Establishment of estimation method for devastation in forest using natural or artificial radionuclides.

由于几十年来的林业萧条，日本的森林遭到了破坏。森林破坏造成的严重问题是林地水土流失、河流泥沙淤积和林木生长衰退。使用一些有用的指标来估计森林的破坏程度是很重要的。因此，本研究的目的是建立一种利用天然或人工放射性核素估算森林破坏的方法，并证实~（60）<137>Cs是估算森林土壤侵蚀量的有效示踪剂。为了提高估算的精度，我们认为，在迁移过程中与有机质有关的^ Cs的行为和化学形态变化<137>是重要的。为了从沉积物中识别侵蚀部位，建议使用放射性核素之间的比值，如^<40>K、^<214>Pb、^<214>Bi、^<208>Tl和^<212>Pb。此外，树木年轮中^ C的分析还可以结合树木年轮学研究森林破坏引起的环境变化<14>。

Forests in Japan have been devastated because of the depression of forestry during a few decades. The serious problems caused by devastation in forest are soil erosion in forest floor, the succeeding muddy water in stream, and growth decline of trees. It is important to estimate the degree of devastation of forest using some useful indicator. Therefore, the purpose of this research is to establish the estimation method of devastation in forest using natural or artificial radionuclides.As a result of this research, we confirmed that ^<137>Cs should be a useful tracer to estimate the amount of soil erosion in forest. In order to improve the precision of the estimation, we concluded that the behavior and change in chemical form of ^<137>Cs during transportation relating with organic matter is important. For the identification of erosion site from the sediments, it was suggested that the ratios between radionuclides such as ^<40>K, ^<214>Pb, ^<214>Bi, ^<208>Tl, and ^<212>Pb are useful. In addition this, the environmental changes caused by forest devastation could be investigated by the analysis using ^<14>C in tree rings combined with dendrochronology.