A review of preferential flow and transport through root channels

Preferential flow can contribute up to 80%–90% of the flow and transport in the vadose zone. The root channels are the most prevalent form of preferential pathways. They create an evolving network of preferential pathways and are biogeochemical hotspots due to preferential transport of nutrients and other organics, colonization of bacteria, and biochemical activity of the roots. This paper reviews and analyses the existing literature on experiments and modeling of flow and transport through root channels at the field and laboratory scales. Preferential flow and transport through root channels varied with types of plants, soil types, root architecture, storm sizes, and depth. Finer roots contributed more to preferential flow and transport. Dye tracing and image analysis were frequently used to delineate the preferential flow pathways but were limited by the sorptive nature of the dyes. Dual permeability models were the most successful in simulating field and laboratory observations. However, these models cannot differentiate between the root channels and other macropores, as these models do not explicitly account for the evolving nature of the root network and are unable to simulate the processes within the preferential flow pathways. In the end, the paper identifies critical future research directions to understand the mechanisms of preferential flow and transport through the root channels.