Pervasive summertime nitrous oxide undersaturation in U.S. lakes and reservoirs
Jake J Beaulieu1, Roy W Martin2, Michael G McManus2
1US Environmental Protection Agency, Office of Research and Development, Cincinnati, OH, USA. beaulieu.jake@epa.gov.
Nature Communications
|July 11, 2026
Summary
Most U.S. lakes absorb nitrous oxide (N2O), acting as sinks rather than sources. This finding challenges existing models that assume aquatic systems emit N2O, indicating a need for revised estimates of greenhouse gas emissions.
Area of Science:
- Environmental Science
- Atmospheric Chemistry
- Limnology
Background:
- Lakes and reservoirs are considered significant global sources of atmospheric nitrous oxide (N2O).
- Recent studies suggest N2O uptake in lakes, questioning the accuracy of current emission estimates.
- Existing models often presume surface waters are N2O sources, potentially overestimating emissions.
Purpose of the Study:
- To assess N2O concentration and emission rates across a large number of U.S. waterbodies.
- To investigate the role of lakes and reservoirs as N2O sinks or sources.
- To evaluate the accuracy of current N2O emission models for aquatic systems.
Main Methods:
- Utilized a national-scale dataset of dissolved N2O concentrations.
- Employed a Bayesian hierarchical model to predict N2O concentrations and emissions.
- Analyzed data from 465,896 waterbodies in the conterminous U.S. (CONUS) during summer 2017.
Main Results:
- N2O undersaturation was widespread in CONUS waterbodies during summer.
- An estimated 72.9% of lakes functioned as N2O sinks, absorbing the gas.
- Model predictions showed N2O concentrations were influenced by nitrate, surface area, and water temperature.
Conclusions:
- Pervasive N2O undersaturation in U.S. waterbodies necessitates a re-evaluation of N2O models.
- Current models assuming surface waters are N2O sources may require significant revision.
- The study highlights the complex role of aquatic ecosystems in the global N2O budget.
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