National Research Institute of Aquaculture, Mie 516-0193, Japan
A new law, which was established in 1999 to prevent environmental deterioration around aquaculture farms, determined that the rates of benthic oxygen uptake (BOU) should be used as an environmental criterion. This criterion is based on the Omori-Takeoka theory in which the peak of BOU against the loaded organic matter is regarded as an indicator of the maximum phase in the process of biological remineralization. The present study aimed to clarify whether this criterion is applicable to fish farms in Gokasho Bay. Organic carbon and nitrogen in the sediment and sediment trap samples and sulfides in the sediment decreased with increasing distance from a cage. However, the peak of BOU was not found in the observed gradient of loaded organic matter. Therefore, we cannot use the criterion based on the Omori-Takeoka theory to the fish farms in Gokasho Bay. This finding may be explained by the severe organic pollution resulting in the decrease of biological remineralization and/or by the possible variation of biological BOU in its immediate response to the change of dissolved oxygen in the overlying, near-sediment-surface water.