Correction of cryogenic vacuum extraction biases and potential effects on soil water isotopes application

2021 ◽  
Vol 603 ◽  
pp. 127011
Author(s):  
Mingyi Wen ◽  
Yanwei Lu ◽  
Min Li ◽  
Dong He ◽  
Wei Xiang ◽  
...  
Keyword(s):  
Soil Water ◽  
Water Isotopes ◽  
Vacuum Extraction ◽  
Cryogenic Vacuum

Origin of the waters sourced by trees in a pre-Alpine forested catchment

2020 ◽  
Author(s):  
Giulia Zuecco ◽  
Chiara Marchina ◽  
Amin Anam ◽  
Michael Engel ◽  
Jay Frentress ◽  
...  
Keyword(s):  
Soil Water ◽  
Water Samples ◽  
Vacuum Distillation ◽  
Stream Water ◽  
Bulk Soil ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Forested Catchment ◽  
Cryogenic Vacuum ◽  
Suction Lysimeters

<p>Stable water isotopes have proven to be useful tracers to determine the origin of water taken up by plants, quantify the relative contributions of water sources to stream runoff and investigate water flow paths. However, the presence of different water pools in a catchment and soil water allocation complicates our understanding of water cycling, and calls for research on processes governing soil water movement and storage, as well as interactions between soil and plants.</p><p>In this study, we used isotopic data from a forested catchment in the Italian pre-Alps to i) investigate the spatial and temporal variability of the isotopic signature of various water sources, and ii) determine which waters are used by beech and chestnut trees in the study area.</p><p> </p><p>Ecohydrological and hydrometeorological monitoring took place in the 2.4-ha Ressi catchment (Northern Italy). Elevations range from 598 to 721 m a.s.l., while average slope is 31°. Average annual precipitation is about 1695 mm, while average annual temperature is 9.7 °C. The entire catchment is covered by deciduous forest, with beech, chestnut, hazel and maple as the main tree species.</p><p>Water samples for isotopic analysis were taken monthly from bulk precipitation, approximately bi-weekly from stream water, groundwater and soil water by two suction lysimeter cups in the riparian zone. Bulk soil water samples and twigs for xylem water extraction by cryogenic vacuum distillation were collected starting in June, 2017. All water samples were analysed by laser spectroscopy, except xylem water that was analysed by mass spectrometry.</p><p> </p><p>Stream water, groundwater and soil water extracted by suction lysimeters were isotopically similar to precipitation and aligned to the local meteoric water line. Bulk soil water obtained by cryogenic vacuum distillation showed an evaporation signature, especially on the hillslope where soil moisture was lower and soil water had been extracted by suction lysimeters only during or just after a large rainfall event. This indicates that soil water sampled by suction lysimeters and extracted by cryogenic vacuum distillation is stored differently in the soil layers due to the different soil tension, and hillslopes tend to store less mobile soil water compared to the riparian zone. At greater depths, bulk soil water extracted by cryogenic vacuum distillation was slightly less evaporated and less enriched in heavy isotopes compared to soil water extracted from shallower layers. The isotopic composition of xylem water had a large temporal and tree-species variability, with chestnut xylem water samples more enriched in heavy isotopes than samples obtained from beech trees. Xylem water was more similar to soil water obtained by cryogenic vacuum distillation, suggesting that in the study area trees likely use more bulk soil water than the mobile soil water, groundwater and stream water.</p><p> </p><p>Keywords: stable water isotopes; soil water; xylem water; forested catchment.</p>

scholarly journals The Soil Water Evaporation Process from Mountains Based on the Stable Isotope Composition in a Headwater Basin and Northwest China

Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2711 ◽  
Author(s):  
Leilei Yong ◽  
Guofeng Zhu ◽  
Qiaozhuo Wan ◽  
Yuanxiao Xu ◽  
Zhuanxia Zhang ◽  
...  
Keyword(s):  
Soil Water ◽  
Environmental Remediation ◽  
Isotope Composition ◽  
Salt Content ◽  
Water Isotopes ◽  
Water Evaporation ◽  
Hydrological Process ◽  
Arid Areas ◽  
Time Dynamics ◽  
Evaporation Loss

Soil water is a link between different water bodies. The study of soil water evaporation is of great significance to understand the regional hydrological process, promote environmental remediation in arid areas, and rationalize ecological water use. On the basis of soil water δ2H and δ18O data from April to October 2017 in the Xiying River basin in the upper reaches of the Qilian mountains, the lc-excess and Craig-Gordon model were applied to reflect the evaporating fractionation of soil water. The results show that the change in evaporation loss drives the enrichment of soil water isotopes. The signal of evaporative fractionation of soil water isotopes at different elevations has spatiotemporal heterogeneity. From the perspective of time dynamics, the evaporation loss of the whole region during the observation period was affected by temperature before July, while after July, it was controlled jointly by temperature and humidity, evaporation was weakened. Soil salt content and vegetation played an important role in evaporation loss. In terms of spatial dynamics, the soil moisture evaporation at the Xiying (2097 m) and Huajian (2390 m) stations in the foothills area is larger than that at the Nichan station (2721 m) on the hillside and Lenglong station (3637 m) on the mountain top. The surface soil water evaporation is strong, and the evaporation becomes weak with the increase of depth. The research has guiding significance for the restoration and protection of vegetation in arid areas and the formulation of reasonable animal husbandry policies.

Soil water balance in the Lake Chad Basin using stable water isotopes and chloride of soil profiles

2019 ◽  
Vol 55 (5) ◽  
pp. 459-477
Author(s):  
Daniel Okubay Tewolde ◽  
Paul Koeniger ◽  
Matthias Beyer ◽  
Christoph Neukum ◽  
Maike Gröschke ◽  
...  
Keyword(s):  
Water Balance ◽  
Soil Water ◽  
Soil Water Balance ◽  
Water Isotopes ◽  
Soil Profiles ◽  
Stable Water Isotopes ◽  
Lake Chad ◽  
Chad Basin ◽  
Lake Chad Basin

scholarly journals Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

2016 ◽  
Vol 20 (9) ◽  
pp. 3873-3894 ◽  
Author(s):  
Natalie Orlowski ◽  
Philipp Kraft ◽  
Jakob Pferdmenges ◽  
Lutz Breuer
Keyword(s):  
Land Use ◽  
Soil Water ◽  
Hydrological Model ◽  
Water Cycle ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Age Dynamics ◽  
Isotopic Signatures ◽  
Spatially Distributed ◽  
Water Isotope

Abstract. A dual stable water isotope (δ2H and δ18O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions between each other. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ values. A spatially distributed snapshot sampling of soil water isotopes at two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that topsoil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils, explaining the isotopic similarities between top- and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence became less pronounced with depth and soil water approached groundwater δ values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depths > 0.9 m and constant values were observed through space and time. Since classic isotope evaluation methods such as transfer-function-based mean transit time calculations did not provide a good fit between the observed and calculated data, we established a hydrological model to estimate spatially distributed groundwater ages and flow directions within the Vollnkirchener Bach subcatchment. Our model revealed that complex age dynamics exist within the subcatchment and that much of the runoff must has been stored for much longer than event water (average water age is 16 years). Tracing stable water isotopes through the water cycle in combination with our hydrological model was valuable for determining interactions between different water cycle components and unravelling age dynamics within the study area. This knowledge can further improve catchment-specific process understanding of developed, human-impacted landscapes.

scholarly journals Temporal dynamics of tree xylem water isotopes: In-situ monitoring and modelling

2021 ◽  
Author(s):  
Stefan Seeger ◽  
Markus Weiler
Keyword(s):  
Soil Water ◽  
Temporal Dynamics ◽  
Length Distribution ◽  
In Situ Monitoring ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Root Tips ◽  
Water Age ◽  
Isotopic Signatures

Abstract. We developed a setup for a fully automated, high frequency in-situ monitoring system of the stable water isotopes Deuterium and 18O in soil water and tree xylem. The setup was tested for 12 weeks within an isotopic labelling experiment during a large artificial sprinkling experiment including three mature European beech (Fagus sylvatica) trees. Our setup allowed for one measurement every 12–20 minutes, enabling us to obtain about seven measurements per day for each of our 15 in-situ probes in the soil and tree xylem. While the labelling induced an abrupt step pulse in the soil water isotopic signature, it took seven to ten days until the isotopic signatures at the trees' stem bases reached their peak label concentrations and it took about 14 days until the isotopic signatures at 8 m stem height levelled off around the same values. During the experiment, we observed the effects of several rain events and dry periods on the xylem water isotopic signatures, which fluctuated between the measured isotopic signatures observed in the upper and lower soil horizons. In order to explain our observations, we combined an already existing root water uptake (RWU) model with a newly developed approach to simulate the propagation of isotopic signatures from the root tips to the stem base and further up along the stem. The key to a proper simulation of the observed short term dynamics of xylem water isotopes, was accounting for sap flow velocities and the flow path length distribution within the root and stem xylem. Our modelling framework allowed us to identify parameter values that relate to root depth, horizontal root distribution and wilting point. The insights gained from this study can help to improve the representation of stable water isotopes in trees within ecohydrological models and the prediction of transit time distribution and water age of transpiration fluxes.

scholarly journals Exploring water cycle dynamics through sampling multitude stable water isotope pools in a small developed landscape of Germany

2015 ◽  
Vol 12 (2) ◽  
pp. 1809-1853 ◽  
Author(s):  
N. Orlowski ◽  
P. Kraft ◽  
L. Breuer
Keyword(s):  
Land Use ◽  
Soil Water ◽  
Agricultural Land ◽  
Water Cycle ◽  
Mean Transit Time ◽  
Arable Land ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Isotopic Signatures ◽  
Water Isotope

Abstract. Conducting a dual stable water isotope (δ2H and δ18O) study in the developed landscape of the Schwingbach catchment (Germany) helped to unravel connectivity and disconnectivity between the different water cycle components. The two-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are decoupled from the annual precipitation cycle but showed bidirectional interactions between each other. Seasonal variations based on temperature effects were observed in the precipitation signal but neither reflected in stream nor in groundwater isotopic signatures. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ-values. A spatially distributed snapshot sampling of soil water isotopes in two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that top soil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils explaining the isotopic similarities between top and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence smoothed out with depth and soil water approached groundwater δ-values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depth > 0.9 m and constant values were observed through space and time. Little variation in individual isotope time series of stream and groundwater restricted the use of classical isotope hydrology techniques e.g. mean transit time estimation or hydrograph separation. Still, tracing stable water isotopes through the water cycle was valuable for determining interactions between different water cycle components and gaining catchment specific process understanding in a developed, human-impacted landscape.

Recharge mechanisms of deep soil water revealed by water isotopes in deep loess deposits

Geoderma ◽  
2020 ◽  
Vol 369 ◽  
pp. 114321 ◽  
Author(s):  
Wei Xiang ◽  
Jaivime Evaristo ◽  
Zhi Li
Keyword(s):  
Soil Water ◽  
Water Isotopes ◽  
Deep Soil ◽  
Loess Deposits

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.

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