Analysis of Long-term Variations of Nitrogen Deposition in Japan (1977-2018)

Abstract

To clarify the long-term trend of nitrogen (N) deposition, the existing monitoring data was analyzed at the regional and national level from 1976 to 2018 . We used the data of annual N depositions from the National Institute for Environmental Studies, the Ministry of the Environment, the Forestry and Forest Products Research Institute, and the Japan Meteorological Agency. Annual median of national N wet deposition was 6.0 kg N ha -1 in 1988 (n＝24) and increased to 7.6 kg N ha -1 in 2000 (n＝92), then it was 7.6 kg N ha -1 in 2010 (n＝82). In 2018 N wet deposition decreased to 6.2 kg N ha -1 (n＝76). The state space model demonstrated that N wet deposition significantly increased, after which tended to decrease at Eastern Japan from 2004, at the Japan Sea area, and in the nation from 2012 . Nitrogen dry deposition averaged 6.0±0.1 kgN ha -1 year -1 (n＝109), total N deposition; the sum of wet and dry deposition, was 11.5±1.6 kgN ha -1 year -1 , N dry deposition ratio ranged from 0.41 to 0.61 during 2003-2018 based on the results of seven stations. Cumulative N deposition was estimated to have exceeded 300 kgN ha -1 over the past 30 years.