◆ 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?

Reference

1. 山口ほか(2013)：バックエンド研究, 20 (2), 53-69
2. Yamaguchi et al. (2014): J. Environ. Radioact. 135, 135-146
3. Kitamura et al. (2014): Anthropocene, 5, 22-31
4. Sakuma et al. (2019): J. Environ. Radioact. 208-209, 106041