title: Sampling design and required sample size for evaluating contamination levels of137Cs in Japanese fir needles in a mixed deciduous forest stand in Fukushima, Japan.
abstract: We estimated the sample size (the number of samples) required to evaluate the concentration of radiocesium (137Cs) in Japanese fir (Abies firma Sieb. & Zucc.), 5 years after the outbreak of the Fukushima Daiichi Nuclear Power Plant accident. We investigated the spatial structure of the contamination levels in this species growing in a mixed deciduous broadleaf and evergreen coniferous forest stand. We sampled 40 saplings with a tree height of 150 cm-250 cm in a Fukushima forest community. The results showed that: (1) there was no correlation between the137Cs concentration in needles and soil, and (2) the difference in the spatial distribution pattern of137Cs concentration between needles and soil suggest that the contribution of root uptake to137Cs in new needles of this species may be minor in the 5 years after the radionuclides were released into the atmosphere. The concentration of137Cs in needles showed a strong positive spatial autocorrelation in the distance class from 0 to 2.5 m, suggesting that the statistical analysis of data should consider spatial autocorrelation in the case of an assessment of the radioactive contamination of forest trees. According to our sample size analysis, a sample size of seven trees was required to determine the mean contamination level within an error in the means of no more than 10%. This required sample size may be feasible for most sites.
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan. Electronic address: oyrk-2012@hiroshima-u.ac.jp.
authors.forename: Yurika
authors.initials: Y
authors.lastname: Oba
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Yamada
mesh_terms: D028202:Abies / Q000737:chemistry*; D002588:Cesium Radioisotopes / Q000032:analysis*; D065928:Forests; D062406:Fukushima Nuclear Accident; D007564:Japan; D018515:Plant Leaves / Q000737:chemistry; D018517:Plant Roots / Q000737:chemistry; D011834:Radiation Monitoring / Q000379:methods*; D018401:Sample Size; D012987:Soil / Q000737:chemistry; D012990:Soil Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D012987:Soil; D012990:Soil Pollutants, Radioactive
keywords: Abies firma; Fukushima nuclear accident; Inter-individual variation; Moran's I; Natural forests; Spatial autocorrelation