Anna Maria Goździejewska

Hydrological connectivity regulates water residence, resource availability and dispersal across freshwater networks, but its links with microbial community organisation remain difficult to resolve in spatially complex deltaic systems. We combined stable water isotopes, hydrochemistry and 16S rRNA gene amplicon sequencing to examine bacterioplankton turnover across riverine, channel and lake habitats in the Danube Delta. Twenty sites were sampled in September 2023. Surface-water δ¹⁸O–δ²H values defined a coherent evaporation line (slope = 5.22, R² = 0.981), ranging from isotopically depleted river waters to enriched lake waters and indicating increasing evaporative influence and effective hydrological retention. Alpha-diversity metrics did not differ significantly among habitats, whereas Bray–Curtis dissimilarities revealed pronounced community turnover along the river–lake continuum. The primary axis of bacterioplankton variation was strongly associated with δ¹⁸O enrichment, linking microbial community organisation to independently resolved water history. Verrucomicrobiota increased towards isotopically enriched, DOC-rich lake waters, whereas Proteobacteria and Actinobacteriota were associated with more connected riverine conditions. A redundancy analysis constrained by DOC, conductivity, total nitrogen and total phosphorus explained 50.3 % of Hellinger-transformed phylum-level variation. Together, these results show that hydrological connectivity and water history are closely coupled to microbial community reorganisation and associated carbon and nutrient conditions across a heterogeneous deltaic network. Stable water isotopes therefore provide a process-based hydrological context for interpreting bacterioplankton turnover in freshwater landscapes.

Hydrological connectivity regulates water residence, resource availability and dispersal across freshwater networks, but its links with microbial community organisation remain difficult to resolve in spatially complex deltaic systems. We combined stable water isotopes, hydrochemistry and 16S rRNA gene amplicon sequencing to examine bacterioplankton turnover across riverine, channel and lake habitats in the Danube Delta. Twenty sites were sampled in September 2023. Surface-water δ¹⁸O–δ²H values defined a coherent evaporation line (slope = 5.22, R² = 0.981), ranging from isotopically depleted river waters to enriched lake waters and indicating increasing evaporative influence and effective hydrological retention. Alpha-diversity metrics did not differ significantly among habitats, whereas Bray–Curtis dissimilarities revealed pronounced community turnover along the river–lake continuum. The primary axis of bacterioplankton variation was strongly associated with δ¹⁸O enrichment, linking microbial community organisation to independently resolved water history. Verrucomicrobiota increased towards isotopically enriched, DOC-rich lake waters, whereas Proteobacteria and Actinobacteriota were associated with more connected riverine conditions. A redundancy analysis constrained by DOC, conductivity, total nitrogen and total phosphorus explained 50.3 % of Hellinger-transformed phylum-level variation. Together, these results show that hydrological connectivity and water history are closely coupled to microbial community reorganisation and associated carbon and nutrient conditions across a heterogeneous deltaic network. Stable water isotopes therefore provide a process-based hydrological context for interpreting bacterioplankton turnover in freshwater landscapes.

Background. A substantial body of scientific evidence indicates a close association between dietary habits, body composition, and athletic performance. Nevertheless, dietary inadequacies remain prevalent among athletes, including adolescents. The present study aimed to assess the body composition and dietary habits of participants in the Junior National Swimming Championships. Methods. The study included 39 female competitors (17.8 ± 0.2 years) and 88 male competitors (17.7 ± 0.4 years), all of whom provided informed consent to participate. Dietary habits were evaluated using a questionnaire developed in accordance with the principles of the Swiss Food Pyramid. Additionally, participants provided information regarding their training workload, including the number of weekly training sessions and the total distance swum during training. Body composition was assessed using bioelectrical impedance analysis (Tanita BC-418 MA). Results. Male swimmers exhibited significantly different values across all body composition variables compared with female swimmers (p < 0.05), whereas no significant differences were observed in training workload between the groups. Regardless of sex, the majority of participants reported consuming at least three meals per day, as well as the recommended amounts of dairy products and fruit. In contrast, fish consumption was below the recommended level. Female swimmers consumed sweet snacks and fast food significantly less frequently than their male counterparts (p < 0.05), whereas male swimmers reported a higher frequency of pork product and sugar-sweetened carbonated beverage consumption (p < 0.05). Conclusions. Young competitive swimmers exhibit several nutritional inadequacies. Although their consumption of fruit and vegetables generally aligns with current dietary recommendations, fish intake remains insufficient. Female swimmers demonstrated more favourable dietary patterns than male swimmers. Accordingly, ongoing nutrition education should constitute an integral component of the athletic training process.

The functioning of the trophic cascade in fishponds determines the ecosystem stability and breeding success. We investigated the trophic and competitive relationships in the meta-network of carp ponds. We hypothesised that small taxa of the zooplankton consumer level would play a dominant role in the community. The importance of taxa for biomass flux and the strength of interspecific relations were assessed using network graph modelling. Critical to the coherence of the meta-network were positive associations initiated by species that exploit different feeding niches and tolerate high cyanobacterial biomass, such as small cladocerans Bosmina longirostris and Chydorus sphaericus, and the rotifers Polyarthra longiremis. Negative associations, potentially reflecting predation and competitive exclusion, were less important. The observed characteristics of dominant species and their relationships made it possible to identify trophic pathways and their potential consequences for common carp culture. This study presents a new approach to understanding the functioning of the pond food web in aquaculture and may contribute to sustainable fisheries management.

Ecological management practices in fishponds are evolving rapidly, and zooplankton communities provide a reliable indicator of these effects. Over an eight-month period, in nine experimental ponds in the Czech Republic, we assessed the taxonomic, functional, and interspecific responses of zooplankton communities to three common carp feeding regimes: natural food with grain (NF), with 100% pellets (PP), and with a grain/pellet combination (WP), using redundancy analysis and correlation-based heat maps. The feeding regimes studied did not affect the taxonomic diversity of zooplankton, but significantly altered the abundance and biomass of Copepoda and raptorials. NF feeding resulted in the elimination of copepods, promoted functional variability of zooplankton, and enhanced interspecific interactions driven by large microphagous cladocerans (Bosmina, Daphnia), active rotifers (Asplanchna priodonta, Polyarthra longiremis), and the commensal Brachionus rubens. In contrast, year-round pellet feeding (PP and WP) preserved the importance of copepods but also led to the dominance of small mixophagous rotifers (Keratella quadrata, Brachionus diversicornis, Brachionus calyciflorus) and protozoa, promoting community homogenization and weakening interspecific zooplankton relationships. As the season progressed and trophic status, turbidity, primary production, and fish biomass increased, euryphagous and actively feeding species became increasingly prominent, resulting in a more heterogenous zooplankton network. Our study provides novel evidence that ecological management, particularly feeding regime, directly shapes zooplankton functional structure and interspecific dynamics in carp ponds.

The objects of this study were lakes Mielenko (LM) (7.8 ha, 1.9 m), Klasztorne Małe (LKM) (13.7 ha, 20.0 m), and Klasztorne Duże (LKD) (57.5 ha, 8.5 m), located in north Poland (Kashubian Lake District). These lakes received raw sanitary and storm wastewater, leading to extreme degradation of these water bodies. This study aimed to present changes in buffer indicators such as reaction, alkalinity, total hardness, and Ca and Mg content that occurred as an effect of their restoration using the sequential application of coagulants as an innovative approach to the phosphorus inactivation method. Sustainable phosphorus inactivation in the study lakes made it possible to achieve nutrient concentrations in the range of values typical for low-trophic lakes. A radical decrease in P concentration in the water resulted in a limitation of production processes. Moreover, after a, it was noticed that the water parameters determining its buffering properties did not show a clear vertical stratification with increasing values toward the bottom. For example, before restoration, the mean e value of alkalinity in LM fluctuated around 2.10 mval/L, and after restoration activities, the average value was 1.97 mval/L. In LKM, the mean alkalinity value in surface water layers was 2.53 mval/L, and in bottom water layers, it was 4.92 mval/L; after restoration treatments, the average alkalinity of surface water was 2.18 mval/L, and in bottom water, it was 2.99 mval/L. In the last LKD, under the influence of the applied restoration, the average alkalinity of surface waters changed from 2.21 to 2.07 mval/L, and in bottom water, it changed from 2.86 to 2.12 mval/L. The values of parameters determining the buffering properties of lake water after restoration activities allow their water to be classified as slightly or medium hard. The changes obtained can be considered beneficial because water that is too hard does not support the development of aquatic organisms, and the values obtained in the study lakes after sustainable restoration are optimal for the construction of plant walls, shells, and fish bones.

Zooplankton are critical indicators of pressures impacting freshwater ecosystems. We analyzed the response of zooplankton communities across different sub-catchment types—headwaters, natural, urban, urban-agricultural, and agricultural—within the Łyna river–lake system in Northern Poland. Using taxonomic groups and functional traits (body size, feeding strategies), we applied Partial Least Squares Regression (PLS-R) to elucidate the relationships between environmental conditions, land use, and zooplankton metacommunity structure. Two-Way Cluster Analysis (TWCA) identified local subsets with characteristic patterns, while Indicator Species Analysis (ISA) determined area-specific taxa. The natural river zone exhibited significant habitat heterogeneity and feeding niches, whereas urban areas created functional homogenization of zooplankton, dominated by small, broad-diet microphages. Agricultural areas promoted diversity among large filter feeders (Crustacea), active suctors (Rotifera), and amoebae (Protozoa). However, intensified agricultural activities, substantially diminished the zooplankton population, biomass, taxonomic richness, and overall ecosystem functionality. The impact of land cover change is more pronounced at small-scale sub-catchments than at the catchment level as a whole. Therefore, assessing these impacts requires detailed spatial and temporal analysis at the sub-catchment level to identify the most affected areas. This study introduces a new sub-catchment-based perspective on ecosystem health assessment and underscores the zooplankton's role as robust indicators of ecological change.

The long-term effect of physical activity on body composition in Master athletes is rarely presented in the literature. The aim of this study was to identify possible changes in body composition of Master swimmers over a period of 4 years, including during the COVID-19 pandemic. Additionally, we wanted to discover if sarcopenia symptoms would occur in Master athletes during the analyzed period. The body compositions of one hundred and sixty-seven Master swimmers were assessed with the InBody 270 analyzer in 2018. In 2022, the measurements were repeated in forty-six men and fourteen women. The Muscle Mass Index and the Skeletal Muscle Index were calculated to identify sarcopenia-related changes in body composition. We surveyed participants to gather data on their training patterns and SARS-CoV-2 infection history. No significant changes in body composition parameters were noted in Master swimmers during the analysis period (p > 0.05). Sarcopenia risk was not identified in examined athletes, and sarcopenia indicators did not change markedly over the 4-year period (p > 0.05). Participants with a history of SARS-CoV-2 infection did not differ from non-infected subjects in terms of body composition. Training cessation during the COVID-19 pandemic and SARS-CoV-2 infection did not induce long-term changes in body composition of Master swimmers. Life-long participation in swimming activities appears to delay negative changes in body composition, including sarcopenia symptoms.