Measurement of sediment oxygen demand for modelling dissolved oxygen distribution in tidal Keelung River

Abstract

AbstractThe Keelung River is one of the major branches of the Danshuei River estuarine system, which runs the metropolitan capital city of Taipei, Taiwan, and receives a large of amount of wastewater. The dissolved oxygen (DO) concentration is generally low in the tidal portion of the Keelung River. Hypoxia/anoxia occurs often, particularly during a low‐flow period. The sediment oxygen demand (SOD) amounts to a significant value, hence increasing the total oxygen demand load of the river. The present work reports on laboratory SOD made on grab sediment core samples in situ that are undisturbed. The results reveal that SOD values fluctuate with variations in seasons and are higher in summer due to a high‐temperature effect. It was found in the laboratory tests that the average SOD (at 20 °C) value is 0.76 g/m2/day and the maximum SOD (at 20 °C) value reaches 1.58 g/m2/day. The mean values of measured SOD at each station were adopted in the vertical two‐dimensional water quality model to simulate the DO distribution along the tidal Keelung River. The simulated results are in reasonable agreement with the measured DO distribution in the river. Model sensitivity analyses were also conducted with increasing and decreasing SOD. It reveals that SOD is an important parameter that affects the DO distribution in the tidal estuary.