Adequacy of transport parameters obtained in soil column experiments for selected chemicals

Abstract

The transport parameters were determined for the 18 O isotope (in the form of H 2 18 O), the Br -ion, and atrazine in intact columns of allophanic Andosol (Mexico State, Mexico). A one dimensional model for the convective dispersive transport of chemicals with account for the decomposition and equilibrium adsorp tion (HYDRUS 1D), which is widely applied for assessing the risk of the chemical and bacterial contamina tion of natural waters, was used. The model parameters were obtained by solving the inverse problem on the basis of laboratory experiments on the transport of the 18 O isotope, the Br -ion, and atrazine in intact soil columns at a fixed filtration velocity. The hydrodynamic dispersion parameters determined for the 18 O and Br -ions in one column were of the same order of magnitude, and those for atrazine were higher by 3-4 times. The obtained parameters were used to calculate the transport of these substances in another column with dif ferent values of the water content and filtration velocity. The transport process was adequately described only for the 18 O isotope. In the case of the Br -ion, the model significantly underestimated the transport velocity; for atrazine, its peak concentration in the column was overestimated. The column study of the transport of the three chemical compounds showed that transport parameters could not be reliably predicted from the results of a single experiment, even when several compounds were used in this experiment.

Relation of reactive solute-transport parameters to basic soil properties

“…The ratio between the clay content and organic carbon content was also hypothesized as a fundamental control of the structure of agricultural topsoil and consequently for the solute transport properties (de Jonge et al, 2009). Despite substantial amount of field and laboratory data on the transport of solutes in soils obtained in the recent decades in different countries, the methods for assessing the chemical parameters from the physical properties of soils remain poorly developed (Raymundo-Raymundo et al, 2012). In the comprehensive review, Koestel et al (2012) analysed information on 733 BTCs, all of which were for inert/conservative tracers, mostly, on undisturbed soil samples and a smaller number on columns filled with glass beads, clean sands, or sieved and repacked soil.…”