Seasonal variability of stable isotopes in precipitation and spring water around Mt Kimpo, Kumamoto, southwestern Japan^*

* Originally presented at the IAEA Symposium on Isotope Hydrology 2019, Vienna, Austria, 20–24 May 2019.

ABSTRACT

Stable isotopes in precipitation and spring water were observed in a low mountain region, because seasonal variability in isotope altitude and amount effects based on their simultaneous observations in low latitude area have not been studied so much. Seasonal variability in spatial averages of monthly δ¹⁸O and d-excess in precipitation ranged from −11.96 to −5.16 ‰ and from 8.0 to 24.2 ‰, respectively, while those in spring water ranged from −7.64 to −7.18 ‰ and from 11.0 to 13.6 ‰. The seasonal variability in spatial average of monthly δ¹⁸O in precipitation was much wider than in spring water. Monthly isotopic composition in spring water was mostly plotted along the local meteoric water lines for precipitation in warm months, suggesting that precipitation in warm months is the main source of spring water. Annual isotope altitude effects in precipitation (−0.12 ‰/100 m) and spring water (−0.13 ‰/100 m) were almost the same, and monthly isotope amount effects for cold months (−7.9 to −0.9 ‰/100 mm) were relatively higher than those for the warm months (−12.0 to −9.6 ‰/100 mm). The isotope amount effect at each sampling sites appeared using only the data in the warm months without extreme weather.

KEYWORDS:

• Altitude effect
• amount effect
• hydrogen-2
• isotope hydrology
• Mt Kimpo
• Japan
• oxygen-18
• precipitation
• spring water
• seasonal variability

Acknowledgments

The authors would like to thank all staffs and students of the Hydrology Laboratory of Kumamoto University for field observation and isotope analyses, especially T. Nagamatsu and M. Nishimachi who graduated in March 2013. And we are thankful to the Matsuo-Kita and Kawachi primary schools and Kyushu regional forest management office for setting the precipitation sampling sites.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

* Originally presented at the IAEA Symposium on Isotope Hydrology 2019, Vienna, Austria, 20–24 May 2019.

Additional information

Funding

This research was partially supported by the JSPS [Japan Society for the Promotion of Science] KAKENHI, grant numbers 24510256, 16H05619 and 16KT0151.