title: Depth distribution of cesium-137 in paddy fields across the Fukushima pollution plume in 2013.
abstract: Large quantities of radiocesium were deposited across a 3000 km(2) area northwest of the Fukushima Dai-ichi nuclear power plant after the March 2011 accident. Although many studies have investigated the fate of (137)Cs in soil in the months following the accident, the depth distribution of this radioactive contaminant in rice paddy fields requires further examination after the typhoons that occurred in this region. Such investigations will help minimize potential human exposure in rice paddy fields. Radionuclide activity concentrations, organic content and particle size were analysed in 10 soil cores sampled from paddy fields in November 2013, 20 km north of the Fukushima power plant. Our results demonstrate limited depth migration of (137)Cs with the majority concentrated in the uppermost layers of soils (<5 cm). More than 30 months after the accident, between 46.8 and 98.7% of the total (137)Cs inventories was found within the top 5 cm of the soil surface, despite cumulative rainfall totalling 3300 mm. Furthermore, there were no significant correlations between (137)Cs depth distribution and the other parameters. We attributed the maximum depth penetration of (137)Cs to grass cutting (73.6-98.5% of (137)Cs in the upper 5 cm) and farming operations (tillage - 46.8-51.6% of (137)Cs in the upper 5 cm). As this area is exposed to erosive events, ongoing decontamination works may increase soil erodibility. We therefore recommend the rapid removal of the uppermost - contaminated - layer of the soil after removing the vegetation to avoid erosion of contaminated material during the subsequent rainfall events. Further analysis is required to thoroughly understand the impacts of erosion on the redistribution of radiocesium throughout the Fukushima Prefecture.
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement (LSCE/IPSL), Unité Mixte de Recherche 8212 (CEA, CNRS, UVSQ), F-91198 Gif-sur-Yvette Cedex, France. Electronic address: hugo.lepage@lsce.ipsl.fr.
authors.forename: Hugo
authors.initials: H
authors.lastname: Lepage
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement (LSCE/IPSL), Unité Mixte de Recherche 8212 (CEA, CNRS, UVSQ), F-91198 Gif-sur-Yvette Cedex, France. Electronic address: olivier.evrard@lsce.ipsl.fr.
authors.forename: Olivier
authors.initials: O
authors.lastname: Evrard
authors.affiliation: Center for Research in Isotopes and Environmental Dynamics (CRIED), Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan. Electronic address: onda@geoenv.tsukuba.ac.jp.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Onda
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement (LSCE/IPSL), Unité Mixte de Recherche 8212 (CEA, CNRS, UVSQ), F-91198 Gif-sur-Yvette Cedex, France. Electronic address: irene.lefevre@lsce.ipsl.fr.
authors.forename: Irène
authors.initials: I
authors.lastname: Lefèvre
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement (LSCE/IPSL), Unité Mixte de Recherche 8212 (CEA, CNRS, UVSQ), F-91198 Gif-sur-Yvette Cedex, France. Electronic address: placeby@lsce.ipsl.fr.
authors.forename: J Patrick
authors.initials: JP
authors.lastname: Laceby
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement (LSCE/IPSL), Unité Mixte de Recherche 8212 (CEA, CNRS, UVSQ), F-91198 Gif-sur-Yvette Cedex, France. Electronic address: sophie.ayrault@lsce.ipsl.fr.
authors.forename: Sophie
authors.initials: S
authors.lastname: Ayrault
mesh_terms: D000383:Agriculture; D002588:Cesium Radioisotopes / Q000032:analysis*; D062406:Fukushima Nuclear Accident; D007564:Japan; D012275:Oryza / Q000254:growth & development; D011834:Radiation Monitoring; D012987:Soil / Q000737:chemistry*; D012990:Soil Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D012987:Soil; D012990:Soil Pollutants, Radioactive
keywords: Cesium-137; Depth distribution; Soil core