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The Guadiana Basin is a transnational basin, presenting historical contamination with potentially toxic metals (PTM), which origin can be both natural and anthropogenic. This study explores the use of a set of observational, chemical and ecotoxicological assays with Heterocypris incongruens, Vibrio fischeri, Pseudokirchneriella subcapitata, Thamnocephalus platyurus, identifying the most sensitive to be included in a toolbox to analyze the quality of freshwater sediments related to this type of contamination. The study included the analysis of a reservoir and streams sediments of Guadiana basin, in two consecutive years with different climate conditions 2017 (dry year) and 2018 (normal year). The results showed high chemical variability along the basin, with greater contamination with PTM in the reservoir sediments. The calculated Enrichment Factors (EF) indicated high anthropogenic contamination by Cd, followed by Pb (EF > 1.5). The geoaccumulation index (Igeo) revealed that the sediments were severely polluted with Cd, and slightly polluted with Pb and Cu, inducing a higher sublethal toxicity to Heterocypris incongruens. Among the parameters evaluated, and after the use of multivariate statistical techniques, the toolbox for assessing sediments quality, in similar climate and geological conditions, should include the analysis of: meteorology, land use/cover in the area, granulometry, organic matter content, PTM concentrations, contamination indices (e.g., Igeo and EF), and sublethal bioassays with H. incongruens (total sediment analysis) and Vibrio fisheri luminescence inhibition (pore water analysis)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Climatic extreme events such as droughts (unpredictable), dry periods (predictable) or even flush floods, threaten freshwater ecosystems worldwide. The filtering mechanisms of these events and their strength on communities, however, can be different among regions. While time-for-adaptation theory defines whether or not water scarcity can be considered as disturbance, the stress-dominance theory predicts an increase in importance of environmental filtering and a decrease in the role of biotic interactions in communities with increasing environmental stress. Here, we tested whether environmental filtering (leading to trait convergence) or limiting similarity (leading to trait divergence) is the main assembly rule shaping the structure and trait composition of benthic diatom assemblages in Mediterranean (Portuguese) and continental (Hungarian) temporary and perennial streams. We assumed that the trait composition of diatom assemblages in the two stream types would be less different in the Mediterranean than in the continental region (addressed to time-for-adaptation theory). We also hypothesized that trait composition would be shaped by environmental filtering in the Hungarian streams while by biotic interactions in Portuguese streams (addressed to stress-dominance theory). Our results supported our first hypothesis since traits, which associated primarily to temporary streams were found only in the continental region. Our findings, however, only partially proved the stress-dominance hypothesis. In the continental region, where drying up of streams were induced by unpredictable droughts, biotic interactions were the main assembly rules shaping community structure. In contrast, environmental filtering was nearly as important as limiting similarity in structuring trait composition in the Mediterranean region during the predictable dry phase with no superficial flow. These analyses also highlighted that drought events (both predictable and unpredictable ones) have a complex and strong influence on benthic diatom assemblages resulting even in irreversible changes in trait composition and thereby in ecosystem functioning., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

The study of intermittent rivers is a critical and timely issue due to their worldwide increase, triggered by several causes including climate change. The need to understand the response of intermittent river biota to water intermittency led us to conduct this study using benthic diatoms collected in southern Portugal. Benthic diatoms were explored in terms of assemblages, diversity indices, the Specific Pollution Sensitivity (SPI) Index, functional metrics (i.e. ecological guilds and life-forms) and conservation status. We verified that changes in water physico-chemical characteristics were highly controlled by flow intermittency, which in turn is directly linked to meteorological variables (air temperature and precipitation). Changes in diatom assemblages reflect the aquatic regime of sites, changes in aquatic states through time and mesohabitats (dry biofilm, samples collected in pools or under flowing conditions). Species richness, on the other hand, did not reflect these differences, whilst Shannon diversity and Pielou's Evenness indices only reflected mesohabitat differences. The SPI distinguished sampling periods, and mesohabitats. The relative abundance of ecological guilds changed with aquatic states, with the low-profile guild dominating in eurheic and arheic conditions (except during Summer), being replaced by motile taxa in summer arheic conditions, reflecting increases in nutrient and siltation. The hypothesis that benthic diatom assemblages in dry biofilm can be used as an indicator of ecological status during the dry-phase was validated, since no differences between the Ecological Quality Ratio determined in dry biofilm collected in Summer 2017 and the previous Spring 2017 in flowing water. A method is proposed for diatom sampling in dry biofilm, contributing to an integrated ecological status evaluation, which considers the dry-phase and enhances the reach of biomonitoring programs., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Occurrence of pharmaceuticals in the aquatic environment is nowadays a well-established issue that has become a matter of both scientific and public concern. Tons of different classes of pharmaceuticals find their way to the environment at variable degrees, after their use and excretion through wastewater and sewage treatment systems. The main goal of this study was to correlate the dynamics and the environmental risk of pharmaceuticals with different temporal and hydrological patterns, at the Guadiana Basin (South of Portugal). Water samples were collected bimonthly during 2017 (classified as a drought year) and 2018 (post-drought year) in: Zebro, Álamos and Amieira (intermittent hydrological streams), and Lucefécit (perennial hydrological stream). The pharmaceuticals quantified in higher concentrations, out of 27 investigated, were diclofenac (up to 4806 ng L - 1 ), ibuprofen (3161 ng L - 1 ), hydrochlorothiazide (2726 ng L - 1 ) and carbamazepine (3223 ng L - 1 ). Zebro and Álamos presented the highest contamination by this group of environmental hazardous substances, which may be correlated with the presence of wastewater treatment plants upstream the sampling point of each stream. Furthermore, the highest concentrations occurred mainly during the dry period (2017), when the flow was nearly inexistent in Zebro, and in Álamos after the first heavy rainfalls. In specific periods, the high concentrations of pharmaceuticals detected may induce risk for the organisms of lowest trophic levels, damaging the balance of the ecosystems at these streams. The risk quotient optimised approach (RQf) integrating exposure, toxicity and persistence factors, ranks the pharmaceuticals investigated in terms of risk for the aquatic ecosystems as follows: diclofenac, ibuprofen and carbamazepine (high risk), clarithromycin (moderate risk), acetaminophen, ofloxacin and bezafibrate (endurable risk), and hydrochlorothiazide (negligible risk)., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Freshwater diatom communities are known to respond to a wide range of environmental factors, however, the depth gradient is usually neglected and few studies are available, especially in large reservoirs. During the ALqueva hydro-meteorological EXperiment (ALEX) field campaign, diatom communities were studied in the margins and in three platforms (from the surface to the bottom of the reservoir) located in the limnetic zone of the Alqueva reservoir, one of the largest artificial lakes in western Europe. A detailed meteorological and physico-chemical characterization of the reservoir was carried out from June to September in Summer 2014, when the reservoir was stratified, to relate these variables with diatom assemblages. Despite the large dimensions of the reservoir, no differences in the water physico-chemical characteristics and diatom descriptors were detected among platforms. Small changes in diatom assemblages, ecological guilds, taxa richness and Shannon diversity index were observed between sampling campaigns. Nevertheless, differences in diatoms were detected along a depth gradient, both in terms of diatom assemblages and ecological guilds. Taxa richness, Shannon diversity index, Pielou's evenness and Specific Pollution sensitivity Index (SPI) also differed with depth, with the lowest values of all indices detected at surface samples, increasing with depth, reaching the highest values at 20 m for taxa richness, Shannon diversity and Pielou's evenness indices., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The mine abandonment is generally associated with the release of potentially toxic metals into the environment, which may depend on metals speciation, soil properties and climate conditions. The goal of the present work was to assess the environmental impact of the abandoned Pb-Zn mine "Las Musas" (Spain) using an integrative approach. The impact on soils and surface waters was performed using: chemical parameters, quantification of potentially toxic metals (Cd, Cu, Pb and Zn), and ecotoxicological responses using lethal and sub-lethal bioassays with organisms' representative of different trophic level ((soil: Eisenia fetida (mortality and reproduction test); Latuca sativa and Lollium perenne (seedling emergence); and water: Vibrio fischeri (luminescence inhibition), Daphnia magna (immobility and reproduction test), Thamnocephalus platyurus (mortality), Pseudokirchneriella subcapitata (growth inhibition)). The results showed soils with neutral to slight alkaline pH (7.64-8.18), low electric conductivity (125-953 μS/cm) and low organic matter levels (0.20-1.85%). For most of the soil samples, Pb was the only metal which surpassed the limit proposed by the Canadian soil quality guidelines, with values ranging from 42.2 to 181.4 mg/kg. The ecotoxicological results showed that the soils with the highest levels of Pb induced a decrease on E. fetida reproduction and on L. sativa germination, indicating negative impacts on the habitat function. The analysis of the surface waters showed levels of Zn surpassing the legal limit adopted from the Water Framework Directive (37.0 to 69.0 μg/L). The ecotoxicological results highlight the importance of bioassays that evaluate the behavior of species, when assessing the risk of mining areas with non-acid soils and waters with high nutrients/organic matter concentrations and low concentrations of potentially toxic metals. The results indicated a moderate environmental risk from potentially toxic metals, at the areas analyzed around the Azuaga mine., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Differences in the structure of diatom assemblages in headwaters with contrasting shading conditions and different land use in the buffer zone and upper catchment were studied in order to evaluate the influence of the lack of riparian vegetation on the biofilm. The objective was to ascertain whether a riparian buffer can mitigate the negative influence of human induced disturbance and pollution on diatom assemblages in headwaters. Four streams were selected in order to maximize the differences in the land cover and minimize other environmental gradients. Multivariate statistics, different comparative and permutation tests and correlations were applied to compare the diatom assemblages, the Specific Polluosensitivity Index (IPS) and the diatom ecological guilds (low profile, high profile and motile) among the sites studied and to evaluate their responses to disturbances. The analysis showed that low profile diatoms typically dominated in forested headwaters with limited resources, whilst assemblages at impacted sites showed a wider range of growth forms. In unimpacted streams, the diatom assemblages were influenced by temperature, pH, conductivity and calcium, as usually reported for oligotrophic streams with high natural disturbance due to fast current and shading. In both shaded and unshaded impacted streams, the importance of nutrients and land use disturbance, especially urbanization, prevailed. This trend was also reflected by the IPS index that showed consistently lower values at impacted sites, correlating most significantly with nutrients. The diatom species composition as well as diatom guilds at impacted sites were similar, regardless of the presence or absence of riparian vegetation, and were significantly influenced by seasonal changes. Our results indicate that diatoms react sensitively to alterations of the water environment in headwaters, induced by anthropogenic activities, and these impacts are not buffered by an intact riparian zone. Diatoms closely reflected land use practices in the upper catchment regardless of the buffer zone status., (Copyright © 2013 Elsevier B.V. All rights reserved.)