The forgotten piece of lakes’ carbon cycle

In this talk, Prof. Perga will explain why lakes and other inland waters are significant CO₂ emitters and why the underlying mechanisms remain debated. For decades, the metabolic theory, which attributes lake carbon cycling primarily to the balance between inorganic carbon fixation by primary production and release through respiration, has dominated our understanding. However, this paradigm fails to explain CO₂ emissions in many lakes, as well as the magnitude and long-term changes observed over the last 150 years. Increasing evidence shows that lake CO₂ excess can also result from inorganic carbon inputs from catchments, yet the role of these inputs remains underappreciated. A key gap lies in understanding how processes affecting total alkalinity (TAC) and dissolved inorganic carbon (DIC) regulate CO₂ fluxes at the lake-atmosphere interface. Drawing on paleo-ecological records, long-term observatories, high-frequency monitoring, and remote sensing, Prof. Perga and her team combined these observations in a physical-biogeochemical model to show how alkalinity inherited from catchment weathering can sustain the net positive CO₂ emissions of Lake Geneva. They further demonstrated that calcite precipitation, a process long overlooked, significantly boosts annual CO₂ outgassing, not only in Lake Geneva but across a variety of lakes worldwide, including some of the largest on Earth.