2016 Volume 29 Issue 3 Pages 45-56
ABSTRACT : Hypoxic water mass often occurs during summer in inner Ariake Bay, and will cause the reduction in the population of bivalves. Aeration techniques have been tested to increase the concentration of dissolved oxygen, but these technologies are not prevailing due to financial reason, usability, etc.
In the present study, an inexpensive and simple technology was proposed to improve hypoxic condition around sea bottom. This technology enables fishermen to supply surface water with rich oxygen to bottom hypoxic layer without any specific heavy equipments. First, laboratory tank experiments were carried out to design the equipment. Then, an actual equipment was developed and tested in the field to verify its operability in the sea. Finally, the performance of the equipment was predicted by numerical computation. By the field trial, the average amount of water supply by the equipment was approximately 14 m3 / min when the equipment was towed at about 1 m/s. According to the effect evaluation which calculated by numerical computation, this technology enables to raise dissolved oxygen concentration to over 2.0mg/L, also to raise dissolved oxygen concentration to over 1.0mg/L in the area of maximum 4 m from the center of the towed line and its duration time of raising dissolved oxygen concentration will be 21.8 seconds. All results above suggests our technology enables to reduce hypoxic condition in the area of 0.0432km2 per day per one fishing boat.
