Japan Geoscience Union Meeting 2022

Presentation information

[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-HW Hydrology & Water Environment

[A-HW24] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

Tue. May 24, 2022 1:45 PM - 3:15 PM 303 (International Conference Hall, Makuhari Messe)

convener:Jun Yasumoto(University of the Ryukyus, Faculty of Agriculuture), convener:Masahiro Kobayashi(Forestry and Forest Products Research Institute), Noboru Okuda(Kobe University), convener:Adina Paytan(University of California Santa Cruz), Chairperson:Masahiro Kobayashi(Forestry and Forest Products Research Institute)

1:45 PM - 2:00 PM

[AHW24-13] Impact of groundwater in the Kanogawa riverine system

★Invited Papers

*Kenji Kato1, Rumi Sohrin1, Akira Tsukagoshi1, Koji Mori2 (1.Shizuoka University, 2.Blue Earth Security Co., Ltd.)

Keywords:Kanogawa River, Groundwater, Microbial DNA, Drone, Phytoplankton

The Kanogawa River with ca. 46 km in length runs through Izu Peninsula toward north from the watershed where the annual rainfall exceeds 2,000 mm. And a huge amount of groundwater over 1.5 million tons inflows into Kanogawa River from affluents, Kakitagawa River and Kisegawa River, which amounts about one thirds of the mainstream. In particular, Kakitagawa River is supplied solely with groundwater of 1 million tons per day.
Locating a groundwater discharge site with a drone
We succeed in locating a site where groundwater is directly discharged into the river using a drone equipped with both visible light and infrared cameras to measure river surface temperature. The annually stable temperature of the groundwater with ca. 15 ℃ at the plane region in this area exceeds surface temperature of the river during winter. Thus, the water at the site was distinguished from the surrounding river water by its temperature. It was compared with the water in the middle of the river in terms of physical and chemical properties, including via an examination of stable isotopes. In addition, microbial DNA analysis was applied to estimate the variations in dominant prokaryotes in the water sample. Results showed that some specific clones as OD1 were retrieved abundantly from the discharged groundwater. The OD1 groups contain clones dominated in deep subsurface environment with high temperature and absolutely anoxic condition. Contrary, some clones predominated in soil and surface aquatic environment were retrieved solely from the river water. Those findings support that the water searched with its temperature by a drone is regarded as the water being discharged of groundwater, which might contain the water originated from deep subsurface environment.
Function of groundwater in ecosystem of the Kanogawa River system and its estuary
The site where groundwater is discharged directly into the river may provide a unique habitat where temperature does not fluctuate through the seasons. Discharged groundwater may also affect the surrounding water supplying different contents of dissolved materials, which results in changes in river ecosystem. The influence may extend to estuary. Incubation experiment was applied to elucidate a possible function of groundwater using the water samples taken from different sites in the Kanogawa riverine system. Addition of iron and manganese to the water of Kakitagawa River enhanced production of phytoplankton. It implies the co-limitation of iron and manganese occurred for the phytoplankton community in the Kakitagawa River water. By mixing with the Kakitagawa River water, phytoplankton production was increased in the Kanogawa River water which was collected from the site before the confluence with the Kakitagawa River during the baseflow season, and it was comparable to that in the Kanogawa River water after the confluence with the Kakitagawa River. This result suggests that phytoplankton in the Kanogawa River was not under the iron and manganese deficiency and their production was stimulated by the major nutrients supplied from the Kakitagawa River water. This study is supported by River Works Technology Research and Development Program from Ministry of Land, Infrastructure, Transport and Tourism for 2019, 2020 and 2021.