Abstract
The sediment oxygen demand (SOD) and the efflux rates of nutrients and hydrogen sulfide (H2S) were determined by the benthic chamber method to estimate the effect of the efflux of N·P·S from sediment in a dredging hollow. The sand capping experiment was carried out with granulated coal ash in a part of the dredging hollow located off-shore of Lake Nakaumi in Hosoi. The SOD maximum was 712 g·m-2·day-1, and the efflux rate maxima of NH4-N, PO4-P and H2S were 640 mg·m-2·day-1, 103 mg·m-2·day-1 and about 12600 mg·m-2·day-1, respectively. The dredging hollow was shown to have a large effect on the internal load flowing into Lake Nakaumi. The rates of load reduction by sand capping with granulated coal ash during examination were as follows. SOD decreased by 23%. The efflux rates of H2S, NH4-N and PO4-P decreased by 69%, 87% and 52%, respectively. Since the effect of sand capping was shown sufficient to improve the oxygen-poor state in the dredging hollow over a long period, it was revealed that sand capping with granulated coal ash could control efflux from sediment from the dredging hollow.
