An evaluation of materials and methods for vapour measurement of the isotopic composition of pore water in deep, unsaturated zones

Pratt, Dyan; Lu, Mengna; Barbour, S. Lee; Hendry, M. Jim

doi:10.1080/10256016.2016.1151423

Cited by 10 publications

(22 citation statements)

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“…Two standard liquid waters (AK and BSS with isotopic values of −101.14‰ and −34.12‰ for δ 2 H and −14.10‰ and −5.90‰ for δ 18 O, Table ) were alternately measured after every four samples (calibration Method 1), in order to transform vapour water isotopic composition to liquid water isotope values and to account for isotopic drift of the instrument. The standards were prepared by adding 20 ml of liquid water into individual Ziploc bags, inflating the bags with dry air, shaking by hand, and allowing to equilibrate for 30 min prior to experiment initiation (Pratt et al, ). During the measurement, NFSQ liquid water, which was used to rehydrated oven‐dried soil, was prepared in the same way as the water standards and measured periodically as a control sample to evaluate the stability of DVE‐LS (21 measurements in total).…”

Section: Methodsmentioning

confidence: 99%

“…In this method (DVE-LS) introduced by Wassenaar, Hendry, Chostner, and Lis (2008), dry air was injected into the headspace of a sealed sample bag containing a soil sample; after a period of equilibration, the air in the headspace was subsequently analysed. In addition, with the development of portable laser spectroscopy, DVE-LS is increasingly used in an in situ, non-destructive manner to track water movement through the subsurface (Gaj et al, 2016;Pratt, Lu, Barbour, & Hendry, 2016;Rothfuss, Vereecken, & Brüggemann, 2013;Volkmann & Weiler, 2014). Due to the cost-effectiveness and portability, DVE-LS has been used increasingly in a variety of applications (Baer, Barbour, & Gibson, 2016;Harrington, Gardner, Smerdon, & Hendry, 2013;Quade et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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Calibration method affects the measured δ²H and δ¹⁸O in soil water by direct H₂O_liquid–H₂O_vapour equilibration with laser spectroscopy

Wang

Cheng

Pratt

et al. 2019

Hydrological Processes

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The direct H 2 O liquid -H 2 O vapour equilibration method utilizing laser spectroscopy (DVE-LS) is a way to measure soil pore water stable isotopes. Various equilibration times and calibration methods have been used in DVE-LS. Yet little is known about their effects on the accuracy of the obtained isotope values. The objective of this study was to evaluate how equilibration time and calibration methods affect the accuracy of DVE-LS. We did both spiking and field soil experiments. For the spiking experiment, we applied DVE-LS to four soils of different textures, each of which was subjected to five water contents and six equilibration times. For the field soil experiment, we applied three calibration methods for DVE-LS to two field soil profiles, and the results were compared with cryogenic vacuum distillation (CVD)-LS. Resultsshowed that DVE-LS demonstrated higher δ 2 H and δ 18 O as equilibration time increased, but 12 to 24 hr could be used as optimal equilibration time. For field soil samples, DVE-LS with liquid waters as standards led to significantly higher δ 2 H and δ 18 O than CVD-LS, with root mean square error (RMSE) of 8.06‰ for δ 2 H and 0.98‰ for δ 18 O. Calibration with soil texture reduced RMSE to 3.53‰ and 0.72‰ for δ 2 H and δ 18 O, respectively. Further, calibration with both soil texture and water content decreased RMSE to 3.10‰ for δ 2 H and 0.73‰ for δ 18 O. Our findings conclude that the calibration method applied may affect the measured soil water isotope values from DVE-LS.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Calibration method affects the measured δ²H and δ¹⁸O in soil water by direct H₂O_liquid–H₂O_vapour equilibration with laser spectroscopy

Wang

Cheng

Pratt

et al. 2019

Hydrological Processes

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“…About 5‐cm porous ceramic filters were attached to lengths of 7‐mm high‐density polyethylene (HDPE) tubing. The HDPE tubing has proven to be suitable for in situ soil vapour collection (Pratt et al, ). The filters were installed horizontally at each depth of interest upon filling the hillslopes with soil.…”

Section: Methodsmentioning

confidence: 99%

“…Once this evacuation procedure was complete, the surface tubing was attached individually to the OA‐ICOS isotope analyzer and measurements were taken for a minimum of 10 minutes until the values had stabilized on the instrument within ±0.5‰ for δ 2 H and ±0.2‰ for δ 18 O. Standard water samples were prepared using the liquid‐equilibration method by adding 10 ml of standard water into a Ziploc bag and inflating with dry air (Pratt et al, ). These standards were measured after every four samples to correct for instrument drift and to normalize the results to the VSMOW scale.…”

Section: Methodsmentioning

confidence: 99%

“…These standards were measured after every four samples to correct for instrument drift and to normalize the results to the VSMOW scale. Flow rates were kept low (85.8 ml·min ‐1 ) as suggested by Thoma et al () to maintain a zone of influence representative of water vapour at the depth of the in‐situ ports (Pratt et al, ). We applied the following correction protocol by Pratt et al () to obtain the pore water isotopic composition: the isotopic composition of the vapour sample was first corrected for relative humidity effects (δ SH ) based on the method of Schmidt et al ().…”

Section: Methodsmentioning

confidence: 99%

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Intercomparison of soil pore water extraction methods for stable isotope analysis and interpretation of hillslope runoff sources

Orlowski

Pratt

McDonnell

2019

Hydrological Processes

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Intercomparison of soil pore water extraction methods for stable isotope analysis has been a focus of recent studies in relation to plant source waters, which found a wide isotopic variance depending on the extraction method. Few studies have yet explored extraction effects for mobile pore waters that relate to hillslope runoff. This is because it is extremely difficult in natural systems to control the boundary conditions in order to assess and compare impacts of pore water extraction on resulting hillslope flow. With our new semicontrolled experiments on outdoor mini‐hillslopes, we studied mixing and runoff processes by means of stable isotopes of water and quantified relations between pore water extraction methods. We tested the null hypothesis that nondestructive and destructive pore water sampling methods sample the same soil water pool. Three hillslopes were mounted on load cells, filled with loamy sand textured soils from the Landscape Evolution Observatoryat Biosphere 2, equipped with soil moisture and temperature sensors, a bottom outflow, and a surface runoff gauge for isotope sampling. We followed the precipitation isotopic composition over and through the soil profile. One hillslope was instrumented with suction cups, on the second we installed sampling ports for in‐situ soil water vapour measurements, and the third hillslope was sampled destructively for applying the centrifugation and vapour equilibrium methods. All hillslopes were sampled at four depths (0–10, 10–20, 20–30, and 30–40 cm) at three different downslope positions. 2H and 18O analyses were performed via laser spectroscopy. We found no isotopic differences between rainfall, surface runoff, and bottom outflow. The in situ vapour ports' soil isotope data showed the widest spread over all hillslope positions and depths. Centrifugation's and suction cups' isotope results plotted closest to the local meteoric water line and within the range of hillslope runoff and bottom outflow data. Hillslope position did not influence the soil isotope results. These results suggest caution be used in the field when selecting an extraction technique for matching soil waters to runoff waters. Soil suction lysimeters and centrifugation appeared to be the most appropriate tools in this regard.

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Organic contamination detection for isotopic analysis of water by laser spectroscopy

Millar

Janzen

Nehemy

et al. 2021

Rapid Comm Mass Spectrometry

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RationaleHydrogen and oxygen stable isotope ratios (δ2H, δ17O, and δ18O values) are commonly used tracers of water. These ratios can be measured by isotope ratio infrared spectroscopy (IRIS). However, IRIS approaches are prone to errors induced by organic compounds present in plant, soil, and natural water samples. A novel approach using 17O‐excess values has shown promise for flagging spectrally contaminated plant samples during IRIS analysis. A systematic assessment of this flagging system is needed to prove it useful.MethodsErrors induced by methanol and ethanol water mixtures on measured IRIS and isotope ratio mass spectrometry (IRMS) results were evaluated. For IRIS analyses both liquid‐ and vapour‐mode (via direct vapour equilibration) methods are used. The δ2H, δ17O, and δ18O values were measured and compared with known reference values to determine the errors induced by methanol and ethanol contamination. In addition, the 17O‐excess contamination detection approach was tested. This is a post‐processing detection tool for both liquid and vapour IRIS triple‐isotope analyses, utilizing calculated 17O‐excess values to flag contaminated samples.ResultsOrganic contamination induced significant errors in IRIS results, not seen in IRMS results. Methanol caused larger errors than ethanol. Results from vapour‐IRIS analyses had larger errors than those from liquid‐IRIS analyses. The 17O‐excess approach identified methanol driven error in liquid‐ and vapour‐mode IRIS samples at levels where isotope results became unacceptably erroneous. For ethanol contaminated samples, a mix of erroneous and correct flagging occurred with the 17O‐excess method. Our results indicate that methanol is the more problematic contaminant for data corruption. The 17O‐excess method was therefore useful for data quality control.ConclusionsOrganic contamination caused significant errors in IRIS stable isotope results. These errors were larger during vapour analyses than during liquid IRIS analyses, and larger for methanol than ethanol contamination. The 17O‐excess method is highly sensitive for detecting narrowband (methanol) contamination error in vapour and liquid analysis modes in IRIS.

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An evaluation of materials and methods for vapour measurement of the isotopic composition of pore water in deep, unsaturated zones

Cited by 10 publications

References 28 publications

Calibration method affects the measured δ²H and δ¹⁸O in soil water by direct H₂O_liquid–H₂O_vapour equilibration with laser spectroscopy

Calibration method affects the measured δ²H and δ¹⁸O in soil water by direct H₂O_liquid–H₂O_vapour equilibration with laser spectroscopy

Intercomparison of soil pore water extraction methods for stable isotope analysis and interpretation of hillslope runoff sources

Organic contamination detection for isotopic analysis of water by laser spectroscopy

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An evaluation of materials and methods for vapour measurement of the isotopic composition of pore water in deep, unsaturated zones

Cited by 10 publications

References 28 publications

Calibration method affects the measured δ2H and δ18O in soil water by direct H2Oliquid–H2Ovapour equilibration with laser spectroscopy

Calibration method affects the measured δ2H and δ18O in soil water by direct H2Oliquid–H2Ovapour equilibration with laser spectroscopy

Intercomparison of soil pore water extraction methods for stable isotope analysis and interpretation of hillslope runoff sources

Organic contamination detection for isotopic analysis of water by laser spectroscopy

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Resources

About

Calibration method affects the measured δ²H and δ¹⁸O in soil water by direct H₂O_liquid–H₂O_vapour equilibration with laser spectroscopy

Calibration method affects the measured δ²H and δ¹⁸O in soil water by direct H₂O_liquid–H₂O_vapour equilibration with laser spectroscopy