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Man-made freshwater habitats have been widely used to successfully modify the environment for human benefit, including purposes of irrigation, flood control or electricity generation. Over the past decade, our knowledge about the mayfly fauna and its ecology in South-East Europe has been growing, yet the data related to lentic assemblages remain very scarce. In this study, littoral mayfly assemblages were investigated at artificial and heavily modified lentic habitats in the Dinaric Western Balkan (n=21) and Pannonian Lowland (n=15) ecoregions. Mayfly nymphs were sampled during the summer months of 2016 or 2017. At each sampling site, ten samples were collected using a benthos hand net. A total of 21 mayfly species were recorded, though species richness per site was rather low (i.e., between zero and seven species). Cloeon dipterum (Linnaeus, 1761) was the most frequent species recorded, while Caenis horaria Linnaeus, 1758 was the most abundant. This study showed that the Croatian mayfly fauna is still growing, with the first record of Siphlonurus aestivalis Eaton, 1903 for the country. The assemblage structure was mainly dominated by lower reaches and lentic (potamal and littoral) elements and detritivores (gatherers/collectors and active filter feeders). Orthophosphates and chemical oxygen demand had the highest influence on mayfly assemblages, reflecting a higher level of pollution at sites in the Pannonian Lowland ecoregion, and consequently markedly lower mayfly abundances. As mayflies are widely used as bioindicators of freshwater ecosystems, detailed information about their assemblages in heavily modified and artificial habitats could contribute to future conservation activities of freshwater habitats and their communities. Additionally, these results could be applied in creating a monitoring system for artificial lakes according to the requirements of the European Water Framework Directive. [ABSTRACT FROM AUTHOR]

Under the EU Water Framework Directive, ecological assessment and management are based on type-specific reference conditions. In the EU it may be difficult to find sites in large rivers with at least near-natural conditions, though this is not the case in southeast Europe, where stretches of large rivers still exist with at least near-natural conditions, meaning that there is little or no disturbance from hydromorphological alteration, water quality, land use in the catchment and alien species. We examined benthic invertebrate assemblages in 45 samples collected from near-natural sites of several large rivers: Sava, Drava, Mura, Kupa and Una. The near-natural benthic invertebrate assemblages of large rivers contained several rare or remarkable species, especially among stoneflies, e.g., Marthamea vitripennis, Xanthoperla apicalis. We compared benthic invertebrate communities in river sections with fine and coarse substrates and in three eco-hydromorphological (ECO-HM) types of large rivers, reflecting habitat heterogeneity: lowland-deep, lowland-braided and intermountain. Multivariate analysis of variance (PERMANOVA) was used to statistically evaluate similarities among assemblages. It was found that the composition of benthic invertebrate assemblages varied by both ECO-HM types and substrate category. Similarity percentage (SIMPER) analysis showed that the average dissimilarity of benthic invertebrate assemblages was high between all ECO-HM type pairs and between fine and coarse substrate. We found that habitat heterogeneity and substrate independently influenced benthic invertebrate assemblages. To achieve ecological goals in the management of large rivers, in addition to functionality, a holistic view with at least near-natural assemblages, including the names of the taxa present, should also be considered. [ABSTRACT FROM AUTHOR]

Predicting anthropogenic actions resulting in undesirable changes in aquatic systems is crucial for the development of effective and sustainable water management strategies. Due to the co-occurrence of stressors and a lack of appropriate data, the effects on large rivers are difficult to elucidate. To overcome this problem, we developed a partial canonical correspondence analyses (pCCA) model using 292 benthic invertebrate taxa from 104 sites that incorporated the effects of three stressors groups: hydromorphology, land use, and water quality. The data covered an environmental gradient from near-natural to heavily altered sites in five large rivers in Southeastern Europe. Prior to developing the multi-stressor model, we assessed the importance of natural characteristics on individual stressor groups. Stressors proved to be the dominant factors in shaping benthic invertebrate assemblages. The pCCA among stressor-groups showed that unique effects dominated over joint effects. Thus, benthic invertebrate assemblages were suitable for disentangling the specific effect of each of the three stressor groups. While the effects of hydromorphology were dominant, both water quality and land use effects were nearly equally important. Quantifying the specific effects of hydromorphological alterations, water quality, and land use will allow water managers to better understand how large rivers have changed and to better define expectations for ecosystem conditions in the future. [ABSTRACT FROM AUTHOR]