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Goal 1
DEVELOP A UNIFYING THEORETICAL FRAMEWORK of critical zone evolution that integrates physical, chemical, and biological processes.


The CZOS are working toward a holistic conceptual model of critical zone evolution that couples hydrological, geochemical, geomorphic, and biological processes. Such a model must consider many spatial and temporal scales.

Conceptual Models >


Goal 2
DEVELOP COUPLED SYSTEMS MODELS to explore how critical zone services respond to anthropogenic, climatic, and tectonic forcings.


The CZOs are building systems models that quantitatively combine multiple processes, often spanning an entire watershed. These models typically track fluxes and storage of energy, water, carbon, sediments, and/or other materials.

Numerical Models >


Goal 3
DEVELOP INTEGRATED, EXTENSIVE DATASETS that document a wide range of critical zone settings, including geology and climate.


The CZOs are assembling the needed infrastructure for an integrated data/ measurement foundation. This foundation will inform our theoretical framework, constrain our models, and help test hypotheses across CZOs.

Data >


Fundamental Questions

Despite the Critical Zone's importance to terrestrial life and many environmental issues, it remains poorly understood. Key questions include:

  • How does the Critical Zone form?
  • How does it operate?
  • How does it evolve?

There are many followup questions as well. For example:

  • How will the Critical Zone respond to projected climate and land use changes?
Specific Questions

Each Critical Zone Observatory is helping work on these fundamental questions along with numerous others. Some questions are specific to the unique characteristics of their field site and the talents of their collaborative research team. Some examples:

  • What is the legacy of climate and geologic history in critical zone architecture?
     - Boulder
  • How does variability in energy input and related mass flux influence critical zone structure and function?
      - Jemez-Catalina
  • How does saprolite advance vary with regolith thickness and landscape position?
     - Luquillo
  • How does water sculpt a landscape on shale bedrock?
     - Shale Hills
  • How does landscape variability control how soil moisture, evapotranspiration and streamflow respond to snowmelt and rainfall?
     - Southern Sierra
Cross-CZO Questions

A key advantage of the coordinated system of Critical Zone Observatories is that it can address the biggest questions by leveraging differing environments and histories.  More specifically, cross-CZO science can begin to answer questions such as:

  • How do processes that nourish ecosystems change over human and geologic time scales?
  • How do biogeochemical processes govern long-term sustainability of water and soil resources?
  • What processes control fluxes of carbon, particulates, and reactive gases over different timescales?
  • How do variations in and perturbations to chemical and physical weathering processes impact the Critical Zone?

An expressed goal of the CZO program is to catalyze transformative Earth surface science in the coming decade by developing cross-site science that helps to establish: 1) a unifying theory of CZ evolution; 2) coupled systems models to explore how CZ services respond to anthropogenic, climatic, and tectonic forcing; and 3) data sets that document differing CZ geologic and climatic settings, inform the theoretical framework, constrain conceptual and coupled systems models, and test model-generated hypotheses.

Cross-CZO studies >


Our Approach

Answering fundamental questions requires much better knowledge of how physical, chemical, and biological processes in the Critical Zone are coupled and at what spatial and temporal scales. Many of these processes are highly non-linear and can range across vast scales - from atomic to global, and from seconds to eons.

Interdisciplinary & Multidisciplinary

To better understand how the complex processes of the Critical Zone are linked, the U.S. NSF National CZO Program employs a systems approach across a broad array of sciences. This interdisciplinary and multidisciplinary approach integrates many disciplines, especially in the geological and biological sciences. Examples include hydrology, ecology, biogeochemistry, and geomorphology.

Multiple Disciplines >


A Common Infrastructure

Our systems approach across disciplines is well supported via our infrastructure. Our nine observatories span a range of climatic, geologic, and physiographic environments, from California to Puerto Rico. Each CZO is working toward a common set of resources, which will enable comparison of whole-watershed energy and mass balances across a variety of settings.

Infrastructure >


  Community & Collaboration

Within each CZO, scientific collaborations are common, often bringing together researchers from different institutions and crossing disciplinary boundaries.  This team-based approach helps foster a strong community, which is further strengthed by graduate student involvement.  Similar collaborations occur between investigators and students at different CZOs as well as with members of other US science programs.  Moreover, the US CZO program also works with an international network of Critical Zone investigators and research sites.

Partner Organizations >


Predictive Ability

An immediate challenge is to develop a robust predictive ability for how the structure and function of the Critical Zone evolves, including how it will respond to projected climate and land-use changes. This predictive ability must be founded on:

  • Broad knowledge of the complex physical, chemical, and biological processes of the Critical Zone
  • The ability to describe interactions between the varied climatic and geologic factors that distinguish different regions.
  • Advances in theory, modeling, and measurement.

Over the next decade, the CZO program will produce a fundamental understanding and four-dimensional data sets that will stimulate, inspire, and test the resulting predictive models. 

Read: Future Directions for CZO Science >

Models >



See Multiple Disciplines

See Infrastructure

See Partner Organizations


Research News

FEATURED NATIONALLY

CZ colleagues: Please contact us about proposals for NSF’s CZ Collaborative Network, due 02 Dec 2019

08 Jul 2019 (National, Boulder, Calhoun, Catalina-Jemez, Christina, Eel, IML, Luquillo, Reynolds, Shale Hills, Sierra) - CZO will end Nov 2020, succeeded by the “CZ Collaborative Network”. Let’s explore how the CZ community can build upon the CZOs via new NSF proposals.

FEATURED NATIONALLY

CZOs at AGU 2019

19 Jun 2019 (National, Boulder, Calhoun, Catalina-Jemez, Eel, IML, Luquillo, Reynolds, Shale Hills, Sierra) - A list of CZ-related sessions, abstracts and events at the 2019 AGU Fall Meeting.

FEATURED NATIONALLY

EOS: Answer to California Landscape Riddle Lies Underground

31 May 2019 (Eel) - Scientists link vegetation mosaics in California to patterns of weathered bedrock.


Graduate Student Critical Zone Reading Group Wraps the Semester with a Field Trip to Calhoun CZO

12 Jun 2019 (Calhoun, Shale Hills) - Five students travelled to Union, South Carolina for a two-day site visit June 6 – June 8 at the Calhoun CZO. This site visit was the...

Mac Callaham’s group presents at the Society for Freshwater Science annual meeting

31 May 2019 (Calhoun) - Mac Callaham and his group shared their research on earthworms at the May 2019 Society for Freshwater Science annual meeting in Salt Lake City.

Two week field experience kick-off for the 2019 GeoPATHs cohort

18 May 2019 (Shale Hills) - Fifteen undergraduates from seven regional institutions arrived at University Park, along with graduate student mentors and faculty experts, to...

2019 SSHCZO All-Hands Meeting at Penn State

10 May 2019 (Shale Hills) - The 2019 All-Hands Meeting brought together our core team, our off-campus collaborators, and our outreach partners at Shaver's Creek in a new...

TeenShale evaluates Wallace Run near abandoned well using macroinvertebrate surveys

07 May 2019 (Shale Hills) - On a warm and sunny day in May, the 2018-2019 cohort took to the field!  Along with Centre County Pennsylvania Senior Environmental Corp member...

More News >


Example Publications

FEATURED NATIONALLY

Carbon Exports from Terrestrial Ecosystems: A Critical-Zone Framework. Keller, C.K. (2019): Ecosystems (National) National

FEATURED NATIONALLY

Reevaluating growing season length controls on net ecosystem production in evergreen conifer forests. Barnard, D.M., Knowles, J.F., Barnard, H.R., Goulden, M.L., Hu, J., Litvak, M.E., Molotch, N.P. (2018): Scientific Reports 8(1): 17973 (Boulder, Catalina-Jemez, Sierra) Cross-CZO

FEATURED NATIONALLY

Clays in the Critical Zone. Paul A. Schroeder (2018): Cambridge University Press (National, Calhoun) Cross-CZO National

FEATURED NATIONALLY

Ideas and perspectives: Strengthening the biogeosciences in environmental research networks. Richter, D.D., S.A. Billings, P.M. Groffman, E.F. Kelly, K.A. Lohse, W.H. McDowell, T.S. White, S. Anderson, D.D. Baldocchi, S. Banwart, S. Brantley, J.J. Braun, Z.S. Brecheisen, C.W. Cook, H.E. Hartnett, S.E. Hobbie, J. Gaillardet, E. Jobbagy, H.F. Jungkunst, C.E. Kazanski, J. Krishnaswamy, D. Markewitz, K. O’Neill, C.S. Riebe, P. Schroeder, C. Siebe, W.L. Silver, A. Thompson, A. Verhoef, G. Zhang (2018): Biogeosciences 15: 4815-4832 (National, Boulder, Calhoun, Luquillo, Reynolds, Shale Hills, Sierra) Cross-CZO National

FEATURED NATIONALLY

A net ecosystem carbon budget for snow dominated forested headwater catchments: linking water and carbon fluxes to critical zone carbon storage. Perdrial J., Brooks P.D., Swetnam T., Lohse K.A., Rasmussen C., Litvak M., Harpold A.A., Zapata-Rios X., Broxton P., Mitra B., Meixner M., Condon K., Huckle D., Stielstra C., Vázquez-Ortega A., Lybrand R., Holleran M., Orem C., Pelletier J., Chorover J. (2018): Biogeochemistry 138{3): 225–243 (Boulder, Catalina-Jemez, Luquillo, Reynolds, Shale Hills) Cross-CZO


Plant Accessible Water Storage Capacity and Tree-Scale Root Interactions Determine How Forest Density Reductions Alter Forest Water Use and Productivity. TAGUE, C.L., & M.A. MORITZ (2019): Frontiers in Forests and Global Change (Sierra)

California forest die-off linked to multi-year deep soil drying in 2012–2015 drought. GOULDEN, M.L. & R.C. BALES (2019): Nature Geoscience, 12 (Sierra)

The changing water cycle: The eco-hydrologic impacts of forest density reduction in Mediterranean (seasonally dry) regions. TAGUE, C.L., MORITZ, M., HANAN, E (2019): WIREs Water (Sierra)

Fight or Flight? Tradeoffs Between Drought Defense and Reproduction in Conifers. LAUDER, J.D. E. V. MORAN, S. J. HART (2019): Tree Physiology (Sierra)

Water residence time (age) and flow path exert synchronous effects on annual characteristics of dissolved organic carbon in terrestrial runoff. JEPSEN, S.M., T.C. HARMON, S. SADRO, B. REID, S. CHANDRA (2019): Science of the Total Environment (Sierra)

Ecological and genomic attributes of novel bacterial taxa that thrive in subsurface soil horizons (Pre-Print). BREWER, T.E., E.L. ARONSON, K. AROGYASWAMY, S.A. BILLINGS, J.K. BOTTHOFF, A.N. CAMPBELL, N.C. DOVE, D. FAIRBANKS, R.E. GALLERY, S.C. HART, J. KAYE, G. KING, G. LOGAN, K.A. LOHSE, M.R. MALTZ, E. MAYORGA, C. O’NEILL, S.M. OWENS, A. PACKMAN, J. PETT-RIDGE, A.F. PLANTE, D.D. RICHTER, W.L. SILVER, W.H. YANG, N. FIERER (2019): bioRxiv (National, Boulder, Calhoun, Catalina-Jemez, Christina, Eel, IML, Luquillo, Reynolds, Shale Hills, Sierra) Cross-CZO National

Toward Better Understanding of Terrestrial Processes through Long-Term Hydrological Observatories (Introduction to Special Section: Hydrological Observatories). BOGENA, H.R., T. WHITE, O. BOUR, K.H. JENSEN (2019): Vadose Zone Journal, 17, 1 (Sierra)

More Publications >