title: Modeling radiocesium transport from a river catchment based on a physically-based distributed hydrological and sediment erosion model.
abstract: The accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in March 2011 resulted in the deposition of large quantities of radionuclides, such as (134)Cs and (137)Cs, over parts of eastern Japan. Since then high levels of radioactive contamination have been detected in large areas, including forests, agricultural land, and residential areas. Due to the strong adsorption capability of radiocesium to soil particles, radiocesium migrates with eroded sediments, follows the surface flow paths, and is delivered to more populated downstream regions and eventually to the Pacific Ocean. It is therefore important to understand the transport of contaminated sediments in the hydrological system and to predict changes in the spatial distribution of radiocesium concentrations by taking the land-surface processes related to sediment migration into consideration. In this study, we developed a distributed model to simulate the transport of water and contaminated sediment in a watershed hydrological system, and applied this model to a partially forested mountain catchment located in an area highly contaminated by the radioactive fallout. Observed discharge, sediment concentration, and cesium concentration measured from June 2011 until December 2012 were used for calibration of model parameters. The simulated discharge and sediment concentration both agreed well with observed values, while the cesium concentration was underestimated in the initial period following the accident. This result suggests that the leaching of radiocesium from the forest canopy, which was not considered in the model, played a significant role in its transport from the catchment. Based on the simulation results, we quantified the long-term fate of radiocesium over the study area and estimated that the effective half-life of (137)Cs deposited in the study area will be approximately 22 y due to the export of contaminated sediment by land-surface processes, and the amount of (137)Cs remaining in the catchment will be reduced to 39% of the initial total within 30 y after contamination. This study provides a perspective on the transport of suspended sediments and radiocesium in catchments with similar land use and radiocesium contamination.
authors.affiliation: Department of Environmental Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuta-cho Midori-ku, Yokohama, 226-8502, Japan. Electronic address: kinouchi.t.ab@m.titech.ac.jp.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kinouchi
authors.affiliation: Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Yoshimura
authors.affiliation: Department of Environmental Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuta-cho Midori-ku, Yokohama, 226-8502, Japan.
authors.forename: Teppei
authors.initials: T
authors.lastname: Omata
mesh_terms: D002586:Cesium / Q000032:analysis; D002588:Cesium Radioisotopes / Q000032:analysis*; D062406:Fukushima Nuclear Accident; D019015:Geologic Sediments / Q000032:analysis; D007564:Japan; D008962:Models, Theoretical; D011834:Radiation Monitoring; D011847:Radioactive Fallout / Q000032:analysis*; D045483:Rivers; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D011847:Radioactive Fallout; D012990:Soil Pollutants, Radioactive; D014875:Water Pollutants, Radioactive; D002586:Cesium
keywords: (137)Cs; Hydrological model; Sediment transport; Soil erosion