List of Titles

A sequential extraction procedure for acid sulfate soils : Partitioning of iron

- Claff, Salirian, Sullivan, Leigh, Burton, Edward, Bush, Richard

Authors: Claff, Salirian , Sullivan, Leigh , Burton, Edward , Bush, Richard
Date: 2010
Type: Text , Journal article
Relation: Geoderma Vol. 155, no. 3-4 (2010), p. 224-230
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Description: A new sequential extraction scheme for acid sulfate soil materials has been evaluated for iron partitioning in a range of synthetic iron-bearing minerals and natural acid sulfate soil materials. This sequential extraction procedure employs six steps to quantify (1) exchangeable (magnesium chloride extractable), (2) acid (hydrochloric acid) soluble, (3) reactive organic-bound (pyrophosphate extractable), (4) crystalline oxide (citrate buffered dithionite (CBD)) extractable, (5) pyrite-bound (nitric acid extractable) and (6) residual (acid/peroxide digestible) forms of iron. Given its intended use for acid sulfate soil materials that frequently contain pyrite, a primary aim of this new sequential extraction procedure was to differentiate iron bound in pyrite from iron contained in other minerals. The results demonstrated that dissolution of pyrite was effectively isolated in the pyrite-bound extraction step, with dissolution of other iron mineral phases (i.e. akaganeite, ferrihydrite, goethite, hematite, jarosite, magnetite, and schwertmannite) occurring within the other five extraction steps. Following a systematic examination of these synthetic iron mineral phases, the sequential extraction scheme was applied to an acid sulfate soil profile, with detailed data presented for two soil layers: one representative of the sulfidic (unoxidised) conditions, and the other sulfuric (oxidised) conditions. Partitioning data for pyrite-bound iron in the acid sulfate soil profile showed good agreement with that calculated via the independently measured pyrite-bound reduced sulfur. This study indicates that the new sequential extraction procedure is suitable for the assessment of iron partitioning in acid sulfate soil materials. © 2009 Elsevier B.V. All rights reserved.

A simple and inexpensive chromium-reducible sulfur method for acid-sulfate soils

- Burton, Edward, Sullivan, Leigh, Bush, Richard, Johnston, Scott, Keene, Annabelle

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
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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.

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

- Johnston, Scott, Burton, Edward, Bush, Richard, Keene, Annabelle, Sullivan, Leigh, Smith, Douglas, McElnea, Angus, Ahern, Col, Powell, Bernard

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
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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 (2-5Ã—) 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 (Î±-FeOOH) and lepidocrocite (Î³-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 (âˆ¼60 Î¼g 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.

Acidity fractions in acid sulfate soils and sediments : Contributions of schwertmannite and jarosite

- Vithana, Chamindra, Sullivan, Leigh, Bush, Richard, Burton, Edward

Authors: Vithana, Chamindra , Sullivan, Leigh , Bush, Richard , Burton, Edward
Date: 2013
Type: Text , Journal article
Relation: Soil Research Vol. 51, no. 3 (2013), p. 203-214
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Description: In Australia, the assessment of acidity hazard in acid sulfate soils requires the estimation of operationally defined acidity fractions such as actual acidity, potential sulfidic acidity, and retained acidity. Acid-base accounting approaches in Australia use these acidity fractions to estimate the net acidity of acid sulfate soils materials. Retained acidity is the acidity stored in the secondary Fe/Al hydroxy sulfate minerals, such as jarosite, natrojarosite, schwertmannite, and basaluminite. Retained acidity is usually measured as either net acid-soluble sulfur (SNAS) or residual acid soluble sulfur (SRAS). In the present study, contributions of schwertmannite and jarosite to the retained acidity, actual acidity, and potential sulfidic acidity fractions were systematically evaluated using S NAS and SRAS techniques. The data show that schwertmannite contributed considerably to the actual acidity fraction and that it does not contribute solely to the retained acidity fraction as has been previously conceptualised. As a consequence, SNAS values greatly underestimated the schwertmannite content. For soil samples in which jarosite is the only mineral present, a better estimate of the added jarosite content can be obtained by using a correction factor of 2 to SNAS values to account for the observed 50-60% recovery. Further work on a broader range of jarosite samples is needed to determine whether this correction factor has broad applicability. The SRAS was unable to reliably quantify either the schwertmannite or the jarosite content and, therefore, is not suitable for quantification of the retained acidity fraction. Potential sulfidic acidity in acid sulfate soils is conceptually derived from reduced inorganic sulfur minerals and has been estimated by the peroxide oxidation approach, which is used to derive the S RAS values. However, both schwertmannite and jarosite contributed to the peroxide-oxidisable sulfur fraction, implying a major potential interference by those two minerals to the determination of potential sulfidic acidity in acid sulfate soils through the peroxide oxidation approach. © 2013 CSIRO.

Anthropogenic forcing of estuarine hypoxic events in sub-tropical catchments : Landscape drivers and biogeochemical processes

- Wong, Vanessa, Johnston, Scott, Burton, Edward, Bush, Richard, Sullivan, Leigh, Slavich, Peter

Authors: Wong, Vanessa , Johnston, Scott , Burton, Edward , Bush, Richard , Sullivan, Leigh , Slavich, Peter
Date: 2011
Type: Text , Journal article
Relation: Science of the Total Environment Vol. 409, no. 24 (2011), p. 5368-5375
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Description: Episodic hypoxic events can occur following summer floods in sub-tropical estuaries of eastern Australia. These events can cause deoxygenation of waterways and extensive fish mortality. Here, we present a conceptual model that links key landscape drivers and biogeochemical processes which contribute to post-flood hypoxic events. The model provides a framework for examining the nature of anthropogenic forcing. Modification of estuarine floodplain surface hydrology through the construction of extensive drainage networks emerges as a major contributing factor to increasing the frequency, magnitude and duration of hypoxic events. Forcing occurs in two main ways. Firstly, artificial drainage of backswamp wetlands initiates drier conditions which cause a shift in vegetation assemblages from wetland-dominant species to dryland-dominant species. These species, which currently dominate the floodplain, are largely intolerant of inundation and provide abundant labile substrate for decomposition following flood events. Decomposition of this labile carbon pool consumes oxygen in the overlying floodwaters, and results in anoxic conditions and waters with excess deoxygenation potential (DOP). Carbon metabolism can be strongly coupled with microbially-mediated reduction of accumulated Fe and Mn oxides, phases which are common on these coastal floodplain landscapes. Secondly, artificial drainage enhances discharge rates during the flood recession phase. Drains transport deoxygenated high DOP floodwaters rapidly from backswamp wetlands to the main river channel to further consume oxygen. This process effectively displaces the natural carbon metabolism processes from floodplain wetlands to the main channel. Management options to reduce the impacts of post-flood hypoxia include i) remodifying drainage on the floodplain to promote wetter conditions, thereby shifting vegetation assemblages towards inundation-tolerant species, and ii) strategic retention of floodwaters in the backswamp wetlands to reduce the volume and rate during the critical post-flood recession phase. © 2011 Elsevier B.V.

Arsenic effects and behavior in association with the fe(II)-catalyzed transformation of schwertmannite

- Burton, Edward, Johnston, Scott, Watling, Kym, Bush, Richard, Keene, Annabelle, Sullivan, Leigh

Authors: Burton, Edward , Johnston, Scott , Watling, Kym , Bush, Richard , Keene, Annabelle , Sullivan, Leigh
Date: 2010
Type: Text , Journal article
Relation: Environmental Science and Technology Vol. 44, no. 6 (2010), p. 2016-2021
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Description: In acid-mine drainage and acid-sulfate soil environments, the cycling of Fe and As are often linked to the formation and fate of schwertmannite(Fe 8O8(OH)8-2x(SO4)x).When schwertmanniterich material is subjected to near-neutral Fe(III)-reducing conditions (e.g., in reflooded acid-sulfate soils or mining-lake sediments), the resulting Fe(II) can catalyze transformation of schwertmannite to goethite. This work examines the effects of arsenic(V) and arsenic(III) on the Fe(II)-catalyzed transformation of schwertmannite and investigates the associated consequences of this mineral transformation for arsenic mobilization. A series of 9-day anoxic transformation experiments were conducted with synthetic schwertmannite and various additions of Fe(II), As(III), and As(V). X-ray diffraction (XRD) and Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy demonstrated that, in the absence of Fe(II), schwertmannite persisted as the dominant mineral phase. Under arsenic-free conditions, 10 mM Fe(II) catalyzed rapid and complete transformation of schwertmannite to goethite. However, the magnitude of Fe(II)-catalyzed transformation decreased to 72% in the presence of 1 mM As(III) and to only 6% in the presence of 1mM As(V). This partial Fe(II)-catalyzed transformation of As(III)-sorbed schwertmannite did not cause considerable As(III) desorption. In contrast, the formation of goethite via partial transformation of As(III)- and As(V)-sorbed schwertmannite significantly decreased arsenic mobilization under Fe(III)-reducing conditions. This implies that the Fe(II)-catalyzed transformation of schwertmannite to goethite may help to stabilize solid-phase arsenic and retard its subsequent release to groundwater. © 2010 American Chemical Society.

Arsenic mobilization during seawater inundation of acid sulfate soils - Hydrogeochemical coupling at the tidal fringe

- Johnston, Scott, Burton, Edward, Keene, Annabelle, Bush, Richard, Sullivan, Leigh

Authors: Johnston, Scott , Burton, Edward , Keene, Annabelle , Bush, Richard , Sullivan, Leigh
Date: 2012
Type: Text , Conference proceedings
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Description: Coastal Acid Sulfate Soils (CASS) are rich in meta-stable iron (Fe - III) minerals that are important sorbents for arsenic (As) under oxic conditions. Tidal seawater inundation to remediate CASS has recently been trialed on a large scale and has potential to mobilize arsenic during the redox transition. Tidal seawater inundation caused reductive dissolution of As(V)-bearing Fe(III) minerals, resulting in elevated concentrations of Fe 2+ (2000 mg L -1) and As (âˆ¼400 Î¼g L -1) in upper-intertidal zone groundwater. Oscillating vertical and horizontal hydraulic gradients caused by tidal pumping promoted upward advection of As and Fe 2+-enriched groundwater within the intertidal zone. This led to flux of As aq and Fe 2+ aq to surface waters and the accumulation of As(V)-enriched Fe(III) (hydr)oxides at the oxic sediment-water interface. Fe(III) (hydr)oxides at the sediment-water interface act as a natural reactive-barrier, retarding As flux to overlying surface waters. However, they also represent a highly transient phase that is prone to reductive dissolution during future redox boundary migration. A conceptual model is presented to explain landscape-scale patterns of As and Fe hydro-geochemical zonation. © 2012 Taylor & Francis Group.

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Arsenic mobilization in a seawater inundated acid sulfate soil

- Johnston, Scott, Keene, Annabelle, Burton, Edward, Bush, Richard, Sullivan, Leigh, McElnea, Angus, Ahern, Col, Smith, C. Douglas, Powell, Bernard, Hocking, Rosalie

Authors: Johnston, Scott , Keene, Annabelle , Burton, Edward , Bush, Richard , Sullivan, Leigh , McElnea, Angus , Ahern, Col , Smith, C. Douglas , Powell, Bernard , Hocking, Rosalie
Date: 2010
Type: Text , Journal article
Relation: Environmental Science and Technology Vol. 44, no. 6 (2010), p. 1968-1973
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Description: 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 (âˆ¼400Î¼g/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. © 2010 American Chemical Society.

Changes in water quality following tidal inundation of coastal lowland acid sulfate soil landscapes

- Johnston, Scott, Bush, Richard, Sullivan, Leigh, Burton, Edward, Smith, Douglas, Martens, Michelle, McElnea, Angus, Ahern, Col, Powell, Bernard, Stephens, Luisa, Wilbraham, Steve, Van Heel, Simon

Authors: Johnston, Scott , Bush, Richard , Sullivan, Leigh , Burton, Edward , Smith, Douglas , Martens, Michelle , McElnea, Angus , Ahern, Col , Powell, Bernard , Stephens, Luisa , Wilbraham, Steve , Van Heel, Simon
Date: 2009
Type: Text , Journal article
Relation: Estuarine, Coastal and Shelf Science Vol. 81, no. 2 (2009), p. 257-266
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Description: This study examines the remediation of surface water quality in a severely degraded coastal acid sulfate soil landscape. The remediation strategy consisted of partial restoration of marine tidal exchange within estuarine creeks and incremental tidal inundation of acidified soils, plus strategic liming of drainage waters. Time-series water quality and climatic data collected over 5 years were analysed to assess changes in water quality due to this remediation strategy. A time-weighted rainfall function (TWR) was generated from daily rainfall data to integrate the effects of antecedent rainfall on shallow groundwater levels in a way that was relevant to acid export dynamics. Significant increases in mean pH were evident over time at multiple monitoring sites. Regression analysis at multiple sites revealed a temporal progression of change in significant relationships between mean daily electrical conductivity (EC) vs. mean daily pH, and TWR vs. mean daily pH. These data demonstrate a substantial decrease over time in the magnitude of creek acidification per given quantity of antecedent rainfall. Data also show considerable increase in soil pH (2-3 units) in formerly acidified areas subject to tidal inundation. This coincides with a decrease in soil pe, indicating stronger reducing conditions. These observations suggest a fundamental shift has occurred in sediment geochemistry in favour of proton-consuming reductive processes. Combined, these data highlight the potential effectiveness of marine tidal inundation as a landscape-scale acid sulfate soil remediation strategy. © 2008 Elsevier Ltd. All rights reserved.

Contemporary pedogenesis of severely degraded tropical acid sulfate soils after introduction of regular tidal inundation

- Johnston, Scott, Keene, Annabelle, Bush, Richard, Burton, Edward, Sullivan, Leigh, Smith, Douglas, McElnea, Angus, Martens, Michelle, Wilbraham, Steve

Authors: Johnston, Scott , Keene, Annabelle , Bush, Richard , Burton, Edward , Sullivan, Leigh , Smith, Douglas , McElnea, Angus , Martens, Michelle , Wilbraham, Steve
Date: 2009
Type: Text , Journal article
Relation: Geoderma Vol. 149, no. 3-4 (2009), p. 335-346
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Description: Marine tidal inundation was partially restored to a severely degraded tropical acid sulfate soil landscape after having been excluded for over 30Â years. The effects on soil acidity and iron-sulfide mineral reformation were investigated by comparing the geochemistry of soils before and after five years of regular tidal inundation. The soil pH increased by 2-3 units and titratable actual acidity (TAA) decreased by âˆ¼ 40-50Â Î¼mol H+ g- 1 within former sulfuric horizons. Relict acidity remained at depth (> 1Â m) in the underlying sulfidic horizons. Î´34S data indicate that tidal inundation caused exchange of marine solutes within former sulfuric horizons, but not within underlying sulfidic material. There was considerable reformation of pyrite within former sulfuric horizons after tidal inundation with reduced inorganic sulfur increasing by âˆ¼ 60Â Î¼mol g- 1. Acid-volatile sulfide also accumulated, but mainly near the soil surface (up to 16Â Î¼mol g- 1). Reduction of Fe(III) minerals strongly influences the geochemistry of the tidally inundated soils. After tidal inundation the soil pH and Eh closely followed the iron redox couple and there was non-sulfidic solid-phase Fe(II) up to 600Â Î¼mol g- 1. There was also substantial diagenetic enrichment of poorly crystalline Fe-oxides near the soil surface following tidal inundation, with reactive Fe spanning 400-1800Â Î¼mol g- 1. While the decreases in soil acidity documented here are likely due to a combination of marine alkalinity inputs and reduction of both Fe and SO42-, the relative importance of each process remains to be determined. This study demonstrates that marine tidal inundation can be an effective landscape-scale strategy for ameliorating severe acidity associated with drained acid sulfate soils. © 2008 Elsevier B.V. All rights reserved.

Decoupling between water column oxygenation and benthic phosphate dynamics in a shallow eutrophic estuary

- Kraal, Peter, Burton, Edward, Rose, Andrew, Cheetham, Michael, Bush, Richard, Sullivan, Leigh

Authors: Kraal, Peter , Burton, Edward , Rose, Andrew , Cheetham, Michael , Bush, Richard , Sullivan, Leigh
Date: 2013
Type: Text , Journal article
Relation: Environmental Science and Technology Vol. 47, no. 7 (2013), p. 3114-3121
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Description: Estuaries are crucial biogeochemical filters at the land-ocean interface that are strongly impacted by anthropogenic nutrient inputs. Here, we investigate benthic nitrogen (N) and phosphorus (P) dynamics in relation to physicochemical surface sediment properties and bottom water mixing in the shallow, eutrophic Peel-Harvey Estuary. Our results show the strong dependence of sedimentary P release on Fe and S redox cycling. The estuary contains surface sediments that are strongly reducing and act as net P source, despite physical sediment mixing under an oxygenated water column. This decoupling between water column oxygenation and benthic P dynamics is of great importance to understand the evolution of nutrient dynamics in marine systems in response to increasing nutrient loadings. In addition, the findings show that the relationship between P burial efficiency and bottom water oxygenation depends on local conditions; sediment properties rather than oxygen availability may control benthic P recycling. Overall, our results illustrate the complex response of an estuary to environmental change because of interacting physical and biogeochemical processes. © 2013 American Chemical Society.

Effect of sample pretreatment on the fractionation of Fe, Cr, Ni, Cu, Mn, and Zn in acid sulfate soil materials

- Claff, Salirian, Burton, Edward, Sullivan, Leigh, Bush, Richard

Authors: Claff, Salirian , Burton, Edward , Sullivan, Leigh , Bush, Richard
Date: 2010
Type: Text , Journal article
Relation: Geoderma Vol. 159, no. 1-2 (2010), p. 156-164
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Description: A sequential extraction procedure was applied to acid sulfate soil materials from a soil profile to investigate the effect of sample pretreatment on the geochemical fractionation of selected metals. The samples were prepared for analysis by oven-drying, sieving and grinding the soil, or were examined as collected in field condition. The soil profile encompassed oxidising conditions near the surface, through to reducing conditions at depth. Six metals (Fe, Cr, Ni, Mn, Cu, and Zn) were measured during the sequential extraction procedure, and their fractionation determined in the oxidised and in the reduced zone. Although cumulative totals (the sum of all steps in the sequential extraction procedure) for the metals extracted from both the field condition and dried/ground samples were similar, some significant differences in fractionation within individual extraction steps were observed. Of particular interest was the redistribution of metals from the sulfide-bearing (pyrite-bound) fraction to the more readily available fractions (i.e. labile and acid-soluble), as a result of oven-drying and grinding. The results indicate that when assessing metal fractionation in acid sulfate soil materials, samples should be analysed in field condition in order to avoid the considerable metal fractionation artifacts that are induced by drying and grinding. © 2010 Elsevier B.V.

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Effects of hyper-enriched reactive Fe on sulfidisation in a tidally inundated acid sulfate soil wetland

- Keene, Annabelle, Johnston, Scott, Bush, Richard, Sullivan, Leigh, Burton, Edward, McElnea, Angus, Ahern, Col, Powell, Bernard

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
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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 Î¼mol/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 Î¼mol/g) and elemental sulfur (S0; up to 41 Î¼mol/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.

Electrochemical analysis of highly reactive pyrite

- Watling, Kym, Burton, Edward, Johnston, Max, Bush, Richard, Sullivan, Leigh

Authors: Watling, Kym , Burton, Edward , Johnston, Max , Bush, Richard , Sullivan, Leigh
Date: 2010
Type: Text , Conference proceedings
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Description: Highly reactive pyritic material, exposed during the construction of the Pennsylvania Interstate Highway 99 (I-99), has been characterized by X-ray diffraction, Raman microprobe spectroscopy, electron microscopy and electrochemical methods. Mineral standards of marcasite, arsenopyrite and pyrite were compared in order to determine the cause of the rapid acidification and liberation of dissolved metals observed in the exposed Pennsylvanian pyritic material. Linear sweep voltammetry found no significant differences in the electrochemical activity, however, a significantly lower open circuit potential was found in the reactive pyrite material than in the pyrite or marcasite standards. In addition to sulfur and iron, high concentrations of zinc and aluminium impurities were observed in Energy Dispersive X-ray analysis of the finest crystals of the Pennsylvanian pyritic material. © The Electrochemical Society.

Enrichment and heterogeneity of trace elements at the redox-interface of Fe-rich intertidal sediments

- Keene, Annabelle, Johnston, Scott, Bush, Richard, Burton, Edward, Sullivan, Leigh, Dundon, Matthew, McElnea, Angus, Smith, C. Douglas, Ahern, Col, Powell, Bernard

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
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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.

Fe and S K-edge XAS determination of iron-sulfur species present in a range of acid sulfate soils : Effects of particle size and concentration on quantitative XANES determinations

- Morgan, Kate, Burton, Edward, Cook, Perran, Raven, Mark, Fitzpatrick, Rob W., Bush, Richard, Sullivan, Leigh, Hocking, Rosalie

Authors: Morgan, Kate , Burton, Edward , Cook, Perran , Raven, Mark , Fitzpatrick, Rob W. , Bush, Richard , Sullivan, Leigh , Hocking, Rosalie
Date: 2009
Type: Text , Conference paper
Relation: 14th International Conference on X-ray Absorption Fine Structure (XAFS14); Camerino, Italy; 26th-31st July 2009. Vol. 190, p. 1-5
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Description: Acid sulfate soils (ASS) are soils and soft sediments in which sulfuric acid may be produced from iron sulfides or have been produced leaving iron oxyhydroxysulfates in amounts that have a long lasting effect on soil characteristics. If soil material is exposed to rotting vegetation or other reducing material, the Fe-oxyhydroxysulfates can be bacterially reduced to sulfides including disulfides (pyrite and marcasite), and Monosulfidic Black Ooze (MBO) a poorly characterised material known to be a mixture of iron sulfides (especially mackinawite) and organic matter. The chemistry of these environments is strongly affected by Fe and S cycling processes and herein we have sought to identify key differences in environments that occur as a function of Fe and S concentration. In addition to our chemical results, we have found that the effects of particle size on self absorption in natural sediments play an important role in the spectroscopic identification of the relative proportions of different species present. © 2009 IOP Publishing Ltd.

Improved identification of sulfidic soil materials by a modified incubation method

- Sullivan, Leigh, Ward, Nicholas, Bush, Richard, Burton, Edward

Authors: Sullivan, Leigh , Ward, Nicholas , Bush, Richard , Burton, Edward
Date: 2009
Type: Text , Journal article
Relation: Geoderma Vol. 149, no. 1-2 (2009), p. 33-38
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Description: This study examines the acidification behaviour and rate of sulfidic-sulfur oxidation in the incubation method that is currently used in soil taxonomies to identify sulfidic materials, for some clayey textured soil materials. 'Sulfidic' in these taxonomies identifies that a soil material is capable of becoming extremely acidic (i.e. pH < 4) as a result of oxidation of sulfide minerals contained in that soil material. As well as examining incubation slabs of acid sulfate soil materials with the standard 10 mm thickness, the utility of thinner (i.e. 2 mm thick) incubation slabs of these soil materials for identification of sulfidic soil materials was also examined. The clayey soil materials in the 2 mm thick slabs exhibited more rapid sulfidic-sulfur oxidation and acidification and resulted in fewer false-negative sulfidic soil material identifications than did the use of 10 mm thick slabs. However, the rates of sulfidic-sulfur oxidation and sulfide-derived acidification within the slabs (whether 2 mm or 10 mm thick) were not always rapid enough during incubation for the full expression of acidification to be evident within the maximum incubation duration of 8 weeks required by soil classification taxonomies. The results indicate the incubation method for determination of the sulfidic nature of soil materials for soil classification purposes could be improved to reduce the risk of false-negative identification by: i. allowing the use of 2 mm thick slabs, and ii. changing the maximum duration of incubation from 8 weeks to until a stable pH is reached after at least 8 weeks of incubation. © 2008.

Iron and arsenic cycling in intertidal surface sediments during wetland remediation

- Johnston, Scott, Keene, Annabelle, Burton, Edward, Bush, Richard, Sullivan, Leigh

Authors: Johnston, Scott , Keene, Annabelle , Burton, Edward , Bush, Richard , Sullivan, Leigh
Date: 2011
Type: Text , Journal article
Relation: Environmental Science and Technology Vol. 45, no. 6 (2011), p. 2179-2185
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Description: The accumulation and behavior of arsenic at the redox interface of Fe-rich sediments is strongly influenced by Fe(III) precipitate mineralogy, As speciation, and pH. In this study, we examined the behavior of Fe and As during aeration of natural groundwater from the intertidal fringe of a wetland being remediated by tidal inundation. The groundwater was initially rich in Fe 2+ (32 mmol L -1) and As (1.81 Î¼mol L -1) with a circum-neutral pH (6.05). We explore changes in the solid/solution partitioning, speciation and mineralogy of Fe and As during long-term continuous groundwater aeration using a combination of chemical extractions, SEM, XRD, and synchrotron XAS. Initial rapid Fe 2+ oxidation led to the formation of As(III)-bearing ferrihydrite and sorption of >95% of the As(aq) within the first 4 h of aeration. Ferrihydrite transformed to schwertmannite within 23 days, although sorbed/coprecipitated As(III) remained unoxidized during this period. Schwertmannite subsequently transformed to jarosite at low pH (2-3), accompanied by oxidation of remaining Fe 2+. This coincided with a repartitioning of some sorbed As back into the aqueous phase as well as oxidation of sorbed/coprecipitated As(III) to As(V). Fe(III) precipitates formed via groundwater aeration were highly prone to reductive dissolution, thereby posing a high risk of mobilizing sorbed/coprecipitated As during any future upward migration of redox boundaries. Longer-term investigations are warranted to examine the potential pathways and magnitude of arsenic mobilization into surface waters in tidally reflooded wetlands. © 2011 American Chemical Society.

Iron geochemical zonation in a tidally inundated acid sulfate soil wetland

- Johnston, Scott, Keene, Annabelle, Bush, Richard, Burton, Edward, Sullivan, Leigh, Isaacson, Lloyd, McElnea, Angus, Ahern, Col, Smith, C. Douglas, Powell, Bernard

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
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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 8000Î¼mol 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 (Î³-FeOOH) and goethite (Î±-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.

Iron(III) accumulations in inland saline waterways, Hunter Valley, Australia : Mineralogy, micromorphology and pore-water geochemistry

- Isaacson, Lloyd, Burton, Edward, Bush, Richard, Mitchell, David, Johnston, Scott, Macdonald, Bennett, Sullivan, Leigh, White, Ian

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
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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 (Fe5HO3Â·4H2O) with lesser amounts of goethite (Î±-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 (Î³-FeOOH), which occurred as nanoparticles as little as âˆ¼5 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.

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