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

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.

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.

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.

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.