István Bácsi

Small hydropower plants are increasingly recognised as important drivers of hydromorphological alteration in river ecosystems, yet their effects on benthic diatoms remain insufficiently understood. We investigated the taxonomic and functional responses of benthic diatom assemblages to two operational-channel hydropower plants along the Hernád River (Hungary). Twenty-five benthic samples were collected from the main channel, operational channels, and hydromorphologically modified river sections. Taxonomic composition differed markedly among habitat types, whereas functional trait composition showed weaker differentiation, indicating functional redundancy despite pronounced taxonomic turnover. Species richness, effective Shannon diversity, and evenness did not differ significantly among habitat categories; however, functional richness and functional divergence revealed significant differences, highlighting functional reorganisation associated with hydromorphological modification. Significant distance–decay relationships were detected within both operational channels and modified river sections, suggesting that spatial structuring persisted despite river fragmentation. Fifteen threatened taxa and several non-native species were recorded, but neither habitat-specific segregation of threatened taxa nor invasion hotspots were identified. Our results demonstrate that small hydropower plants can substantially modify the taxonomic and functional organisation of benthic diatom assemblages without necessarily reducing local taxonomic diversity. The observed responses suggest community reorganisation rather than biodiversity loss and highlight the importance of maintaining longitudinal connectivity in regulated rivers.

Understanding how basin-scale heterogeneity influences phytoplankton in regulated reservoirs is essential for reconciling water management and conservation objectives. We analysed phytoplankton assemblages across five environmentally distinct basins and the Kis-Tisza of Lake Tisza during the exceptionally dry summer of 2022, when water levels were reduced to winter stage. The aim of our study was to investigate how spatial heterogeneity among these areas and temporal environmental variability jointly shape phytoplankton assemblages in a large, shallow reservoir system. Altogether 387 taxa were identified from 79 samples, revealing high species richness despite strong hydrological regulation. Significant spatial differences occurred in transparency, COD and nutrient concentrations, while temporal effects explained a larger proportion of community variation than spatial factors. Rare taxa (≈25% of all records) substantially contributed to basin-level richness, particularly in the protected, shallow Tiszavalk Basin and the relatively isolated Tiszafüred Basin. A clearly distinct assemblage was detected only in the intensively used, deeper Abádszalók Basin, characterized by mixing-tolerant centric diatoms, cryptomonads and euglenoids. Five threatened taxa listed on the Hungarian Red List were recorded, with higher occurrence in protected or isolated basins. Our findings demonstrate that although strong hydrological connectivity constrains basin-scale differentiation, protected and relatively isolated basins can contribute disproportionately to phytoplankton biodiversity and the occurrence of rare taxa. Explicit integration of algological biodiversity into reservoir management is therefore crucial in multi-purpose artificial water bodies facing increasing climatic extremes.

Here, we studied the influence of changes of aquatic phases (standing and flowing phases) and human-induced habitat variability (natural and artificial) on the composition and diversity of benthic diatom assemblages in a small lowland stream in the Pannonian Ecoregion. Significant differences in composition were hypothesized between phases and habitats. Lower diversity was hypothesized in the flowing phase and in the artificial habitat. In addition, worser ecological status were assumed in the artificial habitat and in the standing phase than in the others. Our results only partially supported our hypotheses. While there was no significant difference in the composition of the assemblages between the natural and concreted habitats, the alteration in flow conditions resulted in a significant change. No significant differences in diversity were found between aquatic phases. In contrast, biodiversity was higher in the artificial habitat than in the natural one. While the anthropogenic impact, i.e., concreted streambed has no significant influence on diatom-based ecological status, values of diatom indices were significantly higher in the flowing phase. Our results highlight that extreme weather events play a major role in shaping diatom assemblages even during a short period, which should be taken into account in water management and nature conservation measures.

Diverse macrovegetation can provide heterogeneous habitats for benthic diatoms. The removal of macrophytes as direct plant control, however, can be considered as a threat, which can even lead to remarkable microhabitat alterations. Lake Tisza (Hungary) has a high nature conservation value, but it is also an important recreation centre, which is why very delicate water management is necessary including vegetation thinning. Here, we studied the importance of microhabitat heterogeneity (emergent, submerged and floating macrophytes) in maintaining diverse periphytic diatom assemblages. We hypothesized that the substrate type has greater influencing role on the composition and diversity of diatoms than the lake heterogeneity related to basins. We also assumed that floating vegetation hosts the most different and least diverse diatom assemblages. Our results mostly proved these hypotheses. Heterogeneous assemblages were formed on the different substrates (support hypothesis), however, the basin level differences were also detected (reject hypothesis). Our results also highlighted, that macrophyte species with lesser morphological complexity hosted the least diverse periphytic assemblages (support hypothesis). However, many unique and red list taxa were found on floating plants (reject hypothesis). These findings emphasize the key role of microhabitat complexity in maintaining diverse and healthy functioning of microbial assemblages in a multi-purpose reservoir.

Mass production of microorganisms, algae among them, for new bioactive compounds and renewable innovative products is a current issue in biotechnology. The greatest challenge of basic research on this topic is to find the best solution for both physiology and scalability. In this study, the main goal was to highlight the contradictions of physiological and technological optimization in the same, relatively small, laboratory scale. The green alga Monoraphidium pusillum (Printz) Komárková-Legnorová was cultured in a conventional Erlenmeyer flask (as air bubbled in a tank-type photobioreactor) and in a hybrid (fermenter type + helical tubular type) photobioreactor of the same volume (2.8 L). Higher cell numbers from 1.7–2.3-fold, 2–2.8-fold higher dry masses, and 1.9–2.6-fold higher total lipid contents (mg·L⁻¹) were measured in the tank reactor than in the hybrid reactor. Cultures in the conventional tank reactor were characterized with better nutrient utilization (42.8–77.7% higher phosphate uptake) and more diverse lipid composition than in the hybrid reactor. The study highlights that well-scalable arrangements and settings could be not optimal (or unsuitable in some cases) from a physiological point of view. The results suggest certain developmental directions for complex, well-scalable devices and highlight the importance of testing the gained physiological optima on these systems.

Increased proliferation of algae is a current problem in natural and artificial water bodies. Controlling nutrients is the most sustainable treatment of increased algal proliferation, however in certain cases, it is not sufficiently available, or it does not provide results fast enough. Chemicals derived from natural sources, which could be effective in low concentrations and are biodegradable, may have an advantage over conventional chemical treatments. The main aim of the present study was to investigate the anti-cyanobacterial and anti-algal properties of allyl-isothiocyanate-containing essential oil produced from horseradish roots with a complex approach of the topic: on laboratory strains of cyanobacteria and eukaryotic algae, on microcosms containing natural phytoplankton assemblages, and on semi-natural biofilms. The results show that acute treatment can significantly reduce the viability of all the tested cyanobacteria and eukaryotic algae. Results of microcosm experiments with natural phytoplankton assemblages show that horseradish essential oil from 7.1 × 10⁻⁶% (v/v) is applicable to push back phytoplankton proliferation even in natural assemblages. The individual number in the biofilm was dropped down to one-fifth of the original individual number, so 7.1 × 10⁻⁶% (v/v) and higher concentration of the essential oil can be considered as a successful treatment against biofouling.

In wastewater, nutrient concentrations and salinity vary substantially, however, the optimal N:P ratio for the treatment using microalgae is not well described. In this study, the effects of higher and lower nitrate and phosphate contents and N:P ratios on growth, nutrient removal ability and halotolerance of the common green alga Coelastrum morus were investigated in model solutions. The results suggest that high nitrate content (above 100 mg L⁻¹) with a similarly high phosphate concentration (resulting low N:P ratio) is not favorable for growth. The studied isolate can be considered as a halotolerant species, showing remarkable growth up to 1000 mg L⁻¹ NaCl and it seems that despite the negative effects on growth, higher nutrient content contributes to higher halotolerance. A significant amount of nitrate removal was observed in media with different nutrient contents and N:P ratios with different salt concentrations. High N:P ratios favor phosphate removal, which is more inhibited by increasing NaCl concentration than nitrate uptake. Overall, with a relatively higher nutrient content and a favorable (5 or higher) N:P ratio, a common green algal species such as C. morus could be a promising candidate next to species from the Chlorellaceae and Scenedesmaceae families.

SUMMARY: Appearance of metals as pollutants in the environment is an increasing global problem. Microalgae as subjects of biological remediation methods may provide a cost‐effective and environmentally friendly alternative to the removal of metals during wastewater treatment. Despite the high number of data in the topic, there is still little information on how the type and the concentration of the metal affect the process of removal. In this study, correlations among the algal species, quality and quantity of metals and characteristics of metal removal mechanism were investigated at lower metal concentrations (0.2–5.0 mg L⁻¹) during zinc and copper removal of the green algae Desmodesmus communis and Monoraphidium pusillum. Analyses of the results proved that there is a statistically significant interaction (P < 0.05) between algal species and quality and concentration of the metals, that is, they have a significant effect on the mode and extent of removal. Both metals were mainly extracellularly bound, but at concentrations of 0.2–1.4 mg L⁻¹, intracellular proportion could exceed the extracellular adsorption. Although there were differences between the two algae, generally copper appeared in a higher intracellular proportion than zinc in the whole studied concentration range. Overall, the quality and initial concentration of the metal is decisive for the way of removal, the knowledge of which is useful for planning post treatment retention times or post treatment processes of the used biomass during wastewater treatment.