Springs, as unique ecotonal habitats between surface and hypogean areas, are considered endangered aquatic ecosystems due to direct and indirect human impacts and climate change issues. They are distinctive water habitats that are often inhabited by a diverse but mostly stenotypic group of organisms. The present study considered 31 springs from the Apuseni Mountains (the Romanian Carpathians) that were classified as rheocrene, helocrene, and limnocrene based on their geomorphology and hydrology. Samples from three substrate types (rocks, sand, and bryophytes) were collected using standard methods for crenic invertebrates. A total of 64,462 individuals belonging to 17 invertebrate taxa were identified: aquatic worms, mollusks, crustaceans, water mites, and insects. Amphipoda and Diptera–Chironomidae were the dominant taxa in most springs. At a community level, patterns of habitat preference were demonstrated for 12 invertebrate groups using the standardized selection index (B) and expressed as the number of springs where a certain group selected rocks, sand, and/or bryophytes: Four groups exhibited preferences for bryophytes (Coleoptera, Diptera, Plecoptera, and Trichoptera), Ephemeroptera exhibited preferences for rocks, and Copepoda exhibited preferences for sand. Amphipoda, Platyhelminthes, and Ostracoda displayed preferences for all three substratum types, while Gastropoda, Hydrachnidia, and Oligochaeta recorded lower percentages in springs where habitat preferences were significant. In addition, crenic invertebrates were divided into three guilds, depending on their dispersion abilities in any stage of their life cycle: sedentary (not-winged groups), mobile (winged groups), and ectoparasites (water mites that were able to leave the springs on their winged hosts). Sedentary taxa recorded higher percentages of abundances and habitat preferences towards rocks and sand, while ectoparasites (Hydrachnidia) and the mobile guilds tended to prefer bryophytes. This segregation might be explained by individual adaptations to the particularities of each type of substratum, such as the bodily form of the copepods, which are well suited for sand interstices, a habitat that our data showed that they preferred. Our results represent novel contributions to the knowledge of habitat preferences of spring invertebrates from the Apuseni Mountains, adding value to similar data from the Western Carpathians, the Alps, and the Dinaric region.

We investigated the phytoplankton, periphyton and microcrustacean communities developing on similar limestone substratum, in three karstic lakes: Iezerul Ighiel (Alba County), Dracului and Ochiul Beiului (Caraș-Severin County), during 2014 and 2016. Species richness was significantly higher in the lake greater in size for both algae and microcrustaceans, consistent with the species-area hypothesis. Forty algal taxa and only one microcrustacean species were common in all three lakes, even if comparable physico-chemical characteristics were recorded. Relatively similar saprobic conditions were shown by indicator species, while trophic state differed at some extent. Since current factors existing in the three environments were relatively similar (limestone substratum, physico-chemical parameters, water source etc.), the dissimilarities found in the plankton and periphytic communities were best explained by long-term factors like geographical isolation or the strength of disturbances. Ciorca et al (PDF)

This study examines fish communities in the heavily impacted Bistrița River, located in the Eastern Carpathians of Romania, where diffuse pollution from mining, domestic wastewater, agricultural and forestry activities emerged as the most severe pressures. Fish sampling was conducted at twenty sites across two Natura 2000 protected areas. Results showed that species richness and diversity were higher downstream (Z1–Z5), indicating improved ecological conditions compared to the upstream section (B1–B15). The fish-based Index of Biological Integrity (IBI) suggested overall good biological integrity, with excellent conditions (class I) recorded in 70% of sites. Redundancy analysis (RDA) further revealed that elevation and conductivity significantly shaped community structure, while the site-specific impact score had only marginal effects. To assess water quality and biotic integrity based on different communities, as required by the Water Framework Directive (WFD), five sites were selected for parallel sampling of diatoms and benthic invertebrates. Among these, zoobenthos proved the most sensitive to water quality degradation, with biotic indices indicating classes I to III. These findings demonstrate that assessments based solely on fish may underestimate ecological impacts, underscoring the need for complementary approaches that account for multiple biotic communities when monitoring riverine ecosystem health.

This research is aimed mainly at the assessment of water quality of several drinking water treatment plants and groundwater wells, from the Danube Delta Biosphere Reserve and the habits of the local population in terms of water consumption and use. Thus, the study highlights the presence and distribution of prokaryotic and eukaryotic assemblages, specifically the algal communities which emerged as a dominant group in the investigated drinking water sources. The spatial variation of the pH, EC, turbidity, dissolved oxygen (DO), temperature, algae species and biomass was measured in five drinking water treatment plants (DWTP) and three groundwater wells from villages located in the Danube Delta Biosphere Reserve. No PCR product was present for either genes coding anatoxin, microcystin and saxitoxin. The bbe- Moldaenke technique identified the presence of sligthly more algal groups, than the light microscopic technique; both methods show clear results: the water treated in the drinking water treatment plants has significant algal biomass. The water quality indicated by the algal communities shows oligo-β-mesosaprobic conditions, despite the high number of taxa and individuals from Sf. Gheorghe and C. A. Rosseti samples, they reflect oligotrophic conditions. Torok et al (PDF)

The unique geomorphological and hydrological characteristics along with the stable abiotic parameters have shaped springs into suitable aquatic habitats for a high number of microorganisms. Increasing anthropogenic impact, such as groundwater pollution, alteration or destruction of the eucrenal spring area and high demand for pristine water, are affecting the crenic biodiversity. The present study is the first to focus on taxa belonging to the Bacillariophyta phylum and includes diatom samples taken from 30 karstic springs located in the Apuseni Mountains, Romania. Because diatoms often display distinct preferences for specific substrates, 15 samples were collected from each spring: five from each of the three substrate types (bryophytes, stones, and fine sediments) within the eucrenal area. For qualitative assessment, three mixed samples were subsequently prepared for each substrate type, resulting in a total of 99 analysed samples. A total of 216 taxa were identified in the analysed samples, with 16% found only on bryophytes and 15% occurring only on sand. Two groups of frequent taxa, distinguished by their preferred substrate type and present in at least 25 springs have been observed: Caloneis fontinalis (Grunow) A. Cleve, Cocconeis lineata Ehrenberg and Meridion circulare (Greville) C. Agardh in epibryon, followed by Gomphonema parvulum (Kützing) Kützing and Planothidium dubium (Grunow) Round & Bukhtiyarova in epipsammon; three taxa Achnanthidium minutissimum (Kützing) Czarnecki, Amphora pediculus (Kützing) Grunow and Cocconeis placentula Ehrenberg stand out as a dominant group across all three types of substrates. Moreover, in the epilithon these were the only taxa present in all samples. Microhabitat-specific richness was shaped primarily by light conditions and canopy cover, with oxygen availability contributing as a secondary factor. Gomphonema elegantissimum E. Reichardt & Lange-Bertalot and Caloneis fontinalis, along with other 13 taxa have been identified for the first time in Romania. Article history: Received 26 November 2025; Revised 07 December 2025; Accepted 08 December 2025; Available online 20 December 2025