Sulfur biogeochemical cycling and novel Fe-S mineralization pathways in a tidally re-flooded wetland

Edward D. Burton, Richard T. Bush, Scott G. Johnston, Leigh A. Sullivan, Annabelle F. Keene

Research output: Contribution to journalArticle

88 Citations (Scopus)

Abstract

Sulfur biogeochemical cycling and associated Fe-S mineralization processes exert a major influence over acidity dynamics, electron flow and contaminant mobility in wetlands, benthic sediments and groundwater systems. While S biogeochemical cycling has been studied intensively in many environmental settings, relatively little direct information exists on S cycling in formerly drained wetlands that have been remediated via tidal re-flooding. This study focuses on a tidal wetland that was drained in the 1970s (causing severe soil and water acidification), and subsequently remediated by controlled re-flooding in 2002. We examine SO42- reduction rates and Fe-S mineralization at the tidal fringe, 7years after the commencement of re-flooding. The initial drainage of the wetland examined here caused in-situ pyrite (FeS2) oxidation, resulting in the drained soil layers being highly acidic and rich in SO42--bearing Fe(III) minerals, including jarosite (KFe3(SO4)2(OH)6). Tidal re-flooding has neutralized much of the previous acidity, with the pore-water pH now mostly spanning pH 5-7. The fastest rates of in-situ SO42- reduction (up to ~300nmolcm-3day-1) occur within the inter-tidal zone in the near-surface soil layers (to ~60cm below ground surface). The SO42- reduction rates correlate with pore-water dissolved organic C concentrations, thereby suggesting that electron donor supply was the predominant rate determining factor. Elemental S was a major short-term product of SO42- reduction, comprising up to 69% of reduced inorganic S in the near-surface soil layers. This enrichment in elemental S can be partly attributed to interactions between biogenic H2S and jarosite - a process that also contributed to enrichment in pore-water Fe2+ (up to 55mM) and SO42- (up to 50mM). The iron sulfide thiospinel, greigite (Fe3S4), was abundant in near-surface soil layers within the inter- to sub-tidal zone where tidal water level fluctuations created oscillatory redox conditions. There was evidence for relatively rapid pyrite re-formation within the re-flooded soil layers. However, the results indicate that pyrite re-formation has occurred mainly in the lower formerly drained soil layers, whereas the accumulation of elemental S and greigite has been confined towards the soil surface. The discovery that pyrite formation was spatially decoupled from that of elemental S and greigite challenges the concept that greigite is an essential precursor required for sedimentary pyrite formation. In fact, the results suggest that greigite and pyrite may represent distinct end-points of divergent Fe-S mineralization pathways. Overall, this study highlights novel aspects of Fe-S mineralization within tidal wetlands that have been drained and re-flooded, in contrast to normal, undisturbed tidal wetlands. As such, the long-term biogeochemical trajectory of drained and acidified wetlands that are remediated by tidal re-flooding cannot be predicted from the well-studied behaviour of normal tidal wetlands.

Original languageEnglish
Pages (from-to)3434-3451
Number of pages18
JournalGeochimica et Cosmochimica Acta
Volume75
Issue number12
DOIs
Publication statusPublished - 2011
Externally publishedYes

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Wetlands
Sulfur
greigite
wetland
sulfur
mineralization
Soils
pyrite
flooding
porewater
jarosite
Water
Acidity
acidity
Bearings (structural)
flooded soil
electron
Electrons
Acidification
iron sulfide

Cite this

Burton, Edward D. ; Bush, Richard T. ; Johnston, Scott G. ; Sullivan, Leigh A. ; Keene, Annabelle F. / Sulfur biogeochemical cycling and novel Fe-S mineralization pathways in a tidally re-flooded wetland. In: Geochimica et Cosmochimica Acta. 2011 ; Vol. 75, No. 12. pp. 3434-3451.
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Sulfur biogeochemical cycling and novel Fe-S mineralization pathways in a tidally re-flooded wetland. / Burton, Edward D.; Bush, Richard T.; Johnston, Scott G.; Sullivan, Leigh A.; Keene, Annabelle F.

In: Geochimica et Cosmochimica Acta, Vol. 75, No. 12, 2011, p. 3434-3451.

Research output: Contribution to journalArticle

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AU - Burton, Edward D.

AU - Bush, Richard T.

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