UNIVERSITY OF NOVA GORICA GRADUATE SCHOOL Uroš ŽIBRAT DEVELOPMENT OF A NEW BIOTIC INDEX BASED ON HYPORHEIC FAUNA FOR WATER QUALITY DETERMINATION IN LOTIC ECOSYSTEMS

We assess water quality and the status of water bodies with numerous variables, both abiotic and biotic. Up to date, few water quality assessment and ecoremediation measures took the surface water – groundwater ecotone (i.e. the hyporheic zone) into consideration. We developed a new index based on hyporheic copepod fauna. The copepod biodiversity in the hyporheic of 26 Slovenian rivers, belonging to all five river basins, was assessed, and 49 species, belonging to 6 families were found. Species accumulation curves and richness estimators indicated that our sampling effort was sufficient, all estimates pointed toward a richness of 50 species. Two biodiversity hotspots were identified, but one of them was found to have an uneven species distribution, indicating human-impacted sites. One species (Moraria radovnae) appears to be endemic. Differences in relative abundances of the most common species accounted for most of the differences between river basins. The hyporheic copepod community, combined with an accurate typology and diversity measures, and while considering the limitations of our model, can be used for water quality assessment. The obtained final model is most accurate in mid-range classes, while being inaccurate at extreme values. By developing this index and promoting its use in water quality assessment and environmental impact studies, we can expand currently applied methods.