Abstract: Bacterial production (BP) is essential to ecosystem functioning because of the importance of microorganisms in the biogeochemical cycling of carbon and other nutrients, as well as the transfer of energy through trophic levels. In surface waters, BP is controlled by water temperature, the concentration and chemical composition of dissolved organic carbon (DOC), nutrient availability, and lake mixing. However, certain aspects of individual controls, such as the relative importance of different DOC compositions for BP, as well as how these controls collectively influence BP at the whole-lake scale, are poorly understood. My dissertation work will evaluate how BP is controlled at the ecosystem scale by answering three interconnected questions. First, what is the relative importance of phytoplankton-derived DOC versus terrestrial-derived DOC for BP? Second, what are the interactive effects of DOC composition and temperature on BP. And third, how does weather variability, including rapid changes in temperature, affect BP in lakes? These questions will be answered by analyzing long-term BP and climate records, and by experiments on DOC composition, temperature fluctuation, and DOC-temperature interactions.