ES&T: IPCC Emission Factor Overestimates N2O Emissions from Agricultural Ditches
Agricultural ditches emit disproportionate amounts of nitrous oxide (N2O), but their contributions to regional or global N2O emissions remain unclear due to limited data. The Intergovernmental Panel on Climate Change (IPCC) recommends using emission factors (EF) to estimate indirect N2O emission, but the EF for ditches (EF5g) is categorized with groundwater, which potentially introduces significant bias. This study conducted a regional-scale campaign in the North China Plain, one of the world’s most intensive agricultural regions （Figure 1）, and calculated the EF5g values from agricultural ditches by the concentration method (N2O−N/NO3−−N).
Figure 1 Sampling points in the North China Plain
The results found that the regional-scale mean EF5g value (0.0028) was less than half of the IPCC default value (0.006), illustrating that the current IPCC methodology significantly overestimates N2O emissions from agricultural ditches. Despite the relatively small EF5g values, agricultural ditches exhibited a high mean N2O concentration (3.36 μg L-1) and a large regional emission (1.14 ± 0.86 Gg N2O−N yr-1), which is equal to 3.8 ± 2.9% of direct N2O emission from the croplands in the North China Plain. Since ditches are ubiquitous in agricultural regions and are likely to expand under climate change, refining EF5g is crucial to accurately assess their contribution to global N2O budgets.
Figure 2 N2O concentrations and emission factors (EF) in extensive surveys and monthly surveys
The research has been published in Environmental Science & Technology as the paper “IPCC Emission Factor Overestimates N2O Emissions from Agricultural Ditches.” Dr. Wenxin Wu is the first author of this paper, with Prof. Zhifeng Yan as the corresponding author. This work was supported by the National Natural Science Foundation of China, the National Key R&D Program, the Tianjin Science and Technology Bureau, and the Haihe Laboratory.
Figure 3
Paper Information： Wu, W., Comer-Warner, S.A., Peacock, M., Han, X., Li, S.-L., Ju, X., Liu, C.-Q., Smith, P. and Yan, Z., 2024. IPCC Emission Factor Overestimates N2O Emissions from Agricultural Ditches. Environmental Science & Technology. 2024. https://doi.org/10.1021/acs.est.4c05760
