Tracers Determine Movement of Soil Moisture and Evapotranspiration

Zimmermann, Udo; Münnich, K. O.; Roether, Wolfgang; Kreutz, W.; Schubach, K.; Siegel, O.

doi:10.1126/science.152.3720.346

Cited by 136 publications

(87 citation statements)

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“…Soil water at shallow depth in unsaturated soil responded to recent rainfall input, whereas deeper soil water and water near the stream showed much less variation compared to local precipitation and was considerably delayed and attenuated by ongoing mixing and progressive displacement of subsurface water. This behavior has also been shown by Horton and Hawkins (1965) and Zimmermann et al (1966) with tritiated ( 3 H) water.…”

Section: Introductionsupporting

confidence: 72%

A porewater-based stable isotope approach for the investigation of subsurface hydrological processes

Garvelmann¹,

Külls²,

Weiler³

2012

Hydrol. Earth Syst. Sci.

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Abstract. Predicting and understanding subsurface flowpaths is still a crucial issue in hydrological research. We present an experimental approach to reveal present and past subsurface flowpaths of water in the unsaturated and saturated zone. Two hillslopes in a humid mountainous catchment have been investigated. The H 2 O (liquid) -H 2 O (vapor) equilibration laser spectroscopy method was used to obtain high resolution δ 2 H vertical depth profiles of pore water at various points along two fall lines of a pasture hillslope in the southern Black Forest, Germany. The Porewater-based Stable Isotope Profile (PSIP) approach was developed to use the integrated information of several vertical depth profiles of deuterium along transects at the hillslope.Different shapes of depth profiles were observed in relation to hillslope position. The statistical variability (interquartile range and standard deviation) of each profile was used to characterize different types of depth profiles. The profiles upslope or with a weak affinity for saturation as indicated by a low topographic wetness index preserve the isotopic input signal by precipitation with a distinct seasonal variability. These observations indicate mainly vertical movement of soil water in the upper part of the hillslope before sampling. The profiles downslope or at locations with a strong affinity for saturation do not show a similar seasonal isotopic signal. The input signal is erased in the foothills and a large proportion of pore water samples are close to the isotopic values of δ 2 H in streamwater during base flow conditions indicating the importance of the groundwater component in the catchment. Near the stream indications for efficient mixing of water from lateral subsurface flow paths with vertical percolation are found.

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Section: Introductionsupporting

confidence: 72%

A porewater-based stable isotope approach for the investigation of subsurface hydrological processes

Garvelmann¹,

Külls²,

Weiler³

2012

Hydrol. Earth Syst. Sci.

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“…The extent of this depletion is influenced by the isotopic composition of the atmospheric vapor, the relative humidity, and a fractionation associated with the diffusivity of water molecules across the boundary layer. Good agreement has been observed between theoretical predictions using the Craig-Gordon model and experimental results for soil water undergoing evaporation (Zimmermann et al 1966(Zimmermann et al , 1967Allison and Leaney 1982;Allison and Barnes 1983; Barnes and Allison 1988;Walker and Brunel 1990;Bariac 1996a, 1996b). Soil water becomes gradually enriched in heavy isotopes of 18 O, and a highly enriched "evaporation front" usually develops at 0.1~0.5 m below the dry soil surface (Barnes and Allison 1988).…”

Section: Isotopic Identity Of Different Ecosystem Gas Exchange Componmentioning

confidence: 70%

The use of stable isotopes to study ecosystem gas exchange

Yakir¹,

2000

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Stable isotopes are a powerful research tool in environmental sciences and their use in ecosystem research is increasing. In this review we introduce and discuss the relevant details underlying the use of carbon and oxygen isotopic compositions in ecosystem gas exchange research. The current use and potential developments of stable isotope measurements together with concentration and flux measurements of CO and water vapor are emphasized. For these applications it is critical to know the isotopic identity of specific ecosystem components such as the isotopic composition of CO, organic matter, liquid water, and water vapor, as well as the associated isotopic fractionations, in the soil-plant- atmosphere system. Combining stable isotopes and concentration measurements is very effective through the use of "Keeling plots." This approach allows the identification of the isotopic composition and the contribution of ecosystem, or ecosystem components, to the exchange fluxes with the atmosphere. It also allows the estimation of net ecosystem discrimination and soil disequilibrium effects. Recent modifications of the Keeling plot approach permit examination of CO recycling in ecosystems. Combining stable isotopes with dynamic flux measurements requires precision in isotopic sampling and analysis, which is currently at the limit of detection. Combined with the micrometeorological gradient approach (applicable mostly in grasslands and crop fields), stable isotope measurements allow separation of net CO exchange into photosynthetic and soil respiration components, and the evapotranspiration flux into soil evaporation and leaf transpiration. Similar applications in conjunction with eddy correlation techniques (applicable to forests, in addition to grasslands and crop fields) are more demanding, but can potentially be applied in combination with the Keeling plot relationship. The advance and potential in using stable isotope measurements should make their use a standard component in the limited arsenal of ecosystem-scale research tools.

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“…Such pore water stable isotope analyses have shown to give valuable insights into the hydrological processes in the vadose zone of temperate regions, providing information on the water balance of forest soils (Eichler, 1966;Zimmermann et al, 1966;Blume et al, 1967;Wellings, 1984) and the infiltration and percolation processes (Darling and Bath, 1988;Gazis and Feng, 2004;Koeniger et al, 2010;Thomas et al, 2013), on the influence of vegetation on evaporation , on preferential root water uptake (Gehrels et al, 1998), and on subsurface hydrological processes in hillslopes (Blume et al, 1968;Garvelmann et al, 2012). These and other studies have shown the advantages of stable water isotopes over inert tracers either naturally or artificially introduced.…”

Section: Pore Water Stable Isotope Profilesmentioning

confidence: 99%

Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

Sprenger

Volkmann

Blume

et al. 2015

Hydrol. Earth Syst. Sci.

123

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Abstract. Determining the soil hydraulic properties is a prerequisite to physically model transient water flow and solute transport in the vadose zone. Estimating these properties by inverse modelling techniques has become more common within the last 2 decades. While these inverse approaches usually fit simulations to hydrometric data, we expanded the methodology by using independent information about the stable isotope composition of the soil pore water depth profile as a single or additional optimization target. To demonstrate the potential and limits of this approach, we compared the results of three inverse modelling strategies where the fitting targets were (a) pore water isotope concentrations, (b) a combination of pore water isotope concentrations and soil moisture time series, and (c) a two-step approach using first soil moisture data to determine water flow parameters and then the pore water stable isotope concentrations to estimate the solute transport parameters. The analyses were conducted at three study sites with different soil properties and vegetation. The transient unsaturated water flow was simulated by solving the Richards equation numerically with the finiteelement code of HYDRUS-1D. The transport of deuterium was simulated with the advection-dispersion equation, and a modified version of HYDRUS was used, allowing deuterium loss during evaporation. The Mualem-van Genuchten and the longitudinal dispersivity parameters were determined for two major soil horizons at each site. The results show that approach (a), using only the pore water isotope content, cannot substitute hydrometric information to derive parameter sets that reflect the observed soil moisture dynamics but gives comparable results when the parameter space is constrained by pedotransfer functions. Approaches (b) and (c), using both the isotope profiles and the soil moisture time series, resulted in good simulation results with regard to the Kling-Gupta efficiency and good parameter identifiability. However, approach (b) has the advantage that it considers the isotope data not only for the solute transport parameters but also for water flow and root water uptake, and thus increases parameter realism. Approaches (b) and (c) both outcompeted simulations run with parameters derived from pedotransfer functions, which did not result in an acceptable representation of the soil moisture dynamics and pore water stable isotope composition. Overall, parameters based on this new approach that includes isotope data lead to similar model performances regarding the water balance and soil moisture dynamics and better parameter identifiability than the conventional inverse model approaches limited to hydrometric fitting targets. If only data from isotope profiles in combination with textural information is available, the results are still satisfactory. This method has the additional advantage that it will not only allow us to estimate water balance and response times but also site-specific time variant transit times or solute breakthrough within t...

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Tracers Determine Movement of Soil Moisture and Evapotranspiration

Abstract: The downward movement of water in soil is a layered one. Marking a certain layer with hydrogen-isotope tracer, and watching its displacement, makes possible a water balance and gives information on evaporation and groundwater recharge.

Cited by 136 publications

References 1 publication

A porewater-based stable isotope approach for the investigation of subsurface hydrological processes

A porewater-based stable isotope approach for the investigation of subsurface hydrological processes

The use of stable isotopes to study ecosystem gas exchange

Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

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