Catchment outlet sediments (0–10 cm depth, sieved to <2 mm) collected at a very low density over most of the Australian continent have been analysed using the Mobile Metal Ion (MMI®) partial extraction technique. Of the 54 elements determined, eight are generally regarded as essential nutrients for plant growth: Ca, Cu, Fe, K, Mg, Mn, P and Zn. A further three, Mo, Ni and Se are considered significant micronutrients. Estimation of ‘bioavailability’ from MMI® analysis gives results comparable with standard agricultural measurements for many nutrients. Percentage ‘bioavailability’, operationally defined here as the ratio of MMI® concentration to total element concentration, has been investigated and ranges from 31% for Se to 0.1% for Fe. Smoothed (kriged) colour raster maps for continental Australia have been produced for these 11 nutrients and interpreted in terms of lithology (e.g. presence of carbonates in the MMI® Ca map), mineralization (e.g. known mineral districts in the Cu and Zn maps), environmental processes (e.g. salinity in K map, weathering and acid generation in Fe map) and agricultural practices (e.g. application of fertilizers in the MMI® P map). This first application of a partial extraction technique at the scale of a continent has yielded meaningful, coherent and interpretable results.
- catchment outlet sediment sampling
- MMI® extraction
- ICP-MS analysis
- geochemical mapping
- Received November 11, 2011.
- Accepted April 24, 2012.
- © 2012 AAG/Geological Society of London