Taxonomic and functional Odonata assemblage metrics: macrophyte–driven changes in anthropogenically disturbed floodplain habitats

Floodplains are heterogeneous systems adjacent to large rivers periodically flooded by water originating from the river’s lateral flow. During floods, the water flows into the surrounding channels, ponds and lakes, creating an integrated dynamic system characterized by a mosaic of lotic and lentic habitats and by the exchange of nutrients and inhabiting organisms between the main river and its floodplain. This study included a total of 14 sampling sites in a floodplain of the Danube River, designated as a Ramsar site. Seven study sites were in near natural condition, while seven others were separated from the Danube floodplain by an embankment and thus were anthropogenically disturbed (e.g. by hydro–morphological alterations and pollution from agricultural fields). Odonata nymphs were sampled over a two–year period in each season using a benthos hand net. A total of 20 Odonata species were recorded. Some of the documented species are of national and/or international conservation concern, which confirms the conservation value of the habitats studied. Species richness, abundance, taxonomic and functional diversity of Odonata were significantly higher at the anthropogenically disturbed sites than at the near natural sites within the studied floodplain area and correlated positively with macrophyte assemblage metrics (species richness, abundance, diversity). The macrophyte assemblage metrics, water transparency, copper and nitrate concentrations and oxygen saturation in the water were key environmental factors shaping Odonata assemblages in the studied floodplain. As Odonata are used as bioindicators of freshwater status worldwide, the presented results could be used in the protection of endangered wetland ecosystems and their biota. The importance of aquatic macrophytes for the conservation of the local Odonata diversity should be considered in the management of anthropogenically disturbed habitats in protected areas.