An ecological assessment of rehabilitated bauxite residue

Assessment of soil biological communities and activity may be a valuable indicator of ecological stress and ecosystem function in rehabilitated bauxite residues. Establishment of keystone species and evidence of processes such as decomposition have been demonstrated on a number of mine spoil types but not on alkaline, sodic bauxite residue.Using the litterbag technique the spatial and temporal variation in decomposition rates was examined in a residue rehabilitation series; site A (not rehabilitated), site B (1yr), site C (10yr) and site D (12yrs). Soil arthropods were extracted by Tullgren and species and enzyme activities (β-glucosidase and dehydrogenase) were related to residue properties. The natural establishment of large invertebrates such as earthworms and ants show that sites C and D are in late succession while site B had a large quantity of springtails and Dipteran larvae which typify early succession. The ten year old site showed 'best' soil quality and this was attributed to the lower Na and exchangeable sodium percentage exhibited.The combination of improved physico-chemical properties, increased vegetation diversity, greater biological activity and invertebrate establishment indicate that the alkaline and sodic residues can be rehabilitated to a semi-natural soil quality.