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ISSN 1811-0231 / ISEIS Publication Series Number P002

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  Paper EIA06-019, Volume 4 (2006), Pages 225-232 = complimentary

Temporal variation of sulphide content, pH, salinity and oxidation-reduction potential of tidal flat mud in the Ariake Sea, Japan

M. A. Moqsud1*, S.Hayashi2, Y. J. Du2 and D. Suetsugu2

1. Department of Civil engineering, Saga University, Japan. *Corresponding author: rubel2011@yahoo.com.

2. Institute of Lowland Technology, Saga University, Japan.

 

Abstract

The vast tidal flat mud of the Ariake Sea comprising almost 40% of the total tidal flat area of Japan is famous for its rich fishery products and sea laver cultivation. However, a dramatic decrease in the catch of the fishery products is observed in the tidal flat mud area over the last 20 years. The high sulphide content of the mud is found to be one of the most important causes for this unfavorable geo-environmental condition for the benthos. In order to identify the temporal variation of the sulphide content, pH, salinity and oxidation-reduction potential (ORP) of the mud, field tests were conducted in the Iida and Higashiyoka tidal flat mud area of the Ariake Sea during the period 2003-2005. The field tests consisted of the collection of the mud sample from 0 - 90 cm depth by inserting a steel pipe of length 90 cm and diameter 7 cm into the tidal mud. The collected column of mud was cut into a number of specific layers the thickness of which increased with increasing depth. The sulphide content, pH, salinity and oxidation-reduction potential (ORP) of the mud in each layer were measured along with other physico-chemical properties. The sulphide content of the mud varies from 0.5 to 2.0 mg/g dry-mud, which is above the allowable limit (0.2 mg/g) for the favorable condition of the benthos’ life. In summer (August - September), the peak value of the sulphide content varies from 1.5 to 2.0 mg/g since the bacterial activities increase with the elevated seasonal temperature. The peak value of the sulphide content, on the other hand, is relatively low (0.5 -1.0 mg/g) during the winter (December – February). The highest sulphide content in the mud that decreases gradually from 2.0 mg/g at 2002 to 1.3 mg/g at 2005 indicates growing favorable conditions for the growth of benthos. The pH value, salinity and oxidation reduction potential value are also noticeably changed during the summer and the winter temperature in the tidal flat mud during the year 2003-2005.


Keywords: oxidation-reduction potential, sulphide content, tidal mud, benthos, geo-environment

 

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