Preprints
https://doi.org/10.5194/egusphere-2025-272
https://doi.org/10.5194/egusphere-2025-272
05 Feb 2025
 | 05 Feb 2025
Status: this preprint is open for discussion and under review for Hydrology and Earth System Sciences (HESS).

Technical note: Efficiency of various evaporation barriers for use in automated water samplers for subsequent water isotope analysis 

Christin Mueller, Tim Giorgio Pekarev, and Kay Knoeller

Abstract. High temporal and spatial resolution water sampling of stream water or precipitation for subsequent stable water isotope analysis (δ2H and δ18O) is commonly conducted with self-made or commercial automated samplers. However, prolonged storage of water samples in open bottles inside autosamplers can lead to isotopic alterations caused by evaporative fractionation and vapor mixing.

In this study, we tested the effectiveness of different evaporation barriers—dip-in tubes, ball valves, and siphons—under controlled laboratory conditions. Experiments were conducted using glass bottles with varying filling levels (50 mL to 250 mL in 250 mL bottles) and exposure times of up to 52 days. Our results demonstrate that all tested barriers effectively reduce isotopic alterations. Among these, the dip-in tube emerged as the simplest and most efficient solution, reliably preserving isotopic data even over extended storage durations. We also observed isotopic differences between the water in the dip-in tube and the main bottle. This phenomenon becomes particularly relevant when sample volumes are very low, as water from the dip-in tube may influence the overall isotopic composition of the sample. This finding highlights the need for careful consideration of bottle design, funnel size and sample handling, especially with low water volumes.

These findings provide valuable insights for the design of cost-effective, automated water sampling systems for stable isotope applications, emphasizing the importance of evaporation barriers to ensure reliable and accurate isotopic analyses.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
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Christin Mueller, Tim Giorgio Pekarev, and Kay Knoeller

Status: open (until 19 Mar 2025)

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Christin Mueller, Tim Giorgio Pekarev, and Kay Knoeller
Christin Mueller, Tim Giorgio Pekarev, and Kay Knoeller

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Short summary
Automatic water samplers help to collect water for isotope analysis, but if the samples are stored in open bottles for long periods of time, their composition can change due to evaporation. We have tested various barriers to prevent this and found that dip tubes are the most practical solution. Our results highlight the importance of bottle design and handling, especially for small sample volumes, to ensure accurate water analysis.
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