Soil mesofauna as bioindicators to assess environmental disturbance at a platinum mine

Abstract

South Africa is rich in mineral resources and is one of the leading raw material exporters in the world, of which the more important are gold, diamonds and platinum. Mining is essential for economic development, but also has detrimental environmental consequences, namely in the form of chemical waste products (including a range of heavy metals) which are contained in the effluent being dumped as tailing dam material. It is well known that such tailings may contain metals such as Cu, Zn, Mn, Ni, Al, Pb, Fe and Cd, constituting a range of potential environmental hazards. The aim of this study was to investigate the utilization of soil mesofauna in the assessment of environmental disturbance at different distances away from a tailings dam by comparing the species data with the soil metal analysis. It was also deemed necessary to determine which species or functional groups were influenced most by the metals found in the soil. Six random soil samples (replicates) were collected at seven sites on and away from the tailings dam and mesofauna was extracted. Sampling was done four times over a period of one year during the following months: August 2005, December 2005, March 2006 and May 2006. Both the soil and the mesofauna were physically and chemically analysed. Statistical analysis indicated that some metal concentrations decreased when moving further away from the tailings dam. These specific metals (Cu, Cr and Ni), which are consistent with platinum tailings material, apparently had the greatest influence on the soil mesofauna sampled. Only a few mite species dominated the two sites on the tailings dam, representing the prostigmatic-, cryptostigmatic- and the mesostigmatic taxa. Prostigmatic species were present in the most disturbed areas and may be a good candidate for further bioindication studies. A metal pollution gradient exists at the sites that were sampled and species richness generally increased towards the more natural environment. Seasonal variation was evident in the soil data, as well as in the species data.