Spatial and temporal variation in the stable isotope composition (δ¹⁸O and δ²H) of rain across the tropical island of Sri Lanka

ABSTRACT

Seasonal and spatial variation in δ¹⁸O and δ²H in rainwater was determined in three selected transects across Sri Lanka, the tropical island in the Indian Ocean. Local meteoric water lines (LMWLs) for three distinguished climatic zones; wet, dry and intermediate were constructed. LMWLs show slight variations in their gradients and respective d-excess values, depending on the air moisture origin, circulation and environmental conditions of each climatic zone. The elevation effect and amount effect could be identified but the continental effect is not significantly seen in the isotope composition of rain in the concerned areas. The results reasonably revealed that the distinct rainfall regimes; two monsoonal rains and two convectional (inter-monsoon) rains have characteristic isotopic signatures. Also the impact of (i) terrestrial and oceanic moisture sources, (ii) depression and cyclonic conditions of the Bay of Bengal, and (iii) topography of the country on the variation of the isotopic composition of rain in Sri Lanka could be satisfactorily identified.

KEYWORDS:

• Air moisture
• deuterium excess
• isotope effects
• isotope hydrology
• rainwater
• Sri Lanka
• tropical island

Acknowledgements

We would like to show our gratitude to the Sri Lanka Atomic Energy Board for facilitating the research. We also thank the institutions/persons who took the responsibility of operating and maintaining rain collecting setups in each location throughout the study.

Disclosure statement

No potential conflict of interest was reported by the authors.