Restoration of dump deposits from quarries in a Mediterranean climate using marble industry waste

One of the most frequently used techniques for restoring quarrying operations is to cover the surface of the dump deposit with a layer of topsoil. Sludge from the cutting and polishing of marble has a high water-holding capacity (0.256 kg kg−1) and could increase the success of quarry restorations. In this study, a dump deposit located at the Macael marble quarries (SE Spain), which has a surface of approximately 1100 m2 and a 72% slope, was restored with and without the addition of marble sludge prior to being covered with topsoil to analyse the impact of the sludge on the water-holding capacity and the development of vegetation. In the plots without sludge, the relatively low water-holding capacity of the topsoil and the capillary barrier, which forms when a fine-grained material overlays a coarse-grained material, tended to reduce the success of the restoration. In the plots with the sludge, the mean water content was more than double that of the plots without the sludge (61 dm3 m−2 vs. 27 dm3 m−2). Water tended to accumulate between the deepest 5 cm of the topsoil and the first 10 cm of the sludge, which stimulated the development of the roots in this layer and significantly encouraged the development of aboveground biomass. However, the amount of stored water and the aboveground biomass were significantly related to the thickness of the topsoil; therefore, for a better utilisation of rainwater in semi-arid climates, restorations should include topsoil that is at least 30 cm thick.