Baski Altindaki̇ Siğ Göller: Gölleri̇n Küresel Deği̇şi̇me Verdi̇ği̇ Tepki̇yi̇ Yönlendi̇rmede Zooplanktonun Rolü, Bi̇r Mezokozm Yaklaşimi

Zooplankton communities are key components of lakes because they occupy a central position in the energy flow of freshwater ecosystems. Predictions driven by climate-driven and human-induced factors suggest significant alterations to the structure and function of freshwater ecosystems, with potentially profound impacts on zooplankton, among other components. Lakes are increasingly threatened by stressors: microplastic (MP) pollution associated with anthropogenic effects, inputs of dissolved organic matter from terrestrial sources (tDOM), and rising temperatures associated with climate change. Although some potential effects of these stressors on freshwater ecosystems are well known, their specific effects on zooplankton, particularly regarding trophic interactions within the food web, are poorly understood. To address this gap, this thesis investigates the effects of MP ingestion and presence on zooplankton, including the subsequent bottom-up and top-down consequences, the influence of different tDOM sources on zooplankton with varying qualities, and the combined effects of tDOM and warming on zooplankton. Using a mesocosm approach, the research revealed that while MP ingestion by zooplankton was low and species-specific, it still had the potential to functional feeding groups. tDOM additions had complex effects, with different sources impacting zooplankton biomass and community composition through bottom-up effects mediated by changes in seston quality. Finally, terrestrially derived dissolved organic carbon (tDOC) negatively impacted zooplankton biomass and size and its combination with warming had a synergistic effect on zooplankton. This thesis highlights the significant ways global change stressors can impact zooplankton, emphasising the importance of understanding these effects for predicting future changes in lake ecosystems.