Determination of trophic status of lake kovada (İsparta) with indices

The lakes and dam lakes, among the world's most important aquatic ecosystems, are critical freshwater resources essential to humanity for various purposes; including agricultural irrigation, fisheries and aquaculture, tourism, drinking water sources, recreation, national parks, and water sports. Due to their diverse uses, increasing anthropogenic pressures, and recent global climate change, lakes are subject to growing negative impacts. Consequently, these systems are experiencing undesirable degradation and pollution. Among the most prominent of these issues is the rapid alteration of trophic status, particularly eutrophication. The ecosystem structure, pollution levels, degradation, usability, and sustainability of lakes are closely linked to their trophic status. Therefore, determining and interpreting their trophic status using objective, realistic, easily applicable, and calculation-based methods is crucial for lake management and conservation. For this purpose, various trophic state or level indices have been developed and are now being applied globally. In this study, the trophic status of Kovada lake, located in Isparta province and designated as a national park, was assessed and interpreted using monthly sampling and analyses conducted between May and October 2024. The Carlson Trophic State Index (CTSI), the New Zealand Trophic Level Index (NzTLI), the Turkish Surface Water Quality Regulation Index (TrTLI), and the OECD criteria were employed. Additionally, water quality measurements and analyses were conducted in the Kovada canal, which feeds the lake. The results indicate very high levels of total phosphorus, total nitrogen, and turbidity; alongside extremely low Secchi disk depth. According to all trophic state indices and criteria applied, the lake's trophic condition is classified as eutrophic to hypertrophic. All the indices used are proved as appropriate and effective for this assessment. It was observed that the Kovada canal significantly influences the lake's water quality and trophic state. Agricultural pollutants transported via the canal, along with drought-induced water level declines and progressive lake shallowing, are exacerbating eutrophication.