Effects of Warming and Increased Dissolved Inorganic Carbon on Phytoplankton Chlorophyll-a Concentration in a Freshwater Ecosystem

Freshwater phytoplankton communities are currently being influenced by ongoing climate change. This study aimed to investigate the effects of warming and dissolved inorganic carbon (DIC) on chlorophyll-a concentration and physicochemical variables in a freshwater ecosystem in mesocosm conditions. A 21-day experiment was conducted using freshwater collected from the Tigris River. Four treatments were established: control, warming (+3 °C), DIC, and DIC + 3 °C, with three replicates for each treatment. Chlorophyll-a, DIC, water temperature, pH, dissolved oxygen (DO), nitrate (NO3−), and phosphate (PO43−) were measured throughout the experiment. The results showed that chlorophyll-a concentration increased under warming and DIC treatments. The combined treatment (DIC + 3 °C) showed the highest chlorophyll-a concentration. Water temperature was significantly higher in the warming treatment compared to DIC treatment. In addition, pH, DO, nitrate, and phosphate varied among treatments and over time. Overall, the combined effects of warming and DIC were greater than those of the individual treatments. These findings indicate that warming and increased inorganic carbon availability may play an important role in influencing chlorophyll-a concentration, carbon cycling, nutrient dynamics, and water quality in freshwater ecosystems.