Research progress and hotspot analysis for reactive nitrogen flows in macroscopic systems based on a CiteSpace analysis

Human activities have significantly changed the global nitrogen cycle and its underlying processes. Many scholars have studied flows of reactive nitrogen at a range of spatial and temporal scales. However, due to the complexity of the research subject, the diversified research content and methods, and the wide range of research scales, there has been no systematic synthesis of the research in this field. To provide that synthesis, we performed a literature search in the Web of Science core collection, then used the CiteSpace bibliometric visualization software to summarize the evolution of this field of research from 1962 to March 2020 and visualize both the evolution of and the relationships within these data. We found that the number of publications in the field of reactive nitrogen flows in macroscopic systems exploded after 1990. The co-occurrence author cooperation network (1194 scholars) showed a distribution with many groups, and Cornell University's research team (R.W. Howarth, D.P. Swaney, and E.W. Boyer) has been among the biggest contributors to the field due to the team's large number of publications. Cluster analysis showed that urban metabolism, denitrification, atmospheric deposition, and nitrogen budget are not only research hotspots, but also important knowledge bases. In addition, based on our analysis, we predict that the impact of urbanization on the flows of reactive nitrogen, a single process with clearer flow links and more detailed accounting parameters, and relevant studies serving the goal of efficient and low-pollution management of reactive nitrogen will become hotspots. Our results provide a historical reference and suggest new frontiers for future research in the field of reactive nitrogen flows.

Automated summary

The study found that there has been a significant increase in publications related to reactive nitrogen flows in macroscopic systems since 1990. Research hotspots include urban metabolism, denitrification, atmospheric deposition, and nitrogen budget. The impact of urbanization on reactive nitrogen flows and studies aimed at efficient and low-pollution management of reactive nitrogen are predicted to become future research hotspots.