Estimates of riverine N2O emission contain great uncertainty
because of the lack of quantitative knowledge concerning riverine
N2O sources and fates. Using a 3.5-year record of monthly
N2O measurements from the Yongan River network of eastern
China, we developed a mass-balance model to address the riverine N2O source and sink processes. We achieved reasonable model
efficacies (R2 = 0.44–0.84, Nash–Sutcliffe
coefficients = 0.40–0.80) across three tributaries and the
entire river system. Estimated riverine N2O loads originated
from groundwater (38–88%), surface runoff (3–26%), and
in-stream production (4–48%). Estimated in-stream losses via
atmospheric release + complete denitrification accounted for 76, 95,
25, and 89% of riverine N2O fate for the agricultural,
residential, forest, and entire river system, respectively. Considering
limited complete denitrification, the model estimated an upper-bound
riverine N2O emission rate of 2.65 ton N2O–N
km–2 year–1 for the entire river
system. Riverine N2O emission estimates were of comparable
magnitude to those estimated with a power-law scaling model. Riverine
N2O emissions using the IPCC default emission factor (0.26%)
overestimated emissions by 3–15 times, whereas the dissolved
N2O concentration-based emission factor overestimated or
underestimated emissions. This study highlights the importance of
combining comprehensive information on N2O sources and
fates to achieve accurate riverine N2O emission estimates.