Guadiana River Research Articles

La Política Agraria Común en el Alto Guadiana: evolución de recursos hídricos y de cultivos

There are clear links between supports from the Common Agricultural Policy (CAP) and the overexploitation of aquifers in the upper basin of the Guadiana River. Historically, European supports to agriculture have been linked to the production, which has resulted in the 169 municipalities in the study area, a strong trend towards the expansion of irrigation lands. The implementation of the Single Payment in 2003 implies a decoupling of production supports, going to charge the beneficiaries of supports a subsidy equal to the average of that perceived during the last three years, i.e. from 2003 payments are maintained even though production is zero. However, there are still many payments linked to production, known as coupled payments (primarily those associated with livestock, woody crops, arable crops and irrigated land). These are the ones with higher capacity to affect the environment, and therefore they are which have been considered in this study (except livestock, no directly related to overexploitation of aquifers). To make this paper, ArcGis program has been used, superimposing or comparing different thematic layers: Protected areas, overexploited aquifers and vulnerable areas to nitrates pollution in the Upper Guadiana, the percentage of irrigated hectares in several municipalities, the irrigated area devoted to arable crops and woody crops, and finally support levels of the Common Agricultural Policy (CAP) in each of the selected sectors and for each of the municipalities in the Upper Guadiana in 2009. It is noteworthy that the municipalities with the highest percentage of irrigated area, especially vineyard, receive higher levels of subsidies, despite of using water from overexploited aquifers. In contrast, supports to organic farming are scarce as compensation income from aquifers. This suggests that CAP subsides coupled to woody crops (mainly the vineyard) and herbaceous crops are detrimental for the environmental quality of the study area, especially water resources. As a positive factor it was found that a percentage of one of the two pillars of the CAP (EAFRD) is devoted for investment axes of Environment and Rural Development

Participatory modelling to support decision making in water management under uncertainty: Two comparative case studies in the Guadiana river basin, Spain

A participatory modelling process has been conducted in two areas of the Guadiana river (the upper and the middle sub-basins), in Spain, with the aim of providing support for decision making in the water management field. The area has a semi-arid climate where irrigated agriculture plays a key role in the economic development of the region and accounts for around 90% of water use. Following the guidelines of the European Water Framework Directive, we promote stakeholder involvement in water management with the aim to achieve an improved understanding of the water system and to encourage the exchange of knowledge and views between stakeholders in order to help building a shared vision of the system. At the same time, the resulting models, which integrate the different sectors and views, provide some insight of the impacts that different management options and possible future scenarios could have. The methodology is based on a Bayesian network combined with an economic model and, in the middle Guadiana sub-basin, with a crop model. The resulting integrated modelling framework is used to simulate possible water policy, market and climate scenarios to find out the impacts of those scenarios on farm income and on the environment. At the end of the modelling process, an evaluation questionnaire was filled by participants in both sub-basins. Results show that this type of processes are found very helpful by stakeholders to improve the system understanding, to understand each other's views and to reduce conflict when it exists. In addition, they found the model an extremely useful tool to support management. The graphical interface, the quantitative output and the explicit representation of uncertainty helped stakeholders to better understand the implications of the scenario tested. Finally, the combination of different types of models was also found very useful, as it allowed exploring in detail specific aspects of the water management problems.

Integrated assessment of policy interventions for promoting sustainable irrigation in semi-arid environments: A hydro-economic modeling approach

Sustaining irrigated agriculture to meet food production needs while maintaining aquatic ecosystems is at the heart of many policy debates in various parts of the world, especially in arid and semi-arid areas. Researchers and practitioners are increasingly calling for integrated approaches, and policy-makers are progressively supporting the inclusion of ecological and social aspects in water management programs. This paper contributes to this policy debate by providing an integrated economic-hydrologic modeling framework that captures the socio-economic and environmental effects of various policy initiatives and climate variability. This modeling integration includes a risk-based economic optimization model and a hydrologic water management simulation model that have been specified for the Middle Guadiana basin, a vulnerable drought-prone agro-ecological area with highly regulated river systems in southwest Spain. Namely, two key water policy interventions were investigated: the implementation of minimum environmental flows (supported by the European Water Framework Directive, EU WFD), and a reduction in the legal amount of water delivered for irrigation (planned measure included in the new Guadiana River Basin Management Plan, GRBMP, still under discussion). Results indicate that current patterns of excessive water use for irrigation in the basin may put environmental flow demands at risk, jeopardizing the WFD's goal of restoring the ‘good ecological status’ of water bodies by 2015. Conflicts between environmental and agricultural water uses will be stressed during prolonged dry episodes, and particularly in summer low-flow periods, when there is an important increase of crop irrigation water requirements. Securing minimum stream flows would entail a substantial reduction in irrigation water use for rice cultivation, which might affect the profitability and economic viability of small rice-growing farms located upstream in the river. The new GRBMP could contribute to balance competing water demands in the basin and to increase economic water productivity, but might not be sufficient to ensure the provision of environmental flows as required by the WFD. A thoroughly revision of the basin's water use concession system for irrigation seems to be needed in order to bring the GRBMP in line with the WFD objectives. Furthermore, the study illustrates that social, economic, institutional, and technological factors, in addition to bio-physical conditions, are important issues to be considered for designing and developing water management strategies. The research initiative presented in this paper demonstrates that hydro-economic models can explicitly integrate all these issues, constituting a valuable tool that could assist policy makers for implementing sustainable irrigation policies.

Nutrient and chlorophyll a transports during an upwelling event in the NW margin of the Gulf of Cadiz

The present study describes the fluxes and transports of nutrients and chlorophyll a inferred from direct observations carried out off south Portugal, during a research cruise in early October 2006. The covered area corresponds to the western part of the northern margin of the Gulf of Cadiz, from Cape São Vicente (9.0°W) till the Guadiana River mouth (7.4°W). Unlike in the western Iberian margin, the upwelling in this region is rather intermittent during the summer season. It is interleaved by periods when warm waters coming from the eastern part of the Gulf of Cadiz occupy the coastal region. However, our observations were taken during an intense upwelling event that took place at the end of the upwelling season. Ten meridional transects were sampled in a total of 90 CTD casts. Current velocity profiles were acquired along the ship's track with a hull-mounted acoustic Doppler current profiler (ADCP). The analysis of the circulation field and water masses characteristics led to the quantification of the fluxes and transports of chlorophyll a and nutrients in 5 meridional transects along the coast. Results show the prevalence of the alongshore eastward flow over the offshore Ekman transport in the coastal circulation without formation of upwelling filaments. Transport of chlorophyll a showed a near surface maximum (<30dbar), while transport of nutrients were generally higher in the layer below (30–100dbar). The estimates show net eastward alongshore transports of chlorophyll a and nutrients into the Gulf of Cadiz and weak cross-shore exchanges. At the deepest levels, the estimates of the transports by the shallow vein of the Mediterranean Water show an important input of nutrients to the Atlantic. However, waters in the top 100dbar, impoverished in nutrients by biological utilisation due to upwelling, show that nitrate and phosphate transports provided into the Gulf of Cadiz exceed those carried westward by the shallow vein of the Mediterranean Water.

The influence of coastal processes on inner shelf sediment distribution: The Eastern Algarve Shelf (Southern Portugal)

This study examines sediment distribution patterns in the Southeastern Algarve inner shelf (southern Portugal), an area characterized by marked variations in its coastal environment and low continental supply of sediments. The specific goals of this study were to identify the principal sediment sources and the factors influencing sediment transport paths and deposition. A total of 199 samples, collected along the shelf from the Guadiana River mouth to Olhos de Agua, were analyzed. Grain-size distribution and parameters were measured for all the samples. Terrigenous and biogenic components of sand were identified in 38 samples, and results analyzed using multivariate non-linear multidimension scaling (MDS) and cluster analysis. Patterns of sediment distribution in this area of the inner shelf vary according to water depth and exhibit significant longshore variation, related mainly to coastal processes (littoral drift and storm currents) and to a lower degree to sediment sources. Sand is dominant at all depths, reflecting the influence of littoral drift in the supply and redistribution of shelf sediments. Fine and gravelsized deposits are significant in specific areas and are usually associated with changes in sediment composition. Five sectors have been identified according to sedimentary dynamics. The results, based on geostatistical and multivariate analysis, have allowed detailed sediment distribution maps to be generated, which represent an update of the existing cartography and serve as a tool for the management of coastal and marine resources. They have been furthermore compared with inner shelf sediment dynamics in other regions worldwide, to distinguish between specific regional responses to forcing mechanisms and processes that are more generalized within this type of shelf environments. In this context, the results obtained results in the Algarve study area are of great interest for the understanding of sediment dynamics of sand dominated inner shelves with reduced continental supply.

Different pools of black carbon in sediments from the Gulf of Cádiz (SW Spain): Method comparison and spatial distribution

Black carbon (BC) accounts for a quantitatively important fraction of the carbon sink in marine sediments. Yet, the determination of its role in the environment remains controversial largely due to the large variability of BC estimates yielded by the diversity of analytical techniques presently used. In this study, we combine the application of a thermal oxidation technique (graphitic BC, or GBC) with a molecular method (benzene polycarboxylic acids, or BPCA) for determining the presence of different types of BC in 15 marine sediments from the Gulf of Cádiz (GoC). Accounting for the two condensation end-members of the BC set (chars and graphitic carbon) constitutes the first approach to a comprehensive estimate of the BC burial in the GoC Continental Shelf. Measurements of BC in the GoC sediments ranged from 0.01 to 0.23% dw, with different ranges obtained with each technique (0.01–0.11 for GBC versus 0.01–0.23 for BPCA). BC resulting from the use of the thermal GBC method (measuring soot and graphitic carbon) or the BPCA as molecular markers (detecting mostly char) showed different spatial distributions in the GoC and varied from 13·103 to 26·103t of BC/yr depending on the method used. Mostly petrogenic in origin GBC was less abundant and more homogeneously distributed along the Guadiana River plume, whereas largely pyrogenic BPCA-BC was generally more abundant but specifically enriched in the mid-region of the plume. The Guadiana River plume combined with hydrodynamic sorting is argued to be the main distribution factors for graphitic carbon and charcoals, whereas airborne soot seems to compose an undetermined and potentially overlapping fraction of both analytical measurements (GBC and BPCA). The structural analysis of the thermal residues and the molecular markers provided valuable information on the BC nature in the environmental matrices. The results of this study illustrate the importance of considering different analytical windows of the BC catchall for constraining regional burial sinks of heterogeneous BC sources.

Biomarkers in &lt;i&gt;Nereis diversicolor&lt;/i&gt; (Polychaeta: Nereididae) as management tools for environmental assessment on the southwest Iberian coast

The environmental quality of the southwest Iberian coast was assessed in different areas (Ria Formosa Lagoon, Guadiana Estuary and Cadiz Bay) focusing on metal contamination (Cd, Cu, Ni, Pb and Zn) in Nereis diversicolor whole tissues. In addition, associated toxicological effects were assessed using a multibiomarker approach combining several conventional biomarkers. The set of biomarkers selected included antioxidant enzymes (catalase, superoxide dismutase and glutathione peroxidase), metallothionein and lipid peroxidation. N. diversicolor from the Ria Formosa Lagoon, Guadiana River and Cadiz Bay responded differently to metal contamination with different biomarker responses showing a clear site trend, suggesting different sources and/or magnitudes of contamination. Cadmium was a source of oxidative stress in polychaetes, mainly in Cadiz Bay, with a significant influence on antioxidant enzymes and enhancement of lipid peroxidation. The highest MT concentrations were in the Ria Formosa Lagoon and in the Guadiana River, where there was a direct relationship with high nickel concentrations. Biomarker responses of N. diversicolor are useful tools for environmental quality assessment on the southwest Iberian coast, and more specific metal biomarkers should be included in future assessments.

The combined use of radio frequency‐electromagnetic surveys and chemical and biological analyses to study the role of groundwater discharge into the Guadiana estuary

ABSTRACTThis paper intends to show how the radio frequency‐electromagnetic (RF‐EM) method can be successfully used in coastal wetlands, onshore and in shallow water. It characterizes and reveals geological and hydrogeological singularities that are often hidden by recent sediments and allows target sampling and consequent detection of ecological particularities. RF‐EM methods have traditionally been used to detect the presence of groundwater or the existence of subsurface contamination plumes. The great majority of such studies have been conducted on land and to a lesser extent on freshwater lakes but rarely in coastal waters. Previous research in Portugal has shown that despite the attenuation effect of salt water, very valuable information can be obtained with the use of electromagnetic methods, wherever resistivity contrasts exist. In the current case study, RF‐EM surveys were carried out in the Estuary of the Guadiana River, in order to understand the importance of geological structures on the formation of the wetland and the influence of groundwater discharge on the existing ecosystem. Structures detected on land were also identified in the tidal channels. Freshwater fault springs were localized; their biota is characterized and the nutrients analysed. The results showed a clear increase in nitrate and silica concentration near the submarine springs, with impact on the planktonic communities, which is most evident in chlorophyll a. This is especially relevant during the end of summer and autumn when a potential limitation of these nutrients exists that can increase the occurrence of toxic blooms in the salt marshes and lower estuary. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Sources, background and enrichment of lead and other elements: Lower Guadiana River

The lower sector of the Guadiana River Basin, located in southern Portugal and Spain, hosts soils and plants with elevated Pb, Cu and As near former and current mining sites. Two geogenic and two anthropogenic sources of Pb were identified where elevated concentrations are mostly related to the occurrence of sulphide-rich ore deposits, Volcanic Sedimentary formations and mining. These were generally reflected by the multiple regression analysis (MRA) and confirmed by isotope determinations. Nevertheless, caution was needed in interpreting statistical and isotopic results; therefore the combination of both techniques was important. Elements, such as Ca, Na, Cu and As, show enrichment in soil developed on shale, sandstone and conglomerate of Upper Devonian age belonging to the Phyllite-Quartzite Group. Lead exhibits an enrichment in soil developed on felsic volcanic rocks from the Volcanic Sedimentary Complex (VSC) of Upper Devonian-Lower Carboniferous age, which has been identified by the relationship between topsoil median values of different lithologies and grand subsoil median values. In the same soil, Fe, As, Co, Ni and Cr are depleted. Translocation of Pb to the aerial parts of plants is insignificant in all three plant species studied and analysed (Cistus ladanifer L., Thymus vulgaris, Lavandula luisieri). High Pb concentrations in soil, where Cistus ladanifer L. developed, the only representative number of species analysed, do not correspond generally to elevated Pb contents in plants, except near mine sites, where lower pH of soil, increases Pb bioavailability. The different statistical methodologies combined with Pb isotopic studies were successfully applied in the identification of Pb sources in soil and Cistus ladanifer L. plant of the Lower sector of Guadiana River basin. Therefore, rocks, mineralisations, subsoil, topsoil and plant processes were successfully integrated to understand the migration of Pb into the food chain.

Holocene paleoenvironmental changes from contrasting depositional systems on the continental shelf off the Guadiana River

Holocene paleoenvironmental changes from contrasting depositional systems on the continental shelf off the Guadiana River

Estimating the non-market benefits of water quality improvement for a case study in Spain: A contingent valuation approach

Abstract This article addresses an important topic related to the application of the European Water Framework Directive (WFD) in Spanish watersheds. Results on a contingent valuation study, aimed to assess the non-market benefits of water quality improvements in the Guadiana river basin (GRB), are shown. Special attention has been paid to the issue of zero willingness-to-pay (WTP) responses, while addressing the possible presence of self-selection caused by protest responses. The results (i) indicate that sample selection bias is not a problem in our application, (ii) allow us to identify some key determinants of voting behaviour, and (iii) through the use of different econometric models allows us to find a robust estimate for the mean WTP to accurately inform decision-making.

Evaluation of trace elements mobility from soils to sediments between the Iberian Pyrite Belt and the Atlantic Ocean

An environmental study was conducted in 193 stream sediments and 355 soil samples collected in the lower section of Guadiana River Basin to evaluate the trace elements transfer from one compartment into another. The objective was to evaluate the dispersion of Pb, Cu, Zn and other chemical elements resulting from upstream mines into the lower N-S sector of the Guadiana River Basin to the Atlantic Ocean. The area partly includes the Iberian Pyrite Belt, a known volcanogenic massive sulphide (VMS) province with important mining activity history. Median concentrations of the elements Cu, Pb, Zn, Al, As, Ba, Br, Ca, Mg, Mn and Na are generally higher in the studied sediments than in soils. Soils are normally acidic and mobility of elements is in these conditions higher. When the relations between upstream soils and downstream sediments were established, median values were higher in the upstream soils only for elements such as Co, Ni, K, Pb, Mn and Ti, probably the less mobile, and the Cu, Zn, Al, As, Ba, Br, Ca, Cr, Fe, Mg and Na have highest concentrations in the downstream sediments.Lead was considered the less mobile element and Zn the highly mobile of the base metals in the mining area of the lower Guadiana River. Dispersion of the metals, considering the studied soil and sediment samples is partially restricted to the mining areas or downstream sediments but close to the mine sources, where ore tailings and acid waters occur. Near the mouth, concentrations of As, Cu, Pb and Zn increase in relation with mining and other pollution sources. Interaction with salt water forces chemical elements precipitation from water and subsequent increase of their concentration in sediments. This may be the reason for the increase of those chemical elements concentrations in the sediments.

Larval development of the Iberian cyprinid Anaecypris hispanica

Anaecypris hispanica is the most threatened cyprinid fish in the Iberian Peninsula. The distribution of this Iberian cyprinid is restricted to the Guadiana River drainage and a single tributary in the Guadalquivir River and has been rapidly diminishing over the past thirty years. Several A. hispanica populations have been depleted to a point which individual densities are below a level where adults can be detected, making it necessary to identify A. hispanica larvae to assess populations and to make declarations about local extinctions. This work is the first detailed description of the larval stages of A. hispanica from egg to stage 5 observed from laboratory-reared specimens. The eggs are spherical, adhesive, and transparent, and they measure 1.4 mm (mean diameter). The larvae hatch 72 hours after activation and measure 5.0 mm (mean total length-TL). The notochord flexion occurs at 5.9 mm (mean TL), and larvae have 38-39 total myomeres. Anaecypris hispanica larvae have little cephalic pigmentation with few melanophores anterior to the eyes, although pigmentation intensifies during development. Identifying features are presented here that will enable researchers to distinguish A. hispanica from other sympatric species. This information will allow us to identify larvae and can help to assess whether this species is present at locations where adults are not detected.

Identifying reference benthic diatom communities in an agricultural watershed (Guadiana River, SW Spain)

Determining the ecological status of river ecosystems should be based on reference (near-natural) conditions and on the use of their biological communities. Identifying reference conditions is particularly difficult in largely disturbed watersheds, such as those of agricultural landscapes. Ecotype reference sites and their characteristic diatom communities were identified in the Guadiana watershed. Three different ecotypes were defined: rivers with siliceous bedrocks, upper watershed calcareous rivers, and mainland watercourses. Thirteen key stressors divided in four categories (channel alteration, hydrological pressure, pollution pressure, and river habitat pressure) were used to select reference sites in each ecotype. Multivariate techniques were used to describe type-specific reference diatom community in each ecotype. Because of the difficulty to define reference sites in the mainland watercourses, some sites were selected under the criterion of minimum impacted sites. Diatoms inhabiting sites included species tolerant to high nutrient concentration and mineralized waters, like Nitzschia inconspicua, Gomphonema parvulum, and Navicula veneta. These taxa defined the best condition (near-to-reference) in an ecotype highly impacted by human activities, the best possible in the long-lasting impaired conditions in the large river watercourses in agricultural landscapes.

Benthic invertebrate communities in regulated Mediterranean streams and least-impacted tributaries

Flow regulation is generally perceived to negatively influence fluvial ecosystems through alterations of natural habitat conditions, particularly in highly variable Mediterranean streams. However, the detection of impact may depend on chosen metrics, requiring a multiple-lines-of-evidence approach for ecologically relevant impact assessment. In this study, we compare the community structure, the trophic function, the microhabitat influence and the body condition of benthic invertebrates between the regulated Bullaque River and unregulated tributaries (Guadiana River basin, central Spain). Invertebrates and physical microhabitats were studied seasonally in 2010. Total abundance, EPT abundance, Rheoindex and LIFE metrics were higher in the regulated river during summer, whereas Shannon diversity was lower. Rheoindex and LIFE were higher in the tributaries during winter. Filterers were very abundant in spring and summer in the tributaries and the regulated stream, respectively. Deposit feeders dominated during summer in the tributaries. Despite these differences, ANOSIM revealed similar community structure and feeding groups characteristics in both fluvial system types. In addition, body condition, measured as fluctuating asymmetry level, indicated that daming created favourable developmental conditions for several invertebrate species in the Bullaque River. This suggests that daming surprisingly buffered from the adverse environmental conditions inflicted by seasonal summer drougths, which occur recurrently in Mediterranean areas. Results also suggest that the application of fluctuating asymmetry could therefore be promising for revealing integral ecological responses to different and often combined forms of anthropogenic and natural disturbance.

Natural and human-induced Holocene paleoenvironmental changes on the Guadiana shelf (northern Gulf of Cadiz)

Three contrasting sedimentary environments on the continental shelf off the Guadiana River (northern Gulf of Cadiz) were integrated in a chronological framework and analysed in terms of sedimentology and benthic foraminiferal assemblages to understand the Holocene paleoenvironmental evolution. The analysed environments differ in terms of their depositional regimes and benthic foraminiferal assemblages. However, a dominant fluvial origin of the sand fraction was observed in all three environments. Holocene sedimentary processes were mainly controlled by natural (sea level changes and climate variations) and human-induced processes (e.g. deforestation, agriculture) along four evolutionary stages. The three older stages were mainly influenced by natural processes, such as sea level variations and fluvial inputs, whereas the most recent stage reflects a combination of climatic- and human-induced processes. A deepening of sedimentary environments related to a period of rapid sea level rise, strongly influenced by river discharges occurred from c. 11,500 to c. 10,000 cal. yr BP. A reduction in sediment export to the shelf, as a result of the continuous and rapid sea level rise and enhanced estuary infilling reflects the second stage, from c. 10,000 to c. 5000 cal. yr BP. The beginning of the third stage, from c. 5000 to c. 1500–1000 cal. yr BP, is marked by a sea-level slowdown and the relatively stable climate and environmental conditions. The fourth stage, from c. 1500–1000 cal. yr BP to Recent times, reflects the intensification of human-induced processes and climatic variability in the Guadiana River basin. This stage also reflects modern depositional conditions, with the formation of a proximal prodeltaic wedge and a distal muddy body.

DISTRIBUTION OF LIVING BENTHIC FORAMINIFERA ON THE NORTHERN GULF OF CADIZ CONTINENTAL SHELF

Living (stained) benthic foraminiferal faunas were analyzed in 51 surficial sediment samples taken from the northern Gulf of Cadiz continental shelf between the mouths of the Guadiana and Guadalquivir rivers. The distribution and abundance of 26 species with relative abundance >5% were related to water depth, sediment type, river discharge, water temperature, salinity, turbidity, and primary productivity. Hierarchical classification using R- and Q-mode cluster analyses, and individual distributions, allowed these taxa to be categorized into four general groups. Group 1 is represented by Bolivina ordinaria and Hopkinsina atlantica. These species are linked to river discharge, and are associated with muddy sediments. They are considered the most opportunistic species in the assemblage, and are associated with the limits of productivity. Group 2, contains Ammonia beccarii, Eggerelloides scaber, Elphidium gerthi, Quinqueloculina laevigata, and Q. stelligera, and is characteristic of shallow water depths. Its species are associated with different sediment types and their distribution is influenced by river discharge. Group 3 is dominated by Bulimina aculeata, B. elongata, Elphidium excavatum, E. cuvillieri, Epistominella vitrea, and Rectuvigerina phlegeri. These species display the highest abundances between 30–100 m water depths. They prevail in muds associated with weak hydrodynamics, low oxygenation, and high organic matter. Group 4 includes species that are more abundant in deep stations and is divided into two subgroups. Subgroup 4A includes Bolivina catanensis, B. italica, B. striatula, Cassidulina laevigata, Stainforthia sp., Nouria polymorphinoides, and Nouria sp., with higher abundances in one or two samples. Subgroup 4B, with Brizalina dilatata, B. spathulata, Bulimina marginata, Nonionella iridea, N. stella, and N. turgida, has patchy distribution. Higher abundances of Nonionella species off the Guadiana River are related to low temperature and salinity.

Sea-level rise and anthropogenic activities recorded in the late Pleistocene/Holocene sedimentary infill of the Guadiana Estuary (SW Iberia)

This study reviews data on sea-level rise during the last 13000 yr cal. BP (13 kyr) as recorded in the estuarine sediments of the Guadiana River (SE Portugal, SW Spain). We combined new data from a 63 m-long borehole, drilled through the entire postglacial sedimentary sequence, with information on five previously studied cores. By integrating sedimentological, geochemical and palaeontological proxies, we were able to make a palaeoenvironmental reconstruction of the Guadiana terminal palaeovalley during the last 13 kyr and propose a curve of sea-level rise for the SW Iberian Atlantic margin. Our foraminifera-based palaeoecological reconstruction, anchored to a 14C age model, reveals rapid sea-level rise from 13 kyr, interrupted during the Younger Dryas and resuming ca 11.5 kyr. The pace of marine transgression slackened ca. 7.5 kyr and since then has progressed upwards at a rate of 1.2 mm yr−1.Holocene–Anthropocene sediments from two boreholes were also analysed to assess the timing, levels and sources of trace metals produced by acid mine drainage from the Iberian Pyrite Belt. Study of metal/aluminium ratios through the profiles allowed background metal concentrations to be estimated from lithostratigraphic units older than ca. 5 kyr (i.e. unaffected by anthropogenic activities). Human activities are especially evident from 4.5 kyr (the beginning of the Copper Age), with anthropogenic sources of metal fluxes prevailing over natural sources (especially Pb, Co, Ni, and Mn, and, to a lesser extent, Zn, Cu, and Ni). Mining activities became particularly intensive between the late Bronze Age and the Roman period (3–1.5 kyr), when the highest metal enrichment factors were recorded: EFPb ≈ 2, EFCd > 10, EFCr ≈ 2, EFCu ≈ 3, EFZn = 1.4.This study reveals the utility of postglacial sedimentary records for reconstructing historical changes in regional water-sediment quality and separating natural and anthropogenic sources of geochemical contaminants.

Sedimentary and geochemical characterization and provenance of the Portuguese continental shelf soft-bottom sediments

Grain-size and geochemical analyses for soft-bottom sediments from the Portuguese continental shelf are used to determine their provenance and to identify the main factors governing the sediment distribution patterns. The deeper areas of the northwestern and central sectors of the Portuguese shelf and most of its southwestern sector are covered by fine and very fine sands. Coarse deposits are found in the inner and middle shelf of the northernmost sector and immediately south of the Nazaré and Setúbal canyons, while muddy sediments are restricted to areas located off the mouths of major rivers (Douro and Tagus mud patches). In contrast, the southern shelf corresponds to a low energy environment receiving most of its sediment supply from the Guadiana River. As a result, an expressive mud patch is developed off the Guadiana estuarine system. The application of multivariate analysis to geochemical data allowed the classification of the studied samples into four main groups: (a) a group of mud deposits constituted by detrital clay minerals and authigenic iron-manganese oxyhydroxides, displaying high contents for organic matter and for most major and trace elements; (b) a group of biogenic carbonate-rich sands showing high CaO, Sr and U contents which is well represented throughout the entire Portuguese shelf; (c) a group of quart-rich sediments, with very high SiO 2 contents and moderate Al 2O 3, K 2O and TiO 2 contents, supporting a major terrigenous contribution and (d) a group of coarse sand samples with high As levels from off important rivers, pointing to anthropogenic contamination. Trace metal enrichments observed in the muddy areas from both the western and southern coasts appear to result from natural causes and do not exceed the international sediment quality thresholds. There is, however, local evidence for As, Zn, Cr and Pb anthropogenic contamination in near-shore sediments associated with rivers draining regions characterized by urban, industrial or mine exploration activities, highlighting the potential environmental risk associated with such sites.

Determinants of fine‐scale homogenization and differentiation of native freshwater fish faunas in a Mediterranean Basin: implications for conservation

AbstractAim Increasing threats to freshwater biodiversity are rapidly changing the distinctiveness of regional species pools and local assemblages. Biotic homogenization/differentiation processes are threatening the integrity and persistence of native biodiversity patterns at a range of spatial scales and pose a challenge for effective conservation planning. Here, we evaluate the extent and determinants of fine‐scale alteration in native freshwater fish assemblages among stream reaches throughout a large river basin and consider the implications of these changes for the long‐term conservation of native fishes.Location Guadiana River basin (South‐Western Iberian Peninsula).Methods We quantified the magnitude of change in compositional similarity between observed and reference assemblages and its potential effect on natural patterns of compositional distinctiveness. Reference assemblages were defined as the native species expected to occur naturally (in absence of anthropogenic alterations) and were reconstructed using a multivariate adaptive regression splines predictive model. We also evaluated the role of habitat degradation and introduced species as determinants of biotic homogenization/differentiation.Results We found a significant trend towards homogenization for native fish assemblages. Changes in native fish distributions led to the loss of distinctiveness patterns along natural environmental gradients. Introduced species were the most important factor explaining the homogenization process. Homogenization of native assemblages was stronger in areas close to reservoirs and in lowland reaches where introduced species were more abundant.Main conclusions The implementation of efficient conservation for the maintenance of native fish diversity is seriously threatened by the homogenization processes. The identification of priority areas for conservation is hindered by the fact that the most diverse communities are vanishing, which would require the selection of broader areas to adequately protect all the species. Given the principal role that introduced species play in the homogenization process and their relation with reservoirs, special attention must be paid to mitigating or preventing these threats.