Natural background concentrations of trace elements in Australian soils using overbank sediments as sampling media
1Faculty of Agriculture, Food and Natural Resource, The University of Sydney, NSW 2006, Australia.
2Cooperative Research Centre for Landscape Environments & Mineral Exploration (CRC LEME), c/-Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia.
Defining natural background concentrations of pollution-sensitive elements in sediments and soils is essential to appraise the impact of human activities on the environment. However, trace elements in soils tend to have very large background concentration ranges (two to three orders of magnitude are not uncommon). Moreover, due to long-range transport of some trace elements, not all surface soils can a priori be considered free of anthropogenic contamination. An ideal sampling medium should be able to record both the natural trace element concentrations of the near-surface environment as well as the anthropogenic inputs. Overbank sediments are very suitable for this purpose, because in the subsurface they reflect natural background concentrations of trace elements, whilst at the surface they may record the impact of human activities. Trace element concentrations covary with major elements and soil properties, and these relationships can be used to distinguish between naturally occurring and anthropogenic concentrations. Despite widespread use of overbank sediments in environmental monitoring programs in many European countries, and its easy availability in Australia, the technique has only been used here recently, in the Riverina region. The present collaborative project between University of Sydney and CRC LEME/Geoscience Australia has been started in the southeastern highlands and alpine regions of Australia to (i) contribute to the evaluation of the use of overbank sediments for environmental investigations in Australia, (ii) determine the background concentrations of trace elements there, (iii) investigate correlations between soil bulk properties and trace element concentrations, (iv) determine the influence of parent material over trace element status of soils, and (v) produce a GIS-based geochemical atlas for these regions. Bioregions are relatively large land areas characterized by broad, landscape-scale natural features and environmental processes that influence the functions of entire ecosystems. Across Australia some 85 bioregions have been identified. This project with aforementioned objectives will pay its attention to two of the bioregions (South Eastern Highland and Australian Alps) of Australia. The sampling sites (spill points of large catchments) have been located using ArcHydro™ to obtain samples that will best represent the whole catchments. Sampling sites will be accessed and samples will be collected (one surface sample, 0-10 cm, and one bottom sample, ~80-90 cm) from each overbank sediment profile. Samples will be characterized for various physical and chemical properties. Total abundance of major and trace elements will be determined by ICP-MS and XRF. Further, XRD technique will be employed for the assessment of mineralogical composition of the samples. Data will be analyzed statistically and single and multi-element maps will be produced using GIS.