Revegetation of heavy metal contaminated mine dumps using locally serpentine-adapted grassland species

Abstract

Experimental studies with conventional rehabilitation methods have proven unsuccessful to rehabilitate chrysotile tailings. This is largely due to the unfavourable macro-element ratios and elevated heavy metal concentrations of chrysotile tailings and associated natural soil. This paper investigates the rehabilitation of ameliorated chrysotile tailings using locally adapted ecotypes and available soil. The experimental plots were established in 1995 and were evaluated during 1997, 2002 and 2003 by estimating the crown cover in a 0.5m x 0.1m quadrat. This study reports on the change in vegetation composition during the eight-year period as well as the nutrient status of the topsoil of rehabilitated areas in comparison to chrysotile tailings and natural soil. Typical of serpentine soils, the exchangeable magnesium is abnormally high (9 003.67 ± 1 375.81 mg kg - 1 ) and calcium is nearly devoid (5.4-8.5mg kg - 1 ). The nutrient status of the topsoil on the rehabilitation trials compared favourably with the natural soil samples and could sustain a locally adapted grass cover. The experimental site was initially colonised by Melinis repens and other pioneer grasses. The successional trend portrayed by the DCA predicts that with proper amelioration and topsoil cover, vegetation would develop towards grasslands consisting predominantly of the perennial grasses Hyperthelia disso - luta , Cymbopogon excavatus , Themeda triandra and Heteropogon contortus .