Soil micromorphology, using light microscopy and scanning electron microscopy (SEM), was used to ... more Soil micromorphology, using light microscopy and scanning electron microscopy (SEM), was used to describe detailed soil morphological and compositional changes and determine mineral weathering pathways in acid sulfate soils (ASS) from the following 2 contrasting coastal environments in Barker Inlet, South Australia: (i) a tidal mangrove forest with sulfidic material at St Kilda, and (ii) a former supratidal samphire area at Gillman that was drained in 1954 causing sulfuric material to form from sulfidic material. Pyrite framboids and cubes were identified in sulfidic material from both sites and are associated with sapric and hemic materials. Gypsum crystals, interpreted as a product of sulfide oxidation, were observed to have formed in lenticular voids within organic matter in the tidal mangrove soils at St Kilda. Sulfide oxidation was extensive in the drained soil at Gillman, evidenced by the formation of iron oxyhydroxide pseudomorphs (goethite crystallites and framboids) after pyrite and jarosite, and of gypsum crystals. Gypsum crystals occur where a local source of calcium such as shells or calcareous sand is present. Sporadic oxidation episodes are indicated by the formation of iron oxide and jarosite coatings around coarse biogenic voids. These observations indicate that mineral transformation pathways are strongly influenced by soil physico-chemical characteristics (i.e. oxidation rate, Eh, pH, soil solution chemistry, mineralogy, and spatial distribution of sulfides). This information has been used to illustrate the interrelationships of pyrite, carbonate, gypsum, jarosite, and organic matter and help predict soil evolution under changing hydro-geochemical, redoximorphic, and thermal conditions in soils from coastal environments.
Acid sulfate soils occur in dynamic and geomorphologically complex inland and coastal landscapes ... more Acid sulfate soils occur in dynamic and geomorphologically complex inland and coastal landscapes that are inherently susceptible to natural and human induced changes. These changes can lead to environmental degradation and loss of infrastructure through acidification of soil and water and metal mobilisation. This study has identified and described the interrelationships between acid sulfate soil materials and their geomorphic environment, composition (pedology, mineralogy), redox status and geochemistry, and potential environmental hazards, within a complex estuarine landscape in the Barker Inlet region, north of Adelaide, South Australia. For this purpose two study sites were chosen within Barker Inlet, namely Gillman and St Kilda. 3.5. Land Use 3.6. Summary 4. Field and laboratory methods: conceptual models and mapping 4.1. Field investigations 4.2. Soil descriptions 4.3. Soil sampling and analysis 4.4. Acid sulfate soil analyses 4.4.1. Soil sample preparation 4.4.2. Methodologies used to assess acid sulfate soil properties 4.5. Spatial and temporal variability 4.5.1. Soil-regolith models 4.6. Soil map units 5. Soil Morphology, properties and classification for the intertidal St Kilda floodplain 5.1. Introduction 5.2. Descriptive soil-regolith toposequence process model with strong tidal influence 5.2.1. St Kilda Focus area A with strong tidal influence 5.2.2. St Kilda Focus area B-on an elevated, bare, shell grit chenier ridgeline 5.2.3. St Kilda Focus area C comprising a scalped depression with intertidal samphire shrublands and mangrove woodlands 5.3. Summary 6. Soil morphology and acid sulfate soil characterisation of the Gillman study site 6.1. Descriptive soil toposequence process models for a drained supratidal landscape 6.1.1. Gillman Focus area A 6.1.2. Gillman Focus area B 6.1.3. Gillman Focus area C 6.2. Summary-Gillman study site 7. Mapping 7.1. Soil-landscape maps 7.2. Acid sulfate soil hazards 7.3. Spatial distribution of acid sulfate soil materials in tidal areas 7.3.1. Acid-base characteristics of tidal soils at St Kilda study site 7.3.2. Acid-base characteristics of tidal areas at Gillman study site 7.4. Spatial distribution of acid sulfate soil materials in non-tidal areas at Gillman 7.5. Hazards 7.6. Geomorphic control on the development and distribution of acidity in the Gillman landscape 7.7.
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