scholarly journals Continual in situ monitoring of pore water stable isotopes in the subsurface

2014 ◽  
Vol 18 (5) ◽  
pp. 1819-1833 ◽  
Author(s):  
T. H. M. Volkmann ◽  
M. Weiler
Keyword(s):  
Stable Isotopes ◽  
Stable Isotope ◽  
Pore Water ◽  
Transport Processes ◽  
Water Dynamics ◽  
In Situ Monitoring ◽  
Subsurface Water ◽  
Efficient System ◽  
Stable Isotope Signatures

Abstract. Stable isotope signatures provide an integral fingerprint of origin, flow paths, transport processes, and residence times of water in the environment. However, the full potential of stable isotopes to quantitatively characterize subsurface water dynamics is yet unfolded due to the difficulty in obtaining extensive, detailed, and repeated measurements of pore water in the unsaturated and saturated zone. This paper presents a functional and cost-efficient system for non-destructive continual in situ monitoring of pore water stable isotope signatures with high resolution. Automatic controllable valve arrays are used to continuously extract diluted water vapor in soil air via a branching network of small microporous probes into a commercial laser-based isotope analyzer. Normalized liquid-phase isotope signatures are then obtained based on a specific on-site calibration approach along with basic corrections for instrument bias and temperature dependent isotopic fractionation. The system was applied to sample depth profiles on three experimental plots with varied vegetation cover in southwest Germany. Two methods (i.e., based on advective versus diffusive vapor extraction) and two modes of sampling (i.e., using multiple permanently installed probes versus a single repeatedly inserted probe) were tested and compared. The results show that the isotope distribution along natural profiles could be resolved with sufficiently high accuracy and precision at sampling intervals of less than four minutes. The presented in situ approaches may thereby be used interchangeably with each other and with concurrent laboratory-based direct equilibration measurements of destructively collected samples. It is thus found that the introduced sampling techniques provide powerful tools towards a detailed quantitative understanding of dynamic and heterogeneous shallow subsurface and vadose zone processes.

scholarly journals Continual in-situ monitoring of pore water stable isotopes in the subsurface

2013 ◽  
Vol 10 (11) ◽  
pp. 13293-13331 ◽  
Author(s):  
T. H. M. Volkmann ◽  
M. Weiler
Keyword(s):  
Stable Isotopes ◽  
Water Vapor ◽  
Stable Isotope ◽  
Monitoring System ◽  
Pore Water ◽  
Sampling Method ◽  
Transport Processes ◽  
In Situ Monitoring ◽  
Subsurface Water

Abstract. The stable isotope signature of pore water provides an integral fingerprint of water origin, flow path, transport processes, and residence times and can thus serve as a powerful tracer of hydrological processes in the unsaturated and saturated zone. However, the full potential of stable isotopes to quantitatively characterize subsurface water dynamics is yet unfolded due to the difficulty in obtaining extensive detailed and continual measurements of spatiotemporally variable pore water signatures. With the development of field-deployable laser-based isotope analyzers, such measurements are now becoming feasible. This study presents the development and application of a functional, automatable, and cost-efficient system for non-destructive continual in-situ monitoring of pore water stable isotope signatures with high resolution. The monitoring system uses automatic-controllable valve arrays to continuously extract diluted soil air water vapor via a branching network of multiple small microporous probes into a commercial isotope analyzer. Soil temperature observations are used to convert obtained vapor phase into liquid phase water isotope signatures, but these can also be obtained based on vapor concentration measurements. In-situ sampling was conducted at six depths for each of three plots planted with varying vegetation on an experimental site in SW Germany. Two different methods based on advective and diffusive soil water vapor probing were employed suitable under unsaturated and all (including saturated) moisture conditions, respectively. The advective sampling method was applied using multiple permanently installed probes (continual mode) and using a single probe subsequently inserted to sample the various locations (push-in mode), while the diffusive sampling method was applied in push-in mode only. Using a specific identical treatment onsite calibration approach along with basic corrections for instrument bias and temperature dependent free water-vapor isotopic equilibrium fractionation, the monitoring system facilitated inference of normalized liquid pore water isotopic composition with sufficiently high accuracy and precision at sampling intervals of less than four minutes and resolved the isotopic variability along natural depth profiles. Comparison indicated that the presented in-situ approaches may be used interchangeably with each other and with concurrent laboratory-based direct equilibration measurements of destructively collected samples, such that the choice of method will depend upon the task and anticipated conditions of sampling. The introduced sampling techniques provide powerful tools towards a detailed quantitative understanding of dynamic and heterogeneous shallow subsurface and vadose zone processes.

scholarly journals Improving In-Stream Nutrient Routines in Water Quality Models Using Stable Isotope Tracers: A Review and Synthesis

2018 ◽  
Vol 61 (1) ◽  
pp. 139-157 ◽  
Author(s):  
Alexandria Jensen ◽  
William Ford ◽  
James Fox ◽  
Admin Husic
Keyword(s):  
Water Quality ◽  
Stable Isotopes ◽  
Stable Isotope ◽  
Water Quality Modeling ◽  
Water Quality Model ◽  
Model Structure ◽  
Quality Model ◽  
Quality Models ◽  
Stable Isotope Signatures ◽  
Water Quality Models

Abstract. Water quality models serve as an economically feasible alternative to quantify fluxes of nutrient pollution and to simulate effective mitigation strategies; however, their applicability is often questioned due to broad uncertainties in model structure and parameterization, leading to uncertain outputs. We argue that reduction of uncertainty is partially achieved by integrating stable isotope data streams within the water quality model architecture. This article outlines the use of stable isotopes as a response variable within water quality models to improve the model boundary conditions associated with nutrient source provenance, constrain model parameterization, and elucidate shortcomings in the model structure. To assist researchers in future modeling efforts, we provide an overview of stable isotope theory; review isotopic signatures and applications for relevant carbon, nitrogen, and phosphorus pools; identify biotic and abiotic processes that impact isotope transfer between pools; review existing models that have incorporated stable isotope signatures; and highlight recommendations based on synthesis of existing knowledge. Broadly, we find existing applications that use isotopes have high efficacy for reducing water quality model uncertainty. We make recommendations toward the future use of sediment stable isotope signatures, given their integrative capacity and practical analytical process. We also detail a method to incorporate stable isotopes into multi-objective modeling frameworks. Finally, we encourage watershed modelers to work closely with isotope geochemists to ensure proper integration of stable isotopes into in-stream nutrient fate and transport routines in water quality models. Keywords: Isotopes, Nutrients, Uncertainty analysis, Water quality modeling, Watershed.

In-situ monitoring of electrochemical transport processes in Hanford Grout Vault Soil

1997 ◽  
Vol 55 (1-3) ◽  
pp. 23-37 ◽  
Author(s):  
Daniel T. Schwartz ◽  
Mark F. Buehler ◽  
Derek X. Christiansen ◽  
E.James Davis
Keyword(s):  
Transport Processes ◽  
In Situ Monitoring ◽  
Electrochemical Transport

scholarly journals Application of Statistical Techniques to Study Stable Isotopes (18O and 2H) Characteristics of Precipitation in Iran (Southwest Asia)

2021 ◽  
Vol 8 (1) ◽  
pp. 5
Author(s):  
Mojtaba Heydarizad ◽  
Rogert Sorí
Keyword(s):  
Stable Isotopes ◽  
Stable Isotope ◽  
Close Correlation ◽  
Statistical Techniques ◽  
Southwest Asia ◽  
Climatic Zones ◽  
Stable Isotope Signatures ◽  
Isotope Analyses ◽  
Precipitation Sampling

Various climatic and geographic parameters influence precipitation in Iran, which makes the interpretation of stable isotope signatures in precipitation very complicated. Thus, precipitation sampling stations for stable isotope analyses in Iran have been classified by cluster analysis (CA) into 10 clusters, based on their stable isotope characteristics. The classification of stations by CA also has a close correlation with the Koppen climatic zones across Iran. Finally, the stations in each cluster were plotted on the GMWL and EMMWL. This study shows that classifying precipitation sampling stations can simplify the interpretation of stable isotopes in the precipitation of regions with complicated climatic systems.

scholarly journals In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock Brine

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1082
Author(s):  
Tobias Manzel ◽  
Carolin Podlech ◽  
Georg Grathoff ◽  
Stephan Kaufhold ◽  
Laurence N. Warr
Keyword(s):  
Pore Water ◽  
Packing Density ◽  
In Situ Monitoring ◽  
Opalinus Clay ◽  
X Ray Diffraction ◽  
Interlayer Water ◽  
Steady State Condition ◽  
X Ray ◽  
Cap Rock

Compacted bentonite is currently being considered as a suitable backfill material for sealing underground repositories for radioactive waste as part of a multi-barrier concept. Although showing favorable properties for this purpose (swelling capability, low permeability, and high adsorption capacity), the best choice of material remains unclear. The goal of this study was to examine and compare the hydration behavior of a Milos (Greek) Ca-bentonite sample (SD80) in two types of simulated ground water: i) Opalinus clay pore water, and ii) a diluted saline cap rock brine using a confined volume, flow-through reaction cell adapted for in situ monitoring by X-ray diffraction. Based on wet-cell X-ray diffractometry (XRD) and calculations with the software CALCMIX of the smectite d(001) reflection, it was possible to quantify the abundance of water layers (WL) in the interlayer spaces and the amount of non-interlayer water uptake during hydration using the two types of solutions. This was done by varying WL distributions to fit the CALCMIX-simulated XRD model to the observed data. Hydrating SD80 bentonite with Opalinus clay pore water resulted in the formation of a dominant mixture of 3- and 4-WLs. The preservation of ca. 10% 1-WLs and the apparent disappearance of 2-WLs in this hydrated sample are attributed to small quantities of interlayer K (ca. 8% of exchangeable cations). The SD80 bentonite of equivalent packing density that was hydrated in diluted cap rock brine also contained ca. 15% 1-WLs, associated with a slightly higher concentration of interlayer K. However, this sample showed notable suppression of WL thickness with 2- and 3-WLs dominating in the steady-state condition. This effect is to be expected for the higher salt content of the brine but the observed generation of CO2 gas in this experiment, derived from enhanced dissolution of calcite, may have contributed to the suppression of WL thickness. Based on a comparison with all published wet-cell bentonite hydration experiments, the ratio of packing density to the total layer charge of smectite is suggested as a useful proxy for predicting the relative amounts of interlayer and non-interlayer water incorporated during hydration. Such information is important for assessing the subsequent rates of chemical transport through the bentonite barrier.

scholarly journals Technical note: Unresolved aspects of the direct vapor equilibration method for stable isotope analysis (<i>δ</i><sup>18</sup>O, <i>δ</i><sup>2</sup>H) of matrix-bound water: unifying protocols through empirical and mathematical scrutiny

2021 ◽  
Vol 25 (9) ◽  
pp. 5219-5235
Author(s):  
Benjamin Gralher ◽  
Barbara Herbstritt ◽  
Markus Weiler
Keyword(s):  
Stable Isotope ◽  
Data Quality ◽  
Stable Isotope Analysis ◽  
Isotope Analysis ◽  
Bound Water ◽  
Transport Processes ◽  
Subsurface Water ◽  
Water Volume ◽  
Equilibration Time ◽  
Matrix Bound

Abstract. The direct vapor equilibration laser spectrometry (DVE-LS) method has been developed for obtaining matrix-bound water stable isotope data in soils, the critical zone, and bedrock, deriving therefrom subsurface water flow and transport processes and, ultimately, characterizing, for example, groundwater recharge and vulnerability. Recently, DVE-LS has been increasingly adopted due to its possible high sample throughput, relative simplicity, and cost-efficiency. However, this has come at the cost of a non-unified standard operation protocol (SOP), and several contradictory suggestions regarding protocol details do exist which have not been resolved to date. Particularly, sample container material and equilibration times have not yet been agreed upon. Beside practical constraints, this often limits DVE-LS applicability to interpreting relative isotope dynamics instead of absolute values. It also prevents data comparability among studies or laboratories, and several previous comparisons of DVE-LS with other, more traditional approaches of water extraction and subsequent stable isotope analysis yielded significant discrepancies for various sample matrices and physical states. In a series of empirical tests, we scrutinized the controversial DVE-LS protocol details. Specifically, we tested 10 different easily available and cost-efficient inflatable bags previously employed or potentially suitable for DVE-LS sample collection and equilibration. In storage tests similar to the DVE-LS equilibration process but lasting several weeks, we quickly found heat-sealed bags made of laminated aluminum (Al) sheets to be superior by several orders of magnitude over more frequently used freezer bags in terms of evaporation safety and accompanying adverse isotope effects. For the first time, Al-laminated bags allow the applied equilibration time to be adapted exclusively to sample requirements instead of accepting reduced data quality in a trade-off with material shortcomings. Based on detailed physical considerations, we further describe how to calculate the minimum available container headspace and sample-contained liquid water volume and how their ratio affects analytical precision and accuracy. We are confident that these guidelines will expand DVE-LS applicability and improve data quality and comparability among studies and laboratories by contributing to a more unified, physically well-founded SOP based on more appropriate components.

scholarly journals In-situ unsaturated zone stable water isotope (<sup>2</sup>H and <sup>18</sup>O) measurements in semi-arid environments using tunable off-axis integrated cavity output spectroscopy

2015 ◽  
Vol 12 (6) ◽  
pp. 6115-6149 ◽  
Author(s):  
M. Gaj ◽  
M. Beyer ◽  
P. Koeniger ◽  
H. Wanke ◽  
J. Hamutoko ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Pore Water ◽  
Isotope Analysis ◽  
Vacuum Extraction ◽  
Arid Environments ◽  
Soil Pore Water ◽  
Cavity Output ◽  
Spatio Temporal ◽  
Semi Arid

Abstract. Stable isotopes (deuterium, 2H, and oxygen-18, 18O) of soil pore water were measured directly in the field using tunable off-axis integrated cavity output spectroscopy (OA-ICOS) and commercially available soil gas probes in a semi-arid region of the Cuvelai-Etosha-Basin, Namibia. High spatial and temporal resolution was achieved in the study area with reasonable accuracy and measurements were in agreement with laboratory-based cryogenic vacuum extraction and subsequent cavity ring down laser spectroscopic isotope analysis (CRDS). After drift correction of the isotope data, mean precision for over 140 measurements of two consecutive field campaigns in June and November 2014 were 1.8 and 0.46 ‰ for δ2H and 18O, respectively. Mean Accuracy using quality check standards was 5 and 0.3 ‰ for δ2H and δ18O, respectively. Results support the applicability of an in-situ measurement system for the determination of stable isotopes in soil pore water. Spatio-temporal variability could be deduced with the observed data in an extremely dry evaporation dominated environment which was sporadically affected by intermittent rainfall.

scholarly journals “Live” (stained) benthic foraminiferal living depths, stable isotopes, and taxonomy offshore South Georgia, Southern Ocean: implications for calcification depths

2018 ◽  
Vol 37 (1) ◽  
pp. 25-71 ◽  
Author(s):  
Rowan Dejardin ◽  
Sev Kender ◽  
Claire S. Allen ◽  
Melanie J. Leng ◽  
George E. A. Swann ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Stable Isotope ◽  
Water Chemistry ◽  
Pore Water ◽  
Deep Water ◽  
Benthic Foraminifera ◽  
Species Variation ◽  
The South ◽  
South Georgia ◽  
Pore Water Chemistry

Abstract. It is widely held that benthic foraminifera exhibit species-specific calcification depth preferences, with their tests recording sediment pore water chemistry at that depth (i.e. stable isotope and trace metal compositions). This assumed depth-habitat-specific pore water chemistry relationship has been used to reconstruct various palaeoenvironmental parameters, such as bottom water oxygenation. However, many deep-water foraminiferal studies show wide intra-species variation in sediment living depth but relatively narrow intra-species variation in stable isotope composition. To investigate this depth-habitat–stable-isotope relationship on the shelf, we analysed depth distribution and stable isotopes of living (Rose Bengal stained) benthic foraminifera from two box cores collected on the South Georgia shelf (ranging from 250 to 300 m water depth). We provide a comprehensive taxonomic analysis of the benthic fauna, comprising 79 taxonomic groupings. The fauna shows close affinities with shelf assemblages from around Antarctica. We find live specimens of a number of calcareous species from a range of depths in the sediment column. Stable isotope ratios (δ13C and δ18O) were measured on stained specimens of three species, Astrononion echolsi, Cassidulinoides porrectus, and Buccella sp. 1, at 1 cm depth intervals within the downcore sediment sequences. In agreement with studies in deep-water settings, we find no significant intra-species variability in either δ13Cforam or δ18Oforam with sediment living depth on the South Georgia shelf. Our findings add to the growing evidence that infaunal benthic foraminiferal species calcify at a fixed depth. Given the wide range of depths at which we find living, infaunal species, we speculate that they may actually calcify predominantly at the sediment–seawater interface, where carbonate ion concentration and organic carbon availability is at a maximum.

A coring and squeezing technique for the detailed study of subsurface water chemistry

1978 ◽  
Vol 15 (1) ◽  
pp. 162-169 ◽  
Author(s):  
R. J. Patterson ◽  
S. K. Frape ◽  
L. S. Dykes ◽  
R. A. McLeod
Keyword(s):  
Pore Water ◽  
Subsurface Water ◽  
Immiscible Fluid ◽  
Minor Components ◽  
Southern Ontario ◽  
Fluid Displacement ◽  
Quality Of Waters ◽  
Unsaturated Zones

A coring and squeezing technique has been modified and simplified to permit the collection of closely spaced samples of pore water from both the saturated and unsaturated zones on land, and bottom sediments in lakes and rivers. Samples of the pore water are obtained by placing short sections of sediment from freshly collected cores in a mechanical squeezer and applying pressure to extrude the contained fluid into a syringe. If coarse incompressible sediments are encountered, the pore water is removed by an immiscible-fluid displacement technique. The pore water samples are analyzed by standard methods for major and minor components. Also, in situ measurements of some parameters are carried out by directly inserting electrodes into the fresh sediment. These methods are being applied at a number of locations in southern Ontario to study the quality of waters in the unsaturated zone, the chemistry of natural and contaminated groundwaters, and the significance of seepage and baseflow in lakes and rivers respectively.

scholarly journals Mechanisms of consistently disjunct soil water pools over (pore) space and time

2019 ◽  
Vol 23 (6) ◽  
pp. 2751-2762 ◽  
Author(s):  
Matthias Sprenger ◽  
Pilar Llorens ◽  
Carles Cayuela ◽  
Francesc Gallart ◽  
Jérôme Latron
Keyword(s):  
Stable Isotopes ◽  
Stable Isotope ◽  
Soil Water ◽  
Soil Depth ◽  
Stream Water ◽  
Pore Space ◽  
Bound Water ◽  
Subsurface Water ◽  
Data Set ◽  
Soil Pores

Abstract. The storage and release of water in soils is critical for sustaining plant transpiration and groundwater recharge. However, how much subsurface mixing of water occurs, and how much of the water is available for plants or otherwise percolates to streams and the groundwater is not yet understood. Based on stable isotope (2H and 18O) data, some studies have found that water infiltrating into soils can bypass older pore water. However, the mechanisms leading to the separation of water routed to the streams and water held tightly in smaller pores are still unclear. Here, we address the current limitations of the understanding of subsurface mixing and their consequences regarding the application of stable isotopes in ecohydrological studies. We present an extensive data set, for which we sampled the isotopic composition of mobile and bulk soil water in parallel with groundwater at a fortnightly temporal resolution and stream water and rainfall at a much higher resolution in a Mediterranean long-term research catchment, in Vallcebre, Spain. The data reveal that the mobile and tightly bound water of a silty loam soil in a Scots pine forest do not mix well; however, they constitute two disjunct subsurface water pools with little exchange, despite intense rainfall events leading to high soil wetness. We show that the isotopic compartmentalization results from the rewetting of small soil pores by isotopically depleted winter/spring rain. Thus, stable isotopes, and, in turn, water residence times, do not only vary across soil depth, but also across soil pores. Our findings have important implications for stable isotope applications in ecohydrological studies assessing the water uptake by plants or the process realism of hydrological models, as the observed processes are currently rarely implemented in the simulation of water partitioning into evapotranspiration and recharge in the critical zone.

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