Phosphorus flow analysis for megacities using a coupled city-hinterland approach: Case study of Beijing

Abstract

Rapid urbanization has decoupled phosphorus (P) urban consumption and hinterland production, which has accelerated the need for a broader perspective that includes the city and hinterland in managing the P cycle. However, there is a scarcity of frameworks for the combined city and hinterland approach, aimed at quantifying the transboundary P flow between the city and hinterland. In this study, we developed a coupled city-hinterland framework (using Beijing as a case study) to assess the P flow pattern at the source, waste, and transboundary flow using substance flow analysis, and proposed a pathway to identify the key subsystem in the coupled system by sensitivity analysis. Results shows that the P waste within Beijing is due to human consumption, rather than production, while P waste in the hinterland was nearly twice that observed in Beijing. Further, hinterland crop production subsystems were identified as the key subsystem to reduce P rock demand for the whole coupled system; 39% of P rock demand could be reduced by optimizing fertilizer use in the hinterland. In the scenarios that consider an improvement in technology both in Beijing and its hinterland, 64% and 60% of the total P rock demand and waste were reduced, respectively. Therefore, we provided suggestions to reduce P waste in the coupled system. This study provides a broader perspective to evaluate the impacts of urban consumption on the hinterland, which will serve as a basis for policy decisions for sustainable P flow in the supply chain of other similar cities.