Hydrologic connectivity amplifies riverine N<sub>2</sub>O emission hot spots and hot moments across the contiguous United States.
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- Record sourced from PubMed, PMID 42330281.
- Also identified by DOI 10.1073/pnas.2524113123.
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Abstract
Riverine nitrous oxide (N<sub>2</sub>O) emissions constitute a significant yet uncertain component of global greenhouse gas budgets. Integrating approximately 3,600 observations across the contiguous United States (CONUS), we present a monthly resolved, national-scale estimate of riverine N<sub>2</sub>O emissions (60.7 Gg N<sub>2</sub>O-N y<sup>-1</sup>; 95% CI: 41.9 to 71.2) using a machine-learning framework. Our analysis reveals that enhanced hydrologic connectivity strongly regulates nitrogen and N<sub>2</sub>O delivery to streams, driving emission hot moments during high-flow periods, especially in nutrient-rich low-order streams. The Midwest Corn Belt is identified as a major emission hot spot, where seasonal increases in connectivity (e.g., late-winter thaws and postharvest rainfall) amplify riverine emissions relative to direct soil emissions. Our watershed-specific EF<sub>5r</sub> (0.0005 to 0.029) exceeds the IPCC default (0.0026) by more than twofold on average and up to 10-fold in intensively managed watersheds. These findings highlight the importance of incorporating hydrologic connectivity and nitrogen transport into climate models and watershed nitrogen management strategies.