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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


NSF Discovery: On World Water Day, scientists study spawning salmon through a riverbed lens

22 Mar 2018 (National, Sierra) - NSF Southern Sierra CZO researchers peer into North America’s West Coast salmon rivers


Discussion paper open till April 5th in Biogeosciences

06 Mar 2018 (National, Boulder, Calhoun, Luquillo, Reynolds, Shale Hills, Sierra) - A discussion is open for the manuscript, "Elevating the biogeosciences within environmental research networks".


LTER 2018 Synthesis Webinar Series

04 Jan 2018 (National) - The LTER Network Communications Office is pleased to announce a new webinar series hosted by the NCO and the National Center for Ecological Analysis...


Water Resources Research: Call for Papers on Dynamics in Intensively Managed Landscapes

02 Jan 2018 (National, IML) - Call for papers for “Dynamics in Intensively Managed Landscapes: Water, Sediment, Nutrient, Carbon, and Ecohydrology”


White paper of 2017 CZ Science Meeting in Arlington, VA

01 Jan 2018 (National, Boulder, Calhoun, Catalina-Jemez, Christina, Eel, IML, Luquillo, Reynolds, Shale Hills, Sierra) - New Opportunities for Critical Zone Science Following the June 2017 Arlington Meeting for Critical Zone Science (hosted by CZO), a white booklet...

Researcher Spotlight: Caitlin Collins

13 Mar 2018 (Sierra) - Meet the minds behind the data! Caitlin specializes in modeling water fluxes from drop to catchment scale, tracking water through the Critical Zone.

Recent paper by Rempe and Dietrich on rock moisture featured by NSF and others

02 Mar 2018 (National, Eel) - A recent paper on rock moisture by Danielle Rempe and Bill Dietrich of the Eel River CZO is been featured on NSF News site, SF Chronicle, others

Noah Molotch on KGNU

08 Feb 2018 (Boulder) - The CZO's own Dr. Noah Molotch, director of CWEST, appeared on KGNU during a piece on snow depth and Snow Telemetry (SNOTEL). KGNU is an...

Teachers Data Jam Workshop

22 Jan 2018 (Luquillo) - On Saturday, January 13, we successfully held our third Teacher Data Jam Workshop of the Luquillo LTER Schoolyard Program. On this occasion,...

Researcher Spotlight: Kimber Moreland

18 Jan 2018 (Sierra) - Meet the people behind the research!

More News >

Example Publications


Humidity determines snowpack ablation under a warming climate. Harpold A.A. and Brooks P.D. (2018): PNAS 115(6): 1215-1220 (Boulder, Catalina-Jemez) Cross-CZO


Beyond clay: towards an improved set of variables for predicting soil organic matter content. Rasmussen C., Heckman K., Wieder W.R., Keiluweit M., Lawrence C.R., Berhe A.A., Blankinship J.C., Crow S.E., Druhan J.L., Hicks Pries C.E., Marin-Spiotta E., Plante A.F., Schädel C., Schimel J.P., Sierra C.A., Thompson A., Wagai R. (2018): Biogeochemistry (online) (Calhoun, Catalina-Jemez, Christina, Eel, Luquillo, Sierra) Cross-CZO


Concentration-Discharge Relations in the Critical Zone: Implications for Resolving Critical Zone Structure, Function and Evolution. Chorover, J., Derry, L. A., McDowell, W. H. (2017): Water Resources Research 53(11): 8654–8659 (National, Catalina-Jemez, Luquillo, Shale Hills) Cross-CZO National


Growing new generations of critical zone scientists. Wymore Adam S., Nicole R. West, Kate Maher, Pamela L. Sullivan, Adrian Harpold, Diana Karwan, Jill A. Marshall, Julia Perdrial, Daniella M. Rempe and Lin Ma (2017): Earth Surface Processes and Landforms 42 (14): 2498-2502 (National, Boulder, Calhoun, Catalina-Jemez, Eel, IML, Luquillo, Reynolds, Shale Hills, Sierra) Cross-CZO National


Hydrogeomorphological differentiation between floodplains and terraces. Qina Yan, Toshiki Iwasaki, Andrew Stumpf, Patrick Belmont, Gary Parker, Praveen Kumar (2017): Earth Surface Processes and Landforms (IML)


Regional sensitivities of seasonal snowpack to elevation, aspect, and vegetation cover in western North America. Christopher J. Tennant, Adrian A. Harpold, Kathleen Ann Lohse, Sarah E. Godsey, Benjamin T. Crosby, Laurel G. Larsen, Paul D. Brooks, Robert W. Van Kirk, Nancy F. Glenn (2017): Water Resources Research 53 (National, Boulder, Catalina-Jemez, Reynolds, Sierra) Cross-CZO National


Impacts of hydraulic redistribution on grass–tree competition vs facilitation in a semi-arid savanna. Barron-Gafford G.A., Sanchez-Cañete E.P., Minor R.L., Hendryx S.M., Lee E., Sutter L.F., Tran N., Parra E., Colella T., Murphy P.C., Hamerlynck E.P., Kumar P. and Scott R.L. (2017): New Phytologist 215(4): 1451–1461 (Catalina-Jemez, IML) Cross-CZO


Impacts of Quaternary History on Critical Zone Structure and Processes: Examples and a Conceptual Model from the Intensively Managed Landscapes Critical Zone Observatory. Anders, A.M., Bettis, E.A., Grimley, D.A., Stumpf, A.J., and Kumar, P. (2018): Frontiers in Earth Science (IML)


Research frontiers for improving our understanding of drought‐induced tree and forest mortality. Hartmann, H., Moura, C.F., Anderegg, W.R., Ruehr, N.K., Salmon, Y., Allen, C.D., Arndt, S.K., Breshears, D.D., Davi, H., Galbraith, D., Ruthrof, K.X., Wunder, J., Adams, H.D., Bloemen, J., Cailleret, M., Cobb, R., Gessler, A., Grams, T.E., Jansen, S., Kautz, M., Lloret, F. and O'Brien, M. (2018): New Phytologist 218(1): 15-28 (Catalina-Jemez)

Particle fluxes in groundwater change subsurface shale rock chemistry over geologic time. Kim, H., Gu, X., and Brantley, S.L. (2018): Earth and Planetary Science Letters (submitted) (Shale Hills)

Elevating the biogeosciences within environmental research networks. Richter, D. D., Billings, S. A., Groffman, P. M., Kelly, E. F., Lohse, K. A., McDowell, W. H., Riebe, C., Silver, W. L., White, T. S., Anderson, S., Brantley, S., Brecheisen, Z. S., Chadwick, O. A., Hartnett, H. E., Hobbie, S. E., Kazanski, C. E., Markewitz, D., O'Neill, K., Schroeder, P., and Thompson, A. (2018): Biogeosciences Discussions, in review (National, Calhoun) Cross-CZO National

Faster redox fluctuations can lead to higher iron reduction rates in humid forest soils. Barcellos, Diego, K. Taylor Cyle, Aaron Thompson (2018): Biogeochemistry 137 (3): 367-378 (Luquillo)

Direct observations of rock moisture, a hidden component of the hydrologic cycle. Rempe, D. and Dietrich, W.E. (2018): Proceedings of the National Academy of Sciences (Eel)


Climate, topography, and dust influences on the mineral and geochemical evolution of granitic soils in southern Arizona. Lybrand R.A. and Rasmussen C. (2018): Geoderma 314: 245-261 (Catalina-Jemez)

More Publications >