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Keywords:

  • hillslopes;
  • Critical Zone;
  • Biosphere 2

The structure of Earth's critical zone, which is the interface between the solid Earth and its fluid envelopes and involves the coevolution of biota, soils, and landforms, is governed by processes important to hydrology, geology, biology, and atmospheric science [National Research Council, 2001] (Figure 1). Earth surface scientists have long recognized that temperature, chemical, and gravitational gradients drive energy and water fluxes, thus controlling systems evolution, but understanding the critical zone has been tackled primarily from disciplinary perspectives [Brantley et al., 2006]. Interdisciplinary research is needed, and many such efforts, such as the U.S. National Science Foundation's recent watershed-scale Critical Zone Observatories and the National Ecological Observatory Network, are in formative stages. By and large, these facilities focus on utilizing land surface complexity to elucidate process knowledge. Unfortunately, incorporating such complexity occurs at the expense of the control that characterizes true experimentation.