Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Department of Geography and Spatial Sciences, University of Delaware, Newark, DE, USA; Department of Plant and Soil Sciences, University of Delaware, Newark, DE, USA.
Sci Total Environ. 2022 Apr 20;818:151698. doi: 10.1016/j.scitotenv.2021.151698. Epub 2021 Nov 16.
Aiming to fill a need for data regarding radiocesium transport via both branchflow and stemflow through forests impacted by radioactive fallout, this study examined the vertical variation of radiocesium flux from branchflow and stemflow through the canopies of young Japanese cedar (Cryptomeria japonica (L. f.) D. Don) and Japanese oak (Quercus serrata Murray) trees in the aftermath of the Fukushima Dai-ichi Nuclear Power Plant accident. In forested areas approximately 40 km northwest of the location of the Fukushima Dai-ichi accident, the Cs concentration varied significantly among sampling periods and between the two forests, with the oak stand exhibiting higher Cs concentrations and depositional fluxes than the cedar stand. Expressed per unit trunk basal area, the depositional flux of Cs generated from the cedar and oak stands was 375 and 2810 Bq m year, respectively. Of this total, 71% and 48% originated from the cedar and oak canopy, respectively, while the remainder originated from the trunk. Accordingly, the origin of radiocesium was more balanced for the oak stand with almost half of the flux coming from the canopy (48%) and the other half from the trunk (52%). Only about a quarter (29%) of the radiocesium flux originated from the trunk in Japanese cedar. Results from this work provide needed data that can enable a more thorough conceptualization of radiocesium cycling in forests. Coupling these empirical results with a physically-based model would likely lead to better forest management and proactive strategies for rehabilitating radioactively-contaminated forests and reducing the exposure risk of radiation dose rate for those that utilize forest products.
本研究旨在填补福岛第一核电站事故后放射性沉降物对森林影响下通过支流水和茎流水输运放射性铯的相关数据空白，调查了年轻的日本雪松（Cryptomeria japonica (L. f.) D. Don）和日本栎（Quercus serrata Murray）林通过林冠的支流水和茎流水的放射性铯通量的垂直变化。在福岛第一核电站事故地点西北约 40 公里的森林地区，两个森林的 Cs 浓度在采样期之间存在显著差异，栎树林的 Cs 浓度和沉积通量均高于雪松林。以单位树干基面积表示，来自雪松和栎树林的 Cs 沉积通量分别为 375 和 2810 Bq m 年。其中，71%和 48%分别来自雪松和栎树林冠，其余来自树干。因此，栎树林的放射性铯来源更为均衡，约一半的通量来自树冠（48%），另一半来自树干（52%）。在日本雪松中，只有约四分之一（29%）的放射性铯通量来自树干。本研究结果提供了所需的数据，有助于更全面地了解森林中放射性铯的循环。将这些经验结果与基于物理的模型相结合，可能会导致更好的森林管理和对放射性污染森林的主动恢复策略，并降低那些利用森林产品的人的辐射剂量率暴露风险。
