Relationships between salinity and hydrogen isotopes of n-alkanes in aquatic plants across Chinese natural lakes

Hydrogen isotope compositions (δD) of lipids are widely used in hydrological research, yet there have been limited investigations into the relationships between salinity and δD values of aquatic plants in natural lakes, which hinders the broader application of δD compositions as indicators of paleosalinity reconstructions. In this study, we examined δD compositions of n-alkanes in aquatic plants and lake water from 58 lakes (containing 18 brackish/saline lakes) across diverse regions of China (including the Tibetan Plateau, Inner Mongolia Plateau, Chinese Loess Plateau, Tarim Basin, and Yangtze Plain). Subsequently, we examined the correlations between salinity and n-alkane δD values in aquatic plants. Our findings indicate that δD values of n-alkanes from aquatic plants record variations in lake water δD (R² = 0.53, p < 0.01). Furthermore, δD values of lake water in brackish/saline lakes exhibit a positive correlation with salinity (R² = 0.74, p < 0.01). Thus, a positive correlation (R² = 0.68, p < 0.01) is observed between δD values of n-alkanes from aquatic plants and lake salinity, whose changes both co-vary with lake water δD variations. Therefore, n-alkane δD values of aquatic plants can serve as indirect indicators of salinity for reconstructing paleosalinity in brackish/saline lakes. It is important to note that paleosalinity reconstruction in lakes using n-alkane δD values is generally more effective when lake salinity experiences large variations, whereas caution should be exercised when lake salinity changes are more subtle.