CHARACTERISTICS OF SUSPENDED SEDIMENTS IN DREDGED SITE OF BRACKISH LAKE NAKANOUMI

Abstract

Suspended sediment accumulation in dredged sites of brackish Lake Nakanoumi has caused problems such as the release of nutrients and the generation of hydrogen sulfide. It is of great importance to know the characteristics of the suspended sediments at the dredged sites in order to control these problems. The characteristics of the suspended sediments at the dredged sites are; water content, 700%; ignition loss, 22%; Eh, -170mV; and average grain size, 10μm. By comperison, the characteristics of the suspended sediments away from the dredged site are; water content. 350%; ignition loss, 16%; Eh, +20mV; and average grain size, 20μm. Several kinds of diatoms were found in the suspended sediments at the dredged sites, the dominant species being Skeletonema sp. which frequently appears in the “red tide” of Lake Nakanoumi. Many mineral particles (mainly quartz) were found in the suspended sediments away from the dedged sites.
From these results, it was found that the characteristics of the suspended sediments at dredge site were higher water content and ignition loss, lower Eh value, and smoller grain size, compared to the sediments outside the dredge sites.