Animal Husbandry is the key sector affecting nitrogen metabolism processes within and outside of Beijing with contribution more than 10%

Abstract

Nitrogen is a key metabolic element in urban system. Existing studies lacked the segmentation of specific industrial activities, which made it difficult to serve the precise nitrogen management. In order to fill these gaps, this study constructed a 55-node nitrogen metabolism model, carried out a detailed process analysis of Beijing’s nitrogen metabolism and its interaction with external hinterlands, which fully reflected the perturbation of urban nitrogen flow by human activities. Results showed that Beijing’s external nitrogen input and environmental nitrogen output increased by 15.6% and 19.4% respectively. The pattern of nitrogen metabolism was obviously heterogeneous, with the number and volume of waste flow accounting for more than 30%, which indicated a serious situation of waste nitrogen emission. Foreign countries were Beijing's primary nitrogen supply and demand hinterland, accounting for more than 28% at both ends. The domestic supply hinterlands were concentrated in agricultural provinces of Hebei and Jiangsu, and the demand hinterlands were concentrated in Shanghai and Shandong, both accounting for more than 5%. Animal Husbandry was the key node of internal metabolism and internal/external interactions, contributing more than 10% to the total nitrogen budget and imports/exports. The model constructed in this study can build a universal framework and model for urban nitrogen analysis, and the identified key nodes can serve the Beijing Municipal Government in nitrogen management decision-making.