Soil development on rehabilitated bauxite mines in south-west Australia

Abstract

Rehabilitation after bauxite mining in the jarrah forest aims to re-establish a self-sustaining forest. This implies that ecosystem processes will be re-established and soil nutrient stores will be similar to those of the unmined forest. This study determined the baseline levels of a number of soil properties in areas of jarrah forest typically cleared and mined for bauxite, and the effect of mining and rehabilitation processes on the vertical distribution of soil nitrogen. In addition, the changes in soil nitrogen, extractable phosphorus, extractable potassium, and pH that occurred up to 8.5 years after rehabilitation were investigated. The values of the soil properties in unmined forest found in this study were similar to those previously measured in the jarrah forest. Values of all parameters varied significantly with depth. Considerable mixing of soil horizons occurred when the topsoil was stripped, placed on an area undergoing rehabilitation, and ripped. Many soil parameters showed significant changes in the period 3.5–8.5 years after rehabilitation. Levels of total nitrogen in the top 10 cm of soil in rehabilitated areas increased from around 0.04–0.05% initially to levels approaching those found in good-quality jarrah forest (0.10–0.30%) after 8.5 years. Soil pH declined in the surface layer after rehabilitation. The rate of acidification is likely to decrease in future years. The levels of the soil chemical parameters were mostly within or moving towards the range of values found in areas typically mined for bauxite. The results indicate that ecosystem processes have been re-established on the rehabilitated areas and that there is no obvious soil chemical impediment to the establishment of a self-sustaining forest ecosystem on rehabilitated bauxite mines.

Soil carbon and litter development along a reconstructed biodiverse forest chronosequence of South-Western Australia

“…This is followed by a distinct loss of soil organic C, which has been previously observed and is typical of restored soils after major ecosystem disturbance (Schwenke et al 2000a, b;Banning et al 2008). Initial mixing of surface soil with deeper soil layers, during the post-mined land preparation, resulted in a dilution of soil C concentrations at the surface and increase in SOC in the lower depths (Ward 2000). The subsequent loss of organic C may be attributed to higher mineralisation of SOM by soil microorganisms but not offset by the organic matter input (by litterfall) due to low contribution from the establishing plant community.…”

“…There were increasing amounts of litter with increased restoration age, reflecting the increased organic inputs that occur as the forest develops and its net primary productivity increases (Tibbett 2010). However, the C:N ratios of soils from lower depths that have undergone longer periods of forest growth following restoration were significantly lower than non-mined forest soil, and is most likely due to additional N inputs by the high-density leguminous understorey in restoration (Ward 2000). Only with a reduction in the dominance of the N-fixing species would the C:N ratio return to premining levels (Fig.…”

“…The mining process typically involves removal of all vegetation, burning of residue, removal of 10-15 cm of topsoil for later use in rehabilitation and removal of overburden (approximately 40 cm depth) before the ore is mined (Koch 2007;Tibbett 2010). Pit floors are ripped and reshaped to blend in with the surrounding landscape, overburden and topsoil are returned, and the areas are deep-ripped to about 1.2 m (Ward 2000). All the sites sampled for this study had top soil replaced from other currently mined sites ('direct-return').…”

“…All soil samples were tested with HCl and found to be carbonate-free, hence the measured total C was inferred to be of organic origin. Description of related basic soil chemical changes with increasing restoration age and depth is detailed in Ward (2000).…”

The development of soil organic matter in restored biodiverse Jarrah forests of South-Western Australia as determined by ASE and GCMS

“…The mining process and the regolith material disturbed are eco-toxicologically benign and the landscape can be restored to a high standard after what is primarily a physical disturbance (Tibbett 2010). Pit floors are ripped and reshaped to blend in with the surrounding landscape, overburden and topsoil are returned, and the areas are deep-ripped to about 1.2 m (Ward 2000). Seed of both tree and understorey species are sown, followed by fertilisation.…”