Abstract
The contributions of oxygen consumption by bottom-layer water and sediment were compared by investigating the oxygen consumption rates of bottom-layer water and sediment in Lake Kitaura and using in situ data on thermal stratification and hypoxic water. The oxygen consumption rate of bottom-layer water in Lake Kitaura was 2,550–2,910 mg m-3 d-1 and that of sediment was 652–1,080 mg m-2 d-1. These rates suggest that the contribution of oxygen consumption by sediment becomes greater when the height of the bottom-layer water column is less than 0.16 m. On the other hand, the contribution of oxygen consumption by bottom water becomes greater when the height of the bottom-layer water column exceeds 0.60 m. In addition, the in situ contribution of oxygen consumption was assessed using the vertical time-series data of thermal stratification and hypoxic water from July 28 to August 3, 2019, at Kamaya Observatory in Lake Kitaura. As a result, it was found that the contribution of oxygen consumption of by bottom-layer water was larger than that by sediment. However, it was considered that the effect of oxygen consumption by sediment could not be ignored, because hypoxic water formed gradually from the bottom of the lake.
