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DIVISION S-1-SOIL PHYSICS

Evaluation of a Simple Method for Estimating Solute Transport Parameters

Laboratory Studies

^a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011 USA
^b USDA-ARS, National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011 USA

rhorton{at}iastate.edu

A two-domain, physical nonequilibrium solute transport model has been used to describe the transport and fate of solute in soil. The model contains the parameters _im (immobile water content) and (mass transfer coefficient) which must be determined for a soil before applying the transport model. A simple field method that can estimate both _im and without measuring extensive breakthrough curves (BTCs) has been presented. The purpose of this paper was to test in laboratory soil columns the simple method of estimating parameters by comparing to the conventional BTC analysis method of parameter estimation. The experiments involved 12-cm-long and 4-cm-diam. columns packed with five different soil materials. The BTCs were performed on each column using a sequential application of four fluorobenzoate tracers. Each tracer was applied for a different length of time. The soil columns were sectioned at the end of the BTC experiments. The simple method gave results of _im and based upon the sectioned soil samples, and the BTC analysis gave results of _im and based upon effluent concentrations. The estimates by the two different methods were from the same experiments. Most of the estimated values using the simple method were within the 95% confidence interval (CI) of the BTC estimates. For 7 of 10 soil columns, the estimates of immobile water fraction, _im/, from the simple method were within the 95% CI of the estimates of _im/ obtained from BTC data. Breakthrough curves calculated using the _im and values estimated by the simple method were similar to observed BTCs. The simple method provides estimation of _im and from easy to obtain soil samples in field and can be used as a first approximation to apply the analytical BTC method.

Abbreviations: BTCs, breakthrough curves • CDE, convection–dispersion equation • CI, confidence interval • ME, mean error • MIM, mobile–immobile model • RMSE, root mean square error

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