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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

Water Resources Research Special Collection: Concentration-discharge relations in the critical zone

30 Oct 2017 (National, Boulder, Calhoun, Catalina-Jemez, Christina, Eel, IML, Luquillo, Reynolds, Shale Hills, Sierra) - Water Resources Research published a new special collection in September 2017 featuring concentration-discharge research from multiple CZOs.

FEATURED NATIONALLY

What Causes Ecological Shifts?

17 Oct 2017 (IML) - A new information partitioning methodology allows researchers to identify the factors that drive behavior in an ecohydrologic system.

FEATURED NATIONALLY

Stories in the Soil

17 Oct 2017 (IML) - A series of field experiments in the U.S. Midwest is investigating how past, present, & future human activities and climate affect the health of soil.

FEATURED NATIONALLY

White paper of 2017 CZ Science Meeting in Arlington, VA

17 Oct 2017 (National) - Contribute to public discussion of a draft report: “New Opportunities for Critical Zone Science” based on the June 2017 Arlington CZO meeting.

FEATURED NATIONALLY

NSF News Release: Changes in non-extreme precipitation may have not-so-subtle consequences

18 Sep 2017 (National, IML) - Analysis of more than five decades of data leads to new conclusions

FEATURED NATIONALLY

NSF News Release: What’s killing trees during droughts? Scientists have new answers.

14 Aug 2017 (National, Catalina-Jemez) - Researchers find that carbon starvation and hydraulic failure kill drought-stricken trees.


Ravaged El Yunque viewed as storm-recovery lab

17 Nov 2017 (Luquillo) - Over the millennia, the tropical woodland known today as El Yunque National Forest has been pummeled by rains and rocked by hurricanes. But the...

FEATURED

BcCZO had the honor of hosting a visit from the China Geological Survey

13 Nov 2017 (National, Boulder) - On November 6-10, the BcCZO had the honor of hosting a visit from the China Geological Survey (CGS; http://en.cgs.gov.cn/).

Two new CZO team members begin subsurface investigations at Cole Farm

10 Nov 2017 (Shale Hills) - Perri Silverhart, MS Student Geosciences, and Caitlin Hodges, PhD Student Soil Science, begin the field component of their research at Cole...

Visiting the Water Source: A Tour of the Kings River Headwaters

06 Nov 2017 (Sierra) - By Michelle Gilmore and Leigh Bernacchi   Ever wonder how we know what we know about water? Twenty-five intrepid water and forest managers,...

Delegation from China Geologic Survey visits Shale Hills CZO

03 Nov 2017 (Shale Hills) - During the week of October 30th, Penn State and SSHCZO hosted 15 scientists from the China Geological Survey, with interests ranging from saltwater...

More News >


Example Publications

FEATURED NATIONALLY

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 (online) (National, Catalina-Jemez, Luquillo, Shale Hills) Cross-CZO National

FEATURED NATIONALLY

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

FEATURED NATIONALLY

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)

FEATURED NATIONALLY

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

FEATURED NATIONALLY

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

FEATURED NATIONALLY

A multi-species synthesis of physiological mechanisms in drought-induced tree mortality. Adams H.D., Zeppel M.J.B., Anderegg W.R.L., Hartmann H., Landhausser S.M., Tissue D.T., Huxman T.E., Hudson P.J., Franz T.E., Allen C.D., Anderegg L.D.L., Barron-Gafford G.A., Beerling D.J., Breshears D.D., Brodribb T.J., Bugmann H., Cobb R.C., Collins A.D., Dickman L.T., Duan H., Ewers B.E., Galiano L., Galvez D.A., Garcia-Forner N., Gaylord M.L., Germino M.J., Gessler A., Hacke U.G., Hakamada R., Hector A., Jenkins M.W., Kane J.M., Kolb T.E., Law D.J., Lewis J.D., Limousin J-M., Love D.M., Macalady A.K., Marti­nez-Vilalta J., Mencuccini M., Mitchell P.J., Muss J.D., O'Brien M.J., O'Grady A.P., Pangle R.E., Pinkard E.A., Piper F.I., Plaut J.A., Pockman W.T., Quirk J., Reinhardt K., Ripullone F., Ryan M.G., Sala A., Sevanto S., Sperry J.S., Vargas R., Vennetier M., Way D.A., Xu C., Yepez E.A., and McDowell N.G. (2017): Nature Ecology & Evolution 1: 1285–1291 (Catalina-Jemez)


Global patterns of dust and bedrock nutrient supply to montane ecosystems. Arvin, L.J.; Riebe, C.S.; Aciego, S.M.; Blakowski, M.A. (2017): Science Advances, Vol. 3, no. 12, eeao1588 (Sierra)

Climate preconditions the Critical Zone: Elucidating the role of subsurface fractures in the evolution of asymmetric topography. West, N., Kirby, E., Nyblade, A., and Brantley, S.L. (2017): Proceedings of the National Academy of Sciences (Shale Hills)

ONLINE EXTRA: Bringing the Outdoors In: Application of Hydrogeology Education Tools. Williams JZ, Dykhoff S, Pollak J, and Brantley SL (2017): In The Trenches, 7(4):online (Shale Hills)

Critical zone structure controls concentration-discharge relationships and solute generation in forested tropical montane watersheds. Wymore, A.; Brereton, R. L.; Ibarra, D. E.; Maher, K.; McDowell, W. H. (2017): Water Resources Research 53, 6279–6295 (National, Luquillo) Cross-CZO National

Characterizing hyporheic exchange processes using high-frequency electrical conductivity-discharge relationships on subhourly to interannual timescales. Singley, J. G., Wlostowski, A. N., Bergstrom, A. J., Sokol, E. R., Torres, C. L., Jaros, C., Wilson, C. E., Hendrickson, P. J., Gooseff, M. N. (2017): Water Resources Research 53, 4124–4141 (National, Boulder) Cross-CZO National

Concentration-discharge relationships in headwater streams of the Sierra Nevada, California. Hunsaker, C. T., Johnson, D. W. (2017): Water Resources Research 53, 7869–7884 (Sierra)

Mixing as a driver of temporal variations in river hydrochemistry: 1 Insights from conservative tracers in the Andes-Amazon transition. Torres, M.A.; Baronas, J.J.; Clark, K.E.; Feakins, S.J.; West, A.J. (2017): Water Resources Research 53, 3102–3119 (Luquillo)

More Publications >