Abundance and fractionation of Al, Fe and trace metals following tidal inundation of a tropical acid sulfate soil

作者：Johnston Scott G^*; Burton Edward D; Bush Richard T; Keene Annabelle F; Sullivan Leigh A; Smith Douglas; McElnea Angus E; Ahern Col R; Powel Bernard

来源：Applied Geochemistry, 2010, 25(3): 323-335.

DOI：10.1016/j.apgeochem.2009.11.015

Tidal inundation was restored to a severely degraded tropical acid sulfate soil landscape and subsequent changes in the abundance and fractionation of Al, Fe and selected trace metals were investigated After 5 a of regular tidal inundation there were large decreases in water-soluble and exchangeable Al fractions within former sulfuric horizons. This was strongly associated with decreased soil acidity and increases in pH, suggesting pH-dependent immobilisation of Al via precipitation as poorly soluble phases The water-soluble fractions of Fe, Zn, Ni and Mn also decreased. However, there was substantial enrichment (2-5x) of the reactive Fe fraction (Fe(R); 1 M HCl extractable) near the soil surface, plus a closely corresponding enrichment of 1 M HCl extractable Cr, Zn, Ni and Mn. Surficial accumulations of Fe(III) minerals in the inter-tidal zone were poorly crystalline (up to 38% Fe(R)) and comprised mainly of schwertmannite (Fe(8)O(8)(OH)(6)SO(4)) with minor quantities of goethite (alpha-FeOOH) and lepidocrocite (gamma-FeOOH) These Fe (III) mineral accumulations provide an effective substrate for the adsorption/co-precipitation and accumulation of trace metals Arsenic displayed contrary behaviour to trace metals with peak concentrations (similar to 60 mu g g(-1)) near the redox minima Changes in the abundance and fractionation of the various metals can be primarily explained by the shift in the geochemical regime from oxic-acidic to reducing-circumneutral conditions, combined with the enrichment of reactive Fe near the soil Surface Whilst increasing sequestration of trace metals via sulfidisation is likely to occur over the long-term, the current abundance of reactive Fe near the sediment-water interface favours a dynamic environment with respect to metals in the tidally inundated areas.

• 出版日期2010-3