This study explores how rising temperatures across North America alter lake ecosystems, impacting organic matter (OM) composition, microbial activity, and greenhouse gas (GHG) production. We hypothesize that warming drives changes in OM source material and microbial communities, leading to more readily degradable OM and increased GHG release. Lakes across a temperature gradient (-1.8 °C to 7.2 °C) in the US and Canada will be sampled seasonally for two years. Mixed-effects models will analyze differences in OM composition and microbial function between lakes. This project will improve our understanding of how climate change affects lake ecosystems and their contribution to the global carbon cycle, informing strategies for mitigating climate change's impact on freshwater systems.