Search Results (213)

Mediterranean rivers experience various pressures that cause native fish populations to decline. This is the case of Achondrostoma asturicense, a threatened endemic species recently classified as "endangered" (EN) by the Portuguese Red Book. In northeastern Portugal, the main populations occur in the Carvalhais (Tua basin), Maçãs, and Angueira (Sabor basin) rivers. This study aimed to evaluate the effect of small weirs on the distribution, abundance, and habitat use of A. asturicense populations along the longitudinal gradient of River Angueira. Three river zones (Z1 to Z3) affected by small weirs were selected along the watercourse. In each zone, four sampling sites were distributed relative to the weir, as follows: A1—200 m downstream; A2—immediately downstream; A3—under the influence of the reservoir; and A4—200 m upstream (reference). Sampling was carried out in three seasons: winter, spring, and summer 2025. Physical–chemical (water), hydromorphological (habitats), and biological (fish) elements were assessed in accordance with the protocols of the Water Framework Directive. The results revealed the worst water quality in the summer season due to flow reduction, dissolved oxygen depletion, elevated conductivity, and high nutrient (N, P) concentrations, leading to eutrophication phenomena. The distribution and abundance of A. asturicense were negatively influenced by the presence of small weirs, which were dominated by the non-native species Lepomis gibbosus. PERMANOVA analysis (two-way, p < 0.05) identified significant differences (Pseudo-F = 28.349, p < 0.05) between sampling sites and river zones, and paired similarity analysis tests (ANOSIM; one-way, p < 0.05) confirmed that these differences occur only between the weir reservoir (A3) and the remaining sampling sites. A. asturicense showed a maximum length (Lmax) of 135 mm, isometric growth only in the upstream zone (Z1), and significant differences in body condition (0.75 < K < 0.84). This species showed a preference for rheophilic habitats, with coarse substrate and diversity of currents and distinct cover mainly guaranteed by submerged aquatic macrophytes. A. asturicense populations are severely affected in the River Angueira by habitat fragmentation, riparian degradation, pollution, invasive alien species (e.g., L. gibbosus, P. clarkii, N. vison), and climate change, justifying the development of mitigation and restoration measures for the conservation of natural habitats and native threatened species. Full article

River restoration is increasingly promoted as a nature-based solution, but evidence of its ecological effectiveness in mountain gravel-bed rivers remains limited. Macroinvertebrate responses to hydromorphological restoration are variable and are still rarely evaluated using an integrated approach combining taxonomic, biotic index, and trait-based components. This study examined whether the hydromorphological restoration of the upper Raba River was associated with measurable environmental and ecological differences between the restored and unrestored sections. Six river sections were analyzed, including three restored and three unrestored sections. The environmental characterisation included hydromorphological and physicochemical variables. Benthic macroinvertebrates were sampled in shallow marginal and main-current habitats, and the analyses included assemblage metrics, biotic indices, taxonomic composition, indicator taxa, and functional traits. The restored sections showed greater channel complexity, including a larger active channel zone, a larger number of active channels, and a coarser substrate. These differences were accompanied by higher Shannon diversity, higher values of the Polish Biological Monitoring Working Party index (BMWP-PL), a higher percentage of individuals of Ephemeroptera, Plecoptera and Trichoptera (%EPT), distinct assemblage composition, and shifts in indicator taxa and selected functional traits. The results highlight the value of multidimensional assessment frameworks to evaluate the effects of restoration on mountain rivers. Full article

Introduction: The colossal European catfish (Silurus glanis) is the largest invasive freshwater fish on the Iberian Peninsula, reaching up to 2.8 metres and 130 kg in weight. Its large size makes it a highly valued target for recreational anglers, leading to repeated illegal introductions across several Iberian watersheds. Despite its appeal to anglers, this species is recognised as a high-impact invasive predator with substantial ecological consequences for European freshwater ecosystems. Recently, large catfish aggregations have been reported by anglers and environmentalists in several areas of Portugal and Spain. These impressive aggregations are frequently documented on videos and posted on social media networks (Facebook, WhatsApp groups, etc) or shared directly with our team members. Objective: Such records provide a valuable source of information for identifying the habitats and seasonal periods associated with aggregation behaviours and may therefore support more efficient management and population control actions. Methodology: We compiled information on European catfish aggregation events in Southern Iberia, namely date and location. The catfish aggregations were mapped, and their general habitat characteristics were described. Results: We recorded 10 catfish aggregation events, most of which occurred between May and June. These were generally located in transitional areas between lentic and lotic habitats, especially in narrower river sections. Possible explanations include hydromorphological constraints, seasonal environmental conditions, and species-specific behavioural responses, although these mechanisms require further investigation. Conclusions: Within the LIFE PREDATOR project, which focuses on the management of European catfish in the Tagus watershed, knowledge of aggregation locations is important to direct population control efforts aimed at reducing the abundance of this invasive fish. Moreover, the identification of common habitat characteristics may help predict other potential aggregation sites and improve the planning of future management actions. Full article

LIFE REVIVE aims to restore ecological status and ecosystem services in the Lima and Vouga river basins (NW Iberian Peninsula), where hydromorphological alteration and hydropower-driven flow regulation are major causes of water bodies failing to reach Good Ecological Status under the EU WFD. The project targets key pressures such as longitudinal fragmentation by weirs and dams, artificial flow regimes, degradation of spawning substrates, and the spread of invasive aquatic plants, which strongly affect fish communities, including sea lamprey, salmonids, and other diadromous species. Technically, the project combines barrier removal or eco-adaptation, nature-like fish passes, and spawning-habitat renaturalisation with optimized environmental flow regimes (EFR) downstream of important hydropower systems, explicitly accounting for present and future hydroclimatic scenarios. Multi-scale ecohydrological modelling (species distribution models, habitat suitability models, GLM/GAM approaches) will quantify fish–flow–habitat relationships and support the definition of operational EFR guidelines that balance ecological requirements with hydropower and agricultural constraints through joint work with the main Portuguese hydropower operator, EDP. Impact evaluation is structured around a rigorous BACI monitoring design in intervention and control tributaries, using standard WFD biological indices for fish and aquatic/riparian vegetation, hydromorphological indices (HQA, HMS, RHS), and project-specific Key Performance Indicators for water quality, biodiversity, and habitat. Expected outcomes include the restoration of at least 51 km of rivers towards free-flowing conditions, reduced hydromorphological pressure in more than 20 km of heavily modified river stretches, and measurable increases in the distribution and abundance of fish species and native vegetation. A strong communication and capacity-building programme underpins public engagement, while a decision matrix for barrier prioritization, technical workshops, and pilot replications in additional basins (e.g., Alva, Mouro, Deva, and Tea in Galicia) are designed to maximize transferability, policy uptake, and long-term sustainability of the solutions beyond the project lifetime. Full article

This study presents the revision of the Rabaçal River Recreational Fishing Area Management Plan (ZPL), implemented in 2020, aiming to evaluate its effectiveness and identify the need for adjustments after five years. The study area includes part of Montesinho Natural Park, covering water bodies upstream of the Vale de Armeiro Reservoir (RH3—Douro Basin), excluding the Assureira River sub-basin. The methodology followed the initial study design, with electrofishing conducted at ten stations (30 surveys). Hydromorphological and riparian conditions were assessed using the River Habitat Survey (RHS), enabling the calculation of the Riparian Quality Index (RQI), Habitat Modification Score (HMS), and Habitat Quality Assessemt (HQA). Results indicate high habitat diversity and overall good-to-excellent hydromorphological quality, although they are locally affected by human pressures and global change. Brown trout (Salmo trutta) was recorded at all sites, showing wide spatial distribution. Population structure was dominated by young individuals (≤2 years; 70%), indicating high recruitment rates. However, growth patterns and reduced body condition suggest that habitat features, particularly flow regime and riparian quality, are influencing population dynamics, highlighting the need to explicitly integrate habitat–population relationships into management measures. A notable expansion of the invasive signal crayfish (Pacifastacus leniusculus) was also observed (now present at stations T₃, T₄, and T₅), reinforcing the need for targeted monitoring and control actions. Overall, the results support the continuation of the current management model, aligned with the conservation objectives defined in the initial plan and in project POSEUR-03-2215-FC-000096, while emphasizing the importance of habitat conservation to ensure the long-term sustainability of trout populations and aquatic ecosystems. Full article

Mountain stream ecosystems are often considered among the least disturbed freshwater environments; however, increasing land-use pressures may affect their ecological integrity even under apparently high-water quality conditions. This study aimed to assess the relative influence of landscape, physicochemical, and hydromorphological factors on benthic macroinvertebrate communities in three sub-catchments (Ambroz, Jerte, and Tiétar) of the Sierra de Gredos (Central Spain). A total of 33 sampling sites were surveyed, and macroinvertebrate assemblages were analyzed in relation to environmental variables using partial Redundancy Analysis (pRDA) and variance partitioning. All sites were classified as having “Excellent” ecological status based on the Iberian Biological Monitoring Working Party (IBMWP) index. However, multivariate analyses revealed clear spatial patterns and responses to environmental gradients. Results indicated that catchment-scale landscape characteristics defined the pool of potential colonizers, while local physicochemical and hydromorphological conditions acted as secondary filters structuring macroinvertebrate assemblages. Landscape variables explained the largest fraction of variance in community structure (30.6%), followed by physicochemical parameters (29.0%) and hydromorphological indices (24.9%), with a significant shared component (16.5%) indicating interactions among drivers. Agricultural land use, particularly in the Jerte sub-catchment, was associated with shifts in community composition, favoring tolerant taxa such as Diptera, while sub-catchments dominated by natural vegetation supported higher richness of sensitive groups, including Ephemeroptera and Plecoptera. These findings highlight the importance of multi-scale processes in structuring mountain stream communities and reveal limitations of traditional biotic indices in detecting early ecological changes. The results support the integration of catchment-scale variables into ecological assessment frameworks and emphasize the need for preventive, basin-scale management strategies to maintain ecological integrity under increasing anthropogenic pressure. Full article

Urban streams typically exhibit altered hydromorphology and large fluctuations in water quality variables, creating stressful conditions for biota. In this study, we investigated periphyton along two urban streams (Bliznec, B, and Veliki Potok, VP) in Zagreb (the Croatian capital) over one year. Both streams were sampled in an upstream pristine reach within Medvednica Nature Park, a middle reach influenced by either agriculture or low-density residential areas (houses with gardens) and affected by channelization, and a lower reach, also channelized, impacted by a mix of agricultural influence and more intensive residential development with higher population density. Nutrient concentration, conductivity, COD, and chlorophyll a showed an increasing trend from upper to lower sites, reflecting the influence of urbanization. The number of periphytic taxa and their abundance correlated positively with the increasing urbanization, probably due to increased food sources. Periphyton consisted mainly of ubiquitous taxa, with 55 phagotrophic protist and 10 micro-metazoan taxa. Ciliates dominated both in diversity (44 taxa) and abundance (over 90% of mean abundance), mainly comprising bacterivorous taxa. Periphyton exhibited pronounced seasonal dynamics, with occasional high similarity between the two urban streams studied and high turnover rates of assemblages between samplings. This pattern indicates that urban streams support highly dynamic periphytic communities, strongly shaped by environmental disturbance and that these assemblages have the capacity to withstand frequent environmental variability in urbanization-influenced reaches. Full article

The assessment of the hydromorphological state of a river is fundamental for both correctly evaluating its ecological conditions and planning its restoration. Despite this, there is a critical gap in studies on this topic in Southern Italy, although they are recommended by several EU Framework Directives. This research provides a contribution to filling this gap by assessing the hydromorphological quality of the Middle and Lower Sabato River (Southern Italy), by using the method officially adopted by the Italian Institute for Environmental Protection and Research (ISPRA), named IDRAIM. The method presents the advantage of considering the specific Italian context in terms of channel adjustments and anthropogenic impacts. However, it also considers pre-existing geomorphological approaches developed in other countries that make the method applicable at least in the entire Mediterranean area. To apply the method, in this study, we used data obtained by GIS analysis, remotely sensed data, and field-surveyed data. The study has highlighted that, in the Middle and Lower Sabato R., eight river reaches out-of-fifteen have displayed a “moderate or sufficient” morphological quality, five reaches a “good” morphological quality, while the remaining two reaches have been characterized by a “poor” morphological quality. Functional alterations have seemed to prevail over artificiality and intensity of short-term channel adjustments in conditioning hydromorphological quality. These results will be a key starting point for already planned studies dealing with both the restoration of the Sabato R. and flood hazard and risk assessment. Full article

Mountainous Mediterranean rivers provide essential ecosystem services but are increasingly affected by land-use change, hydraulic works, and inadequate wastewater management. This study investigates the links between geomorphological transformation and river water quality in the Central Eurytania drainage basin (Greece) over the past two decades, within the institutional framework of European and Greek environmental legislation, with emphasis on the protection and restoration of aquatic ecosystems. Georeferenced satellite imagery from 2003/2010 and 2023, Google Earth Engine (GEE, Python Earth Engine API: 1.7.20)-based spatial analysis, high-resolution UAV orthomosaics, and seasonal spectrophotometric analyses were integrated to assess spatial and temporal dynamics. Results indicate that land-use changes, including the construction of solar parks, expansion of tourism infrastructure, and partial agricultural abandonment, reflect ongoing socio-economic shifts influencing fluvial processes. Water-quality analyses further showed that channel alteration and wastewater inputs jointly degrade ecological conditions. The findings highlight the need for integrated watershed management focused on riparian buffer restoration, improved wastewater control, and systematic monitoring of hydromorphological change. The proposed interdisciplinary framework contributes to the assessment of environmental resilience in Mediterranean mountainous watersheds, which are increasingly vulnerable to climatic and socio-economic pressures. Full article

Riparian vegetation plays an important role in the morphological evolution of rivers; here, an alternative numerical methodology for modeling river morphodynamics influenced by vegetation is presented. The approach integrates a vegetation growth and flow-resistance submodule coupled with the TELEMAC–MASCARET system. Vegetation is represented at the patch scale, and its hydraulic effect is incorporated through an additional drag force in the momentum equation, while stem obstruction is accounted for using the porosity formulation in TELEMAC-2D. Vegetation dynamics consider water depth variability, interspecific competition, and nutrient availability. The model is applied to a braided river reach in southeastern Mexico. The results indicate that riparian vegetation promotes more organized flow paths, enhances bar development, and plays a significant role in modulating bar stability. These findings highlight the importance of explicitly representing flow–sediment–vegetation feedback in river hydro-morphological modeling. Full article

The Varna–Beloslav Lake Complex has been subjected to intense anthropogenic pressure over the past century. The excavation of a navigation channel connecting the two lakes with the Black Sea, together with the intensive industrial development in the surrounding area, has led to irreversible alterations in the species composition of the ichthyofauna. This study aimed to document and analyze these changes based on data collected during a four-year survey using a range of ichthyological methods. A total of 28 fish species were recorded, representing approximately one-third of the species historically reported for the complex. Hydromorphological degradation, combined with salinization, heavy ship traffic and pollution, has been identified as the main cause of the observed decline in fish diversity within the system. Full article

Rivers are dynamic systems that flow from higher elevations to lowlands, eventually discharging into lakes, seas, or oceans, and play a key role in sustaining ecosystems and supporting human activities. River basin characterisation extends beyond the watercourse itself, encompassing land uses, tributaries and hydromorphological features that influence ecological processes. This review analyses three river basins in northern Portugal, Ave, Douro, and Vouga, using a holistic characterisation approach. These basins represent contrasting river systems in terms of size, hydrological regulation and dominant land uses, while simultaneously being subject to pressures frequently reported in many other river basins in Europe, and around the world. The analysis includes a general basin description, a hydromorphological assessment with emphasis on land use, and an evaluation of water ecological status, with particular focus on estuarine ecosystems. Water quality in the three basins has been strongly influenced by anthropogenic pressures, including industrial and agricultural activities, and wastewater discharges. Although the implementation of the European Water Framework Directive has led to improvements in recent decades, the degree of recovery varies among basins. Persistent challenges, such as nutrient concentrations, microbial contamination, and heavy metal pollution, highlight the need for integrated river basin management and improved monitoring strategies. This review provides transferable insights for the management of river basins facing similar environmental pressures. Full article

This study analyzes the hydro-morphological dynamics of the lower 40 km of the Magdalena River (Colombia), with particular emphasis on the reach between Malambo and the river mouth at Bocas de Ceniza. Bathymetric profiles obtained from three field campaigns conducted between 2017 and 2018 were used to characterize riverbed morphology and to quantify the evolution of subaqueous bedforms (dunes) under different flow conditions. The results reveal a systematic increase in dune height and wavelength with increasing discharge. The dominant discharge during the observation period was approximately 7400 m³/s, associated with a total measured sediment load of about 2000 kton/day, corresponding to a volumetric concentration of 0.12%. Variations in the Manning roughness coefficient were identified, ranging from 0.020 to 0.037, primarily driven by changes in discharge and, to a lesser extent, by spatial variability in hydraulic roughness, particularly in port areas. Bedforms exhibit significant growth during high-flow periods, consistent with findings reported in the literature. Analysis of mean velocity profiles indicates that the von Kármán coefficient varies with sediment concentration and turbulence intensity. Finally, a nature-based solution is proposed for the river mouth, consisting of reconfiguring the Thalweg in the final kilometers of the channel to replicate the meandering pattern of the adjacent bend. This intervention aims to enhance Thalweg stability, reduce saline wedge intrusion, promote sediment and flow dispersion toward the natural submarine canyon, and improve navigability at the river mouth. Full article

Riverbed siltation in estuaries affects ecosystem functioning, water quality, and navigation. This study investigates the flow-regulated Osellino Canal, a freshwater tributary of the Venice Lagoon that crosses a largely urbanized area and is undergoing progressive siltation. High-resolution measurements of discharge (Q) and suspended sediment concentration (SSC) were performed using hydroacoustic instrumentation from September 2019 to December 2021. The analysis examined discharge dynamics, sediment transport, and rainfall-runoff relationships. Results indicate a mean annual discharge of 2.1 m³ s⁻¹ and an average annual suspended sediment load of ~2900 ± 330 t. Discharge patterns were strongly influenced by water management, resulting in anomalous runoff coefficients (δ > 1) during dry periods. Sediment export proved to be strongly event-driven: episodic high-flow events accounted for about 23% of the total load despite representing only a small fraction of the study period. Furthermore, a strong linear relationship between runoff and sediment load (R² = 0.94) confirms an advection-dominated regime, where net export is regulated primarily by hydrodynamic volume rather than fluctuations in sediment supply. Bathymetric comparisons (2011–2019) reveal a mean annual sediment retention of 400 ± 100 t yr⁻¹, corresponding to a trapping efficiency of approximately 12 ± 3% relative to the gross sediment input. These findings, supported by SSL–runoff regression residuals, consistently indicate net sediment accumulation associated with the long-term malfunction of a miter-gate system that impedes efficient sediment export. This study provides a critical pre-rehabilitation baseline, establishing a benchmark to evaluate the effectiveness of ongoing restoration efforts initiated in March 2022 and the future hydromorphological recovery of the canal. Full article

Phytoplankton are key indicators of water quality and low-cost tools for freshwater monitoring, yet their diversity and ecological drivers remain poorly documented in the Tropical Andes. This study provides the first national-scale, multi-ecosystem assessment of net phytoplanktonic communities (including microalgae and cyanobacteria), across Ecuador, integrating physicochemical, multivariate, and geospatial analyses. Eighteen lakes and rivers from three biogeographic regions and a wide altitudinal gradient were surveyed, yielding 129 taxa, 77 identified at species level, the most comprehensive checklist reported to date for Ecuador. Community structure showed a clear lentic–lotic differentiation driven by hydrodynamic contrasts, while the absence of distance–decay patterns indicated high dispersal and environmental filtering pattern rather than spatial structuring. Anthropogenic pressure acted as a secondary gradient: pristine high-Andean lakes were dominated by desmids and diatoms, whereas agricultural and urban basins showed chlorophyte and potentially toxic cyanobacterial assemblages. Palmer’s Index detected organic pollution but underestimated eutrophication in endorheic, geochemically enriched lakes. Land-use effects presented strong basin-scale signals in lakes but weak correlations in rivers due to overriding hydromorphological constraints. These findings establish a robust spatial baseline for freshwater bioassessment in the Andes, demonstrating the value of phytoplankton as effective, low-cost indicators readily applicable to national water-quality assessment programs. Full article