Application of Experimental Metrics Based on Macrozoobenthos for Ecological Status Assessment of Bulgarian Standing Water Bodies

Surveys on benthic macroinvertebrate communities of ten standing water bodies (Bezbog, Kalin, Choklyovo marsh, Bistraka, Dospat, Stoykovtsi, Drenov dol, Pchelina, Dolna Dikanya, Dyakovo) were conducted in the period July-August 2018. They were chosen to represent natural (lakes) characterized with reference conditions as well as artificial and heavily modified water bodies (dams). They were associated with earlier data for three dams (Studena, Pyasachnik, Ovchi kladenets), studied over the period 2013-2017. The standing waters fall into the West and East Aegean Basin districts and belong to all types of water bodies (identified according to the Bulgarian typology) located in the Ecoregion 7 (L1-Glacial high-mountain lakes/Alpine lakes, L3-Mountain lakes, L4- Lowland and semi-mountain lakes and swamps, L6-Riverside wetlands, L11-Large deep reservoirs, L13-Medium-size and small semi-mountain reservoirs, L15 Large lowland reservoirs up to middle depth, L17-Small and medium size reservoirs). A current evaluation based on the values of the measured physicochemical parameters, regulated by the national water legislation was made. Four experimental biological metrics - Total number of taxa, Biotic index for slow-flowing river stretches, percentage of Oligocheata and PETI were applied to assess the ecological status of the studied water bodies. The Biotic index is leading in the evaluation, others metrics have a supportive role. The lack of type-specific scales of the indices used, insufficiently long ranges of data sets on which to test the methods as well as the anthropogenically induced fluctuations at the water level which affects the distribution of macrozoobenthos in the sampling littoral zone are the main difficulties for a more precise assessment of the ecological status/potential of standing water bodies in Bulgaria.