Volume 35, Issue 3 e14068
RESEARCH ARTICLE

Isotopic temporal and spatial variations of tropical rivers in Thailand reflect monsoon precipitation signals

Jeerapong Laonamsai

Corresponding Author

Jeerapong Laonamsai

Department of Earth and Environmental Sciences, Faculty of Advanced Science and Technology, Kumamoto University, Kumamoto, Japan

Department of Water Resources, Water Crisis Prevention Center, Ministry of Natural Resources and Environment, Bangkok, Thailand

Correspondence

Jeerapong Laonamsai, Department of Earth and Environmental Sciences, Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Chuo-ku, Kumamoto 860-8555, Japan.

Email: [email protected]

Search for more papers by this author
Kimpei Ichiyanagi

Kimpei Ichiyanagi

Department of Earth and Environmental Sciences, Faculty of Advanced Science and Technology, Kumamoto University, Kumamoto, Japan

Search for more papers by this author
Supapap Patsinghasanee

Supapap Patsinghasanee

Department of Water Resources, Water Crisis Prevention Center, Ministry of Natural Resources and Environment, Bangkok, Thailand

Search for more papers by this author
First published: 01 February 2021
Citations: 17

Abstract

Stable isotopic compositions (δ18O and d-excess) from 25 rivers in Thailand were analysed monthly during 2013–2015. Results indicated that monsoon precipitation fundamentally influences the river isotopes. The overland flow supplied from monsoon precipitation and human-altered flow regimes produces considerable isotopic variability. Spatial and temporal variations were observed among four principal geographical regions. The seasonality of monsoon precipitation in mountainous Thailand produced large variations in isotopic compositions because most rainfall occurred during the southwest monsoon, and dry conditions prevailed during the northeast monsoon. The northern and northeastern regions are mountainous, highland areas. Low δ18O values were found in these regions, likely because of altitude effects on precipitation. Conversely, monsoonal precipitation continually supplies rivers in southern Thailand all year round, producing higher and more consistent δ18O values than in the other regions. The Chao Phraya plain in the central region experienced enrichment of δ18O river runoff related to evaporation in irrigation systems. Larger catchment areas and longer residence times resulted in more pronounced evaporation effects, producing lower values of d-excess and local river water line slopes compared with precipitation. The isotopic differences between river waters and precipitation were utilized to determine river recharge elevations and water transit time. The methods presented here can be used to explore hydrological interactions in other tropical river basins.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.

The full text of this article hosted at iucr.org is unavailable due to technical difficulties.