Results(FY 2007)
For more details, please refer 2007 Annual Report( pdf file ).
Research Division of Sediment and Material Transport
- Nowadays, the accumulation of the fine sediments in the upper part of the Ariake Sound is the serious problem relating to the rapid decreasing of the shell fish catchments. From the reviewing of the literature and new analysis, it was clarified that the origin of the fine sediments in the eastern upper part of the Ariake Sound was consisted of the riverine silt. On the other hand, the fine sediments in the western upper part of the Ariake Sound was consisted of the clay with marine organic materials. Especially, the area of the fine sediments in the western upper part of the Ariake Sound gradually expands by burying submarine valley by discharging bottom sediment from the Isahaya Bay.
- Mapping of the parameters for resuspension of the sediments was conducted for the initial condition of the developing numerical sediment transport model of the Ariake Sea Research Project, Saga University. It was clarified that the resuspention limit could estimate from the clay content and vane shear stress of the bottom surface sediments.
- The device for measurement of in situ settling flux of sediments was developed. It was clarified that the settling velocity depended on the root of the SS concentration in the Ariake Sound and the Chikugo River Estuary.
- The extracellular polymeric substances (EPS) of Ariake Sea sediment were isolated from Ariake Sea sediment. Distribution of monosaccharide and uronic acid determined. The soluble EPS fraction showed distribution of monosaccharides with Galactose, Glucose, Xylose, ,Rhamnose, Fucose and size distribution showed polymer of around 103-107, and monomer of 102 Da. The relationship water content, the ratio of chlorophyll-a/feo pigment and carbohydrate were maintained in summer to winter. Result of rheological experiment that EPS, Slurry with EPS and sediment behave as viscose, non-Newtonian flueids. Flow curve for the slurry were unidentical and effects of the addition of EPS in the presence or absence of Ca2+.
Research Division of Environmental Science and Technology of Tidal Flat and Sediment
<Under Construction>
Research Division of Envirionmental Modeling
We found that the bottom sediments in the Isahaya Bay were re-suspended and then transported to the inner area of the Ariake Sea along the longitudinal channel off the Shiota River. In this channel, the bottom intrusion often occurred in neap tide in summer. We found that it was caused by the neap-spring variation of the bottom front of the estuarine plume. The behavior of the low salinity water mass generated by the freshet of the Chikugo River was investigated by the numerical simulation. There was a good agreement between the simulation and the observation. The transport of sediments loaded from the Chikugo River was also simulated with a numerical model. The variation of the currents and waves observed by the Ariake Sea Oceanographic Observation Tower of Saga University from 1975 to 1997 was investigated. The fresh water discharge and pollutant load models of the Midori, Shira, Kikuchi and Chikugo River were constructed. They can be used as the boundary condition for the ocean model of the Ariake Sea.