Key Findings

The Critical Zone, Earth’s living skin, has three dynamic and spatially structured co-evolving surfaces: the top of the vegetation canopy, the ground surface, and a third, deep surface below which Earth’s materials are unweathered.

Key findings emerging from the US National CZO program about the Critical Zone include:

  1. Deep Surface Variability - For the first time, we have obtained observations that reveal how the deep surface of the Critical Zone varies across landscapes.
  2. Deep Surface Predictability - New mechanistic models now provide quantitative predictions of the spatial structure of the deep surface relative to the ground surface topography.
  3. Earth Surface Energy Propagation - For the first time we have obtained observations that reveal that differences in energy inputs at Earth’s surface translate into differences in water, minerals, and biotic activity at depth, and we are starting to detect how these deep properties also impact the biota and climate.

Critical Zone surfaces and components.  Illustration modified from Chorover, J., R. Kretzschmar, F. Garcia-Pichel, and D. L. Sparks.  2007.  Soil biogeochemical processes in the critical zone.  Elements 3, 321-326. (artwork by R. Kindlimann)

Move laterally:

1) DEEP SURFACE VARIABILITY

Fo r the first time, we have obtained observations that reveal how the deep surface of the Critical Zone varies across landscapes.

Befus, K.M., Sheehan, A.F., Leopold, M., Anderson, S.P., and Anderson, R.S. (2011):  Seismic constraints on critical zone architecture, Boulder Creek Watershed, Colorado.  Vadose Zone Journal 10: 915-927, doi:10.2136/vzj2010.0108.

Buss, H. L., S. L. Brantley, F. N. Scatena, E. A. Bazilievskaya, A. Blum, M. Schulz, R. Jimenez, A. F. White, G. Rother, and D. Cole. 2013. Probing the deep critical zone beneath the Luquillo Experimental Forest, Puerto Rico. Earth Surface Processes and Landforms 38:1170-1186. DOI: 10.1002/esp.3409

Leopold, M., Völkel, J., Huber, J., and Dethier, D. (2013):  Subsurface architecture of the Boulder Creek Critical Zone Observatory from electrical resistivity tomography.  Earth Surface Processes and Landforms, doi:10.1002/esp.3420.

Holbrook, W.S., Riebe, C.S., Elwaseif, M., L. Hayes, J., Basler-Reeder, K., L. Harry, D., Malazian, A., Dosseto, A., C. Hartsough, P., and W. Hopmans, J., 2014, Geophysical constraints on deep weathering and water storage potential in the Southern Sierra Critical Zone Observatory: Earth Surface Processes and Landforms, v. 39, no. 3, p. 366–380, doi: 10.1002/esp.3502.

Olyphant, J., Pelletier, J., and Johnson, R.L. (2016): Topographic correlations with soil and regolith thickness from shallow-seismic refraction constraints across upland hillslopes in the Valles Caldera, New Mexico. Earth Surface Processes and Landforms, doi:10.1002/esp.3941.

Orlando, Joe, Xavier Comas, Scott A. Hynek, Heather L. Buss, and Sue L. Brantley (2016): Architecture of the deep critical zone in the Río Icacos watershed (Luquillo Critical Zone Observatory, Puerto Rico) inferred from drilling and ground penetrating radar (GPR). Earth Surface Processes and Landforms, doi: 10.1002/esp.3948

 


2) DEEP SURFACE PREDICTABILITY

New mechanistic models now provide quantitative predictions of the spatial structure of the deep surface relative to the ground surface topography.

Pelletier, J. D., McGuire, L.A., Ash, J.L., Engelder, T.M., Hill, L.E., Leroy, K.W., Orem, C.A., Rosenthal, W.S., Trees, M.A., Rasmussen, C., and Chorover, J. (2011), Calibration and testing of upland hillslope evolution models in a dated landscape: Banco Bonito, New Mexico, J. Geophys. Res., 116, F04004, doi:10.1029/2011JF001976.

Anderson, R.S., Anderson, S.P., and Tucker, G.E. (2013):  Rock damage and regolith transport by frost:  An example of climate modulation of critical zone geomorphology.  Earth Surface Processes and Landforms, 38: 299-316, doi:10.1002/esp3330.  

Rempe, D. and Dietrich, W.E. (2014):  A bottom-up control on fresh-bedrock topography under landscapes.  PNAS 111(18): 6576-6581, doi: 10.1073/pnas.1404763111.

St. Clair, J., Moon, S., Holbrook, W.S., Perron, J.T., Riebe, C.S., Martel, S.J., Carr, B., Harman, C., Singha, K., and Richter, D. deB. (2015):  Geophysical imaging reveals topographic stress control of bedrock weathering. Science 350: 534-538, doi: 10.1126/science.aad2210.

Anderson, R.S. (2015): Pinched topography initiates the critical zone.  Science 350: 506-507, doi: 10.1126/science.aad2266.

 


3) EARTH SURFACE ENERGY PROPAGATION

For the first time we have obtained observations that reveal that differences in energy inputs at Earth’s surface translate into differences in water, minerals, and biotic activity at depth, and we are starting to detect how these deep properties also impact the biota and climate.

Eilers, K, Debenport, S, Anderson, SP, and Fierer, N (2012):  Digging deeper to find unique microbial communities: the strong effect of depth on the structure of bacterial and archaeal communities.  Soil Biology & Biochemistry 50: 58-65, doi:10.1016/j.soilbio.2012.03.011.

Goulden M.L., Anderson R.G., Bales R.C., Kelly A.E., Meadows M., and Winston G.C. (2012) Evapotranspiration along an elevation gradient in California's Sierra Nevada. Journal of Geophysical Research 117 : G03028–709. doi: 10.1029/2012JG002027

Pelletier, J. D., G. A. Barron-Gafford, D. D. Breshears, P. D. Brooks, J. Chorover, M. Durcik, C. J. Harman, T. E. Huxman, K. A. Lohse, R. Lybrand, T. Meixner, J. C. McIntosh, S. A. Papuga, C. Rasmussen, M. Schaap, T. L. Swetnam, and P. A. Troch (2013), Coevolution of nonlinear trends in vegetation, soils, and topography with elevation and slope aspect: A case study in the sky islands of southern Arizona, J. Geophys. Res. Earth Surf., 118, 741–758, doi:10.1002/jgrf.20046.

Gabor, RS, Eilers, KG, McKnight, DM, Fierer, N, and Anderson, SP (2014):  From the litter layer to the saprolite:  Chemical changes in water-soluble soil organic matter and their correlation to microbial community composition, Soil Biology and Biochemistry 68: 166-176, doi:10.1016/j.soilbio.2013.09.029.

Goulden M.L. and Bales R.C. (2014) Mountain runoff vulnerability to increased evapotranspiration with vegetation expansion. Proceedings of the National Academy of Sciences 111 : 14071–14075. doi: 10.1073/pnas.1319316111

Hinckley, E.-L., Ebel, B.A., Barnes, R.T., Anderson, R.S., Williams, M.W., and Anderson, S.P. (2014):  Aspect control of water movement on hillslopes near the rain-snow transition of the Colorado Front Range, U.S.A.  Hydrological Processes 28: 74-85, doi: 10.1002/hyp.9549.

Hinckley, E.-L., Barnes, R.T., Anderson, S.P., Williams, M.W., and Bernasconi, S. (2014):  Ecosystem N retention and transport differ by hillslope aspect at the rain-snow transition of the Colorado Front Range, Journal of Geophysical Research Biogeosciences 119(7): 1281-1296, doi:10.1002/2013JG002588.

Stone, M. M., J. L. DeForest, and A. F. Plante. 2014. Changes in extracellular enzyme activity and microbial community structure with soil depth at the Luquillo Critical Zone Observatory. Soil Biology & Biochemistry 75:237-247. doi: 10.1016/j.soilbio.2014.04.017

Brooks, P. D., J. Chorover, Y. Fan, S. E. Godsey, R. M. Maxwell, J. P. McNamara, and C. Tague.  2015.  Hydrological partitioning in the critical zone:  Recent advances and opportunities for developing transferable understanding of water cycle dynamics.  Water Resour. Res. 51, 6973-6987.  doi: 10.1002/2015WR017039

Langston, A, Tucker, GE, Anderson, RS, and Anderson, SP (2015) Evidence for climatic and hillslope-aspect controls on vadose zone hydrology and implications for saprolite weathering, Earth Surface Processes and Landforms 40:1254-1269, doi:10.1002/esp.3718. 

Riebe, C. S., Sklar, L. S., Lukens, C. E., and Shuster, D. L. 2015. Climate and topography control the size and flux of sediment produced on steep mountain slopes. Proceedings of the National Academy of Science 112(51): 15574-15579. doi: 10.1073/pnas.1503567112

Stone, M. M., J. J. Kan, and A. F. Plante. 2015. Parent material and vegetation influence bacterial community structure and nitrogen functional genes along deep tropical soil profiles at the Luquillo Critical Zone Observatory. Soil Biology & Biochemistry 80:273-282. doi:10.1016/j.soilbio.2014.10.019.

Zapata-Rios, X., J. McIntosh, L. Rademacher, P. A. Troch, P. D. Brooks, C. Rasmussen, and J. Chorover.  2015.  Climatic and landscape controls on water transit times and silicate mineral weathering in the critical zone.  Water Resour. Res. 51, 6036-6051.  DOI: 10.1002/2015WR017018

Fellows, A.W,  and Goulden M.L. (2016): Mapping and understanding dry-season soil-water drawdown by California montane vegetation. Ecohydrology, doi: 10.1002/eco1772.

Zapata-Rios, X., Brooks, P. D., Troch, P. A., McIntosh, J., and Rasmussen, C.: Influence of climate variability on water partitioning and effective energy and mass transfer in a semi-arid critical zone, Hydrol. Earth Syst. Sci., 20, 1103-1115, doi:10.5194/hess-20-1103-2016.