Radioactivity Dynamics in River System
ＱHow much amount of radiocesium discharges into the ocean?
ＡIt was estimated that about 8.4 TBq of 137Cs had discharged from the Abukuma river and the coastal rivers in Fukushima into the ocean during the first year after the fallout. 47 % of discharged 137Cs was from crop field and 41 % was from forest.
◆ 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.
|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.
（Kitamura et al., Anthropocene, 2014）
- 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?