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Diffusion process of radioactive materials in ecosystems of coastal sea area

Diffusion process of radioactive materials in ecosystems of coastal sea area. H. ARAKAWA 1 , T. TOKAI 1 , Y. MIYAMOTO 1 , S. AKIYAMA 1 K. UCHIDA 1 , Y. AGATSUMA 2 , S. KATAYAMA 2 , M. AOKI 2 , I. MATSUMOTO 3 , N. HIRAKAWA 3 1.Tokyo University of Marine Science and Technology

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Diffusion process of radioactive materials in ecosystems of coastal sea area

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  1. 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

  2. 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

  3. 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. Greenling , Hexagrammos otakii • The highest value: 510,000Bq/kg

  4. Fisheries agency of Japan and Fukushima prefecture measured Cs concentration • of 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) Concentration of radioactive Cs of octopus and gastropod decreased immediately. 200 days after the accident, radioactive Cs was not detected in these organisms.

  5. 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.

  6. 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.

  7. To clarify; • how radioactive material is spread in the marine ecosystem? • how the concentration of organisms will change in the future. • Purpose • We have examined 3 steps for this purpose. • 1. Diffusion via food web: measurement of radioactive Cs concentration. • analysis of C-N stable isotope • 2. Diffusion via movements: Biotelemetry • 3. Diffusion within body of fish: measurement of biological half life

  8. 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 ecosystemrock region ecosystem sand region ecosystem Observation period Sep. 2012 – Sep.2013 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. • Souma • Yotsukura • Ena

  9. Gill net ※rock region • buoy Seine net ※sand region • ⇒Cs concentration distribution and stable isotope ratio of each organisms were measured. • ⇒Cs concentration is shown as the sum total value of １３４Cs and １３７Cs . SCUBA diving ※seaweed, invertebrate

  10. Yotsukura • Ena • Limit value 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.

  11. 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.

  12. Seaweed & seagrass 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

  13. Comparison with distance from FNPP • Sep. 2012 • n=5 • Nov. 2012 • n=4 • Spot skate • Concentration of radioactive Cs （Bq/kg） • n=3 • n=10 • n=7 • n=7 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.

  14. B1-20m B1-20m 18 18 B2-20m B2-20m B1-10m B1-10m B2-10m B2-10m 14 14 δ15N 10 10 Zostera marina カジメ E. cava Phytoplankton 底藻 底藻 6 6 -20 -20 -18 -18 -16 -16 -14 -14 -12 -12 -10 -10 δ13C - 30 - 23 ‰ ～ The carbon nitrogen stable isotope ratio of fish was analized. Sand region in Souma • 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.

  15. Diffusion via movement of organisms Method: Biotelemetryof stationary type Object fish：rockfish Sebastes cheni Sea area：off Ena • Schematic of bio-telemetry STATIONARY MONITORING RECEIVERS Stationary system Tracking system Stationary system Positioning system TRACKING RECEIVERS RADIO LINKEDBUOY RECEIVERS transmitters Four rockfishwere caught in this sea area, and an ultrasonic transmitter (Pinger) was implanted in each fish. They were released at the same place. 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. Implanted transmitters transmitters

  16. Change of signal received with time （159 days） Sebastes1 Sebastes 2 Sebastes 4 Sebastes 3 • Temperature • Signal received （times/day） • Temperature （℃） • 2012 • 2013 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. • Date 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. This graph is record of movement from the four fish. The experiment has been continued from November, 2011 to even now.

  17. Conclusion 1.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 rockfishthat had high Cs concentrations remained in a small territorial area of the coast. The 3rd step, Diffusion within body of fishis examined now. Now, ｔhe 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.

  18. Research team • Tokyo University of Marine Science and Technology, • Tohoku University, • Fukushima Prefectural Fisheries Experimental Station • Cooperation • Aqua marine Fukushima aquarium • Fukushima Pref. Fishermen’s cooperative association Acknowledgement This research was supported by the Environment Research and Technology Development Fund (4ZD-1201) of the Ministry of the Environment, Japan. • Thank you for your attention!!!

  19. Methods of bio-telemetry of fish.- Stationary type - 東京海洋大学 実験中 • Marker Flag Float • Ena • Wire • Swivel Temperature logger 15 m • Mid • float • 400m • Receiver • Receiving • range MONITORING RECEIVERS • Tracking of Gill- net • swivel 2m • Bottom • Anchor

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