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Effects on Ecosystem

（2020）

ＱWhere does the radioactive cesium taken in by mountain stream fish come from? How will the cesium concentration in them change in the future? 【Example of analysis】

ＡAn analysis using environmental monitoring data shows that cesium taken in by mountain stream fish is supplied through three different paths (see Fig. A).
Although cesium concentrations in mountain stream fish are expected to continue to decrease steadily, predicting that requires further elucidation of the movement and occurrence of cesium.

[Supply paths of cesium taken in by mountain stream fish through river water]

  1. Cesium leaching out of leaves that have directly fallen from trees into rivers
  2. Cesium leaching or flowing out from the litter layer into rivers
  3. Cesium leaching through the organic soil layer into surface water/groundwater and then into rivers

It is assumed that a rapid decline in the cesium concentration in leaves and the litter layer has caused less amounts of cesium to be supplied through paths 1 and 2. This is considered a major contributor to the decline in cesium concentrations in mountain stream fish (Fig. B).

The contribution of path 3 is expected to increase in the future, but the cesium present in organic soil layers will be gradually transferred along the depth direction and ultimately absorbed into inorganic soil layers.

Cesium concentrations in mountain stream fish are expected to continuously decrease. However, to predict future levels of cesium in mountain stream fish, we need to further elucidate the transfer of cesium from organic to mineral soil layers and where and how cesium exists.

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Reference

  1. Kurikami and Sakuma(2018): JpGU 2018
  2. Kurikami, H. et al. Numerical study of transport pathways of 137Cs from forests to freshwater fish living in mountain streams in Fukushima, Japan, Journal of Environmental Radioactivity, vol. 208-209, 2019, 106005.