Nitrous oxide emissions from rivers in agricultural area under different rainfall scenarios: the effect of typhoons in intensifying the release

In agricultural regions, the chronic enrichment of nitrogen coupled with episodic hydrological disturbances can synergistically amplify riverine Nitrous oxide (N₂O) fluxes through synchronized biogeochemical perturbations. This dual forcing mechanism underscores the critical role of agricultural watersheds as major contributors to terrestrial N₂O budgets. Notably, rainfall events have important impacts on river nitrogen cycle and hydrological processes, indirectly perturb river N₂O emission. However, the impacts of rainfall-particularly under extreme weather conditions-on riverine N₂O dynamics remain poorly understood due to limited empirical data. In this study, we collected data of river environmental factors and associated N₂O concentration and flux in the western part of Guangdong Province, China from 2021 to 2023 under various precipitation scenarios, including non-precipitation (NP), small precipitation (SP), initial rainfall-runoff (IRR), moderate precipitation (MP), heavy precipitation (HP), typhoon (DT), and post-typhoon (PT). Results revealed that N₂O concentration and flux during DT were 12 and 617 times higher than those of NP in Luojiang River. Although typhoon events only accounted for only 1.3 %, 2 %, and 2 % of the total days in 2021, 2022, and 2023, they contributed 21 %, 12 %, and 34 % of the CO₂-equivalent fluxes in these years. N₂O concentration and flux also increased with rainfall, which was, however, not statistically significant. According to variable importance measurements from random forests (RFs) and redundancy analysis (RDA), hydrometeorological factors emerged as the dominant factor influencing N₂O flux (73 %), followed by NO₃^- concentration (23 %)-the key substrate for denitrification-highlighting its critical role in determining N₂O concentration. Our findings address the knowledge gap of river N₂O emissions in agricultural areas during typhoons, providing essential data to support more accurate estimates of waterborne N₂O emissions.