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 <0.05, t life =19.736) and aquaculture (-0.376, p <0.01, t life =13.228) nitrogen use efficiency, whereas livestock and recycling systems exhibited divergent trends (a widening of gaps), reflecting uneven regional coordination. This hybrid framework uniquely links metabolic performance to landscape-mediated risk patterns, diagnosing why hotspots emerge. This provides a systemic basis for spatially differentiated management, underscoring that sustainable N governance in coastal megaregions requires concurrently optimizing system metabolism and ecological connectivity. • Spatial N loss risks, shaped by landscape resistance and metabolic flows, show high heterogeneity. • N use efficiency converged in crop-aquaculture systems but diverged in livestock-recycling systems. • Integrated “risk-efficiency” coupling strategies are proposed for sustainable N management.