DIATOM-BASED ECOLOGICAL STATUS ASSESSMENT OF INTERMITTENT SUB-MEDITERRANEAN RIVERS IN BULGARIA WITHIN TWO HYDROLOGICAL PERIODS

The ecological status of intermittent sub-Mediterranean rivers in Southern Bulgaria using benthic diatoms was studied during two hydrological periods (spring and summer). Epilithic diatom samples from 49 sites (37 intermittent rivers) were analysed following European standard protocols. Taxonomic composition and relative abundance of benthic diatoms were determined. Taxa richness, Shannon's index of diversity and Pielou's evenness index were calculated and compared between the two sampling seasons. The ecological status was established, based on the values of the IPS metric, applying for the first time the most recently developed river type-specific scale for Bulgarian intermittent rivers.