Cs outflow from forest floor adjacent to a residential area; Comparison of decontaminated and non-decontaminated forest floor

生活圏に隣接する森林からのセシウム137流出量; 除染地と未除染地の比較

新里 忠史  ; 渡辺 貴善 

Niizato, Tadafumi; Watanabe, Takayoshi

降雨期の福島県の森林において、土壌侵食に伴うセシウム137流出量の3年間にわたるモニタリングを除染地および未除染地において実施した。その結果、除染地でのセシウム137流出量は未除染地の10から14倍多いものの、除染地からのセシウム137流出率は林床被覆の回復に対応して3.24%から0.61%に減少した。林床被覆が60%以上に達すると、除染地でのセシウム137流出量は変動が小さくなり、流出率は未除染地と同レベルとなった。林床被覆の回復に伴うセシウム137流出量の減少は、雨滴衝撃に対する林床の保護効果の回復および流出物に含まれるセシウム137濃度の比較的高い土壌成分の割合が減少することによると考えられる。

The 3-years monitoring of Cs outflow associated with soil erosion in the decontaminated and no decontaminated sites using experimental plot was conducted in the forest of Fukushima during the rainy season. The Cs outflow in the decontaminated site was 10 to 14 times larger than that of no decontaminated site. However, the outflow in the decontaminated site decreased from 3.24% to 0.61% in corresponding with the recovery of the forest floor cover. When reaching of the forest floor cover to 60% and over, the Cs outflow in the decontaminated site turned into relatively minor fluctuations and similar level to the no decontaminated site. The decrease in the Cs outflow corresponding to the restoration of the forest floor cover was owing to the recovering of the protective effect of forest floor against the raindrop splash and decrease in ratio of the soil component with relatively high Cs activity in the particulate matter.