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@ARTICLE{Graf:20897,
      author       = {Graf, A. and Herbst, M. and Weihermüller, L. and Huisman,
                      J.A. and Prolingheuer, N. and Bornemann, L. and Vereecken,
                      H.},
      title        = {{A}nalyzing spatiotemporal variability of heterotrophic
                      soil respiration at the field scale using orthogonal
                      functions},
      journal      = {Geoderma},
      volume       = {181-182},
      issn         = {0016-7061},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {PreJuSER-20897},
      pages        = {91 - 101},
      year         = {2012},
      note         = {A. Graf gratefully acknowledges financial support by the
                      DFG (Deutsche Forschungsgemeinschaft) project "Links between
                      local scale and catchment scale measurements and modelling
                      of gas exchange processes over land surfaces" (GR2687/3-1).
                      Instrument funding was provided by the Helmholtz project
                      FLOWatch. M. Herbst, L Bornemann, W. Amelung and H.
                      Vereecken would like to thank the DFG for funding in the
                      framework of the Transregional Collaborative Research Centre
                      SFB/TR32. We would like to thank Rainer Harms, Christina
                      Ganz, and Martin Hank for additional help with the manual
                      chamber measurements; Axel Knaps for providing climate
                      information, the ZCH personnel for a part of the chemical
                      analysis and Budiman Minasny (University of Sydney) for
                      providing helpful code for semivariogram analysis. We would
                      also like to thank two anonymous reviewers for suggestions
                      that improved the clarity of the manuscript.},
      abstract     = {Soil CO2 efflux was measured with a closed chamber system
                      along a 180 m transect on a bare soil field characterized by
                      a gentle slope and a gradient in soil properties at 28 days
                      within a year. Principal component analysis (PCA) was used
                      to extract the most important patterns (empirical orthogonal
                      functions, EOFs) of the underlying spatiotemporal
                      variability in CO2 efflux. These patterns were analyzed with
                      respect to their geostatistical properties, their relation
                      to soil parameters obtained from laboratory analysis, and
                      the relation of their loading time series to temporal
                      variability of soil temperature and moisture. A particular
                      focus was set on the analysis of the overfitting behaviour
                      of two statistical models describing the spatiotemporal
                      efflux variability: i) a multiple regression model using the
                      k first EOFs of soil properties to predict the n first EOFs
                      of efflux, which were then used to obtain a prediction of
                      efflux on all days and points: and ii) a modified multiple
                      regression model based on re-sorting of the EOFs based on
                      their expected predictive power. It was demonstrated that
                      PCA helped to separate meaningful spatial correlation
                      patterns and unexplained variability in datasets of soil CO2
                      efflux measurements. The two PCA analyses suggested that
                      only about half of the total variance of efflux could be
                      related to field-scale spatial variability of soil
                      properties, while the other half was "noise" attributed to
                      temporal fluctuations on the minute time scale and
                      short-range spatial heterogeneity on the decimetre scale.
                      The most important spatial pattern in CO2 efflux was clearly
                      related to soil moisture and the driving soil physical
                      properties. Temperature, on the other hand, was the most
                      important factor controlling the temporal variability of the
                      spatial average of soil respiration. (C) 2012 Elsevier B.V.
                      All rights reserved.},
      keywords     = {J (WoSType)},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {Terrestrische Umwelt},
      pid          = {G:(DE-Juel1)FUEK407},
      shelfmark    = {Soil Science},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000303958500010},
      doi          = {10.1016/j.geoderma.2012.02.016},
      url          = {https://juser.fz-juelich.de/record/20897},
}