Spatial variability of the effective retardation factor in an unsaturated field soil

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Authors:Thomasson, Mark J.; Wierenga, Peter J.
Author Affiliations:Primary:
University of Arizona, Department of Hydrology, Tucson, AZ, United States
Other:
Centre for Agricultural Landscape and Land Use Research (ZALF), Federal Republic of Germany
University of Florida, United States
Volume Title:Soil hydrological properties and processes and their variability in space and time
Volume Authors:Hopmans, J. W., editor; Wendroth, Ole; Nkedi-Kizza, P.
Source:Journal of Hydrology, 272(1-4), p.213-225; Soil Science Society of America annual meeting, symposium on Soil physical properties and processes and their variability in space and time, Charlotte, NC, 2001, edited by J. W. Hopmans, Ole Wendroth and P. Nkedi-Kizza. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0022-1694
Publication Date:2003
Note:In English. 27 refs.; illus., incl. 6 tables
Summary:A precisely controlled field study was conducted to determine flow and transport of water and bromide through an unsaturated soil. A 50 m×50 m plot was instrumented with neutron probe access tubes, tensiometers, and solution samplers. Water containing bromide part of the time was applied at a steady flux of 1.85 cm d-1 for 24 days. The average degree of water saturation during water application was about 56%. The Hydrus 1-D model was used to optimize the saturated hydraulic conductivity parameter Ks, and the transport parameters D (dispersion coefficient) and R (used here as a "bulk retardation coefficient"). The van Genuchten flow parameters θr, θs, α, and n were obtained from laboratory measurements on 11 cores taken 1.5 m below the soil surface along a transect through the plot. The estimated field Ks value increased with depth due to higher sand and gravel contents at depth. The mean dispersion coefficient for 13 locations at the 3 m depth was found to be 5.35 cm2 d-1, with a coefficient of variation of 52%. This resulted in a relatively small mean dispersivity value of 0.64 cm. The average R value was 0.63 with a range of 0.45-1.02 at 3 m (CV = 28%). The low R value is indicative of anion exclusion, immobile water, or some other phenomenon difficult to identify from field data. These field data indicate that if a transport model with a bulk retardation factor is used for predicting bromide transport through unsaturated soil a range of retardation values may need to be used. For our soil, the highest R value needed to be at least twice its lowest value. Abstract Copyright (2003) Elsevier, B.V.
Subjects:Case studies; Controls; Convection; Experimental studies; Field studies; Hydraulic conductivity; Hydrology; Mass balance; Pollutants; Pollution; Soils; Solute transport; Spatial variations; Transport; Unsaturated zone; Arizona; Basin and Range Province; North America; Pinal County Arizona; United States; Maricopa Arizona
Coordinates:N330000 N330000 W1120000 W1120000
Record ID:2003024642
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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