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Intensive use of nitrogen (N) fertilizers in agriculture and the release of reduced N in human and animal wastes have substantially enhanced nitrous oxide (N 2 O) production from aquatic systems, mainly through nitrification and denitrification. This study investigated the spatial variation of riverine N 2 O production and emission from a river network in a region dominated by agriculture (Jiulong River) in southeast China, as well as river N 2 O yield [=△N 2 O/(△N 2 O + △N 2 ) × 100]. Three measurements, encompassing 29 sampling sites across two main tributaries (North River and West River), were carried out in February, May and October 2011 under various hydrological conditions. The results showed that dissolved N 2 O concentrations were always far above saturation (112–4133%), indicating that the river is a major source of N 2 O, a potent greenhouse gas. The excess dissolved N 2 O (△N 2 O) ranged from 4.2 to 363 nmol L −1 , and the water–air fluxes of N 2 O varied from 1.1 to 93.8 μmol m −2 d −1 . Dissolved inorganic N (DIN) was the key factor controlling the spatial variation of △N 2 O. High N 2 O production and emission was found in the upper North River where animal and human wastes dominated riverine N sources. River N 2 O yield tends to increase during low flow periods and in dam-modified river stretches, probably due to enhanced in-stream nitrification. Riverine N 2 O export to estuary has increased more than 15-fold since the 1980s. Riverine N 2 O emission from the Jiulong River falls into the lower range of reported values around the world but is anticipated to increase due to changing hydrology and increasing N loading from agriculture. [ABSTRACT FROM AUTHOR]