中海浚渫窪地におけるN·P·Sの溶出速度の見積もりと石炭灰造粒物を用いた覆砂の効果

摘要

The sediment oxygen demand (SOD) and the efflux rates of nutrients and hydrogen sulfide (H_2S) were determined by the benthic chamber method to estimate the effect of the efflux of N·P·S from sediment in a dredging hollow. The sand capping experiment was carried out with granulated coal ash in a part of the dredging hollow located off-shore of Lake Nakaumi in Hosoi. The SOD maximum was 712 g·m~(-2)-day~(-1), and the efflux rate maxima of NH_4-N, PO_4-P and H_2S were 640 mg·m~(-2)-day~(-1), 103 mg·m~(-2)-day~(-1) and about 12600 mg·m~(-2)-day~(-1), respectively. The dredging hollow was shown to have a large effect on the internal load flowing into Lake Nakaumi. The rates of load reduction by sand capping with granulated coal ash during examination were as follows. SOD decreased by 23%. The efflux rates of H_2S, NH_4-N and PO_4-P decreased by 69%, 87% and 52%, respectively. Since the effect of sand capping was shown sufficient to improve the oxygen-poor state in the dredging hollow over a long period, it was revealed that sand capping with granulated coal ash could control efflux from sediment from the dredging hollow.%中海の細井沖浚渫窪地において，底泥酸素要求量(以下，SOD),栄養塩及び硫化水素（以下,H_2S)の溶出速度をチャンバー実験法により検討した。また，浚渫窪地の一部を石炭灰造粒物で覆砂して溶出抑制効果を検証した。その結果，SODは最大で712g·m~(-2)day~(-1),NH_4-N溶出速度は最大で640g·m~(-2)day~(-1),PO_4-P溶出速度は最大で103mg·m~(-2)day~(-1),H_2S溶出速度は最大で約12600mg·m~(-2)day~(-1)であった。 実験期間中の石炭灰造粒物の覆砂による負荷削減効果は，SODが23%,H_2S溶出速度が69%,NH_4-N及びPO_4-P溶出速度がそれぞれ87%,52%であり，貧酸素条件が長期間続く浚渫窪地でも石炭灰造粒物の覆砂効果が期待でき，溶出を抑制できることが明らかになった。