Iron Monosulfide Distribution in Three Coastal Floodplain Acid Sulfate Soils, Eastern Australia

摘要

The distribution of iron monosulfide (quantified as acid volatile sulfur: SAV) was compared with geornchemical properties that are known to affect its formation and accumulation in three coastal Holocene acid rnsulfate soils (ASS) at Tuckean Swamp, McLeods Creek and Bungawalbyn Swamp respectively. These properrnties included pH, reactive iron (FeR), pore-water sulfate (SO42-) and organic carbon (OC). Iron monosulfide rnwas concentrated at the oxic/anoxic boundary. The Tuckean Swamp and McLeods Creek sites are Holocene rnsediments, whereas the Bungawalbyn Swamp is a Holocene peat. The concentration of SAV averaged 0.2rng kg-1 in a 0.5 m thick soil layer at the Tuckean Swamp, but was an order of magnitude lower in the rnoxic/anoxic transition layers at McLeods Creek and Bungawalbyn Swamp. The SAV mineral greigite (FesS4)rnwas identified in the Tuckean Swamp by X-ray diffraction and scanning electron microscopy with quantitative rnenergy dispersive X-ray analysis (SEM-EDX). Very small concentrations of greigite were also observed in the rnMcLeods Creek, based on crystal morphology and elemental composition. The concentration of SAV was a rnsmall fraction of the total reduced sulfur, representing at most 3% of the pyrite sulfur. However, the presence rnof this highly reactive sulfide mineral, distributed within pores where oxygen diffusion is most rapid, has rnimportant implications to the potential rate of acid production from these sediments.