A. H. Grigg

A field study conducted at Kidston Gold Mine, to evaluate the impact of arsenic and zinc from mine tailing to grazing cattle

The grazing trial at Kidston Gold Mine, North Queensland, was aimed specifically to assess the uptake of metals from the tailing and the potential for unacceptable contamination of saleable meat. Further aims included estimating metal dose rates and identifying potential exposure pathways including plant uptake of heavy metals, mine tailings adhered to plants and direct ingestion of mine tailing. It was found that of the 11 metals analysed (As, Zn, Co, Cd, Cr, Sn, Pb, Sb, Hg, Se and Ni) in the animals liver, muscle and blood during the 8-month trial period, only accumulation of arsenic and zinc occurred. A risk assessment including these two metals was conducted to determine the potential for chronic metal toxicity and long-term contamination, using the estimates of metal dose rate. It was concluded that no toxicity or long-term contamination in cattle was likely at this site. Management procedures were therefore not required at this site; however, the results highlight percent ground cover and standing dry matter (DM) as important factors in decreasing metal exposure from direct ingestion of tailings and dust adhered to plants.

The effect of organic mulch amendments on the physical and chemical properties and revegetation success of a saline-sodic minespoil from central Queensland, Australia

Saline-sodic clay minespoil materials excavated during open-cut coal mining in central Queensland, Australia, pose significant challenges for revegetation, particularly where suitable topsoil capping is not available. We examined the ability of sawdust or straw mulch amendments to ameliorate the adverse properties of these minespoils and improve the success of revegetation efforts. In laboratory studies, mulch application improved infiltration, increased soil moisture retention and reduced surface crust strength. In the field, mulches incorporated to a depth of 0.15 m at application rates of at least 20 t/ha straw or 80 t/ha sawdust were needed to mitigate against capillary rise of salts during drying cycles and support satisfactory vegetation cover. Further research is needed to determine whether improvements are maintained beyond the 4-year trial period reported here.

Litter decomposition on directly revegetated tailings at the Kidston Gold Mine, North Queensland, Australia

An investigation of litter decomposition was undertaken at the Kidston Gold Mine in north Queensland, Australia with the aim of assessing the status of nutrient cycling capacity on a directly-revegetated tailings dam. Weight losses from leaf litter contained in litterbags placed in a 5-year old revegetated section of the dam were not significantly different from losses observed at two unmined reference sites over the 18 month study period, representing a rapid improvement in nutrient cycling capacity in the reconstructed ecosystem. However, fitted decay curves for each site predicted a slower decay constant and a longer litter half-life on the dam, which indicated that full pre-mining capability had not yet been achieved. Weight loss in the reconstructed system was most constrained by the low build-up of microbial biomass within the surface soil, which is expected to take at least 10 years to achieve pre-mining levels. In contrast, weight losses in the unmined sites appeared more related to the abundance of invertebrate fauna rather than microbial content. The results presented here of a developing system suggest that the importance of different factors affecting decomposition will reflect those that are most limiting over the course of ecosystem recovery. Additional

The effect of organic mulches on crusting, infiltration and salinity in the revegetation of a saline-sodic coal mine spoil from central Queensland, Australia

Dumping of saline-sodic clay spoil materials at the surface during open-cut coal mining in central Queensland, Australia, poses significant challenges for revegetation, particularly where suitable capping media are not available. Infiltration is low and surface crusting can be severe, limiting seedling emergence and the entry of water into the soil profile and subsequent leaching of salts from the root-zone. High salinities in themselves further limit the availability of water to plants. We examined the role of two different organic mulch amendments (sawdust and straw), either surface-applied or incorporated, in improving plant establishment on a saline-sodic spoil under the sub-tropical climate in central Queensland. Laboratory studies indicated that application of a surface mulch cover improved infiltration, increased surface soil moisture, and reduced surface crust strength. However, under field conditions downward migration of salts out of the root-zone was limited, with consequent negative impacts on overall revegetation success. Recommendations are made on revegetation strategies for saline-sodic spoils in the region. Additional keywords: reclamation, salinity, crusting, straw, sawdust.

A PRELIMINARY MODEL TO PREDICT RAINFALL USE EFFICIENCY OF PASTURES ON OPEN-CUT COAL MINES IN CENTRAL QUEENSLAND, AUSTRALIA 1

Cattle grazing is a potential post-mining land-use option for open-cut coal mines in the dry sub-tropical region of central Queensland, Australia, but no research has been conducted to determine the grazing capacity of these lands. A study was conducted to develop a model for estimating pasture productivity of rehabilitated mined lands, from which long-term sustainable stocking rates could be predicted. Rainfall-use efficiency (RUE), a reliable indicator of pasture productivity in this moisture-limited environment, was calculated for 17 plots across three minesites over a single growing season, and related by linear regression and stepwise multiple linear regression to several site and mine-soil properties. Plots were dominated by Cenchrus ciliaris (buffel grass), and ranged in age from 3 to 25 years since establishment. Slope (r 2 =0.45) and surface cover (r 2 =0.44) were most strongly correlated with RUE. These factors were interpreted as affecting surface retention of rainfall. The factors most correlated with RUE from multiple linear regression were slope (r 2 = 0.45), surface soil exchangeable Mg (cumulative r 2 = 0.71) and surface exchangeable sodium percentage (ESP) (cumulative r 2 = 0.77). ESP is a measure of soil dispersion and surface crusting, which when combined with slope (negative correlation), influenced the ability of incident rainfall to enter the soil profile. Mg was interpreted as a surrogate soil fertility factor, as Mg was strongly correlated with soil total N (r 2 =0.53) and cation exchange capacity (r 2 =0.74). Dry matter yield and RUE results are generally consistent with those observed on unmined pastoral lands in the region, but data from additional sites and over more seasons are required to fully develop and validate the model for minesite conditions.