Author(s): Kazuo Murakami; Yuichiro Nobusawa; Yutaka Kameyama; Tomohiro Kitamura; Toshimasa Koizumi
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Keywords: Contaminated sediments; Nutrient release reduction; Anoxic water; Sand capping technique; Laboratory test; Numerical simulation
Abstract: This paper describes the mechanism of anoxic water generation due to contaminated sea bottom sediments in Tokyo Bay. Water quality in Tokyo Bay has still serious problems in spite of large reduction of wasted loads from surrounding areas. It is considered that the reason of water contamination is influenced by internal loads from contaminated sediments on the sea bottom in Tokyo Bay. The nutrient salts are released from contaminated sediments. In order to reduce the nutrient release rate, a sand capping technique was conducted at Yokohama Port in Tokyo Bay. In order to study the effectiveness of sand capping on nutrient release reduction and its lasting effect, we carried out the field observations of water quality and sediment quality at the sand capping construction area at Yokohama Port. Then undisturbed sediments are extracted from the sea bottom at the study area. From the results of nutrient release test, a large amount of nutrient salts is released from the sediments under the anaerobic condition. By the laboratory tests, it is shown that the sand capping technique has still effect on nutrient release reduction, and the effectiveness is dependent upon the thickness of mud layer accumulated on the capping sand. And it is shown that the nutrient release reduction by sand capping has large effect on the improvement of dissolved oxygen (DO) concentration of bottom water by ecological numerical simulations.
Year: 2005