A high marsh transfer function for sea-level reconstructions in the southern Bay of Biscay.

E. Leorri was supported by a postdoctoral grant from the Basque Government and by the Conseil Gà ©nà ©ral of the Vendà ©e (F). This work has been partially funded by the UNESCO06/08 and IT-332-07/GIU06-10 research contracts and it represents a contribution to IGCP project #495

Impacto humano sobre la costa

Sin resumenSin resume

El registro geológico de la transformación ambiental de la ría de Bilbao durante el Holoceno y el Antropoceno

The northeastern coast of Spain is characterized by Mesozoic-Cenozoic sedimentary rocks forming high cliffs interrupted by short, narrow estuaries that are separated from the open sea by sandbars, beaches and dune deposits. The morphology and extent of the different estuarine sedimentary environments are constantly altered by erosion and deposition of sediments, and they are sensitive to even small changes in sea level. The Holocene transgressive episode caused the deposition of large volumes of well preserved estuarine sediments that can be studied to understand environmental and sea-level changes during this interglacial. The Bilbao estuary was originally the most extensive estuarine area on the Cantabrian coast of northern Spain. The modern estuary is 15 km long, an average of 100 m wide, and its channel depth ranges from 2 m in the upper estuary to 9 m at the mouth. The estuary is formed by the tidal part of the Nervion river, although four other rivers (Kadagua, Asua, Galindo and Gobelas) discharge into the main course. The tidal channel discharges into a wide marine bay called El Abra (average 3.5 km wide; up to 30 m deep). Tides are semidiurnal, with ranges between 4.6 m (spring tides) to 1.2 m (neap tides). The first iron and steel industry was opened on the middle estuary over reclaimed marshes as early as 1854. Since then, the natural features of the Bilbao estuary have been dramatically modified by urban, industrial and port developments. The exploitation of abundant local iron ore led to the early industrial development of Bilbao in the mid-19th century. The original estuary was rapidly reduced in size through land reclamation to form a tidal channel. This was isolated by dyking from its original intertidal areas, to allow a navigable watercourse from the city to the open sea. Today the Bilbao estuary is a largely artificial system which bears little resemblance to the original estuary. It has been calculated that the total amount of the original estuarine surface lost through human activity is approximately 1,000 ha. During the last 150 years, the Bilbao estuary has received wastes from many sources (mineral sluicing, industrial wastes and urban effluents) which have significantly degraded the environmental quality of the estuary. At present, the Bilbao estuary is the most polluted coastal area of northern Spain. A significant decrease in the flux of organic matter and heavy metal contaminants has occurred over the last decades, however, due to the implementation of environmental protection policies, the improvement in waste-treatment systems and the closure of some major factories during recent periods of economic recession. Furthermore, estuarine regeneration is currently being undertaken as part of a Revitalization Strategic Plan. Despite these improvements, the unremoved contaminated sediments from the intertidal areas may act as a long-term source of heavy metals to the aquatic environment through sediment mechanical reworking (e.g. dredging, shipping) and oxidation of anoxic sediments. Thus, these pollutants may continue procedures have been implemented. To reconstruct the palaeoenvironmental evolution of the Bilbao estuary since its formation following the postglacial rise of sea level, it have been analyzed the foraminiferal assemblages contained in eleven boreholes taken in the reclaimed areas of the middle and lower parts of the estuary. Integration of these results with similar data from previously studied boreholes has allowed us to reconstruct the environmental development of the Bilbao estuary during the Holocene. This environmental development has been organized into different systems tracts following a sequence-stratigraphic interpretation. Radiocarbon dating and palynological studies helped to locate in time the different palaeoenvironments and depositional episodes identified in the boreholes. Sediments that compose the estuarine infill range from basal fluvial coarse materials (Lateglacial), almost barren of foraminifera, that are interpreted as the lowstand systems tract (LST). This system tract is followed upwards by lower and middle Holocene transgressive materials (TST; 8500-3000 years cal BP), with upper Holocene regressive sediments on top (HST; 3000 years cal BP-19th century). This general sedimentary sequence is best represented in the middle estuarine area, and its sedimentary and microfaunal features are variable depending on its palaeogeographic setting: increasing muddy sediments and absence of open-marine elements are characteristic of the upper estuary, whereas increasing sandy sediments and reworking of the basal fluviatile materials are typical of the lower estuary. Comparison of these data with other sedimentary sequences from different coastal areas in the Bay of Biscay allows to reconstruct a general picture of the Holocene sea-level changes and coastal evolution in this area for the last 8500 years. On the other side, six cores retrieved from the Bilbao estuary tidal flats have been studied in order to evaluate the historical impact of the long lasting record of anthropogenic inputs, which have led to the disappearance of the indigenous microfauna and to the significant pollution of the sediments. Three different zones can be identified in the recent sedimentary record, reflecting initially the preindustrial estuarine conditions with abundant and diverse foraminiferal assemblages and baseline levels of metals, followed by the industrial-period sedimentary record, when high concentrations of metals in the estuarine environment allowed the development of abundant foraminiferal assemblages during the older industrial zone (period 1850-1950) that disappeared during the younger industrial zone (period 1950-2000) due to complete defaunation of the Bilbao estuary caused by minimum oxygen levels during this period. Obtained data provide important information in planning the restoration of the Bilbao estuary, because sediments have proven to be an important storage reservoir for pollutants and microfossils. Finally, the distribution and abundance of benthic foraminifera (together with geochemical analysis of heavy metals) from surface sediment samples (1997- 2003) and sediment cores collected from the intertidal flats of the Bilbao estuary have been studied to determine recent environmental contitions of this estuary. Furthermore a foraminiferal sampling network has been created in order to evaluate the future progress of the current regeneration schemes on a seasonal and anual basis. Pb-210 and Cs-137 determinations have also been undertaken to provide a chronology for pollutant inputs and ecological changes in the Bilbao estuary

ECOESTRATIGRAFIA (FORAMINIFEROS BENTONICOS) DEL RELLENO ESTUARINO HOLOCENO EN EL LITORAL VASCO (GOLFO DE BIZKAIA)

The Holocene sedimentary filling in the estuaries of the Cantabrian Coast has been studied by the boreholes EL1, Ria of Bilbao, and IS2, Ria of Bidasoa. The micropalaeontological analysis of both litoral sequences has allowed to recognize 5 and 7 different benthic foraminifera assemblages respectively. These have been used to determine the correspondant estuarine depositional subenvironments (from subtidal to middle/upper marsh). Two recurrent phases of sediment build up as sea level rose were distinguished. They were interpreted as the consequence of two different marine advances on this region: a first one dared around 8000 years B.P. (Atlantic stage) and a second one identified around 2500 years B.P. (Subatlantic srage)

Transformación reciente de ambientes intermareales bajo un escenario de ascenso del nivel marino: ejemplos del norte de España

The transformation of two intertidal environments from northern Spain during the last 150 years shows an evolution from a tidal flat into a salt marsh environment, wit han intermediate transitional stage. The environment of deposition was reconstructed based on benthic foraminifera and sand content. Sediments were put into a temporal framework using short-lived radioisotope activities and heavy metal concentrations. The observed natural evolution responds to the availability of abundant sediment and the current sea-level rise scenario, where intertidal environments are trying to adapt to increasing flooding periods by accreting sediment rapidlyLa transformación de dos ambientes intermareales en el norte de España durante los últimos 150 años muestra la evolución desde una llanura intermareal a una marisma, con una etapa de transición intermedia. El paleoambiente se reconstruyó mediante el contenido en foraminíferos bentónicos y en arena. Los sedimentos fueron datados utilizando radioisótopos de vida corta y concentraciones de metales pesados. La evolución natural observada responde a la disponibilidad de abundante sedimento y al escenario actual de ascenso en el nivel del mar, donde los ambientes intermareales están tratando de adaptarse a los crecientes períodos de inundación acrecionando sedimento rápidament

Anthropocene versus Holocene relative sea-level rise rates in the southern Bay of Biscay

Rangos de ascenso marino relativo en el sur del Golfo de Vizcaya durante el Antropoceno frente al Holocen

Rangos de ascenso marino relativo en el sur del Golfo de Vizcaya durante el Antropoceno frente al Holoceno

Con el fin de evaluar la aceleración en el ascenso relativo del nivel marino durante el Antropoceno, se han comparado los resultados previamente establecidos para el siglo XX con los resultados obtenidos a partir del estudio de 61 nuevos puntos indicadores del nivel marino durante el Holoceno en el sur del Golfo de Vizcaya. Estos resultados indican un ascenso rápido hasta los circa 7000 años cal BP que se puede estimar en 9-12 mm año-1. Desde entonces, el nivel del mar ha ascendido suavemente en concordancia con los datos proporcionados a nivel global, con una velocidad media de 0,7 mm año-1. Esta velocidad contrasta netamente con la tasa de ascenso registrada durante el siglo XX de 1,9 mm año-1, confirmando la aceleración detectada a nivel global como resultado de las actividades antropogénicas. Aunque los resultados obtenidos son altamente satisfactorios, los diferentes rangos de error proporcionados por ambos estudios hacen necesarios más estudios de este tipo para reducir los errores asociados a estas reconstruccione

Consecuencias del dragado y vertido de arena estuarina en la Reserva de la Biosfera de Urdaibai (Golfo de Bizkaia): el caso de la “ola izquierda de Mundaka”

ABSTRACT. In the spring of 2003, 240,000 m3 of sand were dredged from the main channel of the lower Oka estuary (Urdaibai Reserve of the Biosphere) and dumped on the southern area of Laida beach located at the estuary mouth. After few months, strong erosion of the deposited sediments occured as a consequence of the northwards migration of the final meander of the main estuarine channel before it reached the estuary inlet. At the same time, the estuarine inlet abandoned its original position near the rocky western margin and migrated eastwards cutting and eroding the sandy ebb delta (Mundaka sand bar). This caused a change in the way the incident wave broke as it reached the shallow water of the ebb tidal delta and beach and made surfing impossible under the same optimal conditions previously enjoyed due to the production of a wave that gradually broke from right to left as it reached shallow water, the so called “Mundaka left wave”. As a consequence, the Billabong Pro surf championship was cancelled in 2005. This paper describes the results obtained during a study of the outer estuary carried out during the period May 2005-April 2006 to characterize the processes operating on the most dynamic area of the estuary throughout the year and to evaluate the influence that the anthropogenic activities in the estuary had on the wave characteristics. No corrective measures were taken in the outer estuary during the study period and the environment recovered its normal morphological features naturally. This natural restoration it is hoped will be more stable, long lasting and reliable to ensure the continuing future of the “Mundaka left wave”.RESUMEN. En primavera del año 2003, la necesidad de mayor calado condujo a la realización de un dragado con la extracción de aproximadamente 240.000 m3 de arena del canal principal del estuario inferior del Oka (Reserva de la Biosfera de Urdaibai) y su vertido en la zona supramareal sur de la playa de Laida situada en la desembocadura del mismo. Desde la finalización de este vertido, se observó en la zona una fuerte erosión debido a la migración lateral del último meandro del canal estuarino antes de su desembocadura. Paralelamente, se produjo una variación morfológica del canal de desembocadura, con el paulatino abandono de su posición original junto al margen rocoso oeste de la ría y la aparición de un canal alternativo hacia el este que seccionaba el delta de reflujo (barra arenosa de Mundaka). Esta variación provocó un cambio en las características del oleaje incidente imposibilitando la práctica del surf en las condiciones idóneas que se disfrutaban hasta entonces y obligando a la cancelación en 2005 de una de las pruebas de surf más importantes del mundo, el Billabong Pro. Este trabajo muestra una síntesis de los resultados obtenidos en el estudio de la zona más externa del estuario del Oka durante el período Mayo 2005-Abril 2006 con el fin de caracterizar los procesos que operan durante todo el año en la zona más dinámica de este estuario y evaluar la influencia que el dragado efectuado tuvo sobre la rotura del oleaje. Como consecuencia de no haber adoptado ninguna medida correctora en la zona exterior de la desembocadura, el propio sistema sedimentario y sus diferentes elementos constitutivos consiguieron de modo natural unas características morfológicas similares a las habituales en esa zona. Esta restauración natural será previsiblemente mucho más estable, duradera y segura de cara a garantizar el futuro de la “ola izquierda de Mundaka”

Holocene palaeoenvironmental evolution of the Ebro Delta (Western Mediterranean Sea) : evidence for an early construction based on the benthic foraminiferal record

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in The Holocene 26 (2016): 1438-1456, doi:10.1177/0959683616640048.Major Mediterranean deltas began to develop during a period between 8000 and 6000 yr BP when the rate of fluvial sediment input overtook the declining rate of sea-level rise. However, different authors have argued that the Ebro Delta primarily formed during the Late Middle Ages as a consequence of increased anthropogenic pressure on its river basin and these arguments are supported by the scarcity of previous geological studies and available radiocarbon dates. To reconstruct the environmental evolution of the Ebro Delta during the Holocene, we used micropalaeontological analysis of continuous boreholes drilled in two different locations (Carlet and Sant Jaume) on the central delta plain. Different lithofacies distributions and associated environments of deposition were defined based on diagnostic foraminiferal assemblages and the application of a palaeowater-depth transfer function. The more landward Carlet sequence shows an older and more proximal progradational delta with a sedimentary record composed of inner bay, lagoonal, and beach materials deposited between 7600 yr BP and >2000 yr BP under rising sea-level and highstand conditions. This phase was followed by a series of delta-plain environments reflected in part by the Carlet deposits that formed before 2000 yr BP. The Sant Jaume borehole is located closer to the present coastline and contains a much younger sequence that accumulated in the 3 last 2.0 ka during the development of three different deltaic lobes under highstand sea40 level conditions. The results of the present study reinforce the idea that the Ebro Delta dates to the early Holocene, similar to other large Mediterranean deltas.Drilling and coring was funded by the US National Science Foundation 686 grant EAR- 0952146. Work on the cores presented in this study was partially financed by the Formation and Research Unit in Quaternary: Environmental Changes and Human Fingerprint (UPV/EHU, UFI11/09) and HAREA-Coastal Geology Research Group (Basque Government, IT767-13) projects. It was supported by an IRTA-URV Santander fellowship to Xavier Benito through “BRDI Trainee Research Personnel Programme funded by University of Rovira and Virgili R+D+I projects” and the European Community’s 7th Framework Programme through the grant to Collaborative Project RISES-AM-, Contract FP7-ENV-2013-two-stage-603396