小林 達明

東日本大震災後人手を加えていない里山林（放置区）と，隣接した2013年に熊手でリター層を除去した里山林（除染区）において，除染の有無が分解に伴う落葉中の放射性Cs濃度・量に及ぼす影響を調査した。試験は福島県川俣町山木屋地区のコナラが優占する里山林で行った。放置区，除染区に1m×1m，深さ30cmの底の開いた木枠を1つずつ設置し，2020年4月に林床の落葉を各木枠内に敷き詰め堆肥化した。数か月ごとに分解中の落葉の重量と放射性Cs (134Cs+137Cs)濃度を測定した。放置区，除染区ともに9月には重量含水率は約80％，重量残存率は約50％となった。除染区の落葉堆肥の放射性Cs濃度および量は放置区の0.4～0.5倍であった。9月の落葉堆肥の放射性Cs濃度は4月に比べて放置区，除染区ともに2.0～2.3倍であった。落葉堆肥の放射性Cs量は放置区，除染区ともに4～9月まで違いがみられなかった。除染により林床の落葉および落葉堆肥の放射性Cs濃度が低下していた。また，落葉堆肥中への系外からの放射性Csの取込みはみられないと考えられた。

This paper describes the involvement of the residents of the Yamakiya district of the Kawamata town, a former evacuation area after the accident of Fukushima Daiichi Nuclear Power Plant (FDNPP), in the on-going research activities of the authors on the behaviour of radioactive caesium in the environment. By relying on dialogue, measuring radiation, and other collaborative practices, this involvement enabled a series of actions to be taken to resolve the challenges related to the recovery after the lifting of the evacuation order that were appreciated by the residents. The paper also discusses the effects of the interactive program led by the Yamakiya School organized by the authors in cooperation with the residents including among others lectures, voluntary works and radiological surveys on local issues. Based on the above, the authors make recommendations on the desirable form of relationship between residents and experts after an event of large-scale environmental pollution including radiological contamination. Through these activities the authors have also gradually changed their research approach.