Landscape indicators and soil properties in a naturally rehabilitated mine waste dump, Western Australia

Volunteer establishment and sustainable growth of native plant species on non-rehabilitated disturbed land is possible and could be a viable alternative to seeding and fertilisation as a strategy in land rehabilitation. Fieldwork to study this natural approach was conducted at the Scotia gold mine waste dump at Norseman, Western Australia. The waste dump consisted of diverse mixtures of weathered and fresh mafic and felsic rocks with particle sizes ranging from clay to boulder. The dump extended over several hectares and was approximately flat topped with steeply sloping sides. The site had been left in an unrehabilitated condition for about 15 years. Soil surface conditions were recorded along four transects on the waste dump and along two transects in adjacent native forest. Indices for stability, infiltration and nutrient cycling were calculated using Landscape Function Analysis technique (Tongway and Hindley, 1995). Soil samples were analysed for their water retention, texture, and nutrient content. Bare soil including rock fragments was the dominant zone (patch) in both landscapes occupying 60 % of the total transects. Stability indices ranged from 49 to 54 for the dump, and 64 to 67 for the reference sites. Likewise, the infiltration indices were lower for the dump (35-42) as compared with the native bush sites (mean = 56). The nutrient cycling indices were half those for the native sites (mean 22 and 41). These figures clearly indicate that after 15 years the waste dump is still not within the range of native sites. Native species, especially Eucalyptus and Melaleuca, are growing on the dump in a marked patchy pattern, which reflects available nutrient and water in localised niches. We now have a baseline and can measure change in the future. For both sites, topsoils were alkaline (pH 8.5-9.5), and EC ranged from 0.15 to 1.50 dS/m (extreme value 5.15 dS/m). Soils were mostly sandy loam (60 % sand and 10 % clay). Plant-available P was low (<10 mg/kg), available K was high (mean 567 mg/kg). Exchangeable Ca was dominant (mean 18 cmol+/kg) and CEC ranged from 21 to 36 cmol+/kg. The dump soils were different from the reference topsoils for water content at –1500 kPa suction (wilting point), gravel content, soil pH, organic carbon, and exchangeable Ca and Na. The first four dimensions in a principal component analysis account for 65 % of data variation with the major contributors being soil texture, organic carbon, exchangeable Ca, water retention, and ESP. A strong separation of sites was obtained by canonical analysis based on soil carbon, total N, pH, ESP and CEC.