Modeling Riverine N₂O Sources, Fates, and Emission Factors in a Typical River Network of Eastern China

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