Longitudinal dynamics of Odonata assemblages in an anthropogenically impacted lotic system

Abstract

European lowland rivers are extensively impacted by hydromorphological pressures, and the relationship between individual benthic macroinvertebrate groups and these degradations are insufficiently investigated. Therefore, we studied distribution and ecological traits of Odonata inhabiting a lotic system in the Pannonian lowland ecoregion (ER 11) in Croatia affected by degraded water quality and hydromorphological stressors. The study encompassed multihabitat sampling of 20 longitudinally distributed sampling sites, selected for their representativeness of disturbances. Only five species were recorded withPlatycnemis pennipes(Pallas, 1771) andOnychogomphus forcipatus(Linnaeus, 1758) dominating. We found woody debris samples contained a disproportionately higher number of Odonata, especially Zygoptera, compared to all other sampled microhabitats. The downstream longitudinal increase in Odonata abundance was not followed by an expected increase in species richness. Only five (oxygen saturation, pH, ammonium, water temperature and total nitrogen) of the sixteen tested water quality parameters were significant variables in determining the variation of Odonata assemblages.Calopteryx virgo(Linnaeus, 1758) and juvenileGomphidaewere associated with sites of somewhat higher ammonium and total nitrogen concentrations while all other taxa showed a negative association to ammonium. Odonata abundances were affected by modification of the river channel where significant decrease in abundance was observed with increased modification. Our results suggest that even species with a broad ecological tolerance are sensitive to hydromorphological pressures and represent an important background for further research and conservation practices of lotic European Odonata.