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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. [ABSTRACT FROM AUTHOR]

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Classifying benthic diatom taxa based on ecological and morphological features became increasingly important in recent years due to the demand of understanding the dynamics and functioning of diatom assemblages. The great potential in using these functional classifications in diatom ecology involves further refinement of current classification. In our experimental study, colonisation processes of diatom assemblages were studied in a typical small lowland stream, using both diatom guilds and cell size categories. We also tested newly proposed combined eco-morphological functional groups (ecological guilds combined with cell size categories) in the study of the colonisation process in benthic diatom assemblages. We hypothesised that (i) there is a decrease in the proportion of low profile guild, while an increase in that of high profile and motile guilds in time with the decreasing rate of physical disturbance; (ii) the presence of small size categories will be pronounced at the beginning of the colonisation processes, while proportion of larger size categories will be higher in the latter phases of colonisation; and (iii) the relationship between taxa and environmental factors are better reflected by the use of combined eco-morphological functional groups than by the sole analyses of rough guilds or cell size categories. The first hypothesis was not confirmed, and our second hypothesis was only partially confirmed by the results. We found that the relationship between environmental factors and guilds, as well as cell size categories was not appropriate to reveal the relationship between abiotic factors and taxa composition. In contrast we found that compositional changes in colonisation were appropriately reflected by the newly defined combined eco-morphological functional groups. In the combined eco-morphological functional groups, such kind of taxonomical and ecological features can be prevailed which are hidden in guilds or cell size categories separately. Thus these combined eco-morphological functional groups could help to come one step closer to develop a widely used ecological classification in diatom researches. [ABSTRACT FROM AUTHOR]

Functional classification based on species traits brought a revolution in community ecology, and also boosted phytoplankton and in phytobenton (diatom) research. Several studies stressed the usefulness of phytoplankton functional groups in ecological status assessment, and there is also a strong emphasis to use combined traits in ecological assessments of diatom assemblages. The Combined Eco-Morphological Functional Groups (CEMFGs) help to reveal species-environmental correlations, which can be hidden, controlling traits separately. Nowadays, there are three types of functional guild classifications simultaneously used in the literature: (i) the original classification proposed by Passy (O); (ii) Passy’s classification complemented with a separated planktic guild (P); (iii) the refined guild classification by Rimet and Bouchez, also containing the planktic guild (RB). One of the most important criteria of the combined functional groups is the well-defined ecological frame of these combined groups; thus it is vital to harmonise the classification of the taxa into guild based combined eco-morphological functional groups (CEMFGs). In this study we tested the similarities and dissimilarities of the correlations between environmental factors and CEMFGs created in the (i)-(iii) classifications. Samples were collected in 138 sampling sites on lowland rivers and streams in the Hungarian Lowland Region. Strong correlations were anticipated between the functional groups and environmental factors due to the presence of common and/or abundant planktic taxa. Our results validated the necessity of a separated planktic guild in ecological assessments of diatom assemblages. Further relevant differences between the correlations of CEMFGs-P or CEMFGs-RB and abiotic factors were hypothesised in the case of those functional groups which contained reassigned taxa with high frequency and/or abundance. Our results confirmed this hypothesis. Furthermore, the present study also highlighted the relevance of well-defined trait classification. Abundant and/or frequent taxa, which are able to change their life forms, can modify significantly the relationship between the functional group containing them and environmental factors. In the future, both field and laboratory studies should focus on revealing the circumstances, which cause the mentioned changes in traits of diatoms. [ABSTRACT FROM AUTHOR]

• Effects of decreasing precipitation and one-off drought events on diatoms were studied. • Continuously decreasing precipitation induced strong compositional changes. • Extremity-tolerant diatom traits were dominant in drying period. • Continuously decreasing precipitation resulted in a biodiversity loss. • Reduced precipitation did not cause deteriorating ecological status. Changing precipitation dynamics is one of the most important mechanisms that, by affecting the water regime, modifies the physical and chemical environment of aquatic assemblages. Thus, hydrological extremes can be considered as key drivers that shape algal assemblages and lead to diversity changes even in large rivers. Here, we investigated the long-term changes in the benthic diatom composition of the Rába River (River Raab), the watershed of which experienced continuous loss of precipitation in the last five years. We aim to answer the main question: Do one-off drought events and trend-like (continuous) precipitation decrease result in similar changes within diatom assemblages of this perennial river? Because, it has been already demonstrated that resilience and resistance of assemblages may vary depending on whether the drought occurs regularly or only occasionally. Our results demonstrated that one-off dry events hardly affected either assemblages' composition or biodiversity. In contrast, continuously decreasing precipitation (drying period) had a pronounced effect on taxa and trait distribution and resulted in a significant decrease in taxonomic diversity and in functional richness. It is important to stress that the observed deteriorating diversity anticipates that a lasting drought period is likely to upset the ecological balance of the ecosystem and lead to remarkable natural damage. Since the climate scenarios project extremes in water regime in the near future, including longer periods of low precipitation, any knowledge that predicts changes in microflora can help to develop action plans by authorities to save lotic ecosystems. [ABSTRACT FROM AUTHOR]