High atmospheric dissolved organic nitrogen deposition in southeast Tibet

Nitrogen deposition has been highlighted in the last decades because it was considered as one control factor of global change. The Yarlung Tsangpo Grand Canyon acts as a major passage of monsoonal moisture transport from the Bay of Bengal into the Tibetan Plateau. However, the characteristics of nitrogen(N) deposition in this area are still unclear. Here, we established five N deposition monitoring sites and quantification the bulk N deposition fluxes from 2200 to 4600m above sea level in southeast Tibet. Results showed that the average precipitation amount of the five sites was 1127.7 mm. The dissolved organic nitrogen (DON) was the dominant species, and the deposition flux was 16.80 kg N ha^-1 yr^-1. The averaged NH₄ ⁺-N deposition flux was 4.92 kg N ha^-1 yr^-1, whereas the NO₃ ^--N deposition flux was 1.49 kg N ha^-1 yr^-1. In addition, the deposition fluxes of TDN, DON and NH₄ ⁺-N were all significantly positive to precipitation amounts at all five sampling sites. However, the deposition flux of NO₃ ^--N was significantly correlated with precipitation amount in the remote environment, and there was no correlation between precipitation amounts and NO₃ ^--N deposition fluxes in human concentrated areas. TDN, DON and NH₄ ⁺-N deposition were all concentrated in the plant growing season at all five sampling sites. In conclusion, the atmospheric TDN deposition flux in the Yarlung Zangbo Grand Canyon in southeast Tibet is mainly controlled by precipitation, and DON was the dominant species, followed by NH₄ ⁺-N, and NO₃ ^--N contribution was limited.