Effects of Long‐Term Storage on the Isotopic Compositions of Different Types of Environmental Waters

Abstract

Rationale: Fog, dew, and rain are crucial for sustaining ecosystem functions, especially in water-limited regions. However, they are subject to isotopic changes during storage due to their usual small sample volumes and inherent sensitivity to atmospheric particulates. Understanding long-term storage effects on these water samples is essential for ensuring isotopic integrity. Methods: In this study, the extent of such changes in the isotopic compositions (δ2H, δ18O, and δ17O) of fog, dew, and rain was investigated under different storage times (4.5-9 years) and different bottle fill levels (4.8%-92.4%) using the Los Gatos Research Inc. GLA431 series analyzer. Results: The long-term storage could lead to a large variation in oxygen isotopes of fog with minor effects on dew and rain samples. The isotopic changes of δ18O for fog waters were negatively correlated with the bottle fill level (p < 0.01) but positively related to storage time (p < 0.01). Chemical reactions between solutes and water molecules within fog samples may induce oxygen fractionation, leading to the high sensitivity of fog oxygen isotopes to long-term storage. No significant changes in δ2H values were observed for the three water types. Conclusions: Our findings could help understand the long-term isotopic accuracy and precision of fog, dew, and rainwaters by providing information on isotopic changes after long-term storage.