Do roots bind soil? Comparing the physical and biological role of plant roots in fluvial streambank erosion: A mini-JET study

Abstract

The roots of riparian vegetation can reduce fluvial streambank erosion by increasing soil resistance to erosion or by altering the applied hydrodynamic force of flowing water; however, the relative importance of these mechanisms is unknown. To assess the physical and biological effects of plant roots on streambank fluvial erosion, laboratory-scale testing was conducted using a mini Jet Erosion Testing (JET) device. Data analysis was conducted on three treatment groupings: (1) no roots (NR, n = 24); (2) synthetic roots (SR, n = 24); and (3) live roots (LR, switchgrass [Panicum virgatum], n = 12). Soil erosion was quantified by measuring the final volume of soil loss and calculating critical shear stress (τc) and the soil erodibility coefficient (kd). Potential explanatory soil and root properties, including percent water stable aggregates, root length density, and extracellular polymeric substances, were also measured. Kd was lower in rooted soil samples compared to NR when root length density was 2 cm cm−3 or higher, indicating that soil with densely packed fibers (either live and synthetic) have an impact on the applied hydrodynamic forces. However, τc was significantly higher in LR compared to both NR and SR, suggesting that only living roots provide additional soil protection by increasing soil resistance to fluvial erosion. The results of this study further emphasize that plant roots protect streambank soils from fluvial erosion through multiple mechanisms; nevertheless, further research is needed to determine which mechanism(s) plays a dominant role.