Bilbao Estuary Research Articles

Subfluvial tunnel layout design: Mapping recent sediment fill in Bilbao Estuary using H/V spectral ratio

Mapping the soil-bedrock interface is crucial for tunnelling projects in engineering geology. This investigation demonstrates the effectiveness of a novel technique to calculate the horizontal-to-vertical (H/V) spectral ratio using ambient vibration measurements to characterize the unconsolidated sediment thickness and geometry of the top of the engineering bedrock in the city of Bilbao (northern Iberian Peninsula). Engineering bedrock is defined here as the consolidated rock layer underlying the Holocene sediments infill in the region. The non-invasive technique was integrated into the geophysical surveys conducted in 2019 for a subfluvial tunnel construction project beneath the Bilbao Estuary. We calculated the H/V transfer function at 37 sites using an AutoRegressive Moving Average (ARMA) model, which has been shown to be robust in extracting the ground fundamental resonant frequency with high spectral resolution. Lithological information from coincident stations and boreholes supports the empirical interpretation of the H/V spectral peaks in terms of peak impedance contrast depth. The estimated engineering bedrock exhibits morphological complexity with depths ranging from ∼10 m to ∼47 m below the surface. The obtained unconsolidated sediment thickness map is consistent with the geology known from the scattered historical borehole data and is supported by the results of the soil geotechnical characterization conducted in 2021 to advance the planning phase of the subfluvial tunnelling project. We show that the novel H/V approach used in this work is robust and yields somewhat higher resolution results than other commonly used H/V methods. The resolution of the method enables the use of H/V estimates to efficiently plan well campaigns and minimise costs, even for relatively shallow targets. We conclude that H/V mapping using this novel technique can help select layout alternatives in the early stages of tunnel construction planning, especially in heavily urbanized areas.

Evaluating ocean health and restoration success: A comprehensive study of the benthic quality index in the Bilbao estuary

Ocean health is a global concern, and effective protection and restoration of estuaries require robust ecological information and appropriate metrics for comprehensive assessments. This study used 16 years of hard-bottom macroinvertebrate data from the formerly polluted Bilbao estuary to calculate the Benthic Quality Index (BQI). The BQI, based on species sensitivity values derived from richness-disturbance associations, was a valuable tool for evaluating the health of the macroinvertebrate community. Our findings demonstrated the responsiveness of the BQI to both natural and anthropogenic stressors, making it a useful indicator for assessing overall community health. Significant increases in BQI values, averaging 47%, were observed in the central section of the estuary, indicating successful restoration efforts. Furthermore, the BQI values showed a positive correlation with distance from the river mouth, reflecting a gradient of improved health. Notably, the BQI reliance on data rather than species-specific knowledge makes it suitable for assessing benthic community health across large temporal and spatial scales, where ecological information may be limited. In conclusion, the BQI provides a standardized measure of health that facilitates a better understanding of the state of our oceans. Its application in assessing estuarine health, as demonstrated in the Bilbao estuary, underscores its value in conservation and restoration efforts. By utilizing the BQI, we can make informed decisions to protect and restore estuarine ecosystems for the benefit of marine biodiversity and the health of our oceans.

Urban socio-environmental vulnerability in Bilbao, Spain: a study through an urban indicator, Geographical Information Systems, and qualitative data analysis

Population trends lean towards urban settings. Its rapid expansion has created inequalities and poverty in urban areas around the world. This research is part of a series of recent publications on Spanish cities (Barcelona and Madrid). The work attempts to evaluate the current situation of urban socio-environmental vulnerability in Bilbao, a city located in the north of Spain. Three spatial scales have been considered: census tract, neighbourhood and district. The 277 census tracts that make up the municipality are analysed through the Synthetic Indicator of Relative Socio-environmental Vulnerability (RSEVuSI). Subsequently, the census tracts identified as vulnerable by the indicator were analysed in depth through a qualitative methodology. Among the main findings, we highlight the spatial distribution patterns of socio-environmental vulnerability in Bilbao. In general, the least vulnerable areas are located near the centre and the Bilbao estuary, while the most vulnerable are located in the peripheral districts (i.e. Otxarkoaga-Txurdinaga and Rekalde). However, some census tracts that present high vulnerability values ​ are located in a central district (i.e. Ibaiondo). In fact, one of the main challenges to be addressed is the gentrification of this area, as many authors argue. The qualitative evaluation reveal that, in general, there is an acceptable level of maintenance and cleaning of public spaces and urban furniture. However, with respect to the urban landscape, there are significant differences between the census tracts with the highest and lowest RSEVuSI values. It should be done more qualitative research so that planning and renewal actions can be implemented where they are really needed.

Designing Cement-Based Grouting in a Rock Mass for Underground Impermeabilization

Fractured rock masses below the water table are a problem in underground excavations because of their low strength and high permeability. Nowadays, these negative connotations can be reduced with techniques such as injection of cement, microcement, or resins grouts. These materials increase the rock mass cohesion while reducing the flow of water through the discontinuities. This paper describes the work carried out to design a waterproofing screen for a three-storey underground basement located in a building near the Bilbao estuary (Northern Spain) and with problems of water seepage from the river. First, a survey of the rock mass is carried out. This survey shows the presence of highly fractured zones and the variability of the permeability as functions of the fractures. Subsequently, the effect on permeability caused by the injection of cement grouts and microcement is studied by means of two pilot injection boreholes and eight control boreholes. Finally, a behavioural model is proposed to explain the heterogeneity observed in the radius of influence of the injection. As a result, a waterproofing screen with three types of treatment is designed: An ordinary treatment with cement grouts, an intensive treatment with microcement grouts, and an isolation treatment with cement-bentonite grouts.

Geological record of extreme floods and anthropogenic impacts on an industrialised bay: The inner Abra of Bilbao (northern Spain)

The Bilbao estuary is one of the most polluted areas on the northern coast of Spain, owing to the direct disposal of urban effluents and wastewaters from mining and industrial activities that has occurred during the last 170 years. Recent sediment records collected from the inner Abra of Bilbao bay were examined using a multidisciplinary approach including geochemical, micropaleontological and isotopic proxies to evaluate heavy metal contamination (Pb, Zn and Cd), ecological condition (benthic foraminifera), and sediment accumulation variability (210Pb). Results evidenced the interplay of both human activities and extreme weather events. Most contaminated materials are buried below a thin layer (1–21 cm) of cleaner sediments which have been deposited since contaminant discharges have substantially decreased, due to industrial reconversion and environmental regulations. However, the fingerprint left in the sedimentary record by the catastrophic floods of 1983 confirms the potential of natural events for sediment relocation, showing catastrophic events may endanger recently-achieved environmental improvements in historically contaminated coastal areas.

Multi-annual survey of health status disturbance in the Bilbao estuary (Bay of Biscay) based on sediment chemistry and juvenile sole (Solea spp.) histopathology

The Bilbao estuary (SE Bay of Biscay) is a recovering ecosystem whose sediments are still contaminated. They represent a potential risk for the biota including benthic and demersal species living in direct contact with the sediment. In this context, the present study aims to survey trends of the health status of the Bilbao estuary based on sediment chemistry and sole (Solea spp.) histopathology. Monitoring campaigns were carried out every autumn from 2011 to 2017 along the estuary. Contaminant levels were measured in sediments; liver, gills and gonads of juvenile fish were collected for histopathology. Overall, contaminant levels fluctuated throughout the years, with highest values recorded in the earlier years of the study period. Sole histopathology showed alterations of mild severity. Results permitted to assess the environmental health status of the Bilbao estuary during 7 years, although no clear temporal trend was detected. Longer-term monitoring programmes are necessary to confirm the ecosystem recovery.

Environmental regeneration processes in the Anthropocene: The Bilbao estuary case (northern Spain)

This work tackles a multidisciplinary study on the recent sedimentary record of the Bilbao estuary (northern Spain), which is the backbone of a city that was primarily industrial and now is widely recognized as a successful example of urban transformation. Although hotspots of heavily polluted materials still remain at the mouth of the two main tributaries (Galindo and Gobelas), the data obtained confirm the ongoing formation of a new layer of sediments (here called “postindustrial zone”) covering historically polluted and azoic deposits. It is characterized by largely variable levels of metals and magnetic susceptibility and moderate-to-high abundances of benthic foraminifera. Monitoring of the evolution of this layer appears a key factor to assess environmental improvement and decision-making in polluted estuaries.

Skeletonema species in a temperate estuary: a morphological, molecular and physiological approach

The genus Skeletonema is frequently found in the Bilbao estuary (Northern Spain) where it is broadly distributed along the salinity gradient. By means of morphological and molecular analyses, six strains belonging to three species, Skeletonema costatum, Skeletonema dohrnii and Skeletonema menzelii, have been identified. To know if they can grow actively in the different water masses or whether they are simply displaced by the tide, their response to salinity (5, 10, 15, 20, 25, 30 and 35 psu) was measured with a Pulse Amplitude Modulation fluorometer, providing the specific growth rates, the maximal quantum efficiency of Photosystem II (Fv/Fm) and the relative electron transport rate. All three species can be considered euryhaline, growing in a good physiological state between 5 and 35 psu. The maximum growth rates were 1.17 d−1 for S. costatum (strain Bc18EHU) at 15 psu; 1.61 d−1 for S. dohrnii (strain Bc21EHU) at 25 psu and 1.7 d−1 for S. menzelii (strain Bc30EHU) at 20 psu. The rapid light curves revealed that the three species are acclimated to the high light intensities which occur in the estuary from March to September.

Health status of the Bilbao estuary: A review of data from a multidisciplinary approach

Estuarine and marine ecosystems are subject to different sources of stress including changes in environmental physicochemical variables (nutrients, oxygen availability, temperature, salinity, pH) or exposure to a large cocktail of environmental pollutants. In the estuary of Bilbao, despite the improvement in environmental quality due to replacement of most polluting industries and the progressive implementation of an integrated sewage treatment plan, chronic pollution by metals and hydrocarbons still remains, together with eutrophication and pollution by emerging contaminants. The Unit of Formation and Research “Protection of Ecosystem Health” was created in 2012 through the strategic aggregation of three consolidated research groups: Cell Biology in Environmental Toxicology (CBET), Phytoplankton of estuaries and coastal areas (FITEAC) and Research on marine and estuarine pelagic environment and planktonic communities (MarEsPlank). The three groups have a long tradition in studying the health of marine and estuarine ecosystems from different perspectives, focusing in the Bay of Biscay and especially in the estuary of Bilbao. In this work we review data on the health status of the Bilbao estuary using early warning tools at the cell and tissue levels, phytoplankton assemblages and zooplankton ecology. In spite of the seasonal and interannual variability recorded for some parameters, a general recovery trend was observed for the health status in the estuary of Bilbao, with sporadic critical events such as the Prestige oil spill.

Molecular and morphological analyses of solitary forms of brackish Thalassiosiroid diatoms (Coscinodiscophyceae), with emphasis on their phenotypic plasticity

Blooms of centric diatoms are a common feature in the Bilbao estuary during summer when river flow is at its lowest and water temperature is above 20ºC. To gain insight into the specific composition of these diatom blooms, net samples and cultures of estuarine isolates were analysed under the scanning electron microscope (SEM) and by molecular analyses of the Internal Transcribed Spacers 1 and 2 plus the coding region 5.8S (ITS region) and the 28S rRNA gene. Seven species of solitary centric diatoms belonging to four genera were found in the estuary including: Conticribra weissflogii, Cyclotella atomus var. atomus, Cyclotella cryptica, Cyclotella marina, Cyclotella meneghiniana, Discostella pseudostelligera and Thalassiosira pseudonana. Dominant species during blooms were C. meneghiniana and Co. weissflogii in the upper estuary and D. pseudostelligera and T. pseudonana in the middle estuary. The morphological traits used to differentiate between species pairs of similar morphology (C. meneghiniana/C. cryptica or D. pseudostelligera/D. woltereckii) were observed to vary with environmental conditions, denoting a great deal of phenotypic plasticity which would hinder accurate identification of the species when using morphological approaches alone.

In-situand laboratory Raman spectroscopic analysis on beachrock deposits: Characterisation of the trapped materials

Raman spectroscopy, including in-situ and laboratory analyses, were carried out in beachrock outcrops located in temperate latitude (Arrigunaga beach, Bilbao Estuary, North of Spain) to characterise the wide variety of sediments and wastes trapped within the cements. In the examined beachrocks (coastal sedimentary structures formed in the intertidal zone through the early precipitation of carbonates) the presence of abundant slag and anthropogenic wastes is noticeable. In-situ Raman analysis revealed the presence of cristobalite (SiO2), tephroite (Mn2SiO4), quartz (SiO2), rhodonite (MnSiO3), labradorite (Ca,Na)(Si,Al)(4)O-8, hematite (-Fe2O3), gypsum (CaSO(4)2H(2)O) and amorphous carbon (C) as the main constituents in the trapped materials. Those were also identified off site together with other phases such as limonite (FeO(OH)nH(2)O), lepidocrocite (-FeOOH), arsenopyrite (FeAsS), fayalite (Fe2SiO4) and anatase (TiO2). As secondary compounds, portlandite (Ca(OH)(2)), C-S-H (Ca(3)Si(2)O(7)3H(2)O), gypsum and possibly ettringite (3CaOAl(2)O(3)3CaSO(4)32H(2)O) were identified only in-situ, and a possible evolution to the more stable thaumasite (3CaOSiO(2)CO(2)SO(3)15H(2)O) was found in the laboratory analyses. Therefore, the applied methodology and specifically the in-situ Raman spectroscopy analyses resulted particularly valuable, allowing an accurate description of the trapped materials and the compounds formed by hydration and/or sulphate attack (probably from the high level of atmospheric aerosols coming from seawater or industrial activity nearby), giving an insight of the complexity of the examined outcrops. Copyright (c) 2015 John Wiley & Sons, Ltd.

The genus Pseudo-nitzschia (Bacillariophyceae) in a temperate estuary with description of two new species: Pseudo-nitzschia plurisecta sp. nov. and Pseudo-nitzschia abrensis sp. nov.

The genus Pseudo-nitzschia contains potentially toxic species of problematic taxonomy, making it one of the most intensively studied diatom genera. The study of 35 clonal strains isolated from the Bilbao estuary, an area that experiences recurrent blooms of Pseudo-nitzschia, revealed the presence of two new species, P.abrensis and P.plurisecta, differing from their congeners in both morphology and gene sequence. The morphological features were analyzed by LM and EM, whereas molecular analyses were based on the internal transcribed spacer (ITS) and large subunit (LSU) regions of the rDNA. P.plurisecta appears closely related to P.cuspidata/P.pseudodelicatissima in the phylogenetic tree, whereas P.abrensis forms a moderately supported clade with P.heimii/P.subpacifica and P.caciantha/P.circumpora. Comparison of the secondary structure of ITS2 regions reveals marked differences in the most highly conserved regions among related taxa. Morphologically, the new species differ from their closest congeners in the arrangement of the poroid sectors and the density of valve striae and fibulae. The two species share similar pigment composition, and belong to the group of Pseudo-nitzschia species containing only chlorophyll c2 and c3 .

Relative deprivation and labour conflict during Spain’s industrialization: the Bilbao estuary, 1914–1936

What drove social conflict in Spain’s industrial areas in the period before the Spanish Civil War? This paper is concerned with contrasting the determinants of working-class conflict in northern Spain at the beginning of the twentieth century. Our hypothesis is that the key determinant of conflicts in emerging industrial areas during the interwar period was the struggle to obtain satisfactory family income in a context of combined high price fluctuation, unemployment and economic boom and bust. We suggest two new ways to decipher how economic factors interact with labour conflict. We introduce the family as the relevant income unit when considering wage struggles and relative deprivation. And secondly, we study the reactions to short-term variations of income on families by using monthly rather than quarterly or annual data.

Dissolved oxygen in contrasting estuaries of the Bay of Biscay: effects of temperature, river discharge and chlorophyll a

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 418:57-71 (2010) - DOI: https://doi.org/10.3354/meps08812 Dissolved oxygen in contrasting estuaries of the Bay of Biscay: effects of temperature, river discharge and chlorophyll a Arantza Iriarte1,*, Guillermo Aravena1, Fernando Villate1, Ibon Uriarte2, Berta Ibáñez3,7, Marcos Llope4,6, Nils Chr. Stenseth4,5 1Laboratory of Ecology, Department of Plant Biology and Ecology, Faculty of Science and Technology, University of the Basque Country, PO Box 644, 48080 Bilbao, Spain 2Laboratory of Ecology, Department of Plant Biology and Ecology, Faculty of Pharmacy, University of the Basque Country, Paseo de la Universidad 7, 01006 Gasteiz, Spain 3Basque Foundation for Health Innovation and Research (BIOEF), 48015 Sondika, Bizkaia, Spain 4Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, 0316 Oslo, Norway 5Flødevigen Marine Research Station, Institute of Marine Research, 4817 His, Norway 6Present address: Instituto Español de Oceanografía (IEO), Centro Oceanográfico de Cádiz, Puerto Pesquero, Muelle de Levante s/n, PO Box 2609, 11006 Cádiz, Andalucía, Spain 7Present address: Biomedical Research Center, 31008 Pamplona, Spain *Email: arantza.iriarte@ehu.es ABSTRACT: The effects of environmental factors on variations of dissolved oxygen (DO) saturation was assessed in 2 estuaries (Bilbao and Urdaibai) in the Bay of Biscay with contrasting hydrography and anthropogenic impact, for the period 1997 to 2006, using generalised additive models (GAMs) and generalised additive mixed models (GAMMs). Spatial and temporal variations in DO saturation and the current severity and extent of hypoxia were higher in the culturally eutrophicated and stratified Bilbao estuary. Seasonal patterns of DO saturation and the hierarchy of factors controlling them differed both between estuaries and between salinity zones. In the inner Bilbao estuary, the main factor explaining DO-saturation variations was temperature, with a dominant effect on oxygen consumption processes. In contrast, in the outer Bilbao estuary, the main factor explaining DO-saturation variations was chlorophyll a, suggesting that the effect of oxygen production through photosynthesis was stronger than that of oxygen consumption. In the inner Urdaibai estuary, both a negative relationship with temperature and a positive relationship with chlorophyll a were detected. The outer Urdaibai estuary showed strong water-column mixing and very high tidal flushing, and ventilation processes were more important than oxygen production or consumption processes. River discharge affected DO saturation only at the inner waters, but when the effects of several variables on DO-saturation variability were tested in an additive model, river discharge was excluded from the models. The effects of temperature-dependent processes on DO-saturation dynamics decreased from the inner to the outer zones of both estuaries. KEY WORDS: Dissolved oxygen · Chlorophyll · Temperature · River discharge · Estuary · Generalised additive models · Bay of Biscay Full text in pdf format PreviousNextCite this article as: Iriarte A, Aravena G, Villate F, Uriarte I, Ibáñez B, Llope M, Stenseth NC (2010) Dissolved oxygen in contrasting estuaries of the Bay of Biscay: effects of temperature, river discharge and chlorophyll a. Mar Ecol Prog Ser 418:57-71. https://doi.org/10.3354/meps08812 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 418. Online publication date: November 18, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Distribution of Organic Microcontaminants, Butyltins, and Metals in Mussels From the Estuary of Bilbao

Mussels are used as bioindicators of chemical pollution in coastal and estuarine waters. We measured the concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), phthalate esters (PEs), butyltins, and metals (Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, and Zn) in mussel tissues collected from the lower Bilbao estuary (Arriluze, north of Spain) every 2 months from November 2002 to March 2004. The concentration (microg g(-1) dry weight) of PAHs, PCBs, and PEs ranged from 5.1 to 18.3, from 0.04 to 0.2, and from 1.5 to 27.6, respectively. Temporal pattern variations, including maximum and minimum values, were determined for metals and BTs from their concentration profiles during a period of 1 year. The main feature of organic microcontaminants was relatively high concentration values, reflecting the overall industrial and harbour activities of the site. Moreover, the ratios of methylated species and certain other diagnostic ratios suggested a petrogenic origin for PAHs. Finally, the relations among the concentrations found in mussel tissues and the levels of several cell biomarkers were established by a partial least squares model.

Zooplankton communities in two contrasting Basque estuaries (1999-2001): reporting changes associated with ecosystem health

This study is a part of the zooplankton monitoring program carried out in the euhaline region of the estuaries of Bilbao and Urdaibai (Basque coast, Bay of Biscay), and analyses between-estuaries differences in zooplankton spatial and temporal patterns in relation to environmental conditions between July 1999 and May 2001. Environmental variables measured were water temperature, dissolved oxygen saturation (DOS), Secchi disk depth (SDD) and chlorophyll a. Relationships between zooplankton community and environmental variables were analysed using canonical correspondence analysis; between-estuaries differences in environmental conditions and distribution of zooplankton taxa in relation to salinity were tested using Mann― Whitney U-test. Spatial differentiation of the zooplankton community was higher in the estuary of Bilbao, with the relative abundance of most of the taxa decreasing more pronouncedly towards the upstream estuary than in the Urdaibai related to significantly lower values of DOS and SDD, reflecting the higher degree of pollution, in the Bilbao estuary. However, the successful establishment of the Acartia discaudata and A. margalefi populations, and the first records of another Acartia species, Calanipeda aquaedulcis and Eurytemora affinis in the Bilbao estuary, along with the increasing similarity between zooplankton assemblages of the Bilbao and Urdaibai estuaries in relation to the period 1997―1999, represent a new step in the recovery of the zooplankton community in the estuary of Bilbao responding to the improvement of water quality.

Levels and spatial distribution of inorganic and organic contaminants in sediments along the Bilbao estuary

Levels and spatial distribution of inorganic and organic contaminants in sediments along the Bilbao estuary

Simultaneous preconcentration of a wide variety of organic pollutants in water samples: Comparison of stir bar sorptive extraction and membrane-assisted solvent extraction

Stir bar soptive extraction (SBSE) coupled to thermal desorption-gas chromatography–mass spectrometry (TD-GC–MS) and membrane-assisted solvent extraction (MASE) coupled to large volume injection-programmed temperature vaporisation-GC–MS (LVI-PTV-GC–MS) were optimised for the simultaneous determination of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), phthalate esters (PEs), nonylphenols (NPs), polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in water samples. In the case of SBSE-TD, variables affecting the extraction (extraction time, addition of sodium chloride or methanol and sample volume) and desorption (cryofocusing temperature, desorption time and temperature, vent pressure and desorption flow) were fitted for the simultaneous determination. The extraction solvent nature ( n-hexane, cyclohexane, n-heptane, ethyl acetate, toluene, dichloromethane or cyclohexane:ethyl acetate mixtures), as well as the addition of methanol (0–30%) and sodium chloride (0–20%), the extraction temperature (30–60 °C), shaking speed (250–750 rpm) and extraction time (5–150 min) were studied for the simultaneous membrane-assisted preconcentration. Finally, PTV-LVI variables such as injection volume (100–600 μL), injection speed (10–40 μL s −1), vent pressure (0–12.7 psi), vent time (0.05–0.8 min), vent flow (30–80 mL min −1), cryofocusing temperature (20–70 °C), split flow (20–100 mL min −1) and split time (1–5 min) were optimised. The optimisation was carried out by means of experimental design approaches in most of the cases. Precision (∼3–19% for both SBSE-TD and MASE-LVI-PTV), accuracy (∼80–120% for both SBSE-TD and MASE-LVI-PTV), limits of detection (LoDs) (0.1–222 ng L −1 for MASE-LVI-PTV and 0.03–20.4 ng L −1 for SBSE-TD in dependence of substance) and linearity (from 25 ng L −1 up to at least 500 ng L −1 for both procedures) were established for both procedures. Finally, the developed methods were applied to the determination of the free concentrations of PAHs, PCBs, PEs, NPs, PBBs and PBDEs in natural water samples (estuarine water and sea water) from the Bilbao estuary (Northern Spain) and comparable results were obtained with both procedures.

Geochemical and microfaunal proxies to assess environmental quality conditions during the recovery process of a heavily polluted estuary: The Bilbao estuary case (N. Spain)

This study explores the eventual environmental improvement of the Bilbao estuary (northern Spain), from 1997 to 2006, in order to assess current estuarine restoration being undertaken as part of a Revitalization Strategic Plan. The monitoring programme is based on spatial and temporal variation in the distributions of both benthic foraminiferal assemblages and heavy metals contained in surficial sediments from the polluted intertidal flats. The overall pattern shows a decreasing metal concentration; however, reversals to this trend are noticed in the middle estuary. From 2000 to 2003, a significant decrease in heavy metal concentration was observed which is most likely related to the implementation in 2001–2002 of the biological treatment at a central wastewater treatment plant. Although the metal concentration decreased by 85% for some elements, these values still remain considerably high. No significant change occurred between 2003 and 2006 in metal concentrations. During the monitoring period the estuary channel presented environmental conditions close to azoic in 3/4 of its watercourse. Only in the year 2006, the two lowermost estuarine samples exhibited an increase in microfaunal densities. These samples were dominated by pollution-resistant estuarine species. The fact that estuarine sediments quality is recovering very slowly seems to be caused mainly by the resuspension of accumulated contaminants in the sediments due to dredging and working activities in the estuary. Thus, local authorities should consider also the clean up of the pollutants stored in the sediments, not seeking only the achievement of the water quality standards, as these polluted sediments can act as source of contamination.

Assessment of metal contamination in dregded sediments using fractionation and Self-Organizing Maps

Although total metal content is frequently the initial approach for measuring pollution, no information is provided about mobility and environmental risk. In this paper, a metal fractionation (sequential extraction) technique and artificial neural networks (Self-Organizing Maps, SOMs) have been used jointly to evaluate the pollution level of the sediments dredged from the dry dock of a former shipyard in the Bilbao estuary (Bizkaia, Spain). The load pollution index (LPI) for the upper, middle and bottom layers of the sediments was 7.65, 8.22 and 10.01, respectively, for six metals (Cu, Mn, Ni, Cr, Pb and Zn). This showed that upper sediments were less polluted than the lower ones. Consequently, a reduction in the pollution level of metal discharged into the river in recent years was confirmed. According to fractionation results, the most mobile minor elements were Cu, Pb and Zn, as they are mainly associated with the non-residual fractions. The statistical approach of Self-Organizing Maps (SOMs) revealed that Ni, Pb and Zn amounts in the residual fraction followed the same pattern associated with simultaneous discharges of slags into the river. However, other hazardous discharge sources are responsible for the high accumulation of those metals in the non-residual fractions.