Spatio‐temporal impact of land use changes on nitrogen emissions in the Guangdong–Hong Kong–Macao Greater Bay Area

Land use changes, especially urban land expansion, exert a profound effect on nitrogen (N) cycles in the interconnected human–natural systems, altering the distribution and intensity of N emissions resulting from anthropogenic activities. However, few studies have revealed the dynamic response of N emissions to diverse land use changes at the regional scale. This study developed a holistic spatial urban metabolism framework that combines land‐use classification, N‐flow modeling, and spatial analysis to examine the heterogeneous land‐related N transitions across cities and timeframes at a fine spatial resolution. Using the Guangdong–Hong Kong–Macao Greater Bay Area (GBA) as the case, we observed a drastic expansion of built‐up land during 1990–2018, mainly converted from cropland (81.35%) and forest (9.55%). Intensified N emissions became increasingly concentrated in densely populated urban areas and croplands in the GBA's western peripheral cities. Land conversion from cropland to built‐up land contributed the most to the rise in N emissions, totaling 368.2 Gg during the study period. The increase in N emission intensity associated with built‐up land expansion gradually fell over time due to enhanced N removal in waste treatment, while the exploitation of water and wetland exhibited the highest average increased intensity of 35.01 t N/km2 after 2010. Our findings highlight the need for tailored and collaborative land management strategies that adapt to different development stages and local conditions to mitigate N pollution in the fast‐urbanizing bay area.