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A porewater-based stable isotope approach for the investigation of subsurface hydrological processes

Copernicus Publications on behalf of European Geosciences Union
Hydrology and Earth System Sciences
Authors:
Jakob Garvelmann at _boden & grundwasser~ Allgäu GmbH
Jakob Garvelmann
  • _boden & grundwasser~ Allgäu GmbH
Christoph J. Kuells at University of Applied Sciences, Lübeck, Germany
Christoph J. Kuells
  • University of Applied Sciences, Lübeck, Germany
Markus Weiler at University of Freiburg
Markus Weiler
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Abstract and Figures

Predicting and understanding subsurface flowpaths is still a crucial issue in hydrological research. We present an experimental approach to reveal present and past subsurface flowpaths of water in the unsaturated and saturated zone. Two hillslopes in a humid mountainous catchment have been investigated. The H2O(liquid) – H2O(vapor) equilibration laser spectroscopy method was used to obtain high resolution δ2H vertical depth profiles of pore water at various points along two fall lines of a pasture hillslope in the southern Black Forest, Germany. The Porewater-based Stable Isotope Profile (PSIP) approach was developed to use the integrated information of several vertical depth profiles of deuterium along transects at the hillslope. Different shapes of depth profiles were observed in relation to hillslope position. The statistical variability (inter-quartile range and standard deviation) of each profile was used to characterize different types of depth profiles. The profiles upslope or with a weak affinity for saturation as indicated by a low topographic wetness index preserve the isotopic input signal by precipitation with a distinct seasonal variability. These observations indicate mainly vertical movement of soil water in the upper part of the hillslope before sampling. The profiles downslope or at locations with a strong affinity for saturation do not show a similar seasonal isotopic signal. The input signal is erased in the foothills and a large proportion of pore water samples are close to the isotopic values of δ2H in streamwater during base flow conditions indicating the importance of the groundwater component in the catchment. Near the stream indications for efficient mixing of water from lateral subsurface flow paths with vertical percolation are found.
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Garvelmann et al hess-16-631-2012
Data
September 2015
Jakob Garvelmann · Christoph J. Kuells · Markus Weiler
... 37 Consequently, Wassenaar et al. 38 introduced the direct vapor equilibration laser spectrometry (DVE-LS) which allows for equilibrated soil water vapor isotope measurements in the headspace of airtight bags. The method was further tested and developed by Garvelmann et al., 39 Hendry et al., 40 Sprenger et al., 41 Mattei et al., 42 and Gralher et al. 43 Recent studies 25,44,45 also applied and compared the method for plant material, whereby co-extraction of organic contaminants potentially causing spectral interference is already described. Based on the water vapor equilibration principle, new in situ methods emerged in the last decade. ...
Coping with spectral interferences when measuring water stable isotopes of vegetables
Article
Full-text available
  • Sep 2024
Rationale Laser‐based analyzers are widely used in ecohydrology to analyze plant water isotopic compositions (δ ¹⁸ O and δ ² H). The suitability of three different water extraction and isotope equilibration techniques was compared. We examined whether co‐extracted volatile organic compounds (VOCs) affect laser‐based isotope measurements and used the instrument's spectral parameters to post‐correct for interfering VOCs. Methods Cryogenic vacuum extraction, vapor headspace equilibration in bags, and vapor equilibration in situ probes were used to extract liquid water or water vapor for laser‐based isotope analysis (cavity ring‐down spectrometry, CRDS). Isotope data were calibrated by standards for each method separately. Spectral parameters of the instrument, appropriate to identify spectral interferences with MeOH and CH 4 , were identified and used for post‐correction. Differences between the three methods and between the origins of the vegetables were identified by statistical tests. Results VOCs were found in various amounts for the three different methods. They were co‐extracted or co‐equilibrated during the different extraction or equilibration methods. Correlation coefficients of isotope data and “CH 4 ” (spectral parameter) were 0.99 or better; however, slopes for δ ¹⁸ O were similar on different instrument types but different for δ ² H. Our correction approach improved results and inter‐comparability of the methods considerably without knowing the chemical composition of the plant sap. Conclusions All three methods were sensitive enough to distinguish and resolve differences in natural abundance. Data quality was improved by the “CH 4 correction” approach but could probably be optimized by a plant species–specific correction. Standardized tools for contaminant removal or post‐correction applications from manufacturers, in particular for vapor‐mode analysis, are still needed.
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... There are many extraction methods to choose from and several studies that compare them (Zhu et al., 2014;Sprenger et al., 2015;Orlowski et al., 2016bOrlowski et al., , 2018. For a brief overview, there are methods using a) various chemical compounds or elements like toluene for azeotropic distillation (Revesz and Woods, 1990;Thorburn et al., 1993), dichloromethane for accelerated solvent extraction techniques (Zhu et al., 2014), zinc or uranium for microdistillation (Kendall and Coplen, 1985;Brumsack et al., 1992); b) microwave water extraction (Munksgard et al., 2014); c) force in 45 terms of mechanical squeezing (Wershaw et al., 1966;White et al., 1985;Böttcher et al., 1997) or centrifugation (Mubarak and Olsen, 1976;Batley and Giles, 1979;Barrow and Whelan, 1980;Peters and Yakir, 2008); d) equilibration methods such as in situ equilibration (Garvelmann et al., 2012;Rothfuss et al., 2013Rothfuss et al., , 2015Volkmann and Weiler, 2014;Gaj et al., 2016), CO2-and H2-equilibration (Jusserand, 1980;Scrimgeour, 1995;Hsieh et al., 1998;McConville et al., 1999;Koehler et al., 2000;Kelln et al., 2001) and the direct liquid-vapour equilibrium laser spectroscopy (DVE-LS) method (Wassenaar et al., 50 2008;Hendry et al., 2015) and e) cryogenic vacuum extraction (CVE) (Dalton, 1988;West et al., 2006;Koeniger et al., 2011;Goebel and Lascano, 2012;Orlowski et al., 2013Orlowski et al., , 2016Gaj et al., 2017), modified CVE -He-purging method (Ignatev et al., 2013) and automatic cryogenic vacuum distillation (ACVD) system LI-2100 (Lica United Technology Limited Inc.). In addition, many laboratories use modifications of these methods (Walker et al., 1994;Munksgaard et al., 2014;Orlowski et al., 2018). ...
Technical note: Simple, exact and reliable way to extract soil water for stable isotope analysis
Preprint
Full-text available
  • Aug 2024
Water stable isotope analysis in ecohydrological studies often requires soil water extraction. Here, we present a new soil water extraction method based on the principle of complete evaporation and condensation of the soil water in a lose circuit. We have developed an apparatus that has four extraction slots and can be used multiple times a day. Thanks to its simple design, there is no need for any chemicals, gases, high pressure or high-temperature regimes. A set of system functionality tests confirmed that the extraction method has high accuracy and high precision and does not cause any isotope fractionation effects leading to erroneous results. When extracting pure water samples, the accuracy is 0.04 ‰ and 0.06 ‰ for δ18O and δ2H, respectively, with a precision of ± 0.06 ‰ and ± 0.35 ‰ respectively. Soil water extraction tests were conducted with three soil types (loamy sand, sandy loam and sandy clay) using 50–80 grams of soil and water content of 20 %. The accuracy for the extraction of oven-dried and rehydrated soils ranged between -0.04 and 0.03 ‰ for δ18O and 0.06 and 0.68 ‰ for δ2H with precision of ± 0.06 to 0.13 ‰ and ± 0.34 to 0.58 ‰ for δ18O and δ2H, respectively in individual tests. These results are more accurate than results achieved by cryogenic vacuum extraction, which is the most widely used extraction method for soils. So far, our method was only tested for soil water extractions.
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... Many studies are starting to monitor the isotope characteristics or use tracing experiments to study the dynamics of the soil water flow Wang et al., 2020). Stable isotopes of water have been widely used in quantitative analysis of the soil water flow transport and residence time (Hrachowitz et al., 2013;Zheng et al., 2019), and the separation of various water source (Brkić et al., 2016;Chen et al., 2023b) within soil profiles (Stumpp et al., 2009) and hillslopes (Garvelmann et al., 2012). Isotopic tracing techniques improve the reliability of understanding soil water movements that are difficult to directly observe including the detailed water flow transport time and pathways (Jones et al., 2006;Reckerth et al., 2017). ...
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... Groundwater is merely water that is below the earth's surface which completely drains pore spaces or fractures in soils and rocks. Fresh water is present not just on top of the earth as streams or lakes, but also underneath as underground water, and the water present there is known as groundwater (Garvelmann and Weiler, 2012). Given the complexity of geology and terrain, the electrical resistivity tomography technique generates an appropriate two-dimensional sub-surface detailed resistivity structure that periodically displays variations in resistivity in both horizontal as well as vertical directions (Loke 2000;Kumar et al. 2014 a, b).The electrical resistivity method has been widely utilised to gather subsurface data regarding the resistivity values of different rock materials across all the geophysical methods applied for groundwater potential exploration (Keller and Frischknecht, 1966). ...
Identification of Groundwater Potential Zones Using Electrical Resistivity Tomography Technique
Conference Paper
  • Nov 2023
The main objective of this study is to assess the potential groundwater zones by employing the electrical resistivity tomography technique. The field data collection was conducted using the Syscal pro switch-72 instrument. Dipole-Dipole, Schlumberger and Wenner-Schlumberger array configurations were utilized during the data acquisition process. Subsequently, the obtained field data was processed using the RES2DINV software, generating inverse model resistivity profiles. The generated profiles have a maximum depth of 36.9m, providing valuable information on the subsurface structures. Moreover, the expansion of the electrodes along the profiles reached a maximum distance of 175m. The resulting profiles provide valuable insights into the variations in lithology at different depths, including clay, boulder, sand, and clayed sand layers. These variations were cross-verified with the lithologs data obtained from borehole records. Additionally, the profiles indicate the possible presence of fracture depths, which serve as indicative markers for potential groundwater zones.
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... Stable isotopes of pore water have been used to provide insights into soil evaporation (Zimmermann et al., 1967;Allison, 1982;Allison et al., 1983;Barnes and Allison, 1988;Walker et al., 1988) and groundwater recharge rates (Dincer et al., 1974;Saxena, 1984;Darling and Bath, 1988;Koeniger et al., 2016). They were used in soil hydrology to study unsaturated and saturated subsurface flow processes and mixing and residence times (Sklash and Farvolden, 1979;Buttle and Sami, 1990;McDonnell, 1990;Stewart and McDonnell, 1991;Gazis and Feng, 2004;Laudon et al., 2004;Garvelmann et al., 2012;Beyer et al., 2016), as well as to quantify evapotranspiration partitioning (Brunel et al., 1997;Hsieh et al., 1998;Yepez et al., 2005;Rothfuss et al., 2010;Wang and Yakir, 2000;Dubbert et al., 2013;Quade et al., 2019). Applications of water stable isotopes in ecology have allowed researchers to identify plant water sources (Dawson and Ehleringer, 1991), to describe water use patterns (Schwinning et al., 2002), and to determine competitive interactions Meißner et al., 2012). ...
Technical note: Discrete in situ vapor sampling for subsequent lab-based water stable isotope analysis
Article
Full-text available
Methodological advancements have been made in in situ observations of water stable isotopes that have provided valuable insights into ecohydrological processes. The continuous measurement capabilities of laser-based analyzers allow for high temporal resolutions and non-destructive minimally invasive study designs of such in situ approaches. However, isotope analyzers are expensive, heavy, and require shelter and access to electrical power, which impedes many in situ assays. Therefore, we developed a new inexpensive technique to collect discrete water vapor samples in the field via diffusion-tight inflatable bags that can later be analyzed in the lab. In a series of structured experiments, we tested different procedural settings, bag materials, and closure types for diffusion tightness during storage as well as for practical handling during filling and extraction. To facilitate reuse of sampling bags, we present a conditioning procedure using ambient air as primer. In order to validate our method, direct measurements through hydrophobic in situ probes were compared to repeated measurements of vapor sampled with our bags from the same source. All steps are summarized in a detailed standard operating procedure (SOP). This procedure represents the preparation and measurement of calibration and validation vapor standards necessary for processing of unknown field-collected vapor samples in the foreseen application. By performing pertinent calibration procedures, accuracy was better than 0.4 ‰ for δ18O and 1.9 ‰ for δ2H after 1 d of storage. Our technique is particularly suitable when used in combination with minimally invasive water vapor sampling in situ probes that have already been employed for soils and tree xylem. It is an important step towards minimally invasive monitoring of stable isotope distributions and also time series in virtually undisturbed soils and trees without the need to have an analyzer in the field. It is therefore a promising tool for many applications in ecohydrology and meteorology.
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Technical note: A fast and objective autosampler for direct vapor equilibration isotope measurements
Preprint
Full-text available
  • Feb 2024
To investigate water movement in environmental systems, stable water isotopes (2H and 18O) are commonly used tracers. Analyzing the isotopic composition of water bonded to substances like soil or plant tissue necessitates its extraction prior to analysis. One such method, direct vapor equilibration, is popular due to its cost-effectiveness and straightforward sample processing. However, sample analysis requires a significant manual labor, thereby limiting the number of samples that can be analyzed. This limitation is compounded by the fact that stored samples undergo isotopic composition changes over time, and in addition manual measurements may lack objectivity. To address these challenges, we have developed a device that automates the analysis process. Our vapor autosampler for vapour samples, named VapAuSa, features a modular design with up to 350 ports for direct vapor equilibration samples. These ports sequentially connect the prepared samples to the analyzer, enabling continuous automatic measurements. Within the accompanying software, measurement criteria can be specified, facilitating objective analysis. VapAuSa measurements have a similar uncertainty compared to manual analysis of identical samples (VapAuSa δ2H = +/− 4.5 ‰ δ18O = +/− 0.58 ‰ vs. manual δ2H = +/− 5.7 ‰ δ18O = +/− 0.37 ‰). However, the increased sample throughput minimizes storage-induced isotopic changes. Moreover, VapAuSa triples sample throughput per week while reducing direct labor time to just 10 % of manual processing.
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Vadose zone water stable isotope profiles for assessing groundwater recharge: Sensitivity to seasonal soil sampling
Article
  • Oct 2023
  • J HYDROL
Groundwater recharge is widely recognized as being the most important parameter for the sustainable management of water resources. In semiarid environments, groundwater recharge can be quantified using the piston displacement method (PDM). From a single soil sampling campaign, the PDM relies on linking the deeper vadose zone soil pore water stable isotope composition (δ2HH2O and δ18OH2O) to the local meteoric water line (LMWL). However, the isotopic composition of precipitation changes seasonally, influencing the water isotope composition of the vadose zone over time. Thus, it is important to test whether the PDM is sensitive to seasonal soil sampling and whether the assessed recharge rate is independent of the time of sampling. This study investigates the effect of seasonal soil sampling on the distribution of vadose zone stable isotope composition to determine whether the sampling time influences the estimate of recharge rate from PDM. Soil samples were obtained along vertical profiles through the vadose zone in a semiarid region during the spring, summer, and autumn seasons. Specifically, the δ2HH2O and δ18OH2O of the soil pore water were determined along vertical profiles, and the PDM was applied to quantify the annual recharge. The δ2HH2O and δ18OH2O values range from −7.3 to −3.5 ‰ and from −54.4 to +7.41 ‰, respectively, and plot along a continuum with a slope less than the LMWL. Samples from deeper in the vadose zone profile had distinct ranges in isotopic composition between the three soil sampling campaigns, with isotopic composition of spring sampling dominated by lower values and those from autumn with higher values. Despite these differences, the resulting annual recharge rates from the different sampling campaigns are comparable (1.5 to 2 % of annual precipitation). Even though the pore water isotopic composition changed over time, the shift between the deeper vadose zone isotopic compositions and the LMWL remained relatively constant, leading to a similar recharge estimate over time. Therefore, the PDM-based recharge assessment in the tested semiarid environment is independent of the sampling time, which indicates that sampling for assessing groundwater recharge can be undertaken during any season.
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Soil Water Movement and Groundwater Recharge Under Different Land Uses in a Flood‐Irrigated Area
Article
  • May 2023
  • GROUND WATER
The water shortage in agriculture area in China requires to reduce the consumption of excessive water in flood irrigation. Therefore, the dynamics of soil water regime is needed to investigate and water-saving irrigation is necessary to alleviate water shortage. This study investigated the impact of flood irrigation on soil water movement and recharge to groundwater in the Yellow River irrigation area of Yinchuan Plain, China. Combining comprehensive field observation, stable isotopic techniques and water balance simulation, we described the soil water mechanism in vadose zone covered with bare soil in 2019 and planted with maize in 2020. The soil layers affected by precipitation infiltration and evaporation were mainly 0-50 cm, while the soil influenced by irrigation was the entire profile in the mode of piston flow. The maize root took up the soil water up to the depth of 100 cm during the tasseling period. The infiltration and capillary rise in 2020 were similar with those in 2019. However, the total deep percolation was 156.5 mm in 2020 which was about 50% of that in 2019 because of the maize root water uptake. The leakage of ditch water was the major recharge resource of groundwater for the fast water table rise. Precise irrigation is required to minimize deep percolation and leakage of ditch water and reduce excessive unproductive evapotranspiration. Therefore, understanding the soil water movement and groundwater recharge is critical for agricultural water management to improve irrigation efficiency and water use efficiency in arid regions. This article is protected by copyright. All rights reserved.
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Isotopic exchange effects in soil water
Chapter
Full-text available
  • Dec 1998
Investigations into the processes affecting the hydrological response of catchments typically revolve around interpreting a time record of the flux of water leaving the catchment outlet (the hydrograph) in response to a time record of precipitation intensity. This chapter reviews the fundamentals of isotopic behavior in soil water, including processes of leading to variations in soil water concentrations. It provides a simple conceptual model for explaining soil water movement and presents suggestions for new research directions. It also discusses exchange process modifications to the isotopic composition of soil water and the dependence of these processes on physical parameters of the catchment. Factors affecting the hydrograph are complex and to some extent non-linear, and inevitably there is a confounding of the effects of different processes, that is, there is insufficient information in the hydrograph record to reconstruct the processes that gave rise to it. The degree to which the original processes can be reconstructed is greatly enhanced if additional independent information can be obtained.
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Effect of Catchment-Scale Subsurface Mixing on Stream Isotopic Response
Article
Full-text available
  • Dec 1991
A 3.8-ha watershed on the west coast of New Zealand was instrumented with suction lysimeters and automatic water samplers to determine the relationship between subsurface isotopic and chemical concentrations to those of rainfall and resulting streamflow. A t test showed that ±2‰ represented a significant difference between successive sample deuterium values. Eleven rainfall episodes were subdivided into two categories: (1) two events where stream isotopic composition did not deflect >2‰ from prestorm values, and (2) four events which demonstrated new water flushing. Detailed analysis of one 47-mm rainfall (9.8-mm runoff) event showed that old water dominated stream water exiting the watershed by 90% using a standard two-component hydrograph separation for deuterium (corroborated by Cl and electrical conductivity). Three-component hydrograph separation indicated that 12–16% was in the form of soil water, with
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Isotopes in Groundwater Hydrology
Chapter
  • Dec 1998
The concentration of stable isotopes in groundwater depends mainly on the origin of the water. The concentration of radioactive isotopes and dissolved compounds in groundwater depends on the initial concentration and residence time of groundwater in the aquifer. These two factors determine the amount of radioactive isotope(s) decayed, removed, or added during water-rock processes. As geochemical tools, stable and radioactive environmental isotopes provide information on the geochemical processes operating on groundwater and on the hydrogeological characteristics of aquifers. Information provided by environmental isotopes is also useful in modeling groundwater systems. This chapter discusses the scientific background of applications of environmental isotope techniques to groundwater hydrology. The stable isotope composition of groundwater reflects that of the precipitation in the recharge area that seeps through the soil and the unsaturated zone to reach the water table. Stable isotopes are often used to identify groundwater recharge by rivers and lakes. These water bodies frequently have isotopic compositions different from that of precipitation over the study area.
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Isotopes in the Water Cycle: Past, Present and Future of a Developing Science
Book
  • Jan 2005
Environmental isotope and nuclear techniques provide unmatched insights into the processes governing the water cycle and its variability under past and present climates. This monograph is recommended to advanced students and specialists and presents historical perspective, state of the art applications and new developments of isotopes in hydrology, environmental disciplines and climate change studies. The spectrum of isotope applications addressed in this monograph ranges from the assessment of groundwater resources in terms of recharge and flow regime, identification of palaeogroundwater, water balance of river basins and lakes, to studies of the past and present global environmental and climate changes.
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Seasonal Isotope Hydrology of Three Appalachian Forest Catchments
Article
  • Dec 1997
  • HYDROL PROCESS
Seasonal oxygen-18 variations in precipitation, throughfall, soil water, spring flow and stream baseflow were analysed to compare the hydrology of two forested basins in West Virginia (WV) (34 and 39 ha) and one in Pennsylvania (PA) (1134 ha). Precipitation and throughfall were measured with funnel/bottle samplers, soil water with ceramic-cup suction lysimeters and spring flow/baseflows by grab and automatic sampling during the period March 1989 to March 1990. Isotopic damping depths, or depths required to reduce the amplitude of subsurface oxygen-18 fluctuations to 37% of the surface amplitude, were generally similar for soil water on the larger PA basin, and baseflows and headwater spring flows on the smaller WV basins. Computed annual isotopic damping depths for these water sources averaged 49 cm using soil depth as the flow path length. The equivalent annual mean hydraulic diffusivity for the soil flow paths was 21 cm2 d-1. Mean transit times, based upon an assumed exponential distribution of transit times, ranged from 0·2 y for soil water at a depth of 30 cm on the larger catchment, to 1·1-1·3 y for most spring flows and 1·4-1·6 y for baseflows on the smaller catchments. Baseflow on the larger PA basin and flow of one spring on a small WV basin showed no detectable seasonal fluctuations in oxygen-18, indicating flow emanated from sources with mean transit times greater than about 5 y. Based upon this soil flow path approach, it was concluded that seasonal oxygen-18 variations can be used to infer mean annual isotopic damping depths and diffusivities for soil depths up to approximately 170 cm.
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