Inland Waters can Act as Nitrous Oxide Sinks: Observation and Modeling Reveal that Nitrous Oxide Undersaturation May Partially Offset Emissions

Inland waters are significant, yet highly uncertain, natural sources of nitrous oxide (N₂O). Many emission models assume that N₂O is only emitted from freshwaters, and that N₂O sink behavior is negligible. However, observational studies have reported N₂O undersaturation, suggesting that inland waters can act as N₂O sinks due to net N₂O consumption. This study leverages data from the National Ecological Observatory Network (NEON) and an existing global emission model to examine the prevalence of and controls on N₂O undersaturation in streams, rivers, and lakes across scales and biomes. We find that N₂O undersaturation is prevalent in the NEON data set (14%–30% of samples) and process-based model outputs (38%), occurring across biomes and spatial scales. Failing to account for undersaturation in the NEON data set could result in an 100% overestimation of N₂O emissions. These results show that consideration of N₂O sink behavior is needed for accurate emission estimates.