Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss¹. Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity². Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity.

The present study provides data on the trophic structure of the benthic macroinvertebrate communities in mountainous and semi-mountainous small streams and river sections belonging to Mesta, Struma and Vardar River catchments from 7th Ecoregion. The benthic macroinvertebrates were assigned to seven Functional Feeding Groups. We analyzed their trophic structure and the dynamics in different seasons. The level of similarity between the sampling localities was analyzed in the context of both the river typology and the water catchment. A comparison between the two trophic indices was conducted in order to analyze the advantages of the application of these indices for assessment of the ecological status at the studied sites. We found that the trophic structure of the benthic macroinvertebrate communities in ostensibly typologically similar river sections differs at the undisturbed vs the impacted sampled sites. To a large extent, these differences were also determined by the presence of anthropogenic influence that resulted in the predominance of deposit feeders amplifying on higher disturbance on some of the studied rivers. Long-term negative pressure has led to changes in microhabitats that affect the structure and functioning of the aquatic ecosystem by transformation of the trophic structure of the macrozoobenthos.

This study is focussed on the redescription of Ecdyonurus (Ecdyonurus) russevi Braasch & Soldán on the basis of the type material (holotype and paratypes) and topotypes collected in the Strandzha Mts. (Bulgaria). Female imago and subimago, larva and egg of the species are described for the first time and the male imago is redescribed in detail. The features distinguishing the species from other representatives of the genus Ecdyonurus are presented. Ecdyonurus russevi differs by the combination of several characters in the colour pattern of abdominal terga and wings, colour of lateral portion of male eyes and male genitalia structure in adults; some overlap has been observed in the number of groups of setae, bristles and hair-like setae on maxillae and labial palps, shape of pronotal projection and colour of tarsi in larvae; and insignificant number of knob-terminated coiled threads on exochorion, with only a few such attachment elements on one pole in eggs. Biology and present distribution of the species are discussed.

Introduction: Aquatic floodplain ecosystems along the Lower Danube are among most biodiverse freshwater habitats in Europe, yet they are increasingly affected by eutrophication, hydrological alteration and climate change. Long-Term Ecosystem Research (LTER) provides a framework for integrating biodiversity observations with environmental drivers across these ecosystems. Scope: The study aimed to assess the biodiversity and ecological status of aquatic ecosystems on two of the largest Danube floodpains - Brăila islands and Danube Delta, Romania. The objectives were to: characterize the qualitative and quantitative composition of phytoplankton, phytobenthos, macrophytes, zooplankton, and macrozoobenthos, and assess ecological status/potential using phytobenthos and macrophytes as biological quality elements. evaluate sensor-based versus microscopy-based monitoring methods for detection and assessment of the main algal groups. characterize the qualitative and quantitative composition of phytoplankton, phytobenthos, macrophytes, zooplankton, and macrozoobenthos, and assess ecological status/potential using phytobenthos and macrophytes as biological quality elements. evaluate sensor-based versus microscopy-based monitoring methods for detection and assessment of the main algal groups. Materials and Methods: Ecological monitoring was conducted in July 2025 at ten sites along the Lower Danube, including two Brăila Island lakes (Blasova and Zaton), two Danube sidearm stations along Brăila islands, three stations at Carasuhat Canal and three in Razim Lake. In situ measurements of temperature, dissolved oxygen, electrical conductivity, pH, as well as concentration of photosynthetic pigments like chlorophyll a , phycocyanin, and fluorescence-based algal group were measured using YSI EXO2 multiparameter probe and FluoroProbe BBE fluorometer. Five groups of organisms - phytoplankton, phytobenthos, zooplankton, macroinvertebrates, and macrophytes were sampled and taxonomically identified. Ecological status was assessed for phytobenthos (IPS/EQR) and macrophytes (AIM, RI/EQR) using national assessment methods for river type R6 and lake type L5. Phytoplankton abundance and biomass, as well as the richness and abundance of macroinvertebrate, zooplankton and macrophyte communities, were also determined. Results: Considerable differences in biodiversity and ecological status were observed among the investigated ecosystems. Phytoplankton richness reached 148 taxa (100 identified to species level): Cyanoprokaryota (35 taxa), Chlorophyta (72), Bacillariophyta (17), Cryptophyta (6), Euglenophyta (12), Chrysophyta (1), Pyrrhophyta (2), and Xanthophyta (3). Species diversity (Shannon index, H’) ranged from 1.59 at lake Blasova to 4.62 in the Danube Delta. Overall, 236 diatom taxa were identified, with nearly half exceeding 1% relative abundance in at least one of the samples. Most of the sites were dominated by halobious taxa, tolerant of higher salinity, particularly Lake Blasova, where marine-brackish species comprised approximately 90% of the diatom flora. The highest macrophyte diversity was recorded in Razim Lake, including the rare species Nuphar lutea and Trapa natans . The Danube sidearm stations were dominated by Vallisneria spiralis and Butomus umbellatus. Macroinvertebrates were most diverse (with more than 10 systematic groups) in Zaton and Blasova Lakes and the coastal part of Razim Lake, whereas the Danube sidearm upstream of Brăila and Carasuhat Canal supported less diverse communities dominated by molluscs, with bivalves prevailing at the river sites. Overall, 74 zooplankton taxa were identified, including 14 Crustacea (7 Cladocera and 7 Copepoda) and 60 Rotifera. Brachionus angularis was the dominant species in Brăila lakes, Brachionus forficula dominated Razim lake , while nauplii and copepodites co-dominated along with several Brachionus species in the Danube sites. The ecological status/potential based on phytobenthos ranged from bad (Lake Blasova and Carasuhat Canal) to poor (Carasuhat Site 2) and moderate (Danube, Razim Lake and Zaton Lake). The assessment based on macrophytes community classified Carasuhat Canal, Zaton Lake and Blasova Lake in bad ecological status/potential, while Razim Lake in moderate ecological status and Danube sidearm stations in moderate and good status. Fluorescence-based estimates of the major phytoplankton groups were comparable with conventional microscopy, with both methods generally identifying the same dominant groups, despite differences in the calculated contributions of cyanobacteria, green algae, and diatoms (PERMANOVA, p = 0.8616). Conclusion: The biodiversity and ecological condition of the investigated floodplain ecosystems differed, reflecting habitat heterogeneity and hydrological connectivity. Most sites exhibited poor to moderate ecological status despite their high biodiversity. The good comparability between fluorescence-based sensor measurements and conventional microscopic analyses indicates that sensor-based monitoring could provide a robust approach for long-term ecosystem assessment within the LTER framework.

The aim of the study is to report new country records of the symphoretic midge Epoicocladius flavens (Malloch, 1915) on its mayfly host Ephemera danica Müller, 1764 (Ephemeroptera: Ephemeridae). Sampling was conducted during spring 2022, in the upper section of the watershed of the Golema Reka River, Republic of North Macedonia. The specimens were collected with a hydrobiological hand net (mesh size 500 μm), through applying the kick-and-sweep multihabitat procedure. According to the published data, the distribution of E. flavens is scattered mainly across the Northern Hemisphere (Europe, North America and Asia). The species is usually found in greater numbers; however, we recorded only one midge of E. flavens on a specimen of E. danica. This finding contributes to the enrichment of the entomofauna of the Republic of North Macedonia but also adds new data on the distribution of the midge E. flavens within the Balkan Peninsula.