Suitability of Time Domain Reflectometry in Determining Reactive Solute Transport through Typic Haplustalf

Reactive solute transport determination by conventional approaches requires large time. Present study explores suitability of time domain reflectometry (TDR) for determining solute-transport parameters, such as dispersion coefficients and retardation factors for reactive solutes through a differentially charged soil. Proposed method is based on peak-to-peak measurements of water and solute velocities through the soil using TDR. Unsaturated leaching experiments were carried-out to evaluate the method in the laboratory on two soil columns packed with differentially charged Typic Haplustalf from Orissa. One column was left bare and the other was planted with sunflower (Helianthus annuus L.) to get the root hindrance impact on solute transport parameters. Pulses of CaBr2 and Ca(NO3)2 were applied to the surface of either wet or dry soil. Columns were leached by water using a rainfall simulator at a steady rate between 30 and 50 mm h−1. Water and solute transport were monitored by collecting the effluent. Simultaneous in situ measurements of the water content and electrical conductivity were made using a TDR. Transport parameters for the convective– dispersive flow equation, with a linear adsorption isotherm, were obtained from the flux concentration and the solute resident concentrations measured by TDR. Anion retardations between 1.4 and 1.9, and dispersivities between 1 and 8 mm, were observed. Using TDR-measured water and solute front velocities, the retardations were calculated. These used TDR measurements of soil-water content and bulk soil electrical conductivity with time, and were similar to those obtained from the effluent. The agreement between predicted and measured solute movement parameters suggests that the TDR could be a valuable in situ technique for obtaining the parameters relating to reactive solute transport through soil.