DISTRIBUTION OF RADIOCESIUM IN BLACK PINE TREE FORESTS IN ROKKASHO, AOMORI, JAPAN

Area of Science:

• Environmental Science
• Radiochemistry
• Forest Ecology

Background:

• The 2011 Fukushima Dai-ichi Nuclear Power Plant (FDNNP) accident released radiocesium isotopes (134Cs, 137Cs).
• Atmospheric deposition of these isotopes was detected in Japan, including areas ~400 km north of FDNNP.

Purpose of the Study:

• To investigate the distribution and inventory of radiocesium (134Cs and 137Cs) within a Japanese black pine forest ecosystem.
• To understand the role of forest components (soil, trees) in retaining and accumulating fallout radionuclides.

Main Methods:

• Measurement of 134Cs and 137Cs activity concentrations in soil and whole black pine trees (including roots).
• Sampling conducted between 2015 and 2019.
• Comparison of radiocesium distribution with historical weapon fallout data.

Main Results:

• Most deposited 134Cs was retained in the forest floor, with a distinct depth distribution compared to weapon fallout.
• In above-ground parts, over 50% of 137Cs was found in tree trunks.
• The forest's total 134Cs inventory was 1.6 times higher than external deposition, attributed to the canopy effect.

Conclusions:

• Japanese black pine forests act as significant sinks for atmospheric radiocesium.
• Forest canopy plays a crucial role in concentrating radiocesium, influencing its environmental fate and distribution.
• Understanding radionuclide behavior in forest ecosystems is vital for post-accident environmental monitoring and remediation strategies.