2016 SRRCE International Symposium (2016/07/08@Fukushima)

Migration behavior of radioactive cesium in forests and mountains

Fukushima Environmental Safety Center Sector of Fukushima Research and Development

Japan Atomic Energy Agency

Kazuki Iijima

Outline • Behavior of radioactive Cs in forests

• Characteristics of distribution and transportation of Cs in the environment

• Short-term countermeasures • Long-term countermeasures • Issues to be considered

2

3 Topographical characteristics of the Fukushima

Fukushima city

Koriyama city

Topography of eastern and central part of the Fukushima prefecture.

FDNPS

4 Contamination by the FDNPS accident

Distribution map of air dose rate in the Fukushima prefecture. (measured from the 1st Sept. to the 7th Nov. 2014 by NRA and corrected to the 7th Nov. 2014 )

FDNPS

Fukushima city

Koriyama city

5 Initial Cs distribution: Forests occupied the most

Wasteland Paddy field Beach Ocean River and Lake Forest Built-up area road / railways Golf field Crop field Other land use

Land use distribution in eastern Fukushima

Land use

Area (km2)

Initial Cs (TBq)

Forest 5,330 920

Total 8,370 1,300

Forest% 64% 69%

Kitamura et al., Anthropocene (2014).

Objective of the F-TRACE project 6

Research area

1F NPP

Odaka

Ukedo/Takase Maeda

Kuma/Ogawara Tomioka/Oginosawa

Kido

Ohta

7

Ide

・Systematic research on each river system from forests to estuary makes it possible to evaluate the behavior in whole catchment.

・Comparing behaviors in several river systems with different characteristics is useful to clarify factors dominate transport of RCs.

8

ca.6 m

Rainfall (gross precipitation)

Throughfall Stem flow

Surface runoff & Soil loss Transport of radioactive

Cs with Surface runoff & Soil loss on the forest slope

Assessment of radioactive Cs input and output in the forest floor per unit period and area from forest [ex. Bq/m2/year]

ca. 20 cm height

Precipitation gauge

Stem flow tank (70 L)

Tanks for soil & water catchment (200 L x 2)

Water Level gauge

Water level gauge

Solar battery panel

Turbidity gauge

Triangular weir (W 30cm, H 25cm, D 60cm)

Water sampler(10 L) (throughfall)

Monitoring of surface runoff and soil loss

Gauge of soil moisture

Flowing into river system

9

Stem

flow

Leaf

(litt

er) f

all Th

roug

hfal

l

Mineral soil

Organic layer Basement

Infil

trat

ion

R a i n f a l l

Surface runoff Soil loss

Water, litter and soil movement

Acc

umul

ated

Cs-

137

on th

floo

r (kB

q/m

2 )

Duration after the accident (d)

Litter fall

Stem flow

Throughfall

FY 2

015

Kato et al., J. Environ. Radioact. (in press).

10

Stemflow and its Cs-137 activity. The Cs-137 activity is a volume-weighted average of triplicate at each experimental plot (KE&KW; Kawamata, KA; Kawauchi).

Niizato et al., J. Environ. Radioact. (2016).

Concentration of Cs in non-filtered stemflow sample was similar to that of filtered.

Dissolved fraction

of Cs was dominant in the stemflow.

Cs in Stemflow

11 Cs transported by soil loss

2013 2014 2015 Kawauchi Evergreen

(Japanese cedar) Steep slope

0.10% 0.06% 0.30%*

Kawamata (KE) Deciduous

Gentle slope 0.02% 0.10%

Kawamata (KW) Deciduous

Steep slope 0.05% 0.11% 0.23%

* The outlet to collect eroded soil of this plot was repaired on Nov. 2014.

Erosion rate of Cs-137 with soil in observation plots in forests from April to November (8 month).

Based on Niizato et al., J. Environ. Radioact. (2016).

12

residue 3rd 1M HCl 2nd 1M HCl 1st 1M HCl 3rd 1M KCl 2nd 1M KCl 1st 1M KCl 3rd 0.01M NaCl 2nd 0.01M NaCl 1st 0.01M NaCl

Original forest soil

After H2O2 treatment (removal of organics)

Sorption duration Initial Cs concentration in sorption experiment

Sorption duration Initial Cs concentration in sorption experiment

Soil samples after sorption experiments were sequentially desorbed by;

- NaCl (simple washing), - KCl (ionic exchange), - HCl (inside the solids). Cs was strongly

adsorbed onto soil regardless of organic contents and hardly desorbed.

Cs adsorbed onto soil

Evolution of dose rate after decontamination 13

©2014 DigitalGlobe

1 2

3 4

5

6

7 8

9

10

11 12

13

14

15 16

17 18

19 20

21

22

Decontaminated area

Measurement points

Expected movement of Cs

Measurement points for dose rate designated at boundary between decontaminated area (in the Decontamination Pilot Project) and not decontaminated forests in Kawauchi.

Evolution of dose rate after decontamination 14

Decontaminated forest (removal of litter and topsoil)

15

Dose rates at the surface were scattered (gray circles). Leaves and soils from forests temporally sedimented. However, they were maybe removed by next flowing water.

Air dose rates showed decrease depending on decay of Cs. => Discharge of Cs from forests was quite limited so that

increase of air dose rate at forest edge was not significant.

Forest slope

ditch

Leaves and soils

Erosion direction 1m

slope road

Direction of flow

Dose rate measurement

0

1

2

3

線量

率 [μ

Sv/

h]日付　（年月）

川内村貝の坂 2　1m空間線量率

　　　　　　　（北・東・南・西） 1m物理減衰計算値 　 1cm表面線量率　　　　　　　白抜き：積雪時

2013/4 2014/4 2015/4 2016/4

Dos

e ra

te (µ

Sv/

h)

Date

Dose rate(1m) NESW Expected decay Dose rate(1cm)

Kawauchi #2

Evolution of dose rate after decontamination

Sampling point

Depth distribution of Cs N 50 m

A

B

0 20 40 60 80 100 120

Distance [m]

380

400

420

Elev

atio

n [m

]

A B

Red Relief Image Map, patent technology by Asia Air Survey Co.Ltd.

Contour intervals: 1 m Sample No. : PAK-1, at crest flat

Brown forest soil

16

2012Inventory (kBq m-2)

1333 kBq/m2

0

5

10

15

20

0 200 400 600 800 1000

2014Inventory (kBq m-2)

1837 kBq/m2

0

5

10

15

20

0 50 100 150 200 250

2012年度Inventory (kBq m-2)

309 kBq/m2 2014Inventory (kBq m-2)

444 kBq/m22014-2-sup_Inventory

(kBq m-2)487 kBq/m2

0

4

8

12

16

20

0 200 400 600

2012-5-supInventory (kBq m-2)

1256 kBq/m2

Cs deposition (kBq/m2/cm)

Cs deposition (kBq/m2/cm)

Dep

th (c

m)

Dep

th (c

m)

•Ridge •Slope: 8° •Sampling Jan. 2013

Oct. 2014

•Middle of slope •Slope: 30° •Sampling

Jan. 2013 Oct. 2014

•Bottom of valley •Slope: 20° •Sampling

Jan. 2013 Oct. 2014

Dep

th (c

m)

Cs deposition (kBq/m2/cm)

- 84-92% of deposited Cs existed within 5 cm on Oct. 2014.

Migration behavior of Cs 17

http://www.jaea.go.jp/02/press2013/p13102901/index.html Nakanishi et al., J. Environ. Radioact. (2014).

2011 2012～

Wash off Degradation

Cs was adsorbed on minerals.

Litter layer

y

y

y

y

Process of supply of Cs to the mineral layer has been changed. Cs is being accumulated in 0 – 10 cm mineral layer.

Cs discharged to river system

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

Cs-134 Cs-137

Concentration of radioactive Cs in the deposits supplied from forests decreased with the elapse of time.

2,500

2,000

1,500

1,000

500

0 Radio

activi

ty c

onc.

（kB

q/kg

）

18

2013.8 2014.12 Site A

Surface deposits inside small dams located between moutainside forest and mountain stream were collected.

2013.8 2014.12 Site B

Site B

2 m

0 200 400 600 800 0 200 400 600 800 0 200 400 600 800

0 200 400 600 800 0 200 400 600 800 0 200 400 600 800 0 200 400 600 800 0 200 400 600 800

137Cs concentration [kBq kg-1]

137Cs concentration [kBq kg-1]

Mas

s de

pth

[g c

m-2

] M

ass

dept

h [g

cm

-2]

0

10

20

30

40

50

0

10

20

30

40

50

St. A 26.7 MBq m-2

St. B 14.5 MBq m-2

St. C 26.8 MBq m-2

St. D 20.2 MBq m-2

St. E 4.6 MBq m-2

St. F 6.6 MBq m-2

St. G 4.7 MBq m-2

St. H 6.7 MBq m-2

St. I 6.7 MBq m-2

Concentration of Cs in the sediments of the Ogaki dam lake 19

St. A；26.7MBq m-2

St. B;14.5MBq m-2

St. C;26.8MBq m-2

St. D;20.2MBq m-2

St. E;4.6MBq m-2

St. F;6.6MBq m-2

St. G;4.7MBq m-2

St. H;76.7MBq m-2

St. I;6.7MBq m-2

0 200 400 600 800

Upstream

Downstream

Cs concentration in the bottom sediments of dam lake also decreased with time.

Countermeasures to keep soil in forests 20

Enough litter layer and vegetation are required.

21

Plants Sampling Plant Cs-137 (Bq/kg-DW)

Soil Cs-137 (Bq/kg-DW) TF

oudo (spikenard) 2015/4 1.5×102 8.6×103 1.7×10-2

western bracken fern 2015/4 1.6×103 1.3×105 1.2×10-2

bamboo shoot 2015/5 9.2×103 1.2×104 7.9×10-1

ostrich fern 2015/5 1.8×102 1.6×104 1.1×10-2

giant butterbur 2015/5 2.0×102 5.8×103 3.4×10-2

giant butterbur 2015/5 8.8×101 5.8×103 1.5×10-2

Eleutherococcus sciadophylloides 2015/5 8.5×103 1.8×104 4.8×10-1

Eleutherococcus sciadophylloides 2015/5 1.1×104 1.5×104 7.0×10-1

chocolate vine 2015/9 4.0×101 1.4×104 2.9×10-3

Vaccinium oldhamii 2015/9 2.0×102 1.1×104 1.8×10-2

Vaccinium oldhamii 2015/9 1.0×102 3.8×103 2.6×10-2

hana peach 2015/9 3.6×101 1.6×104 2.2×10-3

Japanese chestnut 2015/9 1.1×104 2.1×104 5.3×10-1

Japanese chestnut 2015/9 1.5×103 7.2×103 2.1×10-1

Japanese chestnut 2015/9 1.1×103 7.0×104 1.5×10-2

Japanese chestnut 2015/9 4.0×103 3.6×104 1.1×10-1

Mushrooms Sampling Mushroom Cs-137

(Bq/kg-DW) Soil Cs-137 (Bq/kg-DW) TF

Trametes versicolor 2015/4 7.0×103 1.3×104 0.56 Hypholoma sublateritium 2015/10 1.2×104 1.6×104 0.80 Hypholoma sublateritium 2015/11 1.4×104 7.1×104 0.20

Wild plants and mushrooms

Eleutherococcussciadophylloides

Hypholoma sublateritium

22 Trees

• Concentrations in barks were relatively high. => relationship to Cs in stemflow? • Concentrations in sapwood and heartwood were lower than those of barks.

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

スギ*(川内村)

スギ

(川内村)スギ*

(川内村)スギ*

(川内村)スギ

(川内村)

Cs-

137

濃度（B

q/kg

-D

W)

外樹皮

内樹皮

辺材

心材

リター

土壌(0-5cm)

1.0×105

1.0×104

1.0×103

1.0×102

1.0×10

1.0

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

ｲﾇﾌﾞﾅ

(川内村)クヌギ

(川内村)

Cs-

137

濃度

（B

q/kg

-D

W)

外樹皮

内樹皮

木部

(辺材+心材）

リター

土壌(0-5cm)

リター未

採取

1.0×105

1.0×104

1.0×103

1.0×102

1.0×10

1.0

リター未

採取

Cs-

137

(Bq/

kg-D

W)

Cs-

137

(Bq/

kg-D

W)

outer bark inner bark heartwood +sapwood litter soil

Japanese blue beech (Fagus japonica)

Japanese cedar (Cryptomeria japonica)

Sawtooth oak (Quercus acutissima)

outer bark inner bark sapwood heartwood litter soil

heartwood

sapwood Inner bark

Outer bark

Cambium layer

23 Particulate Cs on trees and lichens

Mapping of elemental distribution around the particle with high concentration of Cs, which could be distinguished by autoradiography.

Cs Fe

SEI BEI

Si O

Na Sn

Al K Mg Cl

Zn C Ca K

Lichen

examples of lichens

bark of cherry

examples of lichens

• Cs Concentrated point was observed on barks by autoradiography. => particulate Cs related to dissolved Cs in stemflow?

Dissolved Cs in river water

（Bq/L） Ukedo Takase Dissolved 137Cs 0.31

±0.03 0.05

±0.02 SS-bound 137Cs 2.2

±0.2 2.1

±0.1 134+137Cs 3.3 2.9

0

50

100

150

200

250

300

SS (m

g/L)

>60 um

3-60 um

0.45-3 um

Suspended solids （SS, left） and radiocesium （right） concentration in lower Ukedo and Takase river waters in the tyhpoon in 2013.

24

SS: Ukedo << Takase SS supplied upstream did not

reach to lower Ukedo river due to the presence of the dam.

Dissolved Cs: Ukedo > Takase Higher Cs accumulated along

mountain streams might affect.

Ukedo Takase

Comparison of Ukedo and Takase rivers Ukedo river

- Dam at middle - Upper: Highly contaminated

Takase river - No dam - Upper: Less contaminated

25

Ogaki dam lake

FDNPS

UKER-7

TAKR-3

Concentration of Cs in the Ogaki dam lake water 26

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

2014/6/10 2014/9/18 2014/12/27 2015/4/6 2015/7/15 2015/10/23 2016/1/31

Diss

olve

d 13

7 Cs [

Bq/L

]

流入水（請戸川）

流入水（小出谷川）

放流水

Evolution of concentration of dissolved Cs in inflow and outflow waters of Ogaki dam lake (Ukedo river).

Inflow 1 Inflow 2 Outflow

< 1 Bq/L Seasonal change

Less effect of dissolved Cs on rice

http://www.maff.go.jp/j/kanbo/joho/saigai/pdf/youin_kome2.pdf (in Japanese)

Cs-

137

in b

row

n ric

e (B

q/kg

)

usual irrigation water of site A

irrigation water of site A after raining

water containing designated dissolved Cs

water sampled on the research center of this study

Pot culture using soil from site A where brown rice with > 500 Bq/kg of Cs-137 was gathered. - exchangeable K+: 5.0 mg K2O / 100 g-dw - less micacious clay

Pot culture using soil from the research center where brown rice with < 100 Bq/kg of Cs-137 was gathered. - exchangeable K+: 17.6 mg K2O / 100 g-dw - presence of micacious clay

Lower than 1 Bq/L of dissolved Cs in irrigation water could give lower than 100 Bq/kg in rice.

27

Prediction of Cs discharge from the river

It can be applied to predict the behavior of Cs depending on precipitation.

Wat

er fl

ow [m

3 ]

137 C

s di

scha

rge

[GB

q]

GETFLOWS (physical model for soil loss and water transportation): Water flow, soil loss and Cs-137 discharge for 3 days during each high water event.

Relationship to precipitation

0.0E+0

1.0E+7

2.0E+7

3.0E+7

4.0E+7

5.0E+7

6.0E+7

0.0E+0

2.0E+6

4.0E+6

6.0E+6

8.0E+6

1.0E+7

0.0E+0

1.0E+2

2.0E+2

3.0E+2

4.0E+2

5.0E+2

6.0E+2

0.0E+0

2.0E+6

4.0E+6

6.0E+6

8.0E+6

1.0E+7

0 100 200 3000.0E+0

1.0E+2

2.0E+2

3.0E+2

4.0E+2

5.0E+2

6.0E+2

0 100 200 3000.0E+0

1.0E+7

2.0E+7

3.0E+7

4.0E+7

5.0E+7

6.0E+7

0 100 200 300Precipitation per event [mm]

28

3 da

ys s

oil l

oss

[kg]

3 da

ys w

ater

flow

[m

3 ]

3 da

ys d

isch

arge

of 1

37C

s [G

Bq]

Precipitation per event [mm] Precipitation per event [mm]

Soi

l los

s [k

g]

0

1

10

100

1000

浮遊

土砂

に付

着す

るCs

-137

濃度

(Bq/

L)

Prediction of Cs sedimentation/discharge in the dam

N

Hirusone

Yaguno

Exit

Monitoring station

Current shoreline(water level = EL 140m)

Shoreline before the accident(water level = EL 170m)

Ogaki Dam

0.0E+00

1.0E+06

2.0E+06

3.0E+06

4.0E+06

5.0E+06

6.0E+06

7.0E+06

8.0E+06

9.0E+06

1.0E+07

0

10

20

30

40

50

60

70

80

90

100

Acc

umul

atio

n of

Inflo

ws (

m3)

Rive

r Dis

char

ge R

ate

(m3/

s)

Hirusone (measured)

Yaguno (measured)

Hirusone (boundary condition)

Yaguno (boundary conditionl)

Accumulation (measured)

Accumulation (boundary condition)

29

Inflow 1

Inflow 2

Inflow 1

Inflow 2

Water flow（m3/s）: input data Concentration of137Cs in the inflows（Bq/L）: input data TODAM: 1D transport model for contaminant in rivers

outflow

Calculation agreed well to observation.

0

1

10

100

1000

Conc

entr

atio

n of

Cs -

137

in Fl

ow (B

q/L)

Concentration of 137Cs in the outflow（Bq/L）: output

29

Kurikami et al., J. Environ. Radio., 137, 10 (2014).

Inflow 1

Inflow 2

outflow

Summary • Forests

• Large inventory: 0-10 cm mineral layer of soil adsorbed Cs, leading to less Cs in river system.

• Short-term: decontaminated near living-sphere, hopefully with something to prevent soil loss.

• Long-term: managed so as to keep enough litter layer and vegetation of forest floor.

• To be considered / monitored: • Cs in ecosystem (wild plants, mushrooms, trees) to estimate concentrations in future.

• Dissolved Cs in water system if it would increase due to any changes of circumstances.

30

Thank you for you attention !! 31

http://fukushima.jaea.go.jp/english/decontamination/