Abstract
The study aims to conduct biological monitoring of the Kayaliika and Mechka Rivers (Maritsa River catchment) based on the biological quality element macrozoobenthos. For the study, the lower reaches of the Kayaliika River (Varbitsa biotope) and Mechka River (Debar and Lyubenovo biotopes) were visited. The studied rivers belong to Type R5 “Semi-mountainous rivers” in Ecoregion 7, the Eastern Balkans. Sampling was carried out during the spring and summer seasons of 2024. Forty-one taxa (744 specimens) of macroinvertebrate organisms were identified from the Kayaliika River, and 43 taxa (1722 specimens) from the Mechka River. The discovered macroinvertebrate taxa belong to 17 orders (Allogastropoda, Amphipoda, Arhynchobdellida, Coleoptera, Crassiclitellata, Diptera, Ephemeroptera, Hemiptera, Hygrophila, Isopoda, Littorinimorpha, Odonata, Rhynchobdellida, Sphaeriida, Trichoptera, Tricladida, Tubificida). In the Mechka River, Debar biotope was recorded as having the presence of Nematoda. The biomonitoring was conducted in accordance with a methodology approved by the country and the European Union. Basic metrics (the total number of taxa; number of taxa from the orders Ephemeroptera, Plecoptera and Trichoptera (EPT); % (Oligochaeta and Diptera); % Filtering feeders; % EPT taxa; Shannon-Weaver species diversity index; saprobic index; trophic index; adapted Biotic Index) were calculated and discussed. The study found a deterioration in the ecological state of both rivers in their lower reaches, compared to previous years.
Keywords: Bulgaria, ecological state, indicator taxa, Maritsa River basin, metrics