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.
- 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 (2-5×) 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.
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 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.
- 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.
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 (∼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. © 2010 American Chemical Society.
- 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
- Full Text:
- Reviewed:
- 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 (∼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. © 2010 American Chemical Society.
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 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.
- 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:
- Reviewed:
- 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.
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