Scaling Environmental Processes in Heterogeneous Arid Soils (SEPHAS)

Program Description

SEPHAS is a research program that focuses on the scaling of subsurface and landscape-interface environmental processes. The SEPHAS facility operates three large scale outdoor lysimeters and integrates computation and visual technology with experimental research to collaborate on research proposals, and maximize educational benefits through K-12 educational outreach. This facility allows for the development of student involvement, faculty and research training, and mentorship for post-doctorate fellows.

The SEPHAS program integrates cutting-edge experimental research with computational and visual technology, provides opportunities to collaborate on research projects, faculty and research training, encourages student involvement as well as maximizes educational benefits through K-12 educational outreach.

The SEPHAS program was established in 2005 with a NSF-EPSCoR Research Infrastructure Improvement award (EPS-0447416). The goal was to build research capacity and capability in Nevada to improve our understanding of environmental processes in arid soils. Soils are an important component of the fragile desert environment of the state and relevant to the challenges being posed by a burgeoning human population is this increasingly arid landscape. The SEPHAS program was able to build and expand on Nevada’s leadership in arid ecosystem and subsurface science research.

Core part of the SEPHAS program is its lysimeter facility in Boulder City, NV, consisting of three weighing lysimeters of 2.2 m diameter and 3.0 m depth filled with soil from the Mojave Desert. The lysimeters have been collecting data on precipitation, evaporation, soil moisture, temperature and other relevant environmental parameters since summer 2008. This information is important to better understand water conservation and management, ground and surface water supply, improve flood control measures, and predict possible impacts of climate change for desert environments. Due to their size, the lysimeters bridge a critical gap between benchtop and field-scale experiments, giving Nevada the extraordinary capacity to address basic scientific questions and address practical problems unique to Nevada and other arid regions world-wide.

Root Induced Changes of Soil Physical Properties Using Synchrotron X-Ray Microtomography (CMT) and Micromechanical Simulations
NSF Ecosystem Sciences and Hydrology Research Grant Awarded to Drs. Berli, Menon, Ghezzehei, Nico, Young and Tyler: July 2008

The rhizosphere, i.e. the zone of soil immediately surrounding plant roots, plays a prominent role in supplying plants with water and nutrients. However, surprisingly little is known about rhizosphere physical properties and how they affect root growth, water and nutrient uptake. The lack of non-invasive and non-destructive imaging techniques necessary to observe living roots growing in undisturbed soil have been a main reason for this shortcoming. Recent advances in synchrotron X-ray microtomography (CMT) provide the potential to directly observe soil physical properties around living roots in-situ. Goal of the proposed study is to quantify rhizosphere physical properties by (1) employing CMT to visualize physical root-soil structure interactions, (2) simulating root-induced structural alterations using various micro-mechanical approaches (analytical, finite element, discrete element modeling), and (3) estimating changes in rhizosphere hydraulic properties (water retention and hydraulic conductivity functions) based on CMT imaging and inverse modeling. The proposed study seeks to provide transformative insights into the role of rhizosphere physical properties for water and nutrient uptake by living plants. It serves as a stepping stone for better understanding the role of plants in the critical zone at the soil-atmosphere interface. The project cuts across disciplinary boundaries of biology, soil physics, and soil mechanics to offer new insights on surface runoff, soil compaction and erosion, losses to agricultural productivity, land reclamation, and first-principles of soil-plant interactions.

Research Areas

  • Hydrology – research related to scaling of transport behavior of chemicals and microorganisms; remediation of contaminants; and scaling phenomenon in heterogeneous porous material.
  • Biogeosciences – research related to biotic and abiotic controls on mineral formation; dissolution and transport in Mojave Desert ecosystems; influence of atmospheric CO2, nitrogen deposition, and soil moisture on root activity; stomatal conductance and C sequestration; and investigations of biocomplexity.
  • Mathematics – computational aspects of kinetic effects on very long desorption time frames, and the changes to forms of the transport equations (e.g. fractional derivationes).

Research Hypotheses and Questions

  • The nature of sandbox preconditioning that may be required to yield flow and transport results comparable to field conditions.
  • Biotic and abiotic controls on CaCO3 formation on desert ecosystems.
  • The extent of light, non-aqueous phase smearing with water table fluctuations.
  • Implications of the existence of an enormous nitrate reservoir in the arid West (and other deserts).
  • Energy and mass partitioning in arid soil ecosystems and the role of biogeochemical cycling.
  • How new computational and theoretical methods, tested with data collected at this site can be used to understand energy and mass transport phenomenon.
  • Creation of facility to test and benchmark sensors for subsurface monitoring. What are the environmental limitations and constraints to new classes of sensors, developed as part of the SEPHAS program.
  • What is the role of soil structure in water movement and plant uptake in arid settings? Can we use that knowledge to predict future pedological development?
  • Wetting front instability: no understanding of behavior of wetting front instability beyond ~10 cm; this has delayed progress in our understanding of gravitational fingering as far-reaching fluid flow and transport process in the unsaturated zone.
  • Capillary barriers: theory and bench-scale experiments have shown this to occur, but performance in systems larger than several tens of centimeters is unknown.
Chief, K., M.H. Young, B.F. Lyles, J. Healey, J. Koonce, E. Knight, E. Johnson, J. Mon, M. Berli, M. Menon, and G. Dana. 2009. Scaling Environmental Processes in Heterogeneous Arid Soils: Construction of Large Weighing Lysimeter Facility, p. 370. Desert Reseach Institute. Las Vegas, NV.

Yu, Zhongbo, Young, M.H., Tyler, S.W. Scaling Environmental Processes in Heterogeneous Arid Soils (SEPHAS)

Caldwell, T.G., M.H. Young, and J. Zhu. 2008. Spatial structure of hydraulic properties from canopy to interspace in the Mojave Desert. Geophys. Res. Let. 35, L19406, doi:10.1029/2008GL035095.

Marion, G.M. P.J. Verburg, E. V. McDonald, J. Arnone. 2007. Modeling salt movement through a Mojave Desert soil. J. Arid Env. Submitted.

Meadows, D.G., M.H. Young, E.V. McDonald. 2007. Influence of Surface Age on Infiltration Mechanisms of Desert Pavements, Mojave Desert. Catena. 72:169-178.

Wang, X.-P., M. H. Young, Z. Yu, and Z.-S. Zhang. 2007. Long-term effects of restoration on soil hydraulic properties in revegetation-stabilized desert ecosystems. Geophys. Res.Lett. doi:10.1029/2007GL031725.

Wang, X.P. Y.X. Pan, Z. Yu, M.H. Young, 2007. Effects of rainfall characteristics on infiltration and redistribution patterns in revegetation-stabilized desert ecosystems. J. of Hydrology. Submitted.

Yin, J., M.H. Young, Z. Yu. 2006. Effects of Paleoclimate, Time-Varying Soil Properties and Time-Varying Canopy Structures on Paleorecharge. J. Geophysical Res. – Atmospheres. Accepted.

Young, M.H., G.S. Campbell, J. Yin. 2007. Correcting dual-probe heat-pulse readings for ambient temperature fluctuations. Vadose Zone Journal. Accepted.

Young, M. H., H. Lin, and B. P. Wilcox. 2007. Introduction to special section on Bridging Hydrology, Soil Science, and Ecology: Hydropedology and Ecohydrology, Geophys. Res. Lett., 34, L24S20, doi:10.1029/2007GL031998.

Caldwell, T.G., E.V. McDonald, M.H. Young, E.P. Hamerlynck, S.N. Bacon. 2006. Ecohydrology of an Arid Soil Chronosequence in the Sonoran Desert, Yuma Proving Ground, USA. Presented at the Fall AGU Meeting, San Francisco, CA.

Caldwell, T.G. M.H. Young, J. Zhu, E.V. McDonald. 2007. Small-Scale Heterogeneity of Soil Hydraulic Properties on Large-Scale Water Balance Simulations. Presented at the Am. Soc. Agron. Meetings, New Orleans, LA.

Caldwell, T.G., M.H. Young, J. Zhu, L. Fenstermaker, E.V. McDonald. 2007. Scaling Heterogeneous Soil Hydraulic Properties Using Canopy/Interspace Distributions in a Mojave Desert Ecosystem. Presented at the Fall AGU Meeting, San Francisco, CA.

Meadows, D.G. M.H. Young, L. Fenstermaker. 2006. Impact of Spatial Variability of Soil Properties on Local Water Balance in a Mojave Desert Ecosystem. Presented at the American Soc. Agron meetings, Indianapolis, IN.

Yin, J. M.H. Young, Z. Yu. 2007. Effects of Paleoclimate and Time-Varying Canopy Structures on Paleo-Water Fluxes. Presented at the Fall AGU Meeting, San Francisco, CA.

Young, M.H. 2006. Evolution of soil hydraulic properties on arid alluvial fans: Impacts on near-surface water resources. Hohai University, Nanjing, China (Invited).

Young, M.H. Measuring Water Content in Near-surface Soils With Large Changes In Ambient Temperature. Presented at the Environmental Sensors Symposium. Boise State University, Boise ID, Oct 26-27, 2007 (Invited).

Young, M.H., D.G. Meadows, T.G. Caldwell, D.S. Shafer, E.V. McDonald. 2006. Evolution of soil hydraulic properties on arid alluvial fans. Presented at the AGU – Western Pacific Geophysics Meeting, Beijing, China (Invited).

Young, M.H., T.G. Caldwell, J.J. Miller, G. Dalldorf. 2007. Combining Pedotransfer Functions and Detailed Geomorphic Mapping to Characterize Runoff Potential on an Arid Alluvial Fan Complex. Presented at the Fall AGU Meeting, San Francisco, CA.

Young, M.H. T.G. Caldwell, J. Zhu. 2007. Spatial Variability of Soil Hydraulic Properties at Interspace/Canopy Microsites. Presented at the Am. Soc. Agron. Meetings, New Orleans, LA. (Invited)

Young, M.H. Z. Yu, S.W. Tyler. 2006. Scaling Environmental Processes in Heterogeneous Arid Soils (SEPHAS): A New Research Facility in Nevada USA. Presented at the World Congress of Soil Science, Philadelphia, PA. (Invited).

Young, M.H., Z. Yu, S.W. Tyler. 2007. Large Weighing Lysimeters for Studying Environmental Processes in Arid Soils, Presented at the Unsaturated Zone Interest Group meetings, Los Alamos, NM. August 27-29, 2007.

SEPHAS provides a unique opportunity in education for everyone to explore our facility. We offer specialized tours to K-12 educational system as well as the general public. We also offer exceptional opportunities for Graduate and Post-Doctoral students looking for real world experience.

Educational Outreach

The Desert Research Institute, as a member of the Nevada System of Higher Education (NSHE), is committed to Nevada’s K-12 education system and teachers so they can bring real world knowledge back into their classrooms.

Tours are available for community, school, business, and other groups by appointment.

Educational Opportunities

SEPHAS provides an excellent opportunity to maximize the benefits from educational programs by providing graduate student and post doctoral fellowships. Graduate fellowships are available to UNR, UNLV, and DRI students to conduct research with SEPHAS faculty. Post doctoral fellowships involve large-scale independent projects under the directorate of faculty. Post doctoral fellows are encouraged to further develop research proposals that can be submitted to external funding agencies. Potential applicants have to apply for the admission through the graduate programs in the University of Nevada Las Vegas or University of Nevada Reno.


Markus Berli, Ph.D.
Program Director 


Desert Research Institute
755 East Flamingo Road
Las Vegas, NV 89119


Hydrologic Sciences