资源环境科技发展态势分析平台

Anthropogenic nitrogen (N) emission has been the major cause of rapidly increasing atmospheric N deposition in many regions of the world. However, fluxes, distributions, and physi-chemical compositions of regional N deposition and the response of N deposition levels to N emissions remain poorly characterized, particularly in high N-emission regions. To explore these issues, this study collated observations on N deposition fluxes in the Beijing-Tianjin-Hebei (BTH) region of northern China. We found that total inorganic N (TIN) deposition in the study region averaged 61.3 ± 13 kg-N/ha/yr based on observations from 1998 to 2017. Respectively, about 97%, 73%, 20%, 32%, and 59% of farmland, constructed land, forest, grassland, and water areas had TIN deposition above 50 kg-N/ha/yr. These results indicated substantial ecological risks of atmospheric N loading to these ecosystems. Dry deposition accounted for 59% of TIN deposition and gaseous N accounted for 73% in dry IN deposition. In gaseous N deposition, ammonia, N dioxides, and nitrate acid accounted for 42%, 47%, and 11%, respectively. Ratios of NH₃-N (total N in ammonia) to (NO₂-N + HNO₃-N) (total N in N dioxides, nitric acid) or NH₄-N (total N in ammonium) to NO₃-N (total N in nitrate) averaged 0.8, 2.0, 1.0, 1.9, and 1.3 in gaseous, particulate, dry, wet, and total deposition fluxes, respectively. These indicated different transformation and deposition mechanisms between NH₄-N and NO₃-N under high emissions. Moreover, we found a non-linear relationship between TIN deposition and anthropogenic IN emissions. All these results provide a systematic assessment of the N deposition and its responses to human activities in a high N-emission region, which is valuable for emission mitigation and effect evaluation of regional N pollution.