Abstract:
Chemical composition of 24 elements for sed iments and suspended solids, water parameters and the
diatoms from Yatsushiro Bay tidal flat, Kuma River, and
Arase Dam have been determined to examine changes from
2002 to 2013. In 2002, sediment delivered to the bay by the
Kuma River was restricted by the Arase Dam; however, in
April 2010 two gates were opened and also repeated sea sonal flushing allowing resumption of natural sediment
transport. Bulk chemical composition of the tidal flat sed iments has changed since 2002, with marked decreases in
concentrations of As, Zn, Pb and total sulfur. Decreased
heavy metal contents in 2012 and 2013 for bay sediments
after opening the dam and repeated flushing is attributed to
dilution by previously impounded quartz and feldspar.
Restoration of natural sediment transport by opening the
dam and repeated flushing has thus brought about a
recovery in the Yatsushiro marine environment.
