scholarly journals Isotopic offset between unconfined water and water adsorbed to organic matter in equilibrium

2016 ◽  
Author(s):  
Guo Chen ◽  
Karl Auerswald ◽  
Hans Schnyder
Keyword(s):  
Organic Matter ◽  
Isotopic Composition ◽  
Soil Water ◽  
Filter Paper ◽  
Surface Effect ◽  
Isotope Composition ◽  
Adsorbed Water ◽  
Organic Soil ◽  
Surface Areas ◽  
Isotope Composition Of Water

Abstract. Hydrophilic surfaces influence the structure of water close to them and may thus affect the isotope composition of water. Such an effect should be relevant and detectable for materials with large surface areas and low water contents. The relationship between the volumetric solid:water ratio and the enrichment of heavy isotopes in adsorbed water compared with unconfined water was investigated for the materials silage, hay, organic soil (litter), filter paper, cotton, casein and flour. Each of these materials was equilibrated via the gas phase with unconfined water of known isotopic composition to quantify the isotopic difference between adsorbed water and unconfined water. Across all materials, enrichment of the adsorbed water was significant and negative (on average −0.91 ‰ for 18O and −20.6 ‰ for 2H at an average solid:water ratio of 0.9). The observed enrichment was not caused by solutes, volatiles or old water because the enrichment did not disappear for washed or oven dried silage, the enrichment was also found in filter paper and cotton, and the enrichment was independent of the isotopic composition of the unconfined water. Enrichment became linearly more negative with increasing volumetric solid:water ratio and even exceeded −4 ‰ for 18O and −44 ‰ for 2H. This enrichment behavior could be modeled by assuming two water layers: a thin layer that is in direct contact and influenced by the surface of the solid and a second layer of varying thickness depending on the total moisture content that is in equilibrium with the surrounding vapor. When we applied the model to soil water under grassland, the soil water extracted from 7 cm and 20 cm depth was significantly closer to local meteoric water than without correction for the surface effect. This study has major implications for the interpretation of the isotopic composition of water extracted from organic matter, especially when the volumetric solid:water ratio is larger than 0.5 or for processes occurring at the solid-water interface.

scholarly journals <sup>2</sup>H and <sup>18</sup>O depletion of water close to organic surfaces

2016 ◽  
Vol 13 (10) ◽  
pp. 3175-3186 ◽  
Author(s):  
Guo Chen ◽  
Karl Auerswald ◽  
Hans Schnyder
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Filter Paper ◽  
Surface Effect ◽  
Isotope Composition ◽  
Isotopic Fractionation ◽  
Adsorbed Water ◽  
Organic Soil ◽  
Surface Areas ◽  
Isotope Composition Of Water

Abstract. Hydrophilic surfaces influence the structure of water close to them and may thus affect the isotope composition of water. Such an effect should be relevant and detectable for materials with large surface areas and low water contents. The relationship between the volumetric solid : water ratio and the isotopic fractionation between adsorbed water and unconfined water was investigated for the materials silage, hay, organic soil (litter), filter paper, cotton, casein and flour. Each of these materials was equilibrated via the gas phase with unconfined water of known isotopic composition to quantify the isotopic difference between adsorbed water and unconfined water. Across all materials, isotopic fractionation was significant (p<0.05) and negative (on average −0.91 ± 0.22 ‰ for 18∕16O and −20.6 ± 2.4 ‰ for 2∕1H at an average solid : water ratio of 0.9). The observed isotopic fractionation was not caused by solutes, volatiles or old water because the fractionation did not disappear for washed or oven-dried silage, the isotopic fractionation was also found in filter paper and cotton, and the fractionation was independent of the isotopic composition of the unconfined water. Isotopic fractionation became linearly more negative with increasing volumetric solid : water ratio and even exceeded −4 ‰ for 18∕16O and −44 ‰ for 2∕1H. This fractionation behaviour could be modelled by assuming two water layers: a thin layer that is in direct contact and influenced by the surface of the solid and a second layer of varying thickness depending on the total moisture content that is in equilibrium with the surrounding vapour. When we applied the model to soil water under grassland, the soil water extracted from 7 and 20 cm depth was significantly closer to local meteoric water than without correction for the surface effect. This study has major implications for the interpretation of the isotopic composition of water extracted from organic matter, especially when the volumetric solid : water ratio is larger than 0.5 or for processes occurring at the solid–water interface.

scholarly journals Carbon stable isotope composition of charophyte organic matter in a small and shallow Spanish water body as a baseline for future trophic studies

2015 ◽  
Author(s):  
María Antonia Rodrigo ◽  
Adriana García ◽  
Allan R. Chivas
Keyword(s):  
Organic Matter ◽  
Isotopic Composition ◽  
Isotope Composition ◽  
Myriophyllum Spicatum ◽  
Reproductive Organs ◽  
Cold Season ◽  
Freshwater Ecosystems ◽  
Organic C ◽  
Isotopic Signatures ◽  
C And N

<p>Quantitative descriptions of foodweb structure based on isotope niche space require knowledge of producers’ isotopic signatures. In freshwater ecosystems charophytes are one of the main components of submerged vegetation and the feeding base for many herbivorous consumers, but knowledge about their organic carbon isotopic signatures is sparse. In this study, the δ<sup>13</sup>C organic values (and organic %C and %N) of the four species of submerged macrophytes (three charophytes - <em>Chara hispida</em>, <em>Nitella hyalina</em> and <em>Tolypella glomerata </em>- and one angiosperm, <em>Myriophyllum spicatum</em>) growing in a newly created shallow pond were measured monthly over a period of one year, to discern if i) all charophyte species susceptible to being food for consumers and growing in the same waterbody have the same C isotopic composition; ii) the δ<sup>13</sup>C values of a charophyte species change on a seasonal and spatial scale; iii) the different parts (apical nodes, internodes, rhizoids, reproductive organs, oospores) of a charophyte species have the same isotopic composition. The δ<sup>13</sup>C, %C and %N values of organic matter in the sediments where the plants were rooted were also measured as well as several limnological variables. The δ<sup>13</sup>C values for the angiosperm (-13.7±0.7‰) indicated <sup>13</sup>C-enrichment, whereas the <em>N. hyalina</em> δ<sup>13</sup>C values were the most negative (-22.4±0.7‰). The mean δ<sup>13</sup>C value for <em>C. hispida </em>was -19.0±1.0‰ and -20.7±0.8‰ for <em>T. glomerata.</em> <em>C. hispida</em> δ<sup>13</sup>C values had a significant seasonal variation with <sup>13</sup>C-poor values in the cold season, and slight spatial differences. Statistically significant differences were found between charophyte rhizoids (<sup>13</sup>C-enriched) and the other parts of the thalli. The δ<sup>13</sup>C values in the sediments varied throughout time (-13‰ to -26‰). The C content was lower in the charophytes than in the angiosperm and there were no large differences among the charophytes. Charophyte fructifications were enriched in organic C compared to the thalli parts. The study provides an isotopic baseline for further studies for the elucidation of higher trophic-level relationships which are particularly complex in shallow water bodies where interactions between the pelagic and the benthic zones are intricate.</p>

scholarly journals Combination of soil water extraction methods quantifies isotopic mixing of waters held at separate tensions in soil

2020 ◽  
Author(s):  
William H. Bowers ◽  
Jason J. Mercer ◽  
Mark S. Pleasants ◽  
David G. Williams
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Isotope Exchange ◽  
Sandy Loam ◽  
Isotope Composition ◽  
Chemical Properties ◽  
Mixing Model ◽  
Time Dependent ◽  
High Tension ◽  
Isotopic Mixing

Abstract. Measurements of the isotopic composition of water recovered from soil at different tensions provide a powerful means to identify potential plant water sources and quantify heterogeneity in residence time and connectivity among soil water regions. Yet incomplete understanding of mechanisms affecting isotopic composition of different soil water pools and the interactions between antecedent and new event water hinders interpretation of the isotope composition of extracted soil and plant waters. Here we present an approach for quantifying the time-dependent isotopic mixing of water held at separate tensions in soil. We wetted oven-dried, homogenized sandy loam soil first with isotopically “light” water (𝛿2H = −130 ‰; 𝛿18O = −17.6 ‰) using a sufficient volume to fill only the smallest soil pores, and then with “heavy” water (𝛿2H = −44 ‰; 𝛿18O = −7.8 ‰) to fully saturate the remaining soil regions. Soil water effluents were then sequentially extracted at three tensions (low centrifugation = 0.016 MPa; medium centrifugation = 1.14 MPa; and high cryogenic vacuum distillation at an estimated tension greater than 100 MPa) starting after variable equilibration periods of 0 h, 8 h, 1 d, 3 d and 7 d. We assessed differences in the isotopic composition of extracted effluents over the 7 d equilibration period with a MANOVA and a mixing model describing the time-dependent effects of isotope self-diffusion and exchange. The saturated moisture conditions used in our experiment likely facilitated rapid isotope exchange and equilibration among different pools. Despite this, the isotope composition of waters extracted at medium compared to high tension remained significantly different (MANOVA) for up to 1 day, and that for waters extracted at low compared to high tension remained significantly different for greater than 3 days after soil wetting. Equilibration (assuming no fractionation) predicted from the time-dependent mixing model for water held at high tension occurred after approximately 4.33 days. Our approach will be useful for assessing how soil texture and other physical and chemical properties influence isotope exchange and mixing times for studies aiming to properly characterize and interpret the isotopic composition of extracted soil and plant waters, especially under variably unsaturated conditions.

Temporal shifts in erosion provenance through multiple earthquake cycles

2020 ◽  
Author(s):  
Jin Wang ◽  
Jamie Howarth ◽  
Erin McClymont ◽  
Alexander Densmore ◽  
Sean Fitzsimons ◽  
...  
Keyword(s):  
Organic Matter ◽  
Isotopic Composition ◽  
Soil Depth ◽  
Isotope Composition ◽  
Large Earthquake ◽  
Nitrogen Isotope ◽  
Mountain Range ◽  
Landslide Occurrence ◽  
Alpine Fault ◽  
High Elevations

&lt;p&gt;Landslides are a dominant mechanism of erosion in mountain landscapes. Widespread triggering of landslides by large storms or earthquakes can lead rapid changes in short-term erosion rates. If landslides occur repeatedly in particular parts of a mountain range, then they will dominate the evolution of that section of the landscape and could leave a fingerprint in the topography. Despite this recognition, it has proved difficult to examine shifts in the focus of landslide erosion through time, mainly because remote sensing approaches from single events to a few decades at most. Here we turn to the depositional record of past erosion, attempting to track landslide occurrence and the provenance of eroded material using a novel combination of the isotopic and molecular composition of organic matter (bulk C and N isotopes, molecular abundance and isotopic composition) deposited in Lake Paringa, fed by catchments proximal to the Alpine Fault, New Zealand. In the modern day forest, we find correlations between elevation, soil depth and the bulk &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C values of the organic matter and the carbon preference index of n-alkanes. We find large shifts in these measurements in the lake core. Using an empirical model based on modern soil samples we suggest that the erosion provenance shifts dramatically after each of four large Alpine Fault earthquakes in the last one thousand years. These shifts in inferred erosion altitude match shifts in the hydrogen isotope composition of long-chain n-alkanes (plant wax biomarkers) and the inferred shifts in depth track changes in organic matter radiocarbon activity and nitrogen isotope composition, lending support to our model. The combination of bulk isotopic composition and biomarker ratios has the potential to track erosion provenance in other settings. In the Lake Paringa record, we find that post-seismic periods eroded organic matter from a mean elevation of 722 &lt;sup&gt;+329&lt;/sup&gt;/&lt;sub&gt;-293&lt;/sub&gt; m at the headwaters of source catchments and supplied 43% of the sediment in the core, while inter-seismic periods sourced organic matter primarily from lower elevations (459 &lt;sup&gt;+256&lt;/sup&gt;/&lt;sub&gt;-226&lt;/sub&gt; m). These results demonstrate that repeated large earthquake consistently focus erosion at high elevations, while inter-seismic periods appear less effective at modifying the highest parts of the topography.&amp;#160;&lt;/p&gt;

scholarly journals A combination of soil water extraction methods quantifies the isotopic mixing of waters held at separate tensions in soil

2020 ◽  
Vol 24 (8) ◽  
pp. 4045-4060 ◽  
Author(s):  
William H. Bowers ◽  
Jason J. Mercer ◽  
Mark S. Pleasants ◽  
David G. Williams
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Sandy Loam ◽  
Isotope Composition ◽  
Chemical Properties ◽  
Extraction Methods ◽  
Time Dependent ◽  
High Tension ◽  
Release Curve ◽  
Isotopic Mixing

Abstract. Measurements of the isotopic composition of separate and potentially interacting pools of soil water provide a powerful means to precisely resolve plant water sources and quantify water residence time and connectivity among soil water regions during recharge events. Here we present an approach for quantifying the time-dependent isotopic mixing of water recovered at separate suction pressures or tensions in soil over an entire moisture release curve. We wetted oven-dried, homogenized sandy loam soil first with isotopically “light” water (δ2H =-130 ‰; δ18O =-17.6 ‰) to represent antecedent moisture held at high matric tension. We then brought the soil to near saturation with “heavy” water (δ2H =-44 ‰; δ18O =-7.8 ‰) that represented new input water. Soil water samples were subsequently sequentially extracted at three tensions (“low-tension” centrifugation ≈0.016 MPa; “mid-tension” centrifugation ≈1.14 MPa; and “high-tension” cryogenic vacuum distillation at an estimated tension greater than 100 MPa) after variable equilibration periods of 0 h, 8 h, 1 d, 3 d, and 7 d. We assessed the differences in the isotopic composition of extracted water over the 7 d equilibration period with a MANOVA and a model quantifying the time-dependent isotopic mixing of water towards equilibrium via self-diffusion. The simplified and homogenous soil structure and nearly saturated moisture conditions used in our experiment likely facilitated rapid isotope mixing and equilibration among antecedent and new input water. Despite this, the isotope composition of waters extracted at mid compared with high tension remained significantly different for up to 1 d, and waters extracted at low compared with high tension remained significantly different for longer than 3 d. Complete mixing (assuming no fractionation) for the pool of water extracted at high tension occurred after approximately 4.33 d. Our combination approach involving the extraction of water over different domains of the moisture release curve will be useful for assessing how soil texture and other physical and chemical properties influence isotope exchange and mixing times for studies aiming to properly characterize and interpret the isotopic composition of extracted soil and plant waters, especially under variably unsaturated conditions.

scholarly journals Preliminary results of studying the carbon isotope composition of conodont elements at the border of Devonian and Carboniferous periods (Kamenka river sections, Pechora carbonate platform)

LITOSFERA ◽  
2020 ◽  
Vol 20 (6) ◽  
pp. 829-841
Author(s):  
A. V. Zhuravlev ◽  
I. V. Smoleva
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Isotopic Composition ◽  
Shallow Water ◽  
Carbon Isotope ◽  
Stable Carbon Isotopes ◽  
Carbonate Platform ◽  
Isotope Composition ◽  
Carbon Isotope Composition ◽  
Oligotrophic Ecosystem

Research subject. Changes in the trophic structure of shallow-water pelagic ecosystems at the Devonian/Carboniferous border were investigated by studying the carbon isotope composition of conodont organic matter.Materials and methods. Two Devonian-Carboniferous shallow-water clayey-carbonate sections located in the southern part of the Pechora-Kozhva Uplift (Pechora Plate) were analysed. The Devonian-Carboniferous boundary was detected by the first occurrences of Siphonodella sulcata, S. semichatovae and Patrognathus crassus, as well as by the last occurrence of Pseudopolygnathus graulichi. The carbon isotope composition was investigated both in whole-rock carbonate samples and the conodont organic matter of two dominant species (Polygnathus parapetus and P. communis communis).Results. The distribution of stable carbon isotopes in the organic matter of conodont elements accompanied by the data on carbonate isotope composition allowed us to suggest changes in the food composition of the dominant taxa during the Late Famennian-Early Tournaisian transition. It was assumed that the latest Famennian representatives of Polygnathus parapetus and P. communis communis consumed largely phyto- and zooplankton, which is characterized by a light isotopic composition of organic carbon. The nutrition based on phyto- and zooplankton with a heavier isotopic composition of organic carbon was suggested for the early Tournaisian representatives of these species.Conclusions. The discovered variations in the carbon isotope composition of conodont organic matter in shallow-water facies may correspond to the change from the eutrophic pelagic ecosystem to the oligotrophic ecosystem, and/or global perturbation of the carbon cycle due to climatic changes. Since the available data is limited to two geological sections, it is impossible to unambiguously interpret the scale (local, regional, global) of these variations and their correlation potential.

Development of cryogenic extraction system for δ18O and δ2H measurement of water in soils and plants.

2021 ◽  
Author(s):  
Nunzio Romano ◽  
Carolina Allocca ◽  
Luisa Stellato ◽  
Fabio Marzaioli ◽  
Paolo Nasta
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Isotope Composition ◽  
Isotopic Ratio ◽  
Plant Root ◽  
Root Water Uptake ◽  
Vacuum System ◽  
Operational Parameters ◽  
Vacuum Equipment ◽  
Preliminary Results

&lt;p&gt;The stable isotope composition of water (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H) represents a useful tool to distinguish among different water pools along the soil-plant-atmosphere continuum. Using &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O as tracers helps gain a better understanding of plant root water uptake and dominant ecohydrological processes. To determine which pools of water are used for plant physiologic functions and returned to the atmosphere by transpiration, a common approach is to analyze the isotopic composition of water in both soil and plant. Cryogenic water extraction (CWE; Orlowski et al., 2016) is the most widely used laboratory-based technique to extract water from soil samples for isotopic analysis. However, recent studies have shown that the extraction conditions (time, temperature, and vacuum) and soil physical and chemical properties may affect the extracted soil-water isotope composition even significantly.&lt;/p&gt;&lt;p&gt;We have developed an efficient and cost-effective cryogenic vacuum equipment to extract water from soil or vegetation and this presentation aims at discussing some preliminary results. The equipment has been specifically designed to meet the following requirements: i) enable to quantify the accuracy of a CWE continuous flow extraction line, and ii) identify a specific extraction standard protocol for soil and vegetation samples. Two experiments have been carried out to evaluate the isotope fractionation induced by the system and how different operational parameters (i.e. times and temperature of extraction) can affect the results. Firstly, a known water isotopic ratio was processed by the vacuum system to determine the measurement accuracy and reproducibility by comparing pre- and post-processed water isotopic signatures. The likely causes of observed biases induced by sample processing are assessed and a relevant correction procedure is suggested. Subsequently, measurements were carried out on replicated samples taken from two differently-textured soils that, after being dried, were saturated in the laboratory up to different water content values with water of known isotopic composition. Also, plant samples were collected from plants grown in a greenhouse and irrigated with water of known isotopic composition.&lt;/p&gt;&lt;p&gt;Water from all samples was extracted by our CWE system and then analyzed using an isotope ratio mass spectrometer in Gas Bench mode for analyses and in temperature conversion elemental analysis (TC/EA) mode for. Preliminary results have quantified the isotope fractions on average of -1.6 &amp;#8240; for &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and 14.2 &amp;#8240; for &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H. Normalization of stable isotopes from unknown samples according to observed fractionation has enabled the observed bias to become virtually zero, leading to a replicate reproducibility of &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H for soil water of 0.6 &amp;#8240; and 3 &amp;#8240;, respectively. The analyses carried out up to now did not find statistical evidence that the soil types and soil-water contents may affect the extraction method and the accuracy of our protocol.&lt;/p&gt;

Changes of carbon-isotope ratios in soil organic matter relative to parent vegetation and site specificity

2020 ◽  
Vol 48 (4) ◽  
pp. 2085-2094
Author(s):  
Silviu L. BADEA ◽  
Roxana E. IONETE ◽  
Diana COSTINEL ◽  
Constantin NECHITA ◽  
Mihai BOTU ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Composition ◽  
Carbon Isotope ◽  
Isotope Composition ◽  
C:N Ratio ◽  
Site Specificity ◽  
Natural Environments ◽  
High Concentration ◽  
Industrial Sites

Investigating the correlation between biodiversity and ecosystem function in natural environments using carbon-isotope composition (δ13C) allows distinguishing the nutrient cycling pattern and anthropogenic effects incorporation in plants and soil processes. The mechanisms behind the isotopic composition of soil organic matter (SOM) and parent vegetation in relation to the context of site-specificity was approached in this work. Formation of SOM can be affected by the presence of a high concentration of heavy metals in soils. Still, no systematic studies were performed in most of the industrial sites to support this hypothesis.  In order to explore this incomplete understood influence, investigation of carbon isotope signatures (d13C) variations in soil organic matter were performed in two industrial areas from Romania (Copșa Mică industrial platform and Baia Sprie mining zone). The current study, also, investigated the C:N ratio variation, as well as the influence of N speciation regarding d13C values of SOM. The decrease in C:N ratio indicated an increasing effect of the microbial products on SOM matter at increasing depth, for both regions, while an increase of the denitrification processes with depth was found for both areas. For the most appropriate depth (20-40 cm), the soil from Baia Sprie region was more enriched in 13C comparing with the soil from Copsa Mica region, and this higher isotope fractionation of SOM might be due to a higher carbon content, respectively a higher nitrogen content of Baia Sprie soil. It was concluded that the SOM of the surface soil in the two investigated regions has an 13C isotopic composition similar to the plant remains from which it was formed, offering an integrated value of plant material, time and the local origin and providing useful markers of tree isotopic composition.

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