Emission of nitrous oxide from plain multi-ditch system and its impact factors

Multi-level ditch area is a major component of the hydrographic net of plain area, China. Given the high concentration of nitrogen (N) in the surface water and vigorous biogeochemical interactions, ditch is likely to be the hot spots of N₂O emission. However, N₂O emission flux and emission factor (EF_5r) of multi-level ditches have not been determined. To address this knowledge gap, a 1-year field work in three ditches with different levels in Chengdu Plain was conducted. It is found that the annual flux of N₂O emission and EF_5r was higher in the lateral (0.0020 and 83.94 μg m^-2 h^-1) and field ditches (0.0019 and 110.75 μg m^-2 h^-1) than in the branch ditch (0.0016 and 46.38 μg m^-2 h^-1, P < 0.05). It is found that parameters of groundwater level, discharge, precipitation, and NH₄⁺ were the primary factors, and these parameters can model the N₂O flux well. Furthermore, the content of NH₄⁺ in the surface water of ditches presented better correlation with the emission of N₂O than the content of NO₃^-. Therefore, controlling NH₄⁺ emission and lessening fertilizer usage in summer may be key solutions for indirect reduction of N₂O in Chengdu Plain.