Restoration of ecosystem function in an abandoned sandpit: plant and soil responses to paper de-inking sludge.
In mine spoil reclamation, the establishment of a sustainable plant cover requires the improvement of limiting conditions and the re-initiation of carbon (C) and nutrient cycling. The approach used in this study for reclaiming an abandoned sandpit in Quebec, Canada, was based on a heavy organic amendment as an attempt to accelerate the reconstruction of a functional ecosystem. The single intervention consisted of incorporating paper de-inking sludge into soil at two rates (0 and 105 dry t/ha), supplemented with nitrogen (N) at three rates (3, 6 and 9 g/kg sludge) and phosphorus (P) at two rates (0.5 and 1.0 g/kg sludge) followed by sowing (mid-summer) of Agropyron elongatum [Elymus elongatus]. Standing biomass increased in the presence of sludge after both the first and second full growing seasons. High N application rates further increased yield, more importantly in the second season. The high P rate improved grass establishment in all cases. Ground cover increased with time and doubled in the presence of sludge whereas it decreased in the absence of sludge. P and N uptake were improved consistently in the presence of sludge. Sludge application resulted in improved water retention and cation exchange capacities, and an increase in pH and bulk density of sand pit mine spoil, all of which may have accounted for the significant improvement in plant responses. Levels of soil C and N suggest that this reconstructed system approached sustainability. Adequate N and P supplements will accentuate the positive influence of sludge on revegetation.