Changes in some properties of topsoil at Tarong coal Meandu mine coalmine with time since rehabilitation

Three sites were studied at the Meandu Mine, Tarong, where vegetation had been established for 2, 4, and 6 growing seasons. Topsoil (a grey sandy loam, developed on sandstone) had been spread over sandstone spoil at all sites, to a depth of approximately 200 mm. At each site, areas were studied where either (i) all vegetation had been removed and the soil was disturbed to destroy any macropores that had developed, then allowed to consolidate under rainfall, or (ii) vegetation was clipped and pores in the soil were left undisturbed and intact. This allowed separate assessment of soil pores associated with re-aggregation and of the frequency and importance of stable macropores formed by soil fauna and by plant roots. Disc permeameters were used to measure hydraulic conductivities at the soil surface, and organic carbon and aggregate size distributions at the soil surface following rainfall wetting were measured. For bare, consolidated soil, hydraulic conductivities indicated that development of pores in the topsoil had reached a maximum after 4 seasons. This was consistent with aggregate size distributions after rainfall wetting, which indicated little change between 4 and 6 seasons. Hydraulic conductivities of vegetated areas showed responses to both length of time under vegetation and to plant species. The results showed that measurements of soil structure and of infiltration parameters made when soil was spread and rehabilitation commenced will greatly underestimate the long-term hydraulic conductivity of minesoils. Where long-term runoff, water balance, and vegetation growth are being considered, it would be preferable to measure input parameters on areas of established vegetation (preferably after at least 4 seasons of plant growth).