The frequently observed discrepancy between estimations of N2O emissions at regional or global scale based either on field data or inventories (bottom-up) or on direct atmospheric observations (top-down) suggests that riparian areas and river surfaces play a significant role as hot spots of emission. We developed a modeling procedure to assess N2O emissions occurring during the transfer of water masses from the subroot water pool of the watershed to the outlet of the river drainage network, including their passage through riparian wetlands. The model was applied to three river basins of increasing size located in the sedimentary geological area of the Paris basin (France) and validated by its capability to predict river N2O concentrations and fluxes across the river–atmosphere interface. At the scale of the Seine watershed, indirect emissions, i.e. emissions linked to agricultural practices but occurring elsewhere than directly at the field plot, are estimated to represent approximately 20% of the direct emissions from the watershed soils, in good agreement with previous estimates based on empirical accounting approaches. Denitrification in riparian zones is responsible for the largest share of these indirect emissions. The model results are very sensitive to the value of the ratio of N2O versus (N2 + N2O), in the final products of denitrification in rivers and wetlands. By calibration on river N2O concentrations, a value of 0.015 ± 0.05 is proposed for this ratio, in agreement with recent studies. This represents the main uncertainty factor of the model. In basins with conditions prone to increasing the value of this ratio, higher proportions of indirect N2O emissions might possibly be observed.

中文翻译：

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模拟沿从农田土壤到河流的 N 级联的 N2O 间接排放

基于现场数据或清单（自下而上）或直接大气观测（自上而下）的区域或全球范围内 N2O 排放估算之间经常观察到的差异表明，河岸地区和河流表面作为热点发挥着重要作用排放量。我们开发了一个建模程序来评估水团从流域的亚根水池转移到河流排水网络出口期间发生的 N2O 排放，包括它们通过河岸湿地。该模型应用于位于巴黎盆地（法国）沉积地质区的三个大小不断增加的流域，并通过其预测河流 - 大气界面上的河流 N2O 浓度和通量的能力进行了验证。在塞纳河流域范围内，间接排放，即 与农业实践相关但发生在其他地方而不是直接发生在田间地块的排放估计约占流域土壤直接排放的 20%，与之前基于经验核算方法的估计非常吻合。在这些间接排放中，河岸区的反硝化作用占最大份额。模型结果对河流和湿地反硝化最终产品中 N2O 与 (N2 + N2O) 的比率值非常敏感。通过对河流 N2O 浓度进行校准，建议将此比率的值为 0.015 ± 0.05，与最近的研究一致。这代表了模型的主要不确定因素。在条件容易增加该比率值的盆地中，