Solute Movement through an Allophanic Soil

Abstract

Allophanic soils are widespread around the world, but little research has been done on their transport properties. This study reveals the effect of two soil water potential heads and two water-flow regimes of continuous and intermittent flow on solute transport through undisturbed soil columns of Horotiu silt loam (Typic Hapludand), an allophanic soil. Two different methods--breakthrough curves (BTCs) and time domain reflectometry (TDR)--were employed to determine the extent of preferential solute transport in the topsoil. The TDR data were also used to look at the depth dependence of the transport properties. The convection-dispersion equation (CDE) with the appropriate boundary conditions adequately described the movement of both Br and Cl under the various flow conditions. Although no preferential flow was found under the imposed unsaturated flow conditions, the flow of water and transport of solute became more uniform with depth. The results show that both Br and Cl are retarded in this allophanic soil. Retardation values range from 1.5 to 1.9, and, as the TDR data showed, increase from the depth of 5.0 to 10.0 cm. Intermittent leaching results showed that there was no effect on solute concentrations in the leachate following no-flow periods. This suggests that water and solute transport in this soil were either relatively uniform or that transverse mixing during flow was already fast enough to eliminate concentration gradients between regions of different "mobility."

Competitive adsorption of trace elements in calcareous soils of western Iran

“…Alloway (1995a) stated that Kd is a useful parameter for comparing the sorptive capacities of different soils or materials for any particular ion, when measured under the same experimental conditions. Distribution coefficients have previously been used in studies of mobility and retention of trace elements in the soils (Katou et al, 2001;Martin-Garin et al, 2002;Magesan et al 2003;Voegelin and Kretzschmar, 2003).…”

Nitrate Sorption in a Mexican Allophanic Andisol using Intact and Packed Columns

“…It varies from granular of loose consistency on the surface, to granular with subangular blocky moderately thick of friable consistency at depth. The dispersivity coefficient was calculated as for packed columns, and the values obtained are in the range of those reported by Magesan et al (2003). These authors studied solute movement through intact columns of an allophanic soil under unsaturated flux.…”

“…In Table 1, it can be noted that the pH increases with depth as the carbon (C) content decreases, whereas the retardation increases. As found in many studies on anion transport in variable charge soils where soil conditions are modified (Qafoku, Sumner, and Radcliffe 2000;Magesan et al 2003), retardation is negatively correlated with pH. However, while studying different soil layers under natural conditions, this relationship is not so evident, because other factors affect anion adsorption such as amorphous materials.…”

“…The dispersion and also the dispersivity (n did not vary greatly) were identical in all packed columns, which indicates that the packing method was effective to obtain uniformity. According to Magesan et al (2003), the dispersivity is an indicator of how variable solute mobility is in a soil.…”

Sulfate and Calcium Movement in an Allophanic Soil—The Relevance of Ion‐Pair Adsorption in the Soil–Plant System

“…The experiments were carried out following a procedure similar to that described by Magesan et al (2003). The leaching solution was applied to the top of the column using a disk permeameter.…”