Abstract
In this study, we developed a new measurement method of sediment oxygen demand (SOD) . SOD in the bottom layer of lakes is closely related to the change in dissolved oxygen (DO) which is to be a new environmental standard for aquatic environments. Our method makes use of undisturbed sediment cores and measures SOD more easily and faster than the existing methods. Since the instruments are portable, our method can be widely applied to many lakes. SOD measurements in Lake Kasumigaura and Lake Biwa (the northern and southern basins) revealed that the SOD values were different among the locations and showed a seasonal variation. In Lake Biwa (the southern basin) samples, rapid DO consumption was observed from the beginning of the incubation, implying that DO was consumed by the reduced forms of iron and/or manganese diffused from the sediments. There were significant correlations between the amount of iron and phosphorus eluted to the overlying water and the SOD values, but no correlation was observed between the iron and manganese contents in the sediments and the SOD values. These findings indicate that the amounts of iron eluted from sediment should be evaluated to assess its contribution to SOD.
