浚渫ヘドロを利用した資源循環型の干潟再生実験

上野 成三・高山 百合子・勝井 秀博

 埋立処分される浚渫土は、有機物を多く含むことから生物にとって有用な資源と成り得る。そこで、三重県英虞湾において、浚渫土を利用した干潟再生実験を平成12年9月に開始した。ここでは、現地盤土と浚渫土を混合して干潟を造成し、底質・底生生物の経時変化について追跡調査を実施した。本報では、干潟造成後18ヵ月の追跡調査データのうち、底生生物の復活状況、および、浚渫土の混合割合と底質、底生生物の関係を整理した。その結果、干潟生物相は、浚渫土を用いた干潟でも順調に復活し約1年で安定することが分かった。また、ある程度の有機物を含有している底泥で底生生物種類数が増加することが分かった。以上より、干潟再生に最適な底泥の有機物含有量が指標化され、浚渫土の混合割合の設定が可能となった。

キーワード: 底生生物,浚渫土,底質,沿岸生態系,干潟,英虞湾

A Field Study of Recycling Type of Tidal Flats with The use of Dredged Sediment

Seizo Ueno, Yuriko Takayama and Hidehiro Katsui

Dredged sediment disposed in reclamations can be useful biological resources because they contain organic matter. A field study of tidal flats using dredged sediment at Ago bay in Mie Prefecture has been carried out since September, 2000. The tidal flats were made of mixture of sand obtained at the site and dredged sediment. Quality of sediment and marine species were monitored. The rates of recovering of sediment quality and benthos were investigated and those were related to the mixing rate of dredged sediment using the monitoring data obtained in eighteenth months after the beginning of the field study. As a result, it was shown that the benthos on the tidal flats made of dredged sediment revived well in a year. Also shown was that the number of benthos increased more on the bed containing certain amount of organic matter than those on a clean bed. The concentration of organic matter in the sediment which is most suitable for benthos' reviving was quantified, which came to enable designing the mixing rate of dredged sediment for making tidal flats.

keywords: benthos, dredged sediments, sediments, coastal ecosystem, tidal flats, Ago Bay