Tona Sanchez-Palacios

The successful establishment of vegetation on mine waste tailings relies on the ability of the substrate to sustain plant growth. The phytocap defined as the surface cover system of plants and substrate can convert impacted non-arable mined land into fertile land suitable for cultivation while additionally stabilising tailings. The aim of this study was to investigate the potential to cultivate a fast-growing crop such as industrial hemp (Cannabis sativa L.) as a model plant for phytocapping of mineral waste tailings amended with mixed waste organic outputs (MWOO) from the suburbs of South Sydney, as the capping layer. Chemical characterisation of MWOO revealed high levels of heavy metals including Zn and Pb. Control studies using rhizo lysimeters in the glasshouse showed the potential to cultivate industrial hemp plants in MWOO. Regardless of the content of heavy metals in MWOO, industrial hemp plants showed no symptoms of metal toxicity or deficiency. Determination of total chlorophyll and leaf transpiration confirmed the ability of industrial hemp plants to tolerate high levels of metals in MWOO. Relative stem height growth and total biomass production were used as indicators of performance and showed that MWOO provided the nutrition requirements to cultivate a fast-growing crop such as industrial hemp. Root growth analysis in rhizo lysimeters showed the ability of hemp roots to physically stabilise the MWOO. Determination of soil moisture analysis in rhizo lysimeters showed an increase in evapotranspiration rate with plant development. Further studies will include determination of metals in leachates and below and above ground parts of hemp plants.

An experimental tailings research facility was constructed to allow long-term trials to be conducted in order to investigate the performance and variation in growth and arsenic foliar content in 16 taxa of eucalypts comprising five Eucalyptus spp. with various provenances. A 30 cm deep cover of slurried oxide waste residue was poured on to consolidated arsenic-rich sulphidic gold tailings and was capped with a 10 cm layer of local topsoil. The Eucalyptus were planted in September 2008. The study reported here focusses on the growth responses of candidate Eucalyptus species and provenances in relation to substrate variables (cover depth and arsenic mobility). Three provenances of Eucalyptus cladocalyx grew the fastest and, on average, produced the largest stem volumes. The local provenance of E. goniocalyx was the poorest. Among the other species, Corymbia maculata with provenances from New South Wales and Western Australia (WA) ranked second, E. camaldulensis with provenances from Victoria, WA and South Australia ranked third, and E. tricarpa ranked after these. Owing to its ability to grow under arsenic-rich conditions, more detailed testing of E. cladocalyx involving long-term monitoring of growth, biomass partitioning and foliar arsenic content is required to improve the selection of suitable species and provenances for use in arsenical mineral waste rehabilitation.