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@ARTICLE{Wu:859999,
      author       = {Wu, Bei and Amelung, Wulf and Xing, Ying and Bol, Roland
                      and Berns, Anne E.},
      title        = {{I}ron cycling and isotope fractionation in terrestrial
                      ecosystems},
      journal      = {Earth science reviews},
      volume       = {190},
      issn         = {0012-8252},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier},
      reportid     = {FZJ-2019-00800},
      pages        = {323 - 352},
      year         = {2019},
      abstract     = {The cycling of iron (Fe) is often closely linked with that
                      of carbon, nitrogen, phosphorus and manganese. Therefore,
                      alterations in the Fe cycle may be indicative of concurrent
                      overall changes in the biogeochemistry of terrestrial and
                      aquatic ecosystems. Biogeochemical processes taking part in
                      the Fe cycle frequently fractionate stable Fe isotopes,
                      leaving soil, plant and other compartments of the ecosystems
                      with varied Fe isotopic signatures. In this work, we
                      reviewed the Fe isotope fractionation processes that have
                      been reported so far for terrestrial ecosystems. While
                      parent materials vary in Fe isotope compositions, pedogenic
                      processes can further fractionate Fe isotope signatures,
                      resulting in soil profiles with δ56Fe values (relative to
                      isotope standard IRMM-014) from -0.52 to +0.72‰. Different
                      soil Fe pools, as a result of cycling processes, show an
                      even broader range of δ56Fe values, with secondary Fe
                      oxides being isotopically the lightest, and with Fe
                      sequestered in silicate minerals being the heaviest, due to
                      preferential release of light Fe isotopes during dissolution
                      of minerals. Actually and potentially plant-available Fe in
                      soil can be extracted by 0.5 M HCl, which includes pools of
                      water-extractable and exchangeable Fe, organically bound or
                      adsorbed Fe, and poorly crystalline Fe oxides, altogether
                      showing a depletion of heavy Fe isotopes with δ56Fe values
                      down to -1.08‰. Depending on the Fe speciation and
                      concentration present in the growth medium, plants can adapt
                      their uptake strategy for Fe. Plants of the strategy I type
                      especially take up light iron isotopes, while strategy II
                      plants fractionate less towards light isotopes. Aboveground
                      tissues usually show lighter Fe isotope signatures than the
                      roots, with flowers (δ56Fe: -2.15 to -0.23‰) being
                      isotopically the lightest. In freshwater systems, the most
                      distinct Fe isotope fractionation is usually found at the
                      oxic-anoxic interface, where redox conditions change and
                      thus Fe speciation controls the degree of Fe isotope
                      fractionation. Similar to soils, the δ56Fe values of
                      unfiltered water mainly reflect averaged Fe isotope
                      compositions across fractions with different particle sizes.
                      In filtered freshwater (<0.45 μm), isolated colloid-sized
                      fractions can exhibit either positive or negative δ56Fe
                      values, depending on the chosen size fraction and the origin
                      of the (nano)particles, with δ56Fe values up to +2.79‰
                      for fractions smaller than 0.003 μm from an arctic stream
                      or down to -1.73‰ for dissolved Fe (< 0.02 µm) from a
                      boreal forested catchment. Most freshwater studies showed
                      that rivers with elevated contents of dissolved organic
                      carbon (DOC) tend to be isotopically heavier than those with
                      lower DOC contents, while some studies also showed that
                      rivers with high DOC can display light Fe isotopic
                      signatures owing to the input of groundwater- and/or soil
                      water-derived Fe. Finally, anthropogenic impacts can
                      contribute to Fe isotope fractionation in freshwaters and
                      may widen the range of δ56Fe values in the environment,
                      with the lowest records found down to -5.29‰. Overall, our
                      compilation reveals that Fe pools in different terrestrial
                      system compartments vary in stable Fe isotope compositions,
                      although the current database is still small. In order to
                      use stable Fe isotopes as proxies to reconstruct the
                      biogeochemical processes, future works should not solely
                      rely on bulk δ56Fe assessments, but also involve the
                      assessment of different fractionation factors for all
                      biogeochemical pathways, which includes isotopic analyses
                      among various pools of the terrestrial Fe cycle.},
      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:000462803000014},
      doi          = {10.1016/j.earscirev.2018.12.012},
      url          = {https://juser.fz-juelich.de/record/859999},
}