Temporal and spatial evolution of nitrous oxide emissions in China: Assessment, strategy and recommendation
Introduction
Global anthropogenic greenhouse gas (GHG) emissions have been causing major environmental issues since the 20th century (Meinshausen et al., 2009; Mora et al., 2018; Riahi et al., 2017). Nitrous oxide (N2O) is the fourth most important long-lived (with an estimated atmospheric lifetime of 114 years (Solomon et al., 2007)) anthropogenic GHG following carbon dioxide (CO2), methane (CH4) and chlorofluorocarbon-12 (Davidson, 2009; Tian et al., 2018). It also contributes to the destruction of stratospheric ozone (Davidson, 2009; Pärn et al., 2018). Anthropogenic activities, such as food production and fossil fuel combustion, have intensely accelerated nitrification and denitrification processes, which have been projected to increase N2O emissions, especially in China where serious atmospheric nitrogen (N) pollution widely exists, along with the tremendous socioeconomic development since the late 1970s (Gu et al., 2012; Kuypers et al., 2018). Numerous studies have estimated N2O emissions in limited systems or special aspects in China (e.g., rice paddies and inland fish aquaculture wetlands (Wu et al., 2018a), wheat-maize systems in the North China Plain (Shi et al., 2013), wheat-rice rotation systems (Zhou et al., 2017), vegetable systems (Wang et al., 2018b), bamboo production systems (Zhang et al., 2016a), mountain forest and meadow ecosystems (Zhang et al., 2016b), livestock production systems in peri-urban areas in Beijing, China (Wei et al., 2017) and landfill cover soils in Ningbo, China (Long et al., 2018)). However, spatial and temporal considerations of N2O emissions from agriculture (including cropland, livestock, forestry and aquaculture), industry, human consumption and waste management are still lacking in China, especially under the added pressure of population growth and improvements to living standards. Improved quantitative estimates of the amounts of N2O coming from the various sources are needed to prioritize effective mitigation strategies (Davidson, 2009; Tian et al., 2018; Winiwarter et al., 2018). Quantitative analyses of emission reduction scenarios also have significant implications for the governance of N2O emissions.
To achieve these goals, we develop and conduct a full-cycle analysis based on a coupled human-environment N cycle (CHEN) model (Luo et al., 2018b). This model consideres emissions from agriculture, industry, human consumption and waste management to cover and integrate all specific N2O emission sources and their interactions at both temporal (from 1978 to 2015) and spatial (provincial) scales. We also compare the N2O emissions of China with the world. Finally, we investigate future N2O emission mitigation scenarios from the perspectives of production (technology and management) and consumption (diet habits) and provide relevant policy recommendations to mitigate N2O emissions while meeting the national demands for food, energy and nonfood goods.
Section snippets
Nitrogen cycling, N2O emissions and data sources
The N2O emissions in this study are calculated based on a full-cycle analysis, which is a framework to quantify and track the trajectories of all reactive N (Nr) fluxes in the CHEN model (Luo et al., 2018b). The original CHEN model only calculated Nr flows at the national level for the year 2014. In order to quantify N2O flows in the process of production, processing, consumption and emission of food, energy and nonfood goods in China with a longer time span, we use the model to calculate the
Temporal variations in N2O emissions in China
Over the past three decades, the total N2O emissions in China had increased from 1.02 Tg N yr−1 to 2.43 Tg N yr−1, which is an increase of 140%. During this time, cropland was the largest source of emissions, accounting for 35–48% (Fig. 1). The N2O emissions from livestock almost doubled from 1978 to the beginning of the 21st century, accounting for about 20%, after which they gradually declined and reached a turning point in 2004. The rapid increase in the emissions was associated with the
Concluding remarks
Our comprehensive spatial assessment of the total N2O emissions in China shows that the emissions increased by 140% from 1978 to 2015, and cropland was a major emitter. Over the last 15 years, N2O emissions from industry, aquaculture and waste management have grown rapidly, while those from cropland, livestock, grassland, and human consumption have grown slowly. Meanwhile, the spatial assessment shows that provinces with large N2O emissions, such as Henan, Shandong and Sichuan, as well as
Acknowledgments
This study was financially supported by the Australia-China Joint Research Centre (jointly funded by Australian Government Department of Industry and Science, and the Chinese Ministry of Science and Technology), and the BIP reinvestment funds of the Faculty of Veterinary and Agricultural Sciences of The University of Melbourne.
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