Post-deposition early-phase migration and retention behavior of radiocesium in a litter-mineral soil system in a Japanese deciduous forest affected by the Fukushima nuclear accident.
The fate of radiocesium (137Cs) derived from the Fukushima nuclear accident and associated radiation risks are largely dependent on its migration and retention behavior in the litter-soil system of Japanese forest ecosystems. However, this behavior has not been well quantified. We established field lysimeters in a Japanese deciduous broad-leaved forest soon after the Fukushima nuclear accident to continuously monitor the downward transfer of137Cs at three depths: the litter-mineral soil boundary and depths of 5 cm and 10 cm in the mineral soil. Observations were conducted at two sites within the forest from May 2011 to May 2015. Results revealed similar temporal and depth-wise variations in137Cs downward fluxes for both sites. The137Cs downward fluxes generally decreased year by year at all depths, indicating that137Cs was rapidly leached from the forest-floor litter layer and was then immobilized in the upper (0-5 cm) mineral soil layer through its interaction with clay minerals. The137Cs fluxes also showed seasonal variation, which was in accordance with variations in the throughfall and soil temperature at the sites. There was no detectable137Cs flux at a depth of 10 cm in the mineral soil in the third and fourth years after the accident. The decreased inventory of mobile (or bioavailable)137Cs observed during early stages after deposition indicates that the litter-soil system in the Japanese deciduous forest provides only a temporary source for137Cs recycling in plants.
Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan. Electronic address: koarashi.jun@jaea.go.jp.
Jun
J
Koarashi
Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan.
Syusaku
S
Nishimura
Sector of Fukushima Research and Development, Japan Atomic Energy Agency, Fukushima 970-8026, Japan.
Takahiro
T
Nakanishi
Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan.
Mariko
M
Atarashi-Andoh
Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan.
Erina
E
Takeuchi
Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan.
Kotomi
K
Muto
D002588:Cesium Radioisotopes / Q000032:analysis*; D017753:Ecosystem; D065928:Forests; D062406:Fukushima Nuclear Accident; D007564:Japan; D008903:Minerals / Q000737:chemistry; D018515:Plant Leaves / Q000737:chemistry / Q000528:radiation effects; D011834:Radiation Monitoring / Q000379:methods*; D012621:Seasons; D012987:Soil / Q000737:chemistry; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D014197:Trees / Q000737:chemistry* / Q000528:radiation effects
D002588:Cesium Radioisotopes; D008903:Minerals; D012987:Soil; D012990:Soil Pollutants, Radioactive
Fukushima Daiichi nuclear power plant accident; Litter layer; Lysimeter; Radiocesium; Soil water; Vertical migration