[A-HW23] 同位体水文学2023

[AHW23-04] Revisiting Mt Fuji’s spring water origins with classic and novel tracer methods

*Oliver S. Schilling^1,2、Kazuyo Nagaosa³、Tanja U. Schilling⁴、Matthias S. Brennwald²、Rumi Sohrin³、Yama Tomonaga^1,5、Rolf Kipfer^2,6,7、Philip Brunner⁸、Kenji Kato³ (1.Hydrogeology, Department of Environmental Sciences, University of Basel, Switzerland、2.Eawag, Swiss Federal Institute of Aquatic Science and Technology, Duebendorf, Switzerland、3.Department of Geosciences, Shizuoka University, Shizuoka, Japan、4.Department of Geology and Geological Engineering, Université Laval, Quebec, Quebec, Canada、5.Entracers GmbH, Dübendorf, Switzerland、6.Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, Switzerland、7.Institute of Geochemistry and Petrology, ETH Zurich, Zurich, Switzerland、8.Centre for Hydrogeology and Geothermics (CHYN), University of Neuchatel, Neuchatel, Switzerland)

キーワード：stable water isotopes, noble gases, eDNA, Fuji, groundwater, vanadium

For millennia Japan’s iconic Mt Fuji has provided safe drinking water to millions of people via a vast network of groundwater and freshwater springs. Groundwater, which is recharged at high elevations, flows down Fuji’s flanks within three basaltic aquifers, ultimately forming countless pristine freshwater springs among Fuji’s foothills. As a result of our recent analyses (Schilling et al., 2023), we here challenge the current conceptual model of Fuji being a simple system of laminar groundwater flow with little to no vertical exchange between its three aquifers. This model contrasts strongly with Fuji’s extreme tectonic instability owing to its unique location on top of the only known continental trench–trench–trench triple junction, its complex geology and its unusual microbial spring water communities. We provide evidence for prevailing deep groundwater circulation and a previously unknown deep groundwater contribution to Fuji’s freshwater springs on the basis of a unique combination of microbial environmental DNA, vanadium and helium tracer analyses, coupled to a large meta study of existing tracer data on Mount Fuji watershed. The most substantial deep groundwater upwelling has been found along Japan’s tectonically most active region, the Fujikawa-kako Fault Zone, with increasing contributions of deep groundwater to the freshwater springs in the downstream direction. Our findings demonstrate the vast potential of combining classic isotope and non-isotope tracer data with novel environmental DNA, on-site noble gas and trace element analyses for groundwater science. Moreover, our findings broaden the hydrogeological understanding of the watershed of majestic Mount Fuji.

References
Schilling, O. S., Nagaosa, K., Schilling, T. U., Brennwald, M. S., Sohrin, R., Tomonaga, Y., Kipfer, R., Brunner, P., & Kato, K. (2023). Revisiting Mt. Fuji’s groundwater origins with helium, vanadium and eDNA tracers. Nat. Water, 1, 60-73. https://doi.org/10.1038/s44221-022-00001-4