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 In situ unsaturated zone water stable isotope (<sup>2</sup>H and <sup>18</sup>O) measurements in semi-arid environments: a soil water balance

2016 ◽  
Vol 20 (2) ◽  
pp. 715-731 ◽  
Author(s):  
Marcel Gaj ◽  
Matthias Beyer ◽  
Paul Koeniger ◽  
Heike Wanke ◽  
Josefina Hamutoko ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Water Balance ◽  
Soil Water ◽  
Root Zone ◽  
Soil Water Balance ◽  
Vacuum Extraction ◽  
Rain Event ◽  
Arid Environments ◽  
Semi Arid

Abstract. Stable isotopes (deuterium, 2H, and oxygen-18, 18O) of soil water were measured in the field using a liquid water isotope analyzer (tunable off-axis integrated cavity output spectroscope, OA-ICOS, LGR) and commercially available soil gas probes (BGL-30, UMS, Munich) in the semi-arid Cuvelai–Etosha Basin (CEB), Namibia. Results support the applicability of an in situ measurement system for the determination of stable isotopes in soil pore water. 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, L2120-i, Picarro Inc.). After drift and span correction of the in situ isotope data, precision for over 140 measurements taken during two consecutive field campaigns (June and November 2014) was 1.8 and 0.48 ‰ for δ2H and δ18O, respectively. Mean measurement trueness is determined using quality check standards and was 5 and 0.3 ‰ for δ2H and δ18O, respectively. The isotope depth profiles are used quantitatively to calculate a soil water balance. The contribution of transpiration to total evapotranspiration ranged between 72 and 92 %. Shortly after a rain event, the contribution of transpiration was much lower, at 35 to 50 %. Potential limitations of such an in situ system are related to environmental conditions which could be minimized by using a temperature-controlled chamber for the laser spectrometer. Further, the applicability of the system using previously oven-dried soil material might be limited by physicochemical soil properties (i.e., clay minerals). Uncertainty in the in situ system is suggested to be reduced by improving the calibration procedure and further studying fractionation effects influencing the isotope ratios in the soil water, especially at low water contents. Furthermore, the influence of soil-respired CO2 on isotope values within the root zone could not be deduced from the data.

Pilot-scale in situ bioremediation of HMX and RDX in soil pore water in Hawaii

2013 ◽  
Vol 15 (11) ◽  
pp. 2023 ◽  
Author(s):  
Zachary M. Payne ◽  
Krishna M. Lamichhane ◽  
Roger W. Babcock ◽  
Stephen J. Turnbull
Keyword(s):  
Pore Water ◽  
Pilot Scale ◽  
In Situ Bioremediation ◽  
Soil Pore Water

scholarly journals Evidence for convergent evolution among phylogenetically distant rare species of Tetratheca (Elaeocarpaceae, formerly Tremandraceae) from Western Australia

2007 ◽  
Vol 20 (2) ◽  
pp. 126 ◽  
Author(s):  
Ryonen Butcher ◽  
Margaret Byrne ◽  
Darren M. Crayn
Keyword(s):  
Western Australia ◽  
Rare Species ◽  
Cladistic Analysis ◽  
Geographic Area ◽  
Arid Environments ◽  
High Conservation ◽  
Superficial Similarity ◽  
Evolutionary Lineages ◽  
Semi Arid

Morphological and molecular investigations of taxon relationships among rare species of Tetratheca Sm. occurring near Koolyanobbing, Western Australia, have confirmed the distinctness of T. aphylla F.Muell., T. harperi F.Muell. and T. paynterae Alford and identified three new rare taxa from collections affiliated with T. aphylla and T. paynterae. The recognition of these taxa at specific and sub-specific ranks is based on their different degrees of morphological and molecular divergence, combined with geographic disjunction. Cladistic analysis of nrDNA internal transcribed spacer and cpDNA trnL-trnF sequences from a range of Tetratheca species from Western Australia and the eastern states indicates that T. aphylla, T. harperi and T. paynterae belong to three separate evolutionary lineages and that the endemism displayed among these taxa to small, disjunct ranges within the same geographic area, is a result of in situ speciation due to historical fragmentation. These results exemplify the extremely high conservation value of the Yilgarn banded ironstone ranges. The superficial similarity among the study taxa in having a ‘leafless’ habit can be seen to be adaptive convergence in response to the marginal and semi-arid environments in which they occur, and this character is highly homoplastic within the genus.

scholarly journals Intercomparison of soil pore water extraction methods for stable isotope analysis

2016 ◽  
Vol 30 (19) ◽  
pp. 3434-3449 ◽  
Author(s):  
Natalie Orlowski ◽  
Dyan L. Pratt ◽  
Jeffrey J. McDonnell
Keyword(s):  
Stable Isotope ◽  
Pore Water ◽  
Stable Isotope Analysis ◽  
Isotope Analysis ◽  
Extraction Methods ◽  
Water Extraction ◽  
Soil Pore Water

In-situ sampling of soil pore water: evaluation of linear-type microdialysis probes and suction cups at varied moisture contents

2010 ◽  
Vol 7 (1) ◽  
pp. 123 ◽  
Author(s):  
Manuel Miró ◽  
Walter J. Fitz ◽  
Siegfried Swoboda ◽  
Walter W. Wenzel
Keyword(s):  
Pore Water ◽  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Soil Conditions ◽  
Metal Concentrations ◽  
Soil Pore Water ◽  
Moisture Contents ◽  
Suction Cup ◽  
Suction Cups

Environmental context. There is a need for slightly invasive techniques capable of in-situ probing of target analytes in environmental compartments. Owing to its passive sampling mode and small probe dimensions, microdialysis-based dosimetry is an appealing tool for monitoring of solute concentrations in both water bodies and pore soil waters with minimum disturbance of natural equilibrium. The development of field applications is challenging but will provide novel insights as to the speciation and bioaccessibility of environmental pollutants, e.g. trace metals, at high spatial resolution. Abstract. In-situ sampling of soil pore water is still a challenge for environmental scientists. Here, microdialysis is explored for probing metal concentrations in soil pore water at soil moisture contents ranging from 50 to 115% of the maximal water holding capacity and is compared with traditional sampling by suction cups. Metal concentrations obtained by the suction cup technique were consistently larger than those measured in the dialysate. Good agreement was obtained for Pb and Cu at soil moistures close to saturation after accounting for diffusion resistances whereas corrected Ni and Cd concentrations in the dialysates exceeded those measured by the suction cup technique. These deviations reflect inherent differences in the sampling mode and effects of soil heterogeneity at the microscale. Microdialysis offers new opportunities to probe solute concentrations at high spatial resolution and minimal disturbance of soil conditions at environmental interfaces such as the plant rhizosphere or at the transition between forest floors and the mineral soil.

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 Extending the Spatio-Temporal Applicability of DISPATCH Soil Moisture Downscaling Algorithm: A Study Case Using SMAP, MODIS and Sentinel-3 Data

2021 ◽  
Vol 9 ◽  
Author(s):  
Nitu Ojha ◽  
Olivier Merlin ◽  
Christophe Suere ◽  
Maria José Escorihuela
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Arid Regions ◽  
Data Sets ◽  
Sparse Vegetation ◽  
Thermal Data ◽  
Spatio Temporal ◽  
Temporal Coverage ◽  
Semi Arid

DISPATCH is a disaggregation algorithm of the low-resolution soil moisture (SM) estimates derived from passive microwave observations. It provides disaggregated SM data at typically 1 km resolution by using the soil evaporative efficiency (SEE) estimated from optical/thermal data collected around solar noon. DISPATCH is based on the relationship between the evapo-transpiration rate and the surface SM under non-energy-limited conditions and hence is well adapted for semi-arid regions with generally low cloud cover and sparse vegetation. The objective of this paper is to extend the spatio-temporal coverage of DISPATCH data by 1) including more densely vegetated areas and 2) assessing the usefulness of thermal data collected earlier in the morning. Especially, we evaluate the performance of the Temperature Vegetation Dryness Index (TVDI) instead of SEE in the DISPATCH algorithm over vegetated areas (called vegetation-extended DISPATCH) and we quantify the increase in coverage using Sentinel-3 (overpass at around 09:30 am) instead of MODIS (overpass at around 10:30 am and 1:30 pm for Terra and Aqua, respectively) data. In this study, DISPATCH is applied to 36 km resolution Soil Moisture Active and Passive SM data over three 50 km by 50 km areas in Spain and France to assess the effectiveness of the approach over temperate and semi-arid regions. The use of TVDI within DISPATCH increases the coverage of disaggregated images by 9 and 14% over the temperate and semi-arid sites, respectively. Moreover, including the vegetated pixels in the validation areas increases the overall correlation between satellite and in situ SM from 0.36 to 0.43 and from 0.41 to 0.79 for the temperate and semi-arid regions, respectively. The use of Sentinel-3 can increase the spatio-temporal coverage by up to 44% over the considered MODIS tile, while the overlapping disaggregated data sets derived from Sentinel-3 and MODIS land surface temperature data are strongly correlated (around 0.7). Additionally, the correlation between satellite and in situ SM is significantly better for DISPATCH (0.39–0.80) than for the Copernicus Sentinel-1-based (−0.03 to 0.69) and SMAP/S1 (0.37–0.74) product over the three studies (temperate and semi-arid) areas, with an increase in yearly valid retrievals for the vegetation-extended DISPATCH algorithm.

Fractionation of stable isotopes in perchlorate and nitrate during in situ biodegradation in a sandy aquifer

2009 ◽  
Vol 6 (1) ◽  
pp. 44 ◽  
Author(s):  
Paul B. Hatzinger ◽  
John Karl Böhlke ◽  
Neil C. Sturchio ◽  
Baohua Gu ◽  
Linnea J. Heraty ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Isotope Fractionation ◽  
Isotope Analysis ◽  
Anthropogenic Sources ◽  
In Situ Experiment ◽  
Fractionation Factor ◽  
Pure Cultures ◽  
The Individual ◽  
In Situ Biodegradation

Environmental context. Perchlorate (ClO4–) and nitrate (NO3–) are common co-contaminants in groundwater, with both natural and anthropogenic sources. Each of these compounds is biodegradable, so in situ enhanced bioremediation is one alternative for treating them in groundwater. Because bacteria typically fractionate isotopes during biodegradation, stable isotope analysis is increasingly used to distinguish this process from transport or mixing-related decreases in contaminant concentrations. However, for this technique to be useful in the field to monitor bioremediation progress, isotope fractionation must be quantified under relevant environmental conditions. In the present study, we quantify the apparent in situ fractionation effects for stable isotopes in ClO4– (Cl and O) and NO3– (N and O) resulting from biodegradation in an aquifer. Abstract. An in situ experiment was performed in a shallow alluvial aquifer in Maryland to quantify the fractionation of stable isotopes in perchlorate (Cl and O) and nitrate (N and O) during biodegradation. An emulsified soybean oil substrate that was previously injected into this aquifer provided the electron donor necessary for biological perchlorate reduction and denitrification. During the field experiment, groundwater extracted from an upgradient well was pumped into an injection well located within the in situ oil barrier, and then groundwater samples were withdrawn for the next 30 h. After correction for dilution (using Br– as a conservative tracer of the injectate), perchlorate concentrations decreased by 78% and nitrate concentrations decreased by 82% during the initial 8.6 h after the injection. The observed ratio of fractionation effects of O and Cl isotopes in perchlorate (ϵ18O/ϵ37Cl) was 2.6, which is similar to that observed in the laboratory using pure cultures (2.5). Denitrification by indigenous bacteria fractionated O and N isotopes in nitrate at a ratio of ~0.8 (ϵ18O/ϵ15N), which is within the range of values reported previously for denitrification. However, the magnitudes of the individual apparent in situ isotope fractionation effects for perchlorate and nitrate were appreciably smaller than those reported in homogeneous closed systems (0.2 to 0.6 times), even after adjustment for dilution. These results indicate that (1) isotope fractionation factor ratios (ϵ18O/ϵ37Cl, ϵ18O/ϵ15N) derived from homogeneous laboratory systems (e.g. pure culture studies) can be used qualitatively to confirm the occurrence of in situ biodegradation of both perchlorate and nitrate, but (2) the magnitudes of the individual apparent ϵ values cannot be used quantitatively to estimate the in situ extent of biodegradation of either anion.

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