[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.

Related articles

• What conditions have influenced the radioactive Cs concentration in freshwater fish?
• How is the concentration of radioactive cesium in river fish changing over time?
• When it rains, does radioactive cesium flow out of forests with soil? 【¹³⁷Cs flow in heavy rain】
• Does the concentration of radioactive cesium in river water increase after rainfall? 【Changes of the concentration of ¹³⁷Cs in heavy rain】
• Does the concentration of radioactive cesium in river water increase after rainfall? 【Effect of the upstream dam on the ¹³⁷Cs concentration】

Reference

1. Kurikami, H., Sakuma, K., Malins, A., Sasaki, Y. and Niizato, T. (2019): Numerical study of transport pathways of ¹³⁷Cs from forests to freshwater fish living in mountain streams in Fukushima, Japan, Journal of Envrionmental Radioactivity, vol. 208-209, 106005. https://doi.org/10.1016/j.jenvrad.2019.106005