報告書番号

V13008

タイトル（和文）

樹木の枝・葉における放射性セシウム濃度の経年変化（2011～2013）

タイトル（英文）

Yearly transitions of radiocesium contamination in leaves and twigs of 17 woody species between 2011 and 2013

概要 （図表や脚注は「報告書全文」に掲載しております）

千葉県我孫子市において2011～2013に年1回ずつ17種51本の樹木を対象としてサンプリングを行い、各年次に発生した枝や葉の134+137Cs濃度を測定した。その結果、以下のことが明らかとなった。
１．134+137Cs濃度の経年的変化；134+137Cs濃度は、調査した全樹種・全個体の平均として葉では2011年に比べて2012年は64%、2013年は19%、枝では同じく110%、28%に低下した。
２．樹種や部位による134+137Cs濃度の違い；2011年における葉の134+137Cs濃度は常緑樹種平均が落葉樹種平均より7倍以上高かったが、2013年にはその差は縮小して3倍程度となった。また、2012年以降はほとんどの常緑樹種において、その年に発生した葉や枝（当年葉・枝）の方が同時に採取した前年に発生した葉・枝（前年葉・枝）に比べて134+137Cs濃度が高かった。
以上の結果から、樹木における134+137Cs濃度は全体として経年的な減少傾向が鮮明であるが、樹種や部位毎の生理・生態によって生じた当年葉・枝への134+137Csの移行率の違いなどから、減少の程度はそれぞれ異なることが示された。

概要 （英文）

Radiocesium (134Cs + 137Cs) concentrations, primarily derived from the Fukushima accident in March 2011, were measured in twigs and leaves of 51 stands for 17 woody species (e.g., Prunus x yedoensis cv. Somei-Yoshino, Cryptomeria japonica, Acer buergerianum, and Platanus orientalis). Every stands were grown in Abiko (located at 35.87815N, 140.02487E; approximately 200 km SSW from the FDNPP, the Fukushima Dai-ichi Nuclear Power Plant), and every sampling was conducted at a mid-growth season in each year of 2011, 2012, and 2013. The measurement aimed to see not only differences among species and sampling years, but also to clear those in the effects of transports from parts to parts. Results demonstrated that the radiocesium concentrations were basically decreased depending on time (i.e., years); the total average of radiocesium concentrations in leaves observed in 2012 and 2013 were 64% and 19% of those observed in 2011, respectively, and those in twigs observed in 2012 and 2013 were 110% and 28% of those observed in 2011, respectively. However, the decreasing ratios were varied with the species. In particular, the decreasing ratios were higher in evergreen species than in deciduous species. For example, the average of radiocesium concentrations in entire observed leaves was more than seven times higher in evergreen species than in deciduous species in 2011, whereas that was around three times in 2013. In addition, the radiocesium concentrations were basically higher in the leaves/twigs expanded at the sampling year than in those expanded at the previous year, even though every leaves/twigs was sampled at a simultaneous timing after 2012. This may mean a translocation of radiocesium from older-leaves/twigs to newer-leaves/twigs could be occurred at a considerable level. It is obvious that a decreasing trend in the radiocesium concentration in leaves/twigs was demonstrated irrespective of the species and the parts; however, it is also clear that the decreasing level was varied with the species and the parts. Further observations are necessary to prospect the effect of radio-contamination on trees and/or to safely utilize the forest products.

報告者

キーワード