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@ARTICLE{Gangi:255816,
      author       = {Gangi, Laura and Rothfuss, Youri and Ogée, Jerôme and
                      Wingate, Lisa and Vereecken, Harry and Brüggemann, Nicolas},
      title        = {{A} {N}ew {M}ethod for {I}n {S}itu {M}easurements of
                      {O}xygen {I}sotopologues of {S}oil {W}ater and {C}arbon
                      {D}ioxide with {H}igh {T}ime {R}esolution},
      journal      = {Vadose zone journal},
      volume       = {14},
      number       = {8},
      issn         = {1539-1663},
      address      = {Madison, Wis.},
      publisher    = {SSSA},
      reportid     = {FZJ-2015-05927},
      pages        = {0 - 0},
      year         = {2015},
      abstract     = {The newly developed method allows for the first time
                      simultaneous and continuous measurements of the oxygen
                      isotope composition of H2O and CO2 along soil profiles. Its
                      application in the field will contribute to reducing the
                      uncertainties associated with soil–atmosphere CO2 oxygen
                      isotope fluxes.The oxygen isotope composition of atmospheric
                      CO2 (δ18Oac) can be used to disentangle ecosystem component
                      CO2 fluxes, such as soil respiration and plant assimilation,
                      because the δ18O composition of different water pools is
                      transferred to CO2 during isotopic equilibration. The oxygen
                      isotope exchange between CO2 and water in soils has been
                      widely studied with theoretical models, but experimental
                      data are scarce, albeit indispensable to characterization of
                      the role of soils in determining δ18Oac. Here, we present a
                      new methodology to monitor the δ18O of soil CO2 (δ18Osc)
                      and of soil water (δ18Osw) in situ at varying soil water
                      content. Infrared laser spectroscopy was combined with
                      gas-permeable polypropylene (PP) tubing installed at
                      different depths in a sand column. The permeable tubing did
                      not lead to any isotopic fractionation and was suitable for
                      combined δ18Osc and δ18Osw measurements. Soil water became
                      gradually 18O enriched from the top of the sand over several
                      days. Measured and δ18Osc simulated with the model MuSICA
                      indicated incomplete CO2–H2O isotopic equilibrium.
                      Irrigation of the sand column with tapwater resulted in a
                      temporary reset of δ18Osw along the soil column, while
                      δ18Osc was only influenced when the enzyme carbonic
                      anhydrase was added to the irrigation water. Our study
                      demonstrates that δ18Osc and δ18Osw can now be monitored
                      in situ and online with high time resolution with minimum
                      disturbance. With this new tool at hand, research into the
                      oxygen isotope exchange between soil water and CO2 in
                      natural soils has the potential to advance to a new stage
                      and help to constrain the atmospheric CO2 budget.},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255)},
      pid          = {G:(DE-HGF)POF3-255},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000362065400004},
      doi          = {10.2136/vzj2014.11.0169},
      url          = {https://juser.fz-juelich.de/record/255816},
}