Diffusion process of radioactive materials in ecosystems of coastal sea area

H. ARAKAWA1, T. TOKAI1, Y. MIYAMOTO1, S. AKIYAMA1

K. UCHIDA1, Y. AGATSUMA2, S. KATAYAMA2, M. AOKI2,I. MATSUMOTO3, N. HIRAKAWA3

1.Tokyo University of Marine Science and Technology 2. Tohoku University

3.Fukushima Prefectural Fisheries Station

1

1. Background On March 11, 2011, a great earthquake and tsunami

occurred in North-east Japan. The Fukushima Daiichi nuclear power plant (FNPP)

lost the power supply due to the tsunami. A large amount of radioactive materials was released.

The Fukushima Daiichi nuclear power plant (FNPP) exploded

2

The total amount of the radioactive materials to ocean was 3.6x1015 Bq for 137Cs. （ TEPCO ）

Then, the radioactive materials exceeding the limit level of Japan was detected from various species of fishes caught in the coastal sea area of Fukushima.

⇒Until September 2013, the fishing of Fukushima Pref. was banned.

The highest value: 510,000Bq/kgGreenling , Hexagrammos otakii 3

Radioactive Cs concentration ( 134 Cs +  137 Cs in Bq/kg-wet) in nine representative marine products in Fukushima coast. (Wada et al., 2013)

Concentration of radioactive Cs of octopus and gastropod decreased immediately.

200 days after the accident, radioactive Cs was not detected in these organisms.

4

Fisheries agency of Japan and Fukushima prefecture measured Cs concentrationof marine organisms after the accident.

Radioactive Cs concentration ( 134 Cs +  137 Cs in Bq/kg-wet) in nine representative marine products in Fukushima coast. (Wada et al., 2013)

Concentrations of radioactive Cs of anchovy, bivalve, seaweed decreased with time rapidly.

5

Radioactive Cs concentration ( 134 Cs +  137 Cs in Bq/kg-wet) in nine representative marine products in Fukushima coast. (Wada et al., 2013)

However, concentrations of radioactive Cs of demersal coastal fish decreased slowly.These species indicate concentrations above 100 Bq/kg at present.

6

Purpose To clarify;how radioactive material is spread in the marine ecosystem?how the concentration of organisms will change in the future.

We have examined 3 steps for this purpose. 1. Diffusion via food web: measurement of radioactive Cs concentration. analysis of C-N stable isotope2. Diffusion via movements: Biotelemetry3. Diffusion within body of fish: measurement of biological half life

7

We must measure the spatial and temporal change Cs concentration.

Observation stations We set stations to the North and South of FNPP. 　 North side: Souma city (Distance: 50km) South side: Iwaki city Ena (50km), Yotsukura (35km) Observation field and methods　 Coastal ecosystem 　　　 rock region ecosystem　　　　　　　　　 sand region ecosystem

Observation period

Sep. 2012 – Sep.2013

Souma

Yotsukura

Ena

The ecosystems of rock region and sand region are constituted by the respective different organism species.In this research, we divided into the reef region and the sands region, and examined Cs levels in the organisms.

Gill net※rock region

Seine net※sand region

SCUBA diving 　※seaweed, invertebrate

⇒Cs concentration distribution and stable isotope ratio of each organisms were measured.

⇒Cs concentration is shown as the sum total value of １３４ Cs and １３７ Cs .

buoy

9

Yotsukura Ena

This figure shows the results of the radioactive Cs concentration of the fishes caught in 2012 and 2013.In this sea area, 44 species were caught in all.

Several species from which Cs was not detected are pelagic and surface dwelling fish. As for all other fish, radioactive Cs was detected. It is often over the limit value (100Bq/kg) by rockfish and spot skate.

10

Limit value

This figure shows the results of the radioactive Cs concentration of the invertebrates collected in 2012 and 2013. In this sea area, 21 species were collected in all.

The organisms in which cesium levels were not detected were mollusks like octopus and squid.As for other species, radioactive Cs was detected. The invertebrates which exceeded the limit value were only two species, one of the sponge Porifer sp. and a species of sea urchin.

11

Seaweed & seagrass

0

10

20

30

40

50

60

134+

137C

s co

ncen

trat

ion

(Bq/

kg)

Yotsukura

Seagrass Brown algae Red algae

Zostera 　 　　 Eisenia　　　　　Undaria　　　　　　Laminaria　Sargassum　f.　Sargassum　m.　Gloiopeltis　　Gelidium　　

2012 2013

The Cs concentrations of seaweeds and seagrass.The Cs concentration of each species decreased with time.Red algae had higher concentrations than the other species.There was no difference between annual and perennial species

12

0

100

200

300

400

500

600

9月11月

Yotsukura

Ena

Souma Yotsukura Ena

Souma

Spot skate

Con

cent

rati

on o

f ra

dioa

ctiv

e C

s （

Bq/

kg）

Comparison with distance from FNPP

n=7 n=7

n=5

n=4

n=3 n=10

Sep. 2012

Nov. 2012

Cs concentration of fish on Souma 50km north, Yotsukura 35 km south, and Ena 50km south from FNPP were compared. For example, it was selected a skate which is one of the higher Cs concentration fish.When the distance was same Souma and Ena, the concentration on south was higher than north.In the same direction, the concentration at the stations nearer FNPP were higher.

The carbon nitrogen stable isotope ratio of fish was analized.

Sand region in Souma

- 30 ～ - 23‰

6

10

14

18

-20 -18 -16 -14 -12 -10

δ13C

δ15N

B1-20m

B2-20mB1-10m

B2-10m

底藻Phytoplankton

カジメ

6

10

14

18

-20 -18 -16 -14 -12 -10

B1-20m

B2-20mB1-10m

B2-10m

底藻

E. cava Zostera marina

Benthic microalga

c.f. Land organic matter

These symbols indicate C-N ratio of fish on sand region in Souma.It was thought that the source of the primary production for the fishes of this sea area was benthic microalgae.

14

Diffusion via movement of organisms Method: Biotelemetry of stationary type

Object fish ： rockfish Sebastes cheni 　　 Sea area ： off Ena

Schematic of bio-telemetry

Tracking system

Positioning system

Stationary system

Implanted transmitters

transmitters

transmitters

Stationary systemSTATIONARY MONITORING RECEIVERS

TRACKING RECEIVERSRADIO LINKED BUOY

RECEIVERS

Biotelemetry is the technique of installing a receiver in a sea area, receiving the ultrasonic wave from the fish which has a transmitter embedded in its body, and checking the location from the wave signal.

Four rockfish were caught in this sea area, and an ultrasonic transmitter (Pinger) was implanted in each fish. They were released at the same place.

15

11/22 12/12 1/1 1/21 2/10 3/2 3/22 4/11 5/10

20

40

60

80

100

120

140

160

180

8

9

10

11

12

13

14

15

16メバル 1 メバル 2

メバル 3 メバル 4

Date2012 2013

Sig

nal r

ecei

ved

（tim

es/d

ay）

Temperature （

℃）

Change of signal received with time （ 159 days ）

Temperature

Sebastes1 Sebastes 3

Sebastes 2Sebastes 4

This graph is record of movement from the four fish.The experiment has been continued from November, 2011 to even now.

As for the vertical axis of this graph, the number of signal reception times per day and the right shows the water temperature. When the fish is moving actively, the number of times of signal reception increases.

The number of times of reception fell with the decrease of the water temperature. Rockfish were in the same territory during autumn, winter, and spring.

By previous reports, it was considered that shallow to deep migrations were carried out with the change in water temperature.

However, it was confirmed that the black rockfish in this area has remained in the same place during one year.That is, it was thought that rockfish was polluted with this sea area. 16

Conclusion1.Diffusion via the food web・ Cs concentration of all species decreased with time. However, many coastal, demersal organisms have elevated radioactive Cs concentrations. ・ From viewpoint of the food web, the food source of the food web of many species of organisms originates from organic matter which is assumed as microalgae.

2.Diffusion via movement•Black rockfish that had high Cs concentrations remained in a small territorial area of the coast.

The 3rd step, Diffusion within body of fish is examined now.

Now, ｔ he Fukushima nearshore waters are without the pressure of fisheries. We must observe the radioactive Cs concentrations of marine organisms for a long time, to clarify the distribution and changes of Cs in the future, and to ensure suitable management. 17

AcknowledgementThis research was supported by the Environment Research and Technology Development Fund (4ZD-1201) of the Ministry of the Environment, Japan.

Research teamTokyo University of Marine Science and Technology, Tohoku University,Fukushima Prefectural Fisheries Experimental Station

CooperationAqua marine Fukushima aquariumFukushima Pref. Fishermen’s cooperative association

Thank you for your attention!!! 18

19

Methods of bio-telemetry of fish.

- Stationary type -

Midfloat

swivel

Swivel

Float

Marker Flag

Anchor

Wire

2m

MO

NIT

OR

ING

RE

CE

IVE

RS

15 m

東京海洋大学実験中

Temperature logger

Bottom

400m

Receivingrange

Ena

Tracking of Gill- net

Receiver

21