HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by Walvoord, M. A. Articles by Striegl, R. G. Search for Related Content PubMed Articles by Walvoord, M. A. Articles by Striegl, R. G. GeoRef GeoRef Citation Agricola Articles by Walvoord, M. A. Articles by Striegl, R. G. Related Collections Vadose Zone Processes and Chemical Transport Coupled Flow/Transport Models

SPECIAL SECTION: UNCERTAINTY IN VADOSE ZONE FLOW AND TRANSPORT PROPERTIES

Constraining the Inferred Paleohydrologic Evolution of a Deep Unsaturated Zone in the Amargosa Desert

^a U.S. Geological Survey, Lakewood, CO 80225
^b U.S. Geological Survey, Menlo Park, CA 94025
^c U.S. Geological Survey, Carson City, NV 89706
^* Corresponding author (walvoord{at}usgs.gov).

Received 3 April 2003.

Natural flow regimes in deep unsaturated zones of arid interfluvial environments are rarely in hydraulic equilibrium with near-surface boundary conditions imposed by present-day plant–soil–atmosphere dynamics. Nevertheless, assessments of water resources and contaminant transport require realistic estimates of gas, water, and solute fluxes under past, present, and projected conditions. Multimillennial transients that are captured in current hydraulic, chemical, and isotopic profiles can be interpreted to constrain alternative scenarios of paleohydrologic evolution following climatic and vegetational shifts from pluvial to arid conditions. However, interpreting profile data with numerical models presents formidable challenges in that boundary conditions must be prescribed throughout the entire Holocene, when we have at most a few decades of actual records. Models of profile development at the Amargosa Desert Research Site include substantial uncertainties from imperfectly known initial and boundary conditions when simulating flow and solute transport over millennial timescales. We show how multiple types of profile data, including matric potentials and porewater concentrations of Cl^–, D, ¹⁸O, can be used in multiphase heat, flow, and transport models to expose and reduce uncertainty in paleohydrologic reconstructions. Results indicate that a dramatic shift in the near-surface water balance occurred approximately 16000 yr ago, but that transitions in precipitation, temperature, and vegetation were not necessarily synchronous. The timing of the hydraulic transition imparts the largest uncertainty to model-predicted contemporary fluxes. In contrast, the uncertainties associated with initial (late Pleistocene) conditions and boundary conditions during the Holocene impart only small uncertainties to model-predicted contemporaneous fluxes.

Abbreviations: ADRS, Amargosa Desert Research Site • CMB, chloride mass balance [age] • EVT, enhanced vapor transport • FEHM, Finite Element Heat and Mass Transfer Code • SMOW, Standard Mean Ocean Water • UZ, unsaturated zone

This article has been cited by other articles:

				J. J. Gurdak, R. T. Hanson, P. B. McMahon, B. W. Bruce, J. E. McCray, G. D. Thyne, and R. C. Reedy Climate Variability Controls on Unsaturated Water and Chemical Movement, High Plains Aquifer, USA Vadose Zone J., August 23, 2007; 6(3): 533 - 547. [Abstract] [Full Text] [PDF]

				E. M. Kwicklis, A. V. Wolfsberg, P. H. Stauffer, M. A. Walvoord, and M. J. Sully Multiphase, Multicomponent Parameter Estimation for Liquid and Vapor Fluxes in Deep Arid Systems Using Hydrologic Data and Natural Environmental Tracers Vadose Zone J., August 24, 2006; 5(3): 934 - 950. [Abstract] [Full Text] [PDF]

				C. J. Mayers, B. J. Andraski, C. A. Cooper, S. W. Wheatcraft, D. A. Stonestrom, and R. L. Michel Modeling Tritium Transport Through a Deep Unsaturated Zone in an Arid Environment Vadose Zone J., October 10, 2005; 4(4): 967 - 976. [Abstract] [Full Text] [PDF]

				B. J. Andraski, D. A. Stonestrom, R. L. Michel, K. J. Halford, and J. C. Radyk Plant-Based Plume-Scale Mapping of Tritium Contamination in Desert Soils Vadose Zone J., August 16, 2005; 4(3): 819 - 827. [Abstract] [Full Text] [PDF]

				R. M. Holt and M. J. Nicholl Uncertainty in Vadose Zone Flow and Transport Prediction Vadose Zone J., May 1, 2004; 3(2): 480 - 484. [Full Text] [PDF]