Isotopic (d18O/d2H) integrity of water samples collected and stored by automatic samplers

Authors: Williams, Mark; LARTEY, JESSICA - Northeastern Illinois University; SANDERS, LAURA - Northeastern Illinois University

Submitted to: Agricultural and Environmental Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2018
Publication Date: 3/29/2018
Citation: Williams, M.R., Lartey, J.L., Sanders, L.L. 2018. Isotopic (d18O/d2H) integrity of water samples collected and stored by automatic samplers. Agricultural and Environmental Letters. 3:180009. doi:10.2134/ael2018.02.0009.
DOI: https://doi.org/10.2134/ael2018.02.0009

Interpretive Summary: Stable water isotopes (oxygen-18 and deuterium) can be used to track the movement of water through the landscape. As a result, stable water isotope data are increasingly being collected as part of routine water quality monitoring programs. In this study, we tested how isotope values change over time when they are stored in an automatic water sampler. Results showed that up to 11.8% of the water sample volume evaporated when it was stored in an automatic sampler at 35°C for 24 days. Evaporation results in changes in the isotope values. Thus, to preserve the original isotopic value of the water sample, they need to be retrieved from the sampler <7 d following collection when air temperatures are <22°C and <3 d following sample collection when the air temperature is 35°C. If water samples need to be stored in an automatic sampler for longer periods of time, mineral oil can be added to sample bottles to decrease evaporation. These findings are useful for those collecting water quality samples; that the collected samples need to be retrieved from the sampler in a timely manner to minimize the evaporative loss.

Technical Abstract: Stable water isotopes are increasingly becoming part of routine monitoring programs that utilize automatic samplers. The objectives of this study were to quantify the uncertainty in isotope signatures due to the length of sample storage (1-24 d) inside autosamplers over a range of air temperatures (5-35°C) and evaluate the effectiveness of two evaporation reduction measures (mineral oil and HDPE balls). Results of the laboratory study showed that up to 11.8% of the sample volume evaporated when samples were stored in an autosampler at 35°C for 24 d. To prevent significant water isotope fractionation, samples should be retrieved from autosamplers <7 d following sample collection when air temperatures are <22°C and <3 d following sample collection when the air temperature is 35°C. If samples need to be stored in an autosampler for longer periods of time, mineral oil added to sample bottles effectively decreased evaporation and the potential for isotope fractionation.