Long-term atmospheric wet deposition of dissolved organic nitrogen in a typical red-soil agro-ecosystem, Southeastern China
Dissolved organic nitrogen (DON) from atmospheric deposition has been a growing concern in the world and atmospheric nitrogen (N) deposition is increasing quickly in China especially Southeastern China. In our study, DON wet deposition was estimated by collecting and analyzing rainwater samples continuously over eight years (2005–2012) in a typical red-soil farmland ecosystem, Southeast China. Results showed that the volume–weighted–average DON concentration varied from 0.2 to 3.3 mg N L−1 with an average of 1.2 mg N L−1. DON flux ranged from 5.7 to 71.6 kg N ha−1 year−1 and averaged 19.7 kg N ha−1 year−1 which accounted for 34.6% of the total dissolved nitrogen (TDN) in wet deposition during the eight-year period. Analysis of DON concentration and flux, contribution of DON to TDN, rainfall, rain frequency, air temperature and wind frequency and the application of pig manure revealed possible pollution sources. Significant positive linear relation of annual DON flux and usage of pig manure (P < 0.0001) suggested that agricultural activities, especially application of pig manure, were the main source of DON in the study area. In conclusion, DON wet deposition was an important part of TDN and would have a possible effect on N cycle in the red-soil agro-ecosystem in the future.