The type of flow (homogeneous versus preferential flow) is expected to have a major impact on pollutant transfer. We expect homogeneous flow to favor pollutant access to reactive particles and, thus, enhance pollutant retention. Preferential flow also called macro-pore flow, non-equilibrium, unstable flow or funnel and fingered flow, happens when water and solutes move through a porous medium with a limited number of fast pathways instead of having a uniform distribution. These pathways can be induced by biotic (e.g. earthworm and roots) and abiotic factors and processes (e.g. wet-dry and freeze-thaw cycles, lithology and structure) and they vary in space and time. They can carry substantial movement of water and solutes in both vertical and horizontal directions under saturated or unsaturated conditions and can dominate the flow and transport processes across a wide range of scales. As a result, preferential flow may regulate the mobility, distribution or removal of solutes, nutrients or contaminants. Similarly, preferential flow may affect the efficiency of salt precipitation or dissolution processes. Understanding preferential flow processes cannot be overstated, considering its relevance to the fate and transport of solutes, nutrients and contaminants in agricultural land, landscapes, catchments, mine waste covers and tailings storage facilities.
This session welcomes studies on experimental and theoretical challenges to identify, quantify, and model the effect of flow type on solute, nutrient and contaminant transport in porous media (e.g. soil, mine wastes, waste rocks and rocky and gravelly materials) across scales (from pore scale to catchment scale). The session accepts studies on but not limited to the following topics:
• Effects of flow type within the soil-plant-atmosphere continuum and their consequence for solute, nutrient or contaminant transport in the saturated and unsaturated zone;
• Coupling the physical processes of preferential flows and geochemical processes for improving the understanding of solute sorption and desorption, mineral precipitation and dissolution;
• Modelling of different types of flow and their effects on mass transport across scales, from pore to pedon scale and entire catchments and landscapes.
• Transport of particles and colloids, including nanoparticles, and the influence of flow type, in particular preferential and non-uniform flow, on their mobility, retention and remobilization.