Efecto del drenaje ácido sobre el fraccionamiento de tierras raras ligeras en sedimentos: un caso de estudio en el estuario de los ríos Tinto y Odiel

The effect of acid drainage on light rare earth elements (LREE) has been studied in the estuarine sediment of the Tinto and Odiel system, where the fluvial and marine water mixing cause an important pH and chlorinity gradient inside. Due to the high influence of pH over the LREE partitioning from dissolved toparticulate phases, an anomalous behaviour has been found on La content in these sediments. Large removal of LREE takes place at low chlorinity zones in unaffected estuaries, but in the studied system this natural process is moved out the outer zones of the estuary. So, the relative La depletion in the estuarine mixing zone is due to the low pH values (< 6) that prevents LREE removal in low chlorinity zones. Once the acid neutralization (pH ~ 7) occurs, some La enrichment can be observed in sediments of the marine estuary.Versión de edito

Variaciones estacionales de tierras raras en la materia en suspensión y el agua del estuario del río Odiel (SO de España)

Seasonally distribution of the lanthanides in the suspended matter and dissolved phasehas been studied during a hydrological year in the estuary of the Odiel River. In his system affected by acid mine drainage take place the coexistence of two water mixture processes; a process salt-induced mixture typical in an estuary and a process of acid water neutralization. In the mixing zone of the estuary there is a removal of the dissolved phase to the suspended matter out of the system. REEs concentrations are controlled by the volume of discharge of the river and degree of neutralization process. Thus, during first rains after a dry period, the gradient in concentration of these elements in the mixing zone ismore pronounced in this system.Versión de edito

Evolución de los deltas submarinos de los ríos Guadalfeo y Adra en respuesta a las variaciones de los aportes sedimentarios

The Guadalfeo and the Adra submarine deltas off the northern coast of the Alboran Sea have been built up under the direct influence of short and mountainous rivers. The area is subjected to strong climatic seasonality, with sporadic winter torrential floods and high summer aridity. In addition numerous anthropogenic activities have affected these systems, mostly during the last two centuries. In order to decode the influence of climatic variability and anthropogenic impacts on sediment supplies during the recent past, five sediment cores were collected from the Guadalfeo and Adra submarine deltas. Benthic foraminiferal and sedimentological analyses, combined with radiocarbon dating, were performed. The impact of torrential floods alternating with periods of low rainfall or dry periods were recorded in the Adra and Guadalfeo prodeltas. Periods with low abundance of benthic foraminifera and high amounts of coarse-grained sediments, were interpreted as the result of enhanced sediment supply to the shelf triggered by major flood events. On the other hand, periods with high amounts of fine-grained sediments and high abundances of colonizers and opportunistic foraminiferal species indicate the establishment of new environments with distinct ecological constraints. These environments were driven by lower sediment supplies during low rainfall or dry periods. The most recent sedimentation seems to reflect the human interventions in the rivers basins, such as deviation of the main river courses and dams construction, which reduced the sediment input and promoted the deposition of shallow-water submarine deltas.Versión del edito

Biogeochemistry of surface sediments in mud volcanoes of the Gulf of Cádiz

The shallowest sediment of three mud volcanoes (MVs) located in the middle slope of the Gulf of Cádiz, Anastasya, Pipoca and St. Petersburg, have been seasonally studied during June and December 2016. These structures are locally important contributors of many biogeochemical active substances to the water column, with a special attention in the emission of methane (CH4). Along this study, the role of organic matter diagenesis and its contribution to the diffusive fluxes estimated in the sediment–water interface from the three MVs have been investigated mainly. For this, the first combined analyses of sediment properties (granulometry, porosity, density, organic carbon) and pore water chemistry (major elements, dissolved inorganic carbon (DIC), nutrients, CH4 and nitrous oxide) have been carried out. Anastasya and St. Petersburg MVs presented similar behaviours, with a slight concentration variation for the chemical variables in the top layers of the sedimentary record followed by a more intense vertical variation in deeper layers. Anastasya MV showed some typical processes of these structures, such as the clay dehydration, the dissolution of halite and the precipitation of authigenic carbonates, which was also observed in St. Petersburg MV. Organic matter diagenesis clearly altered the biogeochemical profiles, except for Pipoca MV. Moreover, mud breccia with a mousse-like texture has been identified in the deepest levels of Anastasya and St. Petersburg MVs. Here, anaerobic oxidation of methane is linked to the decrease of SO2−4 and the increases of CH4 and DIC with the core depth. Changes across the sediment–water interface presented low diffusive fluxes in the three MVs due to the presence of other processes as the irrigation by benthic macrofauna, the action of bottom currents and/or the upward fluid migration. From the obtained results, we can conclude that Anastasya MV presents a certain venting activity at present.En prensa1,47

The evolution of the Guadalfeo submarine delta (northern Alboran Sea) during the last ca. 200 years

The Guadalfeo submarine delta is located on the northern Alboran Sea shelf in the western Mediterranean Sea. The sedimentary dynamics of the deltaic system is governed by the discharge of one of the major rivers in this area draining the western sector of the near-coastal Sierra Nevada Mountains. The area is under the influence of a Mediterranean climate, with high spatial and temporal (i.e., inter- and intra-annual) rain variability. Major anthropogenic forcing affected the river system during the 1930’s, with the deviation of the main river channel 2.5 km to the west, to its present position. More recently, the construction of Béznar (1977-1985) and Rules (1993-2003) dams have also contributed to limit the amount of sediments exported to the deltaic system. In order to understand the interaction between river discharges and the evolution of the submarine delta at different timescales, sediment cores were collected off the ancient (core 13) and present-day (cores12 and 15) river courses. A chronological framework was performed and combined with sedimentological and benthic foraminiferal analyses. Radiocarbon dating of plant debris from the base of the cores indicates that the sedimentary record goes back 200 years. In core 13, the variations between coarse and fine fractions along the core and the upward increase of benthic foraminiferal population density, would indicate that deposition possibly occurred until the deviation of the main river course to its present position. In the lower part of core 12, the strong alternation between coarse and fine sediment textures and the variable amounts of benthic foraminiferal species are interpreted as the result of an active fluvial regime. The upper part, with high percentages of fine sediments and high values of population density, could be attributed to the stabilization of the river course in its present-day location. Core 15, located at 11 m water depth, showed the highest content of gravel in the lower part of the core, high contents of silt at two core depths and increased percentages of sand to the top, indicating the strong influence of human interventions in the river basin and consequent changes in the sediment supply to the Guadalfeo submarine delta.info:eu-repo/semantics/publishedVersio

Multi-proxy evidence of rainfall variability recorded in subaqueous deltaic deposits off the Adra River, southeast Iberian Peninsula

The Adra River deltaic system, southeast Iberian Peninsula, shows a steep topography and is subjected to strong climatic seasonality. This system has been affected by alternating wet and dry periods, and it has also undergone numerous anthropogenic activities such as deforestation, mining activities, river channel deviations and dam construction, particularly during the last two centuries. Two sediment cores were retrieved off the Adra River, from the western (MS_V9) and eastern (MS_V4) lobes of the subaqueous deltaic deposit. A multi-proxy study was carried out, including grain size, benthic foraminiferal assemblages, magnetic susceptibility and geochemical element analyses, in order to understand the sedimentary expression of recent climatic cycles and anthropogenic interventions in the river basin. Periods of increased deposition of coarse-grained sediments, low absolute abundance of benthic foraminifera and high elemental ratios indicative of terrigenous contributions, were interpreted as periods of increased sediment supply to the shelf. Four flooding events were recorded in core MS_V9 and three events on core MS_V4, of which two were observed in both cores. They were related to periods with major floods that were documented on the southern Iberian Peninsula around 1770e1810 and 1860 e1870 AD. On the other hand, sediment core intervals exhibiting increasing proportion of fine-grained sediments and higher abundances of foraminiferal species assigned as successful colonizers (Textularia earlandi) and opportunistic species that feed on bacteria or terrestrial organic matter (Bolivina ordinaria, Bulimina elongata, Eggerelloides scaber and Ammonia beccarii or tepida), indicate the establishment of new environments with new ecological constraints. They were related to significant decreases of terrigenous sediment input during low rainfall or dry periods. The increase of opportunistic species feeding on fresh phytodetritus (Nonionella iridea, Nonionella stella, Nonionella sp., Brizalina dilatata, Epistominella vitrea and Bolivinellina pseudopuntata), under more stable environmental conditions, also point to a stronger marine influence on the prodeltaic environments during these periods. The human interventions on the river basin after 1872 AD, with the deviation of the main river channel to the east, led to a drastic reduction of the sediment exported to the western delta lobe. This study showed that the sedimentation on the Adra subaqueous deltaic deposit was mainly controlled by rainfall variability from 1663 to 1872 AD, and afterwards by anthropogenic interventions.En prensa2,247

Análisis y cartografía de riesgos geológicos en el litoral de la ciudad autónoma de Ceuta

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Los Montes Submarinos de la Plataforma Marginal de Motril, Mar de Alborán: Interacción con las Masas de Agua Profunda

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Spatial distribution, inter-annual variability and influence of abiotic factors on molluscan assemblages collected with otter trawl in the northen Alborán Sea

Molluscs constitute one of the most diverse and best represented invertebrate groups in the marine environment. In the northern sectors of the Alborán Sea and Gulf of Cádiz 1200 spp. of the 1800 spp. occurring in the Mediterranean Sea, have been found so far highlighting the importance of this area for the european molluscan fauna (Gofas et al., 2011). Molluscs are also the second group in abundance and biomass in demersal fisheries and an important component of soft-bottom benthic communities, including ecologically important and/or commercial mollusc species that are also exposed to an increasing trawling impact (Snelgrove, 1998; Kaiser & De Groot, 1999). Previous studies on molluscs of the Alborán Sea has primarily focused on those from infralittoral habitats, with few studies focussing on the composition, structure and dynamics of circalittoral and bathyal molluscan assemblages ( Rueda et al., 2015). The study of soft bottom molluscan assemblages where trawling fishing fleet operates is important for improving the fisheries evaluation and management, as well as the implementation of ecosystemic and biodiversity conservation measures in the context of the new Marine Strategy Framework Directive. In the present study, the distribution and inter-annual variability of molluscan assemblages of circalittoral and bathyal soft bottoms of the Alborán Sea have been analyzed as well as the relationships of fauna with different environmental variables. Samples were collected in 190 otter trawl hauls performed between “Punta Europa” and “Cabo de Gata”, including the Alborán Ridge, at depths from 30 to 800 m during four MEDITS-ES trawl surveys in spring between 2012 and 2015. Several environmental variables from the water column (temperature and salinity) and sediment samples were taken where each haul was performed in order to elucidate their relationships with the molluscan assemblages. Abundances of each species (individuals . h-1) of each haul and trawl survey were pooled in a matrix for performing multivariate methods in order to contrast molluscan assemblages of different sites and years. The Bray-Curtis similarity index was then used to perform non-parametric multidimensional scaling ordinations (nMDS). A fourth root transformation pretreatment was applied on the quantitative data in order to minimize the contribution of the most abundant species to the analyses. Analyses of similarities (ANOSIM) were carried out for statistical comparisons of groups of samples according to different factors (e.g. year, location). Analyses of similitude percentage (SIMPER) were used to identify those species that contributed to the similarity and dissimilarity between groups of samples according to factors. These multivariate analyses were executed using the PRIMER v6 (Plymouth Routines in Multivariate Ecological Research). Average values of abundance of molluscs (N), species richness (S), Shannon-Wiener diversity index (H’: log2), evenness index (J’) and taxonomic distinctness index (Δ*) were calculated for each sample group. Statistical differences between these values were tested with the non-parametric Kruskal-Wallis using SPSS software. The relationships between environmental variables and molluscs abundance in the different hauls were only studied for the 2014 trawl survey using a correspondence canonical analysis (CCA). The statistical significance of the adjusted CCA was assessed using a Monte Carlo permutation test. Prior to this, the environmental variables were screened and those which presented a correlation higher than 0.9 (after a Spearman correlation analysis) were not further considered. These analyses were executed using the R software. Three main molluscan assemblages were detected and belonged to the: I) Continental Shelf (30-200 m); II) Upper Continental Slope (201-350 m), and III) Middle Continental Slope (351-800 m). The multivariate analyses revealed geographical differences within the Alborán Sea, being these differences more acute between the Alborán Island, mainly in the shallower assemblages (30-200 m and 201-350 m) and the remaining locations considered. These differences were due to a lower abundance in the island of species that were dominant in the continental margin, such as Alloteuthis media, Sepietta oweniana and Turritella communis and a higher abundance in the island of species that were less abundant in the continental margin, such as Neopycnodonte cochlear, Arca tetragona, Loligo forbesii and Sepia orbignyana. No significant differences of the abundance, biomass, species richness and diversity index were detected in the assemblages over the four years. Nevertheless, significant abundance declines of A. media, S. oweniana, and increases of N. cochlear were detected in the continental shelf over the years as well as abundance declines of Bathypolipus sponsalis and Galeodea rugosa in the slope assemblages. Regarding the environmental variables, the shallower assemblage (30-200 m) showed a significantly higher temperature, lower salinity and wider variety of sediment types than the others, with a predominance of sandy mud textures followed by muddy sand. As depth increases the sedimentary heterogeneity decreases, with dominant muddy sediments. Depth, temperature and mud percentage were the key variables that better explained the variability of the molluscan assemblage in the CCA. In conclusions: (1) Acute geographical differences occurred between the Alborán Island and the locations of the continental margin, due to its location far from the continental influence and, therefore, with lower fisheries activity and a less muddy and more bioclastic sediment, (2) Inter-annual trends in the abundance, biomass, species richness and diversity of assemblages were not detected, but some species displayed inter-annual changes due to biological aspects or accidental catch of gregarious species and (3) depth and some sedimentological variables displayed the most significant relationships with the molluscan assemblages, as previously observed for other invertebrate assemblages in the Alborán Sea