Stable Water Isotopes Across Marsh, River, and Lake Environments in the Zoige Alpine Wetland on the Tibetan Plateau

Water isotope studies in alpine wetlands have revealed the dynamic characteristics of the hydrological cycle and evapotranspiration processes in the Zoige region through hydrogen and oxygen isotope ratios. However, the hydrological continuity between marshes, rivers, and lakes in wetlands is relatively understudied. The study found that the Zoige Alpine Wetland local meteoric water line (LMWL) is δD = 8.33δ¹⁸O + 14.52 (R² = 0.92) by using linear regression analysis to confirm the Craig temperature effect equation backwards. Comparison with the global and Chinese LMWLs revealed that the slope of the Zoige LMWL is significantly higher than those of the global and Chinese LMWLs, indicating that the oceanic warm and humid airflow and the southwest monsoon significantly influence this region. The δ¹⁸O ranges of rivers, lakes, and marshes in the Zoige wetland were −12.86‰ to −2.02‰, −12.9‰ to −2.22‰, and −15.47‰ to −7.07‰, respectively. In terms of δD, marshes had the lowest δD values, with a mean value of −89.58‰, while rivers and lakes had close δD values of about −72‰. Rivers had the most dramatic variation in d-excess values, ranging from −34.16‰ to 3.68‰, while marshes and lakes had more concentrated d-excess values, with particularly negative values in marshes. Regression analysis yielded a trend line of δD = 5.41δ¹⁸O − 29.57 for evaporation from the water bodies, further demonstrating the importance of evaporation effects in this region. By using the Rayleigh fractionation model and estimating the climatic conditions, we found that the lake water had the highest evaporation intensity (41%). Those of the river and marsh water were 40% and 36%, respectively. The results of this study provide new scientific insights into the hydrological connectivity, evaporation processes, and water source characteristics in the Zoige wetland. Future studies can shed more light on how climate change affects wetland hydrological systems and how they change over time and space. This will help to manage water resources in the region and protect the environment.