Dynamic changes of net anthropogenic nitrogen/phosphorus input and its riverine export in the Beijing's subcenter

Due to human activities, the overabundance of regional nitrogen/phosphorus (N/P) has a huge impact on ecological environment worldwide. It is necessary to comprehensively understand the human-induced N/P input and spatiotemporal variations of nutrients in a river. As the adjustment to the spatial structure of Beijing, the Beijing's subcenter is an important strategic position in promoting the coordinated development of Beijing-Tianjin-Hebei. In this study, the dynamic changes of ammonia nitrogen (NH3-N) and total phosphorus (TP) from 2012 to 2022 were analyzed, then the net anthropogenic N input (NANI) and net anthropogenic P input (NAPI) was estimated in the Beijing's subcenter. The results showed that both NH3-N and TP had an overall downward trend with a three-stage pattern. The NANI and NAPI declined from 5.68 x 104 and 0.95 x 104 to 0.78 x 104 and 0.15 x 104 kg km-2 per year, respectively. The chemical fertilizers input accounted for the largest part at 53-81% of NANI and 49-80% of NAPI. There were high values of N and P input in the southeast of Tongzhou, and the fluxes of N and P were positively correlated with the input of anthropogenic N and P in the Chaobai River Basin (Tongzhou District) and the Beiyun River Basin (Tongzhou District). This study would provide the foundation for setting priorities and enacting more targeted N/P management strategies in the Beijing's subcenter. The overabundance of regional nitrogen/phosphorus (N/P) has a great impact on global ecological environment. In this study, the dynamic changes of anthropogenic N/P input, export of N/P by rivers and their relationships were explored. Artificial N/P input mainly from agriculture declined sharply and had a significant correlation with riverine N/P fluxes. image