Sulfur Minerals Cause Acidification of Aquic Podosols On the Swan Coastal Plain, Western Australia.

The very sandy soils on the Swan Coastal Plain, WA consist predominantly of former beach deposits deposited as dunes by the wind.  The Bassendean Dunes are the oldest dune system in this area and are heavily leached consisting of quartz with very little clay.  Drying of the Bassendean dunes due to water extraction and climate change has caused severe acidification.

Wetlands in the Bassendean Dune system are low lying interdunal swales and contain aquic podosols which are acid sulfate soils.  Electron microscopy with EDS/SAD, TEM and synchrotron XRD showed that pyrite, elemental sulfur and rarely marcasite and jarosite are present in these podosols.  Two pyrite morphologies are present: discrete submicron single crystals and 10-20 μm framboids.  The high surface area of pyrite combined with the poor buffering capacity of podosols causes rapid oxidation and acidification of these wetland systems which is likely to persist due to the steadily dropping groundwater table.  Acid buffering capacity is provided by kaolin, gibbsite, Fe-oxides, allophane and minor primary minerals (feldspar, mica, etc) but these are poorly effective buffering agents.