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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
19 Jun 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Earth Surface Dynamics (ESurf) and is expected to appear here in due course.
Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth
Susan L. Brantley1, William H. McDowell2, William E. Dietrich3, Timothy S. White1, Praveen Kumar4, Suzanne Anderson5, Jon Chorover6, Kathleen A. Lohse7, Roger C. Bales8, Daniel Richter9, Gordon Grant10, and Jérôme Gaillardet11 1Earth and Environmental Systems Institute, Department of Geosciences, Pennsylvania State University, University Park, PA, 16802, USA
2Department of Natural Resources and the Environment, University of New Hampshire, Durham, NH, 03823, USA
3Department of Earth and Planetary Science, UC Berkeley, CA, 94720, USA
4Department of Civil and Environmental Engineering, University of Illinois, Urbana, IL, 61801, USA
5Department of Geography, Institute of Arctic and Alpine Research (INSTAAR), University of Coloardo, Boulder, CO, 80309-0450, USA
6Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ, 85750, USA
7Department of Biological Sciences, Idaho State University, Pocatello, ID, 83209, USA
8Sierra Nevada Research Institute, University of California, Merced, CA, 94530, USA
9Nicholas School of the Environment, Duke University, Durham, NC, 27708, USA
10Pacific Northwest Research Station, USDA Forest Service, Corvallis, OR, 97331, USA
11Institut de Physique du Globe de Paris, Sorbonne Paris Cité, CNRS, Paris, France
Abstract. The critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetation canopy through the soil and down to fresh bedrock and the bottom of groundwater. All humans live in and depend on the critical zone. This zone has three co-evolving surfaces: the top of the vegetation canopy, the ground surface, and a deep subsurface below which Earth’s materials are unweathered. The US National Science Foundation supported network of nine critical zone observatories has made advances in three broad critical zone research areas. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response in turn impacts above-ground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences above-ground ecosystems. Third, several mechanistic models providing quantitative predictions of the spatial structure of the subsurface of the CZ have been proposed.

Many countries now fund networks of critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gas, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each U.S. observatory has succeeded in synthesizing observations across disciplines; providing long-term measurements to compare across sites; testing and developing models; collecting and measuring baseline data for comparison to catastrophic events; stimulating new process-based hypotheses; catalyzing development of new techniques and instrumentation; informing the public about the CZ; mentoring students and teaching about emerging multi-disciplinary CZ science; and discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO experiment in the US and identify how such a network could evolve in the future. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a hubs-and-campaigns model that promotes study of the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.

Citation: Brantley, S. L., McDowell, W. H., Dietrich, W. E., White, T. S., Kumar, P., Anderson, S., Chorover, J., Lohse, K. A., Bales, R. C., Richter, D., Grant, G., and Gaillardet, J.: Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth, Earth Surf. Dynam. Discuss.,, in review, 2017.
Susan L. Brantley et al.
Susan L. Brantley et al.


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Publications Copernicus
Short summary
The layer known as the critical zone extends from tree top to groundwater. This zone varies globally as a function of land use, climate, and geology. Energy and materials input from the land surface downward impact the subsurface landscape of water, gas, weathered material, and biota – at the same time that differences at depth also impact the surficial landscape. Scientists are designing observatories to understand the critical zone and how it will evolve into the future.
The layer known as the critical zone extends from tree top to groundwater. This zone varies...