Spatiotemporal variability and controlling factors of indirect N2O emission in a typical complex watershed. (1st February 2023)

• Record Type: Journal Article
• Authors: Liang, Jie; Tang, Wenzhuo; Zhu, Ziqian; Li, Shuai; Wang, Kang; Gao, Xiang; Li, Xin; Tang, Ning; Lu, Lan; Li, Xiaodong
• Is Part Of: Water research. Volume 229(2023)
• Publication Date: 2023-02-01
• Subjects: Indirect N2O emission -- Spatiotemporal pattern -- Controlling factors -- SWAT -- PLS-SEM; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2022.119515
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Spatiotemporal fluctuations of riverine N2 O emissions were identified. The main influencing factors of the temporal and spatial variation were revealed. Key transport processes for riverine N2 O emissions were highlighted. The critical environmental variables in the riverine physicochemical indicators were clarified. Relative importance of environmental factors was quantified. Abstract: The mechanisms of N2 O emissions from inland rivers remain poorly understood because of the high variability of dissolved N2 O concentration and the complexity of influencing factors. Thus, it is necessary to research the spatiotemporal patterns and influencing factors to understand the driving mechanisms of riverine N2 O emissions. We combine the Soil and Water Assessment Tool (SWAT) outputs with established empirical equations to identify the spatiotemporal fluctuations of riverine N2 O emissions and evaluate model performance through field measurements in a typical watershed. The spatiotemporal hotspots of N2 O emissions are then determined, and the relative importance of environmental variables is further determined by correlation and attribution analysis. The results indicate that the riverine N2 O emissions are relatively high from August to October, which accounted for 35.38% of the annual emissions. Temporal changes are attributed to agricultural activities and meteorological factors. Agricultural activities such as planting and fertilization lead to increased diffuse nitrogen loads on the land surface. Meantime, heavy precipitation events enhance the transport of nutrients, resulting in changes in nitrogen levels in the river. Spatial analysis shows that the urban watersheds (191.22 ± 156.19 μmol m −2 d −1 ) are the hotspots of riverine N2 O emission, which are 1.55–3.03 times that of non-urban rivers. Spatial variations are mainly affected by riverine physicochemical indicators for different watersheds. Sewage from various sources received by urban rivers provides appropriate environmental conditions for N2 O production, and transports large exogenous dissolved N2 O. Furthermore, salinity ( r = 0.80; p < 0.001) and nitrogen nutrients in riverine physicochemical indicators show a significant correlation with N2 O fluxes. It emphasizes that N-related (TN, NH4 +, NO3 − ) indicators are important reactants for N2 O generation, which can promote nitrification and denitrification. Meanwhile, the results of structural equation modeling (SEM) also demonstrate that N2 O emissions follow a similar pattern to riverine dissolved N2 O concentration ( r = 0.841, p < 0.001), and non-point source ( r = 0.678, p < 0.001) play an important role in the changes of dissolved N2 O concentrations. Our results highlight that certain hot moments and hot spots of rivers play a disproportionate role in year-round and basin-wide N2 O emissions, respectively. It is necessary to implement more effective management measures by controlling key environmental factors to reduce N2 O emissions. Graphical abstract: Image, graphical abstract