Aggravation of reactive nitrogen flow driven by human production and consumption in Guangzhou City China

Human activities reshape the global nitrogen (N) cycle and affect environment and human health through reactive nitrogen (Nr) loss during production and consumption. In urbanized regions, the N cycle is greatly mediated by complex interactions between human and natural factors. However, the variations in sources, magnitude, spatiotemporal patterns and drivers of Nr flows remain unclear. Here we show by model simulations, anthropogenic perturbations not only intensify Nr input to sustain increasing demands for production and consumption in Guangzhou city, China, but also greatly change the Nr distribution pattern in the urban system, showing a substantial Nr enrichment in the atmosphere and a relatively low retention capacity of Nr in the terrestrial system. Our results highlight the strong anthropogenic effect of urban systems on the N cycle to suggest sustainable human activity changes to harmonize the relationship between Nr behaviors and human drivers. There lacks research to figure out the variations in sources, magnitude, and spatiotemporal patterns of Nr flows in urban system. Here the authors develop a coupled human-natural urban nitrogen flow analysis model and show that anthropogenic perturbations not only intensify Nr input to sustain increasing demands for production and consumption of cities, but also greatly change the Nr distribution pattern in the urban system.