Abstract
Abstract. The Critical Zone (CZ) is a holistic framework for integrated studies of water with soil, rock, air, and biotic resources in the near-surface terrestrial environment. This most heterogeneous and complex region of the Earth ranges from the vegetation top to the aquifer bottom, with a highly variable thickness globally and a yet-to-be clearly defined lower boundary of active water cycle. Interfaces among different compartments in the CZ are critical, which provide fertile ground for interdisciplinary research. The reconciliation of coupled geological and biological cycles (vastly different in space and time scales) is essential to understanding the complexity and evolution of the CZ. Irreversible evolution, coupled cycling, interactive layers, and hierarchical heterogeneity are the characteristics of the CZ, suggesting that forcing, coupling, interfacing, and scaling are grand challenges for advancing CZ science. Hydropedology – the science of the behaviour and distribution of soil-water interactions in contact with mineral and biological materials in the CZ – is an important contributor to CZ study. The pedosphere is the foundation of the CZ, which represents a geomembrance across which water and solutes, as well as energy, gases, solids, and organisms are actively exchanged with the atmosphere, biosphere, hydrosphere, and lithosphere, thereby creating a life-sustaining environment. Hydropedology emphasizes in situ soils in the landscape setting, where distinct pedogenic features and soil-landscape relationships are essential to understanding interactive pedologic and hydrologic processes. Both CZ science and hydropedology embrace an evolutionary and holistic worldview, which offers stimulating opportunities through steps such as integrated systems approach, evolutionary mapping-monitoring-modeling framework, and fostering a global alliance. Our capability to predict the behaviour and evolution of the CZ in response to changing environment can be significantly improved if cross-site scientific comparisons, evolutionary treatment of organized complex systems, and deeper insights into the CZ can be made.
Highlights
Predict the behaviour and evolution of the Critical Zone” (CZ) in response to changing environment can be significantly improved if crosssite scientific comparisons, evolutionary treatment of organized complex systems, and deeper insights into the CZ can be made
Hydropedology has emerged in recent years as an intertwined branch of soil science and hydrology that addresses the interface between the pedosphere and the hydrosphere, with an emphasis on in situ soils in the landscape setting (Lin, 2003; Lin et al, 2006a)
This paper focuses on physical and hydrologic aspects of the CZ, using hydropedology as an example to illustrate the opportunity and the need for integrated, multiscale, and synergistic efforts
Summary
“Our own civilization is being tested in regard to its management of water as well as soil.” Daniel Hillel (1991). The US National Research Council (NRC, 2001) recommended the integrated study of the “Critical Zone” (CZ) as one of the most compelling research areas in Earth sciences in the 21st century This CZ is defined by the NRC (2001) as “a heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air and living organisms regulate the natural habitat and determine availability of life sustaining resources.”. This zone ranges from the top of the vegetation down to the bottom of the aquifer (Fig. 1).
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