Iberian reservoirs are highly vulnerable to droughts, warming temperatures, and agricultural runoff, which accelerate eutrophication. Monitoring these dynamics is crucial for sustainable management. This study investigated long-term trends in chlorophyll-a (Chl-a) and water transparency Secchi depth and developed empirical models for the Alto Rabagao (Rb) and Aguieira (Ag) reservoirs in Portugal. We used Sentinel-2 Level-2A reflectance data coupled with 153 in situ observations (2014-2024) for model calibration (n = 95) and validation (n = 58). Temporal trends were assessed using linear regression and Mann-Kendall analyses. Empirical models based on spectral indices (TBDO1, TBDO, MCI, NDWI) were evaluated using walk-forward time-series cross-validation. Results revealed a significant Chl-a increase (0.38 & micro;g L-1 year(-1); p = 0.016) and a simultaneous decline in transparency (p < 0.001) in Rb, indicating progressive eutrophication. In contrast, no significant trends were detected in Ag. Reservoir-specific models achieved moderate-to-high predictive performance, particularly for Chl-a (R-2 up to 0.75; cross-validated R-2 = 0.67-0.68, RMSE = 1.1 & micro;g L-1, MAE = 0.82 & micro;g L-1). Models using combined datasets showed lower accuracy, highlighting the importance of site-specific calibration. Wilcoxon signed-rank tests confirmed the absence of systematic bias between observed and predicted values. Ultimately, Sentinel-2 imagery combined with time-series cross-validation provides a reliable and cost-effective framework for the long-term monitoring of inland water quality.

Monitoring water quality in large reservoirs is essential yet challenging, particularly in regions with limited in situ coverage. This study presents a robust methodology for integrating a decade-long in situ dataset (2014–2022) with Sentinel-2 multispectral imagery to develop and validate localized algorithms for water quality assessment in the Alqueva Reservoir, the largest artificial lake in Western Europe. Three atmospheric correction algorithms (C2RCC, C2X, C2X-COMPLEX) were evaluated, with C2RCC-COMPLEX identified as the most suitable for capturing the reservoir’s optical complexity, yielding the lowest RMSE for Total Suspended Solids (TSS: 2.4 g/m3) and Secchi Disk Depth (SDD: 0.85 m). Empirical models using Sentinel-2 bands 7 (783 nm), 6 (740 nm), and 8A (865 nm) demonstrated strong correlations (R2 ≈ 0.69–0.71) for Chlorophyll-a (Chl-a) with a range data of 0.1–65 mg/m3, TSS with a range data of 2–13.1 g/m3, and SDD with a range data of 0.4–8 m. Spatially explicit water quality maps illustrate the models’ capacity to capture distinct gradients and seasonal dynamics, e.g., elevated Chl-a (>30 mg/m3) and TSS (>7.5 g/m3) in the reservoir’s nutrient-rich northern section during drought (August 2022), and more uniform conditions following winter recovery (March 2019), with SDD exceeding 2 m near the dam. These results underscore the utility of Sentinel-2 for resolving spatial and temporal variability in optically complex inland waters. The proposed workflow offers a transferable, cost-effective framework for monitoring eutrophication risks and sediment dynamics under increasing hydrological variability.

ABSTRACT Plant litter decomposition in rivers is shaped by multiple environmental conditions, which are modified by riparian zone characteristics and human activities, thereby impacting in situ plant litter decomposition rates. However, disentangling the relative importance of these conditions for plant litter decomposition rates is challenging without large‐scale studies encompassing wide environmental and anthropogenic gradients. We carried out a continental‐scale study on plant litter decomposition in 72 river locations across 7 catchments in Europe (Germany, Italy, Portugal, Spain, Sweden), representing wide gradients in climatic conditions, riparian zone characteristics, land‐use intensity, and human population density. We used remote sensing data and field surveys to quantify catchment, riparian, and river habitat characteristics. To assess decomposition rates, we used standardized wood sticks as a model substrate, representing a globally important source of organic matter in river systems. Wood decomposition rate (percent mass loss per day) increased by 4.3% per 1°C rise in mean annual air temperature but decreased by 3.4% per 10 people increase in population density (per 3.14 km2), 2.3% per 100 mm increase in mean annual precipitation, and 0.5% per 1 m increase in channel width. Land‐use intensity and riparian zone characteristics showed no significant effects on wood decomposition rates across the studied gradients. Our results show that wood decomposition rates in the studied rivers are likely to increase linearly with ongoing global warming, reducing the longevity of wood substrates and their reliability as carbon sinks. However, this warming effect might be offset in rivers experiencing concurrent increases in precipitation and human population density. Consequently, the net effect of global change on wood decomposition rates in rivers may be difficult to predict.

Riparian zones are transitional habitats linking terrestrial and aquatic ecosystems and connecting diverse socio-ecological landscapes within catchments. They naturally support high biodiversity and provide multiple ecosystem services, yet they have been extensively modified and degraded by human activities. Although Europe has established binding nature restoration targets, the absence of a standardised framework for riparian ecosystems across countries often leads to management inconsistencies, further complicated by differing stakeholder perceptions of threats and priorities. We surveyed stakeholders’ views on the ecological roles, threats, and management needs of riparian zones across five European countries (Sweden, Germany, Spain, Portugal and Italy). Responses from more than 500 participants show strong alignment between scientists and practitioners. Approximately half of all respondents considered their local river basins to be in low to moderate condition. Perceptions of key threats varied geographically: invasive species were viewed as a major concern in the Iberian Peninsula, whereas habitat modification was broadly recognized as a critical issue. Conversely, Swedish respondents viewed water-quality degradation as a minor threat. Management priorities also differed regionally, with German respondents frequently emphasising restoration, while Portuguese prioritised environmental education. Awareness of European eco-schemes supporting riparian restoration was generally low, particularly in Sweden. Ultimately, our large-scale survey reveals both shared and divergent stakeholder perspectives that mirror the environmental and ecological characteristics of riparian zones across Europe’s boreal, continental, Atlantic and Mediterranean ecoregions. These findings underscore the need to improve awareness of financial incentives and to strengthen support for riparian conservation and restoration across the EU.

Climate change poses a significant risk to agroecosystems, particularly for perennial fruit trees such as chestnut and olive, by affecting phenological processes, physiological stress, and interactions with pests, diseases, and environmental factors. Although previous research has examined the effects of climate change on crop productivity and plant health, important gaps remain in understanding how long-term climate trends and extreme weather events influence yields across different phenological stages. This study evaluates the effects of climatic variability and extremes on the productivity of chestnut and olive trees in Portugal over a 39-year period. Results show that the timing and intensity of climatic events relative to key phenological phases strongly influence productivity patterns in both species. Excessive rainfall during the fruit-ripening stage was associated with reduced chestnut yields, while excess soil moisture during ripening negatively affected olive production in northern Portugal. In contrast, higher average temperatures, particularly during ripening, were linked to increased olive productivity in southern Portugal. Overall, climate impacts were highly stage-specific and differed between species, with significant interannual legacy effects also contributing to productivity variability. These findings highlight the importance of incorporating phenological timing and lagged responses into crop-climate analyses to improve modelling accuracy and support the development of effective adaptation strategies for Mediterranean agroecosystems.

Microplastics accumulation in freshwater organisms is expected to rise with the level of urbanization occurring near riverbanks, although other factors also contribute to this trend. Benthic macroinvertebrates, in particular, may be disproportionately affected by microplastic accumulation due to their feeding strategies (e.g., filter vs deposit feeders), highlighting feeding type-specific ingestion patterns. Nevertheless, it remains uncertain whether these impacts translate into detectable changes at the community level, underscoring the need for in situ investigations. We quantified the accumulation of microplastics in Chironomidae and Oligochaeta across 15 stream reaches along a rural–urban environmental gradient, within 3 Northern Atlantic rivers in Portugal. Microplastics were detected in organisms regardless of their river’s Ecological Quality Status, suggesting that the impact of urban land use is not the only factor that drives microplastics at a local scale. We also found microplastics across different Chironomidae subfamilies and tribes belonging to different functional feeding groups, potentially facilitating a higher influx of microplastics into the aquatic food web. This study demonstrates that even well-maintained ecosystems are not immune to microplastics pollution, emphasizing the urgent need for enhanced research efforts to develop methods for more effectively assessing and mitigating the impacts of microplastics on aquatic organisms.

Streams are significant contributors of greenhouse gases (GHG) to the atmosphere, and the increasing number of stressors degrading freshwaters may exacerbate this process, posing a threat to climatic stability. However, it is unclear whether the influence of multiple stressors on GHG concentrations in streams results from increases of in-situ metabolism (i.e., local processes) or from changes in upstream and terrestrial GHG production (i.e., distal processes). Here, we hypothesize that the mechanisms controlling multiple stressor effects vary between carbon dioxide (CO 2 ) and methane (CH 4 ), with the latter being more influenced by changes in local stream metabolism, and the former mainly responding to distal processes. To test this hypothesis, we measured stream metabolism and the concentrations of CO 2 ( p CO 2 ) and CH 4 ( p CH 4 ) in 50 stream sites that encompass gradients of nutrient enrichment, oxygen depletion, thermal stress, riparian degradation and discharge. Our results indicate that these stressors had additive effects on stream metabolism and GHG concentrations, with stressor interactions explaining limited variance. Nutrient enrichment was associated with higher stream heterotrophy and p CO 2 , whereas p CH 4 increased with oxygen depletion and water temperature. Discharge was positively linked to primary production, respiration and heterotrophy but correlated negatively with p CO 2 . Our models indicate that CO 2 -equivalent concentrations can more than double in streams that experience high nutrient enrichment and oxygen depletion, compared to those with oligotrophic and oxic conditions. Structural equation models revealed that the effects of nutrient enrichment and discharge on p CO 2 were related to distal processes rather than local metabolism. In contrast, p CH 4 responses to nutrient enrichment, discharge and temperature were related to both local metabolism and distal processes. Collectively, our study illustrates potential climatic feedbacks resulting from freshwater degradation and provides insight into the processes mediating stressor impacts on the production of GHG in streams.

Rivers offer cultural ecosystem services (CES) that improve people's quality of life. Advancements in computing and data storage have primarily focused on terrestrial CES, neglecting riverine areas. This study aims to develop a methodology to assess CES in riverine landscapes from social media and citizen science images related to environmental information. We collected georeferenced pictures from Flickr and iNaturalist for three main test rivers in northwest Portugal (Minho, Lima and C & aacute;vado) and classified them based on content such as 'biodiversity', 'recreation/river beaches', 'historical heritage' and 'landscape', as well as environmental spatial variables. A multimodel inference approach was applied to predict the spatial distribution of the pictures and environmental variables to support CES mapping. The methodology was applied during two time periods, before and during the most restrictive period of the COVID-19 pandemic. Results showed that estuaries were identified as 'hotspots' for CES related to rivers provision. There was distinct prevalence of pictures depending on the targeted river: pictures exhibiting 'recreation/river beaches' prevailed in C & aacute;vado (62%), 'biodiversity' in Lima (70%) and 'historical heritage' in Minho (39%). Only the values and patterns from the category 'biodiversity' were maintained on the two analysed periods, with the other categories not having posts in social media during COVID-19 most restrictive period. The methodology for CES assessment in rivers can be replicated using different time periods and regions due to its simple stepwise framework. The study provides valuable insights for sociocultural approaches, aiding in decision-making on freshwater environment management, despite potential limitations in image distribution.

The escalation of litter accumulation in aquatic environments is recognized as an emerging global concern. Although rivers represent the main conduits for land-based waste into the oceans, the spatial dynamics of litter accumulation in these systems remain poorly investigated. Floods have been identified as major drivers of litter mobilization, including macroplastics, within rivers. However, predicting flood-induced litter accumulation along riverbanks is complex due to the cumulative interplay of multiple environmental (geomorphological and riparian) and anthropogenic factors. Using empirical data collected from 14 stream reaches in two Northern Atlantic rivers, our study evaluates which factors, among geomorphological, riparian and anthropogenic descriptors, best drive riverside litter accumulation after floods, taking into account the longitudinal gradient and the spatial heterogeneity along a rural to an urban continuum. Our model reveals that the combination of the human population density and the stream slope at river reach showed the highest explanatory power for the accumulation of riverside litter. In contrast to our prediction, we found marginal effects of riparian vegetation types on the riverside litter accumulation along the rural-to-urban continuum. This work highlights the importance of gathering consistent field data to identify critical areas of riverside litter accumulation within river basins. Our findings can further support environmental managers in designing and setting up effective cleanup campaigns and implementing plastic recovery strategies at specific areas.

Europe has committed to upscale ecosystems protection to include 30% of land and sea. However, due to historical overexploitation of natural assets, the available area for biodiversity protection is severely limited. Riparian zones are natural ecotones between aquatic and terrestrial ecosystems, contributing disproportionately to regional biodiversity and providing multiple ecosystem functions and services. Due to this and their branching geometry, riparian networks form a vast system of ‘blue-green arteries’ which physically and functionally connect multiple ecosystems over elevation gradients, despite covering a relatively small area of the basin. Hence, RIPARIANET argues that developing approaches able to optimise the spatial conservation of natural stream-riparian networks represent a flagship example of biodiversity protection in the EU. Although the integrity of riparian zones is fundamental for the achievement of multiple EU environmental objectives, the lack of a standardised framework for biodiversity assessment and protection across Member States has led to extensive impairment of riparian areas and frequent stakeholder conflicts. The main objective of RIPARIANET is to leverage the increasing resolution of remote sensing information to provide practitioners with evidence-based guidance and approaches to biodiversity conservation. Key questions include: i) how can we remotely assess riparian integrity and identify areas which provide effective connectivity allowing species biodiversity and ecosystem functions to persist through meta-ecological processes? ii) how can we disentangle the influence of local- and network-scale stressors and processes on riparian biodiversity to better implement river basin management schemes? iii) to what extent do currently existing protected areas in rivers account for the geometry of riparian networks and their multifunctionality? We will address these questions in riparian networks within six river basins in Europe, including Boreal, Continental, Alpine, Temperate and Mediterranean systems. First, we will gather local needs and interests from key stakeholders together with satellite imagery and GIS environmental data for all basins. Then, riparian and river ecosystems functions will be modelled and ecological hotspots will be identified through a GIS-based multi-criteria approach, including stakeholder inputs. Then, we will collect in situ data to assess multiple biodiversity and stressors at the local scale and, subsequently, scale-up this information to the network scale using geostatistical tools and advanced modelling. This knowledge will be conveyed to managers at local and EU scales in the form of decision-support tools allowing decision-makers to identify protection gaps and ecological hotspots along riparian networks, based on multiple biodiversity, functional and connectivity criteria.

Both gradual and extreme weather changes trigger complex ecological responses in river ecosystems. It is still unclear to what extent trend or event effects alter biodiversity and functioning in river ecosystems, adding considerable uncertainty to predictions of their future dynamics. Using a comprehensive database of 71 published studies, we show that event - but not trend - effects associated with extreme changes in water flow and temperature substantially reduce species richness. Furthermore, event effects - particularly those affecting hydrological dynamics - on biodiversity and primary productivity were twice as high as impacts due to gradual changes. The synthesis of the available evidence reveals that event effects induce regime shifts in river ecosystems, particularly affecting organisms such as invertebrates. Among extreme weather events, dryness associated with flow interruption caused the largest effects on biota and ecosystem functions in rivers. Effects on ecosystem functions (primary production, organic matter decomposition and respiration) were asymmetric, with only primary production exhibiting a negative response to extreme weather events. Our meta-analysis highlights the disproportionate impact of event effects on river biodiversity and ecosystem functions, with implications for the long-term conservation and management of river ecosystems. However, few studies were available from tropical areas, and our conclusions therefore remain largely limited to temperate river systems. Further efforts need to be directed to assemble evidence of extreme events on river biodiversity and functioning.

Reservoirs have been subject to anthropogenic stressors, becoming increasingly degraded. The evaluation of ecological potential in reservoirs is remarkably challenging, and consistent and regular monitoring using the traditional in situ methods defined in the WFD is often time- and money-consuming. Alternatively, remote sensing offers a low-cost, high frequency, and practical complement to these methods. This paper proposes a novel approach, using a C2RCC processor to analyze Sentinel-2 imagery data to retrieve information on water quality in two reservoirs of Portugal, Aguieira and Alqueva. We evaluate the temporal and spatial evolution of Chl a and total suspended solids (TSS), between 2018 and 2020, comparing in situ and satellite data. Generally, Alqueva reservoir allowed lower relative (NRMSE = 8.9% for Chl a and NRMSE = 21.9% for TSS) and systematic (NMBE = 1.7% for Chl a and NMBE = 2.0% for TSS) errors than Aguieira, where some fine-tuning would be required. Our paper shows how satellite data can be fundamental for water-quality assessment to support the effective and sustainable management of inland waters. In addition, it proposes solutions for future research in order to improve upon the methods used and solve the challenges faced in this study.

High quality water is vital for human life, and ensuring its availability is a basic requirement and a major societal aim. The Water Framework Directive (WFD; 2000/60/EC) is a key piece of legislation for the protection and sustainable use of water in the European Union. In this work we briefly review the WFD directive and the current status of European inland surface waters. Additionally, we summarize major challenges and threats for the biological assessment of inland surface waters under climate change effects and invasion by alien species, and highlight the emerging tools and approaches that might help improve biological assessments, including molecular indices based on environmental DNA (eDNA), to new data from the Earth Observation programmes, and data-sharing platforms. Finally, we present recommendations to improve monitoring systems and assessments in the context of the WFD. Developments in this field may increase the likelihood of assuring high quality water for society.

The European Water Framework Directive (WFD 2000/60/CE) requires the quantification of anthropogenic pressures for evaluating the risk of failing environmental objectives when setting river basin management plans and for biological data interpretation when assessing ecological status. Many studies emphasized the close relationship between biological communities (e.g., fishes and invertebrates) and land use. The need for evaluating the impact of non-natural land use at different spatial scales is often stated, and relatively small spatial scales can be particularly relevant to understand biotic community changes. Abiotic descriptors derived for the reach scale can thus be used to evaluate the success of restoration measures, and their selection and testing is urgent for river management purposes. In this context we describe a new index, which allows quantification of land use modification at the reach scale, the 'Land Use Index - reach' (LUIr). The LUIr was developed on the basis of data gathered in the field with the CARAVAGGIO method (river habitat survey technique). A full description of the index is presented. In addition, jointly with a series of environmental descriptors developed for the quantification of general or specific anthropogenic stressors (sensu WFD), the effectiveness of the new index (LUIr) in describing environmental gradients as perceived from benthic invertebrates has been evaluated for Mediterranean rivers in Cyprus. The multiple regression analysis performed (all subset regression and relative importance) revealed that among the set of environmental descriptors the LUIr resulted to be the factor best explaining the variation of biological metrics. Additionally, the analysis highlighted that the biological metrics more influenced by land use at the catchment level (LUIc) are those estimating the overall diversity and are consequently more influenced by factors at larger scale. The descriptor derived by physico-chemical parameters was in a few cases selected by regression analysis as the most important factor in explaining variation of biological metrics. The descriptors able to detect variation of other habitat features (i.e., habitat modification, habitat diversity and lentic-lotic character) resulted as weak predictors in the models. Our results support the conclusion that the LUIr index can be a useful and cost-effective tool to interpret invertebrate community variation. Moreover, as urgently requested by WFD, LUIr can be used to set and check effectiveness of measures for the improvement of aquatic ecosystems, particularly for Mediterranean streams where agricultural land use is one of the main anthropogenic pressures. (C) 2014 Elsevier Ltd. All rights reserved.