Guadiana River Basin Research Articles

Climate change impacts on rainfed agriculture in the Guadiana river basin (Portugal)

In this study, the crop yield response of rainfed crops to climate change was evaluated focusing on the most representative crops in the Guadiana river basin. The quantification of crop yields was performed using a simple soil water balance model framework. The herbaceous crop yields were evaluated with the ISAREG model, implementing a water balance approach combined with the Stewart method. A similar water balance approach was used to estimate the yields for the most representative permanent rainfed woody crops in the region using an alternative spreadsheet-based model, but implementing a more detailed water stress evaluation through the crop cycles. Yields were simulated for two future periods (2011–2040) and (2041–2070) using, as climate inputs, temperature and precipitation series, reflecting a combination of five climate change scenarios (CCS) created using the ensemble-delta technique applied to CMIP3 climate projections datasets to represent different alternative climate change bracketing conditions for rainfall and air temperature. The results showed that comparatively with the reference period climate (1961–1990) rainfed crop yields will decrease in future period 1 (2011–2040) and reach even higher losses in future period 2 (2041–2070). Within the herbaceous crops, sunflower and winter wheat were the most susceptible to yield losses under climate change, reaching estimated maximum losses for future period 2 of respectively 18.5% and 13.6%, followed by natural grown pastures with 11.5%. For woody crops, maximum estimated yields losses were considerably higher for almond (27.2%) than grapevine (5.4%) and olive (14.9%).

Metapopulations in temporary streams – The role of drought–flood cycles in promoting high genetic diversity in a critically endangered freshwater fish and its consequences for the future

Genetic factors have direct and indirect impacts in the viability of endangered species. Assessing their genetic diversity levels and population structure is thus fundamental for conservation and management. In this paper we use mitochondrial and nuclear markers to address phylogeographic and demographic data on the critically endangered Anaecypris hispanica, using a broad sampling set which covered its known distribution area in the Iberian Peninsula. Our results showed that the populations of A. hispanica are strongly differentiated (high and significant ФST and FST values, corroborated by the results from AMOVA and SAMOVA) and genetically diversified. We suggest that the restricted gene flow between populations may have been potentiated by ecological, hydrological and anthropogenic causes. Bayesian skyline plots revealed a signal for expansion for all populations (tMRCA between 68kya and 1.33Mya) and a genetic diversity latitudinal gradient was detected between the populations from the Upper (more diversified) and the Lower (less diversified) Guadiana river basin. We postulate a Pleistocenic westwards colonization route for A. hispanica in the Guadiana river basin, which is in agreement with the tempo and mode of paleoevolution of this drainage. The colonization of River Guadalquivir around 60kya with migrants from the Upper Guadiana, most likely by stream capture, is also suggested. This study highlights the view that critically endangered species facing range retreats (about 47% of its known populations have disappeared in the last 15years) are not necessarily small and genetically depleted. However, the extinction risk is not negligible since A. hispanica faces the combined effect of several deterministic and stochastic negative factors and, moreover, recolonization events after localized extinctions are very unlikely to occur due to the strong isolation of populations and to the patchily ecologically-conditioned distribution of fish. The inferred species distribution models highlight the significant contribution of temperature seasonality and isothermality to A. hispanica occurrence in Guadiana environments and emphasize the importance of stable climatic conditions for the preservation of this species. Given the strong population structure, high percentage of private haplotypes and virtual absence of inter-basin gene flow we suggest that each A. hispanica population should be considered as an independent Operational Conservation Unit and that ex-situ and in-situ actions should be conducted in parallel to allow for the long-term survival of the species and the preservation of the genetic integrity of its populations.

Assessment of insurance coverage and claims in rainfall related risks in processing tomato in Western Spain

An extension of guarantees related to rainfall-related risks in the insurance of processing tomato crops has been accompanied with a large increase in claims in Western Spain, suggesting that damages may have been underestimated in previous years. A database was built by linking agricultural insurance records, meteorological data from local weather stations, and topographic data. The risk of rainfall-related damages in processing tomato in the Extremenian Guadiana river basin (W Spain) was studied using a logistic model. Risks during the growth of the crop and at harvesting were modelled separately. First, the risk related to rainfall was modelled as a function of meteorological, terrain and management variables. The resulting models were used to identify the variables responsible for rainfall-related damages, with a view to assess the potential impact of extending insurance coverage, and to develop an index to express the suitability of the cropping system for insurance. The analyses reveal that damages at different stages of crop development correspond to different hazards. The geographic dependence of the risk influences the scale at which the model might have validity, which together with the year dependency, the possibility of implementing index based insurances is questioned.

EFFECTS OF FLOW REGULATION AND NON‐NATIVE SPECIES ON FEEDING HABITS OF EURASIAN OTTER Lutra lutra IN MEDITERRANEAN TEMPORARY RIVERS

ABSTRACTIn Mediterranean temporary rivers, ecological resources greatly fluctuate because of the high hydrological variability throughout the year. However, flow regulation prevents this natural regime and commonly entails associated non‐native species, which change the structure of aquatic communities. Nonetheless, few studies have tested the interaction of these two disruptive factors (flow regulation and non‐native species) and their synergistic effects on the Eurasian otter (Lutra lutra) diet at the river scale. The aim of this study was to compare the seasonal feeding habits of the otter between a temporary non‐regulated stretch and two regulated stretches invaded by non‐native species in a Mediterranean water course. The Bullaque River (Guadiana River Basin, central Spain) was seasonally sampled for otter spraints and prey abundance assessed from December 2009 to November 2010. Three stretches were considered: high (source, non‐regulated), medium (transition, regulated) and low (confluence, regulated). Diet varied from native prey in the high stretch (amphibians, insects and endemic cyprinids) to non‐native species in the low stretch (red‐swamp crayfish Procambarus clarkii and pumpkinseed sunfish Lepomis gibbosus). Seasonally, ingested biomass of native prey increased in spring. Diet was more diverse in the high stretch. Otters neutrally selected native cyprinids in the high stretch throughout the year, whereas crayfish was selected in the other two stretches. Overall results showed that flow regulation and non‐native species have increased prey availability for the otter; however, this paper highlights the importance of maintaining natural regimes in Mediterranean temporary rivers to conserve native communities and thus minimally impact food webs in Iberian freshwaters. Copyright © 2014 John Wiley & Sons, Ltd.

Spatial and temporal variability of the water and sediments quality in the Alqueva reservoir (Guadiana Basin; southern Portugal)

The purpose of this work was to evaluate the dynamic of the water quality from the Alqueva reservoir (Guadiana River Basin, Portugal) and identify the most important parameters that influence its ecological and chemical status. The results could indicate preventive and/or remediation actions that are necessary to improve its quality and status. Water and sediment samples were collected between 2011 and 2012, at five sampling stations, and analyzed for: (i) water — pH, temperature, dissolved oxygen, electrical conductivity, chloride, total phosphorus, total nitrogen, ammonium, nitrate, nitrite, biochemical and chemical oxygen demand, total Fe, Mn, and As; and (ii) sediments — pH, electrical conductivity, organic matter, total nitrogen, total phosphorus, major and trace elements. The results from the water column showed that the organic descriptors exceeded the Portuguese guideline values for water quality for multiple uses at most of the sampling stations. As for nutrients, Ajuda is the station where the concentrations of the total nitrogen and total phosphorus exceeded the guideline values in most months. Ammonium achieved concentrations above the allowed, during the study, in all locations. Trace elements were more abundant in the sediments, surpassing the maximum levels for the protection of aquatic life for As, Cd and Pb, at Alcarrache, Lucefécit and Álamos, respectively. The use of multivariate analysis showed that the major parameters that explained the water quality variability were the nutrients in the water column, and trace elements in the sediments. Comparing the results from this study with results obtained since 2006, we can observe an obvious increment of the organic descriptors and nutrients in the water body. Further, several parameters and observations indicate an increase of the eutrophication process. So, it is urgent to develop preventive actions and remediation processes to stop the degradation so as to improve the quality of the water in this reservoir.

Supporting decision making under uncertainty: Development of a participatory integrated model for water management in the middle Guadiana river basin

Following the Integrated Water Resources Management approach, the European Water Framework Directive demands Member States to develop water management plans at the catchment level. Those plans have to integrate the different interests and must be developed with stakeholder participation. To face these requirements, managers need tools to assess the impacts of possible management alternatives on natural and socio-economic systems. These tools should ideally be able to address the complexity and uncertainties of the water system, while serving as a platform for stakeholder participation. The objective of our research was to develop a participatory integrated assessment model, based on the combination of a crop model, an economic model and a participatory Bayesian network, with an application in the middle Guadiana sub-basin, in Spain. The methodology is intended to capture the complexity of water management problems, incorporating the relevant sectors, as well as the relevant scales involved in water management decision making. The integrated model has allowed us testing different management, market and climate change scenarios and assessing the impacts of such scenarios on the natural system (crops), on the socio-economic system (farms) and on the environment (water resources). Finally, this integrated assessment modelling process has allowed stakeholder participation, complying with the main requirements of current European water laws.

Integrated environmental assessment of freshwater sediments: a chemical and ecotoxicological approach at the Alqueva reservoir

In order to study the pollution of an aquatic ecosystem, it is necessary to analyze not only the levels of chemical pollutants in water, but also those accumulated in the sediment matrix, as well as to assess its ecotoxicological status. The Alqueva reservoir, the largest artificial lake in Europe, was chosen as case study as it constitutes the most important water supply source in southern Portugal. It is located in the Guadiana River Basin, in a semi-arid region with high levels of water scarcity and where agriculture is one of the main activities. The evaluation of sediments comprised: (1) physical and chemical analysis (grain size, pH, organic matter, nitrogen, phosphorus); (2) potentially toxic trace elements (Cu, As, Pb, Cr, Cd, Zn and Ni); and (3) ecotoxicological evaluation with Vibrio fischeri, Thamnocephalus platyurus, Daphnia magna, and Heterocypris incongruens. Total trace element concentrations indicated that As, Cd, and Pb surpassed the Canadian levels for the protection of aquatic life, in most of Alqueva's sites. The results of the toxicity assessment showed that some locations induced acute and chronic toxicity in the species used. Further, the H. incongruens was the most sensitive species as far as the contamination found in the sediment is concerned, followed by the bacteria V. fischeri. This integrative approach, together with the water column quality assessment, allowed a comprehensive evaluation of the environmental quality of this strongly modified water body and will allow the implementation of remediation strategies to obtain a good ecological potential as proposed in the Water Framework Directive.

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.

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.

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.

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.

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.

Distribution patterns of freshwater molluscs along environmental gradients in the southern Guadiana River basin (SW Iberian Peninsula)

The taxonomic status of the freshwater mollusc fauna of the Iberian Peninsula it is reasonably well known, but, unlike other benthic macroinvertebrate, its distribution and ecology has been poorly studied. In this article, I study the relationships between environmental characteristics and distribution and community structure of freshwater molluscs along climatic, hydrological, physicochemical, and heterogeneity gradients in the southwestern Iberian Peninsula. Ninety-four sampling points were analysed, in which, in addition to habitat features, the presence/absence and abundance of species were evaluated. The environmental gradients were measured by use of principal-components analysis (PAC), which orders the variables along two gradients: headwaters-mouth gradient (PC1) and water availability (PC2). According to canonical correspondence analysis (CCA), the main environmental factors related to species distribution and community structure were conductivity, permanency, channel width, turbidity, slope, and distance to the main river axis. The relationship between biodiversity (measured as species richness and the Shannon–Weiner diversity index), the ratio of the number of introduced species to the total number of species (zoogeographic integrity coefficient), and environmental variables was best explained by a regression model incorporating, basically, the permanence of water in streams as the variable that accounted for most of the variance. This study demonstrates that the distribution of freshwater molluscs along a Mediterranean gradient highly stressed by drought depends, mainly, on the hydrological stability and environmental conditions of the headwaters and estuarine sites.

An evaluation of the application of treated sewage effluents in Las Tablas de Daimiel National Park, Central Spain

Summary At the present time there is not enough information available to develop a quantitative model on how inundation takes place in the 1490 ha area of Tablas de Daimiel National Park (Central Spain) located upstream of Morenillo Dam. Given that it is the most important area in the Park from an ecological standpoint, this is a major concern, as it has not been possible to assess the potential effectiveness of the interventions geared towards improving its current state. As a result, it is not feasible to simulate the hydrologic response to the application of treated sewage effluents, an initiative recently implemented by the Public Administration responsible for water management in the Guadiana River Basin, where the Park is located. To help solve this problem, a simplified model of the hydrologic behaviour of the system has been developed focusing on the characterisation of the main trends of the inundation process. Field data from 12 drying processes were used to identify the model parameters. Later, the evolution of the system was examined after the application of treated sewage effluents, assuming the hypothesis of a dry climate. The results show that the 10 Mm 3 of available effluents is sufficient to improve from 2 ha to 60 ha the inundation condition of the areas considered to be high-priority. This therefore demonstrates that, from a hydrologic point of view, it is highly advisable to use treated sewage effluents.

Invasive species and habitat degradation in Iberian streams: an analysis of their role in freshwater fish diversity loss

Mediterranean endemic freshwater fish are among the most threatened biota in the world. Distinguishing the role of different extinction drivers and their potential interactions is crucial for achieving conservation goals. While some authors argue that invasive species are a main driver of native species declines, others see their proliferation as a co-occurring process to biodiversity loss driven by habitat degradation. It is difficult to discern between the two potential causes given that few invaded ecosystems are free from habitat degradation, and that both factors may interact in different ways. Here we analyze the relative importance of habitat degradation and invasive species in the decline of native fish assemblages in the Guadiana River basin (southwestern Iberian Peninsula) using an information theoretic approach to evaluate interaction pathways between invasive species and habitat degradation (structural equation modeling, SEM). We also tested the possible changes in the functional relationships between invasive and native species, measured as the per capita effect of invasive species, using ANCOVA. We found that the abundance of invasive species was the best single predictor of natives' decline and had the highest Akaike weight among the set of predictor variables examined. Habitat degradation neither played an active role nor influenced the per capita effect of invasive species on natives. Our analyses indicated that downstream reaches and areas close to reservoirs had the most invaded fish assemblages, independently of their habitat degradation status. The proliferation of invasive species poses a strong threat to the persistence of native assemblages in highly fluctuating environments. Therefore, conservation efforts to reduce native freshwater fish diversity loss in Mediterranean rivers should focus on mitigating the effect of invasive species and preventing future invasions.

Mid to late Holocene constraints for continental shelf mud deposition in association with river input: the Guadiana Mud Patch (SW Iberia)

This study correlates Holocene sedimentation with regional environmental changes for the Guadiana middle shelf, SW Iberia, based on a detailed sedimentological analysis combined with radiocarbon and amino acid racemization dating. The sedimentary record of vibrocore CRIDA16 (307 cm) from the mud patch off the Guadiana River is characterized by a transgressive signature. Terrigenous sand–gravel dominates the core base up to ca. 5,000 cal. years b.p., enriched in schist/greywackes and non-reworked quartz. The shelf area was under the direct influence of Guadiana bed load discharges, as sea level was lower than today but rising, favouring the entrapment of fines during the Guadiana estuary infilling in the early Holocene. Core upwards, fines dominate the record. Sea-level stabilization at ca. 5,700–3,700 cal. years b.p. led to estuary infilling by coarser sediments and export of suspended sediment to the middle shelf. After ca. 900–700 cal. years b.p., the formation of the Guadiana Mud Patch signifies deposition in a marine environment dominated by suspended material from the Guadiana River. Comparison with earlier publications showed that a similar evolutionary mechanism of middle shelf mud deposition occurred in other parts of the Iberian Margin, pointing to a generalized establishment of this type of sedimentary body in Iberia since the mid to late Holocene. This suggests that the formation of mud belts on the north and south Iberian Margin was to a large extent synchronous. It is likely that the evolution of the Guadiana Mud Patch on the shelf was controlled foremost by the overall climate trends identified for several parts of Iberia during the Holocene (i.e. increased aridity punctuated by significant humidity stages), and less by human occupation of the region. Enhanced humidity stages led to higher rainfall and intensified floods, with a consequent increase of discharges to the shelf which ultimately were responsible for the Guadiana Mud Patch formation. It is expected that this pattern of sedimentary dynamics has been strongly disturbed since 2002, when the closing of the Alqueva Dam (the biggest on the Iberian Peninsula) was completed in the Guadiana River basin.

Assessing the ecological status in species-poor systems: A fish-based index for Mediterranean Rivers (Guadiana River, SW Spain)

The assessment of the ecological status of freshwater ecosystems is a key issue for many international laws such as the Water Framework Directive (WFD) in light of the actual impoverished status of these ecosystems. Different multimetric approaches have been successfully developed in different freshwater environments. However, multimetric indices are difficult to apply to Mediterranean rivers basins, characterized by freshwater fish communities very low in species richness and support a high number of endemics with generalist and opportunistic life strategies. Here we follow a site-specific approach to develop an adaptation of the multimetric procedure usually used in Indices of Biotic Integrity (IBI), resulting in the Index of Community Integrity (ICI). We modeled the presence–absence of 10 native freshwater fish species from the Guadiana River basin using the Assessment of Nearest Neighbor Analyses (ANNA) model, to assess the deviation of the observed and expected community composition at reference condition. ANNA, which is a multi-species model, allowed incorporating in the index some rare species, though not all of them present in the basin. Deviations were transformed into probabilities of belonging to a reference site and species by species measures were then integrated in a final score. The use of presence–absence only data reduces potential errors associated with estimations of species’ abundance and its seasonal changes, which is especially important in Mediterranean environments. The ICI was sensitive to both habitat degradation and the degree of dominance of non-native species within the freshwater fish community (or biotic perturbation), which have been traditionally overlooked in IBIs, but was unresponsive to natural sources of variation. Given the site-specific nature and the simplicity of the index that we propose here, we expect it to be applicable to other Mediterranean basins for which predictive models can be produced.