10:45 AM - 12:15 PM
[ACG40-P02] The property of decomposition of dissolved organic matter in Osaka Bay, Tokyo Bay and Ise Bay
Keywords:coastal sea, CDOM, outflow flux, labile dissolved organic matter
The dynamics of terrestrial materials in coastal waters is complex, and there are many issues in quantifying the process of their transport through coastal waters to offshore areas. This study aims to investigate the decomposition characteristics of DOM in river water and seawater and to determine the treatment methods of the samples based on the results of these investigations, in order to clarify the pathways of terrestrial materials to the offshore areas using colored dissolved organic matter (CDOM) as tracers, which is mainly composed of humic substances, and to determine the balance of terrestrial materials in the coastal waters.
A total of 21 points in Osaka Bay, Tokyo Bay, and Ise Bay, surface water from a total of nine rivers flowing into each bay, and one site of treated sewage water were sampled in September, October, and November 2022. Four sets of seawater and river water samples were collected and treated in four ways: on-board filtration, filtration in the laboratory (refrigeration), filtration after 24 hours (refrigeration), and filtration 48 hours after placement in an incubator set at the water temperature at the time of collection. Dissolved organic carbon (DOC) and the optical absorption coefficient of dissolved organic matter at 443 nm, ay(443), were measured for the samples (CDOM).
In Ise Bay and Osaka Bay, the difference between the values for filtration in the laboratory (refrigeration) and filtration after 24 hours (refrigeration) and those for on-board filtration was less than a few percent, suggesting that the influence of filtration timing was small. The difference between the values of filtration after 48 hours at room temperature and those of on-board filtration was similar, suggesting that the amount of easily degraded DOC and CDOM was relatively small.
In Tokyo Bay, the values for filtration in the laboratory (refrigeration) and filtration after 24 hours (refrigeration) increased by 20~50% compared to on-board filtration, indicating that the timing of filtration had a significant effect on the values. On the other hand, filtration after 48 hours at room temperature increased the values by 5~20% compared to those of on-board filtration, suggesting that DOC and CDOM, which are easily degradable, were degraded once they increased. The increased DOC and CDOM are likely to be derived from the sea area, since river water and treated sewage water have almost no biodegradable fractions.
The above results and the negative correlation between salinity and CDOM both in all bays suggest that the relationship can be used to determine the discharge pathway of land-based materials to the offshore areas. On the other hand as for DOC, it is necessary to measure the river side endmembers and the open ocean side endmembers in each season and to calculate the proportion of land-derived substances, since it was suggested that the fraction derived from the sea area increased in brackish.
A total of 21 points in Osaka Bay, Tokyo Bay, and Ise Bay, surface water from a total of nine rivers flowing into each bay, and one site of treated sewage water were sampled in September, October, and November 2022. Four sets of seawater and river water samples were collected and treated in four ways: on-board filtration, filtration in the laboratory (refrigeration), filtration after 24 hours (refrigeration), and filtration 48 hours after placement in an incubator set at the water temperature at the time of collection. Dissolved organic carbon (DOC) and the optical absorption coefficient of dissolved organic matter at 443 nm, ay(443), were measured for the samples (CDOM).
In Ise Bay and Osaka Bay, the difference between the values for filtration in the laboratory (refrigeration) and filtration after 24 hours (refrigeration) and those for on-board filtration was less than a few percent, suggesting that the influence of filtration timing was small. The difference between the values of filtration after 48 hours at room temperature and those of on-board filtration was similar, suggesting that the amount of easily degraded DOC and CDOM was relatively small.
In Tokyo Bay, the values for filtration in the laboratory (refrigeration) and filtration after 24 hours (refrigeration) increased by 20~50% compared to on-board filtration, indicating that the timing of filtration had a significant effect on the values. On the other hand, filtration after 48 hours at room temperature increased the values by 5~20% compared to those of on-board filtration, suggesting that DOC and CDOM, which are easily degradable, were degraded once they increased. The increased DOC and CDOM are likely to be derived from the sea area, since river water and treated sewage water have almost no biodegradable fractions.
The above results and the negative correlation between salinity and CDOM both in all bays suggest that the relationship can be used to determine the discharge pathway of land-based materials to the offshore areas. On the other hand as for DOC, it is necessary to measure the river side endmembers and the open ocean side endmembers in each season and to calculate the proportion of land-derived substances, since it was suggested that the fraction derived from the sea area increased in brackish.