Dynamic Changes of Nitrogen Loads in Source–Sink Landscapes under Urbanization

Abstract

The dynamic changes of nitrogen (N) loads have been significantly impacted by the rapid expansion of many cities, potentially escalating the risk of N pollution in cities. However, the spatiotemporal changes of N loads in source and sink landscapes remain unclear in urbanization. In this research, we used source–sink landscape theory to identify the source–sink landscape in the process of N flow at the city scale and investigated the spatiotemporal changes of N loads in the source–sink landscape from 2005 to 2015 in Xiamen, a rapidly urbanizing city in southern China. The total N loads of source landscapes increased by 2 times between 2005 and 2015, with an average annual growth of 26%, while the total N loads of sink landscapes climbed gradually, with an average annual increase of 8%, according to our findings. Moreover, in terms of the spatial gradient, the N loads of the source landscape fluctuated downward and reached their peak in the urban center, whereas the N loads of the sink landscape tended to rise and reached their peak outside of the city. Our findings offered a fresh viewpoint on the source–sink landscape in N flows at the city scale and offered useful guidance for N spatial management to support sustainable city development.