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
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- 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 .
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
- 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.
Partitioning of metals in a degraded acid sulfate soil landscape : Influence of tidal re-inundation
- Authors: Claff, Salirian , Sullivan, Leigh , Burton, Edward , Bush, Richard , Johnston, Scott
- Date: 2011
- Type: Text , Journal article
- Relation: Chemosphere Vol. 85, no. 8 (2011), p. 1220-1226
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- Description: The oxidation and acidification of sulfidic soil materials results in the re-partitioning of metals, generally to more mobile forms. In this study, we examine the partitioning of Fe, Cr, Cu, Mn, Ni and Zn in the acidified surface soil (0-0.1. m) and the unoxidised sub-soil materials (1.3-1.5. m) of an acid sulfate soil landscape. Metal partitioning at this acidic site was then compared to an adjacent site that was previously acidified, but has since been remediated by tidal re-inundation. Differences in metal partitioning were determined using an optimised six-step sequential extraction procedure which targets the " labile" , " acid-soluble" , " organic" , " crystalline oxide" , " pyritic" and " residual" fractions. The surficial soil materials of the acidic site had experienced considerable losses of Cr, Cu, Mn and Ni compared to the underlying parent material due to oxidation and acidification, yet only minor losses of Fe and Zn. In general, the metals most depleted from the acidified surface soil materials exhibited the greatest sequestration in the surface soil materials of the tidally remediated site. An exception to this was iron, which accumulated to highly elevated concentrations in the surficial soil materials of the tidally remediated site. The " acid-soluble" , " organic" and " pyritic" fractions displayed the greatest increase in metals following tidal remediation. This study demonstrates that prolonged tidal re-inundation of severely acidified acid sulfate soil landscapes leads to the immobilisation of trace metals through the surficial accumulation of iron oxides, organic material and pyrite. © 2011 Elsevier Ltd.
Anthropogenic forcing of estuarine hypoxic events in sub-tropical catchments : Landscape drivers and biogeochemical processes
- 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.
Stability of schwertmannite and jarosite in an acidic landscape : Prolonged field incubation
- Authors: Vithana, Chamindra , Sullivan, Leigh , Burton, Edward , Bush, Richard
- Date: 2015
- Type: Text , Journal article
- Relation: Geoderma Vol. 239, no. (2015), p. 47-57
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- Description: Schwertmannite and jarosite are two of the main secondary iron(III) minerals commonly found in acidic, iron and sulfate-rich environments such as acid mine drainage and coastal acid sulfate soils (CASS). Both minerals exert major influence on the water and soil quality in these environments. While there are many studies conducted on the stability of these two minerals under controlled laboratory conditions, the behaviour of schwertmannite and jarosite under field conditions and the factors influencing their behaviour have not been investigated directly. In the present study, we examined the net transformation of introduced schwertmannite and jarosite samples incubated in a typical acidic CASS environment. Pure (synthetic) schwertmannite and jarosite samples were exposed to two main chemical regimes: 1) aerobic-acidic water column and 2) anaerobic-neutral sediment in a CASS environment. Changes in mineralogy, micromorphology, and composition of schwertmannite and jarosite samples were monitored over a period of 12months. Schwertmannite suspended in the water column and buried in sediments transformed to goethite by the end of 12months but more quickly in anoxic, reducing sediments. However, schwertmannite incubated in the acidic water column transformed at a much faster rate than those reported for acidic and aerobic conditions in the laboratory. Jarosite incubated in both the water column and sediments was also transformed to goethite but at a much slower rate than schwertmannite. Dissimilatory microbial reduction and Fe2+-catalysed transformation likely played a major role in accelerating the transformation of both minerals to goethite in sediments. The transformation of both minerals in the water column was sensitive to the hydrological conditions and fluctuations in the water column in relation to antecedent rainfall. In comparison, the sediment's geochemistry was relatively stable and consequently the rate of transformation and dissolution of both schwertmannite and jarosite in this environment was not appreciably affected by variable hydrology. © 2014 Elsevier B.V.
Seawater-induced mobilization of trace metals from mackinawite-rich estuarine sediments
- Authors: Wong, Vanessa , Johnston, Scott , Burton, Edward , Bush, Richard , Sullivan, Leigh , Slavich, Peter
- Date: 2013
- Type: Text , Journal article
- Relation: Water Research Vol. 47, no. 2 (2013), p. 821-832
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- Description: Benthic sediments in coastal acid sulfate soil (CASS) drains can contain high concentrations (~1-5%) of acid volatile sulfide (AVS) as nano-particulate mackinawite. These sediments can sequester substantial quantities of trace metals. Because of their low elevation and the connectivity of drains to estuarine channels, these benthic sediments are vulnerable to rapid increases in ionic strength from seawater incursion by floodgate opening, floodgate failure, storm surge and seasonal migration of the estuarine salt wedge. This study examines the effect of increasing seawater concentration on trace metal mobilization from mackinawite-rich drain sediments (210-550
Mobilisation, alteration, and redistribution of monosulfidic sediments in inland river systems
- Authors: Cheetham, Michael , Wong, Vanessa , Bush, Richard , Sullivan, Leigh , Ward, Nicholas , Zawadzki, Atun
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Environmental Management Vol. 112, no. (2012), p. 330-339
- Full Text: false
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- Description: The accumulation of monosulfidic sediments in inland waterways is emerging as a major environmental issue. Mobilisation and suspension of monosulfidic sediments can result in deoxygenation, acidification of the water column and mobilisation of trace metals. The controls on monosulfidic sediment mobilisation and the critical thresholds for its scour and entrainment have not been established. This study examines the effect of a minor flood event (average return interval of 5 years) on sulfidic sediment scour in the Wakool River in southern NSW, Australia. Five profiles were sampled within a small (~300 m) reach before and after a minor flood event to determine the degree of sediment scour and transport. The results indicate substantial scour of both monosulfidic sediments and underlying bed sediments (approximately 2100 m3). Changes in the sediment geochemistry suggest large concentrations of monosulfidic sediments had been suspended in the water column, partially-oxidised and redeposited. This is supported by 210Pb results from one of the profiles. These results suggest that these monosulfidic sediments can move as bed load during minor flood events. © 2012 Elsevier Ltd.
Seawater causes rapid trace metal mobilisation in coastal lowland acid sulfate soils : Implications of sea level rise for water quality
- Authors: Wong, Vanessa , Johnston, Scott , Burton, Edward , Bush, Richard , Sullivan, Leigh , Slavich, Peter
- Date: 2010
- Type: Text , Journal article
- Relation: Geoderma Vol. 160, no. 2 (2010), p. 252-263
- Full Text: false
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- Description: Coastal floodplains are highly vulnerable to inundation with saline water and the likelihood of inundation will increase with sea level rise. Sediment samples from floodplains containing coastal lowland acid sulfate soils (CLASS) in eastern Australia were subjected to increasing seawater concentration to examine the probable effects of sea level rise on acidity and metal desorption. Ten soils were mixed with synthetic seawater concentrations varying from 0% to 100% at a solid:solution ratio of 1:10 for 4h. There was a slight decrease in pH (≈0.5 units) with increasing seawater concentration following treatment, yet, calculated acidity increased significantly. In most soil treatments, Al was the dominant component of the calculated acidity pool. Al dominated the exchange complex in the CLASS and, correspondingly, was the major metal ion desorbed. In general, concentrations of soluble and exchangeable Al, Fe2+, Ni, Mn and Zn in all soil extracts increased with increasing salinity. Increasing trace metal concentrations with increasing seawater concentration is attributed to the combined effects of exchange processes and acidity. The increasing ionic strength of the seawater treatments displaces trace metals and protons adsorbed on sediments, causing an initial decrease in pH. Hydrolysis of desorbed acidic metal cations can further contribute to acidity and increase mobilisation of trace metals. These findings imply that saline inundation of CLASS environments, even by relatively brackish water may cause rapid, shorter-term water quality changes and a pulse release of acidity due to desorption of acidic metal cations. © 2010 Elsevier B.V.