Testing the applicability of diatom indices for ecological assessment of Balkan lakes

Abstract

During 2016-2017 six Balkan lakes were investigated: Sava Lake in Serbia, Ohrid Lake and Prespa Lake in North Macedonia and Albania, Great Lake in Albania, Biogradsko Lake and Crno Lake in Montenegro. Epilithic diatom samples were collected from 6 localities around each lake with the aim to test the applicability of diatom indices for ecological assessment of Balkan lakes. Also, water samples for chemical analysis were taken. Based on the concentrations of total phosphorus and BOD (biochemical oxygen demand) two lakes (Ohrid and Crno) were oligotrophic and oligosaprobic, while the other four lakes were mesotrophic and β-mesosaprobic, respectively. The highest diversity of dominant taxa was recorded in Ohrid and Prespa, and one of the dominant taxa was the endemic species Gomphonema paratergestinum. Diatom communities in lakes Sava and Crno were dominated by Achnanthidim minutissimum and Encyonopsis microcephala. According to Serbian legislation, the IPS index is used for the assessment of the ecological status of lakes, while in North Macedonia, Albania and Montenegro National Monitoring Systems do not yet include officially accepted diatom indices. In our results, the diatom indices IPS and IBD had the highest inclusion of diatom taxa, in some lakes almost 100%. The lowest inclusion of diatom taxa had the TDIL index. Values of IPS and IBD indices indicated very good water quality for Great Lake, Crno and Biogradsko, and good for Prespa. The water quality of Ohrid and Sava was between very good and good. Values of trophic indices (Rott TI and TDIL) indicated a very low concentration of nutrients in the Sava, Great Lake and Biogradsko, low in Ohrid and Prespa and low to the very low concentration of nutrients in Crno. The development and establishment of monitoring systems in lakes according to the requirements of the Water Framework Directive (WFD) is essential for all European countries and more comprehensive ecological investigations of Balkan lakes are necessary to be able to fulfill these demands.