Source: AGU Advances

Rivers, lakes, and reservoirs emit significant amounts of carbon dioxide (CO₂) into the atmosphere. But just how much they contribute to the global carbon cycle is uncertain.

To estimate inland water CO₂ fluxes, researchers measure CO₂ levels and emissions at various points along a waterway or body of water, then use those data to develop an estimate for the whole system based on statistical upscaling methods. But CO₂ concentrations can vary greatly over short distances, leading to uncertain estimates. In addition, these methods don’t allow researchers to precisely determine the sources of the CO₂ being emitted.

Saccardi et al. present a new, process-based model that simulates the physical movement of CO₂ and gauges inland waters’ contributions to overall CO₂ emission fluxes with more accuracy and detail than previous modeling techniques. The new model captures carbon fluxes for the approximately 22 million interconnected rivers, lakes, and reservoirs in the contiguous United States at mean annual flow between 1970 and 2000, calibrated to observations.

The researchers compared two models—their new CO₂ process-based transport model and a statistical upscaling model used in previous studies—that pulled from the same CO₂ dataset of samples from across the world. For their model, the team used data from 6,324 sites across the contiguous United States. The new model estimated CO₂ emission levels 25% lower than what was suggested by the upscaling model. It also suggested differences on a regional level, such as slightly lower fluxes in East Coast and Midwest waterways and slightly higher fluxes in the mountainous West.

The results from the new model suggest that rivers, rather than lakes or reservoirs, are the main driver of CO₂ emissions among inland water sources in the contiguous United States. Stream corridors—the land and complex ecosystems surrounding waterways—may account for 84% of these CO₂ emissions, especially in the West and around larger rivers. Groundwater sources account for the remaining 16%.

Improvements in modeling capabilities could help further quantify the role that inland water sources play in contributing to CO₂ levels in the atmosphere, the researchers say, especially on a global scale. (AGU Advances, https://doi.org/10.1029/2024AV001294, 2024)

—Rebecca Owen (@beccapox), Science Writer

Citation: Owen, R. (2024), New insight into inland water carbon dioxide emissions, Eos, 105, https://doi.org/10.1029/2024EO240526. Published on 21 November 2024.

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