Laboratory study of the influence of continuous and non-continuous macropore layers on solute transport in soil

One of the mechanisms of solute transport in soil is preferential flow or flow in macropores. In this study, to investigate the influence of macropore paths on solute transport, three soil bulks composed of 3% clay, 4.2% silt and 92.8% sand in a box with 200 cm length, 100 cm width and 45 cm height were used. The first soil bulk was homogeneous (without macrpore path), the second one contained soil and layers of 5 cm thickness, composed of gravels with 2-4 mm diameter, from surface to bottom of the box (with continuous macropore layers), and the third one contained also contained soil and layers of same thickness and material, but the layers extended only to a depth of 35 cm (with non-continuous macropore layers). The transport of NaCl solution in these three soil bulks were experimented and then simulated using GeoStudio. In the soil bulk having continuous macropore layers, in comparison with the one with no macropore layer, the solute traveled the distance between the surface and the bottom in a shorter time (about 27%) and the peak concentrations were sooner observed (10-20 min). However, the non-continuous layers had no significant impact on the speed of solute transport. The GeoStudio software satisfactorily simulated the solute transport with the coefficient of determination more than 0.970 and the values of the root mean square error less than 0.25.