Kyushu University Academic Staff Educational and Research Activities Database
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Soichi Yamaguchi Last modified date:2018.11.30



Graduate School
Undergraduate School


E-Mail
Phone
092-583-7560
Fax
092-572-2696
Academic Degree
Doctorate of Science
Field of Specialization
Coastal environmental research
Research
Research Interests
  • Prediction of dynamics of Harmful alga, Karenia mikimotoi , in Imari Bay.
    keyword : Imari Bay, Karenia mikimotoi, HAB, FVCOM
    2018.06~2019.03.
  • Smart Fisheries technology development using ICT
    keyword : ICT Smart Fisheries FVCOM
    2017.03~2020.03.
  • Study on the formation mechanism of Hypoxia/Anoxia in the Ariake sea.
    keyword : Ariake sea, Hypoxia
    2010.04~2020.03.
  • Impact of Porphyra yezoensis (Nori) aquafarming on the water circulation and transparency in Ariake Sea, Japan.
    keyword : Nori cultivation, Ariake sea
    2013.04~2020.03.
  • Development of a new numerical simulation method for tidal current power generation.
    keyword : Tidal current energy, Western Japan
    2012.04~2019.03.
Current and Past Project
  • This study predicts dynamics of Karenia mikimotoi red tides by field monitoring and numerical simulation in Imari Bay, Nagasaki prefecture.
  • Numerical simulation is conducted for obtaining tidal current energy map in detail close to the coast in west Japan, using unstructured-grid finite volume coastal ocean model:FVCOM. Total amount of ocean renewable energy is estimated based on the simulation results.
Academic Activities
Papers
1. DEVELOPMENT AND APPLICATION OF NUMERICAL ECOSYSTEM MODEL WITH FINITE VOLUME COMMUNITY OCEAN MODEL:FVCOM.
2. Soichi Yamaguchi, Yuichi Hayami, Impact of Isahaya dike construction on DO concentration in the Ariake Sea, Journal of Oceanography, https://doi.org/10.1007/s10872-017-0454-9, 74, 6, 565-586, 2017.11, In the Ariake Sea, dike construction in Isahaya Bay in 1997 for reclamation and disaster prevention was thought to cause big anthropogenic impacts on the marine ecosystem. Currently, hypoxia or anoxia occurs every summer in Isahaya Bay and the inner Ariake Sea. However, the effects of the dike construction on the DO concentration are unclarified. The present study evaluated the impact of the dike construction on the DO concentration by applying a numerical ecosystem model. The present calculation showed that the dike construction could affect the DO concentration in summer in wider area than reported before in the steady state with neap-spring tidal cycle. In Isahaya Bay, the DO concentration decreased by greater than 2.0 mg l-1 caused by the dike construction. It was generated by the decrease in DO supply due to the vertical diffusion process with the reduction of tidal current and the intensification of the density stratification. The dike construction also affected the DO concentration in the inner Ariake Sea by decreasing the DO concentration of the water transported by the estuarine circulation and the reduction of the diffusive supply of oxygen vertically with enhanced stratification by the dike construction. This study showed for the first time that the dike construction could affect the DO concentration in wide area of the Ariake Sea with the numerical simulation..
3. Inhibition Effect of Oyster Reef on Occurrence of Hypoxia in Ariake Sea.
4. Generation of Tidal Current Energy Map around Kyushu-Okinawa region.
5. Generation Mechanism of Upwelling current with “Aoshio” occurrence in summer of 2008 in Ariake Sea.
6. Seasonal and Temporal Variation in Flow off Chikugo River Mouth in the Inner Part of Ariake Sea.
7. Generation Mechanism of Hypoxia in Isahaya Bay.
8. Behavior of low salinity water and its implication for the water quality after freshets at the head of the Ariake Sea.
Presentations
1. Soichi Yamaguchi, Naoya. Minamiura, Mechanism of red tide outbreaks in winter in the western area of the inner Ariake Sea, ECSA 57: Changing estuaries, coasts and shelf systems - Diverse threats and opportunities, 2018.09, Aquaculture of fishery resources has been conducted in coastal waters all over the world. In Ariake sea, a region of freshwater influence (ROFI) in Japan, aquaculture of Porphyra yezoensis, namely ”Nori” has been conducted in great magnitude during autumn and winter.
Red tide outbreaks by several phytoplankton species frequently occur during the aquaculture season, which causes color bleaching of the nori due to depletion of nutrients in water column and prevents stable production. One of the characteristics of red tide occurrences is for the red tides to be concentrated in western area of the inner Ariake Sea independently of the phytoplankton species. The mechanism for this is poorly understood. The objective of the present study is to clarify factors for the concentration of red tide outbreaks in the western area of the inner Ariake Sea using numerical simulation and the observed data.
The results of numerical simulation revealed that the sea water residence time was relatively long in the western area of the inner Ariake Sea compared to those in other areas. There was a high correlative relationship between red tide index (cell number × duration time) and the water residence time. On the other hand, growth rate of a representative diatom : Eucampia zodiacus calculated by the observed nutrient concentration and transparency hardly has a correlation with the red tide index. Finally, the impact of nori aquaculture on the water residence time and transparency was evaluated by the numerical simulation with/without the hydrodynamic resistance of the aquaculture facilities. The results of numerical simulations inferred that the aquaculture increased the water residence time in the western area of the inner Ariake Sea and therefore made the hydrographic environment more suitable for the red tide outbreaks. Sustainable practices of the aquaculture is necessary for the future stable production.
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2. SEASONAL CHANGE IN TIDAL CURRENT ENERGY DUE TO TIDE-INDUCED EDDY IN GOTO ISLANDS, JAPAN, [URL].
3. Mechanism of red tide outbreaks in winter in Ariake Sea, [URL].
4. VARIATION OF DO CONCENTRATION IN COLD-DOME WATER IN ARIAKE SEA.
5. METHOD VALIDATION FOR REDUCING PRESSURE GRADIENT FORCE ERROR IN COASTAL OCEAN MODELING
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6. 山口 創一, Tidal Current Energy Potential in Nearshore Waters of Western Japan, International conference on ocean energy 2016, 2016.02, [URL], Much attention has been paid to tidal renewable energy application in Japan since the earthquake in 2011. This study estimates the tidal current energy potential in nearshore waters of western Japan by unstructured-grid finite volume coastal ocean model..
7. Soichi Yamaguchi, Yusaku kyozuka, TIDAL CURRENT ENERGY MAP AROUND KYUSHU-OKINAWA REGION, JAPAN, Grand renewable energy 2014, 2014.07, Numerical simulation is conducted for obtaining tidal current energy map around Kyushu- Okinawa region, Japan, using finite volume coastal ocean model:FVCOM. Calculation domain covers whole area of Kyushu-Okinawa region and consists of unstructured triangular meshes which can have high resolution near coasts with complicated geometry and low resolution in offshore sea area, so that the present model continuously can calculate the detail distribution of tidal current from offshore area to near coasts with computational efficiency. Simulation results are validated with tide-gauge data observed at coasts over the Kyushu-Okinawa region. The present model shows good agreement with the observed. High tidal current was detected in narrow channels such as those in Goto islands, Kanmon strait and Ariake Sea, exceeding 3.0 m sec-1. Based on the calculated current field, tidal energy map is also obtained. This map can be used for estimating electric power gain and selecting the location best suited to tidal energy plant..
8. Numerical simulation is conducted for obtaining tidal current energy map around Okinawa-Kyushu region, Japan, using finite volume coastal ocean model:FVCOM. Calculation domain covers whole area of Kyushu- Okinawa region and consists of unstructured triangular meshes which can have high resolution near coasts with complicated geometry and low resolution in offshore sea area, so that the present model continuously can calculate the detail distribution of tidal current from offshore area to near coasts with computational efficiency. Simulation results are validated with tide-gauge data observed at coasts over the Kyushu- Okinawa region. The present model shows good agreement with the observed. High tidal current was detected in narrow channels such as those in Goto islands, Kanmon strait and Ariake Sea, exceeding 3.0 m sec-1. Based on the calculated current field, tidal energy map is also obtained. This map can be used for estimating electric power and selecting the adequate location for tidal energy plant..
9. Red tides frequently occur in Isahaya Bay, Ariake Sea every summer, especially much attention is paid to the red tide dominated by Chattonella spp. (C. antiqua and C. marina) because it leads to the death of livings in the sea. One of the characteristic phenomena related to the red tide outbreak is the vertical mixing of water column before its occurrence due to meteorological disturbance such as typhoon arrival. In the present study, the author conducted biweekly field measurements on nutrient dynamics in Isahaya Bay before/after the typhoon arrival in summer 2005. Meteorological disturbance by the typhoon caused complete vertical mixing of water column and resuspension of bottom sediment in large quantity. Dissolved inorganic nitrogen (DIN) and phosphorus (DIP) concentration greatly increased after the disturbance, especially by a factor of about 6.4 in vertically averaged DIN concentration. Nutrient budget analysis showed that the nutrient supply from the bottom sediment including pore water and resuspended sediments was dominant for the increase. Estimated nutrient release rate in the present study was more than two times the rate obtained by laboratory experiments that previously conducted using undisturbed bottom sediment. It is important to take into account the effect of bottom sediments dynamics on the nutrient environment in evaluating the flux between water and seabed..
10. Huge tidal flats with tidal creeks develop around rivers in Ariake Sea. River water that contains anthropogenic pollutants flows into the inner sea area over complicated geometry of the tidal flats. Numerical simulation for the Ariake Sea, up to date, has applied low-resolution numerical model incapable of representing the geometry in detail. The present study applied a finite volume coastal ocean model (FVCOM) with high resolution capable of representing such complex geometry. The model results have been validated against extensive observations and showed that the complex geometry of the tidal flats with tidal creeks had great effects on the dynamics of river water. Also shown is the dependence of the model accuracy on the model resolution around rivers by comparing with coarse resolution models, and its effects on the calculated dynamics of river waters., [URL].
11. Generation Mechanism of Upwelling current with “Aoshio” occurrence in summer of 2008 in Ariake Sea.
12. Proposal of open bondary condition for the numerical simulation of Ariake Sea.
13. Variability of Water Quality Due to the Location of a Maga-Float in Tokyo Bay.
Membership in Academic Society
  • Japan Geoscience Union
  • The Open CAE Society of Japan
  • Japan Society of Civil Engineers
  • The Marine Meteorological Society
  • The oceanographic society of Japan