Tightly bound soil water introduces isotopic memory effects on mobile and extractable soil water pools

Newberry, Sarah L.; Prechsl, Ulrich E.; Pace, Matthew; Kahmen, Ansgar

doi:10.1080/10256016.2017.1302446

Cited by 38 publications

(64 citation statements)

References 32 publications

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“…The isotopic composition of the water remaining in soil for exchange in the L or H treatments (δ 2 H = −141.9 mUr and δ 18 O = −13.10 mUr) is strongly depleted compared with the extracted water (δ 2 H = −52.2 mUr and δ 18 O = −7.68 mUr), an effect that has also been observed by Newberry et al and Oshun et al – the latter assumed clay interaction to be the driving force for this effect.…”

Section: Discussionsupporting

confidence: 89%

“…A number of laboratory experiments where oven‐dried soil was spiked with water of known isotopic composition have shown that the added water could not be reliably recovered from the soil . It remained unclear, however, whether this was due to inefficient performance of the cryodistillation setup – which widely differs among laboratories – or to interaction or exchange of the added water with the soil matrix and/or residual soil water, a process that has been referred to as memory effect . The basis for the memory effect is the assumption that soil water can be separated into at least two pools, the mobile soil water (which is assumed to be extractable by cryogenic vacuum extraction) and the soil‐bound water (which is not extracted by cryogenic vacuum extraction, referred to here as residual soil water) .…”

Section: Introductionmentioning

confidence: 99%

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Effects of soil‐bound water exchange on the recovery of spike water by cryogenic water extraction

Thielemann

Gerjets

Dyckmans

2019

Rapid Comm Mass Spectrometry

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Rationale The effects that alter the isotopic composition of water added to soil samples that have been oven‐dried previously are not fully understood. Methods Oven‐dried clay‐rich soil was repeatedly rewetted with two waters of strongly differing isotopic composition. This approach allowed the determination of the amount and the isotopic composition of soil‐bound water that exchanges with spike water after rewetting. Results After oven drying, 1.8% and 1.4% water (gravimetric content) exchanged with the added spike water, for δ2H and δ18O values, respectively. The isotopic composition of this soil residual water was depleted by 89.7 mUr and 5.42 mUr relative to the water extracted from field‐fresh soil for H and O, respectively. The cryogenic extraction method was more efficient than oven drying in terms of water removal from soil. Conclusions Our results show that the isotopic difference between extractable (mobile) water and non‐extractable (soil‐bound) water explains the isotopic effects observed in spike water experiments. This difference, however, can also lead to a considerable isotopic offset between extractable and total soil water.

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Section: Discussionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Effects of soil‐bound water exchange on the recovery of spike water by cryogenic water extraction

Thielemann

Gerjets

Dyckmans

2019

Rapid Comm Mass Spectrometry

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“…Recently reported potential effects of CO 2 on the isotope analysis of vapor with wavelength-scanned cavity ring-down spectroscopy (Gralher et al, 2016) have been shown to not apply to the OA-ICSO that we used, as shown by Sprenger et al (2017a). Potentially fractionating effects of interactions between soil water and surfaces of clay minerals (Oerter et al, 2014;Gaj et al, 2017a, b;Newberry et al, 2017) are of minor relevance for our study, since clay contents were low in the sampled soils (Table 1). We can further ensure that the sampled soil volumes always contained much more than 3 g of water as suggested by Hendry et al (2015).…”

Section: Sampling Design and Analysismentioning

confidence: 92%

Soil water stable isotopes reveal evaporation dynamics at the soil–plant–atmosphere interface of the critical zone

Sprenger

Tetzlaff

Soulsby

2017

Hydrol. Earth Syst. Sci.

160

165

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Abstract. Understanding the influence of vegetation on water storage and flux in the upper soil is crucial in assessing the consequences of climate and land use change. We sampled the upper 20 cm of podzolic soils at 5 cm intervals in four sites differing in their vegetation (Scots Pine (Pinus sylvestris) and heather (Calluna sp. and Erica Sp)) and aspect. The sites were located within the Bruntland Burn longterm experimental catchment in the Scottish Highlands, a low energy, wet environment. Sampling took place on 11 occasions between September 2015 and September 2016 to capture seasonal variability in isotope dynamics. The pore waters of soil samples were analyzed for their isotopic composition (δ 2 H and δ 18 O) with the direct-equilibration method. Our results show that the soil waters in the top soil are, despite the low potential evaporation rates in such northern latitudes, kinetically fractionated compared to the precipitation input throughout the year. This fractionation signal decreases within the upper 15 cm resulting in the top 5 cm being isotopically differentiated to the soil at 15-20 cm soil depth. There are significant differences in the fractionation signal between soils beneath heather and soils beneath Scots pine, with the latter being more pronounced. But again, this difference diminishes within the upper 15 cm of soil. The enrichment in heavy isotopes in the topsoil follows a seasonal hysteresis pattern, indicating a lag time between the fractionation signal in the soil and the increase/decrease of soil evaporation in spring/autumn. Based on the kinetic enrichment of the soil water isotopes, we estimated the soil evaporation losses to be about 5 and 10 % of the infiltrating water for soils beneath heather and Scots pine, respectively. The high sampling frequency in time (monthly) and depth (5 cm intervals) revealed high temporal and spatial variability of the isotopic composition of soil waters, which can be critical, when using stable isotopes as tracers to assess plant water uptake patterns within the critical zone or applying them to calibrate traceraided hydrological models either at the plot to the catchment scale.

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“…Many of these studies report extracted soil water δ 18 O and δ 2 H values that are significantly 2 H‐ or 18 O‐depleted from reference waters. It is suggested that this isotopic depletion can influence δ 2 H and δ 18 O and values independently (Orlowski et al, ) and that these effects can be exacerbated by low soil water content (Walker et al, ), soil physiochemical properties such as soil texture and clay content (Newberry et al, ; Oerter et al, ), as well as carbonate content (Meißner et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…The 2 H‐ and 18 O‐depletion of extracted soil waters from added reference waters has been shown to be particularly relevant during the extraction of a spiked soil in laboratory experiments where the soil was previously dried under high temperatures in a drying oven (Newberry et al, ). It has been proposed that these effects result from the presence of two different water pools in soils: tightly bound cryogenically unextractable soil water (e.g., water adhesively bound to soil particles) and “mobile” cryogenically extractable soil water (free flowing water and capillary water; Araguás‐Araguás et al, ; Hsieh, Savin, Kelly, & Chadwick, ; Koeniger et al, ; Savin & Epstein, ).…”

Section: Introductionmentioning

confidence: 99%

Cryogenic vacuum artifacts do not affect plant water‐uptake studies using stable isotope analysis

2017

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Water movement through the soil‐plant‐atmosphere continuum can be tracked through its hydrogen and oxygen isotopic composition. How the isotopic composition of water evolves as it moves through this continuum provides critical information on ecosystem hydrology and climate change. Cryogenic vacuum extraction is the most applied method to extract waters from soil and plant material for such studies. However, recent experiments where oven dried soils were spiked with a reference water suggest potential for these techniques to bias results. We present results from a greenhouse‐based plant water uptake and cryogenic vacuum distillation experiment using Salix viminalis cuttings. We tested the capacity for cryogenic vacuum extraction to recover irrigation water and the plant‐available water pool from 4 soils that were subject to continuous irrigation as would occur in nature. Results show that δ2H and δ18O values of extracted soil waters reflect those of irrigation water, but with some influence of evaporation that varied with differences in soil humic and clay content. This suggests that isotope effects observed in laboratory experiments with oven‐dried soils may not be relevant under natural conditions. Cryogenic vacuum extraction also recovered xylem water δ2H values that matched the δ2H values of extracted soil water but revealed small, consistent offsets between xylem and soil water δ18O values of 0.84 ± 1.13‰. Although these effects may not significantly bias water isotope sourcing applications, they do result in large extrapolation errors when estimating original source water isotope composition from extracted xylem waters using the back extrapolation to the global meteoric water line method.

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Tightly bound soil water introduces isotopic memory effects on mobile and extractable soil water pools

Cited by 38 publications

References 32 publications

Effects of soil‐bound water exchange on the recovery of spike water by cryogenic water extraction

Effects of soil‐bound water exchange on the recovery of spike water by cryogenic water extraction

Soil water stable isotopes reveal evaporation dynamics at the soil–plant–atmosphere interface of the critical zone

Cryogenic vacuum artifacts do not affect plant water‐uptake studies using stable isotope analysis

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