Simulation of bromide tracer and nitrogen transport in a cracked clay soil with the FLOCR/ANIMO model combination

Two preferential flow models (FLOCR and ANIMO) were combined into a simulation tool that applies widely to field-scale studies of chemical transport in macroporous swelling and shrinking clay soils. The improved model combination was calibrated against measurements of groundwater level, soil moisture content, bromide tracer levels in groundwater, and bromide content in soil profiles. Experiments showed high bromide concentrations in groundwater within three weeks of application to a soil with no visible shrinkage cracks, suggesting preferential flow through permanent macropores. The combined FLOCR/ANIMO model can account for the presence of such macropores, as well as shrinkage cracks, interflow into macropores, and diffusive exchange between macropore water and soil water. The specific contribution of shrinkage cracks to solute transport could not be tested because suitable field data were not available. The model performed moderately well at simulating nitrate transport to groundwater, but further adjustments are needed.