Analysis on the evolution of nitrogen metabolism process and nitrogen supply hinterland pattern in Beijing's food system

Abstract

As one of the main human activities affecting the global nitrogen cycle, food production and consumption caused a series of environmental issues with nitrogen, especially in densely populated cities. To comprehensively quantify these issues of cities, Beijing's food system was chosen as a case to build a refined 18-node nitrogen metabolic network model based on environmental and external support, its nitrogen budgets was innovatively accounted from the perspective of “bigger food system”, which contained the nitrogen flows both involved in and driving food metabolic processes. Then the key nodes were identified according to the principle of contributing more than 10% of total nitrogen inputs and emissions. Based on above, China Multi-Regional Input-Output table was used to further examine its nitrogen supply hinterlands and identify the key supply drivers from the sectoral perspective. The results show that the total nitrogen input of Beijing's food system increased by 32.6% but the nitrogen output increased by 64.8% between 1979 and 2019. The (1) Crop cultivation, (2) Animal husbandry, and (11) Urban residents are not only key nitrogen input nodes but also key nitrogen emission nodes. Besides, they drove the external nitrogen supply to Beijing's food system, thus should be the key managed objects. Hebei, Heilongjiang and Tianjin are the largest inland nitrogen supply hinterlands, while the foreign nitrogen supply increased by 15.8% from 2007 to 2019. Technical assistance, economic compensation and trade strategy adjustment are good ways to reduce hinterlands' nitrogen supply pressure. This study provides targeted management suggestions for the nitrogen sustainable of food system in cities and the nitrogen coordination among regions.