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  • Herbstritt, Barbara  (10)
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  • 1
    In: Water Resources Research, March 2012, Vol.48(3), pp.n/a-n/a
    Description: We developed a method to measure in situ the isotopic composition of liquid water with minimal supervision and, most important, with a temporal resolution of less than a minute. For this purpose a microporous hydrophobic membrane contactor (Membrana) was combined with an isotope laser spectrometer (Picarro). The contactor, originally designed for degassing liquids, was used with N as a carrier gas in order to transform a small fraction of liquid water to water vapor. The generated water vapor was then analyzed continuously by the Picarro analyzer. To prove the membrane's applicability, we determined the specific isotope fractionation factor for the phase change through the contactor's membrane across an extended temperature range (8°C–21°C) and with different waters of known isotopic compositions. This fractionation factor is needed to subsequently derive the liquid water isotope ratio from the measured water vapor isotope ratios. The system was tested with a soil column experiment, where the isotope values derived with the new method corresponded well (R = 0.998 for δO and R = 0.997 for δH) with those of liquid water samples taken simultaneously and analyzed with a conventional method (cavity ring‐down spectroscopy). The new method supersedes taking liquid samples and employs only relatively cheap and readily available components. This makes it a relatively inexpensive, fast, user‐friendly, and easily reproducible method. It can be applied in both the field and laboratory wherever a water vapor isotope analyzer can be run and whenever real‐time isotope data of liquid water are required at high temporal resolution. No more trade‐off between limited temporal resolution and extensive lab work No more significant time lags between sampling and data acquisition New method is field‐deployable and utilizes readily available components only
    Keywords: Crds ; Continuous Analysis ; Equilibrium Fractionation ; Hydrophobic Membrane ; In Situ Monitoring ; Stable Water Isotopes
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 2
    Language: English
    In: Hydrology and Earth System Sciences Discussions, 06/26/2018, pp.1-16
    Description: The isotopic composition of throughfall is affected by complex exchange, enrichment, and mixing processes in the tree canopy. All interception processes occur simultaneously in space and time generating a complex pattern of throughfall in amount and isotopic composition. This pattern ultimately cascades through the entire hydrologic system and is therefore crucial for studies in catchment hydrology where recharge areas are often forested while reference meteorological stations are generally in the open. For the quasi real-time observation of the isotopic composition of both gross precipitation and throughfall we developed an approach combining an off-the-shelf membrane contactor (Membrana) with a laser-based Cavity Ring-Down Spectrometer (CRDS, Picarro), obtaining isotope readings every two seconds. For the continuous observation of the temporal effect of interception processes two setups with two CRDS instruments in parallel were used analysing gross precipitation and throughfall simultaneously. All devices were kept small to minimize dead volume and thereby, with time-lags of only four minutes, to increase the temporal resolution of isotope observations. Complementarily, meteorological variables were recorded in high temporal resolution at the same location. Comparing these high temporally resolved continuous measurements with discrete liquid or event-based bulk samples, this approach proves to be a powerful tool towards more insight in the very dynamic processes contributing to interception during rainfall events.
    Keywords: Geography;
    ISSN: Hydrology and Earth System Sciences Discussions
    E-ISSN: 1812-2116
    Source: CrossRef
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  • 3
    In: Hydrological Processes, 15 December 2015, Vol.29(25), pp.5174-5192
    Description: The vadose zone plays a crucial role in the water cycle for storing water, providing water to vegetation and transporting solutes or degrading contaminants. Earth scientists have long acknowledged the importance of the vadose zone, and numerous methods have been developed to better understand and predict hydrological processes within this ‘critical zone’. For several decades, stable isotopes (O and H) of pore water have been used as environmental tracers to gain insights into vadose zone water movement and other processes. To determine the pore water stable isotopic composition, various sampling procedures have been developed. We present the procedure and the accompanied advantages and drawbacks of each method. We further discuss possible opportunities and limitations regarding the scale of interest and the pore space that is sampled. The methodological review reveals that the choice of sampling method is crucial for the interpretation of pore water stable isotopes in the vadose zone, but a thorough comparison between the different methods is yet missing. Spiking experiments, where water of known isotopic composition is added to oven‐dried soil, have been shown to be questionable, as the extracted water is usually depleted compared with the standard water. A comparative study analysing soil samples with the recently developed direct water vapour equilibration method and the widely used cryogenic extraction shows deviations, which can only be partly explained, but discloses the need for a more thorough experimental comparative study. Especially promising are developments of continuous isotope measurements based on laser‐based spectrometry that will open up new opportunities for analysing pore water isotopes with higher temporal and spatial resolutions, revealing new insights into hydrological processes across various temporal and spatial scales. Copyright © 2015 John Wiley & Sons, Ltd.
    Keywords: Vadose Zone ; Water Stable Isotopes ; Soil Hydrology ; Ecohydrology
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 4
    Language: English
    In: Environmental science & technology, 05 July 2016, Vol.50(13), pp.7074-81
    Description: Recently, laser-based water stable isotope spectrometers have become popular as they enable previously impossible approaches of environmental observations. Consequently, they have been subjected to increasingly heterogeneous atmospheric conditions. However, there is still a severe lack of data on the impact of nonstandardized gas matrices on analyzer performances. Against this background, we investigated the influence of changing proportions of N2, O2, and CO2 in the carrier gas on the isotope measurements of a typical laser-based water stable isotope analyzer (Picarro L2120-i). We combined environmentally relevant mixtures of N2, O2, and CO2 with referenced, flash-evaporated water and found that isotope readings of the same water were altered by up to +14.57‰ for δ(18)O and -35.9‰ for δ(2)H. All tested relationships between carrier gas changes and respective isotope readings were strongly linearly correlated (R(2) 〉 0.99). Furthermore, an analyzer-measured variable allowed for reliable postcorrection of the biased isotope readings, which we additionally tested on field data. Our findings are of importance for environmental data obtained by analyzers based on the same technology. They are relevant for assays where inconsistent gas matrices or a mismatch in this regard between unknown and reference analyses cannot be excluded, which is in particular common when investigating the soil-vegetation-atmosphere continuum.
    Keywords: Oxygen Isotopes ; Water
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 5
    Language: English
    In: Vadose Zone Journal, 01 March 2018, Vol.17(1)
    Description: The isotopic composition (δH, δO) of pore water is an invaluable tracer for the minimally invasive study of subsurface water flow and transport processes. Here, we evaluated a method for pore water isotope analysis that combines laser-based isotope analyzers and water-vapor isotope equilibration using evaporation-proof metalized sample bags. We tested inflation atmospheres (dry air vs. pure N) and the impact of biogenic gas (CO, CH) accumulation for storage times of up to 4 wk. Samples were analyzed with a water isotope analyzer (Picarro L2120-) and a gas chromatograph. Air-inflated water vapor samples showed a greater range of gas matrix effects (δO: 9.63‰; δH: 21.7‰) than N–inflated samples (δO: 7.49‰; δH: 10.6‰) induced by nonuniform buildup of biogenic CO, starting immediately after sample preparation. However, only air-inflated samples could be reliably corrected using instrument-specific sensitivity factors that were empirically determined by interpretation of periodically repeated isotope measurements. Corrected water isotope data were confirmed by similarity with local precipitation and suction cup isotope data. Residual uncertainties were well below the natural variations of soil water isotope values and independent of storage time, thus allowing for consistently reliable interpretations of soil water isotope profiles. We conclude that, especially for pore water sampling that requires small sample volumes and/or long storage times, metalized sample bags should be used to prevent evaporation notwithstanding the enhanced buildup of biogenic gases. Further, if gas matrix effects cannot be excluded, air inflation is preferred over pure N, as only in that case can reliable postcorrections be performed by using internal data only.
    Keywords: Agriculture
    ISSN: 1539-1663
    E-ISSN: 1539-1663
    Source: Directory of Open Access Journals (DOAJ)
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  • 6
    In: Plant, Cell & Environment, September 2016, Vol.39(9), pp.2055-2063
    Description: Field studies analyzing the stable isotope composition of xylem water are providing important information on ecosystem water relations. However, the capacity of stable isotopes to characterize the functioning of plants in their environment has not been fully explored because of methodological constraints on the extent and resolution at which samples could be collected and analysed. Here, we introduce an method offering the potential to continuously monitor the stable isotope composition of tree xylem water via its vapour phase using a commercial laser‐based isotope analyser and compact microporous probes installed into the xylem. Our technique enables efficient high‐frequency measurement with intervals of only a few minutes per sample while eliminating the need for costly and cumbersome destructive collection of plant material and laboratory‐based processing. We present field observations of xylem water hydrogen and oxygen isotope compositions obtained over several days including a labelled irrigation event and compare them against results from concurrent destructive sampling with cryogenic distillation and mass spectrometric analysis. The data demonstrate that temporal changes as well as spatial patterns of integration in xylem water isotope composition can be resolved through direct measurement. The new technique can therefore present a valuable tool to study the hydraulic architecture and water utilization of trees. Analysis of the stable isotope composition of xylem water is a powerful tool for assessing plant water relations, but available methodology has greatly limited the scope of isotope‐based studies. Here, we introduce an technique based on laser spectroscopy that allows monitoring of the isotope composition of xylem water in trees continuously and at high frequency while eliminating the need for costly and cumbersome destructive collection of plant material and laboratory‐based processing. Results from field application demonstrate that temporal dynamics as well as spatial patterns of integration in xylem water isotope composition can now be resolved through direct measurement.
    Keywords: Hydraulic Integration ; Isotope Ratio Infrared Spectroscopy Iris ; Isotope Ratio Mass Spectrometry Irms ; Nutrients ; Stable Isotopes ; Water Relations ; Xylem Transport
    ISSN: 0140-7791
    E-ISSN: 1365-3040
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  • 7
    Language: English
    In: Hydrology and Earth System Sciences, July 6, 2018, Vol.22(7), p.3619
    Description: pFor more than two decades, research groups in hydrology, ecology, soil science, and biogeochemistry have performed cryogenic water extractions (CWEs) for the analysis of [delta].sup.2 H and [delta].sup.18 O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water isotope composition. Here we present results from the first worldwide round robin laboratory intercomparison. We test the null hypothesis that, with identical soils, standards, extraction protocols, and isotope analyses, cryogenic extractions across all laboratories are identical. Two standard soils with different physicochemical characteristics along with deionized (DI) reference water of known isotopic composition were shipped to 16 participating laboratories. Participants oven-dried and rewetted the soils to 8 and 20 % gravimetric water content (WC), using the deionized reference water. One batch of soil samples was extracted via predefined extraction conditions (time, temperature, and vacuum) identical to all laboratories; the second batch was extracted via conditions considered routine in the respective laboratory. All extracted water samples were analyzed for [delta].sup.18 O and [delta].sup.2 H by the lead laboratory (Global Institute for Water Security, GIWS, Saskatoon, Canada) using both a laser and an isotope ratio mass spectrometer (OA-ICOS and IRMS, respectively). We rejected the null hypothesis. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to soil type and soil water content with mean differences compared to the reference water ranging from +18.1 to -108.4 0/00 for [delta].sup.2 H and +11.8 to -14.9 0/00 for [delta].sup.18 O across all laboratories. In addition, differences were observed between OA-ICOS and IRMS isotope data. These were related to spectral interferences during OA-ICOS analysis that are especially problematic for the clayey loam soils used. While the types of cryogenic extraction lab construction varied from manifold systems to single chambers, no clear trends between system construction, applied extraction conditions, and extraction results were found. Rather, observed differences in the isotope data were influenced by interactions between multiple factors (soil type and properties, soil water content, system setup, extraction efficiency, extraction system leaks, and each lab's internal accuracy). Our results question the usefulness of cryogenic extraction as a standard for water extraction since results are not comparable across laboratories. This suggests that defining any sort of standard extraction procedure applicable across laboratories is challenging. Laboratories might have to establish calibration functions for their specific extraction system for each natural soil type, individually.
    Keywords: Hydrology ; Soil Moisture ; Cooling Systems ; Biogeochemistry
    ISSN: 1027-5606
    ISSN: 16077938
    E-ISSN: 16077938
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  • 8
    Language: English
    In: Hydrology and Earth System Sciences Discussions, 03/15/2018, pp.1-36
    ISSN: Hydrology and Earth System Sciences Discussions
    E-ISSN: 1812-2116
    Source: CrossRef
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  • 9
    Language: English
    In: HYDROLOGY AND EARTH SYSTEM SCIENCES, 2018
    Description: For more than two decades, research groups in hydrology, ecology, soil science, and biogeochemistry have performed cryogenic water extractions (CWEs) for the analysis of delta H-2 and delta O-18 of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water isotope composition. Here we present results from the first worldwide round robin laboratory inter comparison. We test the null hypothesis that, with identical soils, standards, extraction protocols, and isotope analyses, cryogenic extractions across all laboratories are identical. Two standard soils with different physicochemical characteristics along with deionized (DI) reference water of known isotopic composition were shipped to 16 participating laboratories. Participants oven-dried and rewetted the soils to 8 and 20 % gravimetric water content (WC), using the deionized reference water. One batch of soil samples was extracted via predefined extraction conditions (time, temperature, and vacuum) identical to all laboratories; the second batch was extracted via conditions considered routine in the respective laboratory. All extracted water samples were analyzed for delta O-18 and delta H-2 by the lead laboratory (Global Institute for Water Security, GIWS, Saskatoon, Canada) using both a laser and an isotope ratio mass spectrometer (OA-ICOS and IRMS, respectively). We rejected the null hypothesis. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to soil type and soil water content with mean differences compared to the reference water ranging from +18.1 to -108.4 parts per thousand for delta H-2 and +11.8 to -14.9 parts per thousand for delta O-18 across all laboratories. In addition, differences were observed between OA-ICOS and IRMS isotope data. These were related to spectral interferences during OA-ICOS analysis that are especially problematic for the clayey loam soils used. While the types of cryogenic extraction lab construction varied from manifold systems to single chambers, no clear trends between system construction, applied extraction conditions, and extraction results were found. Rather, observed differences in the isotope data were influenced by interactions between multiple factors (soil type and properties, soil water content, system setup, extraction efficiency, extraction system leaks, and each lab's internal accuracy). Our results question the usefulness of cryogenic extraction as a standard for water extraction since results are not comparable across laboratories. This suggests that defining any sort of standard extraction procedure applicable across laboratories is challenging. Laboratories might have to establish calibration functions for their specific extraction system for each natural soil type, individually.
    Keywords: Earth And Environmental Sciences ; Ratio Mass-Spectrometry ; Vacuum Extraction ; Plant-Water ; Infrared-Spectroscopy ; Samples ; Fractionation ; Delta-O-18 ; Delta-H-2 ; Oxygen ; O-18
    ISSN: 1607-7938
    ISSN: 10275606
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  • 10
    Language: English
    In: Hydrology and Earth System Sciences, July 17, 2019, Vol.23(7), p.3007
    Description: pThe water isotopic composition of throughfall is affected by complex diffusive exchange with ambient water vapour, evaporative enrichment of heavy isotopes, and mixing processes in the tree canopy. All interception processes occur simultaneously in space and time, generating a complex pattern of throughfall depth and water isotopic composition. This pattern ultimately cascades through the entire hydrologic system and is therefore crucial for isotope studies in catchment hydrology, where recharge areas are often forested, while reference meteorological stations are generally in the open. For the quasi real-time observation of the water isotopic composition ([delta].sup.18 O and [delta].sup.2 H) of both gross precipitation and throughfall, we developed an approach combining a membrane contactor (Membrana) with a laser-based Cavity Ring-Down Spectrometer (CRDS, Picarro), obtaining isotope readings every 2thinsp;s. A setup with two CRDS instruments in parallel analysing gross precipitation and throughfall simultaneously was used for the continuous observation of the temporal effect of interception processes on the stable isotopes of water. All devices were kept small to minimize dead volume with time lags of only 4thinsp;min for water from the rainfall collectors to the isotope analysers to increase the temporal resolution of isotope observations. Complementarily, meteorological variables were recorded at high temporal resolution at the same location. The achieved evolution from discrete liquid or event-based bulk samples to continuous measurements allows for direct comparison of water stable isotope data with common meteorological measurements. Future improvements of the spatial representativeness will make our approach an even more powerful tool towards detailed insight into the dynamic processes contributing to interception during rainfall events.
    Keywords: Recharge Zones – Analysis ; Rain – Analysis ; Hydrology – Analysis
    ISSN: 1027-5606
    E-ISSN: 16077938
    Source: Cengage Learning, Inc.
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