Chloride and Lithium Transport in Large Arrays of Undisturbed Silt Loam and Sandy Loam Soil Columns

Abstract

The transport of Cl− and Li+ was investigated in 90 undisturbed soil columns (28-cm diam., 35 cm deep) representing two soil series: structured silt loam (Hudson; fine, illitic, mesic Glossaquic Hapludalfs) and unstructured sandy loam (Arkport; coarse-loamy, mixed, active, mesic Lamellic Hapludalfs). The columns had previously been operated with two cropping cycles, including two applications of a variety of sewage sludges (biosolids) at agronomic rates. With soil columns at field capacity and with no crops present, a pulse of 3.55 mM LiCl was added in the equivalent of 5.8 cm of water over the surface of the columns, followed by several irrigations (11.6 cm total depth) of deionized water and multiple subsequent irrigations with synthetic acid rain. Tracer concentrations in the outflow water increased almost immediately after application, with the Li+ concentrations an order of magnitude less than Cl− Although there was a great deal of variation in initial Cl− concentrations among the individual columns, the overall pattern was consistent for each soil after the initial 10 cm of flow (when variable preferential flow effects dominated) and was independent of the sludge applications. Outflow Li+ concentrations were extremely variable among columns. Lithium adsorption partition coefficients (kd) from batch equilibrations were lower than those derived from outflow concentrations. Solute losses were described with a simple preferential flow model. Apparent water contents fit a normal distribution for Cl− while Li+ apparent kd values were lognormally distributed. Outliers (i.e., columns with transport parameters very different from the mean) had transport velocities that were slower than would be predicted by the respective distributions. Probabilistic approaches can be used to select the number of experimental columns required to meet a desired level of probability that soils columns with a meaningful range of transport velocities will be represented in the experimental set.