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@ARTICLE{Cai:906270,
      author       = {Cai, Di and Henehan, Michael J. and Uhlig, David and von
                      Blanckenburg, Friedhelm},
      title        = {{M}g isotope composition of runoff is buffered by the
                      regolith exchangeable pool},
      journal      = {Geochimica et cosmochimica acta},
      volume       = {321},
      issn         = {0016-7037},
      address      = {New York, NY [u.a.]},
      publisher    = {Elsevier},
      reportid     = {FZJ-2022-01336},
      pages        = {99 - 114},
      year         = {2022},
      abstract     = {In a small, forested catchment underlain by gneiss
                      (Conventwald, Black Forest, Germany), we found that the
                      magnesiumisotope composition (d26Mg) of creek water did not
                      show seasonal variability, despite variations in dissolved
                      Mg concentrations. To investigate the potential controlling
                      factors on water d26Mg values, we studied the Mg isotope
                      composition of solid samples (bedrock, bulk soil, clay-sized
                      fraction of soil, separated minerals, the exchangeable
                      fraction of regolith) and water samples comprising time
                      series of creek water, groundwater and subsurface flow.
                      Subsurface flow from 0–15 cm depth (?0.80 ± 0.08‰) and
                      15–150 cm depth (?0.66 ± 0.17‰), groundwater (?0.55 ±
                      0.03‰), and creek water (?0.54 ± 0.04‰) are all
                      depleted in heavy Mg isotopes compared to bedrock (?0.21 ±
                      0.05‰). Subsurface flow samples have similar d26Mg values
                      to the regolith exchangeable fraction at the respective
                      sampling depths. Also, groundwater and creek water show
                      d26Mg values that are identical to those of the exchangeable
                      fraction in the deep regolith. We suggest, therefore, that
                      cation-exchange processes in the regolith control Mg
                      concentrations and d26Mg values of creek water at our study
                      site. This assumption was further verified by batch
                      adsorption-desorption experiments using soil samples from
                      this study, which showed negligible Mg isotope fractionation
                      during adsorption-desorption. We propose that the
                      exchangeable fraction of the regolith buffers dissolved Mg
                      concentrations by adsorbing and storing Mg when soil
                      solutions are high in concentration in the dry season and
                      desorbing Mg when rainfall infiltrates and percolates
                      through the regolith in the wet season. This mechanism may
                      explain the near chemostatic behavior of Mg concentrations
                      and the invariance of d26Mg values in creek water. In
                      addition, the depth distribution of exchangeable Mg
                      concentration and isotope composition in the regolith
                      reflects mineral dissolution and secondary mineral formation
                      in deep regolith (>3 m) and biological cycling in shallower
                      depth (0–3 m). Magnesium stable isotopes thus provide an
                      accurate snapshot of the geogenic (weathering) and the
                      organic (bio-cycled) nutrient cycle.},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {2173 - Agro-biogeosystems: controls, feedbacks and impact
                      (POF4-217)},
      pid          = {G:(DE-HGF)POF4-2173},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000783485400006},
      doi          = {10.1016/j.gca.2022.01.011},
      url          = {https://juser.fz-juelich.de/record/906270},
}