Giorgio Pace

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 Rabagão (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 µg 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 (R² up to 0.75; cross-validated R² = 0.67–0.68, RMSE = 1.1 µg L⁻¹, MAE = 0.82 µg 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.

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 like chestnut and olive, by affecting phenological processes, physiological stress, and interactions with pests, diseases, and environmental factors. Although previous research has examined how climate change affects crop productivity and plant health, significant gaps remain in understanding how gradual climate trends and extreme weather events influence crop yields at different plant phenological stages. The effects of long-term climate change and short-term weather extremes on the productivity of chestnut and olive trees, two of the Mediterranean and Portugal's most economically and culturally significant perennial crops across various regions, were examined. Results reveal 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 period was associated with reduced chestnut yields. Concurrently, excess soil moisture during ripening correlated with decreased olive production in northern Portugal. In contrast, higher average temperatures, especially during ripening, improved olive productivity in southern Portugal. Overall, these findings indicate that the impact of climate variability is highly stage-specific and varies between species, emphasising the importance of phenological timing. Results also reveal significant interannual legacy effects, part of the impacts of climate change and extreme weather events. These aspects should be considered to enhance the precision of crop modelling and to develop effective adaptation and mitigation strategies for resilient agricultural systems under future climate scenarios, especially in Mediterranean regions where chestnut and olive trees are essential to rural economies and cultural landscapes.

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.

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.

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 Cávado) 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 Cávado (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.

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 (CO₂) and methane (CH₄), 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 CO₂ (pCO₂) and CH₄ (pCH₄) 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 pCO₂, whereas pCH₄ increased with oxygen depletion and water temperature. Discharge was positively linked to primary production, respiration and heterotrophy but correlated negatively with pCO₂. Our models indicate that CO₂‐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 pCO₂ were related to distal processes rather than local metabolism. In contrast, pCH₄ 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.

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.