Water Quality of Lakes Ohrid and Prespa Based on Physical-chemical and Biological Parameters in 2013-2014

The urbanisation of environment and the application of phosphorus detergents and fertilisers with nitrogen and phosphorus as active components, substantially enrich the aquatic ecosystems with nutrients. This results in a disruption of the natural biological balance of the ecosystem, which certainly reflects on the water quality and trophic state of the aquatic ecosystem. The main aim of our study was to make a comparative analysis of nutrient (phosphorus) and organic loading of water in the littoral and pelagic zones of Lakes Ohrid and Prespa, as most important natural lakes in the Republic of Macedonia. The analysis of water quality was based on the results of monitoring of certain physical-chemical parameters (Secchi depth, biochemical oxygen demand, biodegradable organic matter, concentration of total phosphorus) and biological parameters (total number of heterotrophic bacteria, chlorophyll a concentration), in the period 2013-2014. According to the numeric values of the Carlson's Trophic State Index (TSI), calculated based on the total phosphorus, Secchi depth and chlorophyll a concentration, Lake Ohrid was determined in a stable oligotrophic state, while Lake Prespa was in a mesotrophic state, with a tendency towards an eutrophic state.