Dynamic N transport and N2O emission during rainfall events in the coastal river

Wen-Xi Zhang; Fu-Jun Yue; Yong Wang; Yun Li; Yun-Chao Lang; Si-Liang Li

doi:10.1016/j.scitotenv.2023.166206

Dynamic N transport and N₂O emission during rainfall events in the coastal river

Sci Total Environ. 2023 Dec 10:903:166206. doi: 10.1016/j.scitotenv.2023.166206. Epub 2023 Aug 9.

Authors

Wen-Xi Zhang¹, Fu-Jun Yue², Yong Wang³, Yun Li⁴, Yun-Chao Lang⁵, Si-Liang Li⁶

Affiliations

¹ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
² Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; Tianjin Bohai Rim Coastal Earth Critical Zone National Observation and Research Station, Tianjin University, Tianjin 300072, China. Electronic address: fujun_yue@tju.edu.cn.
³ Hydrology and Water Resources Management Center of Tianjin, Tianjin 300061, China.
⁴ Technical Centre for Soil, Agriculture and Rural Ecology and Environment, Ministry of Ecology and Environment, Beijing 100012, China. Electronic address: liyun@tcare-mee.cn.
⁵ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; Tianjin Bohai Rim Coastal Earth Critical Zone National Observation and Research Station, Tianjin University, Tianjin 300072, China.
⁶ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; Tianjin Bohai Rim Coastal Earth Critical Zone National Observation and Research Station, Tianjin University, Tianjin 300072, China; Haihe Laboratory of Sustainable Chemical Transformations, Tianjin 300192, China.

PMID: 37567291
DOI: 10.1016/j.scitotenv.2023.166206

Abstract

The coastal zone exhibited a high population density with highly impacted by anthropogenic activities, such as river impoundment to prevent saline intrusion, which resulted in weak hydrological conditions. Rainfall events can result in dramatic changes in hydrological and nutrient transportation conditions, especially in rivers with weak hydrological conditions. However, how the nitrogen transport and N₂O emissions or biogeochemistry responds to the different types of rainfall events in the weak hydrodynamics rivers is poorly understood. In this study, the hydrological, nitrogenous characteristic, as well as N₂O dynamics, were studied by high-frequency water sampling during two distinct rainfall events, high-intensity with short duration (E1) and low-intensity with long duration (E2). The results displayed that the hydrologic condition in E1 with a wider range of d-excess values (from -9.50 to 32.1 ‰), were more dynamic than those observed in E2. The N₂O concentrations (0.01-3.33 μmol/L) were higher during E1 compared to E2 (0.03-1.11 μmol/L), which indicated that high-intensity rainfall has a greater potential for N₂O emission. On the contrary, the concentrations of nitrogen (e.g., TN and NO₃^--N) were lower during E1 compared to E2. Additionally, hysteresis was observed in both water and nitrogen components, resulting in a prolonged recovery time for pre-rainfall levels during the long-duration event. Moreover, the results showed that the higher average N₂O flux (78.3 μmol/m²/h) in the rainfall event period was much larger than that in the non-rainfall period (1.63 μmol/m²/h). The frequency dam regulation resulted in the water level fluctuation, which could enhance wet-dry alternation and simulated N₂O emissions. This study highlighted the characteristic of N dynamic and hydrological responses to diverse rainfall events occurrences in the coastal river. Rainfall could increase the N₂O emission, especially during high-intensity rainfall events, which cannot be ignored in the context of annual N₂O release.

Keywords: Coastal rivers; Nitrogen cycle; Nitrous oxide; Rainfall event; d-excess.