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

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Leij, F. J. Articles by Dane, J. H. Search for Related Content PubMed Articles by Leij, F. J. Articles by Dane, J. H. Agricola Articles by Leij, F. J. Articles by Dane, J. H.

Moment Method Applied to Solute Transport with Binary and Ternary Exchange

U.S. Salinity Lab., Riverside, CA

J. H. Dane^*

Dep. of Agronomy and Soils, Auburn Univ., Auburn, AL 36849-5412

* Corresponding author.

ABSTRACT

When modeling transport of exchanging solutes in soils, it is sometimes conveniently assumed that the solutes interact linearly with the solid phase of the soil. In this study, an attempt was made to quantify the influence of nonlinear cation exchange on solute spreading with the moment method. Theoretical expressions for the first four moments were derived based on the equilibrium and physical nonequilibrium models of the advection-dispersion equation (ADE). Displacement experiments were conducted in which either a NaCl pulse (binary exchange) or a pulse of KBr and NaBr (ternary exchange) was applied to a CaBr₂-saturated medium. Values for the transport parameters were determined with moment analysis and curve fitting. The observed breakthrough curves were somewhat better reproduced with parameters obtained from curve fitting than from the moment method. However, the curve-fitting program produced some unrealistic parameter estimates for the nonequilibrium model. A disadvantage of the moment method was that the fourth-order moment sometimes yielded unstable results for the nonequilibrium model. Parameters form the anion displacement were used to estimate the theoretical variance due to hydrodynamic dispersion and nonequilibrium spreading for the cation breakthrough curves. The difference between the variance of the observed cation breakthrough curve and these theoretical variances was used as an approximation of the variance due to nonlinear exchange. Particularly for the ternary exchange, the variance due to nonlinear exchange was often several times greater than predicted according to the transport model. The results enabled us to quantify errors in dispersion coefficient (D) values directly determined from cation-displacement experiments.

Contribution from Alabama Agric. Exp. Stn., Auburn Univ., AAES Journal no. 3-892309P.

Received for publication October 30, 1989.