Representativeness of Monitoring Sites for Ecological Status Evaluation of Water Bodies: Case Study of Chetirka (Logodashka) River and its Tributaries, SW Bulgaria

The study aimed to analyse the representativeness of the monitoring sites for the ecological status assessment of running water bodies through an example of a model systems: Chetirka (Logodashka) River and its tributaries Gabrovska and Leshtinska River as well as the section of the Struma River after the Chetirka inflow. Hydrobiological (benthological and physical-chemical) studies were conducted in the summer of 2016 at six selected representative sites affected by different types of anthropogenic pressures (habitat change, over-exploitation, contamination with nutrients, etc.). The data were compared to the ecological status assessment performed by the Bulgarian West-Aegean Basin Directorate during 2011-2018. The analysis of the associated physical-chemical parameters showed good-high status for all studied rivers and stretches. According to the Biotic Index, the Gabrovska River was determined in a high-good status whereas the Leshtinska, Chetirka and the section of the Struma River after the Chetirka inflow were characterised by moderate ecological status. The results obtained for the polluted sites demonstrate the need for more frequent monitoring observations at vulnerable sites exposed to adverse influences and droughts in order to prevent potential negative impacts on the main river basin.