Controls over hydrogen and oxygen isotopes of surface water and groundwater in the Mun River catchment, northeast Thailand: implications for the water cycle

Yang, Kunhua; Han, Guilin

Controls over hydrogen and oxygen isotopes of surface water and groundwater in the Mun River catchment, northeast Thailand: implications for the water cycle | Contrôle par les isotopes de l’hydrogène et l’oxygène des eaux de surface et souterraines dans le bassin de la rivière Mun, nord-est de la Thaïlande: conséquences pour le cycle de l’eau Controles sobre los isótopos de hidrógeno y oxígeno de las aguas superficiales y subterráneas en la cuenca del río Mun, noreste de Tailandia: implicancias para el ciclo del agua 泰国东北部Mun河流域地表水与地下水中氢氧同位素的控制:对水循环的启示 Controles sobre os isótopos de hidrogênio e oxigênio nas águas superficiais e subterrâneas da bacia do Rio Mun, nordeste da Tailândia: implicações para o ciclo hidrológico

2020

Yang, Kunhua | Han, Guilin

Stable isotopic composition (δ²H, δ¹⁸O) of river water, groundwater, and paddy water in the Mun River catchment, northeast Thailand, were determined to investigate the hydrological processes and the impacts of natural and anthropogenic activities on the water cycle. Quantities of δ²H (−93.9 to −25.4‰) and δ¹⁸O (−12.24 to −2.22‰) in river water in the wet season follow the trend: upper reaches > middle reaches ≈ lower reaches. Trends for δ²H (−52.3 to −22.0‰) and δ¹⁸O (−6.37 to −1.36‰) in the dry season are: upper reaches ≈ middle reaches > lower reaches. In the dry season, groundwater (δ²H: −57.5 to −34.6‰, δ¹⁸O: −8.24 to −4.40‰) shows a lighter isotopic composition, and paddy water (δ²H: −18.2‰, δ¹⁸O: −0.72‰) shows the highest isotopic composition. Spatial variation of δ¹⁸O and deuterium excess suggests that groundwater exchanges with surface water frequently. Rainfall and river water recharge groundwater in the wet season, and groundwater flows back to the river in the dry season, especially in the middle reaches. This process is most likely related to impoundment of the rivers by large dams. On the other hand, the lowest values of stable isotopes of river water are coincident with the extreme flooding that was produced by Tropical Storm Sonca in July 2017. This study contributes to a better understanding of hydrological processes in the Mun River catchment and provides a perspective on the application of stable isotopes to other large tropical monsoon catchments around the world.

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