Nishikawa Jun

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Nishikawa
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Jun
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  • Article
    Fukushima-derived radionuclides in the ocean and biota off Japan
    (National Academy of Sciences, 2012-04-02) Buesseler, Ken O. ; Jayne, Steven R. ; Fisher, Nicholas S. ; Rypina, Irina I. ; Baumann, Hannes ; Baumann, Zofia ; Breier, Crystaline F. ; Douglass, Elizabeth M. ; George, Jennifer ; Macdonald, Alison M. ; Miyamoto, Hiroomi ; Nishikawa, Jun ; Pike, Steven M. ; Yoshida, Sachiko
  • Preprint
    Fukushima 137Cs at the base of planktonic food webs off Japan
    ( 2015-09-18) Baumann, Zofia ; Fisher, Nicholas S. ; Gobler, Christopher J. ; Buesseler, Ken O. ; George, J. A. ; Breier, Crystaline F. ; Nishikawa, Jun
    The potential bioaccumulation of 137Cs in marine food webs off Japan became a concern following the release of radioactive contaminants from the damaged Fukushima nuclear power plant into the coastal ocean. Previous studies suggest that 137Cs activities increase with trophic level in pelagic food webs, however, the bioaccumulation of 137Cs from seawater to primary producers, to zooplankton has not been evaluated in the field. Since phytoplankton are frequently the largest component of SPM (suspended particulate matter) we used SPM concentrations and particle-associated 137Cs to understand bioaccumulation of 137Cs in through trophic pathways in the field. We determined particle-associated 137Cs for samples collected at 20 m depth from six stations off Japan three months after the initial release from the Fukushima nuclear power plant. At 20 m SPM ranged from 0.65 to 1.60 mg L-1 and rapidly declined with depth. The ratios of particulate organic carbon to chlorophyll a suggested that phytoplankton comprised much of the SPM in these samples. 137Cs activities on particles accounted for on average 0.04% of the total 137Cs in seawater samples, and measured concentration factors of 137Cs on small suspended particles were comparatively low (~102). However, when 137Cs in crustacean zooplankton was derived based only on modeling dietary 137Cs uptake, we found predicted and measured 137Cs concentrations in good agreement. We therefore postulate the possibility that the dietary route of 137Cs bioaccumulation (i.e., phytoplankton ingestion) could be largely responsible for the measured levels in the copepod-dominated (%) zooplankton assemblages in Japanese coastal waters. Finally, our data did not support the notion that zooplankton grazing on phytoplankton results in a biomagnification of 137Cs.
  • Preprint
    Marine radioecology after the Fukushima Dai-ichi nuclear accident : are we better positioned to understand the impact of radionuclides in marine ecosystems?
    ( 2017-10-31) Vives i Batlle, Jordi ; Aoyama, Michio ; Bradshaw, Clare ; Brown, Justin E. ; Buesseler, Ken O. ; Casacuberta, Nuria ; Christl, Marcus ; Duffa, Celine ; Impens, Nathalie R. E. N. ; Iosjpe, Mikhail ; Masqué, Pere ; Nishikawa, Jun
    This paper focuses on how a community of researchers under the COMET (CO-ordination and iMplementation of a pan European projecT for radioecology) project has improved the capacity of marine radioecology to understand at the process level the behaviour of radionuclides in the marine environment, uptake by organisms and the resulting doses after the Fukushima Dai-ichi nuclear accident occurred in 2011. We present new radioecological understanding of the processes involved, such as the interaction of waterborne radionuclides with suspended particles and sediments or the biological uptake and turnover of radionuclides, which have been better quantified and mathematically described. We demonstrate that biokinetic models can better represent radionuclide transfer to biota in non-equilibrium situations, bringing more realism to predictions, especially when combining physical, chemical and biological interactions that occur in such an open and dynamic environment as the ocean. As a result, we are readier now than we were before the FDNPP accident in terms of having models that can be applied to dynamic situations. The paper concludes with our vision for marine radioecology as a fundamental research discipline and we present a strategy for our discipline at the European and international levels. The lessons learned are presented along with their possible applicability to assess/reduce the environmental consequences of future accidents to the marine environment and guidance for future research, as well as to assure sustainability of marine radioecology in Europe and globally. This guidance necessarily reflects on why and where further research funding is needed, signalling the way for future investigations.