Dynamics of radiocaesium within forests in Fukushima-results and analysis of a model inter-comparison

Shoji Hashimoto (1) , Taku Tanaka (2) , Masabumi Komatsu (1) , Marc Andre Gonze (3) , Wataru Sakashita (1) , Hiroshi Kurikami (4) , Kazuya Nishina (5) , Masakazu Ota (4) , Shinta Ohashi (1) , Philippe Calmon (3) , Frederic Coppin (6) , Naohira Imamura (1) , Seiji Hayashi (7) , Keizo Hirai (1) , Pierre Hurtevent (6) , Jun Koarashi (4) , Takuya Manaka (1) , Satoru Miura (1) , Yoshiki Shinomiya (1) , G. Shaw (8) , Yves Thiry (9)

1 FFPRI - Forestry and Forest Products Research Institute
2 LNHE
3 IRSN/PSE-ENV/SEREN/LEREN - Laboratoire d'étude et d'expertise sur la radioactivité de l'environnement
4 JAEA - Japan Atomic Energy Agency [Ibaraki]
5 Center for Global Environmental Research, National Institute for Environmental Studies
6 IRSN/PSE-ENV/SRTE/LR2T - Laboratoire de recherche sur les transferts des radionucléides dans les écosystèmes terrestres
7 National Institute for Environmental Science [Fukushima]
8 Division of Agricultural and Environmental Sciences
9 DRD/ST

Forests cover approximately 70% of the area contaminated by the Fukushima Daiichi Nuclear Power Plant accident in 2011. Following this severe contamination event, radiocaesium (137Cs) is anticipated to circulate within these forest ecosystems for several decades. Since the accident, a number of models have been constructed to evaluate the past and future dynamics of 137Cs in these forests. To explore the performance and uncertainties of these models we conducted a model inter-comparison exercise using Fukushima data. The main scenario addressed an evergreen needleleaf forest (cedar/cypress), which is the most common and commercially important forest type in Japan. We also tested the models with two forest management scenarios (decontamination by removal of soil surface litter and forest regeneration) and, furthermore, a deciduous broadleaf forest (konara oak) scenario as a preliminary modelling study of this type of forest. After appropriate calibration, the models reproduced the observed data reliably and the ranges of calculated trajectories were narrow in the early phase after the fallout. Successful model performances in the early phase were probably attributable to the availability of comprehensive data characterizing radiocaesium partitioning in the early phase. However, the envelope of the calculated model end points enlarged in long-term simulations over 50 years after the fallout. It is essential to continue repetitive verification/validation processes using decadal data for various forest types to improve the models and to update the forecasting capacity of the models.

Domaines: Sciences de l'environnement

Shoji Hashimoto, Taku Tanaka, Masabumi Komatsu, Marc Andre Gonze, Wataru Sakashita, et al.. Dynamics of radiocaesium within forests in Fukushima-results and analysis of a model inter-comparison. Journal of Environmental Radioactivity, 2021, 238-239 (106721), pp.10. ⟨10.1016/j.jenvrad.2021.106721⟩. ⟨hal-03589800⟩