2007 Volume 44 Issue 2 Pages 101-111
A Micro Bubble Jetter (MBJ) was used in field experiments on improving bottom sediment quality in order to determine whether this new technology can prevent the mass mortality of shellfish during the summer season due to deteriorating sediment quality in the ark shell fishing ground in inner Ariake Bay. The MBJ is mounted on a small fishing boat and is used to draw up surface water and inject it with microbubles and to improve bottom sediment quality by directly squirting microbubbles into surface mud using a towed nozzle unit. Improvements in bottom sediment quality were measured by investigating surface sediment quality before and after the towed device (including oxidation-reduction potential [Eh] and acid volatile sulfides [AVS-S]), benthic organisms (wet weight, number of species, and numbers of individuals), and ark shell mortality rates. Using this method, there was an increase of 100〜200mV in Eh and a reduction of 0.1〜O.2mg/g DW in AVS-S in the region where the MBJ was towed compared with the control region. Moreover, a reduction in organic C, total-N, and total-P concentrations was observed in the region where the MBJ was towed. Finally, in comparison with the control region, there was a significant decrease in the ark shell mortality rate in the region where the MBJ was towed that was commensurate with amount of MBJ towing performed. Therefore, this study demonstrates that this method is useful in improving bottom sediment quality in inner Ariake Bay.
