Effects of Long-Term Storage on the Isotopic Composition of Different Environmental Waters

Abstract

Water input components such as fog, dew, and rain, are crucial for sustaining ecosystem functions, especially in water-limited regions. However, these water resources are subject to isotopic changes induced by storage due to their small sample volumes and inherent sensitivity to ambient atmospheric particulates. A comprehensive understanding of the long-term storage effect on isotopic compositions of these water inputs is essential for maintaining isotopic integrity throughout both field collection and laboratory analysis. In this study, the extent of such changes in the isotopic compositions (δ2H, δ18O, and δ17O) of fog, rain, and dew was investigated under different storage times (4.5−9 years) and different sample bottle fill levels (4.8% to 92.4%) using the Los Gatos Research Inc. GLA431 series analyzer. The long-term storage could lead to a large variation in oxygen isotopes (δ17O and δ18O) for the fog samples with minor effects on oxygen isotope measurements of dew and rain samples. In addition, no significant difference in δ2H values was observed between present and past measurements for three types of water samples. The isotopic changes of δ18O for fog waters were negatively correlated with the sample bottle fill level (p < 0.01) but positively related to the storage time (p < 0.01). We argue that chemical reactions between high concentrations of solutes and water molecules within fog samples may induce oxygen fractionation, leading to fog oxygen isotopes showing higher sensitivity to long-term storage compared to the δ2H values of dew and rain samples. Our findings could help understand the long-term isotopic accuracy and precision of fog, dew, and rain waters by providing information on isotopic changes after long-term storage.