Assessing various rehabilitation strategies for coarse coal washery reject dumps in the Hunter Valley, Australia: I. Chemical characteristics

At several coal mines in the Hunter Valley (New South Wales, Australia), the use of coarse coal washery reject (chitter) as a top-dressing material has resulted in successful establishment rates of tree and shrub species by direct seeding. However, concerns have arisen about the potential to downgrade the rural capability of the land for grazing, poor understanding of the material's long-term benefits, and spontaneous combustion issues. To ascertain the suitability of chitter as a final landform surface, a revegetation research trial was initiated at United Collieries coal mine in the Hunter Valley of New South Wales. Experimental plots were established in autumn (May 1998) and spring (November 1998) on a freshly shaped stockpile of chitter. The revegetation trials incorporated four substrate treatments, namely a 1 m and 20 cm capping of overburden, a 20 cm topsoil dressing and a treatment of only chitter. Each of the four substrate treatments incorporated five revegetation treatments, namely pasture species and mulch (straw), pasture species and no mulch, native seed (shrub and tree) and mulch, native seed and no mulch, and planted tubestock trees. Chemical characteristics (pH, EC, total N, nitrate-N, available-P, total P, total S, Ca, Na, Mg, K, organic C and soil moisture) across the substrate and vegetation treatments were assessed at 0, 3, 6 and 12 months after establishment.