Liberation of acidity and arsenic from schwertmannite : Effect of fulvic acid
- Authors: Vithana, Chamindra , Sullivan, Leigh , Burton, Edward , Bush, Richard
- Date: 2014
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 372, no. (2014), p. 1-11
- Full Text: false
- Reviewed:
- Description: Schwertmannite is one of the major components that produces acidity in acid mine drainage (AMD) and acid sulfate soils (ASS) and is also known to be an effective scavenger of Arsenic (As) in such environments. Fulvic acid (FA) is an active component of natural organic matter (NOM) and is known to interact strongly with both schwertmannite and As. Two main environmental hazards related to schwertmannite are acidity liberation and potential re-mobilization of adsorbed or co-precipitated As upon hydrolysis. This study focused on understanding the behaviour of As-substituted schwertmannite with regard to the potential of acidity liberation, the effect of FA on acidity liberation from both pure and As-substituted synthetic schwertmannites, and the effect of FA on arsenic mobilization from As-substituted synthetic schwertmannite. This was investigated by means of short-term (48. h) titrations. The liberation of acidity from As-substituted schwertmannite and the effect of FA were examined at two pH values (i.e. 4.5 and 6.5) typical for ASS environments.As-substituted schwertmannite liberated a greater amount of acidity in comparison to pure schwertmannite at both pHs. Concentration of FA and pH each showed a strong influence on the liberation of acidity from both pure and As-schwertmannite. At the acidic pH (4.5), FA inhibited acidity liberation from schwertmannite. At the near neutral pH of 6.5, the concentration of FA played a critical role in affecting the liberation of acidity from schwertmannite. The initial liberation of acidity was enhanced from pure schwertmannite at pH6.5 by low FA concentration (1mgL-1) and from As-schwertmannite by both low (1mgL-1) and moderate (10mgL-1) FA concentrations. Interestingly, higher FA concentrations (25mgL-1) inhibited acidity liberation from both types of schwertmannite in comparison to the control (pure/As-schwertmannite titrated without added FA). FA enhanced the liberation of As from the As-schwertmannite at both pHs under oxidising conditions and the rate of As liberation was greater at the near neutral pH. The present study provides new insights on the effect of As-substitution on acidity liberation from schwertmannite and the role of FA on: a) liberation of acidity, and b) As mobilization, from schwertmannite. © 2014.
Mobility of arsenic and selected metals during re-flooding of iron- and organic-rich acid-sulfate soil
- Authors: Burton, Edward , Bush, Richard , Sullivan, Leigh , Johnston, Scott , Hocking, Rosalie
- Date: 2008
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 253, no. 1-2 (2008), p. 64-73
- Full Text: false
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- Description: The drainage-induced oxidation of iron-sulfide minerals in acid-sulfate soils has adversely affected large areas of coastal floodplains. Re-flooding of these soils, via the re-establishment of more natural drainage regimes, is a potential remediation approach. Here we describe the mobility of Al, As, Fe, Mn, Ni and Zn during controlled re-flooding of an Fe- and organic-rich acid-sulfate soil material. Soil re-flooding caused the onset of microbially-mediated Fe(III)-reduction, which raised the pH of the initially acidic (pH 3.4) soil to pH 6.0 to 6.5, thereby immobilizing Al. The process of Fe(III)-reduction released high concentrations of FeII and was associated with significant mobilization of As. During the early stages of re-flooding, FeII mobility was controlled by dissolution of schwertmannite (Fe8O8(OH)6SO4) with an ion activity product (IAP) of 1019 ± 2. The mobility of FeII was subsequently controlled by the precipitation of siderite (FeCO3) with an IAP spanning 10- 10 to 10- 7.5. The formation of acid-volatile sulfide (AVS), as a product of SO4-reduction, further retarded the mobility of FeII. Interactions with AVS also strongly immobilized Mn, Ni and Zn, yet had little effect on As which remained relatively mobile in the re-flooded soil. This study shows that the mobilization of As and Fe during soil re-flooding should be considered when planning remediation approaches for acid-sulfate soils. © 2008 Elsevier B.V. All rights reserved.
Metal partitioning dynamics during the oxidation and acidification of sulfidic soil
- Authors: Claff, Salirian , Burton, Edward , Sullivan, Leigh , Bush, Richard
- Date: 2011
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 286, no. 3-4 (2011), p. 146-157
- Full Text: false
- Reviewed:
- Description: The oxidation and acidification of sulfidic soil can lead to changes to metal mobility that can have far-reaching environmental consequences. In this study, we examined changes in the partitioning and mobility of Fe, Cr, Cu, Mn, Ni and Zn in four sulfidic soils, due to sulphide oxidation driven acidification, over a 90. day period. These changes were examined using a novel six-step sequential extraction procedure specifically developed for acid sulphate soil materials. The results demonstrate two distinct steps for the mobilisation of metals in disturbed acid sulphate soil materials, associated with (i) oxidation and (ii) acidification. Initially, oxidation causes metals to be redistributed from the "pyritic" and "organic" fractions to the "acid-soluble" fraction. Subsequent acidification, due to exceedance of the acid neutralising capacity of the soil, drives the release of metals to the "labile" fraction. This study demonstrates the importance of these metal pools in understanding the short-term processes which mobilise metals in sulfidic soils. © 2011 Elsevier B.V.
Iron geochemical zonation in a tidally inundated acid sulfate soil wetland
- Authors: Johnston, Scott , Keene, Annabelle , Bush, Richard , Burton, Edward , Sullivan, Leigh , Isaacson, Lloyd , McElnea, Angus , Ahern, Col , Smith, C. Douglas , Powell, Bernard
- Date: 2011
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 280, no. 3-4 (2011), p. 257-270
- Full Text: false
- Reviewed:
- Description: Tidal inundation is a new technique for remediating coastal acid sulfate soils (CASS). Here, we examine the effects of this technique on the geochemical zonation and cycling of Fe across a tidally inundated CASS toposequence, by investigating toposequence hydrology, in situ porewater geochemistry, solid-phase Fe fractions and Fe mineralogy. Interactions between topography and tides exerted a fundamental hydrological control on the geochemical zonation, redistribution and subsequent mineralogical transformations of Fe within the landscape. Reductive dissolution of Fe(III) minerals, including jarosite (KFe3(SO4)2(OH)6), resulted in elevated concentrations of porewater Fe2+ (>30mmol L-1) in former sulfuric horizons in the upper-intertidal zone. Tidal forcing generated oscillating hydraulic gradients, driving upward advection of this Fe2+-enriched porewater along the intertidal slope. Subsequent oxidation of Fe2+ led to substantial accumulation of reactive Fe(III) fractions (up to 8000μmol g-1) in redox-interfacial, tidal zone sediments. These Fe(III)-precipitates were poorly crystalline and displayed a distinct mineralisation sequence related to tidal zonation. Schwertmannite (Fe8O8(OH)6SO4) was the dominant Fe mineral phase in the upper-intertidal zone at mainly low pH (3-4). This was followed by increasing lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) at circumneutral pH within lower-intertidal and subtidal zones. Relationships were evident between Fe fractions and topography. There was increasing precipitation of Fe-sulfide minerals and non-sulfidic solid-phase Fe(II) in the lower intertidal and subtidal zones. Precipitation of Fe-sulfide minerals was spatially co-incident with decreases in porewater Fe2+. A conceptual model is presented to explain the observed landscape-scale patterns of Fe mineralisation and hydro-geochemical zonation. This study provides valuable insights into the hydro-geochemical processes caused by saline tidal inundation of low lying CASS landscapes, regardless of whether inundation is an intentional strategy or due to sea-level rise. © 2010 Elsevier B.V.
Sulfur biogeochemical cycling and novel Fe-S mineralization pathways in a tidally re-flooded wetland
- Authors: Burton, Edward , Bush, Richard , Johnston, Scott , Sullivan, Leigh , Keene, Annabelle
- Date: 2011
- Type: Text , Journal article
- Relation: Geochimica et Cosmochimica Acta Vol. 75, no. 12 (2011), p. 3434-3451
- Full Text: false
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- Description: 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. © 2011 Elsevier Ltd.
Stable sulfur isotope dynamics in an acid sulfate soil landscape following seawater inundation
- Authors: Maher, Crystal , Sullivan, Leigh
- Date: 2016
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 439, no. (2016), p. 205-212
- Full Text: false
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- Description: In 2002 a tidally driven seawater exchange remediation strategy was successfully implemented on a severely acidified tropical coastal landscape dominated by acid sulfate soils (ASS) in northern Australia. This study examined changes in the stable sulfur isotope signatures in a range of sulfide and sulfate (SO4) fractions at three sites with different levels of exposure to the tidally driven seawater exchange remediation. delta S-34 in the acid soluble SO4 fraction (e.g. jarosite) was less depleted in S-34 than the corresponding sulfide, indicating a degree of fractionation during sulfide oxidation and jarosite precipitation. The delta S-34 ofjarositic-SO4 was similar at all three sites indicating the appreciable stability of jarositic-SO4 even after extended exposure to seawater. delta S-34 of the water soluble, exchangeable and schwertmannitic-SO4 reflect conditions post remediation and indicate the relative contributions from two potential SO4 sources - a lighter SO4 derived from the oxidation of pyrite, and a heavier SO4 derived from the seawater. The delta S-34 of the contemporary surficial sulfide accumulations also reflect a SO4 contribution from seawater used for remediation and were isotopically different from the relict sulfides found at depth at all sites. delta S-34 of water soluble sulfate allowed the progress of the remediation to be traced down the soil profile. This study demonstrates the utility of stable sulfur isotope signatures in various sulfide and SO4 fractions to trace the sulfur geochemical pathways occurring in soils, in this case as a result of the introduction of tidally driven sea water. (C) 2016 Elsevier B.V. All rights reserved.
Jarosite quantification in soils : An enhanced sequential extraction procedure
- Authors: Vithana, Chamindra , Sullivan, Leigh , Bush, Richard , Burton, Edward
- Date: 2014
- Type: Text , Journal article
- Relation: Applied Geochemistry Vol. 51, no. (2014), p. 130-138
- Full Text: false
- Reviewed:
- Description: A two-step sequential extraction procedure established for the quantification of acidity producing ferric and ferrous sulfate minerals such as melanterite and jarosite in acid mine wastes was evaluated for quantification of jarosite spiked in soils. The procedure involves in sequence anoxic water extraction, roasting the solid residue after anoxic water extraction at 550. °C for 1. h, and 4. M HCl extraction of the roasted solid. Soil and quartz samples were spiked with known amounts of synthetic and natural jarosite and their recovery was measured using the suggested two-step sequential extraction procedure. The recoveries of synthetic and natural jarosite were calculated on the basis of the S contents of the initially spiked jarosite in soil and quartz samples. Less than 50% of the spiked jarosite was recovered. The missing S is partially attributable to the retention of jarosite by the Teflon filter membrane used during the filtration of the anoxic water extract. Further investigations also demonstrated a lower 4. M HCl-S extractability from jarosite samples roasted at 550. °C than those roasted at 450. °C. S recovery from jarosite-spiked quartz samples increased to 45-70% by replacing the Teflon filter membrane with the Cellulose Acetate filter membrane and including this filter paper in the second step roasting. This modified method is a step forward in the development of methods to accurately and reliably quantify jarosite in soil materials. © 2014 Elsevier Ltd.
A simple and inexpensive chromium-reducible sulfur method for acid-sulfate soils
- Authors: Burton, Edward , Sullivan, Leigh , Bush, Richard , Johnston, Scott , Keene, Annabelle
- Date: 2008
- Type: Text , Journal article
- Relation: Applied Geochemistry Vol. 23, no. 9 (2008), p. 2759-2766
- Full Text: false
- Reviewed:
- Description: A new chromium-reducible sulfur (CRS) method suitable for the quantification of reduced inorganic S (RIS) in acid-sulfate soils is presented. The new method utilises the reduction of RIS by an acidic Cr(II) solution within a sealed reaction chamber and diffusion of the produced H2S(g) into an alkaline Zn solution. It offers rapid sample processing times, without the need for large volumes of high-purity N2(g) or for specialized, expensive glassware. Examination of pyrite-talc mixtures containing up to 11.8% pyrite, revealed that the method achieves 95-98% recovery of RIS. A comparison between CRS measured by the new diffusion-based method and that measured by a standard purge-and-trap method for 25 pyritic soil samples shows a very strong (r2 = 0.996) linear relationship with a slope of 0.995. The ability of the new diffusion-based CRS method to achieve accurate and precise quantification of RIS in acid-sulfate soils is demonstrated. © 2008 Elsevier Ltd. All rights reserved.
Iron(III) accumulations in inland saline waterways, Hunter Valley, Australia : Mineralogy, micromorphology and pore-water geochemistry
- Authors: Isaacson, Lloyd , Burton, Edward , Bush, Richard , Mitchell, David , Johnston, Scott , Macdonald, Bennett , Sullivan, Leigh , White, Ian
- Date: 2009
- Type: Text , Journal article
- Relation: Applied Geochemistry Vol. 24, no. 10 (2009), p. 1825-1834
- Full Text: false
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- Description: Discharge of Fe(II)-rich groundwaters into surface-waters results in the accumulation of Fe(III)-minerals in salinized sand-bed waterways of the Hunter Valley, Australia. The objective of this study was to characterise the mineralogy, micromorphology and pore-water geochemistry of these Fe(III) accumulations. Pore-waters had a circumneutral pH (6.2-7.2), were sub-oxic to oxic (Eh 59-453 mV), and had dissolved Fe(II) concentrations up to 81.6 mg L-1. X-ray diffraction (XRD) on natural and acid-ammonium-oxalate (AAO) extracted samples indicated a dominance of 2-line ferrihydrite in most samples, with lesser amounts of goethite, lepidocrocite, quartz, and alumino-silicate clays. The majority of Fe in the samples was bound in the AAO extractable fraction (FeOx) relative to the Na-dithionite extractable fraction (FeDi), with generally high FeOx:FeDi ratios (0.52-0.92). The presence of nano-crystalline 2-line ferrihydrite (Fe5HO3·4H2O) with lesser amounts of goethite (α-FeOOH) was confirmed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED). In addition, it was found that lepidocrocite (γ-FeOOH), which occurred as nanoparticles as little as ∼5 lattice spacings thick perpendicular to the (0 2 0) lattice plane, was also present in the studied Fe(III) deposits. Overall, the results highlight the complex variability in the crystallinity and particle-size of Fe(III)-minerals which form via oxidation of Fe(II)-rich groundwaters in sand-bed streams. This variability may be attributed to: (1) divergent precipitation conditions influencing the Fe(II) oxidation rate and the associated supply and hydrolysis of the Fe(III) ion, (2) the effect of interfering compounds, and (3) the influence of bacteria, especially Leptothrix ochracea. © 2009 Elsevier Ltd. All rights reserved.
Effects of hyper-enriched reactive Fe on sulfidisation in a tidally inundated acid sulfate soil wetland
- Authors: Keene, Annabelle , Johnston, Scott , Bush, Richard , Sullivan, Leigh , Burton, Edward , McElnea, Angus , Ahern, Col , Powell, Bernard
- Date: 2011
- Type: Text , Journal article
- Relation: Biogeochemistry Vol. 103, no. 1 (2011), p. 263-279
- Full Text:
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- Description: Solid phase Fe and S fractions were examined in an acid sulfate soil (ASS) wetland undergoing remediation via tidal inundation. Considerable diagenetic enrichment of reactive Fe(III) oxides (HCl- and dithionite-extractable) occurred near the soil surface (0-0.05 m depth), where extremely large concentrations up to 3534 μmol/g accounted for ~90% of the total Fe pool. This major source of reactive Fe exerts a substantial influence on S cycling and the formation, speciation and transformation of reduced inorganic S (RIS) in tidally inundated ASS. Under these geochemical conditions, acid volatile sulfide (AVS; up to 57 μmol/g) and elemental sulfur (S0; up to 41 μmol/g) were the dominant fractions of RIS in near surface soils. AVS-S to pyrite-S ratios exceeded 2.9 near the surface, indicating that abundant reactive Fe favoured the accumulation of AVS minerals and S0 over pyrite. This is supported by the significant correlation of poorly crystalline Fe with AVS-S and S0-S contents (r = 0.83 and r = 0.85, respectively, P < 0.01). XANES spectroscopy provided direct evidence for the presence of a greigite-like phase in AVS-S measured by chemical extraction. While the abundant reactive Fe may limit the transformation of AVS minerals and S0 to pyrite during early diagenesis (~5 years), continued sulfidisation over longer time scales is likely to eventually lead to enhanced sequestration of S within pyrite (with a predicted 8% pyrite by mass). These findings provide an important understanding of sulfidisation processes occurring in reactive Fe-enriched, tidally inundated ASS landscapes. © 2010 Springer Science+Business Media B.V.
Schwertmannite transformation to goethite via the Fe(II) pathway : Reaction rates and implications for iron-sulfide formation
- Authors: Burton, Edward , Bush, Richard , Sullivan, Leigh , Mitchell, David
- Date: 2008
- Type: Text , Journal article
- Relation: Geochimica et Cosmochimica Acta Vol. 72, no. 18 (2008), p. 4551-4564
- Full Text: false
- Reviewed:
- Description: Schwertmannite (Fe8O8(OH)6SO4) is a common Fe(III)-oxyhydroxysulfate mineral in acid-sulfate systems, where its formation and fate strongly influence water quality. The present study examines transformation of schwertmannite to goethite (FeOOH), as catalyzed by interactions with Fe(II) in anoxic aquatic environments. This study also evaluates the role of the Fe(II) pathway in influencing the formation of iron-sulfide minerals in such environments. At pH > 5, the rates of Fe(II)-catalyzed schwertmannite transformation were several orders of magnitude faster than transformation in the absence of Fe(II). Complete transformation of schwertmannite occurred within only 3-5 h at pH > 6 and Fe(II)(aq) ≥ 5 mmol L-1. Model calculations indicate that the Fe(II)-catalyzed transformation of schwertmannite to goethite greatly decreases the reactivity of the Fe(III) pool, thereby favoring SO4-reduction and facilitating the formation of iron-sulfide minerals (particularly mackinawite, tetragonal FeS). Examination of in situ sediment geochemistry in an acid-sulfate system revealed that the rapid Fe(II)-catalyzed transformation was consistent with an abrupt shift from an acidic Fe(III)-reducing regime with abundant schwertmannite near the sediment surface, to a near-neutral mackinawite-forming regime where goethite was dominant. This study demonstrates that the Fe(II) pathway exerts a major influence on schwertmannite transformation and iron-sulfide formation in anoxic acid-sulfate systems. These findings have important implications for understanding acidity dynamics and trace element mobility in such systems. © 2008 Elsevier Ltd. All rights reserved.
Abundance and fractionation of Al, Fe and trace metals following tidal inundation of a tropical acid sulfate soil
- Authors: Johnston, Scott , Burton, Edward , Bush, Richard , Keene, Annabelle , Sullivan, Leigh , Smith, Douglas , McElnea, Angus , Ahern, Col , Powell, Bernard
- Date: 2010
- Type: Text , Journal article
- Relation: Applied Geochemistry Vol. 25, no. 3 (2010), p. 323-335
- Full Text: false
- Reviewed:
- Description: 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 (2-5×) of the reactive Fe fraction (FeR; 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% FeR) and comprised mainly of schwertmannite (Fe8O8(OH)6SO4) with minor quantities of goethite (α-FeOOH) and lepidocrocite (γ-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 (∼60 μg 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. © 2009 Elsevier Ltd. All rights reserved.
Quantifying alkalinity generating processes in a tidally remediating acidic wetland
- Authors: Johnston, Scott , Keene, Annabelle , Burton, Edward , Bush, Richard , Sullivan, Leigh
- Date: 2012
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 304-305, no. (2012), p. 106-116
- Full Text: false
- Reviewed:
- Description: Lime-assisted tidal exchange (LATE) is a new remediation technique that is demonstrably effective at decreasing acidity in coastal acid sulfate soils (CASS). However, the relative magnitude of the major in situ alkalinity generating processes and external alkalinity inputs that dominate neutralization of acidity during LATE have not been quantified. Here, we combine investigations of porewater and solid-phase geochemistry from a remediating CASS wetland to derive first-order estimates of alkalinity generating processes and inputs after 6years of LATE. Quantified inputs include: marine derived HCO 3 - from tidal exchange; hydrated lime additions; and in situ alkalinity from anaerobic metabolism of organic carbon coupled with reduction of iron and sulfate. A progressive increase in tidal inundation led to the development of significant relationships (α=0.01) between topography and both non-sulfidic, solid-phase Fe(II) and solid-phase reduced inorganic sulfur species. These topographic relationships were conjoined with a digital elevation model, enabling up-scaling of alkalinity estimates to a sub-catchment level. Estimates indicate the relative order of importance of alkalinity generating processes and inputs is Fe reduction (50-64%)>tidal exchange (25-42%)>sulfate reduction (7-13%)>>hydrated lime addition (<1%). Accurately attributing the relative contributions due to Fe and SO 4 2- reduction was limited by an inability to distinguish between non-sulfidic, solid-phase Fe(II) generated by microbial dissimilatory reduction of Fe(III) or chemical reduction of Fe(III) by H 2S. Nevertheless, the combined alkalinity contribution of these two electron accepting processes accounts for between 58 and 74% of the total. The majority (>99%) of net alkalinity generation was due to either tides or microbial metabolism. This indicates that the LATE remediation technique is both a cost effective means of decreasing soil acidity and is readily transferable to similar CASS landscapes - provided there is adequate supply of suitable electron donors and sufficient regenerative capacity in the adjacent estuarine/marine tidal HCO 3 - pool. © 2012 Elsevier B.V.
Enrichment and heterogeneity of trace elements at the redox-interface of Fe-rich intertidal sediments
- Authors: Keene, Annabelle , Johnston, Scott , Bush, Richard , Burton, Edward , Sullivan, Leigh , Dundon, Matthew , McElnea, Angus , Smith, C. Douglas , Ahern, Col , Powell, Bernard
- Date: 2014
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 383, no. (2014), p. 1-12
- Full Text: false
- Reviewed:
- Description: Redox-interfacial sediments can undergo radical geochemical changes with oscillating tides. In this study, we examine trace element enrichment and availability, at both landscape and pedon-scales, in the surface sediments of a remediating acidic tidal wetland. Fe-rich sediments at the surface-water interface (0-10. mm in depth) were collected across an elevation gradient spanning the supratidal to subtidal range. These sediments were analysed for solid phase Fe fractions and trace elements (As, Pb, Cr, Cu, Mn, Ni, Zn, V, B, Co, Mo, Ba and U) via dilute HCl-extractions and total digests. Their concentrations were compared with those of underlying (0.05-0.65. m in depth) former sulfuric horizon sediments of a coastal acid sulfate soil (CASS). Reactive Fe was enriched at the redox interface by up to 16 times (197. g. Fe/kg) that of the former sulfuric horizon. The proportion of total trace elements associated with reactive phases was high in interfacial sediments, representing over 90% of B and U and 50% of Pb, Cu, Zn, V and Ba extractable by dilute HCl. The interfacial sediments were particularly enriched in reactive Cr, Cu, Ni, Zn, B, Mo and U, with reactive B, Mo and U concentrations between 5 and 10 times greater than in the former sulfuric horizon. Surface enrichment of trace elements is strongly co-associated with Fe(III) mineralisation, likely via sorption and co-precipitation processes. Enrichment is highly spatially heterogeneous and is strongly influenced by elevation and tidal zonation at a landscape-scale and by sediment micro-topography and preferential advective transport via surface connected macropores at the pedon-scale. The results from this study provide new insights to the processes influencing trace element enrichment in Fe-rich redox-interfacial sediments across a remediating acidic tidal wetland. © 2014 Elsevier B.V.
Seawater inundation of coastal floodplain sediments : Short-term changes in surface water and sediment geochemistry
- Authors: Wong, Vanessa , Johnston, Scott , Burton, Edward , Hirst, Phillip , Sullivan, Leigh , Bush, Richard , Blackford, Mark
- Date: 2015
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 398, no. (2015), p. 32-45
- Full Text: false
- Reviewed:
- Description: Coastal floodplains are highly vulnerable to seawater inundation as a result of storm surge and sea-level rise due to their low elevation and proximity to the coastline. Intact soil cores from a levee, acid-sulfate soil scald and four backswamp sites on a coastal floodplain in eastern Australia were inundated with artificial seawater treatments (0%, 50% and 100%) for 14days to examine the short term consequences for surface water and floodplain sediment geochemistry. All sites displayed an initial decrease in surface water pH following inundation with 50% and 100% seawater. In addition, higher concentrations of trace metals (Al, Fe, Mn, Ni and Zn) were observed in most sites inundated with 50% or 100% seawater. This was generally attributed to competitive exchange and desorption of trace metals from sediments due to the higher ionic strength of the seawater solutions and upward diffusive flux of metals from the sediments to surface waters. At one backswamp site, reductive processes had established by day 7, which also resulted in elevated Fe2+ concentrations in the overlying surface waters. Transmission electron microscopy (TEM) identified the presence of poorly crystalline ferrihydrite and schwertmannite, and goethite and jarosite. These meta-stable Fe(III) minerals can act as a source of metals for desorption and can also be readily reduced and act as a source of Fe2+ to surface waters. Importantly, inundation with either 50% or 100% seawater resulted in a similar magnitude of acidity and trace metal mobilisation. The data suggest that an inundation event of ~0.2m depth with either 50% or 100% seawater could cause a pulse mobilisation of up to 64.8 and 9.1kgha-1 of Fe and Al, respectively - quantities of similar magnitude to previous estimates of annual drainage fluxes from similar backswamps. This study suggests that the short term inundation of coastal floodplain sediments by either brackish water or seawater will result in rapid declines in surface water quality as a result of increased liberation of acidity and trace metals. © 2015 .