Radiocesium Transfer in Forest Insect Communities after the Fukushima Dai-ichi Nuclear Power Plant Accident

<div><p>To understand radiocesium transfer in the forest insect food web, we investigated the activity concentrations of radiocesium in forest insects in the Fukushima and Ibaraki Prefectures approximately 1.5–2.5 years after the Fukushima Dai-ichi Nuclear Power Plant. We analyzed 34 species of insects sampled from 4 orders and 4 feeding functional groups (herbivore, carnivore, omnivore, and detritivore) from three sites in each prefecture. ¹³⁷Cs activity concentrations were lowest in herbivorous species and were especially high in detritivorous and omnivorous species that feed on forest litter and fungi. Radiocesium activity concentrations in any given species reflected the degree of contamination of that species’ primary food sources since radiocesium activity concentrations were found to be the lowest in leaves and grass and the highest in litter, bark, and fungi. This study confirmed that litter and other highly contaminated forest components such as fungi, decaying wood, bryophytes, and lichens serve as sources of ¹³⁷Cs transfer into the forest insect community.</p></div

¹³⁷Cs activity concentrations in Forest Components and Insects.

<p>¹³⁷Cs activity concentrations are shown for study sites in Fukushima (upper panel) and Ibaraki (lower panel) in 2012. Litter and leaf samples are shown separately for Japanese cedar forests (Litter_e and Leaf_e) and deciduous forests (Litter_d and Leaf_d). Dark horizontal lines represent the mean, with the box representing the 25th and 75th percentiles, the whiskers the 5th and 95th percentiles, and dots indicating outliers.</p

Concentration Ratio of ¹³⁷Cs in Sampled Insect Species.

<p>CRs were calculated as Bq kg⁻¹ insect dry weight/(Bq kg⁻¹ litter dry weight. Species are grouped by the orders to which they belong (Coleoptera, Hemiptera, Lepdoptera, Orthoptera) with lines separating the orders. Colors indicate the functional feeding group to which species belongs: green, herbivore; yellow, omnivore, gray, carnivore; red, detritivore. Symbols indicate the sampling area: circle, Fukushima; triangle, Ibaraki.</p

¹³⁷Cs Activity Concentrations in Insect Feeding Functional Groups.

<p>¹³⁷Cs activity concentrations of insect species are shown in relation to the ¹³⁷Cs activity concentrations in litter at the site. Colors indicate the functional feeding group to which species belongs: green, herbivore; yellow, omnivore; gray, carnivore; red, detritivore. Symbols indicate the sampling area: circle, Fukushima; triangle, Ibaraki.</p

The final model of GLMM for the ¹³⁷Cs activity concentrations in insectsshowing estimates, standard errors, and <i>P</i>-values.

<p>Coefficients in bold indicate significant effects (<i>P</i> < .05).</p

A bibliography of studies on biodiversity in Japanese retarding basins

This list is a compilation of references describing the biodiversity of Japanese retarding basins. A total of six taxa are covered: birds, amphibians, fish, insects, shellfish, and plants. For each taxon, a list of accepted and rejected references is provided under different tabs. The list of accepted references includes the name of the target retarding basin, the name of the species, and a detailed description of the biodiversity studies. Reasons for rejection are given for the list of rejected references.  In this study, we collected previous findings by three methods: ❶ Japanese search using J-STAGE, ❷ English search using the Web of Science Core Collection, and ❸ other literature search. In ❸, a related literature search was conducted by browsing the lists of references cited in ❶ and ❷, and a search of highly relevant references (in Japanese and English) by authors not included in ❶ and ❷. In addition, keyword searches were performed using Google, limited to PDF files.  A total of 9,183 references were selected. We then screened the literature based on the exclusion criteria as follows. (1) The title in the list of cited references corresponds by search but is not directly related to the literature in question.  (2) Literature in the form of illustrated books, pamphlets, photographs and public documents published by the government, etc., in which the collection period or collection sites of the target taxon are unknown.  (3) Information leaflets and reports on biological observation meetings, environmental education, events, etc. in flood control areas.  (4) Introductory articles of relevant papers.  (5) Special specifications and survey implementation plans for biological surveys in waterways. (6) Other newspaper articles introducing the implementation of biological observation events. As a result, 354 references were included. For the remaining 354 references, the following four criteria were mandatory.  (1) The study site of interest had to be located within a retarding basin. (2) The organisms of interest were taxonomically known in the literature, at least at the family level, and the effects and impacts of the retarding basin were clearly discernible. (3) The survey period is after the construction of the retarding basin. (4) For each taxon, only references from previous studies were to be selected if the results in the target literature overlapped with results from previous studies by the same author, or if the results were cited in books and no new results were added.  As a result, 302 references were included. The references that fulfilled one of the following criteria were then selected. (1) References that are closely related to biodiversity, such as surveys of biota in floodplains, surveys of the discovery or habitat/growth status of rare or new species, surveys of the discovery or habitat/growth status of non-native species, etc. (2) References that contain information on the distribution of biota, new species, rare species and invasive alien species, although the main purpose of the study is not to understand the status of biodiversity. The references were screened and those with the following content were excluded. (1) Physiological studies or studies of factors affecting the growth of specific plant species or the feeding and migration of specific animal species. (2) The study site is not strictly a wetland surface of the retarding basin. (3) Studies where the retarding basin was selected as a demonstration site for new technologies or new analytical methods. As a result, 242 references were selected.</p

Episode Analysis of Deposition of Radiocesium from the Fukushima Daiichi Nuclear Power Plant Accident

Chemical transport models played key roles in understanding the atmospheric behaviors and deposition patterns of radioactive materials emitted from the Fukushima Daiichi nuclear power plant after the nuclear accident that accompanied the great Tohoku earthquake and tsunami on 11 March 2011. However, model results could not be sufficiently evaluated because of limited observational data. We assess the model performance to simulate the deposition patterns of radiocesium (¹³⁷Cs) by making use of airborne monitoring survey data for the first time. We conducted ten sensitivity simulations to evaluate the atmospheric model uncertainties associated with key model settings including emission data and wet deposition modules. We found that simulation using emissions estimated with a regional-scale (∼500 km) model better reproduced the observed ¹³⁷Cs deposition pattern in eastern Japan than simulation using emissions estimated with local-scale (∼50 km) or global-scale models. In addition, simulation using a process-based wet deposition module reproduced the observations well, whereas simulation using scavenging coefficients showed large uncertainties associated with empirical parameters. The best-available simulation reproduced the observed ¹³⁷Cs deposition rates in high-deposition areas (≥10 kBq m^–2) within 1 order of magnitude and showed that deposition of radiocesium over land occurred predominantly during 15–16, 20–23, and 30–31 March 2011

Relationship between the ¹³⁷Cs inventory in the soil and the dose rate on the soil surface.

Relationship between the 137Cs inventory in the soil and the dose rate on the soil surface.</p

¹³⁷Cs activity concentrations in <i>Aralia elata</i> buds collected in Iitate village, Fukushima from 2014 to 2022.

The blue horizontal line indicates the Japanese reference level for foods (100 Bq/kg). Data were retrieved from Iitate village (2022) [11]. 137Cs activity concentrations below the detection limits were regarded as 5 Bq/kg. Reported ratios of 134Cs to 137Cs outside the range of 0.8–1.2 on 11 March 2011 were excluded to ensure reliability.</p

Fig 3 -

Relationship between137Cs activity concentrations in A. elata buds and137Cs depositions at the decontaminated (light blue) and abandoned (pink) sites. The blue horizontal line indicated the Japanese reference level for food (100 Bq/kg).</p