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Soichi Yamaguchi Last modified date:2021.06.29

Assistant Professor / Earth System Science and Technology
Department of Advanced Environmental Science and Engineering
Faculty of Engineering Sciences


Graduate School
Undergraduate School


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Homepage
https://kyushu-u.pure.elsevier.com/en/persons/soichi-yamaguchi
 Reseacher Profiling Tool Kyushu University Pure
Phone
092-583-7560
Fax
092-592-8447
Academic Degree
Doctorate of Science
Country of degree conferring institution (Overseas)
No
Field of Specialization
Coastal environmental research
Total Priod of education and research career in the foreign country
00years00months
Outline Activities
I am studying the ways to improve environmental deterioration such as the occurrence of red tides and oxygen-deficient water masses that occur in coastal waters by making field observations and numerical ecosystem simulations.
Research
Research Interests
  • Development of behavior estimation method for driftwood and oil generated by heavy rain in coastal waters
    keyword : Driftwood, oil, coastal waters, Numerical simulation
    2021.08~2025.03.
  • 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~development of forecasting model of environments in coastal waters~
    keyword : ICT Smart Fisheries FVCOM
    2017.03~2022.03.
  • Study on the formation mechanism of Hypoxia/Anoxia in the Ariake sea.
    keyword : Ariake sea, Hypoxia
    2010.04~2020.03.
  • Numerical study on dynamics and its prediction of harmful algal blooms under high human impacts in coastal waters.
    keyword : harmful algal bloom, aquaculture, Ariake sea
    2013.04~2023.03.
  • Development of a new numerical simulation method for tidal current power generation.
    keyword : Tidal current energy, Western Japan
    2012.04~2021.03.
Current and Past Project
  • We analyze the flow conditions in the southwestern part of the Ariake Sea using continuous observation equipment, etc., and help develop technology to reduce discoloration damage caused by the frequent red tides in the area.
  • We analyze the flow conditions in the southwestern part of the Ariake Sea using continuous observation equipment, etc., and help develop technology to reduce discoloration damage caused by the frequent red tides in the area.
  • 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.
  • Universities in the four prefectures along the Ariake Sea collaborate to investigate and analyze the effects of Isahaya dyke medium- to long-term gate opening, long-term tide changes, open seawater, etc. In the case of Isahaya dyke opening, evaluate the impact from a third-party standpoint and inform the citizens and the government in an easy-to-understand manner. In addition, we support local activities for the restoration of the Ariake Sea.
Academic Activities
Reports
1. High-resolution unstructured grid model was developed using DREAMS_Dash (DR_D) as open boundary conditions based on FVCOM (Chen et al., 2003) to reproduce and predict sea state fluctuations in coastal waters with complex coastal and seafloor topography. UCHI (Unstructured-grid Coastal model with High-resolution Information) was developed. This year, we introduced a rainfall runoff inundation analysis model (RRI model, Sayama et al., 2012) into the UCHI model, and examined it for highly accurate reproduction of the physical environment of the inner bay with complex topography. As a result, the introduction of RRI has made it possible to accurately evaluate the inflow of rivers, confirming the improvement in the reproducibility of the physical environment of the coastal waters..
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 Yamaguchi1, Shota Koide1, Takayuki Mine, Takuya Iwanaga, Observation of red tide in an estuary by a fixed-wind type unmanned aircraft, Japan Geoscience Union Meeting 2021, 2021.06, method, enables spatial monitoring, but in the orbit of the satellite, weather condition (clouds), and sea turbidity and seaweed aquaculture in the inner part of the Ariake Sea, which is the target sea area of this research, makes it difficult to obtain data with sufficient spatiotemporal resolution. Observations using unmanned aerial vehicles (UAVs) have been in the limelight in recent years
because an aircraft observation has a high degree of freedom in observation such as immediacy and directness, and can perform observations with high spatiotemporal resolution that cannot be performed by satellite or ground observation. In this study, we aimed to establish a spatiotemporal high-resolution sea surface Chl-a concentration remote sensing method using a fixed-wing unmanned aircraft equipped with a spectroradiometer, and attempted to detect red tide in coastal waters. A handheld Spectra PAR Meter (PG200N by UPRtek corp.) was mounted on the UAV to estimate the Chl-a concentration in the sea surface. The PG200N can measure spectral data of light in the visible light region (350 nm to 800 nm) with a wavelength resolution of 1 nm, and can estimate the concentration using the optical characteristics of the Chl-a dye possessed by phytoplankton. It is small and lightweight, suitable for installation on UAV. In the observation, the irradiance incident on the sea surface from the sky and the radiance emitted from
the sea surface were measured. In estimating the Chl-a concentration from the obtained spectral data, the reflectance of each wavelength (= upward radiance from the sea surface / downward irradiance from the sky) was calculated, and applied to a three-waveband model (Dall'Olmo, G. and Gitelson, A.A, 2003). Field observations were conducted on December 7 and 18, 2000 and January 5, 2021, and for fixed-wing type unmanned aircraft, OPTiM Hawk V2 (manufactured by OPTiM Corporation) has two PG200N sensors inside the aircraft body, so that it faced directly above and below and measured the spectral data of light from the sky and the sea. The flight speed of OPTiM Hawk V2 was set to 70km / hour, and the spectral data was acquired every 5 seconds, resulting in the spatial resolution of the data to about 100 m. A high correlation was obtained as a whole between the Chl-a concentration estimated by the 3-waveband model and the measured value by the field observation. However, the estimation error tended to increase in the sea area where the Chl-a concentration was high. Generally, when the concentration of phytoplankton is increased, the "packaging effect" that change in the light absorption coefficient per unit Chl-a concentration due to the overlapping of pigments occurs, and the Chl-a concentration estimated by sea color remote sensing is underestimated or overestimated. Therefore, analysis of covariance was
performed to estimate the threshold of Chl-a concentration at which the packaging effect appears. Based on this threshold value, we succeeded in developing an algorithm that can estimate Chl-a concentration with high accuracy even in the high Chl-a concentration sea area. In the three observations, a high-concentration local region, which is considered to be the initial occurrence of red tide, was
detected. Therefore, this observation using UAV has sufficient performance to grasp the spatiotemporal high resolution of red tide in the coastal area..
2. 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.
.
3. SEASONAL CHANGE IN TIDAL CURRENT ENERGY DUE TO TIDE-INDUCED EDDY IN GOTO ISLANDS, JAPAN, [URL].
4. Mechanism of red tide outbreaks in winter in Ariake Sea, [URL].
5. VARIATION OF DO CONCENTRATION IN COLD-DOME WATER IN ARIAKE SEA.
6. METHOD VALIDATION FOR REDUCING PRESSURE GRADIENT FORCE ERROR IN COASTAL OCEAN MODELING
.
7. 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..
8. 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..
9. 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..
10. 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..
11. 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].
12. Generation Mechanism of Upwelling current with “Aoshio” occurrence in summer of 2008 in Ariake Sea.
13. Proposal of open bondary condition for the numerical simulation of Ariake Sea.
14. 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
Educational
Educational Activities
I'm teaching students at bachelar and master course how to conduct research on environmental sciences in coastal sea.