Field-scale solute transport in a heavy clay soil

The transport of a bromide tracer was studied in a heavy clay soil in six soil sampling campaigns. Water samples were taken frequently from the groundwater and drain discharge and analysed for bromide content. Solutes were transported in three domains: large continuous macropores, smaller tortuous mesopores, and the pores between the soil aggregates. The most important transport occurred through the mesopores, characterized by high spatial variability, significant lateral transport, and low mobile water volumes. This resulted in rapid leaching of solute. Preferential flow through large macropores amounted only to a few per cent. Interaggregate solute transport played only an indirect role via solute retardation.