Influence of small run-off HPPs in the Sreden Iskar river section (Iskar River, Bulgaria) on the benthic macroinvertebrate communities – preliminary study results

The effect of three small run-off hydro-power plants (HPPs) situated in the middle part of the Iskar River on the benthic macroinvertebrate communities was studied in 2019 and 2020. The diversity of the main benthic groups and their abundance at five sampling points along the river following the gradient of hydromorphological disturbance were traced. More than 75 taxa of species level, belonging to 15 systematic groups and 44 families were identified. The most diverse groups were Trichoptera (19 taxa), Diptera (17 taxa), Gastropoda (11 taxa) and Ephemeroptera (10 taxa). With a smallest number of species were the orders of Isopoda and Neuroptera, each presented by one species. For the study period the macroinvertebrate communities were very abundant. The groups with the highest number of specimens in total were: Diptera – 10092, Ephemeroptera – 8045, Trichoptera – 7500 and Gastropoda – 1368.