Topographic influence on ecohydrology in volcanic watersheds of the western Pacific monsoon area: evidence from water stable isotope composition of meteoric water, thermal water, and plants

ABSTRACT

In Taiwanese volcanic watersheds, we investigated stable water isotopes in meteoric water, plants, and thermal water. Meteoric water exhibited a seasonal cycle, with heavier isotopes in winter and lighter ones in summer, especially in the southern region. The northern monsoon signal lagged the south by two weeks. In the Tatun mountains, young water fractions indicated prevalent old water sources. In the northern watershed, streamwater mainly came from the winter monsoon, while the southern one was influenced by alternating monsoons. Both indices indicated that winter plants depended on summer rainfall. Streamwater and plants had distinct sources in winter, supporting ecohydrological separation. Thermal spring water’s d-excess helped identify water–rock interactions, with low d value signaling such interactions. The topographic wetness index showed a higher summer monsoon contribution to southern streamwater but a lower one to plants. The mean linear channel direction significantly affected the monsoon contribution fraction, with northeast-oriented channels vulnerable to northeastward winter monsoons. Finally, we developed a model illustrating hydrological processes on short and long timescales. Our findings enhance our understanding of hydrological disturbances’ impact on water resources and ecosystems.

KEYWORDS:

• Deuterium-excess
• ecohydrological separation
• hydrogen-2
• isotope hydrology
• oxygen-18
• seasonal origin index
• Tatun Volcano Group
• young water fraction

Acknowledgements

We extend our gratitude to Mr. Chi-Chu Tung, Mr. Jhen-Nan Lin, Mr. Chun-Chun Huang, and Mr. Wen-Jui Liang for their assistance in the field sampling work, as well as to Miss Wen-Jun Zhan for her laboratory analyses.

Disclosure statement

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

Additional information

Funding

This research has been supported by the Ministry of Science and Technology, Taiwan (grant nos. MOST 106-2116-M-005-001) and the National Science and Technology Council, Taiwan (grant no. NSTC 112-2811-M-005-021).