SPATIALLY-EXPLICIT SCALING OF REGIONAL LAKE CARBON FLUXES (Invited Presentation)

Lakes are areas on intense biogeochemical processing on the landscape, contributing significantly to the global carbon cycle despite their small areal coverage. However, current large-scale models are all generated by multiplying a mean observed areal rate by regional or global lake surface area, which ignores important heterogeneous spatial and temporal processes that regulate lake carbon cycling, and their static nature renders them incapable of predicting how lake carbon cycling will change under future global change scenarios. We have developed a process-based model rooted in first-principles of hydrology, physics, and ecology capable of being applied over large geographic regions and hindcasting or forecasting lake carbon fluxes in response to global change scenarios. Our model simulated daily carbon fluxes and pools for 3675 lakes in the Northern Highlands Lake District (NHLD) from 1980-2010 and produced spatial and seasonal patterns consistent with observations. Variability in lake carbon fluxes were largely driven by hydrologic metrics, such as the fraction of hydrologic export as evaporation, which can be used to predict important carbon processes and fluxes for the region given that it summarizes both hydrologic loads from the watershed and the degree of decoupling between water and carbon cycles. Hydrologic characteristics were evenly distributed across lake sizes; therefore, median areal lake carbon emissions and burial across the lake size gradient were similar, which meant that large lakes constitute an overwhelmingly large proportion of the total lake carbon flux for the region. Furthermore, our model estimated that 78% of dissolved inorganic carbon (DIC) in lakes originated from external loads of DIC, even though the NHLD is a low-carbonate system relative to other regions.