Ariake Sea Research Project, Saga University
For more details, please refer 2008 Annual Report( pdf file ).
For the numerical modeling of the suspended sediment, transport, mapping of the re suspension Coefficient and measuring of the settling velocity of the suspended sediment were performed. The re suspension coefficient in the Ariake Sea could estimated by the clay conet, dry density and vane shear strength of the bottom sediment. Settling velocity of suspended sediment in the Isahata Bay, Ariake Sea and Chikugo River Estuary were proportional to the 0.77 power of the concentration of suspended sediment.
For the numerical modeling of the suspended sediment, transport, mapping of the re suspension Coefficient and measuring of the settling velocity of the suspended sediment were performed. The re suspension coefficient in the Ariake Sea could estimated by the clay conet, dry density and vane shear strength of the bottom sediment. Settling velocity of suspended sediment in the Isahata Bay, Ariake Sea and Chikugo River Estuary were proportional to the 0.77 power of the concentration of suspended sediment.
The macrofauna of three estuarine tidal fiat areas at the mouth of the Chikugo River, Rokkaku Riyer, and Shiota River in the imler part of Ariake Bay is described. Sampling was done from a boat during high tide using a Stnith-McCintyre grab sampler (22,5 x 22.5 cm) at 1 1 stations in each area in December 2005, and May and August, 2006. Multivariate arialyses showed that conmiunity structures differed significantly between the tidal flats. This was mainiy due to differences in the abundance of the the arcid bixralve Scapharca kagoshimensis, the venerid bivalve Ruditapes philippinarum. The disuibution of endangered species and invasive species also differed between tidal fiats, atid those species occurred mainly in the mudflats of the Rokakku River andlor Shiota River estuaries. Differences in sediment grain size should be a factor of the differences in the inacrofauna and the distribution of endangered and invasive species among the tidal flats.
Ariake Sea sediment- stabilizeing effect of extracellular polymeric substances was investigated in a laboratory setting. Extracellular polymeric substances (EPS) in the lyophilized secliment were isolated as colloidal carbohydrate fraction. Evaluate of rheological properties of EPS solution and sediment slurry with EPS, calcium ion were canied out using a shear rate chargeable rehometer. This aqueous solution of EPS behave as Bingham fluids, the shear stress increase with elapsed time. It would be most like due to hydration. The sea sediment slurry with EPS behave as non-Bingham fluids. The stress-strain hysteresis loop width predicts the interaction of sediment and EPS. EPS enhance of sediment stabilization, the effect is greatly improve by calcium ion,
The distribution of turbidity maximum and suspendied sediment (SS) flux were analyzed in a cross seetion of the Chikugegawa rivire estuary. During flood tide,it was observed tha tthe along-rive rcurrent was relativery-week and the suspended sediment concentration was high at the inside of the curve, the river water of near-bottom layer flowed to the inside ofthe curve, furthermore, the thickness of high SS concentration layer increased. The SS flux in each ADCP measurement cell was calculated using the water velocity and SS concentration that was esti- mated from echo intensity ofADCP, the flux was integrated in each segment ofthe cross section by, one tidal period. The total sediment budget showed that considerably more SS passed over the inside of the meander than over the outside, These facts suggest that the secondary current occur in the meander of tidal channel and the suspended sediment transported by the turbidity maximum is moved into the inside ofthe bend. The distribution ofturbidity ma: imum and suspendied sediment (SS) flux were analyzed in a cross seetion ofthe Chikugegawariirerestuar},,Duringfioodtide,itwasobservedthatthealong-rivercurrentNvasrelativery-eekandthe suspended sediment concentration was high at the inside of the curve, the river water of near-bottom layer flowed to the inside ofthe curve, furthermore. the thickness ofhigh SS concentration Iayer increased. The SS flux in each ADCP measurement cell was calculated using the water velocity and SS concentration that was esti- mated from echo intensity ofADCP, the flux "vas integrated in each segrnent ofthe eross section by, onetida1 period. The total sediment budget showed that considerably more SS passed over the inside ofthe meander than oi,er the outside, These facts suggest that the secondary current occur in the meander of tidal channel and the suny)endecl sediment transported by the turbidity maximum is moved into the inside ofthe bend.
Influence of extracelluar substances (EPS) secreted by culitivated laver on both coagulation of susupended solid and sedmientary stabiluzatuib ub Ariake Sea was experimentally examined. The laver culture experiment showed a production of EPS evaluated by total sugar concentration, visocosity and molecular distribution ans showd an increase in dissoloved organic carbon . The powdered from laver increased traspareancy of the suspension prepared using particles if Ariake sediment and increased a stability based in rheological measuremnaver . The results in this study would suggest a contribution of lever to the increase in trasnparancy in Ariake Sea.
under construction
The fresh water discharge and pollutant load models of all the class A rivers flowing into the Ariake Sea were constructed. We made field surveys of material loads from the lowland creek area which made us possible to estimate the direct nutrient loads into the Ariake Sea. In order to improve the accuracy of the sediment transport model, we made a detailed survey concerning about the sediment dynamics in the Isahaya Bay with the Research Division of Sediment and Material Transport. A 3D sediment transport model was successfully constructed based on the FVCOM and validated with observation data taken by a shuttling survey during a tidal cycle. The influence of the construction of the Isahaya Dyke on the sediment transport was examined with this model. Moreover, a 3D eco-system model was developed based on the FVCOM and the neap spring tidal cycle of the hypoxia in the Ariake Sea was successfully reproduced. In summer we made a frequent field survey about phytoplankton for 2 months and clarified the mechanism of the occurrence of the red tide of Chattonella. Moreover field experiments on the cell division cycle of Chattonella were performed. Finally, a blue tide was firstly observed in the Isahaya Bay in last August. We immediately analyzed the monitoring data and clarified the mechanism of the occurrence of this phenomenon.