Seasonal variability of oxygen and hydrogen isotopes in a wetland system of the Yunnan-Guizhou Plateau, southwest China: a quantitative assessment of groundwater inflow fluxes

Cao, Xingxing; Wu, Pan; Zhou, Shaoqi; Han, Zhiwei; Tu, Han; Zhang, Shui

Seasonal variability of oxygen and hydrogen isotopes in a wetland system of the Yunnan-Guizhou Plateau, southwest China: a quantitative assessment of groundwater inflow fluxes | Variabilité saisonnière des isotopes de l’oxygène et de l’hydrogène dans un système de zones humides du Plateau de Guizhou au Yunnan, dans le sud-ouest de la Chine: une évaluation quantitative des flux des apports des eaux souterraines Variabilidad estacional de isótopos de oxígeno e hidrógeno en un sistema de humedales de la meseta de Yunnan Guizhou, suroeste de China: una evaluación cuantitativa de los flujos de entrada del agua subterránea 中国西南部云贵高原一个湿地系统氧氢同位素的季节性变化:地下水流入通量定量评价 Variação sazonal de isótopos de oxigênio e hidrogênio em um sistema de área úmida no planalto de Yunnan Guizhou, sudoeste da China: uma avaliação quantitativa do fluxo de recarga de águas subterrâneas

2018

The Caohai Wetland serves as an important ecosystem on the Yunnan–Guizhou Plateau and as a nationally important nature reserve for migratory birds in China. In this study, surface water, groundwater and wetland water were collected for the measurement of environmental isotopes to reveal the seasonal variability of oxygen and hydrogen isotopes (δ¹⁸O, δD), sources of water, and groundwater inflow fluxes. Results showed that surface water and groundwater are of meteoric origin. The isotopes in samples of wetland water were well mixed vertically in seasons of both high-flow (September) and low-flow (April); however, marked seasonal and spatial variations were observed. During the high-flow season, the isotopic composition in surface wetland water varied from −97.13 to −41.73‰ for δD and from −13.17 to −4.70‰ for δ¹⁸O. The composition of stable isotopes in the eastern region of this wetland was lower than in the western region. These may have been influenced by uneven evaporation caused by the distribution of aquatic vegetation. During the low-flow season, δD and δ¹⁸O in the more open water with dead aquatic vegetation ranged from −37.11 to −11.77‰, and from −4.25 to −0.08‰, respectively. This may result from high evaporation rates in this season with the lowest atmospheric humidity. Groundwater fluxes were calculated by mass transfer and isotope mass balance approaches, suggesting that the water sources of the Caohai Wetland were mainly from groundwater in the high-flow season, while the groundwater has a smaller contribution to wetland water during the low-flow season.

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