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.