Relation of reactive solute-transport parameters to basic soil properties

Abstract

Solute-transport parameters are needed to assess the pollution risks of soil and groundwater resources. A reliable estimate of these parameters from easily measurable soil properties is therefore important. So, the correlations of the transport parameters for one metalloid compound (NaAsO 2 ), six heavy metal compounds (Cd(NO 3 ) 2 , Pb(NO 3 ) 2 , Ni(NO 3 ) 2 , ZnCl 2 , CuSO 4 and Co(NO 3 ) 2 ), two pesticides (cartap and carbendazim) and one inert salt (CaCl 2 ) with some basic properties of eight agricultural soils of Bangladesh were investigated. The purpose of this study was to generate information for development of non-parametric pedo-transfer functions for reactive solute transport through soils. The transport experiments with the solutes were done in repacked soil columns under unsaturated steady-state water flow conditions. The major solute-transport parameters – velocity of transport ( V ), dispersion coefficient ( D ), dispersivity ( l ), retardation factor ( R ) and Peclet number ( P ) – were determined by analysing solute breakthrough curves (BTCs). The basic soil properties pertinent to solute transport: clay content, median grain diameter (D 50 ), pore-size distribution index ( n ), bulk density ( r ), organic carbon content (C) and pH were determined. The associations of the solute-transport parameters with these soil properties were investigated and evaluated. Both the solute dispersivity and retardation factor increased significantly (p<0.05) ( l linearly and R following power law) with the increase in soil clay content. Dispersivity significantly decreased with the increase in median grain diameter following power law. The V , D , l and P values were weakly and negatively correlated with the soil bulk density. Retardation factor, R , was moderately and positively correlated with the ratio of clay content to organic carbon content. Dispersivity decreased but P increased, both significantly, with increasing pore-size distribution index, n . V , D and P were positively correlated with soil pH, while R and l were negatively correlated with it. The correlation of the solute-transport parameters with soil properties being significant (p < 0.05), in most cases, provides strong possibility of predicting solute-transport parameters from the basic soil properties through the development of pedo-transfer functions.