THE EFFECT OF DISSOLVED OXYGEN DEPLETION DUE TO FINE SEDIMENT ON THE CLAM HABITAT IN THE TIDAL FLAT OF BANJO RIVER IN OITA

A field survey has been performed both in the estuary of the Banjo river and in the Saeki bay in order to investigate the effect of water quality on the clam habitat in tidal flat. The result of water quality measurements shows that dissolved oxygen depletes due to fine sediment in the bottom of the Banjo river. Dissolved oxygen profiles near the sediment/water interface on the tidal flat are simulated based on the experimental results of the oxygen consumption rate by the sediment. The dissolved oxygen concentration profile varies considerably near the sediment/water interface and rapidly becomes zero just below the interface regardless of the shear velocity, because all DO that reach the sediment surface are utilized instantly. There is not enough oxygen both at the sediment surface and inside the sediment. A tidal flat that has biologically active sediment accumulating is therefore an inappropriate place for the clam habitat.