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The performance of reclamation cover systems could be affected by the colonization of plant roots, which may modify the hydrogeological properties of the construction materials. A four-year field investigation was conducted using six experimental cells with various soil layering designs over AMD-generating tailings reclaimed with an oxygen-barrier cover combined with an elevated water table. Both herbaceous and woody vegetation were installed on top of the cells to compare the influence on the properties of the cover material. Consecutive and undisturbed cores were collected from the cover's functional layer in 2020 and 2021, respectively. Root parameters, such as root length density, and hydrogeological properties were measured on the core samples to assess the possible relationships between the two categories of variables. Root observation trenches were also cut in each cell to better analyze the root density and occurrence profiles. Results showed that, within the four-year monitoring period of the study, both herbaceous and woody vegetation roots mostly colonized the top overburden layer of the cell (>86% visible roots) and barely occupied the functional layer of the reclamation cover (<10% visible roots). The observed maximum desorption rates for the functional layer were lower than the predicted values, which could be a short-term effect of the fine roots. No significant impact of roots on the main hydrogeological variables controlling the oxygen barrier efficiency were noted. At the end of the four-year study period, the hydrogeological behavior of the functional layer in all cells with/without vegetation/additional soil layers was found to be similar. [ABSTRACT FROM AUTHOR]

Water balance was measured for five field experimental cells with an oxygen-barrier type of reclamation cover combined with elevated water table including a control cell with functional layer of desulfurized tailings over a reactive tailings layer, and four other cells with additional layers and different vegetation. Hydrogeological (moisture content and suction in layers, water table positions in cells), and precipitation data collected throughout three successive growing seasons after revegetation were compared to investigate the effects of different material layering and vegetation scenarios on the water balance. Above- and below-ground vegetation developments were also monitored. Results showed that for all tested scenarios the main water balance component remained the evapotranspiration (79–98% of the total precipitated water). Herbaceous vegetation was found to provide much safer support for the cover performance than woody vegetation, keeping the reactive tailings more saturated during the whole study period (mean Sr > 90.77%). In presence of woody plants, however, the Sr in the reactive tailings could reach a value as low as ~ 32%. Increasing the thickness of the additional layer over 30 cm above the functional layer with fine-grained HDS sludge could also pose a threat against its functionality by stimulating willow growth, lowering the water table position as well as the Sr in the reactive tailings. Finally, adding a coarse-grained capillary break layer impeded the willow root colonization of the functional layer in the short term but increased percolation and should be coupled to water conservation strategies in the overall system to maintain the elevated water table. [ABSTRACT FROM AUTHOR]