Distribution characteristics of radionuclides (137Cs, 239+240Pu, 237Np, and 241Am) in vertical vegetation zone in Changbai Mountain, China

Changbai Mountain has vegetation distribution characteristics, which is an important location in northeast China to study the variation characteristics of radionuclides with vegetation distribution. Soils from three vegetation zones of mixed broadleaf and coniferous forest (MBCF), coniferous forest (CF), and alpine birch forest (ABF) in Changbai Mountain were collected to measure the artificial radionuclides of 239+240Pu, 237Np, and 241Am by SF-ICP-MS, as well as 137Cs by anti-Compton HPGe. The mean values of 240Pu/239Pu and 237Np/239Pu atomic ratios, 241Am/239+240Pu and 137Cs/239+240Pu activity ratios were 0.19 +/- 0.02, 0.37 +/- 0.23, 0.56 +/- 0.31, 22 +/- 17, respectively, indicating that the global fallout was the main source of 239+240Pu, 237Np, 137Cs and 241Am in these regions. 137Cs, 239+240Pu, 237Np, and 241Am activities in the samples are 1.1-218, 0.065-9.1, (0.018-2.9) x 10-3, and 0.039-2.0 Bq/kg, respectively. The activities of 137Cs, 239+240Pu, and 237Np in the surface soil have a similar distribution characteristic, i.e. CF > MBCF > ABF, and 241Am is CF > ABF > MBCF. The simulation results of the CDE model suggest that the migration of these radionuclides is dominant in Changbai Mountain forest soil. The inventories of 137Cs, 239+240Pu, 237Np, and 241Am in the soil cores are 1263-20843, 110-1425, 0.017-0.38, and 91-493 Bq/m2, respectively. The inventories distribution of these nuclides in the vegetation zone were as fol-lows: 137Cs and 239+240Pu had similar distribution characteristics as ABF > CF > MBCF; 237Np as CF > MBCF > ABF; 241Am as ABF > MBCF > CF. These results showed that the content, accumulated inventory, and vertical distribution characteristics of these radionuclides were influenced by the vegetation zone distribution in the Changbai Mountain.