Aquaculture source of atmospheric N2O in China: Comparison of system types, management practices and measurement methods

Aquaculture systems contribute to atmospheric N₂O, but the magnitude of this N₂O source is largely uncertain. Here, we synthesized data from 139 aquaculture sites based on 59 peer-reviewed publications, and estimated that China's aquaculture systems emitted 9.68 Gg N yr⁻¹ (4.12 Tg CO₂-eq yr⁻¹). N₂O emission varied significantly according to system types, farmed species, physical dimensions of the system, hydrographical conditions, and management practices. Of these, inland pond systems had a higher N₂O flux (268.38 ± 75.96 mg N m⁻² yr⁻¹) and indirect N₂O emission factor (4.4 ± 0.9‰) than the other system types. Mixed species farming tended to emit less N₂O than monospecific farming, whereas small (<1 ha) and shallow ponds (<1 m) were hotspots for N₂O emission. Flux values based on different wind-driven diffusion models varied widely, and the model CC98 agreed most closely with direct measurements using floating chamber. Overall, aquaculture waters had a lower emission intensity than streams, rivers and reservoirs, but comparable to estuaries and lakes. Rapid expansion of the aquaculture sector and the limited N₂O data for this sector, especially for rice-aquaculture co-culture systems, highlight the need for better monitoring and on-site measurements to refine the inventory of greenhouse gas emissions from the aquaculture systems.