|Title||Assimilative capacity of fish farm environments as determined by the benthic oxygen uptake rate: Studies using a numerical model|
|Authers||Katsuyuki ABO and Hisashi YOKOYAMA|
|Keywords||environmental criteria, fish farm, numerical simulation, Law to Ensure Sustainable Aquaculture Production|
|Citation||Bull. Fish. Res. Agen. supplement No. 19,79-87, 2007|
In order to promote improvements in the environmental quality of aquaculture grounds, the Japanese government enacted the ”Law to Ensure Sustainable Aquaculture Production” in 1999. In the Basic Guidelines for this law, an environmental criterion based on the benthic oxygen uptake (BOU) rate was adopted to assess the quality of aquaculture environments. Biological mineralization is considered to peak when the BOU rate reaches its maximum, which is an indicator of the maximum desirable level of organic matter loading. The acid volatile sulfide (AVS-S) content of the sediment increases in direct correlation to the organic matter loading, and is used as an indicator of the assimilative capacity of bottom sediments. The AVS-S value corresponding to organic matter loading when the BOU rate is at its maximum is defined as the standard value. Recent studies, however, have suggested that it is difficult to detect the maximum (peak) BOU and to determine the standard value through in situ investigations. The practical applicability of this criterion therefore needs to be re-examined scientifically. To do this, we developed a three-dimensional numerical model that takes into account advection, dispersion, sedimentation, and decomposition of organic matter from fish farming systems. The numerical model should be used instead of in situ investigations for the practical application of the criterion. We also used this model to assess the assimilative capacity of an existing fish farm on the basis of the criterion. The model proved to be an effective tool for evaluating the assimilative capacity of the environment of fish farms.