Toward Modeling Continental-Scale Inland Water Carbon Dioxide Emissions

Inland waters emit significant amounts of carbon dioxide (CO₂) to the atmosphere; however, the global magnitude and source distribution of inland water CO₂ emissions remain uncertain. These fluxes have previously been “statistically upscaled” by independently estimating dissolved CO₂ concentrations and gas exchange velocities to calculate fluxes. This scaling, while robust and defensible, has known limitations in representing carbon source limitations and spatial variability. Here, we develop and calibrate a CO₂ transport model for the continental United States, simulating carbon transport and transformation in >22 million hydraulically connected rivers, lakes, and reservoirs. We estimate 25% lower CO₂ fluxes compared to upscaling estimates forced by the same observational calibration data. While precise CO₂ source distribution estimates are limited by the resolution of model parameterizations, our model suggests that stream corridor CO₂ production dominates over groundwater inputs at the continental scale. Our results further suggest that the lack of observational networks for groundwater CO₂ and scalable metabolic models of aquatic CO₂ production remain the most salient barriers to further coupling of our model with other Earth system components.