The potential risks of high-nitrogen-emitting cities to the global ecology are worthy of in-depth study.This study employed the concept of urban metabolism to construct a nitrogen-flow analysis framework for the Tamsui River watershed region of Taipei, Taiwan, that encompassed three subsystems: atmosphere, land, and water. The proportion
of the total nitrogen discharged to the sea was calculated, and emission reduction methods were discussed. Five
conclusions were drawn from the study. First, the flux emitted by human activities into the atmosphere in Taipei was greater than that resulting from deposition. Second, some nitrogen fertilizers and feeds in urban agriculture were not effectively converted into food. Third, most nitrogen-containing wastewater was received by rainwater pumping stations and discharged into river water without passing through sewage treatment plants. Fourth, the nitrogen flux discharged into river water by the land subsystem was greater than that discharged into the atmosphere. Finally, the total amount of nitrogen discharged to the estuary should be reduced through urban cooperation. The methodology and results of this study may be applicable to follow-up studies on other high-nitrogen-emitting cities and research aiming to alleviate global nitrogen pollution.
Key Words: wastewater, air pollution, urban metabolism, substance flow analysis, Taipei