Investigation of the nitrogen flows of the food supply chain in Beijing-Tianjin-Hebei region, China during 1978-2017

Reactive nitrogen (Nr) is an indispensable material for food production. However, it may cause serious envi-ronmental problems. The enhancement of nitrogen management in the food supply chain is an effective way to reduce Nr loss and increase Nr use efficiency. While Nr flows in association with the food chain have synergy in a mega-region, in-depth investigations at a cross-regional scale have remained relatively undocumented. This study developed a food-related Nr flow model based on a material flow analysis for the Beijing-Tianjin-Hebei region (BTH) during the years 1978-2017. A multi-regional input-output method was applied to investigate the Nr emissions embodied in the transboundary food supply. The results showed that the total Nr emissions from the food system during the years 1978-2017 in the BTH region increased until 2004 and subsequently decreased gradually. In 2017, Beijing exhibited the lowest Nr emissions per capita (2.3 kg N/cap) and per land use (3089 kg N/km(2)), while Hebei and Tianjin demonstrated the greatest Nr emissions intensity by capita (13.6 kg N/cap) and by land use (6392 kg N/km(2)), respectively. While farming and livestock husbandry dominated the regional Nr emissions (i.e., responsible for 90% of the total in 2017), food consumption and waste management have had an increasingly substantial role, as their shared percentage in the total increased by 22% over the study period. Nr emissions resulting from the inner-transboundary food supply chain decreased by 81% between 2012 and 2015 but dramatically increased by 231% between 2015 and 2017. This rebound effect partially resulted from the implementation of coordinated development planning for the BTH region in 2015. This study can facilitate the efficient regulation of regional nitrogen flows and the desired transition of food supply chain.