Identify the Flow Patterns of Nitrogen within Urban Agglomeration: A Case Study of the Pearl River Delta

Abstract

Nitrogen has an essential impact on both sustaining the ecosystem productivity and causing a series of environmental problems, especially for urban agglomeration. The optimization of nitrogen metabolism on urban agglomeration scale can provide strong basis for the reinforcement of sustainable development. Using the Pearl River Delta region, which contains 9 cities in China, as a case study, this research develops a multi-sectoral nitrogen metabolism model based on substance flow analysis, to quantify N flows through urban ecosystem described by four economic sectors: production, processing, consumption, and waste management. Flow patterns of N among nine cities are analyzed and compared. Scenario analysis is conducted to recognize effective measures for promotion of N metabolic performances. Data uncertainty is specially considered by the utilization of Latin hypercube sampling. Results show that in 2016, about 715 Gg N was imported into the production sector. The N use efficiencies of chemical fertilizers and animal fee were around 25% and 29%, respectively. Low N use efficiency in agriculture and low recovery rate of organic waste were the main factors leading to excess N pollution emission. Disparity of socioeconomic features and material exchanges among cities leads to their different N pollution emission features. Optimized scenarios that can enhance the N resource recovery and pollution emission reduction are recognized. Thus, this research provides support to achieve smarter urban metabolism on urban agglomeration scale, from the perspective of both resource utilization efficiency and environmental effect.

Keywords: nitrogen, urban agglomeration, substance flow analysis, scenario analysis