A Century of Human-Driven Changes in the Carbon Dioxide Concentration of Lakes
Abstract:Now that evasion of carbon dioxide (CO2) from inland waters is accounted for in global carbon models, it is crucial to quantify how these fluxes have changed in the past and forecast how they may alter in response to future local and global change.
Here, we developed a sediment proxy for the concentration of summer surface dissolved CO2 concentration and used it to reconstruct changes over the past 150 years for three large lakes that have been affected by climate warming, changes in nutrient load and detrital terrigenous supplies. Initially CO2-neutral to the atmosphere, all three lakes subsequently fluctuated between near-equilibrium and supersaturation. Although catchment inputs have supplied CO2 to the lakes, internal processes have ultimately regulated decadal changes in lake surface CO2 concentration. Nutrient concentration has been the dominant driver of CO2 variability for a century although the reproducible, non-monotonic relationship of CO2 to nutrient concentration suggests the interplay between metabolic and chemical processes. Yet, for two of these lakes, climatic control of CO2 concentrations has been important over the last 30 years, promoting higher surface CO2 concentrations, likely by decreasing hypolimnetic carbon storage. This perspective challenges current knowledge on the processes and environmental drivers of variability in long-term CO2 concentrations in lakes.