Vertical Radiocesium Transfer in Soil via Roots

Wataru Sakashita (Center for Forest Restoration and Radioecology)

Research Field

Radiocesium (¹³⁷Cs) cycle in the forest ecosystem after the Fukushima Daiichi Nuclear Power Plant accident

 

Background

Dissolved ¹³⁷Cs combines with clay minerals in the soil, thus it is not expected to easily infiltrate over time. However, ¹³⁷Cs derived from the older global fallout (1950s-1960s) migrated deeper than that of the Chernobyl accident (1986). This cannot be explained by only the dissolved ¹³⁷Cs vertical migration. In this study, I hypothesized that continuous supply of ¹³⁷Cs via fine root dynamics (Fig. 1) change the vertical distribution of ¹³⁷Cs in forest soil (new perspective).

Main results

I investigated the ¹³⁷Cs inventories (Bq/m2) in both roots and soil matrix at seven study sites in eastern Japan in 2013 (four (0–20 cm) or six (0–30 cm) mineral soil layers taken at every 5 cm), and calculated ratio of fine roots to soil matrix (Table 1). I found There is a difference of about 1% between 5-10 cm and 10-15 cm. When I assume that all fine roots have been decomposed, difference in the ¹³⁷Cs inventory between 5–10 and 10–15 cm layers decrease on a decadal scale.

Table 1. Mean percentage of the¹³⁷Cs inventory in roots compared to the¹³⁷Cs inventory in the soil matrix for each soil layer.

Conclusion

Q：Can fine root turnover affect the change in ¹³⁷Cs distribution in forest soil?

A：Yes. Continuous turnover of fine roots changes the vertical distribution of ¹³⁷Cs on time scale of decades, particularly at deeper soil layers.

 

Future Perspectives

• Improves prediction of ¹³⁷Cs distribution in forest soil
• Collaborate with researchers investigating ¹³⁷Cs dynamics after the Chernobyl accident (e.g., France and UK)

 

Reference

Sakashita W., Miura S., Akama A., Ohashi S., Ikeda S., Saitoh T., Komatsu M., Shinomiya Y., Kaneko S., 2020. Assessment of vertical radiocesium transfer process in soil via roots. Journal of Environmental Radioactivity 222, 106369. https://doi.org/10.1016/j.jenvrad.2020.106369