Assessment of Ecological Potential and the Benthic Macroinvertebrates of Eight Reservoirs in Bulgaria

Hydrobiological monitoring and assessment of ecological status (potential) of eight Bulgarian reservoirs wеre carried out in 2015-2016. The water bodies are located in Ecoregion 7: West (Pchelina Reservoir) and East Aegean River Basins (Chetiridesette Izvora, Konush and Sinyata Reka Reservoirs) and Ecoregion 12: Danube River Basin (Bebresh, Telish, Gorni Dabnik and Sopot Reservoirs). We assessed their ecological potential based on hydrochemical parameters, Secchi disk transparency and chlorophyll a from pelagial samples. Semi - quantitative macrozoobenthic samples were collected from the littoral zone. We identified 102 macroinvertebrate taxa, including alien and (potentially) invasive species: Branchiura sowerbyi (Oligochaeta); Dikerogammarus villosus (Amphipoda); Dreissena polymorpha and Corbicula fluminea (Bivalvia). Based on the bioindicative role of macrozoobenthos, a set of biotic indices and metrics (Irish biotic index, total taxon number and the German trophic index PETI) were also used to estimate the ecological potential of the studied reservoirs. Our results demonstrated a mismatch between macroinvertebrate and abiotic assessment metrics. Therefore, further research is needed to improve the use of benthic macroinvertebrates as a biological quality element for the estimation of ecological potential of reservoirs in Bulgaria.