Assessing eutrophication vulnerability in Köyceğiz Lake: Climate change and basin developments impact trophic status

This study investigated the potential for eutrophication in Köyceğiz Lake, one of Türkiye's most important and sensitive ecosystems. We developed a simple steady-state eutrophication model system using a phosphorus mass balance model for the lake, utilising open-access data from the literature as input. The model was calibrated and validated, with a specific focus on the eutrophic state of Köyceğiz Lake, and it demonstrated good responsiveness to future predictions. Our findings revealed that both the epilimnion (TSI (TP) 56) and hypolimnion (TSI (TP) 70) of Köyceğiz Lake are eutrophic. Considering climate change impacts and developments in the basin, we conducted projections to determine the lake's trophic status between 2035 and 2095. By 2035, a 65% decrease in freshwater inflow and a 4% increase in total TP load will lead to a hypertrophic status, which will persist and gradually worsen to a severe trophic situation by 2095.