JpGU-AGU Joint Meeting 2017

Presentation information

[EJ] Oral

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

[A-HW34] [EJ] Hydrological Cycle and Water Environment

Mon. May 22, 2017 10:45 AM - 12:15 PM 301A (International Conference Hall 3F)

convener:Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Maksym Gusyev(International Centre for Water Hazard Risk Management, Public Works Research Institute), Seiya Nagao(Institute of Nature and Environmental Technology, Kanazawa University), Isao Machida(Geological Survey of Japan), Shin'ichi Iida(Department of Disaster Prevention, Meteorology and Hydrology, Forestry and Forest Products Research Institute), Chairperson:Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Chairperson:Shin'ichi Iida(Forestry and Forest Products Research Institute), Chairperson:Isao Machida(Geological Survey of Japan, AIST), Chairperson:Seiya Nagao(Institute of Nature and Environmental Technology, Kanazawa University), Chairperson:Maksym Gusyev(International Centre for Water Hazard Risk Management, Public Works Research Institute)

11:45 AM - 12:00 PM

[AHW34-10] Learning about future applications of tritium-tracer in Japanese river waters from the Hokkaido headwater catchments

*Maksym Gusyev1, Uwe Morgenstern2, Michael K. Stewart3, Yoshio Tokunaga1 (1.International Centre for Water Hazard Risk Management, Public Works Research Institute, Tsukuba, Japan, 2.GNS Science, Lower Hutt, New Zealand, 3.Aquifer Dynamics & GNS Science, PO Box 30368, Lower Hutt, New Zealand)

Keywords:river water sampling, tritium isotope, lumped parameter model (LPM), mean transit time (MTT)

Tritium-tracer in river water can provide useful information about surface water – groundwater dynamics in Japan as demonstrated at 12 headwater catchments of Hokkaido Island with altitudes between 22 and 831 m above sea level and catchment areas between 14 and 377 km2. For these catchments, we collected 16 water samples at baseflows in June, July, and October 2014 and one river water sample on February 2016 near the south of Sapporo. These water samples were analysed for tritium as well as stable isotopes at the GNS Science low-level tritium laboratory in New Zealand. Measured tritium concentrations were between 4.07 (±0.07) TU and 5.29 (±0.09) TU in June, 5.06 (±0.09) TU in July, and between 3.75 (±0.07) TU and 4.85 (±0.07) TU in October. In the south of Sapporo, the neighboring river catchments clustered in similar hydrogeological settings of Quaternary lava as well as Tertiary propylite formations had similar tritium values suggesting that they drain the same groundwater watershed system: 4.114 (±0.062) TU (Takinosawa) and 4.184 (±0.063) TU (Otarunai), and 3.825 (±0.07) TU (Izariirisawa), 3.926 (±0.061) TU (Honryujyoryu). On February 2016, the Otarunai river water sample collected at winter baseflow had 3.838 (±0.061) TU indicating similar tritium concentrations at subsurface water of the Izariirisawa and Honryujyoryu catchments. For these headwater catchments, we found unique mean transit times (MTTs) using the exponential(70%)-piston flow(30%) model (E70%PM) LPM and very low MTT aggregation errors with the long-term tritium record of Tokyo precipitation scaled for Hokkaido groundwater recharge using wine data. This result suggests that their low tritium concentrations are not ambiguous anymore for the MTT interpretation. However, nine river samples from six other catchments produced up to three possible MTT values with E70%PM due to the interference by the tritium from the atmospheric hydrogen bomb testing 5–6 decades ago. We show that tritium in Japanese groundwater will reach natural levels in a decade, when one tritium measurement will be sufficient to estimate a robust MTT, while using a series of tritium measurements over the next few years with 3 year intervals will enable us to determine the correct MTT without ambiguity in this period. Unique MTTs obtained from tritium-tracer allow us to improve numerical models and to estimate groundwater storage volumes for sustainable water resources management.

References:
Gusyev M.A., Morgenstern U., Stewart M.K., Yamazaki Y., Kashiwaya K., Nishihara T., Kuribayashi D., Sawano H. and Y. Iwami (2016). Application of tritium in precipitation and baseflow in Japan: a case study of groundwater transit times and storage in Hokkaido watersheds. Hydrol. Earth Syst. Sci., 20, 1-16, doi:10.5194/hess-20-1-2016