[A-HW23] Isotope Hydrology 2021

[AHW23-05] The formation of a temporary pond, Akaike, at the Northern Foot of Mount Fuji, Japan, in 2020

*Shinya Yamamoto¹, Takashi Nakamura², Seongwon Lee³, Masaya Yasuhara³ (1.Mount Fuji Research Institute, Yamanashi Prefectural Government, 2.International Research Center for River Basin Environment, University of Yamanashi, 3.Faculty of Geo-Environmental Science, Rissho University)

Keywords:Mount Fuji, temporary pond, water quality, stable isotopes

Akaike is a small, temporary pond that appears about 1 km east of Lake Shoji following heavy precipitation events at the northern foot of Mt. Fuji. It is widely accepted that the pond is connected to Lake Shoji by groundwater. However, such a connection has not yet been established because of the lack of water quality and isotopic data from both the Akaike Pond and Lake Shoji. In this study, we measured the major dissolved ion and trace element contents, the hydrogen (dD) and oxygen (d¹⁸O) stable isotope ratios of water, and the nitrogen and oxygen stable isotope ratios of nitrate ions in water samples from the Akaike Pond in July 2020, and compared these data with surface water and precipitation samples collected from the surrounding area to identify the source of Akaike Pond water. The water qualities and isotopic compositions of Akaike Pond are clearly different from those of Lake Shoji, and showed close proximity in the dD and d¹⁸O values to the precipitation. These results suggest that the water in the Akaike Pond is likely derived from recent precipitation. The major dissolved ion compositions in the Akaike Pond showed lower Ca²⁺ and HCO₃^– concentrations than the water samples around the pond. This suggests that the water in the Akaike Pond accumulates in a relatively short period (within a few days) after precipitation, without deep underground percolation.