The accident of the Fukushima Dai-ichi Nuclear Power Plant in March, 2011, released large amounts of radiocesium into the atmosphere, and contaminated the environment of Gunma Prefecture in eastern Japan. In particular, 640 Bq kg^–1-wet of radiocesium concentration was found in wakasagi (Hypomesus nipponensis) in Lake Onuma on Mt. Akagi in August, 2011. Thus, to elucidate the body-size effect in weight-dependent and dynamics of radiocesium in the ecosystem of Lake Onuma, we determined the age of wakasagi, the body-weight class of the radiocesium concentration in wakasagi and the effective ecological half-life (T_eff) of radiocesium in wakasagi 0+ from 2012 to 2016. The body-size effect was found for the ¹³⁷Cs concentration of wakasagi fished from 2012 to 2015, i.e., the concentration of ¹³⁷Cs increased with the increase in its body weight. On the other hand, no body size effect was found in 2016. This result may be caused by the following two factors: the ¹³⁷Cs concentration of the lake water reached a steady state after May 2014; wakasagi is a small plankton-feeding fish, while it is known that larger piscivorous fishes show the strong body size effect. T_eff of the ¹³⁷Cs concentration in wakasagi 0+ consists of two components, fast- and slow-term ones, and the decay rate of the ¹³⁷Cs concentration in wakasagi 0+ was greatly reduced. As stated above, the radiocesium contamination in Lake Onuma has still been lasting; we are thus continuing our monitoring studies.

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　下水処理場の流入水NH₄-Nの連続計測を3年間実施し，計測結果を使用した運転計画を立案して省エネ施策やN₂O抑制施策，能動的管理を下水処理場シミュレータにより評価した．流入水NH₄-Nの季節変動では，冬場のほうが高い傾向であり，最小値と最大値の幅も大きかった．日間変動では早朝に最小値となり，午前中に最大値となる典型的な変動パターンが年間を通じて見られ，最小値と最大値では2倍以上の差があり，運転管理上の考慮が必要と考えられた．シミュレーションを利用した運転計画として，省エネ施策で流入水窒素負荷の低い時間帯のDO設定値を下げると曝気風量が5.2%削減され，処理場全体GHG排出量は0.5%削減された．水処理N₂O生成抑制施策として負荷の高い時間帯の汚泥返送率を2倍とすると，N₂O排出量は12.0%抑制された．能動的管理では窒素供給量が5%の増加となり，電力消費CO₂は58%の削減となっていた．流入水質を連続計測し運転計画を立案することにより，現状プロセスの運転管理の工夫でGHG排出量の削減が期待できることが確認できた．

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