Tagus River Basin Research Articles

Improving Knowledge and Awareness and Contributing to Policy Making on River Pressures through a Citizen Science Approach: Tagus Web Viewer Case (Spain)

Citizen science is considered one of the most appropriate tools to raise public awareness of environmental issues. With the aim of improving knowledge on river environments, this article presents a web application for mobile phones and other portable devices that allows, through the active participation of society, the collection of detailed and systematic information on the main problems facing rivers. The initiative uses a web viewer (Tagus Web Viewer—TagusWV) developed as a pilot project in the Tagus River basin (Spain). This web viewer allows information on river pressures to be collected and the aggregated data to be visualised and extracted for interpretation and analysis. Pressure is defined as any use or activity, legal/illegal, authorised/unauthorised, that has an impact on water quality, morphology, river dynamics or the ecosystem. The data are mainly collected by different groups of citizens. In addition to contributing to the environmental education of citizens involved in a river environment, the data provided in the TagusWV are of particular interest to river managers. The tool is designed to be relevant for any river basin in the world, by simply loading the map, the names of the rivers and the corresponding locations.

Hydrovars: an R tool to collect hydrological variables

ABSTRACT Hydrological models can benefit from soft calibration, a process by which the proper simulation of hydrological variables is proved while or before addressing hard calibration. Soft calibration reduces the probability of obtaining a statistically accurate but unrealistic model. However, it requires soft data, which is often hard to acquire or unavailable. This work presents HydRoVars, an R tool developed to facilitate the estimation of data which can be implemented in a soft calibration procedure. It allows us to estimate two key hydrological indices (the runoff coefficient and baseflow index) and weather-related variables at the catchment scale for one or numerous basins. The runoff coefficient is calculated automatically from precipitation and streamflow datasets. Groundwater contribution is estimated through a semi-automatic process based on a baseflow filter which considers hydrogeological properties. Modellers would benefit from incorporating soft calibration in their calibration procedures, and this tool might help to estimate these relevant hydrological variables in their modelled area. The tool has been tested in 19 subbasins of the Tagus River basin (Spain) located in different geological regions. In the test cases, we demonstrate the usefulness of this tool to improve the model representation and gain an understanding of the catchments' hydrology.

How to mitigate flood events similar to the 1979 catastrophic floods in the lower Tagus

Abstract. The floods that struck the lower Tagus valley in February 1979 correspond to the most intense floods in this river and affected the largest number of people in a river flow event in Portugal during the last 150 years. In fact, the vast area affected significantly impacted circa 10 000 people in the lower Tagus sector (and an additional 7000 in other regions of Portugal), including thousands of people evacuated or made homeless. In this context, the present study focuses on an in-depth analysis of this event from a hydrodynamic perspective by means of the Iber+ numerical model and on developing strategies to mitigate the flood episodes that occur in the lower section of the Tagus River using the exceptional floods of February 1979 as a benchmark. In this sense, dam operating strategies were developed and analyzed for the most important dam along the Tagus River basin in order to propose effective procedures to take advantage of these infrastructures to minimize the effect of floods. Overall, the numerical results indicate a good agreement with watermarks and some descriptions of the 1979 flood event, which demonstrates the model capability to evaluate floods in the area under study. Regarding flood mitigation, results obtained indicate that the frequency of floods can be reduced with the proposed strategies, which were focused on providing optimal dam operating rules to mitigate flooding in the lower Tagus valley. In addition, hydraulic simulations corroborated an important decrease in water depth and velocity for the most extreme flood events, and also a certain reduction in the flood extension was detected. This confirms the effectiveness of the proposed strategies to help in reducing the flood impact in the lower Tagus valley through the efficient functioning of dams.

Pharmaceutically active compounds (PhACs) in surface water: Occurrence, trends and risk assessment in the Tagus River Basin (Spain)

In this study, the presence of 23 pharmaceutically active compounds (PhACs) including antibiotics, analgesics, anti-inflammatories, psychiatric and cardiovascular drugs, antifungals and metabolites was investigated in surface waters. A total of 89 samples were collected during 3 years (2020, 2021 and 2022) from a European representative river basin (Tagus, Spain). To elucidate PhAC potential sources, sampling points located in areas with low, median and high anthropogenic influence were selected. The analytical method based on solid phase extraction (SPE) followed by UHPLC-MS/MS analysis was validated meeting SANTE/2020/12830 and SANTE/12682/2019 performance criteria. PhACs were quantified above limits of quantification (LOQs) in 96 % of water samples, being the antihypertensives valsartan (648 ng/L, 87 % quantification frequency) and irbesartan (390 ng/L, 75 %) and the antidepressant o-desmethylvenlafaxine (495 ng/L, 76 %) the predominant pollutants. The rest of the target PhACs showed median concentrations between 4 and 172 ng/L with quantification frequencies ranging from 35 to 75 %. ∑PhAC concentrations did not show temporal or seasonal trends. However, valsartan and naproxen presented lower levels in drier (spring and summer) compared to the wetter. Source identification revealed a clear anthropogenic origin since concentrations obtained in highly populated areas were statistically higher (p < 0.01) than those quantified in sparsely populated ones. This finding was also confirmed by calculating PhACs mass flow rates, which ranged between 1.4 and 235 kg/y. Finally, data generated were used to estimate the potential risk to the aquatic ecosystem for three trophic levels (phototrophic, invertebrate and vertebrate organisms). Risk quotient ratios (RQs) were calculated for all PhACs at the median (P50) and worst-case (max) scenarios. Up to 7 PhACs (acetaminophen, carbamazepine, gemfibrozil, ibuprofen, irbesartan, ketoprofen and venlafaxine) showed high risk for the highest trophic level (fish) in >45 % of investigated locations.

Sharing water in the international Tagus River basin: a geopolitical approach to explaining water governance issues in Spain

This paper provides an overview of different policies, political strategies and spatial conflicts on water issues in 21st century Spain, with an illustrating example about the management of the Tagus River. This international river basin, which is shared between Spain and Portugal, must meet the requirements of the Water Framework Directive, as all the river basins in the European Union do. The power granted to Spanish regions, their asymmetric economic development patterns, and the worsening droughts associated with climate change have created a water conflict. This paper shows, through the French geopolitical approach, how water policy in Spain has evolved these last decades and how water scarcity has become a geopolitical representation in certain territories. This study focuses on the territorial observation of power rivalries at different scales, providing new and complementary elements that can help understand water governance challenges in Spain in the years to come.

Morphological characterization of 23 Malus domestica Borkh cultivars from central Spain

The purpose of this work was to morphologically characterize an apple tree collection composed of 67 individuals from 41 accessions belonging to 23 old Spanish apple cultivars (Malus domestica Borkh) alongside 9 reference cultivars. The studied germplasm was collected previously in rural areas of central Spain (Sierra Norte de Madrid and Tagus river basin) and it was analyzed through 67 descriptors mainly from IBPGR and UPOV. We found a very high morphological diversity in the studied old apple cultivars, as 48% of the descriptors (most of them devoted to fruit traits) were significantly different between types of cultivars. In addition, the sample cultivars resulted clearly distinct from reference cultivars in multivariate analysis. In general, no particular structure was found in old cultivars, but a strong differentiation of ‘Agridulce’ and ‘Hojancas’ is reported due to their bigger fruits. Our results support the molecular analysis and call for further analysis of the local apple germplasm and long-term conservation actions.

Climate Adaptation Needs to Reduce Water Scarcity Vulnerability in the Tagus River Basin

In southern Europe, climate change is expected to aggravate water scarcity conditions and challenge current water management practices. The present paper evaluates the impacts of climate change in the highly regulated Tagus River basin and assesses various adaptation options, quantifying the effort needed to maintain the ability to sustain current water uses. A water management and allocation model covering surface and groundwater resources is used to evaluate available and renewable water resources for different climate scenarios. Additionally, the Water Exploitation Index Plus (WEI+) and water supply reliability criteria are used to quantify water scarcity and the ability to satisfy water demands, respectively. The results show that climate change will significantly change the stream flow regime and reduce water availability in the Tagus River basin, but the existing reservoir infrastructure will alleviate some of these impacts, especially in the dry half-year. Until the end of the century, water scarcity levels, measured by annual WEI+, are expected to increase in the Tagus River basin from 0.46 to 0.52 or 0.62, respectively under two Representative Concentration Pathways (RCP 4.5 or RCP 8.5). The benefits of streamflow regulation vary with the hydrological regimen, the current degree of water use and the role of groundwater resources to meet demand. The benefits of streamflow regulation are also dependent on the environmental flow requirements that will be adopted in the future. A reduction of water consumption for irrigation by 25% to 40% will significantly improve the Tagus River system performance and maintain the current scarcity situation in the future, under the expected scenarios of climate change.

Seasonal patterns of microhabitat selection in the Southern Iberian spined-loach Cobitis paludica

The Southern Iberian spined-loach Cobitis paludica is an Iberian endemism threatened by human activities, including habitat destruction. For this reason, the development of conservation and the recovery plans for the species calls for a precise knowledge of its habitat requirements. Here, microhabitat use and selection patterns were investigated to determine the limiting factors for the species in different seasons, corresponding to a gradient in flow conditions. The microhabitat of the loach was analysed in the River Jarama (Tagus River basin, central Spain) in the period of maximum activity between March and September 2013. No significant differences in microhabitat use were found between males and females, and only very weak ontogenetic changes were detected. The microhabitat used by the loach varied significantly throughout the study period, generally adapting to the flow-mediated dynamics of available habitat. The most stable pattern throughout the year was the use of very low water velocities. Additionally, the loach made selective use of certain microhabitat features, with slight adjustments to the seasonally changing habitat conditions. The loach significantly selected positions with abundant silt substrate and aquatic vegetation, and avoided coarser substrates. The availability of fine substrates and abundant vegetation is therefore a critical habitat requirement for the loach, which needs instream structures that provide foraging substrate, refuge and safe positions for spawning. Selection of refuge elements (deep habitats, aquatic vegetation) was especially apparent under low-flow conditions. Human activities leading to the loss of these critical microhabitats may threaten the survival of already scarce loach populations.

High expression of canines in some Mediterranean roe deer (Capreolus capreolus) populations against the general evolutionary trend

Upper canines do not usually appear in the roe deer ( Capreolus capreolus (Linnaeus, 1758)) and their occasional appearance represents the expression of a tooth, as a rudimentary canine, which has been suppressed in the evolution of the group. These dental anomalies could be potentially useful for tracing ancestral genes in local ecotypes and populations. We studied the skulls of 517 adult roe deer males from seven Iberian Peninsula hunting populations looking for canine occurrence and the variations depending on region and ecomorphological variety. A total of 18 specimens had canines (3.48%), but a relationship was detected between the geographic origin and the canine presence. We found upper canines in three populations that were located in the Tagus River Basin, with 6.08%, 10.91%, and 20% prevalences, respectively. In the population with the highest prevalence, we also found a case of duplicated canines on either side of the upper jaw. Here, the high prevalence of upper canines against the evolutionary trend may be a sign of atavistic populations, possibly adapted to a less fibrous diet, in a geographical area connected through the Tagus River Basin, and probably regarding one of the glacial refuges of the Iberian Peninsula.

Analysis of the Evolution of Climatic and Hydrological Variables in the Tagus River Basin, Spain

During the second half of the 20th century, several Spanish rivers experienced a decrease in the availability of water resources which coincided with an increase in human water demands. This situation is expected to be exacerbated by climate change. This study analyses the evolution of annual streamflow in 16 sub-basins of the Tagus River basin (Spain) during the 1950–2010 period and its relationship with selected variables. Our main objective is to characterize changes in in-stream flows and to identify what factors could have contributed to them. First, we used non-parametric tests to detect trends in the hydro-climatic series. Then, we analyzed changes in the runoff coefficient and applied regression-based techniques to detect anthropic drivers that could have influenced the observed trends. The analysis revealed a general decreasing trend in streamflow and an increasing trend in air temperature, while trends in precipitation are less clear. Residuals from regression models indicate that the evolution of several non-climatic factors is likely to have influenced the decline in streamflow. Our results suggest that the combination of the expansion of forested areas (a 60% increase from 1950 to 2010) and irrigated land (a 400% increase since 1950) could have played an important role in the reduction of streamflow in the Tagus basin.

A Shared Vision on the Transboundary Water Management Challenges of the Tagus River Basin

A Shared Vision on the Transboundary Water Management Challenges of the Tagus River Basin

Quantile regression for modelling the impact of climate in cork growth quantiles in Portugal

The annual growth and the thickness of cork are known to be highly variable between trees located in the same geographical location. Researching how climate variables affect different trees within the same site is a step forward for the management of cork production since current knowledge focusses only on the average tree response. Quantile regression methodology was applied for the first time to a large data set containing measurements of cork growth, sampled in 35 stands across the cork oak distribution area in Portugal. This methodology proved to be useful for testing the hypothesis raised: does climate affect differently the annual cork growth, and ultimately cork thickness of individual trees located in the same stand? Estimating the amount of cork produced by one stand that has the required thickness for the production of natural cork stoppers is essential to support cork oak management. However, no model, before this work, had been developed to provide managers with this information. A downward parabolic relationship between annual cork growth and annual precipitation was determined for all quantiles, with optimum annual average precipitation value ranging from 1103 to 1007 mm. April to August monthly temperatures, spring average temperature or summer average temperature, showed a negative relationship with annual cork growth, in particular for lower quantiles. Maximum annual temperature was shown to negatively affect annual cork thickness, in particular for the trees under the 6th quantile. The ratio between annual precipitation and average temperature, that define the Lang index (LI), showed a downward parabolic relationship with annual cork growth. Best cork growth conditions are found for Lang index values around 60, corresponding for the transition between semi-arid climate and humid climate. The application of the final model developed for estimating cork thickness of an eight years’ cork growth period allowed the prediction and mapping of the percentage of cork suitable for natural cork stopper production. It showed that higher values are expected in the Southern and Central coastal regions and along the Tagus River basin. The Northern coastal and mountain regions, characterised by Lang index values higher to 60 (humid climates), present lower estimated values for the percentage of cork suitable for natural cork stopper production. The estimated values are expected to be reduced under climate change scenarios in the Southern and Central coastal regions.

Effects of anthropogenic pollution and hydrological variation on macroinvertebrates in Mediterranean rivers: A case-study in the upper Tagus river basin (Spain)

Seasonal hydrological variation and chemical pollution represent two main drivers of freshwater biodiversity change in Mediterranean rivers. We investigated to what extent low flow conditions can modify the effects of chemical pollution on macroinvertebrate communities. To that purpose, we selected twelve sampling sites in the upper Tagus river basin (central Spain) having different sources of chemical pollution and levels of seasonal hydrological variation. The sites were classified as natural (high flow variation, low chemical impact), agricultural (high flow variation, high agricultural chemical inputs) and urban (limited flow variation, high urban chemical inputs). In these sites, we measured daily water discharge, nutrients, and contaminant concentrations, and we sampled benthic macroinvertebrates, in spring, summer and autumn. Significant differences related to toxic pressure and nutrient concentrations were observed between the three groups of sites. Seasonal patterns were found for some water quality parameters (e.g. nitrites, ammonia, suspended solids, metal toxicity), particularly in agricultural sites. Taxonomic and functional richness were slightly lower in the polluted sites (agricultural and urban), particularly during low flow periods (summer and early autumn). Functional diversity was significantly lower in sites with seasonal flow variation (agricultural sites) as compared to the more constant ones (urban sites). The frequency of traits such as large size, asexual reproduction, aquatic passive dispersion and the production of cocoons increased in response to pollution during low flow periods. This study shows that the impacts of anthropogenic chemical pollution on taxonomic and functional characteristics of macroinvertebrate communities seem to be larger during low flow periods. Therefore, further studies and monitoring campaigns assessing the effects of chemical pollution within these periods are recommended.

Beyond piecewise methods: Modular integrated hydroeconomic modeling to assess the impacts of adaptation policies in irrigated agriculture

The accurate understanding of the human-modified water cycle calls for a detailed representation of human and water systems, including relevant non-linearities, and of the feedback responses between them. This paper couples a microeconomic Positive Multi-Attribute Utility Programming model with a Hydrologic Modeling System (HEC-HMS) with the objective of incorporating the behavior and adaptive responses of human agents into the representation of the human-modified water cycle. The coupling occurs in a sequential fashion using bidirectional protocols that represent the feedback responses between the microeconomic and hydrologic modules through common spatial elements and variables. The proposed model is illustrated with an application to agricultural water management in the Upper Tagus River Basin in Spain. The non-linear responses observed in the modeled human-water system suggest that strengthening the agricultural water allocation constraint can avert or delay drought negative environmental impacts with a less-than-proportional yet incremental impact on Gross Value Added and employment.

La gestión pública de una obra hidráulica compleja, entre el marco internacional y los intereses regionales privados: el caso del trasvase Tajo-Segura (España)

Los procesos económicos globales han agravado los problemas, conflictos y tensiones derivados del uso del agua dulce a escala global, estatal, regional y local. En la época contemporánea, la aceleración derivada de la industrialización y la urbanización ha aumentado el consumo del agua y las infraestructuras artificiales para su utilización. Hoy, el capitalismo de mercado global se ha ido apropiando de los recursos naturales y en el uso del agua predominan los intereses privados. Al mismo tiempo, la degradación medioambiental obliga a intentar compatibilizar el consumo humano y económico con el respeto hacia la naturaleza. En la legislación vigente, en áreas como la Unión Europea, ya se da prioridad a la conservación del medio ambiente sobre la utilización incontrolada del agua como recurso productivo, sobre todo a partir de la aprobación de la Directiva Marco del Agua en 2000. Sin embargo, la política hidráulica española se ha centrado en el agua como bien económico. Con esta premisa se construyeron infraestructuras como el trasvase Tajo-Segura. Actualmente, España, como miembro de la UE, debe adaptarse a la DMA y esto genera un tensa relación internacional-nacional-regional por la gestión pública del trasvase. El artículo se centra en esta cuestión. Se aplicará una metodología deductiva y basada en un análisis teórico crítico a partir del estudio bibliográfico y de la normativa vigente, del apoyo en datos cuantitativos y de las reflexiones de los autores. Se concluye que el trasvase no se ajusta a la sostenibilidad ambiental y ecológica que proclama la DMA, sino que sigue respondiendo a la necesidad de satisfacer la demanda de la cuenca receptora. Además, en periodos de sequía se permite el mercado de cesión de agua de la cuenca cedente a la receptora entre particulares, ignorando el impacto ecológico derivado y superponiendo los intereses económicos. La prioridad debería ser satisfacer la demanda de agua dulce como necesidad de abastecimiento para toda la población y evitar los impactos al medio ambiente. Sin embargo, es evidente que las autoridades públicas están principalmente preocupadas por satisfacer las demandas de agua que tienen que ver con la producción económica aun a sabiendas de no cumplir plenamente con la legislación europea. La contribución resultará de interés a nivel científico y social y se une al debate actual en torno a las políticas de agua dulce en las dinámicas globales.

A machine learning model to assess the ecosystem response to water policy measures in the Tagus River Basin (Spain)

Anthropogenic activities are seriously endangering the conservation of biodiversity worldwide, calling for urgent actions to mitigate their impact on ecosystems. We applied machine learning techniques to predict the response of freshwater ecosystems to multiple anthropogenic pressures, with the goal of informing the definition of water policy targets and management measures to recover and protect aquatic biodiversity. Random Forest and Gradient Boosted Regression Trees algorithms were used for the modelling of the biological indices of macroinvertebrates and diatoms in the Tagus river basin (Spain). Among the anthropogenic stressors considered as explanatory variables, the categories of land cover in the upstream catchment area and the nutrient concentrations showed the highest impact on biological communities. The model was then used to predict the biological response to different nutrient concentrations in river water, with the goal of exploring the effect of different regulatory thresholds on the ecosystem status. Specifically, we considered the maximum nutrient concentrations set by the Spanish legislation, as well as by the legislation of other European Union Member States. According to our model, the current nutrient thresholds in Spain ensure values of biological indices consistent with the good ecological status in only about 60% of the total number of water bodies. By applying more restrictive nutrient concentrations, the number of water bodies with biological indices in good status could increase by almost 40%. Moreover, coupling more restrictive nutrient thresholds with measures that improve the riparian habitat yields up to 85% of water bodies with biological indices in good status, thus proving to be a key approach to restore the status of the ecosystem.

When the river does not naturally flow: a case study of unsustainable management in the Tagus River (Spain)

ABSTRACTThis article assesses the main problems facing the Spanish Tagus River basin, and the management that has caused (or allowed) them. It examines the economic, social, environmental and political-institutional dimensions of Tagus River management in terms of sustainable development. We find that the institutions responsible for designing and implementing water policy in the Tagus basin have been unsuccessful in balancing the three classic dimensions of sustainability, resulting in systematic and recurrent failure to comply with the European Water Framework Directive and the principles of sustainable development.

Genetic Relationships Among Portuguese Cultivated and Wild Vitis vinifera L. Germplasm.

The domesticated grapevine spread along the Mediterranean basin from the primary Near East domestication area, where the greatest genetic diversity is found in its ancestor, the wild vine populations. Portuguese wild populations are on the southwestern fringe of the distribution of the Vitis vinifera L. ssp. sylvestris (C.C. Gmel.) Hegi in Europe. During the last Glacial Period they became isolated from the previous continuum that had been the territory of wild vine populations. Archaeological remains of domesticated vinifera grapevines in Portugal date back from 795 Before Common Era (BCE) in the lower Tagus river basin. In this work, 258 Portuguese vinifera varieties and sylvestris plants were characterized using 261 single nucleotide polymorphism (SNP) markers. The study of the genetic diversity of this local germplasm, its population structure and kinship, all framed in their historical and geographical backgrounds, revealed a complex network of first-degree relationships, where only Iberian varieties are involved. Some Iberian genotypes, like Alfrocheiro (Bruñal, in Spain), Sarigo (Cayetana Blanca), Mourisco Branco (Hebén), Amaral (Caiño Bravo), and Marufo (Moravia Dulce) are ancestors of a considerable fraction of all the autochthonous analyzed varieties. A part of the diversity developed was mostly local in some cases as shown by the closeness of several varieties (Vinhos Verdes) to the wild cluster in different analyses. Besides, several evidences of introgression of domesticated germplasm into wild vines was found, substantiating the high risk of genetic contamination of the sylvestris subspecies. All these findings together to the known matching between the wild maternal lineage of the Iberian Peninsula and an important number of Portuguese grapevine varieties (chlorotype A), point out that some of these varieties derive, directly or indirectly, from originally local wild populations, supporting the possible occurrence of secondary events of local domestication, or, at least, of an introgression process of wild into cultivated grapevines.

Perfluoroalkyl acids (PFAAs): Distribution, trends and aquatic ecological risk assessment in surface water from Tagus River basin (Spain)

Rivers can receive the input of treated or untreated sewage effluents from wastewater treatment plants, urban and industrial discharges and agricultural run-off, becoming an important pathway for the transport and mobilization of pollutants to the oceans. In the present study, the occurrence of 20 PFAAs was determined in the water of Tagus River basin (Spain). PFAAs were detected in 76 out of 92 water samples collected during 5 years (2013–2018), being perfluorooctanesulfonic acid (PFOS) the predominant compound (<0.01–34 ng/L). The annual average PFOS concentrations (2.9–11 ng/L) detected in Tagus River were above the annual average environmental quality standards (AA-EQS) established in the Directive, 2013/39/EU (0.65 ng/L for inland surface waters) but below the maximum allowable concentration (MAC-EQS; 36000 ng/L). The levels of PFAAs detected in urban and industrial areas were statistically higher (p < 0.01) than those at background or remote areas. The mass flow rates amounted to <0.01–46 kg/y for PFOS and <0.01–22 kg/y for perfluorooctanoic acid (PFOA). A quantitative ecotoxicological risk assessment was conducted to evaluate the environmental potential risk related to PFAAs in the aquatic ecosystem. Risk characterization ratios (RCRwater, RCRsed and RCRoral, fish) were below 1 in all cases.

Saltwater Intrusion in the Upper Tagus Estuary during Droughts

Droughts reduce freshwater availability and have negative environmental, economic, and social impacts. In estuaries, the dynamics between the saltwater and the freshwater can be affected during droughts, which can impact several natural resources and economic sectors negatively. The Tagus estuary is one of the largest estuaries in Europe and supports diverse uses and activities that can be affected by the saltwater intrusion (e.g., agriculture). This study assesses the saltwater intrusion in the upper reaches of the Tagus estuary using a process-based model to explore different scenarios of freshwater discharge and sea level rise. For the river discharge and mean sea level rise scenarios analyzed, salinity can reach concentrations that are inadequate for irrigation when the mean Tagus river discharge is similar or lower than the ones observed during recent droughts (22–44 m3/s). Lower river discharges aggravate the consequences. Results also show that the salinity increases with the duration of the droughts. In contrast, the impact of a moderate sea level rise on salinity intrusion is modest when compared with the impact of low river discharges. These findings contribute to support the management of the agricultural activities in the upper Tagus estuary and the water resources in the Tagus river basin.