Spatially targeted nitrogen management in a coastal megaregion: A hybrid framework from food production-consumption to source-sink relationships

Sustainable nitrogen (N) management is urgently needed in coastal megaregions, yet a systematic understanding of the spatial drivers of N losses—linking metabolic inefficiencies (“sources”) to landscape-driven transport (“sinks”)—remains lacking. We address this gap by integrating Substance Flow Analysis, Minimum Cumulative Resistance modeling, and convergence analysis to quantify N flows and efficiency across nine cities in the Shanghai Metropolitan Area (2011-2020). Results revealed that nitrogen losses occurred predominantly through atmospheric dispersion (45.6%) and surface water (39.8%), with high spatial variability linked to landscape resistance and subsystem metabolism. Significant spatial convergence (a narrowing of efficiency gaps among cities) was observed in crop (-0.271, p