Arsenic mobilization in a seawater inundated acid sulfate soil

Scott G. Johnston, Annabelle F. Keene, Edward D. Burton, Richard T. Bush, Leigh A. Sullivan, Angus E. Mcelnea, Col R. Ahern, C. Douglas Smith, Bernard Powell, Rosalie K. Hocking

Research output: Contribution to journalArticlepeer-review

67 Citations (Scopus)


Tidal seawater inundation of coastal acid sulfate soils can generate Fe- and SO4-reducing conditions in previously oxicacidic sediments, This creates potential for mobilization of As during the redox transition. We explore the consequences for As by investigating the hydrology, porewater geochemistry, solid-phase speciation, and mineralogical partitioning of As across two tidal fringe toposequences. Seawater inundation induced a tidally controlled redox gradient. Maximum porewater As (∼400μg/L) occurred in the shallow (<1 m), intertidal, redox transition zone between Fe-oxidizing and SO 4-reducing conditions. Primary mechanisms of As mobilization include the reduction of solid-phase As(V) to As(III), reductive dissolution of As(V)-bearing secondary Fe(III) minerals and competitive anion desorption. Porewater As concentrations decreased in the zone of contemporary pyrite reformation, Oscillating hydraulic gradients caused by tidal pumping promote upward advection of As and Fe2+-enriched porewater in the intertidal zone, leading to accumulation of As(V)-enriched Fe(III) (hydr)oxides at the oxic sediment-water interface. While this provides a natural reactive-Fe barrier, it does not completely retard the flux of porewater As to overtopping surface waters. Furthermore, the accumulated Fe minerals may be prone to future reductive dissolution, A conceptual model describing As hydro-geochemical coupling across an intertidal fringe is presented.

Original languageEnglish
Pages (from-to)1968-1973
Number of pages6
JournalEnvironmental Science and Technology
Issue number6
Publication statusPublished - 2010
Externally publishedYes


Dive into the research topics of 'Arsenic mobilization in a seawater inundated acid sulfate soil'. Together they form a unique fingerprint.

Cite this