Center for Regional Environment Research, National Institute for Environmental Studies, Onogawa, Tsukuba, Ibaraki, Japan.
Fukushima Prefectural Centre for Environmental Creation, Fukasaku, Miharu, Fukushima, Japan.
PLoS One. 2019 Feb 14;14(2):e0212348. doi: 10.1371/journal.pone.0212348. eCollection 2019.
Changes in 137Cs export over time following clearcutting were investigated in a Japanese forested catchment affected by the Fukushima nuclear accident. A total of 13% of the catchment area was clear-cut 2 years after the accident. Annual suspended solids (SS) export at the catchment outlet increased 1.4 to 2.0 times after clearcutting; however, 137Cs export increased slightly (up to 1.1 times), corresponding to 0.21% to 0.30% of the 137Cs inventory in the catchment. The smaller change in 137Cs export than in SS export was due to a rapid decrease in the activity concentration following clearcutting. This decrease was likely caused by both natural attenuation and SS derived from sources with a low activity concentration in the clear-cut area. Monitoring of the sediment transport from hillslopes in small-scale experimental plots showed that the 137Cs yield in the skid trail was 3.6 to 21 times greater than those in clear-cut and unlogged forest floors. This significant 137Cs transport was due to greater soil erosion (by up to two orders of magnitude) along the skid trail, despite the lower activity concentration than those in the other plots. This indicates that while skid trails were involved in the rapid decrease of the activity concentration of SS, they were a potential source of the increased export of 137Cs and SS. Net 137Cs export increased by clearcutting (the export excluding the decrease accompanied by natural attenuation) was estimated to account for only 0.092% of the inventory in the catchment for 2.5 years. These results imply that the impact of clearcutting on 137Cs export was temporary in this catchment.
本研究调查了日本森林流域在福岛核事故后，皆伐对 137Cs 输出随时间变化的影响。事故发生 2 年后，流域总面积的 13%被皆伐。皆伐后，流域出口处的年悬浮物（SS）输出增加了 1.4 至 2.0 倍；然而，137Cs 输出仅略有增加（最多增加 1.1 倍），相当于流域中 137Cs 库存的 0.21%至 0.30%。137Cs 输出的变化小于 SS 输出的变化是由于皆伐后活性浓度的快速下降。这种下降可能是由于自然衰减和源自皆伐区低活性浓度源的 SS 所致。对小尺度实验样地中坡面泥沙输移的监测表明，在滑道上的 137Cs 产率比皆伐和未采伐森林地面高 3.6 至 21 倍。尽管滑道上的活性浓度低于其他样地，但由于滑道上土壤侵蚀较大（高达两个数量级），导致了这种显著的 137Cs 输移。这表明，尽管滑道参与了 SS 活性浓度的快速下降，但它们是 137Cs 和 SS 增加输出的潜在来源。（扣除自然衰减伴随的下降量后的）皆伐引起的净 137Cs 输出增加估计仅占流域库存的 0.092%，持续了 2.5 年。这些结果表明，在本流域，皆伐对 137Cs 输出的影响是暂时的。
