Identifying the water source for subsurface flow with deuterium and oxygen-18 isotopes of soil water collected from tension lysimeters and cores

Zhao, Pei; Tang, Xiangyu; Zhao, Peng; Wang, Chao; Tang, Jialiang

doi:10.1016/j.jhydrol.2013.08.033

Cited by 79 publications

(57 citation statements)

References 30 publications

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“…() observed that the δ 2 H and δ 18 O of soil‐bound water is depleted by 5–10‰ and 0.3–0.5‰, respectively, relative to the mobile water phase. Others have also observed that water extracted by distillation (bound and mobile water phase) is depleted relative to water extraction by suction lysimeters representing only the mobile water phase (Figueroa‐Johnson et al ., ; Brooks et al ., ; Goldsmith et al ., ; Zhao et al ., ). The dual relationships between δ 2 H and δ 18 O along the soil profile has been observed previously (Allison et al ., ; McCutcheon et al ., ), although Allison et al .…”

Section: Discussionmentioning

confidence: 97%

Testing plant use of mobile vs immobile soil water sources using stable isotope experiments

et al. 2017

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We tested for isotope exchange between bound (immobile) and mobile soil water, and whether there is isotope fractionation during plant water uptake. These are critical assumptions to the formulation of the 'two water worlds' hypothesis based on isotope profiles of soil water. In two different soil types, soil-bound water in two sets of 19-l pots, each with a 2-yr-old avocado plant (Persea americana), were identically labeled with tap water. After which, one set received isotopically enriched water whereas the other set received tap water as the mobile phase water. After a dry down period, we analyzed plant stem water as a proxy for soil-bound water as well as total soil water by cryogenic distillation. Seventy-five to 95% of the bound water isotopically exchanged with the mobile water phase. In addition, plants discriminated against O and H during water uptake, and this discrimination is a function of the soil water loss and soil type. The present experiment shows that the assumptions for the 'two water worlds' hypothesis are not supported. We propose a novel explanation for the discrepancy between isotope ratios of the soil water profile and other water compartments in the hydrological cycle.

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Section: Discussionmentioning

confidence: 97%

Testing plant use of mobile vs immobile soil water sources using stable isotope experiments

et al. 2017

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“…Separation of isotopic domains for sources was clear despite samples coming from pools with different residence times associated with the greater temporal variability in xylem water, surface water, TF, and vadose water as compared to groundwater. There is greater variability in those water sources than we measured at both spatial (Zhao et al ., ) and temporal (Pangle et al ., ) scales, which broadens the domain and increases overlap of measured members. However, both the stable isotopic composition of groundwater and the highly variable isotopic composition of TF had substantial d offsets from xylem water and vadose water.…”

Section: Discussionmentioning

confidence: 97%

Hydrologic exchanges and baldcypress water use on deltaic hummocks, Louisiana, USA

et al. 2016

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Coastal forested hummocks support clusters of trees in the saltwater-freshwater transition zone. To examine how hummocks support trees in mesohaline sites that are beyond physiological limits of the trees, we used salinity and stable isotopes ( 2 H and 18 O) of water as tracers to understand water fluxes in hummocks and uptake by baldcypress (Taxodium distichum (L.) Rich.), which is the most abundant tree species in coastal freshwater forests of the southeastern U.S. Hummocks were always partially submerged and were completely submerged 1 to 8% of the time during the two studied growing seasons, in association with high water in the estuary. Salinity, δ 18 O, and δ 2 H varied more in the shallow open water than in groundwater. Surface water and shallow groundwater were similar to throughfall in isotopic composition, which suggested dominance by rainfall. Salinity of groundwater in hummocks increased with depth, was higher than in swales, and fluctuated little over time. Isotopic composition of xylem water in baldcypress was similar to the vadose zone and unlike other measured sources, indicating that trees preferentially use unsaturated hummock tops as refugia from higher salinity and saturated soil in swales and the lower portions of hummocks. Sustained upward gradients of salinity from groundwater to surface water and vadose water, and low variation in groundwater salinity and isotopic composition, suggested long residence time, limited exchange with surface water, and that the shallow subsurface of hummocks is characterized by episodic salinization and slow dilution.

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“…Recent studies have shown that the isotopic ratios of suction lysimeter waters differ from cryogenically extracted waters (Brooks et al ., ; Figueroa‐Johnson et al ., ; Landon et al ., ; Zhao et al ., ). While there is of course a large literature on isotopes in plant ecophysiology (see review articles of Adams and Grierson, ; Dawson et al ., ; Newton, ), there has been rather little comment on the techniques we use to extract low mobility waters in soils.…”

Section: Introductionmentioning

confidence: 99%

Critical issues with cryogenic extraction of soil water for stable isotope analysis

2016

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Cryogenic water extraction is the most widely used method to facilitate the laboratory removal of soil pore water for isotopic analysis. However, recent studies have suggested that cryogenic extraction conditions (extraction time, temperature, vacuum threshold) and physicochemical soil properties can influence extracted water isotopic signatures. Here, we argue that new work is needed to analyse the full extent of these effects on the extracted water isotopic composition. We illustrate this need with a simple lab experiment and show that in addition to extraction times, soil organic matter and its exchangeable bonded hydrogen fraction influence the resulting isotope composition. We hope these comments stimulate discussion on the assumptions and limitations of cryogenic extraction for soil water and lead ultimately to a standardization of testing approaches.

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Identifying the water source for subsurface flow with deuterium and oxygen-18 isotopes of soil water collected from tension lysimeters and cores

Cited by 79 publications

References 30 publications

Testing plant use of mobile vs immobile soil water sources using stable isotope experiments

Testing plant use of mobile vs immobile soil water sources using stable isotope experiments

Hydrologic exchanges and baldcypress water use on deltaic hummocks, Louisiana, USA

Critical issues with cryogenic extraction of soil water for stable isotope analysis

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