Influence of vegetation and additional surface layers on the water balance of a reclamation cover with elevated water table

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.