2026 Volume 49 Pages 27-36
The decomposition process of particulate organic carbon (POC) and dissolved organic carbon (DOC) in the surface waters of Osaka Bay was investigated in biodegradation experiments lasting up to 100 days, and the decomposition rates and decomposition times of POC and DOC were calculated. POC was rapidly biodegraded by the 20th day of the experiment, whereas most DOC remained even after 50 days. During the experiment period, there was almost no net conversion from POC to DOC. The mean decomposition rate of POC at 20 ℃ was 0.12 day-1 (mean decomposition time was 8.5 days) . The amount of open-sea-origin DOC was calculated using salinity, and the amount of DOC subtracted by that of open-sea-origin DOC was defined as internally produced DOC, which includes both terrestrial and marine origins. A two-component model of recalcitrant and semi-labile components was applied to the internally produced DOC to calculate the decomposition rate of the semi-labile component. Regardless of the location and time (season) of water sampling, 48% of the internally produced DOC was recalcitrant and the remaining 52% was the semi-labile component with a mean decomposition rate of 0.031 day-1 (mean decomposition time of 32 days) .
