedo beach-lagoon complex is situated in an embayment on the northwestern coast of Spain. The 4.1 m tidal range and southwesterly winds are the main agents of sediment transportation. The sediments are hybrid arenites (siliciclastic + bioclastic), with carbonate percentages ranging from 27.36 to 54.10%; silt, clay and organic matter occur in minor amounts. Repeated mapping and sampling of the beach, tidal channels, salt marshes and active and vegetated dunes recorded the vertical facies associations and their temporal evolution. Two peat layers at 0.6 and 1.7 m below the present-day marsh have yielded ages of 2280 ± 60 yrs B.P. and 1045 ± 125 yrs B.P. respectively. The possible causes of the relative sea-level rise are discussed.

Simulating the influence of physicochemical parameters on subsurface oil on beaches: preliminary results.

Monitoring of sandy beaches after the Prestige oil spill revealed thick subsurface layers (up to 1m thick) of grey-coloured sand. These horizons were sometimes found under more than 3m of clean sand. Examination of the sand by electron microscopy confirmed that the colouring was due to oil-coated sand grains, and revealed a sequence of degradation of buried oil. Further analysis of the sand revealed high concentrations of hydrocarbon in the oil-coated sand and that the main biomarkers were indicative of biodegradation, even though the oil was buried. A set of experiments was designed to analyze the evolution of oil from tar balls to coatings. The results revealed that biodegradation is a secondary process in the changes that take place in the buried oil, and that water flow slows down the appearance of grey sand and that low salinity may hinder the oil degradation process.

Las glauconitas de la plataforma continental gallega: indicadores geoquímicos del grado de evolución.

La interpretacion estratigrafica de unidades que contienen glauconita requiere de una adecuada caracterizacion del grado de evolucion, definido a partir del concepto de madurez (Amorosi, 1995). Su utilizacion es util para determinar la duracion de periodos asociados a bajas tasas de sedimentacion o para caracterizar condiciones paleoceanograficas y paleoambientales en la interfase sedimento-agua del mar. En este tipo de estudios se asume implicitamente que la glauconita actua como un sistema abierto, susceptible de continuos cambios en la estequiometria, como resultado del intercambio de cationes con el agua del mar que, a su vez, inducen reajustes estructurales. La determinacion del grado de evolucion de glauconitas esta asociada habitualmente a la presencia de determinados marcadores, algunos de tipo cualitativo como es el color o bien asociados a la variacion de alguna de sus propiedades fisicas, como es la susceptibilidad magnetica o composicionales y estructurales, como son la determinacion del contenido en K+ o la distancia entre las reflexiones 001, 020 en diagramas de difraccion de rayos X. Sin embargo, una caracterizacion adecuada del proceso evolutivo en glauconita que pueda ser aplicada de forma general debe ser capaz de establecer una relacion precisa entre los cambios quimicos con el medio durante el proceso de creci 233 S. Fernandez-Bastero et al. Las glauconitas de la plataforma continental gallega... miento y la tendencia hacia una mayor estabilidad termodinamica, conectada con modificaciones estructurales, desde una etapa inicial de formacion, casi amorfa, hasta alcanzar los ultimos terminos de la solucion solida, mas ordenados. En este sentido, este trabajo se ha planteado con una doble finalidad: en una primera etapa se ha determinado la variabilidad composicional en glauconitas de la plataforma continental gallega y en segundo lugar, estos valores han sido comparados con la variabilidad estructural al objeto de establecer patrones de comportamiento durante las diferentes etapas del proceso evolutivo. El desarrollo de este estudio esta basado en el analisis cuantitativo de los diagramas de difraccion de rayos X de 50 muestras de sedimento superficial, mediante el metodo de Rietveld. Con este fin, se ha desarrollado una aplicacion particular de este procedimiento de analisis, basada en el ajuste simultaneo de los factores de ocupacion para las distintas sustituciones en lugares tetraedricos y octaedricos, asi como en las intercapas de la estructura. De este modo, las modificaciones en la estequiometria, inducidas por los procesos de intercambio cationico entre la superficie mineral y el agua del mar se pueden relacionar con cambios estructurales asociados a las diferentes etapas del proceso evolutivo. Como resultado de este analisis, ha sido posible la elaboracion de mapas de contenido geoquimico que reflejan la distribucion espacial, tanto para la variabilidad composicional como para la cristalinidad en las glauconitas asociadas a sedimentos superficiales de la plataforma continental gallega.

Propiedades magnéticas de los sedimentos de tipo estuarino. El caso de las Rías Baixas.

Este trabajo establece la utilidad de la susceptibilidad magnetica como indicador de la influencia marina y evolucion diagenetica en sedimentos costeros de las Rias Baixas. Para ello se investigo la variabilidad geografica de la susceptibilidad en 200 muestras de sedimentos marinos superficiales en las Rias de Vigo y Pontevedra. Su variabilidad vertical se estudio en 80 muestras de tres testigos de entre 60 y 90 cm de longitud extraidos en la Ria de Pontevedra. La susceptibilidad de las muestras superficiales aumenta progresivamente hacia mar abierto, y a medida que nos alejamos de las zonas de mayor influencia continental, estando relacionada con la textura y composicion del sedimento, y por tanto, con su procedencia. Los testigos, mas homogeneos litologicamente, mostraron una disminucion muy importante de la susceptibilidad con la profundidad, estando esta asociada a la evolucion diagenetica del sedimento. Para estudiar mejor estos procesos, se determino la composicion elemental y mineralogica, y ademas se midieron otras propiedades magneticas de muestras representativas. Estos resultados se analizaron conjuntamente con los datos sedimentologicos disponibles, lo que permitio establecer que la variabilidad de 151 D. Rey et al. Propiedades magneticas de los sedimentos de tipo estuarino... la susceptibilidad dependia de tres factores principales: (a) procedencia y origen de los sedimentos, (b) regimen hidrodinamico de la zona y (c) presencia de particulas contaminantes discretas de origen antropogenico. Tambien puede concluirse que la evolucion de las fases magnetomineralogicas durante la diagenesis temprana esta controlada por el contenido en materia organica, lo que a su vez determina el potencial de oxidacion-reduccion.

Aplicación del Sonar de Barrido Lateral a la cartografía de fondos marinos. Ejemplo de la Ría de Pontevedra (Galicia, NO España).

Se realiza una cartografia de detalle de los fondos actuales de la Ria de Pontevedra basandose en los registros de sonar de barrido lateral. El analisis de los sonogramas obtenidos permite diferenciar cuatro patrones de reflectividad. Los datos de muestras directas del fondo obtenidas dentro de la zona que caracteriza a cada patron establecen la relacion directa entre reflectividad-textura. La correlacion de las sonografias con la geologia de la zona emergida hacen posible distinguir en los registros los dos tipos de basamento (granitico y metamorfico) en funcion de sus reflectividades y rasgos estructurales (fracturas). El sistema acustico aplicado permite discriminar entre formas sedimentarias (megaripples) y antropicas (bateas, marcas de arrastre), a la vez que se establece su relacion directa con las condiciones hidrodinamicas y rasgos morfologicos de la Ria de Pontevedra.

Optimization of Itrax Core Scanner Measurement Conditions for Sediments from Submarine Mud Volcanoes

XRF scanners allow fast, high-resolution delivery of geochemical and physical property data from sediment cores. However, lack of standardized protocols for measuring parameter settings can lead to results of inferior quality to the instrument’s real potential, particularly regarding light elements. In this study, a sediment core from a mud volcano in the Alboran Sea (off SE Spain) with very heterogeneous sedimentological character was analyzed using an Itrax™ Core Scanner (ITRAX). This study assesses some of the factors that influence measurements: type of anode used, X-ray exposure time, and effects resulting from the sample’s exposure to room temperature during analysis as well as those caused by refrigerated storage. Quality and accuracy of the ITRAX data was evaluated by comparison with quantitative measurements obtained by conventional XRF and ICP-OES on discrete samples. The results obtained suggest 20 s is an optimal exposure time as this gives good quality results for the majority of elements analyzed, including light elements and trace elements (e.g. Al (1.9–6.6 %), Cr (84–161 µg g−1), Ni (35–62.5 µg g−1)). Additionally, this analysis time is not significantly detrimental to core condition. The ITRAX capacity to identify diagenetic and authigenic processes in this type of geochemical environment is also demonstrated.

Factors Controlling the Incorporation of Trace Metals to Coastal Marine Sediments: Cases of Study in the Galician Rías Baixas (NW Spain)

Transitional coastal environments such as the Galician Rias in the Atlantic coast of NW Spain are densely populated areas. Their environmental problems are highlighted by the conflicting interests of different economic sectors: extensive mariculture activities are located in its waters and intertidal zone; shipbuilding, carbuilding, canning and other industries compete with tourism on their shores; and dairy farming is the main agricultural activity in its surrounding hills and hinterland (Vilas et al., 2008). As a result, the management of the coastal zone is highly complex and it is difficult to balance quality of coastal waters with economic activities. For instance, in the Ria de Vigo, the southernmost of the Rias Baixas, wastewater treatment plants were not installed until the 1990s, and in spite of regional environmental legislation (Lei 8/2001), their capacity was still insufficient in 2005 when the European Court of Justice found Spain guilty of failure to fulfill its obligations under the Article 5 of the Council Directive 79/923/EEC on the quality required for shellfish waters (Case C-26/04 ECJ). This case was closed following Spains submission of a pollution-reducing programme specifically pertinent to shellfish waters; success of this plan will depend critically on the behaviour of the sediments on the ria bottom. Galician Rias experience seasonal upwelling, which increases marine productivity. This promotes the deposition of high organic matter contents in the bottom sediments and contributes to the observed intense sedimentation rates of 1-6 mm yr-1 (Alvarez-Iglesias et al., 2007; Rubio et al., 2001). Current levels of trace metals (Prego & Cobelo, 2003) in sediments of these Rias have caused a significant concern by local and European authorities in the last ten years, especially in relation to the application of the Water Framework Directive (WFD), aimed to ensure that all waters reach “good status” by 2015. Some of these studies (Alvarez-Iglesias et al., 2003; Belzunce-Segarra et al., 2008; Rubio et al., 2000a) showed that the highest concentration of trace metals occurs in the muddiest surficial