Estimation of retardation factor of dissolved organic carbon in sandy soils using batch experiments

Abstract

Dissolved organic carbon (DOC) can be transported in soil solution through the soil, and may influence water quality. The transport of DOC in soils can be described by a convection-dispersion model in which the retardation factor is one of the important coefficients. Soil column experiments are frequently used to estimate the retardation factor. Because the retardation factor is related to the adsorption distribution coefficient, it may be evaluated using batch experiments which are much easier to carry out in the laboratory. In this study, four types of sandy soils were selected. Columns of 1.0 kg soil (1.46 kg 1 −1 bulk density) for each soil type were leached with poultry litter extract (DOC: 2.34 g 1 −1). The outflow DOC concentrations were regressed using CXTFIT to calculate retardation factors. In the batch experiments, the soil samples were equilibrated with poultry litter extract at a ratio of 1:4 (soil:solution). The adsorption distribution coefficients for DOC (0.096 to 0.661 ml g −1) were determined by measuring the differences between initial and final concentrations and retardation factors were calculated (1.46 to 4.48). The results showed that batch experiments can predict retardation factors for the sandy soils at an acceptable level of precision. The batch experiments apparently underestimated the retardation factor for the Cecil soil which has relatively more clay content. This result might be because adsorption isotherms of fine-textured soils are not linear. In general, batch experiments can be employed to predict retardation factors for sandy soils for which, we suggest, clay content should be lower than 150 g kg −1.