HR: 1340h
AN: H43F-0553    [Abstracts]
TI: Submarine groundwater discharge variation due to tidal change in Setouchi Inland Sea, Japan
AU: * Ishitobi, T
EM: tomotoshi@chikyu.ac.jp
AF: Research Institute for Humanity and Nature, 335 Takashima-cho, Kamigyo-ku, Kyoto 602-0878, Japan, Kyoto, 602-0878 Japan
AU: Taniguchi, M
EM: makoto@chikyu.ac.jp
AF: Research Institute for Humanity and Nature, 335 Takashima-cho, Kamigyo-ku, Kyoto 602-0878, Japan, Kyoto, 602-0878 Japan
AU: Onodera, S
EM: sonodera@hiroshima-u.ac.jp
AF: Faculty of Integrated Arts and Sciences, Hiroshima University, 1-7-1, Kagamiyama, Higashi-hiroshima, 739-8521, Japan, Higashi-hiroshima, 739-8521 Japan
AU: Hayashi, M
EM: hayashi-m@hiroshima-u.ac.jp
AF: Graduate School of Biosphere Sciences, Hiroshima University, 1-7-1, Kagamiyama, Higashi-hiroshima, 739-8521, Japan, Higashi-hiroshima, 739-8521 Japan
AU: Saito, M
EM: misaito@hiroshima-u.ac.jp
AF: Graduate School of Biosphere Sciences, Hiroshima University, 1-7-1, Kagamiyama, Higashi-hiroshima, 739-8521, Japan, Higashi-hiroshima, 739-8521 Japan
AB: Submarine groundwater discharge (SGD) is recently recognized as a potentially significant water and material pathway from the land to the ocean. However, quantitative evaluations have not been done because the measurement is difficult. Therefore, a lot of uncertain points exist about SGD. The objective of this study is to make clear SGD phenomenon in small island where large SGD rate is expected. Study area is a coastal zone of Ikuchijima-island in Setouchi Inland Sea, Japan. The average of tidal change of Setouchi Inland Sea ranges from 2 to 3m. Continuous measurements of SGD rates, conductivity and temperature of SGD have been done by automated seepage meters and CT sensors in the study area. Resistivity measurements also have been made across the coastal aquifer by resistivity cable. As the results, submarine groundwater discharge was found near shore, however submarine groundwater recharge was found in offshore. Resistivity measurements showed the existence of terrestrial groundwater in near shore. The separation of SGD into the fresh terrestrial groundwater discharge and recirculated seawater discharge were also made by using the electric conductivities of the water of two end members, groundwater in the coast and seawater. This result revealed that fresh terrestrial groundwater discharge rates are higher in offshore where terrestrial groundwater exists. The area of terrestrial groundwater discharge observed from seepage meter agree with the area measured by resistivity cable. Moreover, resistivity measurement shows existence of bed rock in about 20m depth. Additionally, discharge of terrestrial groundwater by seepage meter and existence of terrestrial groundwater by resistivity measurement are found in only intertidal zone. Therefore, it is clarified that terrestrial groundwater discharge occurs in only intertidal zone in this area.
DE: 1829 Groundwater hydrology
DE: 1830 Groundwater/surface water interaction
SC: Hydrology [H]
MN: Fall Meeting 2005