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

几十年来，由于森林的萧条，日本的森林遭到了破坏。森林破坏造成的严重问题是林地土壤侵蚀、溪水浑浊、树木生长衰退。重要的是使用一些有用的指标来估计森林的破坏程度。因此，本研究的目的是建立利用天然或人工放射性核素估算森林破坏程度的方法。研究结果表明，~(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，我们认为与有机质有关的~(137)Cs和~(137)Cs在运输过程中的行为和化学形态的变化是重要的。为了从沉积物中识别侵蚀地点，提出了放射性核素之间的比值，如^&lt；40&gt；K，^&lt；214&gt；铅，^&lt；214&gt；铋，^&lt；208&gt；Tl和^&lt；212&gt；铅。此外，森林破坏引起的环境变化可以通过树轮14&gt；C的分析结合树的年代学来研究。

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.