◆ Discharge amount of ¹³⁷Cs from catchment during the first year

• Annual discharge of ¹³⁷Cs was calculated.
• 8.4 TBq of ¹³⁷Cs discharged from the catchment into the ocean during the first year after the fallout. It represents about 0.3 to 0.7 % of the total inventory in the catchment.
• 3.0 TBq of ¹³⁷Cs discharged from the Abukuma river to the ocean during the first year.
• 2.9 TBq of ¹³⁷Cs discharged from the five coastal rivers (Odaka, Ukedo, Maeda, Kuma and Tomioka rivers) to the ocean during the first year.

Table 1　Annual amount of sediment and ¹³⁷Cs exported into the ocean

River	Basin area (km2)	Sediment discharge to ocean (t/y)	137Cs diacharge to ocean (Bq/y)	137Cs to ocean/sediment to ocean (Bq/kg)
Abukuma	5,423	2.4 ×105	3.0 ×1012	1.2 ×104
Ukedo	420	2.7 ×104	2.0 ×1012	7.2 ×104
Niida	261	1.6 ×104	1.1 ×1012	6.5 ×104
Maeda	48	1.6 ×103	4.0 ×1011	2.5 ×105
Kuma	74	2.5 ×103	2.8 ×1011	1.1 ×105
Ota	79	1.7 ×103	2.7 ×1011	1.6 ×105
Mano	167	5.5 ×103	2.0 ×1011	3.7 ×104
Kido	260	1.5 ×104	1.4 ×1011	9.0 ×103
Odaka	67	2.5 ×103	1.3 ×1011	5.3 ×104
Tomioka	63	2.0 ×103	1.1 ×1011	5.8 ×104
Natsui	685	4.2 ×104	1.1 ×1011	2.6 ×103
Same	592	5.1 ×104	8.9 ×1010	1.7 ×103
Ide	40	3.0 ×103	6.9 ×1010	2.3 ×104
Uda	173	2.4 ×103	6.4 ×1010	2.6 ×104
Total	8,352	4.2 ×105	8.4 ×1012	2.0 ×104

◆ Land use and ¹³⁷Cs discharge

• Crop filed covers only 10 % of the land, but contributes 58 % of soil loss and 47 % of ¹³⁷Cs discharge.
• Forest occupies 64 % of the land. 24 % of soil and 41 % of ¹³⁷Cs discharged into the ocean are from forest.

Table 2　Amount of soil erosion and ¹³⁷Cs runoff in individual land-use factors

（Kitamura et al., Anthropocene, 2014）

Related articles

• In future, what will be radiation exposures to forest workers? Are there any methods to reduce it?
• Does the concentration of radioactive cesium deposited in mountain forests vary by altitude and location?
• Dose the radiocesium discharge ratio from rivers depend on the local environment?
• Where is the radiocesium in river water coming from?
• Cs released to the environment by the forest fire?

References

1. 山口正秋, 前川恵輔, 竹内真司, 北村哲浩, 大西康夫(2013): 土砂移動に着目した福島第一原子力発電所事故後の放射性物質分布に関する解析手法の開発, バックエンド研究, vol. 20, no. 2, 53-69. https://doi.org/10.3327/jnuce.20.53
2. Sakuma, K., Nakanishi, T., Yoshimura, K., Kurikami, H., Namba, K. and Zheleznyak, M. (2019): A Modeling approach to estimate the ¹³⁷Cs discharge in rivers from immediately after the Fukushima accident until 2017, Journal of Environmental Radioactivity, vol. 208-209, 106041. https://doi.org/10.1016/j.jenvrad.2019.106041