Vegetation response of Australian native grass species redgrass (Bothriochloa macra (Steudel) S.T. Blake) and spider grass (Enteropogon acicularis (Lindl.) Lazarides) in saline and arsenic contaminated gold mine tailings: A glasshouse study

The stabilization of sulphidic wastes produced by underground gold mining is challenging because these materials are often structureless, saline and contain elevated levels of toxic metalloids. A glasshouse study was conducted to test a milled benign waste rock and topsoil. The test species were, Bothriochloa macra (Steud) S.T. Blake and Enteropogon acicularis (Lindl.) Lazarides, two warm season drought-tolerant native grasses from Australia with the potential to be used for phytostabilization. Rhizocylinders were used in order to examine root structures for plants grown in the various treatments. Soil water samples were also extracted from the various substrates and analyzed for soluble arsenic (As), along with pH, electrical conductivity and redox potential. Growth trials were carried out for 100 days. Growth indices, including biomass accumulation, leaf area, root:shoot ratio and chlorophyll fluorescence were measured along with relative growth rate (RGR) calculations. Results showed a significant decrease in growth across all growth indices for grasses grown on mine tailings. An oxidized waste rock layer and topsoil exhibited high growth, especially for the species E. acicularis. Small amounts of As were detected in the leaf tissue of B. macra and E. acicularis after growth in As contaminated substrates, but it was found that As levels in plant tissue did not correlate with As levels in the soil water. These grasses did not readily accumulate As, and it is highly unlikely that any As contained in the grass material will biomagnified through the food chain or increase environmental pollution from mine sites. Substrate analysis found the highest bioavailable levels of As occurred in the crushed oxidized rock matrix. However, when compared to growth results, this substrate supported significantly high growth.