Impact of Roots on Hydrogeological Parameters Supporting the Performance of a Cover with Capillary Barrier Effects

Abstract

One of the main environmental risks related to the surface storage of reactive mine tailings is acid mine drainage (AMD). AMD generation is often managed by limiting oxygen access to the reactive tailings. To do so, engineered cover systems such as covers with a capillary barrier effect (CCBEs) can be used. Over time, plants may colonize CCBE materials as a result of natural or assisted processes. Plant roots can have an impact on the hydrogeological properties that govern the performance of a CCBE, including saturated hydraulic conductivity (ksat) and water retention curves (WRCs). In the present work, flexible wall permeameters and water retention tests were used to characterize the moisture-retaining layer (MRL) of a CCBE colonized by roots. The obtained hydrogeological properties were compared with root colonization measurements using two-dimensional (2D) and three-dimensional (3D) root trait analysis techniques. Results showed that coarser root (diameter >0.5 mm) length density had a positive linear correlation with ksat(R2=0.90) and that, as total root length density (RLD) increased, air entry values dropped (R2=0.70). Desorption rates were also shown to decrease with increasing RLD. Although these results suggest that the hydrogeological properties of the studied MRL were not significantly affected by roots seventeen years after construction, they also suggest that, with time, roots could eventually have a negative impact on a CCBE’s performance, and that further research is needed.