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Radioactivity Dynamics in River System

（2015）

ＱWill the concentration of radioactive cesium in lake water remain high unless contaminated sediments are removed from reservoir beds? 【Tendency of the change of the concentration in reservoir beds】

ＡInvestigations at the Mano dam (Hayama lake) in Fukushima Prefecture have revealed that most of the radioactive cesium flowing into the dam is deposited into the bottom sediment. Nevertheless, the concentration of radioactive cesium in the lake water does not increase.

Fig.1　Sampling spots at Hayama lake (Mano dam)

  • Sampling spots at Hayama lake (Mano dam) and vertical depth distribution of 137Cs and dry density of bottom sediments

    Fig.2　Vertical depth distribution of 137Cs and dry density of bottom sediments (Collected in autumn 2014(①, ②), spring 2015(③))

  • Fig.3　Dissolved state 137Cs concentration of lake surface water and bottom water (collected in 2015)

  • In the Mano dam lake, the largest amount of cesium seems to be deposited in the deeper sediments due to the initial accident fallout.
  • Now, the cesium concentration in the soil inflow is low. This is deposited on top of the layer with high cesium content.
  • Many dams play a role in reducing the migration of cesium from upstream to downstream and re-accumulation.

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